Grain growth behavior at absolute zero during nanocrystalline metal indentation

NASA Astrophysics Data System (ADS)

Sansoz, F.; Dupont, V.

2006-09-01

The authors show using atomistic simulations that stress-driven grain growth can be obtained in the athermal limit during nanocrystalline aluminum indentation. They find that the grain growth results from rotation of nanograins and propagation of shear bands. Together, these mechanisms are shown to lead to the unstable migration of grain boundaries via process of coupled motion. An analytical model is used to explain this behavior based on the atomic-level shear stress acting on the interfaces during the shear band propagation. This study sheds light on the atomic mechanism at play during the abnormal grain coarsening observed at low temperature in nanocrystalline metals.

Invited paper: Dielectric properties of CaCu3Ti4O12 polycrystalline ceramics

NASA Astrophysics Data System (ADS)

Lee, Sung Yun; Hong, Youn Woo; Yoo, Sang Im

2011-12-01

We investigated the relationship between the microstructures and dielectric properties of various CaCu3Ti4O12 (CCTO) polycrystalline ceramics sintered in air. An abrupt increase in the dielectric constant ( ɛ r) from ˜3,000 to ˜170,000 at 1 kHz occurred with increasing the sintering temperature from 980 to 1000°C for 12 h, respectively, which was accompanied by a very large increase in the average grain size from 5 to 300 µm, respectively, due to an abnormal grain growth. With further increasing the sintering temperature, the ɛ r value at 1 kHz was slightly decreased to ˜150,000 at 1020°C with no variation in the average grain size, significantly decreased to ˜77,000 at 1040°C with a large decrease in the average grain size (˜150 µm), and then maintained the values of ˜76,000 and ˜69,000 at 1060 and 1080°C, respectively, without noticeable variation in the average grain size. While no abnormal grain growth occurred in the CCTO samples sintered at 980°C for the holding time to 24 h and thus their ɛ r values showed relatively lower ɛ r values (< ˜4,000 at 1 kHz), the abnormal grain growth occurred in the samples after a certain holding time at a given sintering temperature of higher than 1000°C and thus their ɛ r values abruptly increased. Analyses by the complex impedance ( Z*) and modulus ( M*) spectroscopy revealed that the ɛ r values of the CCTO samples were dominantly affected by the electrical properties of grain boundary so that high ɛ r values over 10,000 at 1 kHz were attributable to the high capacitance ( C) of grain boundary, which is in good agreement with grain boundary internal barrier layer capacitor (IBLC) model.

Evidence that abnormal grain growth precedes fatigue crack initiation in nanocrystalline Ni-Fe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Furnish, Timothy A.; Bufford, Daniel C.; Ren, Fang

Prior studies on the high-cycle fatigue behavior of nanocrystalline metals have shown that fatigue fracture is associated with abnormal grain growth (AGG). However, those previous studies have been unable to determine if AGG precedes fatigue crack initiation, or vice-versa. The present study shows that AGG indeed occurs prior to crack formation in nanocrystalline Ni-Fe by using a recently developed synchrotron X-ray diffraction modality that has been adapted for in-situ analysis. The technique allows fatigue tests to be interrupted at the initial signs of the AGG process, and subsequent microscopy reveals the precursor damage state preceding crack initiation.

Evidence that abnormal grain growth precedes fatigue crack initiation in nanocrystalline Ni-Fe

DOE PAGES

Furnish, Timothy A.; Bufford, Daniel C.; Ren, Fang; ...

2018-09-06

Prior studies on the high-cycle fatigue behavior of nanocrystalline metals have shown that fatigue fracture is associated with abnormal grain growth (AGG). However, those previous studies have been unable to determine if AGG precedes fatigue crack initiation, or vice-versa. The present study shows that AGG indeed occurs prior to crack formation in nanocrystalline Ni-Fe by using a recently developed synchrotron X-ray diffraction modality that has been adapted for in-situ analysis. The technique allows fatigue tests to be interrupted at the initial signs of the AGG process, and subsequent microscopy reveals the precursor damage state preceding crack initiation.

An examination of abnormal grain growth in low strain nickel-200

DOE PAGES

Underwood, O.; Madison, J.; Martens, R. M.; ...

2016-06-21

Here, this study offers experimental observation of the effect of low strain conditions (ε < 10%) on abnormal grain growth (AGG) in Nickel-200. At such conditions, stored mechanical energy is low within the microstructure enabling one to observe the impact of increasing mechanical deformation on the early onset of AGG compared to a control, or nondeformed, equivalent sample. The onset of AGG was observed to occur at specific pairings of compressive strain and annealing temperature and an empirical relation describing the influence of thermal exposure and strain content was developed. The evolution of low-Σ coincident site lattice (CSL) boundaries andmore » overall grain size distributions are quantified using electron backscatter diffraction preceding, at onset and during ensuing AGG, whereby possible mechanisms for AGG in the low strain regime are offered and discussed.« less

CH3NH3PbI3 grain growth and interfacial properties in meso-structured perovskite solar cells fabricated by two-step deposition

PubMed Central

Yao, Zhibo; Wang, Wenli; Shen, Heping; Zhang, Ye; Luo, Qiang; Yin, Xuewen; Dai, Xuezeng; Li, Jianbao; Lin, Hong

2017-01-01

Abstract Although the two-step deposition (TSD) method is widely adopted for the high performance perovskite solar cells (PSCs), the CH3NH3PbI3 perovskite crystal growth mechanism during the TSD process and the photo-generated charge recombination dynamics in the mesoporous-TiO2 (mp-TiO2)/CH3NH3PbI3/hole transporting material (HTM) system remains unexploited. Herein, we modified the concentration of PbI2 (C (PbI2)) solution to control the perovskite crystal properties, and observed an abnormal CH3NH3PbI3 grain growth phenomenon atop mesoporous TiO2 film. To illustrate this abnormal grain growth mechanism, we propose that a grain ripening process is taking place during the transformation from PbI2 to CH3NH3PbI3, and discuss the PbI2 nuclei morphology, perovskite grain growing stage, as well as Pb:I atomic ratio difference among CH3NH3PbI3 grains with different morphology. These C (PbI2)-dependent perovskite morphologies resulted in varied charge carrier transfer properties throughout the mp-TiO2/CH3NH3PbI3/HTM hybrid, as illustrated by photoluminescence measurement. Furthermore, the effect of CH3NH3PbI3 morphology on light absorption and interfacial properties is investigated and correlated with the photovoltaic performance of PSCs. PMID:28458747

CH3NH3PbI3 grain growth and interfacial properties in meso-structured perovskite solar cells fabricated by two-step deposition

NASA Astrophysics Data System (ADS)

Yao, Zhibo; Wang, Wenli; Shen, Heping; Zhang, Ye; Luo, Qiang; Yin, Xuewen; Dai, Xuezeng; Li, Jianbao; Lin, Hong

2017-12-01

Although the two-step deposition (TSD) method is widely adopted for the high performance perovskite solar cells (PSCs), the CH3NH3PbI3 perovskite crystal growth mechanism during the TSD process and the photo-generated charge recombination dynamics in the mesoporous-TiO2 (mp-TiO2)/CH3NH3PbI3/hole transporting material (HTM) system remains unexploited. Herein, we modified the concentration of PbI2 (C(PbI2)) solution to control the perovskite crystal properties, and observed an abnormal CH3NH3PbI3 grain growth phenomenon atop mesoporous TiO2 film. To illustrate this abnormal grain growth mechanism, we propose that a grain ripening process is taking place during the transformation from PbI2 to CH3NH3PbI3, and discuss the PbI2 nuclei morphology, perovskite grain growing stage, as well as Pb:I atomic ratio difference among CH3NH3PbI3 grains with different morphology. These C(PbI2)-dependent perovskite morphologies resulted in varied charge carrier transfer properties throughout the mp-TiO2/CH3NH3PbI3/HTM hybrid, as illustrated by photoluminescence measurement. Furthermore, the effect of CH3NH3PbI3 morphology on light absorption and interfacial properties is investigated and correlated with the photovoltaic performance of PSCs.

CH3NH3PbI3 grain growth and interfacial properties in meso-structured perovskite solar cells fabricated by two-step deposition.

PubMed

Yao, Zhibo; Wang, Wenli; Shen, Heping; Zhang, Ye; Luo, Qiang; Yin, Xuewen; Dai, Xuezeng; Li, Jianbao; Lin, Hong

2017-01-01

Although the two-step deposition (TSD) method is widely adopted for the high performance perovskite solar cells (PSCs), the CH 3 NH 3 PbI 3 perovskite crystal growth mechanism during the TSD process and the photo-generated charge recombination dynamics in the mesoporous-TiO 2 (mp-TiO 2 )/CH 3 NH 3 PbI 3 /hole transporting material (HTM) system remains unexploited. Herein, we modified the concentration of PbI 2 ( C (PbI2) ) solution to control the perovskite crystal properties, and observed an abnormal CH 3 NH 3 PbI 3 grain growth phenomenon atop mesoporous TiO 2 film. To illustrate this abnormal grain growth mechanism, we propose that a grain ripening process is taking place during the transformation from PbI 2 to CH 3 NH 3 PbI 3 , and discuss the PbI 2 nuclei morphology, perovskite grain growing stage, as well as Pb:I atomic ratio difference among CH 3 NH 3 PbI 3 grains with different morphology. These C (PbI2) -dependent perovskite morphologies resulted in varied charge carrier transfer properties throughout the mp-TiO 2 /CH 3 NH 3 PbI 3 /HTM hybrid, as illustrated by photoluminescence measurement. Furthermore, the effect of CH 3 NH 3 PbI 3 morphology on light absorption and interfacial properties is investigated and correlated with the photovoltaic performance of PSCs.

Large-scale grain growth in the solid-state process: From "Abnormal" to "Normal"

NASA Astrophysics Data System (ADS)

Jiang, Minhong; Han, Shengnan; Zhang, Jingwei; Song, Jiageng; Hao, Chongyan; Deng, Manjiao; Ge, Lingjing; Gu, Zhengfei; Liu, Xinyu

2018-02-01

Abnormal grain growth (AGG) has been a common phenomenon during the ceramic or metallurgy processing since prehistoric times. However, usually it had been very difficult to grow big single crystal (centimeter scale over) by using the AGG method due to its so-called occasionality. Based on the AGG, a solid-state crystal growth (SSCG) method was developed. The greatest advantages of the SSCG technology are the simplicity and cost-effectiveness of the technique. But the traditional SSCG technology is still uncontrollable. This article first summarizes the history and current status of AGG, and then reports recent technical developments from AGG to SSCG, and further introduces a new seed-free, solid-state crystal growth (SFSSCG) technology. This SFSSCG method allows us to repeatedly and controllably fabricate large-scale single crystals with appreciable high quality and relatively stable chemical composition at a relatively low temperature, at least in (K0.5Na0.5)NbO3(KNN) and Cu-Al-Mn systems. In this sense, the exaggerated grain growth is no longer 'Abnormal' but 'Normal' since it is able to be artificially controllable and repeated now. This article also provides a crystal growth model to qualitatively explain the mechanism of SFSSCG for KNN system. Compared with the traditional melt and high temperature solution growth methods, the SFSSCG method has the advantages of low energy consumption, low investment, simple technique, composition homogeneity overcoming the issues with incongruent melting and high volatility. This SFSSCG could be helpful for improving the mechanical and physical properties of single crystals, which should be promising for industrial applications.

Mechanisms of Texture Development in Lead-Free Piezoelectric Ceramics with Perovskite Structure Made by the Templated Grain Growth Process

PubMed Central

Kimura, Toshio; Yi, Yuan; Sakurai, Fumito

2010-01-01

The mechanisms of texture development were examined for BaTiO3 and a (K,Na,Li)(Nb,Ta)O3 solid solution made by the templated grain growth method, and compared with the mechanism in Bi0.5(Na,K)0.5TiO3. The dominant mechanism was different in each material; grain boundary migration in BaTiO3, solid state spreading in Bi0.5(Na,K)0.5TiO3, and abnormal grain growth in the (K,Na,Li)(Nb,Ta)O3 solid solution. The factor determining the dominant mechanism is the degree of smoothness of surface structure at an atomic level. PMID:28883364

Investigation of Abnormal Grain Growth in a Friction Stir Welded and Spin-Formed Al-Li Alloy 2195 Crew Module

NASA Technical Reports Server (NTRS)

Tayon, Wesley A.; Domack, Marcia S.; Hoffman, Eric K.; Hales, Stephen J.

2013-01-01

In order to improve manufacturing efficiency and reduce structural mass and costs in the production of launch vehicle structures, NASA is pursuing a wide-range of innovative, near-net shape manufacturing technologies. A technology that combines friction stir welding (FSW) and spin-forming has been applied to manufacture a single-piece crew module using Aluminum-Lithium (AL-Li) Alloy 2195. Plate size limitations for Al-Li alloy 2195 require that two plates be FSW together to produce a spin-forming blank of sufficient size to form the crew module. Subsequent forming of the FSW results in abnormal grain growth (AGG) within the weld region upon solution heat treatment (SHT), which detrimentally impacts strength, ductility, and fracture toughness. The current study seeks to identify microstructural factors that contribute to the development of AGG. Electron backscatter diffraction (EBSD) was used to correlate driving forces for AGG, such as stored energy, texture, and grain size distributions, with the propensity for AGG. Additionally, developmental annealing treatments prior to SHT are examined to reduce or eliminate the occurrence of AGG by promoting continuous, or uniform, grain growth

Large forging manufacturing process

DOEpatents

Thamboo, Samuel V.; Yang, Ling

2002-01-01

A process for forging large components of Alloy 718 material so that the components do not exhibit abnormal grain growth includes the steps of: a) providing a billet with an average grain size between ASTM 0 and ASTM 3; b) heating the billet to a temperature of between 1750.degree. F. and 1800.degree. F.; c) upsetting the billet to obtain a component part with a minimum strain of 0.125 in at least selected areas of the part; d) reheating the component part to a temperature between 1750.degree. F. and 1800.degree. F.; e) upsetting the component part to a final configuration such that said selected areas receive no strains between 0.01 and 0.125; f) solution treating the component part at a temperature of between 1725.degree. F. and 1750.degree. F.; and g) aging the component part over predetermined times at different temperatures. A modified process achieves abnormal grain growth in selected areas of a component where desirable.

Abnormal grain growth in iron-silicon

NASA Astrophysics Data System (ADS)

Bennett, Tricia A.

Abnormal grain growth (AGG) was studied in an Fe-1%Si alloy using automated Electron Backscattered Diffraction (EBSD) to determine the driving force for this phenomenon. Experiments were performed with the knowledge that there are several possible driving forces and, the intent to determine the true driving force by elimination of the other potential candidates. These potential candidates include surface energy anisotropy, anisotropic grain boundary properties and the stored energy of deformation. In this work, surface energy and grain boundary anisotropies as well as the stored energy of deformation were investigated as the possible driving forces for AGG. Accordingly, industrially processed samples that were temper rolled to 1.5% and 8% were annealed in air for various times followed by quenching in water. The results obtained were compared to those from heat treatments performed in wet 15%H2-85%N2 at a US Steel facility. In addition, for a more complete study of the effect of surface energy anisotropies on AGG, the 1.5% temper-rolled material was heat-treated in other atmospheres such as 5%H2-95%Ar, 98%H2-2%He, 98%H2-2%H 2S, and 98%H2-2%N2 for 1 hour followed by quenching in water. The character of the grain boundaries in the materials was also examined for each set of experiments conducted, while the influence of stored energy was evaluated by examining intragranular orientation gradients. AGG occurred regardless of annealing atmosphere though the most rapid progression was observed in samples annealed in air. In general, grains of varying orientations grew abnormally. One consistently observed trend in all the detailed studies was that the matrix grains remained essentially static and either did not grow or only grew very slowly. On the other hand, the abnormally large grains (ALG), on average, were approximately 10 times the size of the matrix. Analysis of the grain boundary character of the interfaces between abnormal grains and the matrix showed no significant variation from the overall population of boundaries. This suggested that grain boundary character was not a factor in controlling AGG. When the effect of stored energy differences was considered, it was observed that grains that experienced AGG had low orientation gradients. Based on these results and cross comparison of all classes of experiments performed, it was determined that stored energy differences were the main driving force for AGG in this Fe-1%Si alloy.

Synthesis, Deposition, and Microstructure Development of Thin Films Formed by Sulfidation and Selenization of Copper Zinc Tin Sulfide Nanocrystals

NASA Astrophysics Data System (ADS)

Chernomordik, Boris David

Significant reduction in greenhouse gas emission and pollution associated with the global power demand can be accomplished by supplying tens-of-terawatts of power with solar cell technologies. No one solar cell material currently on the market is poised to meet this challenge due to issues such as manufacturing cost, material shortage, or material toxicity. For this reason, there is increasing interest in efficient light-absorbing materials that are comprised of abundant and non-toxic elements for thin film solar cell. Among these materials are copper zinc tin sulfide (Cu2ZnSnS4, or CZTS), copper zinc tin selenide (Cu2ZnSnSe4, or CZTSe), and copper zinc tin sulfoselenide alloys [Cu2ZnSn(SxSe1-x )4, or CZTSSe]. Laboratory power conversion efficiencies of CZTSSe-based solar cells have risen to almost 13% in less than three decades of research. Meeting the terawatt challenge will also require low cost fabrication. CZTSSe thin films from annealed colloidal nanocrystal coatings is an example of solution-based methods that can reduce manufacturing costs through advantages such as high throughput, high material utilization, and low capital expenses. The film microstructure and grain size affects the solar cell performance. To realize low cost commercial production and high efficiencies of CZTSSe-based solar cells, it is necessary to understand the fundamental factors that affect crystal growth and microstructure evolution during CZTSSe annealing. Cu2ZnSnS4 (CZTS) nanocrystals were synthesized via thermolysis of single-source cation and sulfur precursors copper, zinc and tin diethyldithiocarbamates. The average nanocrystal size could be tuned between 2 nm and 40 nm, by varying the synthesis temperature between 150 °C and 340 °C. The synthesis is rapid and is completed in less than 10 minutes. Characterization by X-ray diffraction, Raman spectroscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy confirm that the nanocrystals are nominally stoichiometric kesterite CZTS. The ~2 nm nanocrystals synthesized at 150 °C exhibit quantum confinement, with a band gap of 1.67 eV. Larger nanocrystals have the expected bulk CZTS band gap of 1.5 eV. Several micron thick films deposited by drop casting colloidal dispersions of ~40 nm CZTS nanocrystals were crack-free, while those cast using 5 nm nanocrystals had micron-scale cracks. We showed the applicability of these nanocrystal coatings for thin film solar cells by demonstrating a CZTS thin film solar cell using coatings annealed in a sulfur atmosphere. We conducted a systematic study of the factors controlling crystal growth and microstructure development during sulfidation annealing of films cast from colloidal dispersions of CZTS nanocrystals. The film microstructure is controlled by concurrent normal and abnormal grain growth. At 600 °C to 800 °C and low sulfur pressures (50 Torr), abnormal CZTS grains up to 10 microm in size grow on the surface of the CZTS nanocrystal film via transport of material from the nanocrystals to the abnormal grains. Meanwhile, the nanocrystals coarsen, sinter, and undergo normal grain growth. The driving force for abnormal grain growth is the reduction in total energy associated with the high surface area nanocrystals. The eventual coarsening of the CZTS nanocrystals reduces the driving force for abnormal crystal growth. Increasing the sulfur pressure by an order of magnitude to 500 Torr accelerates both normal and abnormal crystal growth though sufficient acceleration of the former eventually reduces the latter by reducing the driving force for abnormal grain growth. For example, at high temperatures (700-800 oC) and sulfur pressures (500 Torr) normal grains quickly grow to ~500 nm which significantly reduces abnormal grain growth. The use of soda lime glass as the substrate, instead of quartz, accelerates normal grain growth. Normal grains grow to ~500 nm at lower temperatures and sulfur pressures (i.e., 600 °C and 50 Torr) than those required to grow the same size grains on quartz (700 °C and 500 Torr). Moreover, carbon is removed by volatilization from films where normal crystal growth is fast. There are significant differences in the chemistry and in the thermodynamics involved during selenization and sulfidation of CZTS colloidal nanocrystal coatings to form CZTSSe or CZTS thin films, respectively. To understand these differences, the roles of vapor pressure, annealing temperature, and heating rate in the formation of different microstructures of CZTSSe films were investigated. Selenization produced a bi-layer microstructure where a large CZTSSe-crystal layer grew on top of a nanocrystalline carbon-rich bottom layer. Differences in the chemistry of carbon and selenium and that of carbon and sulfur account for this segregation of carbon during selenization. For example, CSe 2 and CS2, both volatile species, may form as a result of chalcogen interactions with carbon during annealing. Unlike CS2, however, CSe2 may readily polymerize at room temperature and one atmosphere. Carbon segregation may be occurring only during selenization due to the formation of a Cu-Se polymer [i.e., (CSe 2-x)] within the nanocrystal film. The (CSe2-x) inhibits sintering of nanocrystals in the bottom layer. Additionally, a fast heating rate results in temperature variations that lead to transient condensation of selenium on the film. This is observed only during selenization because the equilibrium vapor pressure of selenium is lower than that of sulfur. The presence of liquid selenium during sintering accelerates coarsening and densification of the normal crystal layer (no abnormal crystal layer) by liquid phase sintering. Carbon segregation does not occur where liquid selenium was present.

Microstructural evolution during sintering of copper particles studied by laboratory diffraction contrast tomography (LabDCT).

PubMed

McDonald, S A; Holzner, C; Lauridsen, E M; Reischig, P; Merkle, A P; Withers, P J

2017-07-12

Pressureless sintering of loose or compacted granular bodies at elevated temperature occurs by a combination of particle rearrangement, rotation, local deformation and diffusion, and grain growth. Understanding of how each of these processes contributes to the densification of a powder body is still immature. Here we report a fundamental study coupling the crystallographic imaging capability of laboratory diffraction contrast tomography (LabDCT) with conventional computed tomography (CT) in a time-lapse study. We are able to follow and differentiate these processes non-destructively and in three-dimensions during the sintering of a simple copper powder sample at 1050 °C. LabDCT quantifies particle rotation (to <0.05° accuracy) and grain growth while absorption CT simultaneously records the diffusion and deformation-related morphological changes of the sintering particles. We find that the rate of particle rotation is lowest for the more highly coordinated particles and decreases during sintering. Consequently, rotations are greater for surface breaking particles than for more highly coordinated interior ones. Both rolling (cooperative) and sliding particle rotations are observed. By tracking individual grains the grain growth/shrinkage kinetics during sintering are quantified grain by grain for the first time. Rapid, abnormal grain growth is observed for one grain while others either grow or are consumed more gradually.

Improved magnetic properties and growth anisotropy of chemically modified Sr ferrites

NASA Astrophysics Data System (ADS)

Lee, Jung W.; Cho, Yong S.; Amarakoon, Vasantha R. W.

1999-04-01

Magnetic properties and microstructural characteristics of SrOṡ5.9Fe2O3 chemically modified with Si and Ca were investigated by changing experimental parameters such as additive composition, the ratio of Ca/Si, and sintering condition. A novel particulate coating method utilizing sol-gel reactions was used to uniformly incorporate the additives of Si and Ca. This method was very successful in obtaining homogeneous grain growth and fine grains. A sample containing the gel additives of 0.6 wt % SiO2 and 0.7 wt % CaO and sintered at 1200 °C for 4 h was found to significantly suppress abnormal grain growth, resulting in submicron-sized grains and high density. A distinct grain boundary phase containing Si and Ca was observed by increasing the sintering temperature to 1250 °C. The resultant microstructural characteristics favorably affected magnetic properties. For example, the chemically modified sample exhibited a higher coercivity of 3530 Oe compared to a value of 2050 Oe obtained for the sample without the additives. On the other hand, an increase in the ratio of Ca/Si or in sintering temperature tended to induce a large anisotropy during grain growth.

Mitigating Abnormal Grain Growth for Friction Stir Welded Al-Li 2195 Spun Formed Domes

NASA Technical Reports Server (NTRS)

Chen, Po-Shou; Russell, Carolyn

2012-01-01

Formability and abnormal grain growth (AGG) are the two major issues that have been encountered for Al alloy spun formed dome development using friction stir welded blanks. Material properties that have significant influence on the formability include forming range and strain hardening exponent. In this study, tensile tests were performed for two 2195 friction stir weld parameter sets at 400 F to study the effects of post weld anneal on the forming range and strain hardening exponent. It was found that the formability can be enhanced by applying a newly developed post weld anneal to heat treat the friction stir welded panels. This new post weld anneal leads to a higher forming range and much improved strain hardening exponent. AGG in the weld nugget is known to cause a significant reduction of ductility and fracture toughness. This study also investigated how AGG may be influenced by the heating rate to the solution heat treatment temperature. After post-weld annealing, friction stir welds were strained to 15% and 39% by compression at 400 F before they were subjected to SHT at 950 F for 1 hour. Salt bath SHT is very effective in reducing the grain size as it helps arrest the onset of AGG and promote normal recrystallization and grain growth. However, heat treating a 18 ft dome using a salt bath is not practical. Efforts are continuing at Marshall Space Flight Center to identify the welding parameters and heat treating parameters that can help mitigate the AGG in the friction stir welds.

Oxidation-assisted graphene heteroepitaxy on copper foil.

PubMed

Reckinger, Nicolas; Tang, Xiaohui; Joucken, Frédéric; Lajaunie, Luc; Arenal, Raul; Dubois, Emmanuel; Hackens, Benoît; Henrard, Luc; Colomer, Jean-François

2016-11-10

We propose an innovative, easy-to-implement approach to synthesize aligned large-area single-crystalline graphene flakes by chemical vapor deposition on copper foil. This method doubly takes advantage of residual oxygen present in the gas phase. First, by slightly oxidizing the copper surface, we induce grain boundary pinning in copper and, in consequence, the freezing of the thermal recrystallization process. Subsequent reduction of copper under hydrogen suddenly unlocks the delayed reconstruction, favoring the growth of centimeter-sized copper (111) grains through the mechanism of abnormal grain growth. Second, the oxidation of the copper surface also drastically reduces the nucleation density of graphene. This oxidation/reduction sequence leads to the synthesis of aligned millimeter-sized monolayer graphene domains in epitaxial registry with copper (111). The as-grown graphene flakes are demonstrated to be both single-crystalline and of high quality.

Thermal Stabilization and Mechanical Properties of Nanocrystalline Iron-Nickel-Zirconium Alloys

NASA Astrophysics Data System (ADS)

Kotan, Hasan

Ultrafine grained and nanostructured materials are promising for structural applications because of the high strength compared to coarse grained counterparts. However, their widespread application is limited by an inherently high driving force for thermally induced grain growth, even at low temperatures. Accordingly, the understanding of and control over grain growth in nanoscale materials is of great technological and scientific importance as many physical properties (i.e. mechanical properties) are functions of the average grain size and the grain size distribution within the microstructure. Here, we investigate the microstructural evolution and grain growth in Fe-Ni alloys with Zr addition and differentiate the stabilization mechanisms acting on grain boundaries. Fe-Ni alloys are chosen for stability investigations since they are important for understanding the behavior of many steels and other ferrous alloys. Zirconium is proven to be an effective grain size stabilizer in pure Fe and Fe-base systems. In this study, nanocrystalline alloys were prepared by high energy ball milling. In situ and ex situ experiments were utilized to directly follow grain growth and microstructural evolution as a function of temperature and composition. The information obtained from these experiments enables the real time observation of microstructural evolution and phase transformation and provides a unique view of dynamic reactions as they occur. The knowledge of the thermal stability will exploit the potential high temperature applications and the consolidation conditions (i.e. temperature and pressure) to obtain high dense materials for advanced mechanical tests. Our investigations reveal that the grain growth of Fe-Ni alloys is not affected by Ni content but strongly inhibited by the addition of 1 at% Zr up to about 700 °C. The microstructural stability is lost due to the bcc-to-fcc transformation (occurring at 700°C) by the sudden appearance of abnormally grown fcc grains. However it was determined grain growth can be suppressed kinetically at higher temperatures for high Zr containing alloys by precipitation of intermetallic compounds. Eventually at high enough temperatures the retention of nanocrystallinity was lost, leaving behind fine micron grains filled with nanoscale intermetallic precipitates. Despite the loss of stability the in-situ formed precipitates were found to induce an Orowan hardening affect. The results from the mechanical tests show that Orowan particle strengthening can be as significant as Hall Petch hardening is at the smallest grain sizes.

Effects of sputtering mode on the microstructure and ionic conductivity of yttria-stabilized zirconia films

NASA Astrophysics Data System (ADS)

Yeh, Tsung-Her; Lin, Ruei-De; Cherng, Bo-Ruei; Cherng, Jyh-Shiarn

2018-05-01

The microstructure and ionic conductivity of reactively sputtered yttria-stabilized zirconia (YSZ) films are systematically studied. Those films were reactively sputtered in various sputtering modes using a closed-loop controlled system with plasma emission monitoring. A transition-mode sputtering corresponding to 45% of target poisoning produces a microstructure with ultrafine crystallites embedded in an amorphous matrix, which undergoes an abnormal grain growth upon annealing at 800 °C. At 500 °C, the measured ionic conductivity of this annealed film is higher, by about a half order of magnitude, than those of its poisoned-mode counterparts, which are in turn significantly higher than that of the YSZ bulk by about two orders of magnitude. The abnormally-grown ultra-large grain size of the film deposited in the transition mode and then annealed is believed to be responsible for the former comparison due to the suppression of the grain boundary blocking effect, while the latter comparison can be attributed to the interface effect.

High pressure FAST of nanocrystalline barium titanate

DOE PAGES

Fraga, Martin B.; Delplanque, Jean -Pierre; Yang, Nancy; ...

2016-06-01

Here, this work studies the microstructural evolution of nanocrystalline (<1 µm) barium titanate (BaTiO 3), and presents high pressure in field-assisted sintering (FAST) as a robust methodology to obtain >100 nm BaTiO 3 compacts. Using FAST, two commercial ~50 nm powders were consolidated into compacts of varying densities and grain sizes. Microstructural inhomogeneities were investigated for each case, and an interpretation is developed using a modified Monte Carlo Potts (MCP) simulation. Two recurrent microstructural inhomogeneities are highlighted, heterogeneous grain growth and low-density regions, both ubiqutously present in all samples to varying degrees. In the worst cases, HGG presents an areamore » coverage of 52%. Because HGG is sporadic but homogenous throughout a sample, the catalyst (e.g., the local segregation of species) must be, correspondingly, distributed in a homogenous manner. MCP demonstrates that in such a case, a large distance between nucleating abnormal grains is required—otherwise abnormal grains prematurely impinge on each other, and their size is not distinguishable from that of normal grains. Compacts sintered with a pressure of 300 MPa and temperatures of 900 °C, were 99.5% dense and had a grain size of 90±24 nm. These are unprecedented results for commercial BaTiO 3 powders or any starting powder of 50 nm particle size—other authors have used 16 nm lab-produced powder to obtain similar results.« less

Crystallographic analysis of the solid-state dewetting of polycrystalline gold film using automated indexing in a transmission electron microscope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jang, S. A.; Lee, H. J.; Oh, Y. J., E-mail: yjoh@hanbat.ac.kr

We analyzed the effect of crystallographic anisotropy on the morphological evolution of a 12-nm-thick gold film during solid-state dewetting at high temperatures using automated indexing tool in a transmission electron microscopy. Dewetting initiated at grain-boundary triple junctions adjacent to large grains resulting from abnormal grain growth driven by (111) texture development. Voids at the junctions developed shapes with faceted edges bounded by low-index crystal planes. The kinetic mobility of the edges varied with the crystal orientation normal to the edges, with a predominance of specific edges with the slowest retraction rates as the annealing time was increased.

COLLAPSED ABNORMAL POLLEN1 Gene Encoding the Arabinokinase-Like Protein Is Involved in Pollen Development in Rice1[C][W][OA

PubMed Central

Ueda, Kenji; Yoshimura, Fumiaki; Miyao, Akio; Hirochika, Hirohiko; Nonomura, Ken-Ichi; Wabiko, Hiroetsu

2013-01-01

We isolated a pollen-defective mutant, collapsed abnormal pollen1 (cap1), from Tos17 insertional mutant lines of rice (Oryza sativa). The cap1 heterozygous plant produced equal numbers of normal and collapsed abnormal grains. The abnormal pollen grains lacked almost all cytoplasmic materials, nuclei, and intine cell walls and did not germinate. Genetic analysis of crosses revealed that the cap1 mutation did not affect female reproduction or vegetative growth. CAP1 encodes a protein consisting of 996 amino acids that showed high similarity to Arabidopsis (Arabidopsis thaliana) l-arabinokinase, which catalyzes the conversion of l-arabinose to l-arabinose 1-phosphate. A wild-type genomic DNA segment containing CAP1 restored mutants to normal pollen grains. During rice pollen development, CAP1 was preferentially expressed in anthers at the bicellular pollen stage, and the effects of the cap1 mutation were mainly detected at this stage. Based on the metabolic pathway of l-arabinose, cap1 pollen phenotype may have been caused by toxic accumulation of l-arabinose or by inhibition of cell wall metabolism due to the lack of UDP-l-arabinose derived from l-arabinose 1-phosphate. The expression pattern of CAP1 was very similar to that of another Arabidopsis homolog that showed 71% amino acid identity with CAP1. Our results suggested that CAP1 and related genes are critical for pollen development in both monocotyledonous and dicotyledonous plants. PMID:23629836

Evaluation of microstructure stability at the interfaces of Al-6061 welds fabricated using ultrasonic additive manufacturing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sridharan, Niyanth S.; Gussev, Maxim N.; Parish, Chad M.

Here, ultrasonic additive manufacturing (UAM) is a solid-state additive manufacturing process that uses fundamental principles of ultrasonic welding and sequential layering of tapes to fabricate complex three-dimensional (3-D) components. One of the factors limiting the use of this technology is the poor tensile strength along the z-axis. Recent work has demonstrated the improvement of the z-axis properties after post-processing treatments. The abnormally high stability of the grains at the interface during post-weld heat treatments is, however, not yet well understood. In this work we use multiscale characterization to understand the stability of the grains during post-weld heat treatments. Aluminum alloymore » (6061) builds, fabricated using ultrasonic additive manufacturing, were post-weld heat treated at 180, 330 and 580 °C. The grains close to the tape interfaces are stable during post-weld heat treatments at high temperatures (i.e., 580 °C). This is in contrast to rapid grain growth that takes place in the bulk. Transmission electron microscopy and atom-probe tomography display a significant enrichment of oxygen and magnesium near the stable interfaces. Based on the detailed characterization, two mechanisms are proposed and evaluated: nonequilibrium nano-dispersed oxides impeding the grain growth due to grain boundary pinning, or grain boundary segregation of magnesium and oxygen reducing the grain boundary energy.« less

Evaluation of microstructure stability at the interfaces of Al-6061 welds fabricated using ultrasonic additive manufacturing

DOE PAGES

Sridharan, Niyanth S.; Gussev, Maxim N.; Parish, Chad M.; ...

2018-03-06

Here, ultrasonic additive manufacturing (UAM) is a solid-state additive manufacturing process that uses fundamental principles of ultrasonic welding and sequential layering of tapes to fabricate complex three-dimensional (3-D) components. One of the factors limiting the use of this technology is the poor tensile strength along the z-axis. Recent work has demonstrated the improvement of the z-axis properties after post-processing treatments. The abnormally high stability of the grains at the interface during post-weld heat treatments is, however, not yet well understood. In this work we use multiscale characterization to understand the stability of the grains during post-weld heat treatments. Aluminum alloymore » (6061) builds, fabricated using ultrasonic additive manufacturing, were post-weld heat treated at 180, 330 and 580 °C. The grains close to the tape interfaces are stable during post-weld heat treatments at high temperatures (i.e., 580 °C). This is in contrast to rapid grain growth that takes place in the bulk. Transmission electron microscopy and atom-probe tomography display a significant enrichment of oxygen and magnesium near the stable interfaces. Based on the detailed characterization, two mechanisms are proposed and evaluated: nonequilibrium nano-dispersed oxides impeding the grain growth due to grain boundary pinning, or grain boundary segregation of magnesium and oxygen reducing the grain boundary energy.« less

Influence of friction stir processing on the room temperature fatigue cracking mechanisms of A356 aluminum alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nelaturu, Phalgun; Jana, Saumyadeep; Mishra, Rajiv S.

Here, failure by fatigue is a common problem associated with cast aluminum alloys due to defects like shrinkage porosities, non-metallic inclusions, etc. Friction stir processing (FSP) has recently emerged as an effective technique for local modification of microstructure. This study investigates the fatigue crack initiation and growth mechanisms in cast and FSPed A356 aluminum alloy. Two sets of parameters were used to friction stir the cast alloy resulting in the complete modification the cast microstructure to a wrought microstructure. Both the FSPed microstructures exhibited severe abnormal grain growth (AGG) after heat treatment leading to a multimodal grain size distribution –more » the grain sizes ranging from a few microns to a few millimeters. One of the FSP conditions displayed an excellent improvement in fatigue life by an order of magnitude, while the other condition displayed an unexpectedly large scatter in fatigue lives. Detailed study of the fractured fatigue specimens by electron back scattered diffraction (EBSD) revealed that both, fatigue crack initiation and propagation, were intimately tied to the grain size as well as the grain misorientations in the microstructure.« less

Influence of friction stir processing on the room temperature fatigue cracking mechanisms of A356 aluminum alloy

DOE PAGES

Nelaturu, Phalgun; Jana, Saumyadeep; Mishra, Rajiv S.; ...

2018-01-11

Here, failure by fatigue is a common problem associated with cast aluminum alloys due to defects like shrinkage porosities, non-metallic inclusions, etc. Friction stir processing (FSP) has recently emerged as an effective technique for local modification of microstructure. This study investigates the fatigue crack initiation and growth mechanisms in cast and FSPed A356 aluminum alloy. Two sets of parameters were used to friction stir the cast alloy resulting in the complete modification the cast microstructure to a wrought microstructure. Both the FSPed microstructures exhibited severe abnormal grain growth (AGG) after heat treatment leading to a multimodal grain size distribution –more » the grain sizes ranging from a few microns to a few millimeters. One of the FSP conditions displayed an excellent improvement in fatigue life by an order of magnitude, while the other condition displayed an unexpectedly large scatter in fatigue lives. Detailed study of the fractured fatigue specimens by electron back scattered diffraction (EBSD) revealed that both, fatigue crack initiation and propagation, were intimately tied to the grain size as well as the grain misorientations in the microstructure.« less

Structural, topographical and electrical properties of cerium doped strontium barium niobate (Ce:SBN60) ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raj, S. Gokul; Mathivanan, V.; Mohan, R.

2016-05-06

Tungsten bronze type cerium doped strontium barium niobate (Ce:SBN - Sr{sub 0.6}B{sub 0.4}Nb{sub 2}O{sub 6}) ceramics were synthesized by solid state process. Cerium was used as dopant to improve its electrical properties. Influence of Ce{sup +} ions on the photoluminescence properties was investigated in detail. The grain size topographical behavior of SBN powders and their associated abnormal grain growth (AGG) were completely analyzed through SEM studies. Finally dielectric, measurement discusses about the broad phase transition observed due to cerium dopant The results were discussed in detail.

The Microstructural Evolution and Special Flow Behavior of Ti-5Al-2Sn-2Zr-4Mo-4Cr During Isothermal Compression at a Low Strain Rate

NASA Astrophysics Data System (ADS)

Sun, J. Z.; Li, M. Q.; Li, H.

2017-09-01

The microstructural evolution and special flow behavior of Ti-5Al-2Sn-2Zr-4Mo-4Cr during isothermal compression at a strain rate of 0.0001 s-1 were investigated. The dislocation climbs in elongated α grains resulted in the formation of low-angle boundaries that transform into high-angle boundaries with greater deformation, and the elongated α grains subsequently separated into homogenous globular α grains with the penetration of the β phase. The simultaneous occurrence of discontinuous dynamic recrystallization and continuous dynamic recrystallization in the primary β grains resulted in a trimode grain distribution. The β grains surrounded by dislocations presented an equilateral-hexagonal morphology, which suggests that grain boundary sliding through dislocation climbs was the main deformation mechanism. The true stress-strain curves for 1073 and 1113 K abnormally intersect at a strain of 0.35, related to the α → β phase transformation and distinct growth of the β grain size.

The effect of postprocessing on tensile property and microstructure evolution of friction stir welding aluminum alloy joint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Z.L., E-mail: zhilihuhit@163.com; State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001; State Key Laboratory of Materials Processing and Die & Mould Technology, Huazhong University of Science and Technology

Friction stir welding is an efficient manufacturing method for joining aluminum alloy and can dramatically reduce grain size conferring excellent plastic deformation properties. Consequently, friction stir welding is used to manufacture tailor welded blanks to optimize weight or performance in the final component. In the study, the microstructural evolution and mechanical properties of friction stir welding joint during plastic forming and subsequent heat treatment were investigated. The microstructural characteristics of the friction stir welding joints were studied by Electron Backscattered Diffraction and Transmission Electron Microscopy. The mechanical properties were evaluated by tensile and microhardness tests. It is found that themore » tensile and yield strengths of friction stir welding joints are significantly improved after severe plastic deformation due to the grain refinement. Following heat treatment, the strength of the friction stir welding joints significantly decrease due to the obvious abnormal grain growth. Careful attention must be given to the processing route of any friction stir welding joint intended for plastic forming, especially the annealing between forming passes. Severe plastic deforming of the friction stir welding joint leads to a high level of stored energy/dislocation density, which causes the abnormal grain growth during subsequent heat treatment, and consequently reduce the mechanical properties of the friction stir welding joint. - Highlights: • Great changes are observed in the microstructure of FSW joint after postprocessing. • Postprocessing shows great effect on the microstructure stability of FSW joint. • The weld shows more significant decrease in strength than the BM due to the AGG. • Attention must be given to the processing route of FSW joint for plastic forming.« less

[World population growth and the food supply].

PubMed

Huang, Y

1982-07-29

The general trend in the last several hundred years has been that the speed of growth in the food supply exceeds the speed of the population growth. For the time being, 2 major problems still exist. The 1st problem is that food production is still influenced by natural conditions. For example, abnormal weather conditions may cause regional food shortages. The 2nd problem is the imbalance of food consumption by the world population. This phenomenon exists between different social classes as well as between developed and developing countries. According to statistics released by the World Bank, 1 billion suffer from malnutrition today and most of them are in developing countries. In developed countries, about half of their increase in the food supply is for feed grains, and those countries follow the policy of reducing farm land for the purpose of maintaing stabl e grain prices. Up to the present time, grain prices have been unstable, and this has become a rather heavy economic burden for numerous developing countries. Many developing countries are trying to increase grain production by increasing their arable land and promoting their cultivating techniques. However, these countries are facing the problems of finding and adequate water supply, fertilizer, and pesticides. In addition, a rapid population growth in these countries has offset their endeavors in agriculture. In recent years, these counties have realized the necessity of birth control. The world population growth rate has decreased from 2% to about 1.7% in 1981. Birth control and an increase in the food supply will bring new hope to the world's problems of overpopulation and food supply.

Chemical signature of a migrating grain boundaries in polycrystalline olivine

NASA Astrophysics Data System (ADS)

Boneh, Y.; Marquardt, K.; Skemer, P. A.

2017-12-01

Olivine is the most abundant phase and influences strongly the physical and chemical properties of the upper mantle. The structure and chemistry of olivine grain-boundaries is important to understand, as these interfaces provide a reservoir for incompatible elements and partial melt, and serve as a fast pathway for chemical diffusion. This project investigates the chemical characteristics of grain boundaries in an olivine-rich aggregate. The sample is composed of Fo50 olivine crystals with minor amounts of enstatite. It was previously deformed (Hansen et al., 2016) and then annealed (Boneh et al., 2017) to investigate the microstructural changes during recrystallization. This transient microstructure has a bimodal grain size distribution and includes grains that experienced abnormal grain-growth, (porphyroblasts) and highly strained grains with no significant recrystallization or growth (matrix). Using high-resolution transmission electron microscopy (HR-TEM) with energy dispersive X-ray (EDX) at the Bayerisches Geoinstitut (BGI), we characterized boundaries between pairs of porphyroblasts, pairs of matrix grains, and mixed boundaries between porphyroblast and matrix grains. It was found that the boundary between porphyroblasts is enriched in Al and Ca and depleted in Mg, in comparison to grain interiors. However, matrix-matrix boundaries show less chemical segregation of these elements. The relatively high level of chemical segregation to porphyroblast grain boundaries offers different possible interpretations: 1) During grain boundary migration incompatible elements are swept up by the migrating grain boundary. 2) Large angle grain boundaries provide a large density of energetically favorable storage sites for incompatible elements. 3) Diffusion along low angle grain boundaries is too slow to allow for fast chemical equilibration between the different grain boundaries. 4) Dislocations cores serve as an important transport media for impurities (i.e., Cottrell atmosphere). We will further discuss these different interpretations, their feasibility, and implications for the geochemistry of the mantle.

Titanium oxide as substrate for neural cell growth.

PubMed

Carballo-Vila, Mónica; Moreno-Burriel, Berta; Chinarro, Eva; Jurado, José R; Casañ-Pastor, Nieves; Collazos-Castro, Jorge E

2009-07-01

Titanium oxide has antiinflammatory activity and tunable electrochemical behavior that make it an attractive material for the fabrication of implantable devices. The most stable composition is TiO2 and occurs mainly in three polymorphs, namely, anatase, rutile, and brookite, which differ in its crystallochemical properties. Here, we report the preparation of rutile surfaces that permit good adherence and axonal growth of cultured rat cerebral cortex neurons. Rutile disks were obtained by sinterization of TiO2 powders of commercial origin or precipitated from hydrolysis of Ti(IV)-isopropoxide. Commercial powders sintered at 1300-1600 degrees C produced rutile surfaces with abnormal grain growth, probably because of impurities of the powders. Neurons cultured on those surfaces survived in variable numbers and showed fewer neurites than on control materials. On the other hand, rutile sintered from precipitated powders had less contaminants and more homogenous grain growth. By adjusting the thermal treatment it was possible to obtain surfaces performing well as substrate for neuron survival for at least 10 days. Some surfaces permitted normal axonal elongation, whereas dendrite growth was generally impaired. These findings support the potential use of titanium oxide in neuroprostheses and other devices demanding materials with enhanced properties in terms of biocompatibility and axon growth promotion.

AtTMEM18 plays important roles in pollen tube and vegetative growth in Arabidopsis

PubMed Central

Dou, Xiao‐Ying; Yang, Ke‐Zhen; Ma, Zhao‐Xia; Chen, Li‐Qun; Zhang, Xue‐Qin; Bai, Jin‐Rong

2016-01-01

Abstract In flowering plants, pollen tube growth is essential for delivery of male gametes into the female gametophyte or embryo sac for double fertilization. Although many genes have been identified as being involved in the process, the molecular mechanisms of pollen tube growth remains poorly understood. In this study, we identified that the Arabidopsis Transmembrane Protein 18 (AtTMEM18) gene played important roles in pollen tube growth. The AtTMEM18 shares a high similarity with the Transmembrane 18 proteins (TMEM18s) that are conserved in most eukaryotes and may play important roles in obesity in humans. Mutation in the AtTMEM18 by a Ds insertion caused abnormal callose deposition in the pollen grains and had a significant impact on pollen germination and pollen tube growth. AtTMEM18 is expressed in pollen grains, pollen tubes, root tips and other vegetative tissues. The pollen‐rescued assays showed that the mutation in AtTMEM18 also caused defects in roots, stems, leaves and transmitting tracts. AtTMEM18‐GFP was located around the nuclei. Genetic assays demonstrated that the localization of AtTMEM18 around the nuclei in the generative cells of pollen grains was essential for the male fertility. Furthermore, expression of the rice TMEM18‐homologous protein (OsTMEM18) driven by LAT52 promoter could recover the fertility of the Arabidopsis attmem18 mutant. These results suggested that the TMEM18 is important for plant growth in Arabidopsis. PMID:26699939

Ultra-thin grain-oriented silicon steel sheet fabricated by a novel way: Twin-roll strip casting and two-stage cold rolling

NASA Astrophysics Data System (ADS)

Wang, Yin-Ping; Liu, Hai-Tao; Song, Hong-Yu; Liu, Jia-Xin; Shen, Hui-Ying; Jin, Yang; Wang, Guo-Dong

2018-04-01

0.05-0.15 mm-thick ultra-thin grain-oriented silicon steel sheets were successfully produced by a novel processing route including strip casting, hot rolling, normalizing, two-stage cold rolling with intermediate annealing, primary recrystallization annealing and secondary recrystallization annealing. The evolutions of microstructure, texture and inhibitor along the processing were briefly investigated. The results showed that the initial Goss orientation originated due to the heterogenous nucleation of δ-ferrite grains during solidification. Because of the lack of shear deformation, only a few Goss grains were observed in the hot rolled sheet. After the first cold rolling and intermediate annealing, Goss texture was enhanced and distributed in the whole thickness. A small number of Goss grains having a high fraction of high energy boundaries exhibited in the primary recrystallization annealed sheet. A large number of fine and dispersed MnS and AlN and a few co-precipitates MnS and AlN with the size range of 10-70 nm were also observed. Interestingly, a well-developed secondary recrystallization microstructure characterized by 10-60 mm grains and a sharp Goss texture were finally produced in the 0.05-0.15 mm-thick ultra-thin sheets. A magnetic induction B8 of 1.72-1.84 T was obtained. Another new finding was that a few {2 3 0}〈0 0 1〉 and {2 1 0}〈1 2 7〉 grains also can grow up abnormally because of the high fraction of high energy boundaries and the size and number advantage, respectively. These non-Goss grains finally deteriorated the magnetic properties of the ultra-thin sheets. In addition, low surface energies of {hk0} planes may also contribute to the abnormal growth of Goss, {2 3 0}〈0 0 1〉 and {2 1 0}〈1 2 7〉 grains.

Experimental Equipment for Powder Processing

DTIC Science & Technology

2009-08-20

for a series of alumina and zirconia powder mixtures by TMDAR, CR-15 (alumina), as well as TZ3YS and CERAC-2003 (zirconia). The proportion of TMDAR...is known to cause abnormal grain growth. Fig.15 shows the seven representative curves obtained for our zirconia powder system. The 10% and 20...various zirconia powder mixtures. The maximum densification rate for each of our zirconia powder mixtures occurs within the relative density range of

Patterned solid state growth of barium titanate crystals

NASA Astrophysics Data System (ADS)

Ugorek, Michael Stephen

An understanding of microstructure evolution in ceramic materials, including single crystal development and abnormal/enhanced grain growth should enable more controlled final ceramic element structures. In this study, two different approaches were used to control single crystal development in a patterned array. These two methods are: (1) patterned solid state growth in BaTiO 3 ceramics, and (2) metal-mediated single crystal growth in BaTiO 3. With the patterned solid state growth technique, optical photolithography was used to pattern dopants as well as [001] and [110] BaTiO3 single crystal template arrays with a 1000 microm line pattern array with 1000 microm spacings. These patterns were subsequently used to control the matrix grain growth evolution and single crystal development in BaTiO3. It was shown that the growth kinetics can be controlled by a small initial grain size, atmosphere conditions, and the introduction of a dopant at selective areas/interfaces. By using a PO2 of 1x10-5 atm during high temperature heat treatment, the matrix coarsening has been limited (to roughly 2 times the initial grain size), while retaining single crystal boundary motion up to 0.5 mm during growth for dwell times up to 9 h at 1300°C. The longitudinal and lateral growth rates were optimized at 10--15 microm/h at 1300°C in a PO2 of 1x10 -5 atm for single crystal growth with limited matrix coarsening. Using these conditions, a patterned microstructure in BaTiO3 was obtained. With the metal-mediated single crystal growth technique, a novel approach for fabricating 2-2 single crystal/polymer composites with a kerf < 5 microns was demonstrated. Surface templated grain growth was used to propagate a single crystal interface into a polycrystalline BaTiO3 or Ba(Zr0.05 Ti0.95)O3 matrix with lamellar nickel layers. The grain growth evolution and texture development were studied using both [001] and [110] BaTiO3 single crystals templates. By using a PO 2 of 1x10-11 atm during high temperature heat treatment, matrix coarsening was limited while enabling single crystal boundary motion up to 0.35 mm during growth between 1250°C and 1300°C with growth rates ˜ 3--4 microm/h for both single crystal orientations. By removing the inner electrodes, 2-2 single crystal (or ceramic) composites were prepared. The piezoelectric and dielectric properties of the composites of the two compositions were measured. The d33 and d31 of the composites were similar to the polycrystalline ceramic of the same composition.

Effects of rolling conditions on recrystallization microstructure and texture in magnetostrictive Fe-Ga-Al rolled sheets

NASA Astrophysics Data System (ADS)

Li, Jiheng; Liu, Yangyang; Li, Xiaojuan; Mu, Xing; Bao, Xiaoqian; Gao, Xuexu

2018-07-01

The effects of different rolling conditions on the microstructure and texture of primary and secondary recrystallization in magnetostrictive Fe82Ga9Al9+0.1at%NbC alloy sheets were investigated. After the primary recrystallization annealing at 850 °C for 5 min, the as-rolled sheets prepared by warm-cold rolling with an intermediate annealing, can be fully recrystallized, and obtain the homogeneous matrix in which the fine dispersed NbC precipitate particles are distributed. The primary recrystallization textures of sheets with different rolling conditions consist mostly of strong {1 0 0} textures, γ-fiber textures, {4 1 1}〈1 4 8〉 texture and weak Goss texture. In the primary recrystallized sheets prepared by warm-cold rolling with an intermediate annealing, the high energy grain boundaries and ∑9 boundaries have the highest proportion. After high temperature annealing, the secondary recrystallizations of Goss grains in these sheets are more complete, and the size of abnormal grown Goss grain is up to several centimeters, which results in the strongest Goss texture. Correspondingly, the largest magnetostriction of 183 ppm is observed. The sample prepared by warm-cold rolling with an intermediate annealing, has homogeneous primary matrix, special texture components and grain boundary distribution, all of which provide a better surrounding for the abnormal growth of Goss grains. This work indicates that the control of rolling conditions of Fe-Ga-Al alloy sheets is necessary to achieve the strong Goss texture and obtain a possible high magnetostriction if other appropriate conditions (stress, domain structure) are achieved.

On the use of copper-based substrates for YBCO coated conductors

NASA Astrophysics Data System (ADS)

Vannozzi, A.; Fabbri, F.; Augieri, A.; Angrisani Armenio, A.; Galluzzi, V.; Mancini, A.; Rizzo, F.; Rufoloni, A.; Padilla, J. A.; Xuriguera, E.; De Felicis, D.; Bemporad, E.; Celentano, G.

2014-05-01

It is well known that the recrystallization texture of heavily cold-rolled pure copper is almost completely cubic. However, one of the main drawbacks concerning the use of pure copper cube-textured substrates for YBCO coated conductor is the reduced secondary recrystallization temperature. The onset of secondary recrystallization (i.e., the occurrence of abnormal grains with unpredictable orientation) in pure copper substrate was observed within the typical temperature range required for buffer layer and YBCO processing (600-850 °C). To avoid the formation of abnormal grains the effect of both grain size adjustment (GSA) and recrystallization annealing was analyzed. The combined use of a small initial grain size and a recrystallization two-step annealing (TSA) drastically reduced the presence of abnormal grains in pure copper tapes. Another way to overcome the limitation imposed by the formation of abnormal grains is to deposit a buffer layer at temperatures where secondary recrystallization does not occur. For example, La2Zr2O7 (LZO) film with a high degree of epitaxy was grown by metal-organic decomposition (MOD) at 1000 °C on pure copper substrate. In several samples the substrate underwent secondary recrystallization. Our experiments indicate that the motion of grain boundaries occurring during secondary recrystallization process does not affect the quality of LZO film.

ZrB2-CNTs Nanocomposites Fabricated by Spark Plasma Sintering

PubMed Central

Jin, Hua; Meng, Songhe; Xie, Weihua; Xu, Chenghai; Niu, Jiahong

2016-01-01

ZrB2-based nanocomposites with and without carbon nanotubes (CNTs) as reinforcement were prepared at 1600 °C by spark plasma sintering. The effects of CNTs on the microstructure and mechanical properties of nano-ZrB2 matrix composites were studied. The results indicated that adding CNTs can inhibit the abnormal grain growth of ZrB2 grains and improve the fracture toughness of the composites. The toughness mechanisms were crack deflection, crack bridging, debonding, and pull-out of CNTs. The experimental results of the nanograined ZrB2-CNTs composites were compared with those of the micro-grained ZrB2-CNTs composites. Due to the small size and surface effects, the nanograined ZrB2-CNTs composites exhibited stronger mechanical properties: the hardness, flexural strength and fracture toughness were 18.7 ± 0.2 GPa, 1016 ± 75 MPa, and 8.5 ± 0.4 MPa·m1/2, respectively. PMID:28774087

ZrB₂-CNTs Nanocomposites Fabricated by Spark Plasma Sintering.

PubMed

Jin, Hua; Meng, Songhe; Xie, Weihua; Xu, Chenghai; Niu, Jiahong

2016-11-29

ZrB₂-based nanocomposites with and without carbon nanotubes (CNTs) as reinforcement were prepared at 1600 °C by spark plasma sintering. The effects of CNTs on the microstructure and mechanical properties of nano-ZrB₂ matrix composites were studied. The results indicated that adding CNTs can inhibit the abnormal grain growth of ZrB₂ grains and improve the fracture toughness of the composites. The toughness mechanisms were crack deflection, crack bridging, debonding, and pull-out of CNTs. The experimental results of the nanograined ZrB₂-CNTs composites were compared with those of the micro-grained ZrB₂-CNTs composites. Due to the small size and surface effects, the nanograined ZrB₂-CNTs composites exhibited stronger mechanical properties: the hardness, flexural strength and fracture toughness were 18.7 ± 0.2 GPa, 1016 ± 75 MPa, and 8.5 ± 0.4 MPa·m 1/2 , respectively.

Liquid-Phase Processing of Barium Titanate Thin Films

NASA Astrophysics Data System (ADS)

Harris, David Thomas

Processing of thin films introduces strict limits on the thermal budget due to substrate stability and thermal expansion mismatch stresses. Barium titanate serves as a model system for the difficulty in producing high quality thin films because of sensitivity to stress, scale, and crystal quality. Thermal budget restriction leads to reduced crystal quality, density, and grain growth, depressing ferroelectric and nonlinear dielectric properties. Processing of barium titanate is typically performed at temperatures hundreds of degrees above compatibility with metalized substrates. In particular integration with silicon and other low thermal expansion substrates is desirable for reductions in costs and wider availability of technologies. In bulk metal and ceramic systems, sintering behavior has been encouraged by the addition of a liquid forming second phase, improving kinetics and promoting densification and grain growth at lower temperatures. This approach is also widespread in the multilayer ceramic capacitor industry. However only limited exploration of flux processing with refractory thin films has been performed despite offering improved dielectric properties for barium titanate films at lower temperatures. This dissertation explores physical vapor deposition of barium titanate thin films with addition of liquid forming fluxes. Flux systems studied include BaO-B2O3, Bi2O3-BaB2O 4, BaO-V2O5, CuO-BaO-B2O3, and BaO-B2O3 modified by Al, Si, V, and Li. Additions of BaO-B2O3 leads to densification and an increase in average grain size from 50 nm to over 300 nm after annealing at 900 °C. The ability to tune permittivity of the material improved from 20% to 70%. Development of high quality films enables engineering of ferroelectric phase stability using residual thermal expansion mismatch in polycrystalline films. The observed shifts to TC match thermodynamic calculations, expected strain from the thermal expansion coefficients, as well as x-ray diffract measurements . Our system exhibits flux-film-substrate interactions that can lead to dramatic changes to the microstructure. This effect is especially pronounced onc -sapphire, with Al diffusion from the substrate leading to formation of an epitaxial BaAl2O4 second phase at the substrate-film interface. The formation of this second phase in the presence of a liquid phase seeds {111} twins that drive abnormal grain growth. The orientation of the sapphire substrate determines the BaAl2O 4 morphology, enabling control the abnormal grain growth behavior. CuO additions leads to significant grain growth at 900 °C, with average grain size approaching 500 nm. The orthorhombic-tetragonal phase transition is clearly observable in temperature dependent measurements and both linear and nonlinear dielectric properties are improved. All films containing CuO are susceptible to aging. A number of other systems were investigated for efficacy at temperatures below 900 °C. Pulsed laser deposition was used to study flux + BaTiO 3 targets, layered flux films, and in situ liquids. RF-magnetron sputtering using a dual-gun approach was used to explore integration on flexible foils with Ba1-xSrxTiO3. Many of these systems were based on the BaO-B2O3 system, which has proven effective in thin films, multilayer ceramic capacitors, and bulk ceramics. Modifiers allow tailoring of the microstructure at 900 °C, however no compositions were found, and no reports exist in the open literature, that provide significant grain growth or densification below 900 °C. Liquid phase fluxes offer a promising path forward for low temperature processing of barium titanate, with the ultimate goal of integration with metalized silicon substrates. This work demonstrates significant improvements to dielectric properties and the necessity of understanding interactions in the film-flux-substrate system.

Abnormal development of floral meristem triggers defective morphogenesis of generative system in transgenic tomatoes.

PubMed

Chaban, Inna; Khaliluev, Marat; Baranova, Ekaterina; Kononenko, Neonila; Dolgov, Sergey; Smirnova, Elena

2018-04-21

Parthenocarpy and fruit malformations are common among independent transgenic tomato lines, expressing genes encoding different pathogenesis-related (PR) protein and antimicrobal peptides. Abnormal phenotype developed independently of the expression and type of target genes, but distinctive features during flower and fruit development were detected in each transgenic line. We analyzed the morphology, anatomy, and cytoembryology of abnormal flowers and fruits from these transgenic tomato lines and compared them with flowers and fruits of wild tomatoes, line YaLF used for transformation, and transgenic plants with normal phenotype. We confirmed that the main cause of abnormal flower and fruit development was the alterations of determinate growth of generative meristem. These alterations triggered different types of anomalous growth, affecting the number of growing ectopic shoots and formation of new flowers. Investigation of the ovule ontogenesis did not show anomalies in embryo sac development, but fertilization did not occur and embryo sac degenerated. Nevertheless, the ovule continued to differentiate due to proliferation of endothelium cells. The latter substituted embryo sac and formed pseudoembryonic tissue. This process imitated embryogenesis and stimulated ovary growth, leading to the development of parthenocarpic fruit. We demonstrated that failed fertilization occurred due to defective male gametophyte formation, which was manifested in blocked division of the nucleus in the microspore and arrest of vegetative and generative cell formation. Maturing pollen grains were overgrown microspores, not competent for fertilization but capable to induce proliferation of endothelium and development of parthenocarpic ovary. Thus, our study provided new data on the structural transformations of reproductive organs during development of parthenocarpic fruits in transgenic tomato.

Grain boundary, triple junction and quadruple point mobility controlled normal grain growth

NASA Astrophysics Data System (ADS)

Rios, P. R.; Glicksman, M. E.

2015-07-01

Reduction in stored free energy provides the thermodynamic driving force for grain and bubble growth in polycrystals and foams. Evolution of polycrystalline networks exhibit the additional complication that grain growth may be controlled by several kinetic mechanisms through which the decrease in network energy occurs. Polyhedral boundaries, triple junctions (TJs), and quadruple points (QPs) are the geometrically distinct elements of three dimensional networks that follow Plateau's rules, provided that grain growth is limited by diffusion through, and motion of, cell boundaries. Shvindlerman and co-workers have long recognized the kinetic influences on polycrystalline grain growth of network TJs and QPs. Moreover, the emergence of interesting polycrystalline nanomaterials underscored that TJs can indeed influence grain growth kinetics. Currently there exist few detailed studies concerned either with network distributions of grain size, number of faces per grain, or with 'grain trajectories', when grain growth is limited by the motion of its TJs or QPs. By contrast there exist abundant studies of classical grain growth limited by boundary mobility. This study is focused on a topological/geometrical representation of polycrystals to obtain statistical predictions of the grain size and face number distributions, as well as growth 'trajectories' during steady-state grain growth. Three limits to grain growth are considered, with grain growth kinetics controlled by boundary, TJ, and QP mobilities.

Enhanced thermoelectric performance of Nb-doped SrTiO3 by nano-inclusion with low thermal conductivity

PubMed Central

Wang, Ning; Chen, Haijun; He, Hongcai; Norimatsu, Wataru; Kusunoki, Michiko; Koumoto, Kunihito

2013-01-01

Authors reported an effective path to increase the electrical conductivity while to decrease the thermal conductivity, and thus to enhance the ZT value by nano-inclusions. By this method, the ZT value of Nb-doped SrTiO3 was enhanced 9-fold by yttria stabilized zirconia (YSZ) nano-inclusions. YSZ inclusions, located inside grain and in triple junction, can reduce the thermal conductivity by effective interface phonon scattering, enhance the electrical conductivity by promoting the abnormal grain growth, and thus lead to the obvious enhancement of ZT value, which strongly suggests that, it is possible to not only reduce the thermal conductivity, but also increase the electrical conductivity by nano-inclusions with low thermal conductivity. This study will give some useful enlightenment to the preparation of high-performance oxide thermoelectric materials. PMID:24316665

Grain growth mechanism and magnetic properties in L10-FePt thin films

NASA Astrophysics Data System (ADS)

Li, W.; Chen, L.

2017-08-01

This paper focuses on the grain growth mechanisms and magnetic properties of FePt thin films during an annealing process. The grain size and grain orientation distribution have been quantitatively investigated by electron backscatter diffraction (EBSD), and the grain growth kinetics of thin films were described by the phenomenological kinetic grain growth model. The results show that the grain growth exponent and activation energy of the FePt thin films were 4.26 and 136 kJ/mol respectively, indicating that the grain growth mechanism is mainly controlled by the stochastic jumping of atoms crossing the grain boundaries. X-ray diffraction (XRD) results show that disorder-order transformation was concurrent with grain growth during the annealing process, slowing down the velocity of grain growth. The hysteresis loops reveal that the out-of-plane coercivity and squareness is enhanced with increasing annealing temperature and this can be attributed to the improvement of L10-ordered phase volume fraction and texture intensity.

Irradiation-induced grain growth and defect evolution in nanocrystalline zirconia with doped grain boundaries

DOE PAGES

Dey, Sanchita; Mardinly, John; Wang, Yongqiang; ...

2016-05-27

Grain boundaries are effective sinks for radiation-induced defects, ultimately impacting the radiation tolerance of nanocrystalline materials (dense materials with nanosized grains) against net defect accumulation. However, irradiation-induced grain growth leads to grain boundary area decrease, shortening potential benefits of nanostructures. A possible approach to mitigate this is the introduction of dopants to target a decrease in grain boundary mobility or a reduction in grain boundary energy to eliminate driving forces for grain growth (using similar strategies as to control thermal growth). Here, in this study, we tested this concept in nanocrystalline zirconia doped with lanthanum. Although the dopant is observedmore » to segregate to the grain boundaries, causing grain boundary energy decrease and promoting dragging forces for thermally activated boundary movement, irradiation induced grain growth could not be avoided under heavy ion irradiation, suggesting a different growth mechanism as compared to thermal growth. Furthermore, it is apparent that reducing the grain boundary energy reduced the effectiveness of the grain boundary as sinks, and the number of defects in the doped material is higher than in undoped (La-free) YSZ.« less

Influence of modes of metal transfer on grain structure and direction of grain growth in low nickel austenitic stainless steel weld metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mukherjee, Manidipto; Saha, Saptarshi; Pal, Tapan Kumar, E-mail: tkpal.ju@gmail.com

2015-04-15

The present study elaborately discussed the effect of different modes of metal transfer (i.e., short circuit mode, spray mode and pulse mode) on grain structure and direction of grain growth in low nickel austenitic stainless steel weld metals. Electron backscattered diffraction (EBSD) analysis was used to study the grain growth direction and grain structure in weld metals. The changes in grain structure and grain growth direction were found to be essentially varied with the weld pool shape and acting forces induced by modes of metal transfer at a constant welding speed. Short circuit mode of metal transfer owing to highermore » Marangoni force (M{sub a}) and low electromagnetic force (R{sub m}) promotes the lower weld pool volume (Γ) and higher weld pool maximum radius (r{sub m}). Short circuit mode also shows curved and tapered columnar grain structures and the grain growth preferentially occurred in <001> direction. In contrast, spray mode of metal transfer increases the Γ and reduces the r{sub m} values due to very high R{sub m} and typically reveals straight and broad columnar grain structures with preferential growth direction in <111>. In the pulse mode of metal transfer relatively high M{sub a} and R{sub m} simultaneously increase the weld pool width and the primary penetration which might encourage relatively complex grain growth directions in the weld pool and cause a shift of major intensity from <001> to <111> direction. It can also be concluded that the fusion zone grain structure and direction of grain growth are solely dependent on modes of metal transfer and remain constant for a particular mode of metal transfer irrespective of filler wire used. - Highlights: • Welded joints of LNiASS were prepared by varying modes of metal transfer. • Weld pool shape, grain structure and grain growth direction were studied. • Short circuit mode shows curved and tapered grain growth in <001> direction. • Spray mode shows straight and broad columnar grain growth in <111> direction. • Pulse mode shows complex grain growth with a shift in growth direction.« less

A Phase Field Study of the Effect of Microstructure Grain Size Heterogeneity on Grain Growth

NASA Astrophysics Data System (ADS)

Crist, David J. D.

Recent studies conducted with sharp-interface models suggest a link between the spatial distribution of grain size variance and average grain growth rate. This relationship and its effect on grain growth rate was examined using the diffuse-interface Phase Field Method on a series of microstructures with different degrees of grain size gradation. Results from this work indicate that the average grain growth rate has a positive correlation with the average grain size dispersion for phase field simulations, confirming previous observations. It is also shown that the grain growth rate in microstructures with skewed grain size distributions is better measured through the change in the volume-weighted average grain size than statistical mean grain size. This material is based upon work supported by the National Science Foundation under Grant No. 1334283. The NSF project title is "DMREF: Real Time Control of Grain Growth in Metals" and was awarded by the Civil, Mechanical and Manufacturing Innovation division under the Designing Materials to Revolutionize and Engineer our Future (DMREF) program.

On the role of grain boundary character distribution in grain growth of Al-Mg alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsumoto, K.; Shibayanagi, T.; Umakoshi, Y.

1997-02-01

Grain growth behavior of recrystallized Al-Mg alloys containing 0.3 and 2.7 mass% Mg was investigated, focusing on the interconnection between development of the texture and grain boundary character distribution. An Al-0.3 mass% Mg alloy showed two stages in the change of microstructure during grain growth: the frequency of cube oriented grains and the {Sigma}1 boundary significantly increased at an early stage and then decreased. In the second stage a small amount of isolated large grains with the non-cube component grew and consumed the surrounding cube grains. In contrast, the frequency of cube oriented grains and the grain boundary character distributionmore » showed no significant change during grain growth of Al-2.7 mass% Mg. Small clusters composed of several cube grains containing {Sigma}1 boundaries were formed and their spatial distribution played an important role in the change of microstructure during grain growth. The effect of the spatial distribution on the grain growth behavior was discussed considering the energy balance at triple junctions of grain boundaries.« less

Toward single-mode active crystal fibers for next-generation high-power fiber devices.

PubMed

Lai, Chien-Chih; Gao, Wan-Ting; Nguyen, Duc Huy; Ma, Yuan-Ron; Cheng, Nai-Chia; Wang, Shih-Chang; Tjiu, Jeng-Wei; Huang, Chun-Ming

2014-08-27

We report what we believe to be the first demonstration of a facile approach with controlled geometry for the production of crystal-core ceramic-clad hybrid fibers for scaling fiber devices to high average powers. The process consists of dip coating a solution of polycrystalline alumina onto a high-crystallinity 40-μm-diameter Ti:sapphire single-crystalline core followed by thermal treatments. Comparison of the measured refractive index with high-resolution transmission electron microscopy reveals that a Ca/Si-rich intragranular layer is precipitated at grain boundaries by impurity segregation and liquid-phase formation due to the relief of misfit strain energy in the Al2O3 matrix, slightly perturbing the refractive index and hence the optical properties. Additionally, electron backscatter diffractions supply further evidence that the Ti:sapphire single-crystalline core provides the template for growth into a sacrificial polycrystalline cladding, bringing the core and cladding into a direct bond. The thus-prepared doped crystal core with the undoped crystal cladding was achieved through the abnormal grain-growth process. The presented results provide a general guideline both for controlling crystal growth and for the performance of hybrid materials and provides insights into how one might design single-mode high-power crystal fiber devices.

Correlation of Fracture Behavior With Microstructure in Friction Stir Welded, and Spin Formed AI-Li 2195 Domes

NASA Technical Reports Server (NTRS)

Tayon, Wesley A.; Domack, Marcia S.; Hales, Stephen J.

2012-01-01

Single-piece, spin-formed domes manufactured from friction stir welded (FSW) plates of Al-Li alloy 2195 have the potential to reduce the cost of fabricating cryogenic propellant tanks. Mechanical properties in the completed domes can be related directly to the final material condition and the microstructures developed. However, these new fabrication techniques have resulted in unexpected material challenges, such as abnormal grain growth in the weld nugget and the propensity for fracture in the adjacent thermo-mechanically affected zone (TMAZ). In this study, the microstructure and texture transformations within the TMAZ are related to fracture location in the vicinity of the weldment. The texture variations in the TMAZ are caused primarily by the varying amounts of shear deformation introduced during the FSW process. Grain morphology and microtexture characteristics are examined as a function of location in the TMAZ via electron backscatter diffraction (EBSD). A strong correlation between fracture location and the presence of texture banding in the TMAZ is observed. The fracture path tends to follow a distinct region of low Taylor Factor (TF) grains.

Correlation of Fracture Behavior with Microstructure in Friction Stir Welded, and Spin-Formed Al-Li 2195 Domes

NASA Astrophysics Data System (ADS)

Tayon, Wesley A.; Domack, Marcia S.; Hales, Stephen J.

Single-piece, spin-formed domes manufactured from friction stir welded (FSW) plates of Al-Li alloy 2195 have the potential to reduce the cost of fabricating cryogenic propellant tanks. Mechanical properties in the completed domes can be related directly to the final material condition and the microstructures developed. However, these new fabrication techniques have resulted in unexpected material challenges, such as abnormal grain growth in the weld nugget and the propensity for fracture in the adjacent thermo-mechanically affected zone (TMAZ). In this study, the microstructure and texture transformations within the TMAZ are related to fracture location in the vicinity of the weldment. The texture variations in the TMAZ are caused primarily by the varying amounts of shear deformation introduced during the FSW process. Grain morphology and microtexture characteristics are examined as a function of location in the TMAZ via electron backscatter diffraction (EBSD). A strong correlation between fracture location and the presence of texture banding in the TMAZ is observed. The fracture path tends to follow a distinct region of low Taylor Factor (TF) grains.

New alnico magnets fabricated from pre-alloyed gas-atomized powder through diverse consolidation techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, W.; Zhou, L.; Kassen, A. G.

2015-05-25

Fine Alnico 8 spherical powder produced by gas atomization was consolidated through hot pressing (HP), hot isostatic pressing (HIP), and compression molding and subsequent sintering (CMS) techniques. The effects of different fabrication techniques and processing parameters on microstructure and magnetic properties were analyzed and compared. The HP, HIP, and CMS magnets exhibited different features in microstructures and magnetic properties. Magnetically annealed at 840°C for 10 min and subsequently tempered at 650°C for 5h and 580°C for 15h, the HIP sample achieved the best coercivity (H cj =1845 Oe) due to spinodally decomposed (SD) phases with uniform and well-faceted mosaic morphology.more » As a result, the CMS sample had a lower Hcj than HIP and HP samples, but a higher remanence and thus the best energy product (6.5 MGOe) due to preferential grain alignment induced by abnormal grain growth.« less

In situ synchrotron investigation of grain growth behavior of nano-grained UO 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miao, Yinbin; Yao, Tiankai; Lian, Jie

Here, we report on the study of grain growth kinetics in nano-grained UO 2 samples. Dense nano-grained UO 2 samples with well-controlled stoichiometry and grain size were fabricated using the spark plasma sintering technique. To determine the grain growth kinetics at elevated temperatures, a synchrotron wide-angle X-ray scattering (WAXS) study was performed in situ to measure the real-time grain size evolution based on the modified Williamson-Hall analysis. The unique grain growth kinetics of nanocrystalline UO 2 at 730 °C and 820 °C were observed and explained by the difference in mobility of various grain boundaries.

In situ synchrotron investigation of grain growth behavior of nano-grained UO 2

DOE PAGES

Miao, Yinbin; Yao, Tiankai; Lian, Jie; ...

2017-01-09

Here, we report on the study of grain growth kinetics in nano-grained UO 2 samples. Dense nano-grained UO 2 samples with well-controlled stoichiometry and grain size were fabricated using the spark plasma sintering technique. To determine the grain growth kinetics at elevated temperatures, a synchrotron wide-angle X-ray scattering (WAXS) study was performed in situ to measure the real-time grain size evolution based on the modified Williamson-Hall analysis. The unique grain growth kinetics of nanocrystalline UO 2 at 730 °C and 820 °C were observed and explained by the difference in mobility of various grain boundaries.

The pleiotropic ABNORMAL FLOWER AND DWARF1 affects plant height, floral development and grain yield in rice.

PubMed

Ren, Deyong; Rao, Yuchun; Wu, Liwen; Xu, Qiankun; Li, Zizhuang; Yu, Haiping; Zhang, Yu; Leng, Yujia; Hu, Jiang; Zhu, Li; Gao, Zhenyu; Dong, Guojun; Zhang, Guangheng; Guo, Longbiao; Zeng, Dali; Qian, Qian

2016-06-01

Moderate plant height and successful establishment of reproductive organs play pivotal roles in rice grain production. The molecular mechanism that controls the two aspects remains unclear in rice. In the present study, we characterized a rice gene, ABNORMAL FLOWER AND DWARF1 (AFD1) that determined plant height, floral development and grain yield. The afd1 mutant showed variable defects including the dwarfism, long panicle, low seed setting and reduced grain yield. In addition, abnormal floral organs were also observed in the afd1 mutant including slender and thick hulls, and hull-like lodicules. AFD1 encoded a DUF640 domain protein and was expressed in all tested tissues and organs. Subcellular localization showed AFD1-green fluorescent fusion protein (GFP) was localized in the nucleus. Meantime, our results suggested that AFD1 regulated the expression of cell division and expansion related genes. © 2015 The Authors. Journal of Integrative Plant Biology published by John Wiley & Sons Australia, Ltd on behalf of Institute of Botany, Chinese Academy of Sciences.

Implications of mitotic and meiotic irregularities in common beans (Phaseolus vulgaris L.).

PubMed

Lima, D C; Braz, G T; Dos Reis, G B; Techio, V H; Davide, L C; de F B Abreu, A

2016-05-23

The common bean has great social and economic importance in Brazil and is the subject of a high number of publications, especially in the fields of genetics and breeding. Breeding programs aim to increase grain yield; however, mitosis and meiosis represent under explored research areas that have a direct impact on grain yield. Therefore, the study of cell division could be another tool available to bean geneticists and breeders. The aim of this study was to investigate irregularities occurring during the cell cycle and meiosis in common bean. The common bean cultivar used was BRSMG Talismã, which owing to its high yield and grain quality is recommended for cultivation in Brazil. We classified the interphase nuclei, estimated the mitotic and meiotic index, grain pollen viability, and percentage of abnormalities in both processes. The mitotic index was 4.1%, the interphase nucleus was non-reticulated, and 19% of dividing somatic cells showed abnormal behavior. Meiosis also presented irregularities resulting in a meiotic index of 44.6%. Viability of pollen grains was 94.3%. These results indicate that the common bean cultivar BRSMG Talismã possesses repair mechanisms that compensate for changes by producing a large number of pollen grains. Another important strategy adopted by bean plants to ensure stability is the elimination of abnormal cells by apoptosis. As the common bean cultivar BRSMG Talismã is recommended for cultivation because of its good agronomic performance, it can be concluded that mitotic and meiotic irregularities have no negative influence on its grain quality and yield.

Grain growth and pore coarsening in dense nano-crystalline UO 2+x fuel pellets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yao, Tiankai; Mo, Kun; Yun, Di

Dense nano-sized UO 2+x pellets are synthesized by spark plasma sintering with controlled stoichiometries (UO 2.03 and UO 2.11) and grain sizes (~100 nm), and subsequently isothermally annealed to study their effects on grain growth kinetics and microstructure stability. The grain growth kinetics is determined and analyzed focusing on the interaction between grain boundary migration, pore growth and coalescence. Grains grow much bigger in nano-sized UO 2.11 than UO 2.03 upon thermal annealing, consistent with the fact that hyper-stoichiometric UO 2+x is beneficial for sintering due to enhanced U ion diffusion from excessive O ion interstitials. The activation energies ofmore » the grain growth for UO 2.03 and UO 2.11 are determined as ~1.0 and 1.3~2.0 eV, respectively. As compared with the micron-sized UO 2 in which volumetric diffusion dominates the grain coarsening with an activation energy of ~3.0 eV, the enhanced grain growth kinetics in nano-sized UO 2+x suggests that grain boundary diffusion controls grain growth. Lastly, the higher activation energy of more hyper-stoichiometric nano-sized UO 2.11 may be attributed to the excessive O interstitials pinning grain boundary migration.« less

Grain growth and pore coarsening in dense nano-crystalline UO 2+x fuel pellets

DOE PAGES

Yao, Tiankai; Mo, Kun; Yun, Di; ...

2017-03-25

Dense nano-sized UO 2+x pellets are synthesized by spark plasma sintering with controlled stoichiometries (UO 2.03 and UO 2.11) and grain sizes (~100 nm), and subsequently isothermally annealed to study their effects on grain growth kinetics and microstructure stability. The grain growth kinetics is determined and analyzed focusing on the interaction between grain boundary migration, pore growth and coalescence. Grains grow much bigger in nano-sized UO 2.11 than UO 2.03 upon thermal annealing, consistent with the fact that hyper-stoichiometric UO 2+x is beneficial for sintering due to enhanced U ion diffusion from excessive O ion interstitials. The activation energies ofmore » the grain growth for UO 2.03 and UO 2.11 are determined as ~1.0 and 1.3~2.0 eV, respectively. As compared with the micron-sized UO 2 in which volumetric diffusion dominates the grain coarsening with an activation energy of ~3.0 eV, the enhanced grain growth kinetics in nano-sized UO 2+x suggests that grain boundary diffusion controls grain growth. Lastly, the higher activation energy of more hyper-stoichiometric nano-sized UO 2.11 may be attributed to the excessive O interstitials pinning grain boundary migration.« less

Thickness effects on the texture development of fluorine-doped SnO2 thin films: The role of surface and strain energy

NASA Astrophysics Data System (ADS)

Consonni, V.; Rey, G.; Roussel, H.; Bellet, D.

2012-02-01

Polycrystalline fluorine-doped SnO2 thin films have been grown by ultrasonic spray pyrolysis with a thickness varying in the range of 40 to 600 nm. A texture transition from ⟨110⟩ to ⟨100⟩ and ⟨301⟩ crystallographic orientations has experimentally been shown by x-ray diffraction measurements as film thickness is increased, showing that a process of abnormal grain growth has occurred. The texture effects are considered within a thermodynamic approach, in which the minimization of total free energy constitutes the driving force for grain growth. For very small film thickness, it is found that the ⟨110⟩ preferred orientation is due to surface energy minimization, as the (110) planes have the lowest surface energy in the rutile structure. In contrast, as film thickness is increased, the ⟨100⟩ and ⟨301⟩ crystallographic orientations are progressively predominant, owing to elastic strain energy minimization in which the anisotropic character is considered in the elastic biaxial modulus. A texture map is eventually determined, revealing the expected texture as a function of elastic strain and film thickness.

Brassinosteroid insensitive 1-associated kinase 1 (OsI-BAK1) is associated with grain filling and leaf development in rice.

PubMed

Khew, Choy-Yuen; Teo, Chin-Jit; Chan, Wai-Sun; Wong, Hann-Ling; Namasivayam, Parameswari; Ho, Chai-Ling

2015-06-15

Brassinosteroid Insensitive 1 (BRI1)-Associated Kinase I (BAK1) has been reported to interact with BRI1 for brassinosteroid (BR) perception and signal transduction that regulate plant growth and development. The aim of this study is to investigate the functions of a rice OsBAK1 homologue, designated as OsI-BAK1, which is highly expressed after heading. Silencing of OsI-BAK1 in rice plants produced a high number of undeveloped green and unfilled grains compared to the untransformed plants. Histological analyses demonstrated that embryos were either absent or retarded in their development in these unfilled rice grains of OsI-BAK1 RNAi plants. Down regulation of OsI-BAK1 caused a reduction in cell number and enlargement in leaf bulliform cells. Furthermore, transgenic rice plants overexpressing OsI-BAK1 were demonstrated to have corrugated and twisted leaves probably due to increased cell number that caused abnormal bulliform cell structure which were enlarged and plugged deep into leaf epidermis. The current findings suggest that OsI-BAK1 may play an important role in the developmental processes of rice grain filling and leaf cell including the bulliform cells. Copyright © 2015 Elsevier GmbH. All rights reserved.

Recrystallization and grain growth phenomena in a particle-reinforced aluminum composite

NASA Astrophysics Data System (ADS)

van Aken, D. C.; Krajewski, P. E.; Vyletel, G. M.; Allison, J. E.; Jones, J. W.

1995-06-01

Recrystallization and grain growth in a 2219/TiC/15p composite were investigated as functions of the amount of deformation and deformation temperature. Both cold and hot deformed samples were annealed at the normal solution treatment temperature of 535 °C. It was shown that large recrystallized grain diameters, relative to the interparticle spacing, could be produced in a narrow range of deformation for samples cold-worked and those hot-worked below 450 °C. For cold-worked samples, between 4 to 6 pct deformation, the recrystallized grain diameters varied from 530 to 66 μm as the amount of deformation increased. Subsequent grain growth was not observed in these recrystallized materials and noncompact grain shapes were observed. For deformations greater than 15 pct, recrystallized grain diameters less than the interparticle spacing were observed and subsequent grain growth produced a pinned grain diameter of 27 μm. The pinned grain diameter agreed well with an empirical model based on three dimensional (3-D) Monte Carlo simulations of grain growth and particle pinning in a two-phase material. Tensile properties were determined as a function of grain size, and it was shown that grain size had a weak influence on yield strength. A maximum in the yield strength was observed at a grain size larger than the normal grain growth and particle-pinned diameter.

Thermal stability of the microstructure of silver films

NASA Astrophysics Data System (ADS)

Sursaeva, V. G.; Straumal, A. B.

2017-04-01

The thermal stability of freely suspended silver films 100 nm thick is studied during isothermal annealing at temperatures of 350-600°C for different times. At temperatures of 350-450°C, only grain growth is observed. Above 450°C, along with grain growth, the formation and growth of hillocks and holes take place; in this case, grain boundaries are essential in the processes. A continuous film transforms into a cellular one. At 500°C, the growth processes of both grains and holes have the same incubation period, during which no grain growth, hole formation, and hole growth take place.

The W alloying effect on thermal stability and hardening of nanostructured Cu-W alloyed thin films.

PubMed

Zhao, J T; Zhang, J Y; Hou, Z Q; Wu, K; Feng, X B; Liu, G; Sun, J

2018-05-11

In order to achieve desired mechanical properties of alloys by manipulating grain boundaries (GBs) via solute decoration, it is of great significance to understand the underlying mechanisms of microstructural evolution and plastic deformation. In this work, nanocrystalline (NC) Cu-W alloyed films with W concentrations spanning from 0 to 40 at% were prepared by using magnetron sputtering. Thermal stability (within the temperature range of 200 °C-600 °C) and hardness of the films were investigated by using the x-ray diffraction, transmission electron microscope (TEM) and nanoindentation, respectively. The NC pure Cu film exhibited substantial grain growth upon all annealing temperatures. The Cu-W alloyed films, however, displayed distinct microstructural evolution that depended not only on the W concentration but also on the annealing temperature. At a low temperature of 200 °C, all the Cu-W alloyed films were highly stable, with unconspicuous change in grain sizes. At high temperatures of 400 °C and 600 °C, the microstructural evolution was greatly controlled by the W concentrations. The Cu-W films with low W concentration manifested abnormal grain growth (AGG), while the ones with high W concentrations showed phase separation. TEM observations unveiled that the AGG in the Cu-W alloyed thin films was rationalized by GB migration. Nanoindentation results showed that, although the hardness of both the as-deposited and annealed Cu-W alloyed thin films monotonically increased with W concentrations, a transition from annealing hardening to annealing softening was interestingly observed at the critical W addition of ∼25 at%. It was further revealed that an enhanced GB segregation associated with detwinning was responsible for the annealing hardening, while a reduced solid solution hardening for the annealing softening.

The W alloying effect on thermal stability and hardening of nanostructured Cu–W alloyed thin films

NASA Astrophysics Data System (ADS)

Zhao, J. T.; Zhang, J. Y.; Hou, Z. Q.; Wu, K.; Feng, X. B.; Liu, G.; Sun, J.

2018-05-01

In order to achieve desired mechanical properties of alloys by manipulating grain boundaries (GBs) via solute decoration, it is of great significance to understand the underlying mechanisms of microstructural evolution and plastic deformation. In this work, nanocrystalline (NC) Cu–W alloyed films with W concentrations spanning from 0 to 40 at% were prepared by using magnetron sputtering. Thermal stability (within the temperature range of 200 °C–600 °C) and hardness of the films were investigated by using the x-ray diffraction, transmission electron microscope (TEM) and nanoindentation, respectively. The NC pure Cu film exhibited substantial grain growth upon all annealing temperatures. The Cu–W alloyed films, however, displayed distinct microstructural evolution that depended not only on the W concentration but also on the annealing temperature. At a low temperature of 200 °C, all the Cu–W alloyed films were highly stable, with unconspicuous change in grain sizes. At high temperatures of 400 °C and 600 °C, the microstructural evolution was greatly controlled by the W concentrations. The Cu–W films with low W concentration manifested abnormal grain growth (AGG), while the ones with high W concentrations showed phase separation. TEM observations unveiled that the AGG in the Cu–W alloyed thin films was rationalized by GB migration. Nanoindentation results showed that, although the hardness of both the as-deposited and annealed Cu–W alloyed thin films monotonically increased with W concentrations, a transition from annealing hardening to annealing softening was interestingly observed at the critical W addition of ∼25 at%. It was further revealed that an enhanced GB segregation associated with detwinning was responsible for the annealing hardening, while a reduced solid solution hardening for the annealing softening.

O(minus 2) grain boundary diffusion and grain growth in pure dense MgO

NASA Technical Reports Server (NTRS)

Kapadia, C. M.; Leipold, M. H.

1973-01-01

Grain growth behavior in fully dense compacts of MgO of very high purity was studied, and the results compared with other similar behaving materials. The activation energy for the intrinsic self-diffusion of Mg(2minus) is discussed along with the grain boundary diffusion of O(2minus). Grain boundary diffusion of O(2minus) is proposed as the controlling mechanism for grain growth.

Rotation-induced grain growth and stagnation in phase-field crystal models.

PubMed

Bjerre, Mathias; Tarp, Jens M; Angheluta, Luiza; Mathiesen, Joachim

2013-08-01

We consider grain growth and stagnation in polycrystalline microstructures. From the phase-field crystal modeling of the coarsening dynamics, we identify a transition from a grain-growth stagnation upon deep quenching below the melting temperature T(m) to a continuous coarsening at shallower quenching near T(m). The grain evolution is mediated by local grain rotations. In the deep quenching regime, the grain assembly typically reaches a metastable state where the kinetic barrier for recrystallization across boundaries is too large and grain rotation with subsequent coalescence or boundary motion is infeasible. For quenching near T(m), we find that the grain growth depends on the average rate of grain rotation, and follows a power-law behavior with time, with a scaling exponent that depends on the quenching depth.

Effects of local film properties on the nucleation and growth of tin whiskers and hillocks

NASA Astrophysics Data System (ADS)

Sarobol, Pylin

Whiskers and hillocks grow spontaneously on Pb-free Sn electrodeposited films as a response to thin film stresses. Stress relaxation occurs by atom deposition to specific grain boundaries in the plane of the film, with hillocks being formed when grain boundary migration accompanies growth out of the plane of the film. The implication for whisker formation in electronics is serious: whiskers can grow to be millimeters long, sometimes causing short circuiting between adjacent components and, thereby, posing serious electrical reliability risks. In order to develop more effective whisker mitigation strategies, a predictive physics-based model has been needed. A growth model is developed, based on grain boundary faceting, localized Coble creep, as well as grain boundary sliding for whiskers, and grain boundary sliding with shear induced grain boundary migration for hillocks. In this model of whisker formation, two mechanisms are important: accretion of atoms by Coble creep on grain boundary planes normal to the growth direction inducing a grain boundary shear and grain boundary sliding in the direction of whisker growth. The model accurately captures the importance of the geometry of "surface grains"---shallow grains on film surfaces whose depths are significantly less than their in-plane grain sizes. A critical factor in the analysis is the ratio of the grain boundary sliding coefficient to the in-plane film compressive stress. If the accretion-induced shear stresses are not coupled to grain boundary motion and sliding occurs, a whisker forms. If the shear stress is coupled to grain boundary migration, a hillock forms. Based on this model, long whiskers grow from shallow surface grains with easy grain boundary sliding in the direction of growth. Other observed growth morphologies will be discussed in light of our model. Additional insights into the preferred sites for whisker and hillock growth were developed based on elastic anisotropy, local film microstructure, grain misorientation, and elastic strain energy density (ESED) as the driving force for growth. Local grain orientations and strains measured by synchrotron micro-diffraction in regions containing whiskers or hillocks were compared with elastic finite element analysis simulations, including Sn elastic anisotropy. Whisker and hillock grains were observed to have higher crystallographic misorientations with neighboring grains than generally observed in the microstructure. While elastic simulations predicted higher local out-of-plane elastic strains and ESEDs for whisker and hillock grains, synchrotron measurements of out-of-plane strains of whisker and hillock grains after growth showed relaxation, with correspondingly low ESEDs calculated from measured strains. This suggests that, before whisker or hillock formation, highly misoriented grains with high out-of-plane elastic strains and ESEDs relative to their neighbors determined, at least in part, which grains became whiskers or hillocks. Based on the models and experiments in this thesis, a clearer picture emerges of the necessary and sufficient conditions for tin whisker and hillock formation in thin films.

Accretion growth of water-ice grains in astrophysically-relevant dusty plasma experiment

NASA Astrophysics Data System (ADS)

Chai, Kil-Byoung; Marshall, Ryan; Bellan, Paul

2016-10-01

The grain growth process in the Caltech water-ice dusty plasma experiment has been studied using a high-speed camera equipped with a long-distance microscope lens. It is found that (i) the ice grain number density decreases four-fold as the average grain length increases from 20 to 80 um, (ii) the ice grain length has a log-normal distribution rather than a power-law dependence, and (iii) no collisions between ice grains are apparent. The grains have a large negative charge so the agglomeration growth is prevented by their strong mutual repulsion. It is concluded that direct accretion of water molecules is in good agreement with the observed ice grain growth. The volumetric packing factor of the ice grains must be less than 0.25 in order for the grain kinetic energy to be sufficiently small to prevent collisions between ice grains; this conclusion is consistent with ice grain images showing a fractal character.

Grain boundary oxidation and fatigue crack growth at elevated temperatures

NASA Technical Reports Server (NTRS)

Liu, H. W.; Oshida, Y.

1986-01-01

Fatigue crack growth rate at elevated temperatures can be accelerated by grain boundary oxidation. Grain boundary oxidation kinetics and the statistical distribution of grain boundary oxide penetration depth were studied. At a constant delta K-level and at a constant test temperature, fatigue crack growth rate, da/dN, is a function of cyclic frequency, nu. A fatigue crack growth model of intermittent micro-ruptures of grain boundary oxide is constructed. The model is consistent with the experimental observations that, in the low frequency region, da/dN is inversely proportional to nu, and fatigue crack growth is intergranular.

Austenite grain growth kinetics in Al-killed plain carbon steels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Militzer, M.; Giumelli, A.; Hawbolt, E.B.

1996-11-01

Austenite grain growth kinetics have been investigated in three Al-killed plain carbon steels. Experimental results have been validated using the statistical grain growth model by Abbruzzese and Luecke, which takes pinning by second-phase particles into account. It is shown that the pinning force is a function of the pre-heat-treatment schedule. Extrapolation to the conditions of a hot-strip mill indicates that grain growth occurs without pinning during conventional processing. Analytical relations are proposed to simulate austenite grain growth for Al-killed plain carbon steels for any thermal path in a hot-strip mill.

Rotation-limited growth of three-dimensional body-centered-cubic crystals

NASA Astrophysics Data System (ADS)

Tarp, Jens M.; Mathiesen, Joachim

2015-07-01

According to classical grain growth laws, grain growth is driven by the minimization of surface energy and will continue until a single grain prevails. These laws do not take into account the lattice anisotropy and the details of the microscopic rearrangement of mass between grains. Here we consider coarsening of body-centered-cubic polycrystalline materials in three dimensions using the phase field crystal model. We observe, as a function of the quenching depth, a crossover between a state where grain rotation halts and the growth stagnates and a state where grains coarsen rapidly by coalescence through rotation and alignment of the lattices of neighboring grains. We show that the grain rotation per volume change of a grain follows a power law with an exponent of -1.25 . The scaling exponent is consistent with theoretical considerations based on the conservation of dislocations.

Effects of film growth kinetics on grain coarsening and grain shape.

PubMed

Reis, F D A Aarão

2017-04-01

We study models of grain nucleation and coarsening during the deposition of a thin film using numerical simulations and scaling approaches. The incorporation of new particles in the film is determined by lattice growth models in three different universality classes, with no effect of the grain structure. The first model of grain coarsening is similar to that proposed by Saito and Omura [Phys. Rev. E 84, 021601 (2011)PLEEE81539-375510.1103/PhysRevE.84.021601], in which nucleation occurs only at the substrate, and the grain boundary evolution at the film surface is determined by a probabilistic competition of neighboring grains. The surface grain density has a power-law decay, with an exponent related to the dynamical exponent of the underlying growth kinetics, and the average radius of gyration scales with the film thickness with the same exponent. This model is extended by allowing nucleation of new grains during the deposition, with constant but small rates. The surface grain density crosses over from the initial power law decay to a saturation; at the crossover, the time, grain mass, and surface grain density are estimated as a function of the nucleation rate. The distributions of grain mass, height, and radius of gyration show remarkable power law decays, similar to other systems with coarsening and particle injection, with exponents also related to the dynamical exponent. The scaling of the radius of gyration with the height h relative to the base of the grain show clearly different exponents in growth dominated by surface tension and growth dominated by surface diffusion; thus it may be interesting for investigating the effects of kinetic roughening on grain morphology. In growth dominated by surface diffusion, the increase of grain size with temperature is observed.

Fatigue stress concentration and notch sensitivity in nanocrystalline metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Furnish, Timothy A.; Boyce, Brad L.; Sharon, John A.

Recent studies have shown the potential for nanocrystalline metals to possess excellent fatigue resistance compared to their coarse-grained counterparts. Although the mechanical properties of nanocrystalline metals are believed to be particularly susceptible to material defects, a systematic study of the effects of geometric discontinuities on their fatigue performance has not yet been performed. In the present work, nanocrystalline Ni–40 wt%Fe containing both intrinsic and extrinsic defects were tested in tension–tension fatigue. The defects were found to dramatically reduce the fatigue resistance, which was attributed to the relatively high notch sensitivity in the nanocrystalline material. Microstructural analysis within the crack-initiation zonesmore » underneath the defects revealed cyclically-induced abnormal grain growth (AGG) as a predominant deformation and crack initiation mechanism during high-cycle fatigue. Furthermore, the onset of AGG and the ensuing fracture is likely accelerated by the stress concentrations, resulting in the reduced fatigue resistance compared to the relatively defect-free counterparts.« less

Fatigue stress concentration and notch sensitivity in nanocrystalline metals

DOE PAGES

Furnish, Timothy A.; Boyce, Brad L.; Sharon, John A.; ...

2016-03-11

Recent studies have shown the potential for nanocrystalline metals to possess excellent fatigue resistance compared to their coarse-grained counterparts. Although the mechanical properties of nanocrystalline metals are believed to be particularly susceptible to material defects, a systematic study of the effects of geometric discontinuities on their fatigue performance has not yet been performed. In the present work, nanocrystalline Ni–40 wt%Fe containing both intrinsic and extrinsic defects were tested in tension–tension fatigue. The defects were found to dramatically reduce the fatigue resistance, which was attributed to the relatively high notch sensitivity in the nanocrystalline material. Microstructural analysis within the crack-initiation zonesmore » underneath the defects revealed cyclically-induced abnormal grain growth (AGG) as a predominant deformation and crack initiation mechanism during high-cycle fatigue. Furthermore, the onset of AGG and the ensuing fracture is likely accelerated by the stress concentrations, resulting in the reduced fatigue resistance compared to the relatively defect-free counterparts.« less

Mechanism for selective growth in electrical steel

NASA Astrophysics Data System (ADS)

Oh, Eun Jee; Heo, Nam Hoe; Kwon, Se Kyun; Koo, Yang Mo

2018-01-01

Through the competitive selective growth process between {100}, {110}, and {111} grains during final annealing which is governed by the primary grain size and the surface segregation concentration of sulfur, the sharp {110}<001> annealing texture can be developed in a C-and Al-free Fe-3%Si-0.1%Mn electrical steel. Generally, the selective growth of the {110} grains occurs actively under the low surface segregation concentration of sulfur. In spite of the surface energy disadvantage, the selective growth of a {hkl} grain can however occur, if the {hkl} grain size is larger than the critical grain size linearly proportional to the strip thickness.

Grain Growth in Nanocrystalline Mg-Al Thin Films

NASA Astrophysics Data System (ADS)

Kruska, Karen; Rohatgi, Aashish; Vemuri, Rama S.; Kovarik, Libor; Moser, Trevor H.; Evans, James E.; Browning, Nigel D.

2017-12-01

An improved understanding of grain growth kinetics in nanocrystalline materials, and in metals and alloys in general, is of continuing interest to the scientific community. In this study, Mg-Al thin films containing 10 wt pct Al and with 14.5 nm average grain size were produced by magnetron sputtering and subjected to heat treatments. The grain growth evolution in the early stages of heat treatment at 423 K, 473 K, and 573 K (150 °C, 200 °C, and 300 °C) was observed with transmission electron microscopy and analyzed based upon the classical equation developed by Burke and Turnbull. The grain growth exponent was found to be 7 ± 2 and the activation energy for grain growth was 31.1 ± 13.4 kJ/mol, the latter being significantly lower than in bulk Mg-Al alloys. The observed grain growth kinetics are explained by the Al supersaturation in the matrix and the pinning effects of the rapidly forming beta precipitates and possibly shallow grain boundary grooves. The low activation energy is attributed to the rapid surface diffusion which is dominant in thin film systems.

Effect of carbide additions on grain growth in TiC-Ni cermets

NASA Astrophysics Data System (ADS)

Shin, Soon-Gi; Lee, Jun-Hee

2006-02-01

The growth of carbide particles in TiC-XC-2 vol.% Ni and TiC-XC-30 vol.% Ni alloys, where X=Zr, Cr, W, Ta and Mo, was fitted to an equation of the form d3-do 3=Kt. The grain growth behavior during liquid phase sintering at 1673K decreased markedly with the addition of Mo2C or WC, changed little for TaC, and increased with the addition of ZrC or Cr3C2. The grain contiguity decreased with increasing Ni content in the TiC-Mo2C-Ni alloy and was greater in the alloys with smaller growth rate constant. Consequently, the effect of carbide addition on the grain growth of 2 vol.% Ni alloys was found to be similar to that of 30 vol.% Ni alloys. The grain growth mechanism could be explained by the effect of contiguous carbide grain boundaries in restricting the overall grain growth, as well as the area of the solid/liquid interfaces in the alloy by the usual solution/reprecipitation model.

Phase-field model with plastic flow for grain growth in nanocrystalline material

NASA Astrophysics Data System (ADS)

Steinbach, Ingo; Song, Xiaoyan; Hartmaier, Alexander

2010-01-01

A phase-field model is presented which considers the accumulation of structural defects in grain boundaries by an isotropic eigenstrain associated with the grain boundaries. It is demonstrated that the elastic energy caused by dilatation of the grain boundary with respect to the bulk crystal contributes largely to the grain boundary energy. The sign of this contribution can be both positive and negative dependent on the local stress state in the grain boundary. Self-diffusion of atoms is taken into account to relax the stress caused by the dilatation of the grain boundary. Application of the model to discontinuous grain growth in pure nanocrystalline cobalt material is presented. Linear grain growth is found in the nanocrystalline state, which is explained by the interpretation of grain boundary motion as a diffusive process defining an upper limit of the grain boundary velocity independent of the grain boundary curvature but dependent on temperature. The transition to regular grain growth at a critical temperature, as observed experimentally, is explained by the drop of theoretical grain boundary velocity due to its mean curvature during coarsening of the nanograin structure below the maximum velocity.

Static Grain Growth in Contact Metamorphic Calcite: A Cathodoluminescence Study.

NASA Astrophysics Data System (ADS)

Vogt, B.; Heilbronner, R.; Herwegh, M.; Ramseyer, K.

2009-04-01

In the Adamello contact aureole, monomineralic mesozoic limestones were investigated in terms of grain size evolution and compared to results on numerical modeling performed by Elle. The sampled area shows no deformation and therefore represents an appropriate natural laboratory for the study of static grain growth (Herwegh & Berger, 2003). For this purpose, samples were collected at different distances to the contact to the pluton, covering a temperature range between 270 to 630°C. In these marbles, the grain sizes increase with temperature from 5 µm to about 1 cm as one approaches the contact (Herwegh & Berger, 2003). In some samples, photomicrographs show domains of variable cathodoluminescence (CL) intensities, which are interpreted to represent growth zonations. Microstructures show grains that contain cores and in some samples even several growth stages. The cores are usually not centered and the zones not concentric. They may be in touch with grain boundaries. These zonation patterns are consistent within a given aggregate but differ among the samples even if they come from the same location. Relative CL intensities depend on the Mn/Fe ratio. We assume that changes in trace amounts of Mn/Fe must have occurred during the grain size evolution, preserving local geochemical trends and their variations with time. Changes in Mn/Fe ratios can either be explained by (a) locally derived fluids (e.g. hydration reactions of sheet silicate rich marbles in the vicinity) or (b) by the infiltration of the calcite aggregates by externally derived (magmatic?) fluids. At the present stage, we prefer a regional change in fluid composition (b) because the growth zonations only occur at distances of 750-1250 m from the pluton contact (350-450°C). Closer to the contact, neither zonations nor cores were found. At larger distances, CL intensities differ from grain to grain, revealing diagenetic CL patterns that were incompletely recrystallized by grain growth. The role of infiltration of magmatic fluids is also manifest in the vicinity of dikes, where intense zonation patterns are prominent in the marbles. The software Elle was developed to simulate microstructural evolution in rocks. The numerical model with the title "Grain boundary sweeping" was performed by M. Jessell and was found on http://www.materialsknowledge.org/elle. It displays the grain size evolution and the development of growth zonations during grain boundary migration of a 2D foam structure. This simulation was chosen because the driving force is the minimization of isotropic surface energies. It will be compared to the natural microstructures. At the last stage of the simulation the average grain and core sizes have increased. All, even the smallest grains, show growth zonations. Grains can be divided into two groups: (a) initially larger grains, increasing their grain size and maintaining their core size and (b) initially smaller grains with decreasing grain and decreasing core size. Group (a) grains show large areas swept by grain boundaries into the direction of small grains. Grain boundaries between large grains move more slowly. Their cores do not touch any grain boundaries. Cores of group (b) grains are in contact with the grain boundary network and are on the way to be consumed. In the numerical model and in the natural example similar features can be observed: The cores are not necessarily centered, the zonations are not necessarily concentric and some of the cores touch the grain boundary network. In the simulation, grain boundary migration velocity between large grains is smaller than between a large and a small grain. From this we would predict that - given enough time - a well sorted grain size distribution of increased grain size could be generated. But since many small grains occur we infer that this equilibrium has not been obtained. Analytical results of some natural samples that could be analyzed up to now indicate a relatively well sorted grain size distribution suggesting a more mature state of static grain growth. In comparison to the simulation, grain and core boundaries in the marbles are not always straight. For lobate grain boundaries the surface area has not been minimized in respect to the grain size. An explanation for this might be grain boundary pinning or a local dynamic overprint. Some cores and growth zones in the investigated calcites show a continuous change in luminescence. This is interpreted to be an effect of late diffusion within the grain and/or a continuous change of fluid composition and supply. The absence of zonation in samples close to the contact might be explained by fast grain growth due to high temperatures and/or fast fluid transport. Possibly, this is combined with an enhanced component of volume diffusion. Thus concentration variations of Mn/Fe are diminished and not visible in form of a growth zonation. Herwegh M, Berger A (2003) Differences in grain growth of calcite: a field-based modeling approach. Contr. Min. Pet. 145: 600-611

Grain growth kinetics in pyrolite material under lower mantle condition: Implications for the rheology of the lower mantle

NASA Astrophysics Data System (ADS)

Imamura, M.; Kubo, T.; Takumi, K.

2016-12-01

Rheology of the lower mantle largely depends on the grain-size evolution in constituent minerals. The pioneering work on the grain growth kinetics in MgSiO3 bridgmanite and MgO periclase (Yamazaki et al., 1996) has raised the problem that the grain growth rate is too slow to explain the lower-mantle viscosity. This inconsistency may arise from effects of elastic stress due to the eutectoid transformation (e.g., Solomatov et al., 2002) and it may be difficult to extrapolate the slow kinetics obtained to geological timescales. We conducted grain growth experiments in pyrolitic material at 25-27 GPa, and 1600-1950°C for 30-3000 min using Kawai-type high pressure apparatus at Kyushu University. Four phases of bridgmanite, ferro-priclase, Ca-perovskite and majoritic garnet were present in recovered samples annealed at 25 GPa. To avoid the effects of the eutectoid texture, we took the grain growth data only from the sample exhibiting relatively homogeneous equi-granular texture. That was achieved after annealing for 30 minutes at 1800-1950°C (use these grain sizes as d0), and not achieved even after annealing for 3000 minutes at 1600°C. We preliminarily obtained kinetic parameters of n=4.9 and H* 420 kJ/mol for bridgmanite, and n=4.7 and H* 160 kJ/mol for ferro-pericalse. The ratio of grain sizes of bridgmanite and ferro-periclase is almost constant during the grain growth process. These results indicate faster kinetics compared to the previous study, and can be reasonably interpreted as the grain growth occurred by Ostwald ripening. On the other hand, three phases without majoritic garnet were present at higher pressure of 27 GPa and 1800°C, in which the grain size was slightly larger probably due to the smaller proportion of the secondary phases. When extrapolating the grain growth kinetics obtained in the four phases, the grain size of bridgmanite is roughly estimated to be 4-50 µm at 800-1200°C and 200-600 µm at 1600-2000°C in 108 years. These grain sizes may explain the lower-mantle viscosity in diffusion creep regime if we consider the effects of deformation-induced grain growth in convecting mantle (Hiraga et al., 2010).

Austenite grain growth simulation considering the solute-drag effect and pinning effect.

PubMed

Fujiyama, Naoto; Nishibata, Toshinobu; Seki, Akira; Hirata, Hiroyuki; Kojima, Kazuhiro; Ogawa, Kazuhiro

2017-01-01

The pinning effect is useful for restraining austenite grain growth in low alloy steel and improving heat affected zone toughness in welded joints. We propose a new calculation model for predicting austenite grain growth behavior. The model is mainly comprised of two theories: the solute-drag effect and the pinning effect of TiN precipitates. The calculation of the solute-drag effect is based on the hypothesis that the width of each austenite grain boundary is constant and that the element content maintains equilibrium segregation at the austenite grain boundaries. We used Hillert's law under the assumption that the austenite grain boundary phase is a liquid so that we could estimate the equilibrium solute concentration at the austenite grain boundaries. The equilibrium solute concentration was calculated using the Thermo-Calc software. Pinning effect was estimated by Nishizawa's equation. The calculated austenite grain growth at 1473-1673 K showed excellent correspondence with the experimental results.

Microstructure evolution of a ZrC coating layer in TRISO particles during high-temperature annealing

NASA Astrophysics Data System (ADS)

Kim, Daejong; Chun, Young Bum; Ko, Myeong Jin; Lee, Hyeon-Geun; Cho, Moon-Sung; Park, Ji Yeon; Kim, Weon-Ju

2016-10-01

The influence of high-temperature annealing on the microstructure of zirconium carbide (ZrC) was investigated in relation to its application as a coating layer of a nuclear fuel in a very high temperature gas cooled reactor. ZrC was deposited as a constituent coating layer of TRISO coated particles by a fluidized bed chemical vapor deposition method using a ZrCl4-CH4-Ar-H2 system. The grain growth of ZrC during high-temperature annealing was strongly influenced by the co-deposition of free carbon. Sub-stoichiometric ZrC coatings have experienced a significant grain growth during high-temperature annealing at 1800 °C and 1900 °C for 1 h. On the other hand, a dual phase of stoichiometric ZrC and free carbon experienced little grain growth. It was revealed that the free carbon of the as-deposited ZrC was primarily distributed within the ZrC grains but was redistributed to the grain boundaries after annealing. Consequently, carbon at the grain boundary retarded the grain growth of ZrC. Electron backscatter diffraction (EBSD) results showed that as-deposited ZrC had (001) a preferred orientation that kept its favored direction after significant grain growth during annealing. The hardness slightly decreased as the grain growth progressed.

Modelling grain growth in the framework of Rational Extended Thermodynamics

NASA Astrophysics Data System (ADS)

Kertsch, Lukas; Helm, Dirk

2016-05-01

Grain growth is a significant phenomenon for the thermomechanical processing of metals. Since the mobility of the grain boundaries is thermally activated and energy stored in the grain boundaries is released during their motion, a mutual interaction with the process conditions occurs. To model such phenomena, a thermodynamic framework for the representation of thermomechanical coupling phenomena in metals including a microstructure description is required. For this purpose, Rational Extended Thermodynamics appears to be a useful tool. We apply an entropy principle to derive a thermodynamically consistent model for grain coarsening due to the growth and shrinkage of individual grains. Despite the rather different approaches applied, we obtain a grain growth model which is similar to existing ones and can be regarded as a thermodynamic extension of that by Hillert (1965) to more general systems. To demonstrate the applicability of the model, we compare our simulation results to grain growth experiments in pure copper by different authors, which we are able to reproduce very accurately. Finally, we study the implications of the energy release due to grain growth on the energy balance. The present unified approach combining a microstructure description and continuum mechanics is ready to be further used to develop more elaborate material models for complex thermo-chemo-mechanical coupling phenomena.

Grain Growth in Nanocrystalline Mg-Al Thin Films

DOE PAGES

Kruska, Karen; Rohatgi, Aashish; Vemuri, Rama S.; ...

2017-10-05

We report that an improved understanding of grain growth kinetics in nanocrystalline materials, and in metals and alloys in general, is of continuing interest to the scientific community. In this study, Mg-Al thin films containing ~10 wt pct Al and with 14.5 nm average grain size were produced by magnetron sputtering and subjected to heat treatments. The grain growth evolution in the early stages of heat treatment at 423 K, 473 K, and 573 K (150 °C, 200 °C, and 300 °C) was observed with transmission electron microscopy and analyzed based upon the classical equation developed by Burke and Turnbull.more » The grain growth exponent was found to be 7 ± 2 and the activation energy for grain growth was 31.1 ± 13.4 kJ/mol, the latter being significantly lower than in bulk Mg-Al alloys. The observed grain growth kinetics are explained by the Al supersaturation in the matrix and the pinning effects of the rapidly forming beta precipitates and possibly shallow grain boundary grooves. In conclusion, the low activation energy is attributed to the rapid surface diffusion which is dominant in thin film systems.« less

Strength of Rocks Affected by Deformation Enhanced Grain Growth

NASA Astrophysics Data System (ADS)

Kellermann Slotemaker, A.; de Bresser, H.; Spiers, C.

2005-12-01

One way of looking into the possibility of long-term strength changes in the lithosphere is to study transient effects resulting from modifications of the microstructure of rocks. It is generally accepted that mechanical weakening may occur due to progressive grain size refinement resulting from dynamic recrystallization. A decrease in grain size may induce a switch from creep controlled by grain size insensitive dislocation mechanisms to creep governed by grain size sensitive (GSS) mechanisms involving diffusion and grain boundary sliding processes. This switch forms a well-known scenario to explain localization in the lithosphere. However, fine-grained rocks in localized deformation zones are prone to grain coarsening due to surface energy driven grain boundary migration (SED-GBM). This might harden the rock, affecting its role in localizing strain in the long term. The question has arisen if grain growth by SED-GBM in a rock deforming in the GSS creep field can be significantly affected by strain. The broad aim of this study is to shed more light onto this. We have experimentally investigated the microstructural and strength evolution of fine-grained (~0.6 μm) synthetic forsterite and Fe-bearing olivine aggregates that coarsen in grain size while deforming by GSS creep at elevated pressure (600 MPa) and temperature (850-1000 °C). The materials were prepared by `sol-gel' method and contained 0.3-0.5 wt% water and 5-10 vol% enstatite. We performed i) static heat treatment tests of various time durations involving hot isostatic pressing (HIP), and ii) heat treatment tests starting with HIP and continuing with deformation up to 45% axial strain at strain rates in the range 4x10-7 - 1x10-4 s-1. Microstructures were characterized by analyzing full grain size distributions and textures using SEM/EBSD. In addition to the experiments, we studied microstructural evolution in simple two-dimensional numerical models, combining deformation and SED-GBM by means of the modeling package ELLE. Synthetic olivine samples that were heat treated without straining showed only minor grain growth. Presumably, the second phase (enstatite) and/or porosity remaining in the starting material after densification slowed down or inhibited SED-GBM in the static situation. In contrast, samples heat treated and deformed for time durations similar to those of the static tests demonstrated, at identical temperature, an increase in grain size with increasing strain up to a value twice that of the static counterpart. This grain coarsening was associated with continuous hardening of the material, witnessed by the stress-strain curves. A random lattice preferred orientation combined with a low stress sensitivity (n~2) suggested dominant GSS creep controlled by grain boundary sliding. A dynamic grain growth model involving an increase in the fraction of non-hexagonal grains, related to grain neighbor switching, appears applicable to the observed grain growth that is held responsible for the hardening. The ELLE numerical modeling demonstrated that a combination of SED-GBM and geometrical deformation of a 2D grain aggregate can indeed result in enhanced grain growth compared to static grain growth tests. The fraction of non-hexagonal grains was found to remain more or less constant during static grain growth but increased during deformation. We suggest that the application of the dynamic grain growth model to the long-term microstructural evolution of fine-grained lithospheric shear zones can further improve our understanding of the transient or permanent character of strain localizations and related rheological behavior.

Grain growth kinetics in liquid-phase-sintered zinc oxide-barium oxide ceramics

NASA Technical Reports Server (NTRS)

Yang, Sung-Chul; German, Randall M.

1991-01-01

Grain growth of ZnO in the presence of a liquid phase of the ZnO-BaO system has been studied for temperatures from 1300 to 1400 C. The specimens were treated in boiling water and the grains were separated by dissolving the matrix phase in an ultrasonic bath. As a consequence 3D grain size measurements were possible. Microstructural examination shows some grain coalescence with a wide range of neck size ratios and corresponding dihedral angles, however, most grains are isolated. Lognormal grain size distributions show similar shapes, indicating that the growth mechanism is invariant over this time and temperature. All regressions between G exp n and time for n = 2 and 3 proved statistically significant. The rate constants calculated with the growth exponent set to n = 3 are on the same order of magnitude as in metallic systems. The apparent activation energy for growth is estimated between 355 and 458 kJ/mol.

Evaluation of bakanae disease progression caused by Fusarium fujikuroi in Oryza sativa L.

PubMed

Hwang, In Sun; Kang, Woo-Ri; Hwang, Duk-Ju; Bae, Shin-Chul; Yun, Sung-Hwan; Ahn, Il-Pyung

2013-12-01

Bakanae disease caused by Fusarium fujikuroi is an important fungal disease in rice. Among the seven strains isolated from symptomatic rice grains in this study, one strain, FfB14, triggered severe root growth inhibition and decay in the crown and root of rice seedlings. The remaining six strains caused typical Bakanae symptoms such as etiolation and abnormal succulent rice growth. To reveal the relationship between mycelial growth in the infected tissues and Bakanae disease progression, we have established a reliable quantification method using real time PCR that employs a primer pair and dual-labeled probe specific to a unigene encoding F. fujikuroi PNG1 (FfPNG1), which is located upstream of the fumonisin biosynthesis gene cluster. Plotting the crossing point (CP) values from the infected tissue DNAs on a standard curve revealed the active fungal growth of FfB14 in the root and crown of rice seedlings, while the growth rate of FfB20 in rice was more than 4 times lower than FfB14. Massive infective mycelial growth of FfB14 was evident in rice stems and crown; however, FfB20 did not exhibit vigorous growth. Our quantitative evaluation system is applicable for the identification of fungal virulence factors other than gibberellin.

Modeling of Austenite Grain Growth During Austenitization in a Low Alloy Steel

NASA Astrophysics Data System (ADS)

Dong, Dingqian; Chen, Fei; Cui, Zhenshan

2016-01-01

The main purpose of this work is to develop a pragmatic model to predict austenite grain growth in a nuclear reactor pressure vessel steel. Austenite grain growth kinetics has been investigated under different heating conditions, involving heating temperature, holding time, as well as heating rate. Based on the experimental results, the mathematical model was established by regression analysis. The model predictions present a good agreement with the experimental data. Meanwhile, grain boundary precipitates and pinning effects on grain growth were studied by transmission electron microscopy. It is found that with the increasing of the temperature, the second-phase particles tend to be dissolved and the pinning effects become smaller, which results in a rapid growth of certain large grains with favorable orientation. The results from this study provide the basis for the establishment of large-sized ingot heating specification for SA508-III steel.

Study of the Effects of Metallurgical Factors on the Growth of Fatigue Microcracks.

DTIC Science & Technology

1987-11-25

polycrystalline) yield stress. 8. The resulting model, predicated on the notion of orientation-dependent microplastic grains, predicts quantitatively the entire...Figure 5. Predicted crack growth curves for small cracks propagating from a microplastic grain into elastic-plastic, contiguous grains; Ao is defined as...or the crack tip opening *displacement, 6. Figure 5. Predicted crack growth curves for small cracks propagating from a microplastic grain into

Microstructure development in Kolmogorov, Johnson-Mehl, and Avrami nucleation and growth kinetics

NASA Astrophysics Data System (ADS)

Pineda, Eloi; Crespo, Daniel

1999-08-01

A statistical model with the ability to evaluate the microstructure developed in nucleation and growth kinetics is built in the framework of the Kolmogorov, Johnson-Mehl, and Avrami theory. A populational approach is used to compute the observed grain-size distribution. The impingement process which delays grain growth is analyzed, and the effective growth rate of each population is estimated considering the previous grain history. The proposed model is integrated for a wide range of nucleation and growth protocols, including constant nucleation, pre-existing nuclei, and intermittent nucleation with interface or diffusion-controlled grain growth. The results are compared with Monte Carlo simulations, giving quantitative agreement even in cases where previous models fail.

Austenite grain growth simulation considering the solute-drag effect and pinning effect

PubMed Central

Fujiyama, Naoto; Nishibata, Toshinobu; Seki, Akira; Hirata, Hiroyuki; Kojima, Kazuhiro; Ogawa, Kazuhiro

2017-01-01

Abstract The pinning effect is useful for restraining austenite grain growth in low alloy steel and improving heat affected zone toughness in welded joints. We propose a new calculation model for predicting austenite grain growth behavior. The model is mainly comprised of two theories: the solute-drag effect and the pinning effect of TiN precipitates. The calculation of the solute-drag effect is based on the hypothesis that the width of each austenite grain boundary is constant and that the element content maintains equilibrium segregation at the austenite grain boundaries. We used Hillert’s law under the assumption that the austenite grain boundary phase is a liquid so that we could estimate the equilibrium solute concentration at the austenite grain boundaries. The equilibrium solute concentration was calculated using the Thermo-Calc software. Pinning effect was estimated by Nishizawa’s equation. The calculated austenite grain growth at 1473–1673 K showed excellent correspondence with the experimental results. PMID:28179962

Understanding and Tailoring Grain Growth of Lead-Halide Perovskite for Solar Cell Application.

PubMed

Ma, Yongchao; Liu, Yanliang; Shin, Insoo; Hwang, In-Wook; Jung, Yun Kyung; Jeong, Jung Hyun; Park, Sung Heum; Kim, Kwang Ho

2017-10-04

The fundamental mechanism of grain growth evolution in the fabrication process from the precursor phase to the perovskite phase is not fully understood despite its importance in achieving high-quality grains in organic-inorganic hybrid perovskites, which are strongly affected by processing parameters. In this work, we investigate the fundamental conversion mechanism from the precursor phase of perovskite to the complete perovskite phase and how the intermediate phase promotes growth of the perovskite grains during the fabrication process. By monitoring the morphological evolution of the perovskite during the film fabrication process, we observed a clear rod-shaped intermediate phase in the highly crystalline perovskite and investigated the role of the nanorod intermediate phase on the growth of the grains of the perovskite film. Furthermore, on the basis of these findings, we developed a simple and effective method to tailor grain properties including the crystallinity, size, and number of grain boundaries, and then utilized the film with the tailored grains to develop perovskite solar cells.

Grain growth in U–7Mo alloy: A combined first-principles and phase field study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mei, Zhi-Gang; Liang, Linyun; Kim, Yeon Soo

2016-05-01

Grain size is an important factor in controlling the swelling behavior in irradiated U-Mo dispersion fuels. Increasing the grain size in UeMo fuel particles by heat treatment is believed to delay the fuel swelling at high fission density. In this work, a multiscale simulation approach combining first-principles calculation and phase field modeling is used to investigate the grain growth behavior in U-7Mo alloy. The density functional theory based first-principles calculations were used to predict the material properties of U-7Mo alloy. The obtained grain boundary energies were then adopted as an input parameter for mesoscale phase field simulations. The effects ofmore » annealing temperature, annealing time and initial grain structures of fuel particles on the grain growth in U-7Mo alloy were examined. The predicted grain growth rate compares well with the empirical correlation derived from experiments. (C) 2016 Elsevier B.V. All rights reserved.« less

Breakthrough revisited: investigating the requirements for growth of dust beyond the bouncing barrier

NASA Astrophysics Data System (ADS)

Booth, Richard A.; Meru, Farzana; Lee, Man Hoi; Clarke, Cathie J.

2018-03-01

For grain growth to proceed effectively and lead to planet formation, a number of barriers to growth must be overcome. One such barrier, relevant for compact grains in the inner regions of the disc, is the `bouncing barrier' in which large grains (˜mm size) tend to bounce off each other rather than sticking. However, by maintaining a population of small grains, it has been suggested that cm-size particles may grow rapidly by sweeping up these small grains. We present the first numerically resolved investigation into the conditions under which grains may be lucky enough to grow beyond the bouncing barrier by a series of rare collisions leading to growth (so-called `breakthrough'). Our models support previous results, and show that in simple models breakthrough requires the mass ratio at which high-velocity collisions transition to growth instead of causing fragmentation to be low, ϕ ≲ 50. However, in models that take into account the dependence of the fragmentation threshold on mass ratio, we find that breakthrough occurs more readily, even if mass transfer is relatively inefficient. This suggests that bouncing may only slow down growth, rather than preventing growth beyond a threshold barrier. However, even when growth beyond the bouncing barrier is possible, radial drift will usually prevent growth to arbitrarily large sizes.

Cryomilled Aluminum with Diamantane: Thermal Characterization by DSC and Effects of Magnesium

NASA Astrophysics Data System (ADS)

Arnold, Michael Colin

Many structural applications require a material that is both lightweight and corrosion resistant, for which aluminum and its alloys may be considered for use if not for their relatively low strength. By improving strength of aluminum through the Hall-Petch mechanism, it could become a more suitable choice for many structural applications. Cryomilling is used as a production technique to strengthen aluminum by reduction of grain size to the 20-50 nm range. Although the powders produced by cryomilling are well within the nanocrystalline regime, the powders experience significant grain growth during consolidation to a solid body. Cryomilled powders have been shown to remain nanocrystalline by introducing a nano-diamond, diamantane to the grain boundaries. To better characterize the thermal stability of the cryomilled powder with diamantane, Differential Scanning Calorimetry (DSC) was used to measure the isothermal heat flow in the 0.6Tm to 0.9Tm range. A model was developed to correlate the isothermal DSC signal to a grain growth curve and grain growth parameters were elucidated by assuming variable boundary mobility with a sigmoidal form. The model revealed a tendency for boundary mobility to transition from an athermal grain growth mechanism to standard thermally activated grain growth. Grain growth parameters were compared to shed light on possible mechanisms of aluminum-diamantane involvement during grain growth. Powders and consolidated samples with very low concentrations of diamantane and with magnesium were observed by TEM, SEM and XRD, and compared both separately and together to characterize the how thermal stability is affected by diamantane concentration and the presence of magnesium.

Formation and characterization of metallic iron grains in coal-based reduction of oolitic iron ore

NASA Astrophysics Data System (ADS)

Sun, Yong-sheng; Han, Yue-xin; Li, Yan-feng; Li, Yan-jun

2017-02-01

To reveal the formation and characteristics of metallic iron grains in coal-based reduction, oolitic iron ore was isothermally reduced in various reduction times at various reduction temperatures. The microstructure and size of the metallic iron phase were investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and a Bgrimm process mineralogy analyzer. In the results, the reduced Fe separates from the ore and forms metallic iron protuberances, and then the subsequent reduced Fe diffuses to the protuberances and grows into metallic iron grains. Most of the metallic iron grains exist in the quasi-spherical shape and inlaid in the slag matrix. The cumulative frequency of metallic iron grain size is markedly influenced by both reduction time and temperature. With increasing reduction temperature and time, the grain size of metallic iron obviously increases. According to the classical grain growth equation, the growth kinetic parameters, i.e., time exponent, growth activation energy, and pre-exponential constant, are estimated to be 1.3759 ± 0.0374, 103.18 kJ·mol-1, and 922.05, respectively. Using these calculated parameters, a growth model is established to describe the growth behavior of metallic iron grains.

Kinetic model for thin film stress including the effect of grain growth

NASA Astrophysics Data System (ADS)

Chason, Eric; Engwall, A. M.; Rao, Z.; Nishimura, T.

2018-05-01

Residual stress during thin film deposition is affected by the evolution of the microstructure. This can occur because subsurface grain growth directly induces stress in the film and because changing the grain size at the surface affects the stress in new layers as they are deposited. We describe a new model for stress evolution that includes both of these effects. It is used to explain stress in films that grow with extensive grain growth (referred to as zone II) so that the grain size changes throughout the thickness of the layer as the film grows. Equations are derived for different cases of high or low atomic mobility where different assumptions are used to describe the diffusion of atoms that are incorporated into the grain boundary. The model is applied to measurements of stress and grain growth in evaporated Ni films. A single set of model parameters is able to explain stress evolution in films grown at multiple temperatures and growth rates. The model explains why the slope of the curvature measurements changes continuously with thickness and attributes it to the effect of grain size on new layers deposited on the film.

Model Fe-Al Steel with Exceptional Resistance to High Temperature Coarsening. Part II: Experimental Validation and Applications

NASA Astrophysics Data System (ADS)

Zhou, Tihe; Zhang, Peng; O'Malley, Ronald J.; Zurob, Hatem S.; Subramanian, Mani

2015-01-01

In order to achieve a fine uniform grain-size distribution using the process of thin slab casting and directing rolling (TSCDR), it is necessary to control the grain-size prior to the onset of thermomechanical processing. In the companion paper, Model Fe- Al Steel with Exceptional Resistance to High Temperature Coarsening. Part I: Coarsening Mechanism and Particle Pinning Effects, a new steel composition which uses a small volume fraction of austenite particles to pin the growth of delta-ferrite grains at high temperature was proposed and grain growth was studied in reheated samples. This paper will focus on the development of a simple laboratory-scale setup to simulate thin-slab casting of the newly developed steel and demonstrate the potential for grain size control under industrial conditions. Steel bars with different diameters are briefly dipped into the molten steel to create a shell of solidified material. These are then cooled down to room temperature at different cooling rates. During cooling, the austenite particles nucleate along the delta-ferrite grain boundaries and greatly retard grain growth. With decreasing temperature, more austenite particles precipitate, and grain growth can be completely arrested in the holding furnace. Additional applications of the model alloy are discussed including grain-size control in the heat affected zone in welds and grain-growth resistance at high temperature.

Reduced grain boundary energies in rare-earth doped MgAl 2O 4 spinel and consequent grain growth inhibition

DOE PAGES

Hasan, Md M.; Dholabhai, Pratik P.; Dey, Sanchita; ...

2017-05-15

In this paper, grain growth inhibition in MgAl 2O 4 spinel nanostructure was achieved by grain boundary (GB) segregation of rare-earth dopants. Microcalorimetric measurements showed that dense spinel compacts doped with 3 mol% of R 2O 3 (R = Y, Gd, and La) had decreased GB energies as compared to the undoped spinel, representing reduction in the driving force for grain growth. Segregation energies of the three dopants to the Σ3 (111) GB were calculated by atomistic simulation. The dopants with higher ionic radius tend to segregate more strongly to GBs. The GB energies were calculated from atomistic simulation and,more » consistent with experiments, a systematic reduction in GB energy with dopant ionic size was found. Finally, high temperature grain growth experiments revealed a significant reduction of grain growth in the doped nanostructures as compared to the undoped one, which was attributed to increased metastability or possibly also a GB dragging originated from the dopant segregation.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kruska, Karen; Rohatgi, Aashish; Vemuri, Rama S.

An improved understanding of grain growth kinetics in nanocrystalline materials, and in metals and alloys in general, is of continuing interest to the scientific community. In this study, Mg - Al thin films containing ~10 wt.% Al and with 14.5 nm average grain size were produced by magnetron-sputtering and subjected to heat-treatments. The grain growth evolution in the early stages of heat treatment at 423 K (150 °C), 473 K (200 °C) and 573K (300 °C) was observed with transmission electron microscopy and analyzed based upon the classical equation developed by Burke and Turnbull. The grain growth exponent was foundmore » to be 7±2 and the activation energy for grain growth was 31.1±13.4 kJ/mol, the latter being significantly lower than in bulk Mg-Al alloys. The observed grain growth kinetics are explained by the Al supersaturation in the matrix and the pinning effects of the rapidly forming beta precipitates and possibly shallow grain boundary grooves. The low activation energy is attributed to the rapid surface diffusion which is dominant in thin film systems.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kruska, Karen; Rohatgi, Aashish; Vemuri, Rama S.

We report that an improved understanding of grain growth kinetics in nanocrystalline materials, and in metals and alloys in general, is of continuing interest to the scientific community. In this study, Mg-Al thin films containing ~10 wt pct Al and with 14.5 nm average grain size were produced by magnetron sputtering and subjected to heat treatments. The grain growth evolution in the early stages of heat treatment at 423 K, 473 K, and 573 K (150 °C, 200 °C, and 300 °C) was observed with transmission electron microscopy and analyzed based upon the classical equation developed by Burke and Turnbull.more » The grain growth exponent was found to be 7 ± 2 and the activation energy for grain growth was 31.1 ± 13.4 kJ/mol, the latter being significantly lower than in bulk Mg-Al alloys. The observed grain growth kinetics are explained by the Al supersaturation in the matrix and the pinning effects of the rapidly forming beta precipitates and possibly shallow grain boundary grooves. In conclusion, the low activation energy is attributed to the rapid surface diffusion which is dominant in thin film systems.« less

Serial sectioning of grain microstructures under junction control: An old problem in a new guise

NASA Astrophysics Data System (ADS)

Zöllner, D.; Streitenberger, P.

2015-04-01

In the present work the importance of 3D and 4D microstructure analyses are shown. To that aim, we study polycrystalline grain microstructures obtained by grain growth under grain boundary, triple line and quadruple point control. The microstructures themselves are obtained by mesoscopic computer simulations, which enjoy a far greater control over the kinetic and thermodynamic parameters affecting grain growth than can be realized experimentally. In extensive simulation studies we find by 3D respectively 4D microstructure analyses that metrical and topological properties of the microstructures depend strongly on the microstructural feature controlling the growth kinetics. However, the differences between the growth kinetics vanish when we look at classical 2D sections of the 3D ensembles making a differentiation of the controlling grain feature near impossible.

PECTATE LYASE-LIKE 9 from Brassica campestris is associated with intine formation.

PubMed

Jiang, Jingjing; Yao, Lina; Yu, Youjian; Liang, Ying; Jiang, Jianxia; Ye, Nenghui; Miao, Ying; Cao, Jiashu

2014-12-01

Brassica campestris pectate lyase-like 9 (BcPLL9) was previously identified as a differentially expressed gene both in buds during late pollen developmental stage and in pistils during fertilization in Chinese cabbage. To characterize the gene's function, antisense-RNA lines of BcPLL9 (bcpll9) were constructed in Chinese cabbage. Self- and cross-fertilization experiments harvested half seed yields when bcpll9 lines were used as pollen donors. In vivo and in vitro pollen germination assays showed that nearly half of the pollen tubes in bcpll9 were irregular with shorter length and uneven surface. Aniline blue staining identified abnormal accumulation of a specific bright blue unknown material in the bcpll9 pollen portion. Scanning electron microscopy observation verified the abnormal outthrust material to be near the pollen germinal furrows. Transmission electron microscopy observation revealed the internal endintine layer was overdeveloped and predominantly occupied the intine. This abnormally formed intine likely induced the wavy structure and growth arrest of the pollen tube in half of the bcpll9 pollen grains, which resulted in less seed yields. Collectively, this study presented a novel PLL gene that has an important function in B. campestris intine formation. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

Evolution of grain boundary character distributions in alloy 825 tubes during high temperature annealing: Is grain boundary engineering achieved through recrystallization or grain growth?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bai, Qin; Zhao, Qing

Grain boundary engineering (GBE) of nickel-based alloy 825 tubes was carried out with different cold drawing deformations by using a draw-bench on a factory production line and subsequent annealing at various temperatures. The microstructure evolution of alloy 825 during thermal-mechanical processing (TMP) was characterized by means of the electron backscatter diffraction (EBSD) technique to study the TMP effects on the grain boundary network and the evolution of grain boundary character distributions during high temperature annealing. The results showed that the proportion of ∑ 3{sup n} coincidence site lattice (CSL) boundaries of alloy 825 tubes could be increased to > 75%more » by the TMP of 5% cold drawing and subsequent annealing at 1050 °C for 10 min. The microstructures of the partially recrystallized samples and the fully recrystallized samples suggested that the proportion of low ∑ CSL grain boundaries depended on the annealing time. The frequency of low ∑ CSL grain boundaries increases rapidly with increasing annealing time associating with the formation of large-size highly-twinned grains-cluster microstructure during recrystallization. However, upon further increasing annealing time, the frequency of low ∑ CSL grain boundaries decreased markedly during grain growth. So it is concluded that grain boundary engineering is achieved through recrystallization rather than grain growth. - Highlights: •The grain boundary engineering (GBE) is applicable to 825 tubes. •GBE is achieved through recrystallization rather than grain growth. •The low ∑ CSL grain boundaries in 825 tubes can be increased to > 75%.« less

Identification of Accretion as Grain Growth Mechanism in Astrophysically Relevant Water&ice Dusty Plasma Experiment

NASA Astrophysics Data System (ADS)

Marshall, Ryan S.; Chai, Kil-Byoung; Bellan, Paul M.

2017-03-01

The grain growth process in the Caltech water-ice dusty plasma experiment has been studied using a high-speed camera and a long-distance microscope lens. It is observed that (I) the ice grain number density decreases fourfold as the average grain major axis increases from 20 to 80 μm, (II) the major axis length has a log-normal distribution rather than a power-law dependence, and (III) no collisions between ice grains are apparent. The grains have a large negative charge resulting in strong mutual repulsion and this, combined with the fractal character of the ice grains, prevents them from agglomerating. In order for the grain kinetic energy to be sufficiently small to prevent collisions between ice grains, the volumetric packing factor (I.e., ratio of the actual volume to the volume of a circumscribing ellipsoid) of the ice grains must be less than ˜0.1 depending on the exact relative velocity of the grains in question. Thus, it is concluded that direct accretion of water molecules is very likely to dominate the observed ice grain growth.

Manufacturing process to reduce large grain growth in zirconium alloys

DOEpatents

Rosecrans, P.M.

1984-08-01

It is an object of the present invention to provide a procedure for desensitizing zirconium-based alloys to large grain growth (LGG) during thermal treatment above the recrystallization temperature of the alloy. It is a further object of the present invention to provide a method for treating zirconium-based alloys which have been cold-worked in the range of 2 to 8% strain to reduce large grain growth. It is another object of the present invention to provide a method for fabricating a zirconium alloy clad nuclear fuel element wherein the zirconium clad is resistant to large grain growth.

Kinetic Modeling of Sunflower Grain Filling and Fatty Acid Biosynthesis

PubMed Central

Durruty, Ignacio; Aguirrezábal, Luis A. N.; Echarte, María M.

2016-01-01

Grain growth and oil biosynthesis are complex processes that involve various enzymes placed in different sub-cellular compartments of the grain. In order to understand the mechanisms controlling grain weight and composition, we need mathematical models capable of simulating the dynamic behavior of the main components of the grain during the grain filling stage. In this paper, we present a non-structured mechanistic kinetic model developed for sunflower grains. The model was first calibrated for sunflower hybrid ACA855. The calibrated model was able to predict the theoretical amount of carbohydrate equivalents allocated to the grain, grain growth and the dynamics of the oil and non-oil fraction, while considering maintenance requirements and leaf senescence. Incorporating into the model the serial-parallel nature of fatty acid biosynthesis permitted a good representation of the kinetics of palmitic, stearic, oleic, and linoleic acids production. A sensitivity analysis showed that the relative influence of input parameters changed along grain development. Grain growth was mostly affected by the specific growth parameter (μ′) while fatty acid composition strongly depended on their own maximum specific rate parameters. The model was successfully applied to two additional hybrids (MG2 and DK3820). The proposed model can be the first building block toward the development of a more sophisticated model, capable of predicting the effects of environmental conditions on grain weight and composition, in a comprehensive and quantitative way. PMID:27242809

BcMF8, a putative arabinogalactan protein-encoding gene, contributes to pollen wall development, aperture formation and pollen tube growth in Brassica campestris

PubMed Central

Lin, Sue; Dong, Heng; Zhang, Fang; Qiu, Lin; Wang, Fangzhan; Cao, Jiashu; Huang, Li

2014-01-01

Background and Aims The arabinogalactan protein (AGP) gene family is involved in plant reproduction. However, little is known about the function of individual AGP genes in pollen development and pollen tube growth. In this study, Brassica campestris male fertility 8 (BcMF8), a putative AGP-encoding gene previously found to be pollen specific in Chinese cabbage (B. campestris ssp. chinensis), was investigated. Methods Real-time reverse transcription–PCR and in situ hybridization were used to analyse the expression pattern of BcMF8 in pistils. Prokaryotic expression and western blots were used to ensure that BcMF8 could encode a protein. Antisense RNA technology was applied to silence gene expression, and morphological and cytological approaches (e.g. scanning electron microscopy and transmission electron microscopy) were used to reveal abnormal phenotypes caused by gene silencing. Key Results The BcMF8 gene encoded a putative AGP protein that was located in the cell wall, and was expressed in pollen grains and pollen tubes. The functional interruption of BcMF8 by antisense RNA technology resulted in slipper-shaped and bilaterally sunken pollen with abnormal intine development and aperture formation. The inhibition of BcMF8 led to a decrease in the percentage of in vitro pollen germination. In pollen that did germinate, the pollen tubes were unstable, abnormally shaped and burst more frequently relative to controls, which corresponded to an in vivo arrest of pollen germination at the stigma surface and retarded pollen tube growth in the stylar transmitting tissues. Conclusions The phenotypic defects of antisense BcMF8 RNA lines (bcmf8) suggest a crucial function of BcMF8 in modulating the physical nature of the pollen wall and in helping in maintaining the integrity of the pollen tube wall matrix. PMID:24489019

A robust seeding technique for the growth of single grain (RE)BCO and (RE)BCO-Ag bulk superconductors

NASA Astrophysics Data System (ADS)

Namburi, Devendra K.; Shi, Yunhua; Dennis, Anthony R.; Durrell, John H.; Cardwell, David A.

2018-04-01

Bulk, single grains of RE-Ba-Cu-O [(RE)BCO] high temperature superconductors have significant potential for a wide range of applications, including trapped field magnets, energy storage flywheels, superconducting mixers and magnetic separators. One of the main challenges in the production of these materials by the so-called top seeded melt growth technique is the reliable seeding of large, single grains, which are required for high field applications. A chemically aggressive liquid phase comprising of BaCuO2 and CuO is generated during the single grain growth process, which comes into direct contact with the seed crystal either instantaneously or via infiltration through a buffer pellet, if employed in the process. This can cause either partial or complete melting of the seed, leading subsequently to growth failure. Here, the underlying mechanisms of seed crystal melting and the role of seed porosity in the single grain growth process are investigated. We identify seed porosity as a key limitation in the reliable and successful fabrication of large grain (RE)BCO bulk superconductors for the first time, and propose the use of Mg-doped NdBCO generic seeds fabricated via the infiltration growth technique to reduce the effects of seed porosity on the melt growth process. Finally, we demonstrate that the use of such seeds leads to better resistance to melting during the single grain growth process, and therefore to a more reliable fabrication technique.

Effects of heat treatment on U-Mo fuel foils with a zirconium diffusion barrier

NASA Astrophysics Data System (ADS)

Jue, Jan-Fong; Trowbridge, Tammy L.; Breckenridge, Cynthia R.; Moore, Glenn A.; Meyer, Mitchell K.; Keiser, Dennis D.

2015-05-01

A monolith fuel design based on U-Mo alloy has been selected as the fuel type for conversion of the United States' high performance research reactors (HPRRs) from highly enriched uranium (HEU) to low-enriched uranium (LEU). In this fuel design, a thin layer of zirconium is used to eliminate the direct interaction between the U-Mo fuel meat and the aluminum-alloy cladding during irradiation. The co-rolling process used to bond the Zr barrier layer to the U-Mo foil during fabrication alters the microstructure of both the U-10Mo fuel meat and the U-Mo/Zr interface. This work studied the effects of post-rolling annealing treatment on the microstructure of the co-rolled U-Mo fuel meat and the U-Mo/Zr interaction layer. Microscopic characterization shows that the grain size of U-Mo fuel meat increases with the annealing temperature, as expected. The grain sizes were ∼9, ∼13, and ∼20 μm for annealing temperature of 650, 750, and 850 °C, respectively. No abnormal grain growth was observed. The U-Mo/Zr interaction-layer thickness increased with the annealing temperature with an Arrhenius constant for growth of 184 kJ/mole, consistent with a previous diffusion-couple study. The interaction layer thickness was 3.2 ± 0.5 μm, 11.1 ± 2.1 μm, 27.1 ± 0.9 μm for annealing temperature of 650, 750, to 850 °C, respectively. The homogeneity of Mo improves with post rolling annealing temperature and with U-Mo coupon homogenization. The phases in the Zr/U-Mo interaction layer produced by co-rolling, however, differ from those reported in the previous diffusion couple studies.

Effects of heat treatment on U–Mo fuel foils with a zirconium diffusion barrier

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jue, Jan-Fong; Trowbridge, Tammy L.; Breckenridge, Cynthia R.

A monolith fuel design based on U–Mo alloy has been selected as the fuel type for conversion of the United States’ high performance research reactors (HPRRs) from highly enriched uranium (HEU) to low-enriched uranium (LEU). In this fuel design, a thin layer of zirconium is used to eliminate the direct interaction between the U–Mo fuel meat and the aluminum-alloy cladding during irradiation. The co-rolling process used to bond the Zr barrier layer to the U–Mo foil during fabrication alters the microstructure of both the U–10Mo fuel meat and the U–Mo/Zr interface. This work studied the effects of post-rolling annealing treatmentmore » on the microstructure of the co-rolled U–Mo fuel meat and the U–Mo/Zr interaction layer. Microscopic characterization shows that the grain size of U–Mo fuel meat increases with the annealing temperature, as expected. The grain sizes were ~9, ~13, and ~20 μm for annealing temperature of 650, 750, and 850 °C, respectively. No abnormal grain growth was observed. The U–Mo/Zr interaction-layer thickness increased with the annealing temperature with an Arrhenius constant for growth of 184 kJ/mole, consistent with a previous diffusion-couple study. The interaction layer thickness was 3.2 ± 0.5 μm, 11.1 ± 2.1 μm, 27.1 ± 0.9 μm for annealing temperature of 650, 750, to 850 °C, respectively. The homogeneity of Mo improves with post rolling annealing temperature and with U–Mo coupon homogenization. The phases in the Zr/U–Mo interaction layer produced by co-rolling, however, differ from those reported in the previous diffusion couple studies.« less

A multiscale coupled finite-element and phase-field framework to modeling stressed grain growth in polycrystalline thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jamshidian, M., E-mail: jamshidian@cc.iut.ac.ir; Institute of Structural Mechanics, Bauhaus-University Weimar, Marienstrasse 15, 99423 Weimar; Thamburaja, P., E-mail: prakash.thamburaja@gmail.com

A previously-developed finite-deformation- and crystal-elasticity-based constitutive theory for stressed grain growth in cubic polycrystalline bodies has been augmented to include a description of excess surface energy and grain-growth stagnation mechanisms through the use of surface effect state variables in a thermodynamically-consistent manner. The constitutive theory was also implemented into a multiscale coupled finite-element and phase-field computational framework. With the material parameters in the constitutive theory suitably calibrated, our three-dimensional numerical simulations show that the constitutive model is able to accurately predict the experimentally-determined evolution of crystallographic texture and grain size statistics in polycrystalline copper thin films deposited on polyimide substratemore » and annealed at high-homologous temperatures. In particular, our numerical analyses show that the broad texture transition observed in the annealing experiments of polycrystalline thin films is caused by grain growth stagnation mechanisms. - Graphical abstract: - Highlights: • Developing a theory for stressed grain growth in polycrystalline thin films. • Implementation into a multiscale coupled finite-element and phase-field framework. • Quantitative reproduction of the experimental grain growth data by simulations. • Revealing the cause of texture transition to be due to the stagnation mechanisms.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahmed, K.; Tonks, M.; Zhang, Y.

A detailed phase field model for the effect of pore drag on grain growth kinetics was implemented in MARMOT. The model takes into consideration both the curvature-driven grain boundary motion and pore migration by surface diffusion. As such, the model accounts for the interaction between pore and grain boundary kinetics, which tends to retard the grain growth process. Our 2D and 3D simulations demonstrate that the model capture all possible pore-grain boundary interactions proposed in theoretical models. For high enough surface mobility, the pores move along with the migrating boundary as a quasi-rigid-body, albeit hindering its migration rate compared tomore » the pore-free case. For less mobile pores, the migrating boundary can separate from the pores. For the pore-controlled grain growth kinetics, the model predicts a strong dependence of the growth rate on the number of pores, pore size, and surface diffusivity in agreement with theroretical models. An evolution equation for the grain size that includes these parameters was derived and showed to agree well with numerical solution. It shows a smooth transition from boundary-controlled kinetics to pore-controlled kinetics as the surface diffusivity decreases or the number of pores or their size increases. This equation can be utilized in BISON to give accurate estimate for the grain size evolution. This will be accomplished in the near future. The effect of solute drag and anisotropy of grain boundary on grain growth will be investigated in future studies.« less

Influence of initial heating during final high temperature annealing on the offset of primary and secondary recrystallization in Cu-bearing grain oriented electrical steels

NASA Astrophysics Data System (ADS)

Rodriguez-Calvillo, P.; Leunis, E.; Van De Putte, T.; Jacobs, S.; Zacek, O.; Saikaly, W.

2018-04-01

The industrial production route of Grain Oriented Electrical Steels (GOES) is complex and fine-tuned for each grade. Its metallurgical process requires in all cases the abnormal grain growth (AGG) of the Goss orientation during the final high temperature annealing (HTA). The exact mechanism of AGG is not yet fully understood, but is controlled by the different inhibition systems, namely MnS, AlN and CuxS, their size and distribution, and the initial primary recrystallized grain size. Therefore, among other parameters, the initial heating stage during the HTA is crucial for the proper development of primary and secondary recrystallized microstructures. Cold rolled 0.3 mm Cu-bearing Grain Oriented Electrical Steel has been submitted to interrupted annealing experiments in a lab tubular furnace. Two different annealing cycles were applied:• Constant heating at 30°C/h up to 1000°C. Two step cycle with initial heating at 100°C/h up to 600°C, followed by 18 h soaking at 600°C and then heating at 30°C/h up to 1050°C. The materials are analyzed in terms of their magnetic properties, grain size, texture and precipitates. The characteristic magnetic properties are analyzed for the different extraction temperatures and Cycles. As the annealing was progressing, the coercivity values (Hc 1.7T [A/m]) decreased, showing two abrupt drops, which can be associated to the on-set of primary and secondary recrystallization. The primary recrystallized grain sizes and recrystallized fractions are fitted to a model using a non-isothermal approach. This analysis shows that, although the resulting grain sizes were similar, the kinetics for the two step annealing were faster due to the lower recovery. The on-set of secondary recrystallization was also shifted to higher temperatures in the case of the continuous heating cycle, which might end in different final grain sizes and final magnetic properties. In both samples, nearly all the observed precipitates are Al-Si-Mn nitrides, ranging from pure AlN to Si4Mn-nitride.

Repeated growth and bubbling transfer of graphene with millimetre-size single-crystal grains using platinum.

PubMed

Gao, Libo; Ren, Wencai; Xu, Huilong; Jin, Li; Wang, Zhenxing; Ma, Teng; Ma, Lai-Peng; Zhang, Zhiyong; Fu, Qiang; Peng, Lian-Mao; Bao, Xinhe; Cheng, Hui-Ming

2012-02-28

Large single-crystal graphene is highly desired and important for the applications of graphene in electronics, as grain boundaries between graphene grains markedly degrade its quality and properties. Here we report the growth of millimetre-sized hexagonal single-crystal graphene and graphene films joined from such grains on Pt by ambient-pressure chemical vapour deposition. We report a bubbling method to transfer these single graphene grains and graphene films to arbitrary substrate, which is nondestructive not only to graphene, but also to the Pt substrates. The Pt substrates can be repeatedly used for graphene growth. The graphene shows high crystal quality with the reported lowest wrinkle height of 0.8 nm and a carrier mobility of greater than 7,100 cm(2) V(-1) s(-1) under ambient conditions. The repeatable growth of graphene with large single-crystal grains on Pt and its nondestructive transfer may enable various applications.

Repeated growth and bubbling transfer of graphene with millimetre-size single-crystal grains using platinum

PubMed Central

Gao, Libo; Ren, Wencai; Xu, Huilong; Jin, Li; Wang, Zhenxing; Ma, Teng; Ma, Lai-Peng; Zhang, Zhiyong; Fu, Qiang; Peng, Lian-Mao; Bao, Xinhe; Cheng, Hui-Ming

2012-01-01

Large single-crystal graphene is highly desired and important for the applications of graphene in electronics, as grain boundaries between graphene grains markedly degrade its quality and properties. Here we report the growth of millimetre-sized hexagonal single-crystal graphene and graphene films joined from such grains on Pt by ambient-pressure chemical vapour deposition. We report a bubbling method to transfer these single graphene grains and graphene films to arbitrary substrate, which is nondestructive not only to graphene, but also to the Pt substrates. The Pt substrates can be repeatedly used for graphene growth. The graphene shows high crystal quality with the reported lowest wrinkle height of 0.8 nm and a carrier mobility of greater than 7,100 cm2 V−1 s−1 under ambient conditions. The repeatable growth of graphene with large single-crystal grains on Pt and its nondestructive transfer may enable various applications. PMID:22426220

Molecular dynamics simulations investigating consecutive nucleation, solidification and grain growth in a twelve-million-atom Fe-system

NASA Astrophysics Data System (ADS)

Okita, Shin; Verestek, Wolfgang; Sakane, Shinji; Takaki, Tomohiro; Ohno, Munekazu; Shibuta, Yasushi

2017-09-01

Continuous processes of homogeneous nucleation, solidification and grain growth are spontaneously achieved from an undercooled iron melt without any phenomenological parameter in the molecular dynamics (MD) simulation with 12 million atoms. The nucleation rate at the critical temperature is directly estimated from the atomistic configuration by cluster analysis to be of the order of 1034 m-3 s-1. Moreover, time evolution of grain size distribution during grain growth is obtained by the combination of Voronoi and cluster analyses. The grain growth exponent is estimated to be around 0.3 from the geometric average of the grain size distribution. Comprehensive understanding of kinetic properties during continuous processes is achieved in the large-scale MD simulation by utilizing the high parallel efficiency of a graphics processing unit (GPU), which is shedding light on the fundamental aspects of production processes of materials from the atomistic viewpoint.

Experimental Study of Oxygen-Assisted Crack Growth in Alloy 718 and Alloy TI-1100

DTIC Science & Technology

1993-02-01

Ghonem et al [21 proposed that the crack growth rate increases as the grain boundary area exposed to oxygen penetration increases Consequently, the grain...recent work by Chang and al is worthwhile to be mentioned to this respect [3]. These authors used a modified heat treatment to produce a coarser grain...interesting experiment was carried out in the work of Ghonem et al [8] on a fine grain size (20-50jurm) Alloy 718. They carried out crack growth

Low temperature sintered giant dielectric permittivity CaCu3Ti4O12 sol-gel synthesized nanoparticle capacitors

NASA Astrophysics Data System (ADS)

Puli, Venkata Sreenivas; Adireddy, Shiva; Kothakonda, Manish; Elupula, Ravinder; Chrisey, Douglas B.

This paper reports on synthesis of polycrystalline complex perovskite CaCu3Ti4O12 (as CCTO) ceramic powders prepared by a sol-gel auto combustion method at different sintering temperatures and sintering times, respectively. The effect of sintering time on the structure, morphology, dielectric and electrical properties of CCTO ceramics is investigated. Tuning the electrical properties via different sintering times is demonstrated for ceramic samples. X-ray diffraction (XRD) studies confirm perovskite-like structure at room temperature. Abnormal grain growth is observed for ceramic samples. Giant dielectric permittivity was realized for CCTO ceramics. High dielectric permittivity was attributed to the internal barrier layer capacitance (IBLC) model associated with the Maxwell-Wagner (MW) polarization mechanism.

{1 1 1} facet growth laws and grain competition during silicon crystallization

NASA Astrophysics Data System (ADS)

Stamelou, V.; Tsoutsouva, M. G.; Riberi-Béridot, T.; Reinhart, G.; Regula, G.; Baruchel, J.; Mangelinck-Noël, N.

2017-12-01

Directional solidification from mono-crystalline Si seeds having different orientations along the growth direction is studied. Due to the frequent twinning phenomenon, new grains soon nucleate during growth. The grain competition is then characterized in situ by imaging the dynamic evolution of the grain boundaries and of the corresponding grain boundary grooves that are formed at the solid-liquid interface. To perform this study, an experimental investigation based on Bridgman solidification technique coupled with in situ X-ray imaging is conducted in an original device: GaTSBI (Growth at high Temperature observed by X-ray Synchrotron Beam Imaging). Imaging characterisation techniques using X-ray synchrotron radiation at ESRF (European Synchrotron Radiation Facility, Grenoble, France) are applied during the solidification to study the growth dynamics. Facetted/facetted grain boundary grooves only are studied due to their importance in the grain competition because of their implication in the twinning mechanism. The maximum undercooling inside the groove is calculated from the groove depth knowing the local temperature gradient. Additionally, thanks to dynamic X-ray images, the global solid-liquid interface growth rate and the normal growth rate of the {1 1 1} facets existing at the grooves and at the edges are measured. From these measurements, experimental growth laws that correlate the normal velocity of the {1 1 1} facets with the maximum undercooling of the groove are extracted and compared to existing theoretical models. Finally, the experimental laws found for the contribution to the undercooling of the {1 1 1} facets are in good agreement with the theoretical model implying nucleation and growth eased by the presence of dislocations. Moreover, it is shown that, for the same growth parameters, the undercooling at the level of the facets (always lower than 1 K) is higher at the edges so that there is a higher probability of twin nucleation at the edges which is in agreement with the grain structure development characterised in the present experiments as well as in the literature.

Grain growth kinetics of ringwoodite and majorite garnet mixtures and implications for the rheology of the transition zone

NASA Astrophysics Data System (ADS)

Ezad, I.; Dobson, D. P.; Brodholt, J. P.; Thomson, A.; Hunt, S.

2017-12-01

The grain size of the transition zone is a poorly known but important geophysical parameter. Among others, the grain size may control the rheology, seismic attenuation and radiative thermal conductivity of the mantle. However, the grain size of the transition zone minerals ringwoodite (Mg,Fe)2SiO4 and majorite garnet MgSiO3 under appropriate zone conditions is currently unknown and there are very few experiments with which to constrain it. In order to determine the grain size of the transition zone, the grain growth kinetics must be determined for a range of mantle compositions. We have, therefore, experimentally determined the grain growth kinetics of the lowermost transition zone minerals through multi anvil experiments at University College London (UCL). This is achieved through a comprehensive set of time series experiments at pressures of 21 GPa and temperatures relevant to the transition zone. We have also determined the effect of varying water content, oxygen fugacity, iron content and aluminium content also discussed by Dobson and Mariani., (2014). Our initial grain growth experiments conducted at 1200°C and 1400°C at 18 GPa show extremely slow grain growth kinetics; time series experiments extended to 105.8 seconds are unable to produce grains larger than 100 nm. This suggests that fine-grained material at the base of the transition zone will persist on geological timescales. Such small grains size suggests that diffusion creep might be the dominant deformation mechanism in this region. Reference: Dobson, D.P., Mariani, E., 2014. The kinetics of the reaction of majorite plus ferropericlase to ringwoodite: Implications for mantle upwellings crossing the 660 km discontinuity. Earth Planet. Sci. Lett. 408, 110-118. doi:10.1016/j.epsl.2014.10.009

Micron-Resolution X-ray Structural Microscopy Studies of 3-D Grain Growth in Polycrystalline Aluminum

NASA Astrophysics Data System (ADS)

Budai, J. D.; Yang, W.; Tischler, J. Z.; Liu, W.; Larson, B. C.; Ice, G. E.

2004-03-01

We describe a new polychromatic x-ray microdiffraction technique providing 3D measurements of lattice structure, orientation and strain with submicron point-to-point spatial resolution. The instrument is located on the UNI-CAT II undulator beamline at the Advanced Photon Source and uses Kirkpatrick-Baez focusing mirrors, differential aperture CCD measurements and automated analysis of spatially-resolved Laue patterns. 3D x-ray structural microscopy is applicable to a wide range of materials investigations and here we describe 3D thermal grain growth studies in polycrystalline aluminum ( ˜1% Fe,Si) from Alcoa. The morphology and orientations of the grains in a hot-rolled aluminum sample were initially mapped. The sample was then annealed to induce grain growth, cooled to room temperature, and the same volume region was re-mapped to determine the thermal migration of all grain boundaries. Significant grain growth was observed after annealing above ˜350^oC where both low-angle and high-angle boundaries were mobile. These measurements will provide the detailed 3D experimental input needed for testing theories and computer models of 3D grain growth in bulk materials.

Molecular and Functional Characterization of GR2-R1 Event Based Backcross Derived Lines of Golden Rice in the Genetic Background of a Mega Rice Variety Swarna

PubMed Central

Bollinedi, Haritha; S., Gopala Krishnan; Prabhu, Kumble Vinod; Singh, Nagendra Kumar; Mishra, Sushma; Khurana, Jitendra P.; Singh, Ashok Kumar

2017-01-01

Homozygous Golden Rice lines developed in the background of Swarna through marker assisted backcross breeding (MABB) using transgenic GR2-R1 event as a donor for the provitamin A trait have high levels of provitamin A (up to 20 ppm) but are dwarf with pale green leaves and drastically reduced panicle size, grain number and yield as compared to the recurrent parent, Swarna. In this study, we carried out detailed morphological, biochemical and molecular characterization of these lines in a quest to identify the probable reasons for their abnormal phenotype. Nucleotide blast analysis with the primer sequences used to amplify the transgene revealed that the integration of transgene disrupted the native OsAux1 gene, which codes for an auxin transmembrane transporter protein. Real time expression analysis of the transgenes (ZmPsy and CrtI) driven by endosperm-specific promoter revealed the leaky expression of the transgene in the vegetative tissues. We propose that the disruption of OsAux1 disturbed the fine balance of plant growth regulators viz., auxins, gibberellic acid and abscisic acid, leading to the abnormalities in the growth and development of the lines homozygous for the transgene. The study demonstrates the conserved roles of OsAux1 gene in rice and Arabidopsis. PMID:28068433

Molecular and Functional Characterization of GR2-R1 Event Based Backcross Derived Lines of Golden Rice in the Genetic Background of a Mega Rice Variety Swarna.

PubMed

Bollinedi, Haritha; S, Gopala Krishnan; Prabhu, Kumble Vinod; Singh, Nagendra Kumar; Mishra, Sushma; Khurana, Jitendra P; Singh, Ashok Kumar

2017-01-01

Homozygous Golden Rice lines developed in the background of Swarna through marker assisted backcross breeding (MABB) using transgenic GR2-R1 event as a donor for the provitamin A trait have high levels of provitamin A (up to 20 ppm) but are dwarf with pale green leaves and drastically reduced panicle size, grain number and yield as compared to the recurrent parent, Swarna. In this study, we carried out detailed morphological, biochemical and molecular characterization of these lines in a quest to identify the probable reasons for their abnormal phenotype. Nucleotide blast analysis with the primer sequences used to amplify the transgene revealed that the integration of transgene disrupted the native OsAux1 gene, which codes for an auxin transmembrane transporter protein. Real time expression analysis of the transgenes (ZmPsy and CrtI) driven by endosperm-specific promoter revealed the leaky expression of the transgene in the vegetative tissues. We propose that the disruption of OsAux1 disturbed the fine balance of plant growth regulators viz., auxins, gibberellic acid and abscisic acid, leading to the abnormalities in the growth and development of the lines homozygous for the transgene. The study demonstrates the conserved roles of OsAux1 gene in rice and Arabidopsis.

A continuum theory of grain size evolution and damage

NASA Astrophysics Data System (ADS)

Ricard, Y.; Bercovici, D.

2009-01-01

Lithospheric shear localization, as occurs in the formation of tectonic plate boundaries, is often associated with diminished grain size (e.g., mylonites). Grain size reduction is typically attributed to dynamic recrystallization; however, theoretical models of shear localization arising from this hypothesis are problematic because (1) they require the simultaneous action of two creep mechanisms (diffusion and dislocation creep) that occur in different deformation regimes (i.e., in grain size stress space) and (2) the grain growth ("healing") laws employed by these models are derived from normal grain growth or coarsening theory, which are valid in the absence of deformation, although the shear localization setting itself requires deformation. Here we present a new first principles grained-continuum theory, which accounts for both coarsening and damage-induced grain size reduction in a monomineralic assemblage undergoing irrecoverable deformation. Damage per se is the generic process for generation of microcracks, defects, dislocations (including recrystallization), subgrains, nuclei, and cataclastic breakdown of grains. The theory contains coupled macroscopic continuum mechanical and grain-scale statistical components. The continuum level of the theory considers standard mass, momentum, and energy conservation, as well as entropy production, on a statistically averaged grained continuum. The grain-scale element of the theory describes both the evolution of the grain size distribution and mechanisms for both continuous grain growth and discontinuous grain fracture and coalescence. The continuous and discontinuous processes of grain size variation are prescribed by nonequilibrium thermodynamics (in particular, the treatment of entropy production provides the phenomenological laws for grain growth and reduction); grain size evolution thus incorporates the free energy differences between grains, including both grain boundary surface energy (which controls coarsening) and the contribution of deformational work to these free energies (which controls damage). In the absence of deformation, only two mechanisms that increase the average grain size are allowed by the second law of thermodynamics. One mechanism, involving continuous diffusive mass transport from small to large grains, captures the essential components of normal grain growth theories of Lifshitz-Slyosov and Hillert. The second mechanism involves the aggregation of grains and is described using a Smoluchovski formalism. With the inclusion of deformational work and damage, the theory predicts two mechanisms for which the thermodynamic requirement of entropy positivity always forces large grains to shrink and small ones to grow. The first such damage-driven mechanism involving continuous mass transfer from large to small grains tends to homogenize the distribution of grain size toward its initial mean grain size. The second damage mechanism favors the creation of small grains by discontinuous division of larger grains and reduces the mean grain size with time. When considered separately, most of these mechanisms allow for self-similar grain size distributions whose scales (i.e., statistical moments such as the mean, variance, and skewness) can all be described by a single grain scale, such as the mean or maximum. However, the combination of mechanisms, e.g., one that captures the competition between continuous coarsening and mean grain size reduction by breakage, does not generally permit a self-similar solution for the grain size distribution, which contradicts the classic assumption that grain growth laws allowing for both coarsening and recrystallization can be treated with a single grain scale such as the mean size.

Respiratory profiles of grain handlers and sedentary workers.

PubMed Central

Herbert, F. A.; Woytowich, V.; Schram, E.; Baldwin, D.

1981-01-01

During 1978, grain handlers employed at three large inland grain terminals were studied along with an equal number of office workers matched for sex, age and smoking history. Respiratory symptoms and spirometric abnormalities were no more frequent in 16 grain handlers who were non-smokers than in their controls. However, 20 grain handlers who were smokers complained significantly more (P less than 0.01) of grade 1 dyspnea and had significantly lower ratios of forced expiratory volume in the first second to forced vital capacity (P less than 0.05) than their controls. Only 3% of the grain handlers were sensitive to grain dust, and 18% were found to be atopic but to have good lung function. A family history of asthma or allergic rhinitis was no more frequent in the grain handlers than in the control subjects. We conclude that the combination of cigarette smoking and exposure to grain dust causes a deterioration in lung function. PMID:7260809

Grain orientations and grain boundaries in tungsten nonotendril fuzz grown under divertor-like conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parish, Chad M.; Wang, Kun; Doerner, Russel P.

2016-09-19

We grew nanotendril “fuzz” on tungsten via plasma exposure and performed transmission Kikuchi diffraction (tKD) in scanning electron microscopy of isolated nanotendrils. 900 °C, 10 23 He/m 2sec, 4 × 10 26 He/m 2 exposure of tungsten produced a deep and fully developed nanotendril mat. tKD of isolated nanotendrils indicated that there was no preferred crystallographic direction oriented along the long axes of the tendrils, and the grain boundary character showed slightly preferential orientations. In conclusion, tendril growth is sufficiently non-equilibrium to prevent any preference of growth direction to manifest measurably, and that new high-angle boundaries (with new grains andmore » grain-growth axes) nucleate randomly along the tendrils during growth.« less

Potential contributions of figured wood to the practice of sustainable forestry

Treesearch

Don C. Bragg

2006-01-01

The birdseye grain of sugar maple (Acer saccharum Marsh.) can showcase the potential of figured wood in sustainable forestry. This poorly understood but valuable grain abnormality commands such a premium that its presence alone can influence timber management. Good forestry and logging practices can help assure that quality birdseye maple logs are not relegated to low-...

Effect of grain growth of [beta]-silicon nitride on strength, Weibull modulus, and fracture toughness

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hirosaki, Naota; Akimune, Yoshio; Mitomo, Mamoru

1993-07-01

[beta]-Si[sub 3]N[sub 4] powder containing 1 mol% of equimolar Y[sub 2]O[sub 3]-Nd[sub 2]O[sub 3] was gas-pressure sintered at 2,000C for 2 h (SN2), 4 h (SN4), and 8 h (SN8) in 30-MPa nitrogen gas. These materials had a microstructure of in-situ composites'' as a result of exaggerated grain growth of some [beta]-Si[sub 3]N[sub 4] grains during firing. Growth of elongated grains was controlled by the sintering time, so that the desired microstructures were obtained. SN2 had a Weibull modulus as high as 53 because of the uniform size and spatial distribution of its large grains. SN4 had a fracture toughnessmore » of 10.3 MPa[center dot]m[sup 1/2] because of toughening provided by the bridging of elongated grains, whereas SN8 showed a lower fracture toughness, possibly caused by extensive microcracking resulting from excessively large grains. Gas-pressure sintering of [beta]-Si[sub 3]N[sub 4] powder was shown to be effective in fostering selective grain growth for obtaining the desired composite microstructure.« less

Effect of Charged-Magnetic Grains in Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Perry, Jonathan; Matthews, Lorin; Hyde, Truell

Effects of Charged-Magnetic Grains in Protoplanetary Disks Jonathan, Perry, Lorin Swint Matthews, and Truell W. Hyde Center for Astrophysics, Space Physics, and Engi-neering Research, addressPlaceNamePlaceNameplaceBaylor StreetPlaceTypeUniversity, Stree-taddressOne Bear Place 97316 Waco, TX 76798 USA The interaction and growth of dust grains is an important process in early planetesimal formation. The structure of aggregates formed from dust depend largely on the initial properties within the dust population, whether the grains are charged or uncharged, magnetic or non-magnetic. Theoretical simulations exam-ining pair-wise interactions between aggregates indicate that charged magnetic grains exhibit different growth behavior than populations consisting of exclusively charged or exclusively mag-netic grains. This study extends that work to predict how charged-magnetic grains influence grain growth within a protoplanetary disk. An N-body simulation containing various mixtures of dust materials is used to examine the differences in dust coagulation in the presence of charged magnetic aggregates. The growth of the dust aggregates is analyzed to determine the effects that charged magnetic grains contribute to the evolution of the dust cloud. Comparison of the rate of aggregation as well as the dynamic exponent relating mass of a cluster to the elapsed time will both be discussed.

Experimental and simulation studies on grain growth in TiC and WC-based cermets during liquid phase sintering

NASA Astrophysics Data System (ADS)

Shin, Soon-Gi

2000-06-01

The grain growth behaviors of TiC and WC particles in TiC-Ni, TiC-Mo2C-Ni, WC-Co and WC-VC-Co alloys during liquid phase sintering were investigated for different Ni or Co contents and compared with the results of Monte Carlo simulations. In the experimental study, TiC-Ni and WC-Co alloys had a maximum grain size at a certain liquid volume fraction, while the grain size in TiC-Mo2C-Ni and WC-VC-Co alloys increased monotonically with an increasing liquid volume fraction. These results mean that the grain growth of these alloys cannot be explained by the conventional mechanisms for Ostwald ripening, namely diffusion or reaction controlled processes. Monte Carlo simulations with different energy relationships between solidliquid interfaces predicted the effect of the liquid volume fraction on grain size similar to the experimental results. The contiguous boundaries between solid (carbide) particles appear to influence the grain growth behavior in TiC- and WC-based alloys during liquid phase sintering.

Microstructure stability of ultra-fine grained magnesium alloy AZ31 processed by extrusion and equal-channel angular pressing (EX–ECAP)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stráská, Jitka, E-mail: straska.jitka@gmail.com; Janeček, Miloš, E-mail: janecek@met.mff.cuni.cz; Čížek, Jakub, E-mail: jcizek@mbox.troja.mff.cuni.cz

Thermal stability of the ultra-fine grained (UFG) microstructure of magnesium AZ31 alloy was investigated. UFG microstructure was achieved by a combined two-step severe plastic deformation process: the extrusion (EX) and subsequent equal-channel angular pressing (ECAP). This combined process leads to refined microstructure and enhanced microhardness. Specimens with UFG microstructure were annealed isochronally at temperatures 150–500 °C for 1 h. The evolution of microstructure, mechanical properties and dislocation density was studied by electron backscatter diffraction (EBSD), microhardness measurements and positron annihilation spectroscopy (PAS). The coarsening of the fine-grained structure at higher temperatures was accompanied by a gradual decrease of the microhardnessmore » and decrease of dislocation density. Mechanism of grain growth was studied by general equation for grain growth and Arrhenius equation. Activation energies for grain growth were calculated to be 115, 33 and 164 kJ/mol in temperature ranges of 170–210 °C, 210–400 °C and 400–500 °C (443–483 K, 483–673 K and 673–773 K), respectively. - Highlights: • Microhardness of UFG AZ31 alloy decreases with increasing annealing temperature. • This fact has two reasons: dislocation annihilations and/or grain growth. • The activation energies for grain growth were calculated for all temperature ranges.« less

Short communication on Kinetics of grain growth and particle pinning in U-10 wt.% Mo

NASA Astrophysics Data System (ADS)

Frazier, William E.; Hu, Shenyang; Overman, Nicole; Lavender, Curt; Joshi, Vineet V.

2018-01-01

The alloy U-10 wt% Mo was annealed at temperatures ranging from 700 °C to 900 °C for periods lasting up to 24 h. Annealed microstructures were examined using Electron Backscattered Diffraction (EBSD) to obtain average grain sizes and grain size distributions. From the temporal evolution of the average grain size, the activation energy of grain growth was determined to be 172.4 ± 0.961 kJ/mol. Grain growth over the annealing period stagnated after a period of 1-4 h. This stagnation is apparently caused by the pinning effect of second-phase particles in the materials. Back-scattered electron imaging (BSE) was used to confirm that these particles do not appreciably coarsen or dissolve during annealing at the aforementioned temperatures.

Calcium aluminate in alumina

NASA Astrophysics Data System (ADS)

Altay, Arzu

The properties of ceramic materials are determined not only by the composition and structure of the phases present, but also by the distribution of impurities, intergranular films and second phases. The phase distribution and microstructure both depend on the fabrication techniques, the raw materials used, the phase-equilibrium relations, grain growth and sintering processes. In this dissertation research, various approaches have been employed to understand fundamental phenomena such as grain growth, impurity segregation, second-phase formation and crystallization. The materials system chosen was alumina intentionally doped with calcium. Atomic-scale structural analyses of grain boundaries in alumina were carried on the processed samples. It was found that above certain calcium concentrations, CA6 precipitated as a second phase at all sintering temperatures. The results also showed that abnormal grain growth can occur after precipitation and it is not only related to the calcium level, but it is also temperature dependent. In order to understand the formation mechanism of CA6 precipitates in calcium doped alumina samples, several studies have been carried out using either bulk materials or thin films The crystallization of CA2 and CA6 powders has been studied. Chemical processing techniques were used to synthesize the powders. It was observed that CA2 powders crystallized directly, however CA6 powders crystallized through gamma-Al 2O3 solid solution. The results of energy-loss near-edge spectrometry confirmed that gamma-Al2O3 can dissolve calcium. Calcium aluminate/alumina reaction couples have also been investigated. All reaction couples were heat treated following deposition. It was found that gamma-Al2O3 was formed at the interface as a result of the interfacial reaction between the film and the substrate. gamma-Al 2O3 at the interface was stable at much higher temperatures compared to the bulk gamma-Al2O3 formed prior to the CA6 crystallization. In order to complement the studies carried out on the calcium aluminate phases, energy-loss near-edge structure (ELNES) fingerprints of CA2 and CA6 were obtained. It was shown that it is possible to distinguish these phases from each other by comparing the ELNES fingerprints. Theoretical calculations of ELNES were used to assign spectral features to certain symmetry environments that can later be used to understand the structures of unknown materials.

Supplying materials needed for grain growth characterizations of nano-grained UO 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mo, Kun; Miao, Yinbin; Yun, Di

2015-09-30

This activity is supported by the US Nuclear Energy Advanced Modeling and Simulation (NEAMS) Fuels Product Line (FPL) and aims at providing experimental data for the validation of the mesoscale simulation code MARMOT. MARMOT is a mesoscale multiphysics code that predicts the coevolution of microstructure and properties within reactor fuel during its lifetime in the reactor. It is an important component of the Moose-Bison-Marmot (MBM) code suite that has been developed by Idaho National Laboratory (INL) to enable next generation fuel performance modeling capability as part of the NEAMS Program FPL. In order to ensure the accuracy of the microstructuremore » based materials models being developed within the MARMOT code, extensive validation efforts must be carried out. In this report, we summarize our preliminary synchrotron radiation experiments at APS to determine the grain size of nanograin UO 2. The methodology and experimental setup developed in this experiment can directly apply to the proposed in-situ grain growth measurements. The investigation of the grain growth kinetics was conducted based on isothermal annealing and grain growth characterization as functions of duration and temperature. The kinetic parameters such as activation energy for grain growth for UO 2 with different stoichiometry are obtained and compared with molecular dynamics (MD) simulations.« less

Effect of grain alignment distribution on magnetic properties in (MM, Nd)-Fe-B sintered magnets

NASA Astrophysics Data System (ADS)

Yu, Xiaoqiang; Yue, Ming; Zhu, Minggang; Liu, Weiqiang; Li, Yuqing; Xi, Longlong; Li, Jiajie; Zhang, Jiuxing; Li, Wei

2018-03-01

H cj of (MM x Nd1-x )-Fe-B sintered magnets decreases distinctly with x increasing when misch metal (MM) content (x) ranges from 0.3 to 1. Practical application is taken into consideration so that the (MM0.6Nd0.4)-Fe-B components are chosen to analyze the changes in behavior of the magnetic properties. Both Magnet II and Magnet III belong to (MM0.6Nd0.4)-Fe-B sintered magnets, however, it should be noted that Magnet II is prepared by the single alloying method (SAM) and Magnet III is prepared by the double main phase alloy method (DMPAM). Core-shell structures of the magnets prepared by DMPAM can result in the higher H cj and lower knee-point coercivity (H k) compared with that by SAM. Furthermore, for Magnet II, the abnormal grain growth contributes to a better grain alignment and smaller distribution coefficient (σ) defined as the degree of grain alignment, which will enforce a higher tendency of the H cj decreasing and H k increasing. The expression of their normalized coercivity h(σ) is deduced by combining Gao’s starting field model with Kronmüller’s nucleation mechanism. Based on the overall h(σ) ~ σ curve, the best desirable h(σ) value is calculated when σ  =  0.09. Theoretically, for Magnet III, the resultant larger σ should be attributed to the more uniform grain alignment. In addition, the deviations of grain size distributions on the c-plane become more remarkable with more MM concentrates, which can be presented by SEM images. Meanwhile, by means of the pole figures, it is also verified that the grain alignment distribution becomes much more diverse with x increasing. Therefore, it can be predicted whether the grain alignment distribution is significant for H k and H cj of (MM x Nd1-x )-Fe-B sintered magnets (x  ≠  0.6) prepared by SAM/DMPAM or not.

Dynamic Grain Growth in Forsterite Aggregates Experimentally Deformed to High Strain

NASA Astrophysics Data System (ADS)

Kellermann Slotemaker, A.; de Bresser, H.; Spiers, C.; Drury, M.

2004-12-01

The dynamics of the outer Earth are largely controlled by olivine rheology. From previous work it has become clear that if olivine rocks are deformed to high strain, substantial weakening may occur before steady state mechanical behaviour is approached. This weakening appears directly related to progressive modification of the grain size distribution through competing effects of dynamic recrystallization and syn-deformational grain growth. However, most of our understanding of these processes in olivine comes from tests on coarse-grained materials that were reduced in grain size during straining by grain size insensitive (dislocation) creep mechanisms. The aim of the present study was to investigate microstructure evolution of fine-grained olivine rocks that coarsen in grain size while deforming by grain size sensitive (GSS) creep. We used fine-grained (~1 μ m) olivine aggregates (i.e., forsterite/Mg2SiO4), containing ~0.5 wt% water and 10 vol% enstatite (MgSiO3). Two types of experiments were carried out: 1) Hot isostatic pressing (HIP) followed by axial compression to varying strains up to a maximum of ~45%, at 600 MPa confining pressure and a temperature of 950°C, 2) HIP treatment without axial deformation. Microstructures were characterized by analyzing full grain size distributions and texture using SEM/EBSD. Our stress-strain curves showed continuous hardening. When samples were temporally unloaded for short time intervals, no difference in flow stress was observed before and after the interruption in straining. Strain rate sensitivity analysis showed a low value of ~1.5 for the stress exponent n. Measured grain sizes show an increase with strain up to a value twice that of the starting value. HIP-only samples showed only minor increase in grain size. A random LPO combined with the low n ~1.5 suggests dominant GSS creep controlled by grain boundary sliding. These results indicate that dynamic grain growth occurs in forsterite aggregates deforming by GSS creep, and we relate the continuous strain hardening to this process. A dynamic grain growth model involving an increase in cellular defect fraction seems best applicable to the grain growth observed in this study. We suggest that the employment of this model to fine-grained olivine rocks can further improve our understanding of the microstructural evolution of this material and related rheological behaviour.

Grain dust and the lungs.

PubMed Central

Chan-Yeung, M.; Ashley, M. J.; Grzybowski, S.

1978-01-01

Grain dust is composed of a large number of materials, including various types of grain and their disintegration products, silica, fungi, insects and mites. The clinical syndromes described in relation to exposure to grain dust are chronic bronchitis, grain dust asthma, extrinsic allergic alveolitis, grain fever and silo-filler's lung. Rhinitis and conjunctivitis are also common in grain workers. While the concentration and the quality of dust influence the frequency and the type of clinical syndrome in grain workers, host factors are also important. Of the latter, smoking is the most important factor influencing the frequency of chronic bronchitis. The role of atopy and of bronchial hyperreactivity in grain dust asthma has yet to be assessed. Several well designed studies are currently being carried out in North America not only to delineate the frequency of the respiratory abnormalities, the pathogenetic mechanisms and the host factors, but also to establish a meaningful threshold limit concentration for grain dust. Images p1272-a PMID:348288

Tungsten Carbide Grain Size Computation for WC-Co Dissimilar Welds

NASA Astrophysics Data System (ADS)

Zhou, Dongran; Cui, Haichao; Xu, Peiquan; Lu, Fenggui

2016-06-01

A "two-step" image processing method based on electron backscatter diffraction in scanning electron microscopy was used to compute the tungsten carbide (WC) grain size distribution for tungsten inert gas (TIG) welds and laser welds. Twenty-four images were collected on randomly set fields per sample located at the top, middle, and bottom of a cross-sectional micrograph. Each field contained 500 to 1500 WC grains. The images were recognized through clustering-based image segmentation and WC grain growth recognition. According to the WC grain size computation and experiments, a simple WC-WC interaction model was developed to explain the WC dissolution, grain growth, and aggregation in welded joints. The WC-WC interaction and blunt corners were characterized using scanning and transmission electron microscopy. The WC grain size distribution and the effects of heat input E on grain size distribution for the laser samples were discussed. The results indicate that (1) the grain size distribution follows a Gaussian distribution. Grain sizes at the top of the weld were larger than those near the middle and weld root because of power attenuation. (2) Significant WC grain growth occurred during welding as observed in the as-welded micrographs. The average grain size was 11.47 μm in the TIG samples, which was much larger than that in base metal 1 (BM1 2.13 μm). The grain size distribution curves for the TIG samples revealed a broad particle size distribution without fine grains. The average grain size (1.59 μm) in laser samples was larger than that in base metal 2 (BM2 1.01 μm). (3) WC-WC interaction exhibited complex plane, edge, and blunt corner characteristics during grain growth. A WC ( { 1 {bar{{1}}}00} ) to WC ( {0 1 1 {bar{{0}}}} ) edge disappeared and became a blunt plane WC ( { 10 1 {bar{{0}}}} ) , several grains with two- or three-sided planes and edges disappeared into a multi-edge, and a WC-WC merged.

Solidification kinetics of a near eutectic Al-Si alloy, unmodified and modified with Sr

NASA Astrophysics Data System (ADS)

Aparicio, R.; Barrera, G.; Trapaga, G.; Ramirez-Argaez, M.; Gonzalez-Rivera, C.

2013-07-01

The purpose of this work was to explore the differences in solidification kinetics between unmodified and Sr modified eutectic Al-Si alloy as revealed by Fourier Thermal Analysis (FTA) and grain-growth kinetics characterization. Thermal analysis were performed in cylindrical stainless steel cups coated with a thin layer of boron nitride, using two type-K thermocouples connected to a data acquisition system. Grain growth kinetics characterization was carried out using solid fraction evolution and grain density data. FTA results for the non modified and modified alloys suggest that there are changes in the solidification rate during eutectic nucleation followed, during growth, by similar solidification rate evolutions, suggesting that this parameter is governed principally by the heat extraction conditions. On the other hand the change of the grain growth parameters estimated for the experimental probes suggest that the presence of Sr may modify the relationship between grain growth rate and undercooling in eutectic Al-Si.

High Temperature Fatigue Crack Growth Behavior of Alloy 10

NASA Technical Reports Server (NTRS)

Gayda, John

2001-01-01

Methods to improve the high temperature, dwell crack growth resistance of Alloy 10, a high strength, nickel-base disk alloy, were studied. Two approaches, heat treat variations and composition modifications, were investigated. Under the heat treat approach, solution temperature, cooling rates, and stabilization, were studied. It was found that higher solution temperatures, which promote coarser grain sizes, coupled with a 1550 F stabilization treatment were found to significantly reduce dwell crack growth rates at 1300 F Changes in the niobium and tantalum content were found to have a much smaller impact on crack growth behavior. Lowering the niobium:tantalum ratio did improve crack growth resistance and this effect was most pronounced for coarse grain microstructures. Based on these findings, a coarse grain microstructure for Alloy 10 appears to be the best option for improving dwell crack growth resistance, especially in the rim of a disk where temperatures can reach or exceed 1300 T. Further, the use of advanced processing technologies, which can produce a coarse grain rim and fine grain bore, would be the preferred option for Alloy 10 to obtain the optimal balance between tensile, creep, and crack growth requirements for small gas turbine engines.

The Coupling of Macrosegregation with Grain Nucleation, Growth and Motion in DC Cast Aluminum Alloy Ingots

NASA Astrophysics Data System (ADS)

Založnik, Miha; Kumar, Arvind; Combeau, Hervé; Bedel, Marie; Jarry, Philippe; Waz, Emmanuel

The phenomena responsible for the formation of macrosegregations, and grain structures during solidification are closely intertwined. We present a model study of the formation of macrosegregation and grain structure in an industrial sized (350 mm thick) direct chill (DC) cast aluminum alloy slab. The modeling of these phenomena in DC casting is a challenging problem mainly due to the size of the products, the variety of the phenomena to be accounted for, and the non-linearities involved. We used a volume-averaged multiscale model that describes nucleation on grain refiner particles and grain growth, coupled with macroscopic transport: fluid flow driven by natural convection and shrinkage, transport of free-floating globular equiaxed grains, heat transfer, and solute transport. We analyze the heat and mass transfer in the slurry moving-grain zone that is a result of the coupling of the fluid flow and of the grain nucleation, growth and motion. We discuss the impact of the flow structure in the slurry zone and of the grain packing fraction on the macrosegregation.

Grain size evolution and convection regimes of the terrestrial planets

NASA Astrophysics Data System (ADS)

Rozel, A.; Golabek, G. J.; Boutonnet, E.

2011-12-01

A new model of grain size evolution has recently been proposed in Rozel et al. 2010. This new approach stipulates that the grain size dynamics is governed by two additive and simultaneous processes: grain growth and dynamic recrystallization. We use the usual normal grain growth laws for the growth part. For dynamic recrystallization, reducing the mean grain size increases the total area of grain boundaries. Grain boundaries carry some surface tension, so some energy is required to decrease the mean grain size. We consider that this energy is available during mechanical work. It is usually considered to produce some heat via viscous dissipation. A partitioning parameter f is then required to know what amount of energy is dissipated and what part is converted in surface tension. This study gives a new calibration of the partitioning parameter on major Earth materials involved in the dynamic of the terrestrial planets. Our calibration is in adequation with the published piezometric relations available in the literature (equilibrium grain size versus shear stress). We test this new model of grain size evolution in a set of numerical computations of the dynamics of the Earth using stagYY. We show that the grain size evolution has a major effect on the convection regimes of terrestrial planets.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Iwamoto, Y.; Shin, S.G.; Matsubara, H.

The grain growth behavior of ceramic materials under the existence of a liquid phase was investigated for Si{sub 3}N{sub 4}-Y{sub 2}O{sub 3}-SiO{sub 2}, TiC-Ni, and WC-Co systems. The kinetics of grain growth behavior of these systems closely fitted to the cubic relation of d{sup 3} - d{sub 0}{sup 3} = Kt. The growth rate of {beta}-Si{sub 3}N{sub 4} grain was approximately one order of magnitude larger in length direction than that in width direction. The growth rate slightly increased with increasing liquid phase content in both these directions of the {beta}-Si{sub 3}N{sub 4} grain. TiC-Ni and WC-Co cermets had amore » peak in growth rate at a certain liquid phase content. The rate constant values of these systems were much smaller by a factor of 10{sup 3}{approximately}10{sup 5} compared to the theoretical values expected from the diffusion-controlled growth model. The experimental growth rates tended to decrease with increasing contiguity of the solid phase. The grain growth behavior of these systems could be explained by the mechanism resulting from the existence of contiguous boundaries of solid phase, which suppressed the movement of solid/liquid interfaces during liquid phase sintering.« less

Growth of surface and corner cracks in beta-processed and mill-annealed Ti-6Al-4V

NASA Technical Reports Server (NTRS)

Bell, P. D.

1975-01-01

Empirical stress-intensity expressions were developed to relate the growth of cracks from corner flaws to the growth of cracks from surface flaws. An experimental program using beta-processed Ti-6Al-4V verified these expressions for stress ratios, R greater than or equal to 0. An empirical crack growth-rate expression which included stress-ratio and stress-level effects was also developed. Cracks grew approximately 10 percent faster in transverse-grain material than in longitudinal-grain material and at approximately the same rate in longitudinal-grain mill-annealed Ti-6Al-4V. Specimens having surface and corner cracks and made of longitudinal-grain, beta-processed material were tested with block loads, and increasing the stresses in a block did not significantly change the crack growth rates. Truncation of the basic ascending stress sequence within a block caused more rapid crack growth, whereas both the descending and low-to-high stress sequences slowed crack growth.

Screening of Different Media and Substrates for Cultural Variability and Mass Culture of Arthrobotrys dactyloides Drechsler

PubMed Central

Kumar, D.; Jaiswal, R. K.

2005-01-01

Variability in growth and sporulation of five isolates of Arthrobotrys dactyloides was studied on five agar, 6 bran and 5 grain media. Potato dextrose agar (PDA) supported maximum growth of isolate A, C and E, while growth of isolate B and D was significantly lower on this medium. On Czapek's agar and yeast glucose agar media the differentiation in the isolates in relation to growth was poor than PDA. The other two media showed much poorer differentiation. On Czapek's agar medium, sporulation was recorded in isolate B only, whereas other isolates showed rare sporulation. Among the bran media, pea bran agar medium supported maximum growth of all the isolates except isolate B. Gram and rice bran agar media were next best. However, the growth of isolate B on the gram bran agar medium was more or less equal as other isolates. On pigeon pea bran agar medium, isolate E failed to grow while other isolates recorded poor growth. On lentil bran agar medium, only isolate B and D recorded little growth, whereas other isolates failed to grow. All the isolates recorded good sporulation on bran agar media except pigeon pea and lentil bran agar media. The grain agar media supported moderate to very good growth of all the isolates. In general isolate B remained slow growing on these media except gram grain and sorghum grain agar media on which growth of this isolate was comparable to other isolates. Sporulation in general, was good on all the grain agar media. Among different substrates screened, barley grain and pea bran were found superior to others for mass culture of isolate A of A. dactyloides. PMID:24049504

Grain dust and respiratory health in South African milling workers.

PubMed Central

Bachmann, M; Myers, J E

1991-01-01

Respiratory health was investigated in 224 grain milling workers. The likelihood of respiratory symptoms and chronic airflow limitation was raised for workers exposed to dust independent of the effects of smoking. Smokers were more likely than non-smokers to respond to a bronchodilator at the end of the working week. Dust was more strongly associated with most abnormal outcomes than was smoking. Subjective categories of exposure to dust were more strongly associated with most abnormal outcomes than were objective categories. The prevalence of all symptoms at the time of a survey conducted at the mill six years before was higher in workers who subsequently left the mill than in those who remained employed although the differences were not significant. PMID:1931723

In Vivo Test for Chemical Induction of Micronucleated Polychromatic Erythrocytes in Mouse Bone Marrow Cells. Test Article: Dimethylamine-2-2ethyl azide (DMAZ)

DTIC Science & Technology

2008-06-25

Hunched Back Unusual Body Secretions - Nasal Discharge - Lacrimation - Salivation - Bloody Stool - Dianhea Abnormal Behavior - Convulsions...WetGroin - Hunched Back Unusual Body Secretions - Nasal Discharge - Lacrimation - Salivation - Bloody Stool - Diarrhea Abnormal Behavior...Ataxia - Piloerection - WetGrain - Hunched Back Unusual Body Secretions - Nasal Discharge - Lacrimation - Salivation - Bloody Stool

Microstructural and Mechanical-Property Manipulation through Rapid Dendrite Growth and Undercooling in an Fe-based Multinary Alloy

PubMed Central

Ruan, Ying; Mohajerani, Amirhossein; Dao, Ming

2016-01-01

Rapid dendrite growth in single- or dual-phase multicomponent alloys can be manipulated to improve the mechanical properties of such metallic materials. Rapid growth of (αFe) dendrites was realized in an undercooled Fe-5Ni-5Mo-5Ge-5Co (wt.%) multinary alloy using the glass fluxing method. The relationship between rapid dendrite growth and the micro-/nano-mechanical properties of the alloy was investigated by analyzing the grain refinement and microstructural evolution resulting from the rapid dendrite growth. It was found that (αFe) dendrites grow sluggishly within a low but wide undercooling range. Once the undercooling exceeds 250 K, the dendritic growth velocity increases steeply until reaching a plateau of 31.8 ms−1. The increase in the alloy Vickers microhardness with increasing dendritic growth velocity results from the hardening effects of increased grain/phase boundaries due to the grain refinement, the more homogeneous distribution of the second phase along the boundaries, and the more uniform distribution of solutes with increased contents inside the grain, as verified also by nanohardness maps. Once the dendritic growth velocity exceeds ~8 ms−1, the rate of Vickers microhardness increase slows down significantly with a further increase in dendritic growth velocity, owing to the microstructural transition of the (αFe) phase from a trunk-dendrite to an equiaxed-grain microstructure. PMID:27539749

Investigation of the instability and low water kefir grain growth during an industrial water kefir fermentation process.

PubMed

Laureys, David; Van Jean, Amandine; Dumont, Jean; De Vuyst, Luc

2017-04-01

A poorly performing industrial water kefir production process consisting of a first fermentation process, a rest period at low temperature, and a second fermentation process was characterized to elucidate the causes of its low water kefir grain growth and instability. The frozen-stored water kefir grain inoculum was thawed and reactivated during three consecutive prefermentations before the water kefir production process was started. Freezing and thawing damaged the water kefir grains irreversibly, as their structure did not restore during the prefermentations nor the production process. The viable counts of the lactic acid bacteria and yeasts on the water kefir grains and in the liquors were as expected, whereas those of the acetic acid bacteria were high, due to the aerobic fermentation conditions. Nevertheless, the fermentations progressed slowly, which was caused by excessive substrate concentrations resulting in a high osmotic stress. Lactobacillus nagelii, Lactobacillus paracasei, Lactobacillus hilgardii, Leuconostoc mesenteroides, Bifidobacterium aquikefiri, Gluconobacter roseus/oxydans, Gluconobacter cerinus, Saccharomyces cerevisiae, and Zygotorulaspora florentina were the most prevalent microorganisms. Lb. hilgardii, the microorganism thought to be responsible for water kefir grain growth, was not found culture-dependently, which could explain the low water kefir grain growth of this industrial process.

What Controls Ooid Grain Size?

NASA Astrophysics Data System (ADS)

Trower, L.; Lamb, M. P.; Fischer, W. W.

2015-12-01

Ooids are subspherical chemical sand grains composed of concentric layers of CaCO₃ surrounding a central nucleus. These grains represent a common mode of carbonate sedimentation, making them potentially powerful proxies for paleoenvironmental conditions, provided a mechanistic understanding of the physical, chemical, and perhaps biological conditions necessary for their formation. At a basic level, growth of an ooid reflects that precipitation has outpaced abrasion over the ooid's lifetime. We can describe change in ooid size over time (net growth rate) mechanistically as the sum of a growth rate (the rate of carbonate precipitation on the ooid surface) and an abrasion rate (the rate of removal of material through grain-grain and grain-bed collisions). Previous studies have addressed the growth rate, investigating the extent to which microbial activity affects and/or controls carbonate precipitation on ooid surfaces, and the net growth rate, using stepwise acid digestion and radiocarbon dating to determine the ages of cortical layers. We focused on the abrasion rate and designed an experimental study to measure abrasion rates of ooids as a function of grain size and sediment transport stage. Preliminary experiments with medium-sand-sized ooids at a Rouse number of ~1.2 yielded an abrasion rate of 0.04 g/hr (or ~40 ng/ooid/hr), which is four orders of magnitude greater than the fastest net growth rates reported in the recent high resolution ooid cortex radiocarbon dating study by Beaupre et al. (2015). This result requires that either: 1) ooids are essentially not moving and therefore not being abraded or 2) precipitation rates are also much more rapid than the net growth rates estimated by incremental radiocarbon dating. The former constraint is inconsistent with field observations that most marine ooids occur in high energy shoal environments, both in modern examples and in the rock record. Precipitation rates must therefore also be relatively rapid compared with net growth rates in order to offset the effects of abrasion. This disparity in magnitude between abrasion/precipitation rates and net growth rate implies that ooids spend much of their lifetime near a dynamic equilibrium in ooid size, perhaps explaining why ooid populations tend to be unimodal with relatively narrow distributions of grain size.

Friction-Stir-Welded and Spin-Formed End Domes for Cryogenic Tanks

NASA Technical Reports Server (NTRS)

Hales, S. J.; Tayon, W. A.; Domack, M. S.

2012-01-01

Manufacturing of single-piece end domes for cryogenic tanks employing spin forming of tailored, friction-stir-welded blanks of Al-Li alloy 2195 plate offers cost and reliability benefits. The introduction of plastic deformation into a friction stir weld is a unique feature of the proposed manufacturing route. This investigation addressed abnormal grain growth [AGG] within the friction stir weldments during postfabrication processing of a prototype dome. The phenomenon of AGG was observed during the solution heat treatment [SHT] phase of T8 tempering and is a major concern for meeting specifications. Such abrupt microstructural transitions can be detrimental to notch-sensitive mechanical properties, such as ductility and/or fracture toughness. If the issue of AGG cannot be resolved, then the acceptance of this approach as a viable manufacturing route may be in jeopardy. The innovative approach adopted in this investigation was the insertion of a stand-alone, Intermediate Annealing Treatment [IAT] between the spin forming and T8 processing operations. A simple, recovery annealing step was deemed to be the most readily-scalable solution when fabricating thin-walled, ellipsoidal domes. The research effort culminated in the development of an effective IAT, which resulted in a significant decrease in AGG following SHT. The processing philosophy adopted in designing the IAT is outlined and the microstructural reasons for success are discussed. The analytical results presented are consistent with promoting continuous grain growth during the IAT, thereby suppressing AGG during the SHT.

Unraveling irradiation induced grain growth with in situ transmission electron microscopy and coordinated modeling

DOE PAGES

Bufford, D. C.; Abdeljawad, F. F.; Foiles, S. M.; ...

2015-11-09

Here, nanostructuring has been proposed as a method to enhance radiation tolerance, but many metallic systems are rejected due to significant concerns regarding long term grain boundary and interface stability. This work utilized recent advancements in transmission electron microscopy (TEM) to quantitatively characterize the grain size, texture, and individual grain boundary character in a nanocrystalline gold model system before and after in situ TEM ion irradiation with 10 MeV Si. The initial experimental measurements were fed into a mesoscale phase field model, which incorporates the role of irradiation-induced thermal events on boundary properties, to directly compare the observed and simulatedmore » grain growth with varied parameters. The observed microstructure evolution deviated subtly from previously reported normal grain growth in which some boundaries remained essentially static. In broader terms, the combined experimental and modeling techniques presented herein provide future avenues to enhance quantification and prediction of the thermal, mechanical, or radiation stability of grain boundaries in nanostructured crystalline systems.« less

The Effects of Atmosphere on the Sintering of Ultrafine-Grained Tungsten with Ti

NASA Astrophysics Data System (ADS)

Ren, Chai; Koopman, Mark; Fang, Z. Zak; Zhang, Huan

2016-11-01

Tungsten (W) is a brittle material at room temperature making it very difficult to fabricate. Although the lack of ductility remains a difficult challenge, nano-sized and ultrafine-grained (UFG) structures offer the potential to overcome tungsten's room-temperature brittleness. One way to manufacture UFG W is to compact and sinter nano-sized W powder. It is challenging, however, to control grain growth during sintering. As one method to inhibit grain growth, the effect of Ti-based additives on the densification and grain growth of nano-W powders was investigated in this study. Addition of 1% Ti into tungsten led to more than a 63% decrease in average grain size of sintered samples at comparable density levels. It was found that sintering in Ar yielded a finer grain size than sintering in H2 at similar densities. The active diffusion mechanisms during sintering were different for W-1% Ti nano powders sintered in Ar and H2.

REX3DV1.0

DOE Office of Scientific and Technical Information (OSTI.GOV)

Holm, Elizabeth A.

2002-03-28

This code is a FORTRAN code for three-dimensional Monte Carol Potts Model (MCPM) Recrystallization and grain growth. A continuum grain structure is mapped onto a three-dimensional lattice. The mapping procedure is analogous to color bitmapping the grain structure; grains are clusters of pixels (sites) of the same color (spin). The total system energy is given by the Pott Hamiltonian and the kinetics of grain growth are determined through a Monte Carlo technique with a nonconserved order parameter (Glauber dynamics). The code can be compiled and run on UNIX/Linux platforms.

The Influence of Grain Structure on Intermetallic Compound Layer Growth Rates in Fe-Al Dissimilar Welds

NASA Astrophysics Data System (ADS)

Xu, Lei; Robson, Joseph D.; Wang, Li; Prangnell, Philip B.

2018-02-01

The thickness of the intermetallic compound (IMC) layer that forms when aluminum is welded to steel is critical in determining the properties of the dissimilar joints. The IMC reaction layer typically consists of two phases ( η and θ) and many attempts have been made to determine the apparent activation energy for its growth, an essential parameter in developing any predictive model for layer thickness. However, even with alloys of similar composition, there is no agreement of the correct value of this activation energy. In the present work, the IMC layer growth has been characterized in detail for AA6111 aluminum to DC04 steel couples under isothermal annealing conditions. The samples were initially lightly ultrasonically welded to produce a metallic bond, and the structure and thickness of the layer were then characterized in detail, including tracking the evolution of composition and grain size in the IMC phases. A model developed previously for Al-Mg dissimilar welds was adapted to predict the coupled growth of the two phases in the layer, whilst accounting explicitly for grain boundary and lattice diffusion, and considering the influence of grain growth. It has been shown that the intermetallic layer has a submicron grain size, and grain boundary diffusion as well as grain growth plays a critical role in determining the thickening rate for both phases. The model was used to demonstrate how this explains the wide scatter in the apparent activation energies previously reported. From this, process maps were developed that show the relative importance of each diffusion path to layer growth as a function of temperature and time.

Economic Perspectives on Organic Grains: Past, Present, and Future

USDA-ARS?s Scientific Manuscript database

The organic food industry has seen tremendous growth over the past decade. This growth has led to an increase in demand for organic grains, and has been accompanied by an increase in the number of organic farms and an expansion in organic grain acreage in the U.S. Through this period, price premium...

Effects of Non-equilibrium Solidification on the Material Properties of Brick Silicon for Photovoltaics

NASA Technical Reports Server (NTRS)

Regnault, W. F.; Yoo, K. C.; Soltani, P. K.; Johnson, S. M.

1984-01-01

Silicon ingot growth technologies like the Ubiquitous Crystallization Process (UCP) are solidified within a shaping crucible. The rate at which heat can be lost from this crucible minus the rate at which heat is input from an external source determines the rate at which crystallization will occur. Occasionally, when the process parameters for solidification are exceeded, the normally large multi-centimeter grain size material assocated with the UCP will break down into regions containing extremely small, millimeter or less, grain size material. Accompanying this breakdown in grain growth is the development of so called sinuous grain boundaries. The breakdown in grain growth which results in this type of small grain structure with sinuous boundaries is usually associated with the rapid crystallization that would accompany a system failure. This suggests that there are limits to the growth velocity that one can obtain and still expect to produce material that would possess good photovoltaic properties. It is the purpose to determine the causes behind the breakdown of this material and what parameters will determine the best rates of solidification.

A theoretical model of grain boundary self-diffusion in metals with phase transitions (case study into titanium and zirconium)

NASA Astrophysics Data System (ADS)

Semenycheva, Alexandra V.; Chuvil'deev, Vladimir N.; Nokhrin, Aleksey V.

2018-05-01

The paper offers a model describing the process of grain boundary self-diffusion in metals with phase transitions in the solid state. The model is based on ideas and approaches found in the theory of non-equilibrium grain boundaries. The range of application of basic relations contained in this theory is shown to expand, as they can be used to calculate the parameters of grain boundary self-diffusion in high-temperature and low-temperature phases of metals with a phase transition. The model constructed is used to calculate grain boundary self-diffusion activation energy in titanium and zirconium and an explanation is provided as to their abnormally low values in the low-temperature phase. The values of grain boundary self-diffusion activation energy are in good agreement with the experiment.

Non-wetting surface-driven high-aspect-ratio crystalline grain growth for efficient hybrid perovskite solar cells

DOE PAGES

Bi, Cheng; Wang, Qi; Shao, Yuchuan; ...

2015-07-20

Large-aspect-ratio grains are needed in polycrystalline thin-film solar cells for reduced charge recombination at grain boundaries; however, the grain size in organolead trihalide perovskite (OTP) films is generally limited by the film thickness. Here we report the growth of OTP grains with high average aspect ratio of 2.3–7.9 on a wide range of non-wetting hole transport layers (HTLs), which increase nucleus spacing by suppressing heterogeneous nucleation and facilitate grain boundary migration in grain growth by imposing less drag force. The reduced grain boundary area and improved crystallinity dramatically reduce the charge recombination in OTP thin films to the level inmore » OTP single crystals. Combining the high work function of several HTLs, a high stabilized device efficiency of 18.3% in low-temperature-processed planar-heterojunction OTP devices under 1 sun illumination is achieved. As a result, this simple method in enhancing OTP morphology paves the way for its application in other optoelectronic devices for enhanced performance.« less

Yield prediction by analysis of multispectral scanner data

NASA Technical Reports Server (NTRS)

Colwell, J. E.; Suits, G. H.

1975-01-01

A preliminary model describing the growth and grain yield of wheat was developed. The modeled growth characteristics of the wheat crop were used to compute wheat canopy reflectance using a model of vegetation canopy reflectance. The modeled reflectance characteristics were compared with the corresponding growth characteristics and grain yield in order to infer their relationships. It appears that periodic wheat canopy reflectance characteristics potentially derivable from earth satellites will be useful in forecasting wheat grain yield.

Growth mechanism of extension twin variants during annealing of pure magnesium: An ‘ex situ’ electron backscattered diffraction investigation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sabat, R.K.

Pure magnesium was subjected to plastic deformation through CSM (continuous stiffness measurement) indentation followed by annealing at 200 °C for 30 min. Nucleation of no new grains was observed neither at the twin–twin intersections nor at the multiple twin variants of a grain after annealing. Significant growth of off-basal twin orientation compared to basal twin orientation was observed in the sample after annealing and is attributed to the partial coherent nature of twin boundary in the later case. Further, growth of twins was independent of the strain distribution between parent and twinned grains. - Highlights: • An ‘ex situ’ EBSDmore » of pure Mg during annealing was investigated. • Nucleation of no new grains was observed. • Significant growth of off-basal twin orientation was observed. • Growth of twins may be attributed to the partial coherent nature of twin boundary.« less

Effect of Solutes on Grain Refinement of As-Cast Fe-4Si Alloy

NASA Astrophysics Data System (ADS)

Li, Ming; Li, Jian-Min; Zheng, Qing; Wang, Geoff; Zhang, Ming-Xing

2018-06-01

Grain size is one of the key microstructural factors that control the mechanical properties of steels. The present work aims to extend the theories of grain refinement which were established for cast light alloys to steel systems. Using a designed Fe-4 wt pct Si alloy (all-ferrite structure during whole solidification process), the solute effect on grain refinement/grain coarsening in ferritic systems was comprehensively investigated. Experimental results showed that boron (B), which is associated with the highest Q value (growth restriction factor) in ferrite, significantly refined the as-cast structure of the Fe-4 wt pct Si alloy. Cu and Mo with low Q values had no effect on grain refinement. However, although Y and Zr have relatively high Q values, addition of these two solutes led to grain coarsening in the Fe-4Si alloy. Understanding the results in regards to the growth restriction factor and the driving force for the solidification led to the conclusion that in addition to the grain growth restriction effect, the changes of thermodynamic driving force for solidification due to the solute addition also played a key role in grain refinement in ferritic alloys.

Effect of Solutes on Grain Refinement of As-Cast Fe-4Si Alloy

NASA Astrophysics Data System (ADS)

Li, Ming; Li, Jian-Min; Zheng, Qing; Wang, Geoff; Zhang, Ming-Xing

2018-03-01

Grain size is one of the key microstructural factors that control the mechanical properties of steels. The present work aims to extend the theories of grain refinement which were established for cast light alloys to steel systems. Using a designed Fe-4 wt pct Si alloy (all-ferrite structure during whole solidification process), the solute effect on grain refinement/grain coarsening in ferritic systems was comprehensively investigated. Experimental results showed that boron (B), which is associated with the highest Q value (growth restriction factor) in ferrite, significantly refined the as-cast structure of the Fe-4 wt pct Si alloy. Cu and Mo with low Q values had no effect on grain refinement. However, although Y and Zr have relatively high Q values, addition of these two solutes led to grain coarsening in the Fe-4Si alloy. Understanding the results in regards to the growth restriction factor and the driving force for the solidification led to the conclusion that in addition to the grain growth restriction effect, the changes of thermodynamic driving force for solidification due to the solute addition also played a key role in grain refinement in ferritic alloys.

``Particle traps'' at planet gap edges in disks: effects of grain growth and fragmentation

NASA Astrophysics Data System (ADS)

Gonzalez, J.-F.; Laibe, G.; Maddison, S. T.; Pinte, C.; Ménard, F.

2014-12-01

We model the dust evolution in protoplanetary disks (PPD) with 3D, Smoothed Particle Hydrodynamics (SPH), two-phase (gas+dust) hydrodynamical simulations. The gas+dust dynamics, where aerodynamic drag leads to the vertical settling and radial migration of grains, is consistently treated. In a previous work, we characterized the spatial distribution of non-growing dust grains of different sizes in a disk containing a gap-opening planet and investigated the gap's detectability with ALMA. Here we take into account the effects of grain growth and fragmentation and study their impact on the distribution of solids in the disk. We show that rapid grain growth in the ``particle traps'' at the edges of planet gaps are strongly affected by fragmentation. We discuss the consequences for ALMA and NOEMA observations.

Interstellar grains within interstellar grains

NASA Technical Reports Server (NTRS)

Bernatowicz, Thomas J.; Amari, Sachiko; Zinner, Ernst K.; Lewis, Roy S.

1991-01-01

Five interstellar graphite spherules extracted from the Murchison carbonaceous meteorite are studied. The isotopic and elemental compositions of individual particles are investigated with the help of an ion microprobe, and this analysis is augmented with structural studies of ultrathin sections of the grain interiors by transmission electron microscopy. As a result, the following procedure for the formation of the interstellar graphite spherule bearing TiC crystals is inferred: (1) high-temperature nucleation and rapid growth of the graphitic carbon spherule in the atmosphere of a carbon-rich star, (2) nucleation and growth of TiC crystals during continued growth of the graphitic spherule and the accretion of TiC onto the spherule, (3) quenching of the graphite growth process by depletion of C or by isolation of the spherule before other grain types could condense.

Quarzt Fabric Insights Across a Low P-High T Shear Zone

NASA Astrophysics Data System (ADS)

Gomez Barreiro, J.; Martinez-Catalan, J. R.; Benitez Perez, J.; Wenk, H.; Vogel, S. C.; Alcock, J. E.

2013-12-01

The evolution of mylonitic fabric in quartzites across a Low-P / High-T gradient within the Lugo Dome Extensional system (NW Spain) is analyzed. Quantitative texture measurements with TOF neutron diffraction, Shape preferred orientation (SPO) and Crystal Size Distribution (CSD) analyses were correlated with tectonothermal data to constraint the prevalence of ductile deformative fabrics exposed to cycles of dynamic and static recrystallization. Results suggest two stages in the evolution of mylonites in close correlation to thermal gradient, 1) a pervasive ductile deformation affecting most of the shear zone volume, with the development of symmetric cross girdle c-axes fabric suggesting slip on {c,r,m} and dynamically recrystallized microstructures which resulted into the refinement of the grain-size. 2) An heterogeneous deformation stage where strain partition led to the formation of relatively active and passive domains. During this late stage, at deeper levels, High T detachments show [c]{m} slip system and dynamic recrystallization activation, with monoclinic texture patterns, meanwhile, passive domains followed an static recrystallization with abnormal grain growth and minor variation of early orthogonal texture patterns Neutron diffraction data (cross) and Rietveld model obtained with MAUD (solid line) of a mylonitic quartzite. Some important planes are indicated for the major phases.

Strain induced grain boundary migration effects on grain growth of an austenitic stainless steel during static and metadynamic recrystallization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paggi, A., E-mail: alpaggi@tenaris.com; Angella, G.; Donnini, R.

Static and metadynamic recrystallization of an AISI 304L austenitic stainless steel was investigated at 1100 °C and 10{sup −} {sup 2} s{sup −} {sup 1} strain rate. The kinetics of recrystallization was determined through double hit compression tests. Two strain levels were selected for the first compression hit: ε{sub f} = 0.15 for static recrystallization (SRX) and 0.25 for metadynamic recrystallization (MDRX). Both the as-deformed and the recrystallized microstructures were investigated through optical microscopy and electron back-scattered diffraction (EBSD) technique. During deformation, strain induced grain boundary migration appeared to be significant, producing a square-like grain boundary structure aligned along themore » directions of the maximum shear stresses in compression. EBSD analysis revealed to be as a fundamental technique that the dislocation density was distributed heterogeneously in the deformed grains. Grain growth driven by surface energy reduction was also investigated, finding that it was too slow to explain the experimental data. Based on microstructural results, it was concluded that saturation of the nucleation sites occurred in the first stages of recrystallization, while grain growth driven by strain induced grain boundary migration (SIGBM) dominated the subsequent stages. - Highlights: • Recrystallization behavior of a stainless steel was investigated at 1100 °C. • EBSD revealed that the dislocation density distribution was heterogeneous during deformation. • Saturation of nucleation sites occurred in the first stages of recrystallization. • Strain induced grain boundary migration (SIGBM) effects were significant. • Grain growth driven by SIGBM dominated the subsequent stages.« less

Microstructure-sensitive small fatigue crack growth assessment. Effect of strain ratio multiaxial strain state and geometric discontinuities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Castelluccio, Gustavo M.; McDowell, David L.

Fatigue crack initiation in the high cycle fatigue regime is strongly influenced by microstructural features. Research efforts have usually focused on predicting fatigue resistance against crack incubation without considering the early fatigue crack growth after encountering the first grain boundary. However, a significant fraction of the variability of the total fatigue life can be attributed to growth of small cracks as they encounter the first few grain boundaries, rather than crack formation within the first grain. Our paper builds on the framework previously developed by the authors to assess microstructure-sensitive small fatigue crack formation and early growth under complex loadingmore » conditions. Moreover, the scheme employs finite element simulations that explicitly render grains and crystallographic directions along with simulation of microstructurally small fatigue crack growth from grain to grain. The methodology employs a crystal plasticity algorithm in ABAQUS that was previously calibrated to study fatigue crack initiation in RR1000 Ni-base superalloy. Our work present simulations with non-zero applied mean strains and geometric discontinuities that were not previously considered for calibration. Results exhibit trends similar to those found in experiments for multiple metallic materials, conveying a consistent physical description of fatigue damage phenomena.« less

Microstructure-sensitive small fatigue crack growth assessment. Effect of strain ratio multiaxial strain state and geometric discontinuities

DOE PAGES

Castelluccio, Gustavo M.; McDowell, David L.

2015-09-16

Fatigue crack initiation in the high cycle fatigue regime is strongly influenced by microstructural features. Research efforts have usually focused on predicting fatigue resistance against crack incubation without considering the early fatigue crack growth after encountering the first grain boundary. However, a significant fraction of the variability of the total fatigue life can be attributed to growth of small cracks as they encounter the first few grain boundaries, rather than crack formation within the first grain. Our paper builds on the framework previously developed by the authors to assess microstructure-sensitive small fatigue crack formation and early growth under complex loadingmore » conditions. Moreover, the scheme employs finite element simulations that explicitly render grains and crystallographic directions along with simulation of microstructurally small fatigue crack growth from grain to grain. The methodology employs a crystal plasticity algorithm in ABAQUS that was previously calibrated to study fatigue crack initiation in RR1000 Ni-base superalloy. Our work present simulations with non-zero applied mean strains and geometric discontinuities that were not previously considered for calibration. Results exhibit trends similar to those found in experiments for multiple metallic materials, conveying a consistent physical description of fatigue damage phenomena.« less

Synchrotron characterization of nanograined UO 2 grain growth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mo, Kun; Miao, Yinbin; Yun, Di

2015-09-30

This activity is supported by the US Nuclear Energy Advanced Modeling and Simulation (NEAMS) Fuels Product Line (FPL) and aims at providing experimental data for the validation of the mesoscale simulation code MARMOT. MARMOT is a mesoscale multiphysics code that predicts the coevolution of microstructure and properties within reactor fuel during its lifetime in the reactor. It is an important component of the Moose-Bison-Marmot (MBM) code suite that has been developed by Idaho National Laboratory (INL) to enable next generation fuel performance modeling capability as part of the NEAMS Program FPL. In order to ensure the accuracy of the microstructuremore » based materials models being developed within the MARMOT code, extensive validation efforts must be carried out. In this report, we summarize our preliminary synchrotron radiation experiments at APS to determine the grain size of nanograin UO 2. The methodology and experimental setup developed in this experiment can directly apply to the proposed in-situ grain growth measurements. The investigation of the grain growth kinetics was conducted based on isothermal annealing and grain growth characterization as functions of duration and temperature. The kinetic parameters such as activation energy for grain growth for UO 2 with different stoichiometry are obtained and compared with molecular dynamics (MD) simulations.« less

Grain size constraints on twin expansion in hexagonal close packed crystals

DOE PAGES

Kumar, Mariyappan Arul; Beyerlein, Irene Jane; Tome, Carlos N.

2016-10-20

Deformation twins are stress-induced transformed domains of lamellar shape that form when polycrystalline hexagonal close packed metals, like Mg, are strained. Several studies have reported that the propensity of deformation twinning reduces as grain size decreases. Here, we use a 3D crystal plasticity based micromechanics model to calculate the effect of grain size on the driving forces responsible for expanding twin lamellae. The calculations reveal that constraints from the neighboring grain where the grain boundary and twin lamella meet induce a stress reversal in the twin lamella. A pronounced grain size effect arises as reductions in grain size cause thesemore » stress-reversal fields from twin/grain boundary junctions to affect twin growth. We further show that the severity of this neighboring grain constraint depends on the crystallographic orientation and plastic response of the neighboring grain. We show that these stress-reversal fields from twin/grain boundary junctions will affect twin growth, below a critical parent grain size. Finally, these results reveal an unconventional yet influential role that grain size and grain neighbors can play on deformation twinning.« less

Densification and Grain Growth in Polycrystalline Olivine Rocks Synthesized By Evacuated Hot-Pressing

NASA Astrophysics Data System (ADS)

Meyers, C. D.; Kohlstedt, D. L.; Zimmerman, M. E.

2017-12-01

Experiments on laboratory-synthesized olivine-rich rocks form the starting material for many investigations of physical processes in the Earth's upper mantle (e.g., creep behavior, ionic diffusion, and grain growth). Typically, a fit of a constitutive law to experimental data provides a description of the kinetics of a process needed to extrapolate across several orders of magnitude from laboratory to geological timescales. Although grain-size is a critical parameter in determining physical properties such as viscosity, broad disagreement persists amongst the results of various studies of grain growth kinetics in olivine-rich rocks. Small amounts of impurities or porosity dramatically affect the kinetics of grain growth. In this study, we developed an improved method for densifying olivine-rich rocks fabricated from powdered, gem-quality single crystals that involves evacuating the pore space, with the aim of refining measurements of the kinetics of mantle materials. In previous studies, olivine powders were sealed in a metal can and hydrostatically annealed at roughly 300 MPa and 1250 °C. These samples, which appear opaque and milky-green, typically retain a small amount of porosity. Consequently, when annealed at 1 atm, extensive pore growth occurs, inhibiting grain growth. In addition, Fourier-transform infrared and confocal Raman spectroscopy reveal absorption peaks characteristic of CO2 in the pores of conventionally hot-pressed material. To avoid trapping of adsorbed contaminants, we developed an evacuated hot-pressing method, wherein the pore space of powder compacts is vented to vacuum during heating and pressurization. This method produces a highly dense, green-tinted, transparent material. No CO2 absorptions peaks exist in evacuated hot-pressed material. When reheated to annealing temperatures at 1 atm, the evacuated hot-pressed material undergoes limited pore growth and dramatically enhanced grain-growth rates. High-strain deformation experiments on this new material provide new insights into the kinetics of recovery of deformation microstructures.

Preannealing, Annealing Atmosphere, and Surface-Energy-Induced Selective Growth in 0.1 Pct Mn-Added 3 Pct Si-Fe Alloy Containing 95 ppm Sulfur

NASA Astrophysics Data System (ADS)

Jung, Y. C.; Lee, J. K.; Kim, K. T.; Heo, N. H.

2009-05-01

The total number of {110} grains after final annealing increased with preannealing and was greater in a hydrogen atmosphere than under a high vacuum. Magnetic induction decreased with increasing total number of the {110} grains. This is attributed to the increase in {110} grain size, the decrease in a range for the selective growth of {100} or {111} grains, and thus the increase in number of {110} grains that show a deviation angle between the < 001rangle crystal and the rolling directions.

A highly efficient 3D level-set grain growth algorithm tailored for ccNUMA architecture

NASA Astrophysics Data System (ADS)

Mießen, C.; Velinov, N.; Gottstein, G.; Barrales-Mora, L. A.

2017-12-01

A highly efficient simulation model for 2D and 3D grain growth was developed based on the level-set method. The model introduces modern computational concepts to achieve excellent performance on parallel computer architectures. Strong scalability was measured on cache-coherent non-uniform memory access (ccNUMA) architectures. To achieve this, the proposed approach considers the application of local level-set functions at the grain level. Ideal and non-ideal grain growth was simulated in 3D with the objective to study the evolution of statistical representative volume elements in polycrystals. In addition, microstructure evolution in an anisotropic magnetic material affected by an external magnetic field was simulated.

Growth kinetics of white graphene (h-BN) on a planarised Ni foil surface

PubMed Central

Cho, Hyunjin; Park, Sungchan; Won, Dong-Il; Kang, Sang Ook; Pyo, Seong-Soo; Kim, Dong-Ik; Kim, Soo Min; Kim, Hwan Chul; Kim, Myung Jong

2015-01-01

The morphology of the surface and the grain orientation of metal catalysts have been considered to be two important factors for the growth of white graphene (h-BN) by chemical vapour deposition (CVD). We report a correlation between the growth rate of h-BN and the orientation of the nickel grains. The surface of the nickel (Ni) foil was first polished by electrochemical polishing (ECP) and subsequently annealed in hydrogen at atmospheric pressure to suppress the effect of the surface morphology. Atmospheric annealing with hydrogen reduced the nucleation sites of h-BN, which induced a large crystal size mainly grown from the grain boundary with few other nucleation sites in the Ni foil. A higher growth rate was observed from the Ni grains that had the {110} or {100} orientation due to their higher surface energy. PMID:26156068

Monte Carlo grain growth modeling with local temperature gradients

NASA Astrophysics Data System (ADS)

Tan, Y.; Maniatty, A. M.; Zheng, C.; Wen, J. T.

2017-09-01

This work investigated the development of a Monte Carlo (MC) simulation approach to modeling grain growth in the presence of non-uniform temperature field that may vary with time. We first scale the MC model to physical growth processes by fitting experimental data. Based on the scaling relationship, we derive a grid site selection probability (SSP) function to consider the effect of a spatially varying temperature field. The SSP function is based on the differential MC step, which allows it to naturally consider time varying temperature fields too. We verify the model and compare the predictions to other existing formulations (Godfrey and Martin 1995 Phil. Mag. A 72 737-49 Radhakrishnan and Zacharia 1995 Metall. Mater. Trans. A 26 2123-30) in simple two-dimensional cases with only spatially varying temperature fields, where the predicted grain growth in regions of constant temperature are expected to be the same as for the isothermal case. We also test the model in a more realistic three-dimensional case with a temperature field varying in both space and time, modeling grain growth in the heat affected zone of a weld. We believe the newly proposed approach is promising for modeling grain growth in material manufacturing processes that involves time-dependent local temperature gradient.

Time-evolution of grain size distributions in random nucleation and growth crystallization processes

NASA Astrophysics Data System (ADS)

Teran, Anthony V.; Bill, Andreas; Bergmann, Ralf B.

2010-02-01

We study the time dependence of the grain size distribution N(r,t) during crystallization of a d -dimensional solid. A partial differential equation, including a source term for nuclei and a growth law for grains, is solved analytically for any dimension d . We discuss solutions obtained for processes described by the Kolmogorov-Avrami-Mehl-Johnson model for random nucleation and growth (RNG). Nucleation and growth are set on the same footing, which leads to a time-dependent decay of both effective rates. We analyze in detail how model parameters, the dimensionality of the crystallization process, and time influence the shape of the distribution. The calculations show that the dynamics of the effective nucleation and effective growth rates play an essential role in determining the final form of the distribution obtained at full crystallization. We demonstrate that for one class of nucleation and growth rates, the distribution evolves in time into the logarithmic-normal (lognormal) form discussed earlier by Bergmann and Bill [J. Cryst. Growth 310, 3135 (2008)]. We also obtain an analytical expression for the finite maximal grain size at all times. The theory allows for the description of a variety of RNG crystallization processes in thin films and bulk materials. Expressions useful for experimental data analysis are presented for the grain size distribution and the moments in terms of fundamental and measurable parameters of the model.

Grain growth effects on magnetic properties of Ni0.6Zn0.4Fe2O4 material prepared using mechanically alloyed nanoparticles

NASA Astrophysics Data System (ADS)

Syazwan, M. M.; Hapishah, A. N.; Azis, R. S.; Abbas, Z.; Hamidon, M. N.

2018-06-01

The effect of grain growth via sintering temperature on some magnetic properties is reported in this research. Ni0.6Zn0.4Fe2O4 nanoparticles were mechanically alloyed for 6 h and the sintering process starting from 600 to 1200 °C with 25 °C increment with only one sample subjected to all sintering scheme. The resulting change in the material was observed after each sintering. Single phase has been formed at 600 °C and above and the intensity peaks increased with sintering temperature as well as crystallinity increment. The morphological studies showed grain size increment as the sintering temperature increased. Moreover, the density increased while the porosity decreased with increasing sintering temperature. The saturation induction, Bs increased with the increased of grain size. On the other hand, the coercivity-vs-grain size plot reveals the critical single-domain-to-multidomain grain size to be about ∼400 nm. The initial permeability, μi value was increased with grain size enhancement. The microstructural grain growth, as exposed for the first time by this research, is shown as a process of multiple activation energy barriers.

Recrystallization and grain growth induced by ELMs-like transient heat loads in deformed tungsten samples

NASA Astrophysics Data System (ADS)

Suslova, A.; El-Atwani, O.; Sagapuram, D.; Harilal, S. S.; Hassanein, A.

2014-11-01

Tungsten has been chosen as the main candidate for plasma facing components (PFCs) due to its superior properties under extreme operating conditions in future nuclear fusion reactors such as ITER. One of the serious issues for PFCs is the high heat load during transient events such as ELMs and disruption in the reactor. Recrystallization and grain size growth in PFC materials caused by transients are undesirable changes in the material, since the isotropic microstructure developed after recrystallization exhibits a higher ductile-to-brittle transition temperature which increases with the grain size, a lower thermal shock fatigue resistance, a lower mechanical strength, and an increased surface roughening. The current work was focused on careful determination of the threshold parameters for surface recrystallization, grain growth rate, and thermal shock fatigue resistance under ELM-like transient heat events. Transient heat loads were simulated using long pulse laser beams for two different grades of ultrafine-grained tungsten. It was observed that cold rolled tungsten demonstrated better power handling capabilities and higher thermal stress fatigue resistance compared to severely deformed tungsten. Higher recrystallization threshold, slower grain growth, and lower degree of surface roughening were observed in the cold rolled tungsten.

Growth of Pleurotus ostreatus on wheat straw and wheat-grain-based media: Biochemical aspects and preparation of mushroom inoculum.

PubMed

Sainos, E; Díaz-Godínez, G; Loera, O; Montiel-González, A M; Sánchez, C

2006-10-01

Mycelial growth, intracellular activity of proteases, laccases and beta-1,3-glucanases, and cytoplasmic protein were evaluated in the vegetative phase of Pleurotus ostreatus grown on wheat straw and in wheat-grain-based media in Petri dishes and in bottles. The productivity of the wheat straw and wheat-grain-based spawn in cylindrical polyethylene bags containing 5 kg of chopped straw was also determined. We observed high activity of proteases and high content of intracellular protein in cultures grown on wheat straw. This suggests that the proteases are not secreted into the medium and that the protein is an important cellular reserve. On the contrary, cultures grown on wheat straw secreted laccases into the medium, which could be induced by this substrate. P. ostreatus grown on media prepared with a combination of wheat straw and wheat grain showed a high radial growth rate in Petri dishes and a high level of mycelial growth in bottles. The productivities of wheat straw and wheat-grain-based spawn were similar. Our results show that cheaper and more productive mushroom spawn can be prepared by developing the mycelium on wheat straw and wheat-grain-based substrates.

Recrystallization and grain growth induced by ELMs-like transient heat loads in deformed tungsten samples

PubMed Central

Suslova, A.; El-Atwani, O.; Sagapuram, D.; Harilal, S. S.; Hassanein, A.

2014-01-01

Tungsten has been chosen as the main candidate for plasma facing components (PFCs) due to its superior properties under extreme operating conditions in future nuclear fusion reactors such as ITER. One of the serious issues for PFCs is the high heat load during transient events such as ELMs and disruption in the reactor. Recrystallization and grain size growth in PFC materials caused by transients are undesirable changes in the material, since the isotropic microstructure developed after recrystallization exhibits a higher ductile-to-brittle transition temperature which increases with the grain size, a lower thermal shock fatigue resistance, a lower mechanical strength, and an increased surface roughening. The current work was focused on careful determination of the threshold parameters for surface recrystallization, grain growth rate, and thermal shock fatigue resistance under ELM-like transient heat events. Transient heat loads were simulated using long pulse laser beams for two different grades of ultrafine-grained tungsten. It was observed that cold rolled tungsten demonstrated better power handling capabilities and higher thermal stress fatigue resistance compared to severely deformed tungsten. Higher recrystallization threshold, slower grain growth, and lower degree of surface roughening were observed in the cold rolled tungsten. PMID:25366885

Recrystallization and grain growth induced by ELMs-like transient heat loads in deformed tungsten samples.

PubMed

Suslova, A; El-Atwani, O; Sagapuram, D; Harilal, S S; Hassanein, A

2014-11-04

Tungsten has been chosen as the main candidate for plasma facing components (PFCs) due to its superior properties under extreme operating conditions in future nuclear fusion reactors such as ITER. One of the serious issues for PFCs is the high heat load during transient events such as ELMs and disruption in the reactor. Recrystallization and grain size growth in PFC materials caused by transients are undesirable changes in the material, since the isotropic microstructure developed after recrystallization exhibits a higher ductile-to-brittle transition temperature which increases with the grain size, a lower thermal shock fatigue resistance, a lower mechanical strength, and an increased surface roughening. The current work was focused on careful determination of the threshold parameters for surface recrystallization, grain growth rate, and thermal shock fatigue resistance under ELM-like transient heat events. Transient heat loads were simulated using long pulse laser beams for two different grades of ultrafine-grained tungsten. It was observed that cold rolled tungsten demonstrated better power handling capabilities and higher thermal stress fatigue resistance compared to severely deformed tungsten. Higher recrystallization threshold, slower grain growth, and lower degree of surface roughening were observed in the cold rolled tungsten.

In vitro and in vivo studies of biodegradable fine grained AZ31 magnesium alloy produced by equal channel angular pressing.

PubMed

Ratna Sunil, B; Sampath Kumar, T S; Chakkingal, Uday; Nandakumar, V; Doble, Mukesh; Devi Prasad, V; Raghunath, M

2016-02-01

The objective of the present work is to investigate the role of different grain sizes produced by equal channel angular pressing (ECAP) on the degradation behavior of magnesium alloy using in vitro and in vivo studies. Commercially available AZ31 magnesium alloy was selected and processed by ECAP at 300°C for up to four passes using route Bc. Grain refinement from a starting size of 46μm to a grain size distribution of 1-5μm was successfully achieved after the 4th pass. Wettability of ECAPed samples assessed by contact angle measurements was found to increase due to the fine grain structure. In vitro degradation and bioactivity of the samples studied by immersing in super saturated simulated body fluid (SBF 5×) showed rapid mineralization within 24h due to the increased wettability in fine grained AZ31 Mg alloy. Corrosion behavior of the samples assessed by weight loss and electrochemical tests conducted in SBF 5× clearly showed the prominent role of enhanced mineral deposition on ECAPed AZ31 Mg in controlling the abnormal degradation. Cytotoxicity studies by MTT colorimetric assay showed that all the samples are viable. Additionally, cell adhesion was excellent for ECAPed samples particularly for the 3rd and 4th pass samples. In vivo experiments conducted using New Zealand White rabbits clearly showed lower degradation rate for ECAPed sample compared with annealed AZ31 Mg alloy and all the samples showed biocompatibility and no health abnormalities were noticed in the animals after 60days of in vivo studies. These results suggest that the grain size plays an important role in degradation management of magnesium alloys and ECAP technique can be adopted to achieve fine grain structures for developing degradable magnesium alloys for biomedical applications. Copyright © 2015 Elsevier B.V. All rights reserved.

Fused lobed anther and hooked stigma affect pollination, fertilization and fruit set in mango: a scanning electron microscopy study.

PubMed

Rani, Varsha; Ansari, Mohammad Wahid; Shukla, Alok; Tuteja, Narendra; Bains, Gurdeep

2013-03-01

Mango malformation is the most threaten disease that limits mango production, worldwide. For a long time, due to its complex nature, the cause and causal agents were strongly disputed. Diverse Fusaria, including Fusarium mangiferae, are known to be associated with the disease. There are indications that augmented level of endogenous ethylene in response to various abiotic and biotic stresses alters the morphology of reproductive organs. Here, scanning electron microscopy (SEM) of healthy and malformed reproductive organs of mango cv. Baramasi was performed to compare the functional morphology. The SEM study revealed that anthers of hermaphrodite healthy flowers were bilobed with large number of turgid pollen grains whereas malformed flowers showed fused lobed anthers with scanty deformed pollen grains. Furthermore, the stigma of healthy flowers exhibited a broad landing pad as compared to malformed stigma which showed hooked and pointed tip. All these impaired morphology of male and female reproductive organs lead to failure of sexual reproduction. This is the first evidence to show fused lobed anther with impaired pollen grains and hooked stigma with poor stigmatic receptivity are mainly responsible for restricting the pollen germination and pollen tube growth. Here we suggest that abnormal development of anthers and pistils is due to endogenously produced stress ethylene. Further, added load of cyanide, a byproduct of ethylene biosynthesis, may also contribute to the development of necrosis which lead to desiccation of anther and pistil during hypersensitive response of plants.

Optimization of strength and ductility in nanotwinned ultrafine grained Ag: twin density and grain orientations

DOE PAGES

Ott, R. T.; Geng, J.; Besser, M. F.; ...

2015-06-27

Nanotwinned ultrafine grained Ag thick films with different twin densities and orientations have been synthesized by magnetron sputtering with a wide-range of deposition rates. The twin boundary (TB) spacings and orientations as well as the grain size for the different deposition conditions have been characterized by both synchrotron X-ray scattering and transmission electron microscopy (TEM). Structural characterization combined with uniaxial tensile tests of the free-standing films reveals a large increase in the yield strength for films deposited at high deposition rates without any accompanying change in the TB spacing – a behavior that is in contrast with what has beenmore » reported in the literature. We find that films deposited at lower deposition rates exhibit more randomly oriented grains with a lower overall twin density (averaged over all the grains) than the more heavily twinned grains with strong <111> fiber texture in the films deposited at higher deposition rates. The TB spacing in the twinned grains, however, does not show any significant dependence on the deposition rate. The dependence of the strength and ductility on the twin density and orientations can be described by two different soft deformation modes: 1) untwinned grains and 2) nanowinned grains that are not oriented with <111> along the growth direction. The untwinned grains provide relatively low resistance to slip, and thus decreased strength, while the nanotwinned grains that are not oriented with <111> along the growth direction are softer than nanotwinned grains that are oriented with <111> along the growth direction. We reveal that an ultrafine-grained (150-200 nm) structure consisting of a mixture of nanotwinned (~ 8-12 nm spacing) and untwined grains yields the best combination of high strength and uniform tensile ductility.« less

Grain growth of nanocrystalline 3C-SiC under Au ion irradiation at elevated temperatures

NASA Astrophysics Data System (ADS)

Zhang, Limin; Jiang, Weilin; Dissanayake, Amila; Varga, Tamas; Zhang, Jiandong; Zhu, Zihua; Hu, Dehong; Wang, Haiyan; Henager, Charles H., Jr.; Wang, Tieshan

2016-01-01

Nanocrystalline silicon carbide (SiC) represents an excellent model system for a fundamental study of interfacial (grain boundary) processes under nuclear radiation, which are critical to the understanding of the response of nanostructured materials to high-dose irradiation. This study reports on a comparison of irradiation effects in cubic phase SiC (3C-SiC) grains of a few nanometres in size and single-crystal 3C-SiC films under identical Au ion irradiation to a range of doses at 700 K. In contrast to the latter, in which the lattice disorder is accumulated to a saturation level without full amorphization, the average grain size of the former increases with dose following a power-law trend. In addition to coalescence, the grain grows through atomic jumps and mass transport, where irradiation-induced vacancies at grain boundaries assist the processes. It is found that a higher irradiation temperature leads to slower grain growth and a faster approach to a saturation size of SiC nanograins. This unusual behaviour could be associated with irradiation-induced grain nucleation and growth in amorphous SiC matrix in which the 3C-SiC grains are embedded. The results could potentially have a positive impact on structural components of advanced nuclear energy systems.

Stabilizing Nanocrystalline Oxide Nanofibers at Elevated Temperatures by Coating Nanoscale Surface Amorphous Films.

PubMed

Yao, Lei; Pan, Wei; Luo, Jian; Zhao, Xiaohui; Cheng, Jing; Nishijima, Hiroki

2018-01-10

Nanocrystalline materials often exhibit extraordinary mechanical and physical properties but their applications at elevated temperatures are impaired by the rapid grain growth. Moreover, the grain growth in nanocrystalline oxide nanofibers at high temperatures can occur at hundreds of degrees lower than that would occur in corresponding bulk nanocrystalline materials, which would eventually break the fibers. Herein, by characterizing a model system of scandia-stabilized zirconia using hot-stage in situ scanning transmission electron microscopy, we discover that the enhanced grain growth in nanofibers is initiated at the surface. Subsequently, we demonstrate that coating the fibers with nanometer-thick amorphous alumina layer can enhance their temperature stability by nearly 400 °C via suppressing the surface-initiated grain growth. Such a strategy can be effectively applied to other oxide nanofibers, such as samarium-doped ceria, yttrium-stabilized zirconia, and lanthanum molybdate. The nanocoatings also increase the flexibility of the oxide nanofibers and stabilize the high-temperature phases that have 10 times higher ionic conductivity. This study provides new insights into the surface-initiated grain growth in nanocrystalline oxide nanofibers and develops a facile yet innovative strategy to improve the high-temperature stability of nanofibers for a broad range of applications.

Textured silicon nitride: processing and anisotropic properties

PubMed Central

Zhu, Xinwen; Sakka, Yoshio

2008-01-01

Textured silicon nitride (Si3N4) has been intensively studied over the past 15 years because of its use for achieving its superthermal and mechanical properties. In this review we present the fundamental aspects of the processing and anisotropic properties of textured Si3N4, with emphasis on the anisotropic and abnormal grain growth of β-Si3N4, texture structure and texture analysis, processing methods and anisotropic properties. On the basis of the texturing mechanisms, the processing methods described in this article have been classified into two types: hot-working (HW) and templated grain growth (TGG). The HW method includes the hot-pressing, hot-forging and sinter-forging techniques, and the TGG method includes the cold-pressing, extrusion, tape-casting and strong magnetic field alignment techniques for β-Si3N4 seed crystals. Each processing technique is thoroughly discussed in terms of theoretical models and experimental data, including the texturing mechanisms and the factors affecting texture development. Also, methods of synthesizing the rodlike β-Si3N4 single crystals are presented. Various anisotropic properties of textured Si3N4 and their origins are thoroughly described and discussed, such as hardness, elastic modulus, bending strength, fracture toughness, fracture energy, creep behavior, tribological and wear behavior, erosion behavior, contact damage behavior and thermal conductivity. Models are analyzed to determine the thermal anisotropy by considering the intrinsic thermal anisotropy, degree of orientation and various microstructure factors. Textured porous Si3N4 with a unique microstructure composed of oriented elongated β-Si3N4 and anisotropic pores is also described for the first time, with emphasis on its unique mechanical and thermal-mechanical properties. Moreover, as an important related material, textured α-Sialon is also reviewed, because the presence of elongated α-Sialon grains allows the production of textured α-Sialon using the same methods as those used for textured β-Si3N4 and β-Sialon. PMID:27877995

Microstructural evolution during thermal annealing of ice-Ih

NASA Astrophysics Data System (ADS)

Hidas, Károly; Tommasi, Andréa; Mainprice, David; Chauve, Thomas; Barou, Fabrice; Montagnat, Maurine

2017-06-01

We studied the evolution of the microstructure of ice-Ih during static recrystallization by stepwise annealing experiments. We alternated thermal annealing and electron backscatter diffraction (EBSD) analyses on polycrystalline columnar ice pre-deformed in uniaxial compression at temperature of -7 °C to macroscopic strains of 3.0-5.2. Annealing experiments were carried out at -5 °C and -2 °C up to a maximum of 3.25 days, typically in 5-6 steps. EBSD crystal orientation maps obtained after each annealing step permit the description of microstructural changes. Decrease in average intragranular misorientation at the sample scale and modification of the misorientation across subgrain boundaries provide evidence for recovery from the earliest stages of annealing. This initial evolution is similar for all studied samples irrespective of their initial strain or annealing temperature. After an incubation period ≥1.5 h, recovery is accompanied by recrystallization (nucleation and grain boundary migration). Grain growth proceeds at the expense of domains with high intragranular misorientations, consuming first the most misorientated parts of primary grains. Grain growth kinetics fits the parabolic growth law with grain growth exponents in the range of 2.4-4.0. Deformation-induced tilt boundaries and kink bands may slow down grain boundary migration. They are stable features during early stages of static recrystallization, only erased by normal growth, which starts after >24 h of annealing.

B2 Grain Growth Behavior of a Ti-22Al-25Nb Alloy Fabricated by Hot Pressing Sintering

NASA Astrophysics Data System (ADS)

Jia, Jianbo; Liu, Wenchao; Xu, Yan; Chen, Chen; Yang, Yue; Luo, Junting; Zhang, Kaifeng

2018-05-01

Grain growth behavior of a powder metallurgy (P/M) Ti-22Al-25Nb alloy was investigated by applying a series of isothermal treatment tests over a wide range of temperatures and holding times. An isothermal treatment scheme was conducted in the B2 phase region (1070-1110 °C) and α 2 + B2 phase region (1010-1050 °C) at holding times of 10, 30 min, 1, 2, and 3 h, respectively. The effects of temperature and holding time on the microstructure evolution and microhardness of the P/M Ti-22Al-25Nb alloy at elevated temperatures were evaluated using optical microscope, scanning electron microscope, x-ray diffraction, and Vickers hardness test techniques. The results revealed that the alloy's treated microstructure was closely linked to temperature and holding time, respectively. The change law of B2 grain growth with holding time and temperature can be well interpreted by the Beck equation and Hillert equation, respectively. The B2 grain growth exponent n and activation energy Q were acquired based on experimental data in the α 2 + B2 and B2 phase regions. In addition, the grain growth contour map for the P/M Ti-22Al-25Nb alloy was constructed to depict variations in B2 grain size based on holding time and temperature.

Ultrafast visualization of crystallization and grain growth in shock-compressed SiO2

PubMed Central

Gleason, A. E.; Bolme, C. A.; Lee, H. J.; Nagler, B.; Galtier, E.; Milathianaki, D.; Hawreliak, J.; Kraus, R. G.; Eggert, J. H.; Fratanduono, D. E.; Collins, G. W.; Sandberg, R.; Yang, W.; Mao, W. L.

2015-01-01

Pressure- and temperature-induced phase transitions have been studied for more than a century but very little is known about the non-equilibrium processes by which the atoms rearrange. Shock compression generates a nearly instantaneous propagating high-pressure/temperature condition while in situ X-ray diffraction (XRD) probes the time-dependent atomic arrangement. Here we present in situ pump–probe XRD measurements on shock-compressed fused silica, revealing an amorphous to crystalline high-pressure stishovite phase transition. Using the size broadening of the diffraction peaks, the growth of nanocrystalline stishovite grains is resolved on the nanosecond timescale just after shock compression. At applied pressures above 18 GPa the nuclueation of stishovite appears to be kinetically limited to 1.4±0.4 ns. The functional form of this grain growth suggests homogeneous nucleation and attachment as the growth mechanism. These are the first observations of crystalline grain growth in the shock front between low- and high-pressure states via XRD. PMID:26337754

Ultrafast visualization of crystallization and grain growth in shock-compressed SiO 2

DOE PAGES

Gleason, A. E.; Bolme, C. A.; Lee, H. J.; ...

2015-09-04

Pressure- and temperature-induced phase transitions have been studied for more than a century but very little is known about the non-equilibrium processes by which the atoms rearrange. Shock compression generates a nearly instantaneous propagating high-pressure/temperature condition while in situ X-ray diffraction (XRD) probes the time-dependent atomic arrangement. Here we present in situ pump–probe XRD measurements on shock-compressed fused silica, revealing an amorphous to crystalline high-pressure stishovite phase transition. Using the size broadening of the diffraction peaks, the growth of nanocrystalline stishovite grains is resolved on the nanosecond timescale just after shock compression. At applied pressures above 18 GPa the nuclueationmore » of stishovite appears to be kinetically limited to 1.4 ± 0.4 ns. The functional form of this grain growth suggests homogeneous nucleation and attachment as the growth mechanism. As a result, these are the first observations of crystalline grain growth in the shock front between low- and high-pressure states via XRD.« less

The free growth criterion for grain initiation in TiB 2 inoculated γ-titanium aluminide based alloys

NASA Astrophysics Data System (ADS)

Gosslar, D.; Günther, R.

2014-02-01

γ-titanium aluminide (γ-TiAl) based alloys enable for the design of light-weight and high-temperature resistant engine components. This work centers on a numerical study of the condition for grain initiation during solidification of TiB2 inoculated γ-TiAl based alloys. Grain initiation is treated according to the so-called free growth criterion. This means that the free growth barrier for grain initiation is determined by the maximum interfacial mean curvature between a nucleus and the melt. The strategy presented in this paper relies on iteratively increasing the volume of a nucleus, which partially wets a hexagonal TiB2 crystal, minimizing the interfacial energy and calculating the corresponding interfacial curvature. The hereby obtained maximum curvature yields a scaling relation between the size of TiB2 crystals and the free growth barrier. Comparison to a prototypical TiB2 crystal in an as cast γ-TiAl based alloy allowed then to predict the free growth barrier prevailing under experimental conditions. The validity of the free growth criterion is discussed by an interfacial energy criterion.

Microstructure evolution in the fusion zone of laser-welded Mg–Gd–Y–Zr alloy during solution and aging treatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Lyuyuan

The microstructure evolution in the fusion zone of laser-welded Mg-Gd-Y-Zr alloy during solution and aging treatment is investigated. The morphology of the Mg{sub 24}(Gd,Y){sub 5} in the divorced eutectic at the grain boundary transforms from a continuous network to disconnected and fragmentized islands and then to spheroidal particles before complete dissolution during the solution treatment at 430 °C. During the subsequent aging treatment at 225 °C, the precipitation sequence in the fusion zone follows the order of supersaturated solid solution (SSSS) → βʺ(D0{sub 19}) → βʹ(cbco) → β{sub 1}(fcc) → β(fcc). High-density precipitates are present at the original grain boundariesmore » of the fusion zone from the welded structure but there are less precipitates in the interior of the original grains. The grain growth during the solution treatment at 430 °C comprises the slowly increasing stage, rapidly increasing stage, and stable stage. The network-distributed Mg{sub 24}(Gd,Y){sub 5} impedes migration of the grain boundaries, restricts grain growth in the first slowly increasing stage, and segregation of zirconium near the grain boundaries also affects migration of the grain boundaries. - Highlights: •Different quantities of precipitates are present at different location of grain. •The network-distributed Mg{sub 24}(Gd,Y){sub 5} restricts grain growth. •Segregation of Zr affects migration of grain boundaries.« less

Natural variation in PTB1 regulates rice seed setting rate by controlling pollen tube growth.

PubMed

Li, Shuangcheng; Li, Wenbo; Huang, Bin; Cao, Xuemei; Zhou, Xingyu; Ye, Shumei; Li, Chengbo; Gao, Fengyan; Zou, Ting; Xie, Kailong; Ren, Yun; Ai, Peng; Tang, Yangfan; Li, Xuemei; Deng, Qiming; Wang, Shiquan; Zheng, Aiping; Zhu, Jun; Liu, Huainian; Wang, Lingxia; Li, Ping

2013-01-01

Grain number, panicle seed setting rate, panicle number and grain weight are the most important components of rice grain yield. To date, several genes related to grain weight, grain number and panicle number have been described in rice. However, no genes regulating the panicle seed setting rate have been functionally characterized. Here we show that the domestication-related POLLEN TUBE BLOCKED 1 (PTB1), a RING-type E3 ubiquitin ligase, positively regulates the rice panicle seed setting rate by promoting pollen tube growth. The natural variation in expression of PTB1 which is affected by the promoter haplotype and the environmental temperature, correlates with the rice panicle seed setting rate. Our results support the hypothesis that PTB1 is an important maternal sporophytic factor of pollen tube growth and a key modulator of the rice panicle seed setting rate. This finding has implications for the improvement of rice yield.

Evolution of microstructure and surface topography of gold thin films under thermal annealing

NASA Astrophysics Data System (ADS)

Dash, P.; Rath, H.; Dash, B. N.; Mallick, P.; Basu, T.; Som, T.; Singh, U. P.; Mishra, N. C.

2012-07-01

In the present study, we probe into evolution of microstructure and surface morphology of gold thin films of 10 to 50 nm thickness deposited on Si (100) substrate by thermal evaporation method. These films were annealed at 250°C under vacuum. The as-deposited and annealed films were characterized by glancing angle X-Ray diffraction (GAXRD) and atomic force microscopy (AFM), techniques. XRD indicated improvement of crystallinity up to 2 hours of annealing and degradation of the same thereafter. In agreement with XRD result, the grain size distribution histogram obtained from AFM indicated grain growth with annealing time up to 2 hours and saturation or decrease of grain size thereafter. The observed result is explained by the occurrence of two competing phenomena like roughening induced grain growth and smoothening induced inhibition of grain growth with increasing annealing time.

Phase-field study of grain boundary tracking behavior in crack-seal microstructures

NASA Astrophysics Data System (ADS)

Ankit, Kumar; Nestler, Britta; Selzer, Michael; Reichardt, Mathias

2013-12-01

In order to address the growth of crystals in veins, a multiphase-field model is used to capture the dynamics of crystals precipitating from a super-saturated solution. To gain a detailed understanding of the polycrystal growth phenomena in veins, we investigate the influence of various boundary conditions on crystal growth. In particular, we analyze the formation of vein microstructures resulting from the free growth of crystals as well as crack-sealing processes. We define the crystal symmetry by considering the anisotropy in surface energy to simulate crystals with flat facets and sharp corners. The resulting growth competition of crystals with different orientations is studied to deduce a consistent orientation selection rule in the free-growth regime. Using crack-sealing simulations, we correlate the grain boundary tracking behavior depending on the relative rate of crack opening, opening trajectory, initial grain size, and wall roughness. Further, we illustrate how these parameters induce the microstructural transition between blocky (crystals growing anisotropically) to fibrous morphology (isotropic) and formation of grain boundaries. The phase-field simulations of crystals in the free-growth regime (in 2D and 3D) indicate that the growth or consumption of a crystal is dependent on the orientation difference with neighboring crystals. The crack-sealing simulation results (in 2D and 3D) reveal that crystals grow isotropically and grain boundaries track the opening trajectory if the wall roughness is high, opening increments are small, and crystals touch the wall before the next crack increment starts. Further, we find that within the complete crack-seal regime, anisotropy in surface energy results in the formation of curved/oscillating grain boundaries (instead of straight) when the crack-opening velocity is increased and wall roughness is not sufficiently high. Additionally, the overall capability of phase-field method to simulate large-scale polycrystal growth in veins (in 3D) is demonstrated enumerating the main advantages of adopting the novel approach.

Investigating the Thermal and Phase Stability of Nanocrystalline Ni-W Produced by Electrodeposition, Sputtering, and Mechanical Alloying

NASA Astrophysics Data System (ADS)

Marvel, Christopher Jonathan

The development of nanocrystalline materials has been increasingly pursued over the last few decades. They have been shown to exhibit superior properties compared to their coarse-grain counterparts, and thus present a tremendous opportunity to revolutionize the performance of nanoscale devices or bulk structural materials. However, nanocrystalline materials are highly prone to grain growth, and if the nanocrystalline grains coarsen, the beneficial properties are lost. There is a strong effort to determine the most effective thermal stability mechanisms to avoid grain growth, but the physical nature of nanocrystalline grain growth is still unclear due to a lack of detailed understanding of nanocrystalline microstructures. Furthermore, the influence of contamination has scarcely been explored with advanced transmission electron microscopy techniques, nor has there been a direct comparison of alloys fabricated with different bulk processes. Therefore, this research has applied aberration-corrected scanning transmission electron microscopy to characterize nanocrystalline Ni-W on the atomic scale and elucidate the physical grain growth behavior. Three primary objectives were pursued: (1) explore the thermal stability mechanisms of nanocrystalline Ni-W, (2) evaluate the phase stability of Ni-W and link any findings to grain growth behavior, and (3) compare the influences of bulk fabrication processing, including electrodeposition, DC magnetron sputtering, and mechanical alloying, on the thermal stability and phase stability of Ni-W. Several thermal stability mechanisms were identified throughout the course of this research. First and foremost, W-segregation was scarcely observed to grain boundaries, and it is unclear if W-segregation improves thermal stability contrary to most reports in the 2 literature. Long-range Ni4W chemical ordering was observed in alloys with more than 20 at.% W, and it is likely Ni4W domains reduce grain boundary mobility. In addition, lattice diffusivity calculations conceptually suggested that increasing W alloying concentrations can decrease the grain growth rate. The strongest evidence of grain growth stagnation was via nanoscale oxide particle drag in highly contaminated electrodeposited alloys. Interestingly, W-segregation was also detected to the oxide phase boundaries and revealed a potential indirect mechanism of thermal stability. The phase stability of pure and contaminated Ni-W alloys was investigated with density functional theory. Primarily, the calculations suggested that the intermetallic phases NiW and NiW2 are thermodynamically unstable, meaning the binary phase diagram is incorrect, but the ternary carbides Ni 6W6C and Ni2W4C are stable. Several Ni-W binary and Ni-W-C ternary phase diagrams were constructed using a simplified CALPHAD approach to improve the understanding of Ni-W phase stability. Lastly, it was determined that the fabrication process greatly influences the impurity types and concentrations of the alloys, and therefore greatly dictate which thermal stability mechanisms are active. Mechanically alloyed samples were found to be the most resistant to grain growth. The findings of this research will hopefully guide future efforts to design more thermally stable nanocrystalline alloys. The link between phase stability and grain growth behavior of Ni-W was thoroughly discussed, as well as the dependence of bulk fabrication processing on the contamination found in the alloys. Ultimately, this research has greatly expanded the general understanding of nanocrystalline Ni-W microstructures, and it is likely that similar phenomena occur in other nanocrystalline systems.

Growth rate models for short surface cracks in AI 2219-T851

NASA Astrophysics Data System (ADS)

Morris, W. L.; James, M. R.; Buck, O.

1981-01-01

Rates of fatigue propagation of short Mode I surface cracks in Al 2219-T851 are measured as a function of crack length and of the location of the surface crack tips relative to the grain boundaries. The measured rates are then compared to values predicted from crack growth models. The crack growth rate is modeled with an underlying assumption that slip responsible for early propagation does not extend in significant amounts beyond the next grain boundary in the direction of crack propagation. Two models that contain this assumption are combined: 1) cessation of propagation into a new grain until a mature plastic zone is developed; 2) retardation of propagation by crack closure stress, with closure stress calculated from the location of a crack tip relative to the grain boundary. The transition from short to long crack growth behavior is also discussed.

Grain growth in uranium nitride prepared by spark plasma sintering

NASA Astrophysics Data System (ADS)

Johnson, Kyle D.; Lopes, Denise Adorno

2018-05-01

Uranium mononitride (UN) has long been considered a potential high density, high performance fuel candidate for light water reactor (LWR) and fast reactor (FR) applications. However, deployability of this fuel has been limited by the notable resistance to sintering and subsequent difficulty in producing a desirable microstructure, the high costs associated with 15N enrichment, as well as the known proclivity to oxidation and interaction with steam. In this study, the stimulation of grain growth in UN pellets sintered using SPS has been investigated. The results reveal that by using SPS and controlling temperature, time, and holding pressure, grain growth can be stimulated and controlled to produce a material featuring both a desired porosity and grain size, at least within the range of interest for nuclear fuel candidates. Grain sizes up to 31 μm were obtained using temperatures of 1650 °C and hold times of 15 min. Evaluation by EBSD reveal grain rotation and coalescence as the dominant mechanism in grain growth, which is suppressed by the application of higher external pressure. Moreover, complete closure of the porosity of the material was observed at relative densities of 96% TD, resulting in a material with sufficient porosity to accommodate LWR burnup. These results indicate that a method exists for the economic fabrication of an 15N-bearing uranium mononitride fuel with favorable microstructural characteristics compatible with use in a light water-cooled nuclear reactor.

Multiple seeding for the growth of bulk GdBCO-Ag superconductors with single grain behaviour

NASA Astrophysics Data System (ADS)

Shi, Y.; Durrell, J. H.; Dennis, A. R.; Huang, K.; Namburi, D. K.; Zhou, D.; Cardwell, D. A.

2017-01-01

Rare earth-barium-copper oxide bulk superconductors fabricated in large or complicated geometries are required for a variety of engineering applications. Initiating crystal growth from multiple seeds reduces the time taken to melt-process individual samples and can reduce the problem of poor crystal texture away from the seed. Grain boundaries between regions of independent crystal growth can reduce significantly the flow of current due to crystallographic misalignment and the agglomeration of impurity phases. Enhanced supercurrent flow at such boundaries has been achieved by minimising the depth of the boundary between A growth sectors generated during the melt growth process by reducing second phase agglomerations and by a new technique for initiating crystal growth that minimises the misalignment between different growth regions. The trapped magnetic fields measured for the resulting samples exhibit a single trapped field peak indicating they are equivalent to conventional single grains.

Effect of Machining Parameters on Oxidation Behavior of Mild Steel

NASA Astrophysics Data System (ADS)

Majumdar, P.; Shekhar, S.; Mondal, K.

2015-01-01

This study aims to find out a correlation between machining parameters, resultant microstructure, and isothermal oxidation behavior of lathe-machined mild steel in the temperature range of 660-710 °C. The tool rake angles "α" used were +20°, 0°, and -20°, and cutting speeds used were 41, 232, and 541 mm/s. Under isothermal conditions, non-machined and machined mild steel samples follow parabolic oxidation kinetics with activation energy of 181 and ~400 kJ/mol, respectively. Exaggerated grain growth of the machined surface was observed, whereas, the center part of the machined sample showed minimal grain growth during oxidation at higher temperatures. Grain growth on the surface was attributed to the reduction of strain energy at high temperature oxidation, which was accumulated on the sub-region of the machined surface during machining. It was also observed that characteristic surface oxide controlled the oxidation behavior of the machined samples. This study clearly demonstrates the effect of equivalent strain, roughness, and grain size due to machining, and subsequent grain growth on the oxidation behavior of the mild steel.

Mechanism of secondary recrystallization of Goss grains in grain-oriented electrical steel

NASA Astrophysics Data System (ADS)

Hayakawa, Yasuyuki

2017-12-01

Since its invention by Goss in 1934, grain-oriented (GO) electrical steel has been widely used as a core material in transformers. GO exhibits a grain size of over several millimeters attained by secondary recrystallization during high-temperature final batch annealing. In addition to the unusually large grain size, the crystal direction in the rolling direction is aligned with <001>, which is the easy magnetization axis of α-iron. Secondary recrystallization is the phenomenon in which a certain very small number of {110}<001> (Goss) grains grow selectively (about one in 106 primary grains) at the expense of many other primary recrystallized grains. The question of why the Goss orientation is exclusively selected during secondary recrystallization has long been a main research subject in this field. The general criterion for secondary recrystallization is a small and uniform primary grain size, which is achieved through the inhibition of normal grain growth by fine precipitates called inhibitors. This paper describes several conceivable mechanisms of secondary recrystallization of Goss grains mainly based on the selective growth model.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marshall, Ryan S.; Chai, Kil-Byoung; Bellan, Paul M.

The grain growth process in the Caltech water–ice dusty plasma experiment has been studied using a high-speed camera and a long-distance microscope lens. It is observed that (i) the ice grain number density decreases fourfold as the average grain major axis increases from 20 to 80 μ m, (ii) the major axis length has a log-normal distribution rather than a power-law dependence, and (iii) no collisions between ice grains are apparent. The grains have a large negative charge resulting in strong mutual repulsion and this, combined with the fractal character of the ice grains, prevents them from agglomerating. In ordermore » for the grain kinetic energy to be sufficiently small to prevent collisions between ice grains, the volumetric packing factor (i.e., ratio of the actual volume to the volume of a circumscribing ellipsoid) of the ice grains must be less than ∼0.1 depending on the exact relative velocity of the grains in question. Thus, it is concluded that direct accretion of water molecules is very likely to dominate the observed ice grain growth.« less

Mechanism of secondary recrystallization of Goss grains in grain-oriented electrical steel

PubMed Central

Hayakawa, Yasuyuki

2017-01-01

Abstract Since its invention by Goss in 1934, grain-oriented (GO) electrical steel has been widely used as a core material in transformers. GO exhibits a grain size of over several millimeters attained by secondary recrystallization during high-temperature final batch annealing. In addition to the unusually large grain size, the crystal direction in the rolling direction is aligned with <001>, which is the easy magnetization axis of α-iron. Secondary recrystallization is the phenomenon in which a certain very small number of {110}<001> (Goss) grains grow selectively (about one in 106 primary grains) at the expense of many other primary recrystallized grains. The question of why the Goss orientation is exclusively selected during secondary recrystallization has long been a main research subject in this field. The general criterion for secondary recrystallization is a small and uniform primary grain size, which is achieved through the inhibition of normal grain growth by fine precipitates called inhibitors. This paper describes several conceivable mechanisms of secondary recrystallization of Goss grains mainly based on the selective growth model. PMID:28804524

Mechanism of secondary recrystallization of Goss grains in grain-oriented electrical steel.

PubMed

Hayakawa, Yasuyuki

2017-01-01

Since its invention by Goss in 1934, grain-oriented (GO) electrical steel has been widely used as a core material in transformers. GO exhibits a grain size of over several millimeters attained by secondary recrystallization during high-temperature final batch annealing. In addition to the unusually large grain size, the crystal direction in the rolling direction is aligned with <001>, which is the easy magnetization axis of α-iron. Secondary recrystallization is the phenomenon in which a certain very small number of {110}<001> (Goss) grains grow selectively (about one in 10 6 primary grains) at the expense of many other primary recrystallized grains. The question of why the Goss orientation is exclusively selected during secondary recrystallization has long been a main research subject in this field. The general criterion for secondary recrystallization is a small and uniform primary grain size, which is achieved through the inhibition of normal grain growth by fine precipitates called inhibitors. This paper describes several conceivable mechanisms of secondary recrystallization of Goss grains mainly based on the selective growth model.

Tailored Net-Shape Powder Composites by Spark Plasma Sintering

NASA Astrophysics Data System (ADS)

Khaleghi, Evan Aryan

This dissertation investigates the ability to produce net-shape and tailored composites in spark plasma sintering (SPS), with an analysis of how grain growth, densification, and mechanical properties are affected. Using alumina and four progressively anisotropic dies, we studied the impact of specimen shape on densification. We found specimen shape had an impact on overall densification, but no impact on localized properties. We expected areas of the specimen to densify differently, or have higher grain growth, based on current anisotropy in the specimen during sintering, and preliminary results indicated this, but further investigation showed this did not occur. Overall average grain size and porosity decreased as shape complexity increased. In Fe-V-C steel, we mechanical alloyed two rapidly solidified powders, and used spark sintering to retain the properties imparted during the rapid solidification. We noticed VC grains being produced during densification, which improved the final properties. We conducted spark plasma extrusion (SPE) of aluminum to understand the effect on microstructure. We found, through an analysis of the grain structure, that SPE did have a grain deformation potential, and grain size was severely decreased compared to conventional sintering. Dynamic recrystallization did not occur, due to the reduced temperatures we were able to extrude with SPS. Finally, we examined whether there were particular sintering conditions for SPS that reduced the complexity of the grain growth and porosity relationship to one similar to conventional sintering, of the form G = k G0 ε -1/. We found that although a reasonable case could be made for free sintering, as found in the literature, for hot-pressing and SPS the conditions required go against the common knowledge in grain growth and densification kinetics. We were able to fit our data very well to the model, but the correlated results do not make physical sense.

Selective Growth of Low Stored Energy Grains During δ Sub-solvus Annealing in the Inconel 718 Nickel-Based Superalloy

NASA Astrophysics Data System (ADS)

Agnoli, Andrea; Bernacki, Marc; Logé, Roland; Franchet, Jean-Michel; Laigo, Johanne; Bozzolo, Nathalie

2015-09-01

The microstructure stability during δ sub-solvus annealing in Inconel 718 was investigated, focusing on the conditions that may lead to the development of very large grains (about 100 μm) in a recrystallized fine grained matrix (4 to 5 μm) despite the presence of second-phase particles. Microstructure evolution was analyzed by EBSD (grain size, intragranular misorientation) and SEM ( δ phase particles). Results confirm that, in the absence of stored energy, the grain structure is controlled by the δ phase particles, as predicted by the Smith-Zener equation. If the initial microstructure is strained ( ɛ < 0.1) before annealing, then low stored energy grains grow to a large extent, despite the Zener pinning forces exerted by the second-phase particles on the grain boundaries. Those selectively growing grains could be those of the initial microstructure that were the least deformed, or they could result from a nucleation process. The balance of three forces acting on boundary migration controls the growth process: if the sum of capillarity and stored energy driving forces exceeds the Zener pinning force, then selective grain growth occurs. Such phenomenon could be simulated, using a level set approach in a finite element context, by taking into account the three forces acting on boundary migration and by considering a realistic strain energy distribution (estimated from EBSD measurements).

The importance of grain size to mantle dynamics and seismological observations

NASA Astrophysics Data System (ADS)

Gassmoeller, R.; Dannberg, J.; Eilon, Z.; Faul, U.; Moulik, P.; Myhill, R.

2017-12-01

Grain size plays a key role in controlling the mechanical properties of the Earth's mantle, affecting both long-timescale flow patterns and anelasticity on the timescales of seismic wave propagation. However, dynamic models of Earth's convecting mantle usually implement flow laws with constant grain size, stress-independent viscosity, and a limited treatment of changes in mineral assemblage. We study grain size evolution, its interplay with stress and strain rate in the convecting mantle, and its influence on seismic velocities and attenuation. Our geodynamic models include the simultaneous and competing effects of dynamic recrystallization resulting from dislocation creep, grain growth in multiphase assemblages, and recrystallization at phase transitions. They show that grain size evolution drastically affects the dynamics of mantle convection and the rheology of the mantle, leading to lateral viscosity variations of six orders of magnitude due to grain size alone, and controlling the shape of upwellings and downwellings. Using laboratory-derived scaling relationships, we convert model output to seismologically-observable parameters (velocity, attenuation) facilitating comparison to Earth structure. Reproducing the fundamental features of the Earth's attenuation profile requires reduced activation volume and relaxed shear moduli in the lower mantle compared to the upper mantle, in agreement with geodynamic constraints. Faster lower mantle grain growth yields best fit to seismic observations, consistent with our re-examination of high pressure grain growth parameters. We also show that ignoring grain size in interpretations of seismic anomalies may underestimate the Earth's true temperature variations.

Near-Threshold Fatigue Crack Growth Behavior of Fine-Grain Nickel-Based Alloys

NASA Technical Reports Server (NTRS)

Newman, John A.; Piascik, Robert S.

2003-01-01

Constant-Kmax fatigue crack growth tests were performed on two finegrain nickel-base alloys Inconel 718 (DA) and Ren 95 to determine if these alloys exhibit near-threshold time-dependent crack growth behavior observed for fine-grain aluminum alloys in room-temperature laboratory air. Test results showed that increases in K(sub max) values resulted in increased crack growth rates, but no evidence of time-dependent crack growth was observed for either nickel-base alloy at room temperature.

Grain growth in nanocrystalline iron and Fe-Al alloys

NASA Astrophysics Data System (ADS)

Mirzadeh, Hamed; Zomorodian, Amir

2010-02-01

The effects of the annealing temperature and time, cryomilling in liquid nitrogen, and the addition of aluminum powder on the thermal stability and grain growth behavior of nanocrystalline iron were modeled using the Artificial Neural Network (ANN) technique. The developed model can be used as a guide for the quantification of the grain growth by considering the effects of annealing temperature and time. The model also quantified the effect of Al on the thermal stability of cryomilled nanocrystalline Fe. The model results showed that the cryomilling of Fe has a tangible effect on the stabilization of the nanostructure.

Modeling and simulation of the deposition/relaxation processes of polycrystalline diatomic structures of metallic nitride films

NASA Astrophysics Data System (ADS)

García, M. F.; Restrepo-Parra, E.; Riaño-Rojas, J. C.

2015-05-01

This work develops a model that mimics the growth of diatomic, polycrystalline thin films by artificially splitting the growth into deposition and relaxation processes including two stages: (1) a grain-based stochastic method (grains orientation randomly chosen) is considered and by means of the Kinetic Monte Carlo method employing a non-standard version, known as Constant Time Stepping, the deposition is simulated. The adsorption of adatoms is accepted or rejected depending on the neighborhood conditions; furthermore, the desorption process is not included in the simulation and (2) the Monte Carlo method combined with the metropolis algorithm is used to simulate the diffusion. The model was developed by accounting for parameters that determine the morphology of the film, such as the growth temperature, the interacting atomic species, the binding energy and the material crystal structure. The modeled samples exhibited an FCC structure with grain formation with orientations in the family planes of < 111 >, < 200 > and < 220 >. The grain size and film roughness were analyzed. By construction, the grain size decreased, and the roughness increased, as the growth temperature increased. Although, during the growth process of real materials, the deposition and relaxation occurs simultaneously, this method may perhaps be valid to build realistic polycrystalline samples.

Burkholderia ambifaria and B. caribensis Promote Growth and Increase Yield in Grain Amaranth (Amaranthus cruentus and A. hypochondriacus) by Improving Plant Nitrogen Uptake

PubMed Central

Parra-Cota, Fannie I.; Peña-Cabriales, Juan J.; de los Santos-Villalobos, Sergio; Martínez-Gallardo, Norma A.; Délano-Frier, John P.

2014-01-01

Grain amaranth is an emerging crop that produces seeds having high quality protein with balanced amino-acid content. However, production is restricted by agronomic limitations that result in yields that are lower than those normally produced by cereals. In this work, the use of five different rhizobacteria were explored as a strategy to promote growth and yields in Amaranthus hypochondriacus cv. Nutrisol and A. cruentus cv. Candil, two commercially important grain amaranth cultivars. The plants were grown in a rich substrate, high in organic matter, nitrogen (N), and phosphorus (P) and under greenhouse conditions. Burkholderia ambifaria Mex-5 and B. caribensis XV proved to be the most efficient strains and significantly promoted growth in both grain amaranth species tested. Increased grain yield and harvest index occurred in combination with chemical fertilization when tested in A. cruentus. Growth-promotion and improved yields correlated with increased N content in all tissues examined. Positive effects on growth also occurred in A. cruentus plants grown in a poor soil, even after N and P fertilization. No correlation between non-structural carbohydrate levels in roots of inoculated plants and growth promotion was observed. Conversely, gene expression assays performed at 3-, 5- and 7-weeks after seed inoculation in plants inoculated with B. caribensis XV identified a tissue-specific induction of several genes involved in photosynthesis, sugar- and N- metabolism and transport. It is concluded that strains of Burkholderia effectively promote growth and increase seed yields in grain amaranth. Growth promotion was particularly noticeable in plants grown in an infertile soil but also occurred in a well fertilized rich substrate. The positive effects observed may be attributed to a bio-fertilization effect that led to increased N levels in roots and shoots. The latter effect correlated with the differential induction of several genes involved in carbon and N metabolism and transport. PMID:24533068

Residual-stress-induced grain growth of twinned grains and its effect on formability of magnesium alloy sheet at room temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Se-Jong; Kim, Daeyong, E-mail: daeyong@kims.re.kr; Lee, Keunho

2015-11-15

A magnesium alloy sheet was subjected to in-plane compression along with a vertical load to avoid buckling during compression. Pre-compressed specimens machined from the sheet were annealed at different temperatures and the changes in microstructure and texture were observed using electron back scattered diffraction (EBSD). Twinned grains preferentially grew during annealing at 300 °C, so that a strong texture with the < 0001 > direction parallel to the transverse direction developed. EBSD analysis confirmed that the friction caused by the vertical load induced inhomogeneous distribution of residual stress, which acted as an additional driving force for preferential grain growth ofmore » twinned grain during annealing. The annealed specimen showed excellent formability. - Highlights: • A magnesium alloy sheet subjected to in-plane compression under a vertical load • The vertical load induced inhomogeneous distribution of the residual stress. • The residual stress acted as an additional driving force for grain growth. • The annealed specimen with strong non-basal texture showed excellent formability.« less

Biocontrol Activity of Volatile-Producing Bacillus megaterium and Pseudomonas protegens against Aspergillus flavus and Aflatoxin Production on Stored Rice Grains

PubMed Central

Mannaa, Mohamed; Oh, Ji Yeon

2017-01-01

In our previous study, three bacterial strains, Bacillus megaterium KU143, Microbacterium testaceum KU313, and Pseudomonas protegens AS15, were selected as effective biocontrol agents against Aspergillus flavus on stored rice grains. In this study, we evaluated the inhibitory effects of the volatiles produced by the strains on A. flavus growth and aflatoxin production on stored rice grains. The three strains significantly reduced mycelial growth of A. flavus in dual-culture assays compared with the negative control strain, Sphingomonas aquatilis KU408, and an untreated control. Of these tested strains, volatiles produced by B. megaterium KU143 and P. protegens AS15 markedly inhibited mycelial growth, sporulation, and conidial germination of A. flavus on agar medium and suppressed the fungal populations in rice grains. Moreover, volatiles produced by these two strains significantly reduced aflatoxin production in the rice grains by A. flavus. To our knowledge, this is the first report of the suppression of A. flavus aflatoxin production in rice grains using B. megaterium and P. protegens volatiles. PMID:29138628

A Model of Silicate Grain Nucleation and Growth in Circumstellar Outflows

NASA Technical Reports Server (NTRS)

Paquette, John A.; Ferguson, Frank T.; Nuth, Joseph A., III

2011-01-01

Based on its abundance, high bond energy, and recent measurements of its vapor pressure SiO is a natural candidate for dust nucleation in circumstellar outflows around asymptotic giant branch stars. In this paper, we describe a model of the nucleation and growth of silicate dust in such outflows. The sensitivity of the model to varying choices of poorly constrained chemical parameters is explored, and the merits of using scaled rather than classical nucleation theory are briefly considered, An elaboration of the model that includes magnesium and iron as growth species is then presented and discussed. The composition of the bulk of the grains derived from the model is consistent with olivines and pyroxenes, but somewhat metal-rich grains and very small, nearly pure SiO grains are also produced,

Introducing Overlapping Grain Boundaries in Chemical Vapor Deposited Hexagonal Boron Nitride Monolayer Films

PubMed Central

2017-01-01

We demonstrate the growth of overlapping grain boundaries in continuous, polycrystalline hexagonal boron nitride (h-BN) monolayer films via scalable catalytic chemical vapor deposition. Unlike the commonly reported atomically stitched grain boundaries, these overlapping grain boundaries do not consist of defect lines within the monolayer films but are composed of self-sealing bilayer regions of limited width. We characterize this overlapping h-BN grain boundary structure in detail by complementary (scanning) transmission electron microscopy techniques and propose a catalytic growth mechanism linked to the subsurface/bulk of the process catalyst and its boron and nitrogen solubilities. Our data suggest that the overlapping grain boundaries are comparatively resilient against deleterious pinhole formation associated with grain boundary defect lines and thus may reduce detrimental breakdown effects when polycrystalline h-BN monolayer films are used as ultrathin dielectrics, barrier layers, or separation membranes. PMID:28410557

Polycystic ovary syndrome

MedlinePlus

... regular. These medicines may also help reduce abnormal hair growth and acne after you take them for several ... nurse may also suggest other treatments for abnormal hair growth. Some are: Spironolactone or flutamide pills Eflornithine cream ...

Zn uptake, translocation and grain Zn loading in rice (Oryza sativa L.) genotypes selected for Zn deficiency tolerance and high grain Zn

PubMed Central

Impa, Somayanda M.; Morete, Mark J.; Ismail, Abdelbagi M.; Schulin, Rainer; Johnson-Beebout, Sarah E.

2013-01-01

Zn deficiency is a widespread problem in rice (Oryza sativa L.) grown under flooded conditions, limiting growth and grain Zn accumulation. Genotypes with Zn deficiency tolerance or high grain Zn have been identified in breeding programmes, but little is known about the physiological mechanisms conferring these traits. A protocol was developed for growing rice to maturity in agar nutrient solution (ANS), with optimum Zn-sufficient growth achieved at 1.5 μM ZnSO4.7H2O. The redox potential in ANS showed a decrease from +350 mV to −200 mV, mimicking the reduced conditions of flooded paddy soils. In subsequent experiments, rice genotypes contrasting for Zn deficiency tolerance and grain Zn were grown in ANS with sufficient and deficient Zn to assess differences in root uptake of Zn, root-to-shoot Zn translocation, and in the predominant sources of Zn accumulation in the grain. Zn efficiency of a genotype was highly influenced by root-to-shoot translocation of Zn and total Zn uptake. Translocation of Zn from root to shoot was more limiting at later growth stages than at the vegetative stage. Under Zn-sufficient conditions, continued root uptake during the grain-filling stage was the predominant source of grain Zn loading in rice, whereas, under Zn-deficient conditions, some genotypes demonstrated remobilization of Zn from shoot and root to grain in addition to root uptake. Understanding the mechanisms of grain Zn loading in rice is crucial in selecting high grain Zn donors for target-specific breeding and also to establish fertilizer and water management strategies for achieving high grain Zn. PMID:23698631

An Explanation for Bends of 1-Dimensional Nanorods

NASA Astrophysics Data System (ADS)

Mukaida, Masashi; Ichinose, Ataru; Mele, Paolo; Mtsumoto, Kaname; Horii, Shigeru; Yoshida, Yutaka

Growth of artificial pinning centers (APCs) in YBa2Cu3O7-J (YBCO) films are discussed. The APCs used in this research are BaZrO3 and BaSnO3 nanorods which are reported by Mele et al. TEM images show these nanorods graduallybend accordinglywith approachingtoasurfaceof films. This featureshowedagrowth patternlikeafirework. Weexplainthe featureofthe nanorodsas follows;Atanearlygrowth stage, filmsgrowinalayerbylayergrowth mode. The surface of the films is flat and very smooth. After the early growth stage, the film surface gradually becomes rough, indicating the film grows in a Stranski-Krastanov growth mode. This roughness was caused by a spiral growth of films with manysteps. At the step of YBCO films, nanorod materials such as BaZrO3 are supplied from one direction. Then, the center of nanorods sifts to the same direction of the step flow. Then, the nanorods bend to the edge of the grains in the films. As a grain in spiral growth had a convex surface, nanorods bent to the direction perpendicular to the grain surface. Finally, nanorods in rough grains form firework structures.

Grain setting defect1, Encoding a Remorin Protein, Affects the Grain Setting in Rice through Regulating Plasmodesmatal Conductance1[W

PubMed Central

Gui, Jinshan; Liu, Chang; Shen, Junhui; Li, Laigeng

2014-01-01

Effective grain filling is one of the key determinants of grain setting in rice (Oryza sativa). Grain setting defect1 (GSD1), which encodes a putative remorin protein, was found to affect grain setting in rice. Investigation of the phenotype of a transfer DNA insertion mutant (gsd1-Dominant) with enhanced GSD1 expression revealed abnormalities including a reduced grain setting rate, accumulation of carbohydrates in leaves, and lower soluble sugar content in the phloem exudates. GSD1 was found to be specifically expressed in the plasma membrane and plasmodesmata (PD) of phloem companion cells. Experimental evidence suggests that the phenotype of the gsd1-Dominant mutant is caused by defects in the grain-filling process as a result of the impaired transport of carbohydrates from the photosynthetic site to the phloem. GSD1 functioned in affecting PD conductance by interacting with rice ACTIN1 in association with the PD callose binding protein1. Together, our results suggest that GSD1 may play a role in regulating photoassimilate translocation through the symplastic pathway to impact grain setting in rice. PMID:25253885

Grain formation around carbon stars. 1: Stationary outflow models

NASA Technical Reports Server (NTRS)

Egan, Michael P.; Leung, Chun Ming

1995-01-01

Asymptotic giant branch (AGB) stars are known to be sites of dust formation and undergo significant mass loss. The outflow is believed to be driven by radiation pressure on grains and momentum coupling between the grains and gas. While the physics of shell dynamics and grain formation are closely coupled, most previous models of circumstellar shells have treated the problem separately. Studies of shell dynamics typically assume the existence of grains needed to drive the outflow, while most grain formation models assume a constant veolcity wind in which grains form. Furthermore, models of grain formation have relied primarily on classical nucleation theory instead of using a more realistic approach based on chemical kinetics. To model grain formation in carbon-rich AGB stars, we have coupled the kinetic equations governing small cluster growth to moment equations which determine the growth of large particles. Phenomenological models assuming stationary outflow are presented to demonstrate the differences between the classical nucleation approach and the kinetic equation method. It is found that classical nucleation theory predicts nucleation at a lower supersaturation ratio than is predicted by the kinetic equations, resulting in significant differences in grain properties. Coagulation of clusters larger than monomers is unimportant for grain formation in high mass-loss models but becomes more important to grain growth in low mass-loss situations. The properties of the dust grains are altered considerably if differential drift velocities are ignored in modeling grain formation. The effect of stellar temperature, stellar luminosity, and different outflow velocities are investigated. The models indicate that changing the stellar temperature while keeping the stellar luminosity constant has little effect on the physical parameters of the dust shell formed. Increasing the stellar luminosity while keeping the stellar temperature constant results in large differences in grain properties. For small outflow velocities, grains form at lower supersaturation ratios and close to the stellar photosphere, resulting in larger but fewer grains. The reverse is true when grains form under high outflow velocities, i.e., they form at higher supersaturation ratios, farther from the star, and are much smaller but at larger quantities.

SUMMARY OF PROGRESS ON THE STUDY OF BETA TREATMENT OF URANIUM, NOVEMBER 1, 1959-AUGUST 31, 1960

DOE Office of Scientific and Technical Information (OSTI.GOV)

Russell, R.B.

Variables affecting the texture and grain size of uranium during beta treatment are summarized. The study of the effect of time and temperature in the beta phase on the growth index (G3) and grain size of the final alpha product is tentatively believed to show that higher beta temperatures for short times (up to about seven minutes) tend to promote slightly more negative growth indices and that higher beta temperatures give rise to somewhat finer grain sizes. Results of studies of both Jominy end-quenched bars and several full-sized rods and tubes quenched by total immersion showed that large thermal gradientsmore » promoted negative growth indices and produced grains somewhat elongated in the direction of the thermal gradient. The effects of endcooling in full-sized pieces quenched by total immersion in cold water showed that the axial growth index is negative up to distances from the end of about half the wall thickness of tubes and about half the radial dimension of rods. The grain refinement penetrates to a lesser distance from the ends. In the radial direction the growth index for these same pieces is largely negative to a distance below the outer diameter of about midwall in two tubes studied. In the case of one tube which was studied more completely, the growth index became negative again as the inner diameter was approached. A water-quenched rod was found to have a negative growth index down to a distance from the surface of about midradius. (auth)« less

A novel, two-step top seeded infiltration and growth process for the fabrication of single grain, bulk (RE)BCO superconductors

NASA Astrophysics Data System (ADS)

Namburi, Devendra K.; Shi, Yunhua; Palmer, Kysen G.; Dennis, Anthony R.; Durrell, John H.; Cardwell, David A.

2016-09-01

A fundamental requirement of the fabrication of high performing, (RE)-Ba-Cu-O bulk superconductors is achieving a single grain microstructure that exhibits good flux pinning properties. The top seeded melt growth (TSMG) process is a well-established technique for the fabrication of single grain (RE)BCO bulk samples and is now applied routinely by a number of research groups around the world. The introduction of a buffer layer to the TSMG process has been demonstrated recently to improve significantly the general reliability of the process. However, a number of growth-related defects, such as porosity and the formation of micro-cracks, remain inherent to the TSMG process, and are proving difficult to eliminate by varying the melt process parameters. The seeded infiltration and growth (SIG) process has been shown to yield single grain samples that exhibit significantly improved microstructures compared to the TSMG technique. Unfortunately, however, SIG leads to other processing challenges, such as the reliability of fabrication, optimisation of RE2BaCuO5 (RE-211) inclusions (size and content) in the sample microstructure, practical oxygenation of as processed samples and, hence, optimisation of the superconducting properties of the bulk single grain. In the present paper, we report the development of a near-net shaping technique based on a novel two-step, buffer-aided top seeded infiltration and growth (BA-TSIG) process, which has been demonstrated to improve greatly the reliability of the single grain growth process and has been used to fabricate successfully bulk, single grain (RE)BCO superconductors with improved microstructures and superconducting properties. A trapped field of ˜0.84 T and a zero field current density of 60 kA cm-2 have been measured at 77 K in a bulk, YBCO single grain sample of diameter 25 mm processed by this two-step BA-TSIG technique. To the best of our knowledge, this value of trapped field is the highest value ever reported for a sample fabricated by an infiltration and growth process. In this study we report the successful fabrication of 14 YBCO samples, with diameters of up to 32 mm, by this novel technique with a success rate of greater than 92%.

Experimental Analysis and Mathematical Modeling on Mg-Li Alloy Sheets with Three Crystal Structures during Cold Rolling and Heat Treatment.

PubMed

Tang, Yan; Le, Qichi; Wang, Tong; Chen, Xingrui

2017-10-12

The microstructural evolution, mechanical properties, and mathematical relationship of an α, α + β, and β phase Mg-Li alloy during the cold rolling and annealing process were investigated. The results showed that the increased Li element gradually transformed the Mg matrix structure from hcp to bcc. Simultaneously, the alloy plasticity was improved remarkably during cold rolling. In the annealing process, a sort of abnormal grain growth was found in Mg-11Li-3Al-2Zn-0.2Y, but was not detected in Mg-5Li-3Al-2Zn-0.2Y and Mg-8Li-3Al-2Zn-0.2Y. Moreover, the mechanical properties of alloy were evidently improved through a kind of solid solution in the β matrix. To accurately quantify this strengthening effect, the method of mathematical modeling was used to determine the relationship between strength and multiple factors.

Plate-tectonic boundary formation by grain-damage and pinning

NASA Astrophysics Data System (ADS)

Bercovici, David

2015-04-01

Shear weakening in the lithosphere is an essential ingredient for understanding how and why plate tectonics is generated from mantle convection on terrestrial planets. I present continued work on a theoretical model for lithospheric shear-localization and plate generation through damage, grain evolution and Zener pinning in two-phase (polycrystalline) lithospheric rocks. Grain size evolves through the competition between coarsening, which drives grain-growth, with damage, which drives grain reduction. The interface between phases controls Zener pinning, which impedes grain growth. Damage to the interface enhances the Zener pinning effect, which then reduces grain-size, forcing the rheology into the grain-size-dependent diffusion creep regime. This process thus allows damage and rheological weakening to co-exist, providing a necessary shear-localizing feedback. Moreover, because pinning inhibits grain-growth it promotes shear-zone longevity and plate-boundary inheritance. This theory has been applied recently to the emergence of plate tectonics in the Archean by transient subduction and accumulation of plate boundaries over 1Gyr, as well as to rapid slab detachment and abrupt tectonic changes. New work explores the saturation of interface damage at low interface curvature (e.g., because it is associated with larger grains that take up more of the damage, and/or because interface area is reduced). This effect allows three possible equilibrium grain-sizes for a given stress; a small-grain-size high-shear state in diffusion creep, a large grain-size low shear state in dislocation creep, and an intermediate state (often near the deformation map phase-boundary). The low and high grain-size states are stable, while the intermediate one is unstable. This implies that a material deformed at a given stress can acquire two stable deformation regimes, a low- and high- shear state; these are indicative of plate-like flows, i.e, the coexistence of both slowly deforming plates and rapidly deforming plate boundaries.

Experimental studies of Micro- and Nano-grained UO 2: Grain Growth Behavior, Sufrace Morphology, and Fracture Toughness

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miao, Yinbin; Mo, Kun; Jamison, Laura M.

This activity is supported by the US Nuclear Energy Advanced Modeling and Simulation (NEAMS) Fuels Product Line (FPL) and aims at providing experimental data for the validation of the mesoscale simulation code MARMOT. MARMOT is a mesoscale multiphysics code that predicts the coevolution of microstructure and properties within reactor fuel during its lifetime in the reactor. It is an important component of the Moose-Bison-Marmot (MBM) code suite that has been developed by Idaho National Laboratory (INL) to enable next generation fuel performance modeling capability as part of the NEAMS Program FPL. In order to ensure the accuracy of the microstructure-basedmore » materials models being developed within the MARMOT code, extensive validation efforts must be carried out. In this report, we summarize the experimental efforts in FY16 including the following important experiments: (1) in-situ grain growth measurement of nano-grained UO 2; (2) investigation of surface morphology in micrograined UO 2; (3) Nano-indentation experiments on nano- and micro-grained UO 2. The highlight of this year is: we have successfully demonstrated our capability to in-situ measure grain size development while maintaining the stoichiometry of nano-grained UO 2 materials; the experiment is, for the first time, using synchrotron X-ray diffraction to in-situ measure grain growth behavior of UO 2.« less

Nanoscale Investigation of Grain Growth in RF-Sputtered Indium Tin Oxide Thin Films by Scanning Probe Microscopy

NASA Astrophysics Data System (ADS)

Lamsal, B. S.; Dubey, M.; Swaminathan, V.; Huh, Y.; Galipeau, D.; Qiao, Q.; Fan, Q. H.

2014-11-01

This work studied the electronic characteristics of the grains and grain boundaries of indium tin oxide (ITO) thin films using electrostatic and Kelvin probe force microscopy. Two types of ITO films were compared, deposited using radiofrequency magnetron sputtering in pure argon or 99% argon + 1% oxygen, respectively. The average grain size and surface roughness increased with substrate temperature for the films deposited in pure argon. With the addition of 1% oxygen, the increase in the grain size was inhibited above 150°C, which was suggested to be due to passivation of the grains by the excess oxygen. Electrostatic force microscopy and Kelvin probe force microscopy (KPFM) images confirmed that the grain growth was defect mediated and occurred at defective interfaces at high temperatures. Films deposited at room temperature with 1% oxygen showed crystalline nature, while films deposited with pure argon at room temperature were amorphous as observed from KPFM images. The potential drop across the grain and grain boundary was determined by taking surface potential line profiles to evaluate the electronic properties.

Grain Growth and Precipitation Behavior of Iridium Alloy DOP-26 During Long Term Aging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pierce, Dean T.; Muralidharan, Govindarajan; Fox, Ethan E.

The influence of long term aging on grain growth and precipitate sizes and spatial distribution in iridium alloy DOP-26 was studied. Samples of DOP-26 were fabricated using the new process, recrystallized for 1 hour (h) at 1375 C, then aged at either 1300, 1400, or 1500 C for times ranging from 50 to 10,000 h. Grain size measurements (vertical and horizontal mean linear intercept and horizontal and vertical projection) and analyses of iridium-thorium precipitates (size and spacing) were made on the longitudinal, transverse, and rolling surfaces of the as-recrystallized and aged specimens from which the two-dimensional spatial distribution and meanmore » sizes of the precipitates were obtained. The results obtained from this study are intended to provide input to grain growth models.« less

Synthesis of Large-grain, Single-crystalline Monolayer and AB-stacking Bilayer Graphene

NASA Astrophysics Data System (ADS)

Zhang, Luyao; Lin, Yung-Chen; Zhang, Yi; Chang, Han-Wen; Yeh, Wen-Cheng; Zhou, Chongwu; USC Nanotechnology Research Laboratory Team

2013-03-01

We report the growth of large-grain, single-crystalline monolayer and AB-stacking bilayer graphene by the combination of ambient pressure chemical vapor deposition and low pressure chemical vapor deposition. The shape of the monolayer graphene was modified to be either hexagons or flowers under different growth conditions. The size of the bilayer graphene region was enlarged under ambient pressure growth conditions with low methane concentration. Raman spectra and selected area electron diffraction of individual graphene grain indicated that the each graphene grain is single-crystalline. With electron beam lithography patterned PMMA seeds, graphene nucleation can be controlled and graphene monolayer and bilayer arrays were synthesized on copper foil. Electron backscatter diffraction study revealed that the graphene morphology had little correlation with the crystalline orientation of underlying copper substrate. Mork Family Department of Chemical Engineering and Materials Science

Growth rate of YBCO-Ag superconducting single grains

NASA Astrophysics Data System (ADS)

Congreve, J. V. J.; Shi, Y. H.; Dennis, A. R.; Durrell, J. H.; Cardwell, D. A.

2017-12-01

The large scale use of (RE)Ba2Cu3O7 bulk superconductors, where RE=Y, Gd, Sm, is, in part, limited by the relatively poor mechanical properties of these inherently brittle ceramic materials. It is reported that alloying of (RE)Ba2Cu3O7 with silver enables a significant improvement in the mechanical strength of bulk, single grain samples without any detrimental effect on their superconducting properties. However, due to the complexity and number of inter-related variables involved in the top seeded melt growth (TSMG) process, the growth of large single grains is difficult and the addition of silver makes it even more difficult to achieve successful growth reliably. The key processing variables in the TSMG process include the times and temperatures of the stages within the heating profile, which can be derived from the growth rate during the growth process. To date, the growth rate of the YBa2Cu3O7-Ag system has not been reported in detail and it is this lacuna that we have sought to address. In this work we measure the growth rate of the YBCO-Ag system using a method based on continuous cooling and isothermal holding (CCIH). We have determined the growth rate by measuring the side length of the crystallised region for a number of samples for specified isothermal hold temperatures and periods. This has enabled the growth rate to be modelled and from this an optimized heating profile for the successful growth of YBCO-Ag single grains to be derived.

Influence of Temperature and Water Activity on Deleterious Fungi and Mycotoxin Production during Grain Storage

PubMed Central

Mannaa, Mohamed

2017-01-01

Cereal grains are the most important food source for humans. As the global population continues to grow exponentially, the need for the enhanced yield and minimal loss of agricultural crops, mainly cereal grains, is increasing. In general, harvested grains are stored for specific time periods to guarantee their continuous supply throughout the year. During storage, economic losses due to reduction in quality and quantity of grains can become very significant. Grain loss is usually the result of its deterioration due to fungal contamination that can occur from preharvest to postharvest stages. The deleterious fungi can be classified based on predominance at different stages of crop growth and harvest that are affected by environmental factors such as water activity (aw) and eco-physiological requirements. These fungi include species such as those belonging to the genera Aspergillus and Penicillium that can produce mycotoxins harmful to animals and humans. The grain type and condition, environment, and biological factors can also influence the occurrence and predominance of mycotoxigenic fungi in stored grains. The main environmental factors influencing grain fungi and mycotoxins are temperature and aw. This review discusses the effects of temperature and aw on fungal growth and mycotoxin production in stored grains. The focus is on the occurrence and optimum and minimum growth requirements for grain fungi and mycotoxin production. The environmental influence on aflatoxin production and hypothesized mechanisms of its molecular suppression in response to environmental changes are also discussed. In addition, the use of controlled or modified atmosphere as an environmentally safe alternative to harmful agricultural chemicals is discussed and recommended future research issues are highlighted. PMID:29371792

Understanding and controlling low-temperature aging of nanocrystalline materials.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Battaile, Corbett Chandler; Boyce, Brad Lee; Brons, Justin G.

2013-10-01

Nanocrystalline copper lms were created by both repetitive high-energy pulsed power, to produce material without internal nanotwins; and pulsed laser deposition, to produce nan- otwins. Samples of these lms were indented at ambient (298K) and cryogenic temperatures by immersion in liquid nitrogen (77K) and helium (4K). The indented samples were sectioned through the indented regions and imaged in a scanning electron microscope. Extensive grain growth was observed in the lms that contained nanotwins and were indented cryogenically. The lms that either lacked twins, or were indented under ambient conditions, were found to exhibit no substantial grain growth by visual inspection.more » Precession transmission elec- tron microscopy was used to con rm these ndings quantitatively, and show that 3 and 7 boundaries proliferate during grain growth, implying that these interface types play a key role in governing the extensive grain growth observed here. Molecular dynamics sim- ulations of the motion of individual grain boundaries demonstrate that speci c classes of boundaries - notably 3 and 7 - exhibit anti- or a-thermal migration, meaning that their mobilities either increase or do not change signi cantly with decreasing temperature. An in-situ cryogenic indentation capability was developed and implemented in a transmission electron microscope. Preliminary results do not show extensive cryogenic grain growth in indented copper lms. This discrepancy could arise from the signi cant di erences in con g- uration and loading of the specimen between the two approaches, and further research and development of this capability is needed.« less

Tension-controlled single-crystallization of copper foils for roll-to-roll synthesis of high-quality graphene films

NASA Astrophysics Data System (ADS)

Jo, Insu; Park, Subeom; Kim, Dongjin; San Moon, Jin; Park, Won Bae; Kim, Tae Hyeong; Hyoun Kang, Jin; Lee, Wonbae; Kim, Youngsoo; Lee, Dong Nyung; Cho, Sung-Pyo; Choi, Hyunchul; Kang, Inbyeong; Park, Jong Hyun; Lee, Jeong Soo; Hong, Byung Hee

2018-04-01

It has been known that the crystalline orientation of Cu substrates plays a crucial role in chemical vapor deposition (CVD) synthesis of high-quality graphene. In particular, Cu (1 1 1) surface showing the minimum lattice mismatch with graphene is expected to provide an ideal catalytic reactivity that can minimize the formation of defects, which also induces larger single-crystalline domain sizes of graphene. Usually, the Cu (1 1 1) substrates can be epitaxially grown on single-crystalline inorganic substrates or can be recrystallized by annealing for more than 12 h, which limits the cost and time-effective synthesis of graphene. Here, we demonstrate a new method to optimize the crystalline orientations of vertically suspended Cu foils by tension control during graphene growth, resulting in large-area recrystallization into Cu (1 1 1) surface as the applied tension activates the grain boundary energy of Cu and promotes its abnormal grain growth to single crystals. In addition, we found a clue that the formation of graphene cooperatively assists the recrystallization into Cu (1 1 1) by minimizing the surface energy of Cu. The domain sizes and charge carrier mobility of graphene grown on the single-crystalline Cu (1 1 1) are 5 times and ~50% increased, respectively, in comparison with those of graphene from Cu (1 0 0), indicating that the less lattice mismatch and the lower interaction energy between Cu (1 1 1) and graphene allows the growth of larger single-crystalline graphene with higher charge carrier mobility. Thus, we believe that our finding provides a crucial idea to design a roll-to-roll (R2R) graphene synthesis system where the tension control is inevitably involved, which would be of great importance for the continuous production of high-quality graphene in the future.

Hetero-Orientation Epitaxial Growth of TiO2 Splats on Polycrystalline TiO2 Substrate

NASA Astrophysics Data System (ADS)

Chen, Lin; Yang, Guan-Jun

2018-05-01

In the present study, the effect of titania (TiO2) substrate grain size and orientation on the epitaxial growth of TiO2 splat was investigated. Interestingly, the splat presented comparable grain size with that of substrate, indicating the hereditary feature of grain size. In addition, hetero- and homo-orientation epitaxial growth was observed at deposition temperatures below 400 °C and above 500 °C, respectively. The preferential growth of high-energy (001) face was also observed at low deposition temperatures (≤ 400 °C), which was found to result from dynamic nonequilibrium effect during the thermal spray deposition. Moreover, thermal spray deposition paves the way for a new approach to prepare high-energy (001) facets of TiO2 crystals.

Grain growth prediction based on data assimilation by implementing 4DVar on multi-phase-field model

NASA Astrophysics Data System (ADS)

Ito, Shin-ichi; Nagao, Hiromichi; Kasuya, Tadashi; Inoue, Junya

2017-12-01

We propose a method to predict grain growth based on data assimilation by using a four-dimensional variational method (4DVar). When implemented on a multi-phase-field model, the proposed method allows us to calculate the predicted grain structures and uncertainties in them that depend on the quality and quantity of the observational data. We confirm through numerical tests involving synthetic data that the proposed method correctly reproduces the true phase-field assumed in advance. Furthermore, it successfully quantifies uncertainties in the predicted grain structures, where such uncertainty quantifications provide valuable information to optimize the experimental design.

Microwave sintering of nanophase ceramics without concomitant grain growth

DOEpatents

Eastman, Jeffrey A.; Sickafus, Kurt E.; Katz, Joel D.

1993-01-01

A method of sintering nanocrystalline material is disclosed wherein the nanocrystalline material is microwaved to heat the material to a temperature less than about 70% of the melting point of the nanocrystalline material expressed in degrees K. This method produces sintered nanocrystalline material having a density greater than about 95% of theoretical and an average grain size not more than about 3 times the average grain size of the nanocrystalline material before sintering. Rutile TiO.sub.2 as well as various other ceramics have been prepared. Grain growth of as little as 1.67 times has resulted with densities of about 90% of theoretical.

Grain-damage hysteresis and plate tectonic states

NASA Astrophysics Data System (ADS)

Bercovici, David; Ricard, Yanick

2016-04-01

Shear localization in the lithosphere is an essential ingredient for understanding how and why plate tectonics is generated from mantle convection on terrestrial planets. The theoretical model for grain-damage and pinning in two-phase polycrystalline rocks provides a frame-work for understanding lithospheric shear weakening and plate-generation, and is consistent with laboratory and field observations of mylonites. Grain size evolves through the competition between coarsening, which drives grain-growth, and damage, which drives grain reduction. The interface between crystalline phases controls Zener pinning, which impedes grain growth. Damage to the interface enhances the Zener pinning effect, which then reduces grain-size, forcing the rheology into the grain-size-dependent diffusion creep regime. This process thus allows damage and rheological weakening to co-exist, providing a necessary positive self-weakening feedback. Moreover, because pinning inhibits grain-growth it promotes shear-zone longevity and plate-boundary inheritance. However, the suppression of interface damage at low interface curvature (wherein inter-grain mixing is inefficient and other energy sinks of deformational work are potentially more facile) causes a hysteresis effect, in which three possible equilibrium grain-sizes for a given stress coexist: (1) a stable, large-grain, weakly-deforming state, (2) a stable, small-grain, rapidly-deforming state analogous to ultramylonites, and (3) an unstable, intermediate grain-size state perhaps comparable to protomylonites. A comparison of the model to field data suggests that shear-localized zones of small-grain mylonites and ultra-mylonites exist at a lower stress than the co-existing large-grain porphyroclasts, rather than, as predicted by paleopiezometers or paleowattmeters, at a much higher stress; this interpretation of field data thus allows localization to relieve instead of accumulate stress. The model also predicts that a lithosphere that deforms at a given stress can acquire two stable deformation regimes indicative of plate-like flows, i.e., it permits the coexistence of both slowly deforming plate interiors, and rapidly deforming plate boundaries. Earth seems to exist squarely inside the hysteresis loop and thus can have coexisting deformation states, while Venus appears to straddle the end of the loop where only the weakly deforming branch exists.

Hypopituitarism in pediatric survivors of inflicted traumatic brain injury.

PubMed

Auble, Bethany A; Bollepalli, Sureka; Makoroff, Kathi; Weis, Tammy; Khoury, Jane; Colliers, Tracy; Rose, Susan R

2014-02-15

Endocrine dysfunction is common after accidental traumatic brain injury (TBI). Prevalence of endocrine dysfunction after inflicted traumatic brain injury (iTBI) is not known. The aim of this study was to examine endocrinopathy in children after moderate-to-severe iTBI. Children with previous iTBI (n=14) were evaluated for growth/endocrine dysfunction, including anthropometric measurements and hormonal evaluation (nocturnal growth hormone [GH], thyrotropin surge, morning and low-dose adrenocorticotropin stimulated cortisol, insulin-like growth factor 1, IGF-binding protein 3, free thyroxine, prolactin [PRL], and serum/urine osmolality). Analysis used Fisher's exact test and Wilcoxon's rank-sum test, as appropriate. Eighty-six percent of subjects had endocrine dysfunction with at least one abnormality, whereas 50% had two or more abnormalities, significantly increased compared to an estimated 2.5% with endocrine abnormality in the general population (p<0.001). Elevated prolactin was common (64%), followed by abnormal thyroid function (33%), short stature (29%), and low GH peak (17%). High prolactin was common in subjects with other endocrine abnormalities. Two were treated with thyroid hormone and 2 may require GH therapy. In conclusion, children with a history of iTBI show high risk for endocrine dysfunction, including elevated PRL and growth abnormalities. This effect of iTBI has not been well described in the literature. Larger, multi-center, prospective studies would provide more data to determine the extent of endocrine dysfunction in iTBI. We recommend that any child with a history of iTBI be followed closely for growth velocity and pubertal changes. If growth velocity is slow, PRL level and a full endocrine evaluation should be performed.

Mechanical behavior and failure phenomenon of an in situ-toughened silicon nitride

NASA Technical Reports Server (NTRS)

Salem, Jonathan A.; Choi, Sung R.; Freedman, Marc R.; Jenkins, Michael G.

1990-01-01

The Weibull modulus, fracture toughness and crack growth resistance of an in-situ toughened, silicon nitride material used to manufacture a turbine combustor were determined from room temperature to 1371 C. The material exhibited an elongated grain structure that resulted in improved fracture toughness, nonlinear crack growth resistance, and good elevated temperature strength. However, low temperature strength was limited by grains of excessive length (30 to 100 microns). These excessively long grains were surrounded by regions rich in sintering additives.

Effect of Sn Micro-alloying on Recrystallization Nucleation and Growth Processes of Ferritic Stainless Steels

NASA Astrophysics Data System (ADS)

He, Tong; Bai, Yang; Liu, Xiuting; Guo, Dan; Liu, Yandong

2018-04-01

We investigated the effect of Sn micro-alloying on recrystallization nucleation and growth processes of ferritic stainless steels. The as-received hot rolled sheets were cold rolled up to 80% reduction and then annealed at 740-880 °C for 5 min. The cold rolling and recrystallization microstructures and micro-textures of Sn-containing and Sn-free ferritic stainless steels were all determined by electron backscatter diffraction. Our Results show that Sn micro-alloying has important effects on recrystallization nucleation and growth processes of ferritic stainless steels. Sn micro-alloying conduces to grain fragmentation in the deformation band, more fragmented grains are existed in Sn-containing cold rolled sheets, which provides more sites for recrystallization nucleation. Sn micro-alloying also promotes recrystallization process and inhibits the growth of recrystallized grains. The recrystallization nucleation and growth mechanism of Sn-containing and Sn-free ferritic stainless steels are both characterized by orientation nucleation and selective growth, but Sn micro-alloying promotes the formation of γ-oriented grains. Furthermore, Sn micro-alloying contributes to the formation of Σ13b CSL boundaries and homogeneous γ-fiber texture. Combining the results of microstructure and micro-texture, the formability of Sn-containing ferritic stainless steels will be improved to some extent.

Shear-Coupled Grain Growth and Texture Development in a Nanocrystalline Ni-Fe Alloy during Cold Rolling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Li; Ungár, Tamás; Toth, Laszlo S.

The evolution of texture, grain size, grain shape, dislocation and twin density has been determined by synchrotron X-ray diffraction and line profile analysis in a nanocrystalline Ni- Fe alloy after cold rolling along different directions related to the initial fiber and the long axis of grains. The texture evolution has been simulated by the Taylor-type relaxed constraints viscoplastic polycrystal model. The simulations were based on the activity of partial dislocations in correlation with the experimental results of dislocation density determination. The concept of stress-induced shear-coupling is supported and strengthened by both the texture simulations and the experimentally determined evolution ofmore » the microstructure parameters. Grain-growth and texture evolution are shown to proceed by the shear-coupling mechanism supported by dislocation activity as long as the grain size is not smaller than about 20 nm.« less

Phase field models for heterogeneous nucleation: Application to inoculation in alpha-solidifying Ti-Al-B alloys

NASA Astrophysics Data System (ADS)

Apel, M.; Eiken, J.; Hecht, U.

2014-02-01

This paper aims at briefly reviewing phase field models applied to the simulation of heterogeneous nucleation and subsequent growth, with special emphasis on grain refinement by inoculation. The spherical cap and free growth model (e.g. A.L. Greer, et al., Acta Mater. 48, 2823 (2000)) has proven its applicability for different metallic systems, e.g. Al or Mg based alloys, by computing the grain refinement effect achieved by inoculation of the melt with inert seeding particles. However, recent experiments with peritectic Ti-Al-B alloys revealed that the grain refinement by TiB2 is less effective than predicted by the model. Phase field simulations can be applied to validate the approximations of the spherical cap and free growth model, e.g. by computing explicitly the latent heat release associated with different nucleation and growth scenarios. Here, simulation results for point-shaped nucleation, as well as for partially and completely wetted plate-like seed particles will be discussed with respect to recalescence and impact on grain refinement. It will be shown that particularly for large seeding particles (up to 30 μm), the free growth morphology clearly deviates from the assumed spherical cap and the initial growth - until the free growth barrier is reached - significantly contributes to the latent heat release and determines the recalescence temperature.

Cosmic dust synthesis by accretion and coagulation

NASA Technical Reports Server (NTRS)

Praburam, G.; Goree, J.

1995-01-01

The morphology of grains grown by accretion and coagulation is revaled by a new laboratory method of synthesizing cosmic dust analogs. Submicron carbon particles, grown by accretion of carbon atoms from a gas, have a spherical shape with a cauliflower-like surface and an internal micro-structure of radial columns. This shape is probably common for grains grown by accretion at a temperature well below the melting point. Coagulated grains, consisting of spheres that collided to form irregular strings, were also synthesized. Another shape we produced had a bumpy non- spherical morphology, like an interplanetary particle collected in the terrestrial stratosphere. Besides these isolated grains, large spongy aggregates of nanometer-size particles were also found for various experimental conditions. Grains were synthesized using ions to sputter a solid target, producing an atomic vapor at a low temperature. The ions were provided by a plasma, which also provided electrostatic levitation of the grains during their growth. The temporal development of grain growth was studied by extinguishing the plasma after various intervals.

Assessment of MARMOT Grain Growth Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fromm, B.; Zhang, Y.; Schwen, D.

2015-12-01

This report assesses the MARMOT grain growth model by comparing modeling predictions with experimental results from thermal annealing. The purpose here is threefold: (1) to demonstrate the validation approach of using thermal annealing experiments with non-destructive characterization, (2) to test the reconstruction capability and computation efficiency in MOOSE, and (3) to validate the grain growth model and the associated parameters that are implemented in MARMOT for UO 2. To assure a rigorous comparison, the 2D and 3D initial experimental microstructures of UO 2 samples were characterized using non-destructive Synchrotron x-ray. The same samples were then annealed at 2273K for grainmore » growth, and their initial microstructures were used as initial conditions for simulated annealing at the same temperature using MARMOT. After annealing, the final experimental microstructures were characterized again to compare with the results from simulations. So far, comparison between modeling and experiments has been done for 2D microstructures, and 3D comparison is underway. The preliminary results demonstrated the usefulness of the non-destructive characterization method for MARMOT grain growth model validation. A detailed analysis of the 3D microstructures is in progress to fully validate the current model in MARMOT.« less

Chemical and microbiological characterisation of kefir grains.

PubMed

Garrote, G L; Abraham, A G; De Antoni, G L

2001-11-01

Chemical and microbiological composition of four Argentinean kefir grains from different sources as well as characteristics of the corresponding fermented milk were studied. Kefir grains CIDCA AGK1, AGK2 and AGK4 did not show significant differences in their chemical and microbiological composition. In contrast, protein and yeast content of AGK3 was higher than in the other grains. Although grain microflora comprised lactobacilli, lactococcus, acetic acid bacteria and yeast, we found an important difference regarding species. Lactococcus lactis subsp. lactis, Lactobacillus kefir, Lactobacillus plantarum, Acetobacter and Saccharomyces were present in all types of kefir grain. While Leuconostoc mesenteroides was only isolated from grains CIDCA AGK1 and Lactococcus lactis subsp. lactis biovar diacetylactis, Lactobacillus parakefir and Kluyveromyces marxianus were only isolated from CIDCA AGK2 grains. All grains produced acid products with pH between 3.5 and 4.0. The apparent viscosity of AGK1 fermented milk was greater than the product obtained with AGK4. All fermented milks had inhibitory power towards Escherichia coli but AGK1 and AGK2 supernatants were able to halt the bacterial growth for at least 25 h. Grain weight increment in AGK1, AGK2 and AGK3 during growth in milk did not show significant differences. Despite their fermenting activity, AGK4 grains did not increase their weight.

Process-scale modelling of microstructure in direct chill casting of aluminium alloys

NASA Astrophysics Data System (ADS)

Bedel, M.; Heyvaert, L.; Založnik, M.; Combeau, H.; Daloz, D.; Lesoult, G.

2015-06-01

The mechanical properties of an alloy being related to its microstructure, the understanding of the mechanisms responsible for the grain structure formation in direct chill casting is crucial. However, the grain size prediction by modelling is difficult since a variety of multi-scale coupled phenomena have to be considered. Nucleation and growth of the grains are interrelated, and the macroscopic transport phenomena such as the motion of grains and inoculant particles with the flow impact the nucleation-gowth competition. Thus we propose to study the grain size distribution of a 5182 alloy industrial scale slab of 510 mm thickness, both non-inoculated and inoculated with Al-3Ti-1B, for which experimental grain size measurements are available. We use a volume-averaged two-phase multi-scale model that describes nucleation from inoculant particles and grain growth, fully coupled with macroscopic transport phenomena: fluid flow induced by natural convection and solidification shrinkage, heat, mass and solute mass transport, grains and inoculant particles motion. We analyze the effect of liquid and grain motion as the effect of grain morphology on microstructure formation and we show in which extent those phenomena are responsible for the grain size distribution observed experimentally. The effect of the refiner level is also studied.

Nucleation and Growth of Crystalline Grains in RF-Sputtered TiO 2 Films

DOE PAGES

Johnson, J. C.; Ahrenkiel, S. P.; Dutta, P.; ...

2009-01-01

Amore » morphous TiO 2 thin films were radio frequency sputtered onto siliconmonoxide and carbon support films on molybdenum transmission electron microscope (TEM) grids and observed during in situ annealing in a TEM heating stage at 250 ∘ C. The evolution of crystallization is consistent with a classical model of homogeneous nucleation and isotropic grain growth. The two-dimensional grain morphology of the TEM foil allowed straightforward recognition of amorphous and crystallized regions of the films, for measurement of crystalline volume fraction and grain number density. By assuming that the kinetic parameters remain constant beyond the onset of crystallization, the final average grain size was computed, using an analytical extrapolation to the fully crystallized state. Electron diffraction reveals a predominance of the anatase crystallographic phase.« less

Thermal Impacts in Vibration-assisted Laser Deep Penetration Welding of Aluminum

NASA Astrophysics Data System (ADS)

Radel, T.

Mechanical vibrations affect the nucleation and grain growth conditions during welding. In order to understand the vibration-induced influences on the grain formation conditions in laser beam welding of aluminum the thermal impacts of simultaneously applied vibrations are analyzed in this study. Therefore, laser deep penetration welding at vibration frequencies between 0.5 kHz and 5 kHz is investigated. Besides full penetration, partial penetration experiments were carried out. The results show that the thermal and absorption efficiencies are not significantly affected by the applied excitation. The solidification time increases in case of applied excitation which is rather disadvantageous regarding grain refinement. Thus, mechanical-metallurgical and not thermal-metallurgical effects should be responsible for the change in grain nucleation and grain growth conditions in laser beam welding with simultaneously applied vibrations.

Formation of highly preferred orientation of β-Sn grains in solidified Cu/SnAgCu/Cu micro interconnects under temperature gradient effect

NASA Astrophysics Data System (ADS)

Zhao, N.; Zhong, Y.; Dong, W.; Huang, M. L.; Ma, H. T.; Wong, C. P.

2017-02-01

β-Sn grain orientation and configuration are becoming crucial factors to dominate the lifetime of solder interconnects in three-dimensional integrated circuit packaging. In this paper, we found that a temperature gradient during solidification significantly dominated the orientation and configuration of the final β-Sn grains in Cu/SnAgCu/Cu micro interconnects. Being different from the random orientations and growth fronts meeting or cyclic twin boundary forming near the center after homogeneous temperature bonding, the β-Sn grains solidified under a certain temperature gradient were observed to follow a highly preferred orientation with their c-axis departing from the direction of temperature gradient by about 45°-88°. Meanwhile, these preferred oriented β-Sn grains consisted of low angle grain boundary structures with misorientation in the range of 0°-15°. The mechanism was explained in terms of the anisotropy and directional growth of β-Sn grains. The results pave the way for grain orientation control in 3D packaging technology.

Exogenously Applied Plant Growth Regulators Enhance the Morpho-Physiological Growth and Yield of Rice under High Temperature.

PubMed

Fahad, Shah; Hussain, Saddam; Saud, Shah; Hassan, Shah; Ihsan, Zahid; Shah, Adnan N; Wu, Chao; Yousaf, Muhammad; Nasim, Wajid; Alharby, Hesham; Alghabari, Fahad; Huang, Jianliang

2016-01-01

A 2-year experiment was conducted to ascertain the effects of exogenously applied plant growth regulators (PGR) on rice growth and yield attributes under high day (HDT) and high night temperature (HNT). Two rice cultivars (IR-64 and Huanghuazhan) were subjected to temperature treatments in controlled growth chambers and four different combinations of ascorbic acid (Vc), alpha-tocopherol (Ve), brassinosteroids (Br), methyl jasmonates (MeJA), and triazoles (Tr) were applied. High temperature severely affected rice morphology, and also reduced leaf area, above-, and below-ground biomass, photosynthesis, and water use efficiency, while increased the leaf water potential of both rice cultivars. Grain yield and its related attributes except number of panicles, were reduced under high temperature. The HDT posed more negative effects on rice physiological attributes, while HNT was more detrimental for grain formation and yield. The Huanghuazhan performed better than IR-64 under high temperature stress with better growth and higher grain yield. Exogenous application of PGRs was helpful in alleviating the adverse effects of high temperature. Among PGR combinations, the Vc+Ve+MejA+Br was the most effective treatment for both cultivars under high temperature stress. The highest grain production by Vc+Ve+MejA+Br treated plants was due to enhanced photosynthesis, spikelet fertility and grain filling, which compensated the adversities of high temperature stress. Taken together, these results will be of worth for further understanding the adaptation and survival mechanisms of rice to high temperature and will assist in developing heat-resistant rice germplasm in future.

Self-assembly and continuous growth of hexagonal graphene flakes on liquid Cu

NASA Astrophysics Data System (ADS)

Cho, Seong-Yong; Kim, Min-Sik; Kim, Minsu; Kim, Ki-Ju; Kim, Hyun-Mi; Lee, Do-Joong; Lee, Sang-Hoon; Kim, Ki-Bum

2015-07-01

Graphene growth on liquid Cu has received great interest, owing to the self-assembly behavior of hexagonal graphene flakes with aligned orientation and to the possibility of forming a single grain of graphene through a commensurate growth of these graphene flakes. Here, we propose and demonstrate a two-step growth process which allows the formation of self-assembled, completely continuous graphene on liquid Cu. After the formation of full coverage on the liquid Cu, grain boundaries were revealed via selective hydrogen etching and the original grain boundaries were clearly resolved. This result indicates that, while the flakes self-assembled with the same orientation, there still remain structural defects, gaps and voids that were not resolved by optical microscopy or scanning electron microscopy. To overcome this limitation, the two-step growth process was employed, consisting of a sequential process of a normal single-layer graphene growth and self-assembly process with a low carbon flux, followed by the final stage of graphene growth at a high degree of supersaturation with a high carbon flux. Continuity of the flakes was verified via hydrogen etching and a NaCl-assisted oxidation process, as well as by measuring the electrical properties of the graphene grown by the two-step process. Two-step growth can provide a continuous graphene layer, but commensurate stitching should be further studied.Graphene growth on liquid Cu has received great interest, owing to the self-assembly behavior of hexagonal graphene flakes with aligned orientation and to the possibility of forming a single grain of graphene through a commensurate growth of these graphene flakes. Here, we propose and demonstrate a two-step growth process which allows the formation of self-assembled, completely continuous graphene on liquid Cu. After the formation of full coverage on the liquid Cu, grain boundaries were revealed via selective hydrogen etching and the original grain boundaries were clearly resolved. This result indicates that, while the flakes self-assembled with the same orientation, there still remain structural defects, gaps and voids that were not resolved by optical microscopy or scanning electron microscopy. To overcome this limitation, the two-step growth process was employed, consisting of a sequential process of a normal single-layer graphene growth and self-assembly process with a low carbon flux, followed by the final stage of graphene growth at a high degree of supersaturation with a high carbon flux. Continuity of the flakes was verified via hydrogen etching and a NaCl-assisted oxidation process, as well as by measuring the electrical properties of the graphene grown by the two-step process. Two-step growth can provide a continuous graphene layer, but commensurate stitching should be further studied. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03352g

Determination of grain boundary mobility during recrystallization by statistical evaluation of electron backscatter diffraction measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Basu, I., E-mail: basu@imm.rwth-aachen.de; Chen, M.; Loeck, M.

One of the key aspects influencing microstructural design pathways in metallic systems is grain boundary motion. The present work introduces a method by means of which direct measurement of grain boundary mobility vs. misorientation dependence is made possible. The technique utilizes datasets acquired by means of serial electron backscatter diffraction (EBSD) measurements. The experimental EBSD measurements are collectively analyzed, whereby datasets were used to obtain grain boundary mobility and grain aspect ratio with respect to grain boundary misorientation. The proposed method is further validated using cellular automata (CA) simulations. Single crystal aluminium was cold rolled and scratched in order tomore » nucleate random orientations. Subsequent annealing at 300 °C resulted in grains growing, in the direction normal to the scratch, into a single deformed orientation. Growth selection was observed, wherein the boundaries with misorientations close to Σ7 CSL orientation relationship (38° 〈111〉) migrated considerably faster. The obtained boundary mobility distribution exhibited a non-monotonic behavior with a maximum corresponding to misorientation of 38° ± 2° about 〈111〉 axes ± 4°, which was 10–100 times higher than the mobility values of random high angle boundaries. Correlation with the grain aspect ratio values indicated a strong growth anisotropy displayed by the fast growing grains. The observations have been discussed in terms of the influence of grain boundary character on grain boundary motion during recrystallization. - Highlights: • Statistical microstructure method to measure grain boundary mobility during recrystallization • Method implementation independent of material or crystal structure • Mobility of the Σ7 boundaries in 5N Al was calculated as 4.7 × 10{sup –8} m{sup 4}/J ⋅ s. • Pronounced growth selection in the recrystallizing nuclei in Al • Boundary mobility values during recrystallization 2–3 orders of magnitude larger vis-à-vis curvature driven motion.« less

Solid-state diffusion-controlled growth of the phases in the Au-Sn system

NASA Astrophysics Data System (ADS)

Baheti, Varun A.; Kashyap, Sanjay; Kumar, Praveen; Chattopadhyay, Kamanio; Paul, Aloke

2018-01-01

The solid state diffusion-controlled growth of the phases is studied for the Au-Sn system in the range of room temperature to 200 °C using bulk and electroplated diffusion couples. The number of product phases in the interdiffusion zone decreases with the decrease in annealing temperature. These phases grow with significantly high rates even at the room temperature. The growth rate of the AuSn4 phase is observed to be higher in the case of electroplated diffusion couple because of the relatively small grains and hence high contribution of the grain boundary diffusion when compared to the bulk diffusion couple. The diffraction pattern analysis indicates the same equilibrium crystal structure of the phases in these two types of diffusion couples. The analysis in the AuSn4 phase relating the estimated tracer diffusion coefficients with grain size, crystal structure, the homologous temperature of experiments and the concept of the sublattice diffusion mechanism in the intermetallic compounds indicate that Au diffuses mainly via the grain boundaries, whereas Sn diffuses via both the grain boundaries and the lattice.

High fidelity polycrystalline CdTe/CdS heterostructures via molecular dynamics

DOE PAGES

Aguirre, Rodolfo; Chavez, Jose Juan; Zhou, Xiaowang; ...

2017-06-20

Molecular dynamics simulations of polycrystalline growth of CdTe/CdS heterostructures have been performed. First, CdS was deposited on an amorphous CdS substrate, forming a polycrystalline film. Subsequently, CdTe was deposited on top of the polycrystalline CdS film. Cross-sectional images show grain formation at early stages of the CdS growth. During CdTe deposition, the CdS structure remains almost unchanged. Concurrently, CdTe grain boundary motion was detected after the first 24.4 nanoseconds of CdTe deposition. With the elapse of time, this grain boundary pins along the CdS/CdTe interface, leaving only a small region of epitaxial growth. CdTe grains are larger than CdS grainsmore » in agreement with experimental observations in the literature. Crystal phase analysis shows that zinc blende structure dominates over the wurtzite structure inside both CdS and CdTe grains. Composition analysis shows Te and S diffusion to the CdS and CdTe films, respectively. Lastly, these simulated results may stimulate new ideas for studying and improving CdTe solar cell efficiency.« less

Crystal grain growth at the α -uranium phase transformation in praseodymium

NASA Astrophysics Data System (ADS)

Cunningham, Nicholas C.; Velisavljevic, Nenad; Vohra, Yogesh K.

2005-01-01

Structural phase transformations under pressure are examined in praseodymium metal for the range 0-40GPa at ambient temperature. Pressure was generated with a diamond-anvil cell, and data were collected using high-resolution synchrotron x-ray diffraction and the image plate technique. The structural sequence double hexagonal close packed (dhcp)→face centered cubic (fcc)→distorted-fcc (d-fcc)→ α -uranium (α-U) is observed with increasing pressure. Rietveld refinement of all crystallographic phases provided confirmation of the hR24 structure for the d-fcc phase while the previously reported monoclinic phase between the d-fcc and the α-U phase was not confirmed. We observe dramatic crystal grain growth during the volume collapse concurrent with the symmetry-lowering transition to the α-U structure. No preferred orientation axis is observed, and the formation process for these large grains is expected to be via a nucleation and growth mechanism. An analogous effect in rare earth metal cerium suggests that the grain growth during transformation to the α-U structure is a common occurrence in f -electron metals at high pressures.

Development of Bulk Nanocrystalline Tungsten Alloys for Fusion Reactor Structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fang, Zhigang Zak

This project developed a technology for manufacturing bulk ultrafine tungsten materials that are at or near full density for fusion reactor structural applications, aiming to improve ductility and toughness of tungsten before and after irradiation. The project involved the development of fabrication processes for making bulk ultrafine grained W, the development of new alloys of ultrafine grained W and evaluations of properties of these specific materials. The goal of this fabrication process is to produce fully dense bulk W with ultrafine grain sizes, with uniform distributions of grain size and additives. To date there is no known process that couldmore » be used to make ultrafine grained tungsten in a fully dense state and in a cost-acceptable fashion. The specific technology described in this proposal for making ultrafine grained tungsten involves a suite of nano-particle processing and sintering techniques. The program also developed new alloys of ultrafine grained W, e.g. W-(Ta,V,Ti)-TiC alloys to improve ductility and toughness before and after irradiation. By completing this project, we achieved the following objectives: • Demonstrated experimentally the feasibility of producing bulk ultrafine grained tungsten alloys (at or near 100% dense, <1000 nm grain size) using the proposed process • Demonstrated the proposed ultrafine grained W alloys, namely, W-(Ta, V, Ti)-TiC, can indeed be made using the proposed process • Demonstrated that the properties of nano tungsten alloys meet the requirements for fusion reactor applications. The overall goal was to harness the potential of ultrafine grained W produced using the proposed processes as the core structural materials for future fusion reactors. The project was very successful overall, meeting all milestones and surpassing project goals in terms of process development and material’s blistering resistance properties. A novel process similar to the conventional press-and-sinter powder metallurgy method was developed for producing ultrafine grain tungsten from nanosize tungsten powders. Grain growth was significantly controlled during sintering by certain alloy compositions, particularly Ti, and most compositions sintered to maximum densification. To optimize this process, the effect of processing parameters on the densification and grain growth of nano-W powders was investigated. Near-fully densified tungsten was obtained at sintering temperatures between 1100 and 1300 °C, and both Ar and H2 sintering atmospheres were investigated. The Ar sintering atmosphere was determined to more favorably promote densification and minimize grain growth. The nanosized tungsten powder compacts were subjected to reduction in H2 as a part of the sintering cycle. The reduction temperature was found to have significant effects on the sintering of nano-W powder, primarily as a result of grain coarsening, which was seen at temperatures as low as 700 °C. In an effort to inhibit grain growth, the effect of Ti-based additives on the densification and grain growth of nano-W powders was investigated in this project. The addition of 1 wt.% Ti into tungsten led to more than a 63% decrease in average grain size of sintered samples at comparable density levels. Compared to conventional high temperature sintering, a lower temperature sintering cycle for a longer hold time resulted in both near-full density and fine grain size. The roles of the Ti additives include not only the inhibition of grain growth, but also the potential absorption of oxygen from W particles. The project has resulted in the publication; thus far, of six peer reviewed journal articles and seven conference presentations, as well as a master’s thesis. Two additional journal articles are currently in preparation. Presentations and articles were a particular focus of the second half of the project, once significant experimentation had been performed and analyzed. As part of our efforts to disseminate information of our results, the W research teams with Prof. Fang had a strong presence at multiple international conferences during 2015 and 2016. Several research groups in the US are now performing experiments using the ultrafine grained W materials.« less

LEOPARD syndrome: what are café noir spots?

PubMed

Rodríguez-Bujaldón, Alfonso; Vazquez-Bayo, Carmen; Jimenez-Puya, Rafael; Galan-Gutierrez, Manuel; Moreno-Gimenez, José; Rodriguez-Garcia, Alfonso; Tercedor, Jesus; Velez-Garcia, Antonio

2008-01-01

Lentigines, electrocardiographic abnormalities, ocular hypertelorism, pulmonary stenosis, abnormalities of genitalia, retarded growth, and deafness syndrome (multiple lentigines syndrome) is most often characterized by multiple lentigines and cardiac conduction defects. Café noir spot is a term proposed, by analogy to café au lait spots, for the larger and darkly pigmented patches that are frequently observed in patients with this syndrome. Although presumed by some authors to represent lentigines, the histologic features of café noir spots have not been well documented in the literature. Only two previous cases have been reported in which a biopsy of the café noir spots than melanocytic nevi. We describe the histologic characteristics of seven café noir spots in six patients with lentigines, electrocardiographic abnormalities, ocular hypertelorism, pulmonary stenosis, abnormalities of genitalia, retarded growth, and deafness syndrome. Three lesions represented melanocytic nevi (one with dysplastic features), and four were compatible with lentigo simplex. These findings help our understanding of the histologic spectrum of pigmented lesions in lentigines, electrocardiographic abnormalities, ocular hypertelorism, pulmonary stenosis, abnormalities of genitalia, retarded growth, and deafness syndrome.

The Influence of Impurities and Metallic Capping Layers on the Microstructure of Copper Interconnects

NASA Astrophysics Data System (ADS)

Rizzolo, Michael

As copper interconnects have scaled to ever smaller dimensions on semiconductor devices, the microstructure has become increasingly detrimental for performance and reliability. Small grains persist in interconnects despite annealing at high temperatures, leading to higher line resistance and more frequent electromigration-induced failures. Conventionally, it was believed that impurities from the electrodeposition pinned grain growth, but limitations in analytical techniques meant the effect was inferred rather than observed. Recent advances in analytical techniques, however, have enabled this work to quantify impurity content, location, and diffusion in relation to microstructural changes in electroplated copper. Surface segregation of impurities during the initial burst of grain growth was investigated. After no surface segregation was observed, a microfluidic plating cell was constructed to plate multilayer films with regions of intentionally high and low impurity concentrations to determine if grain growth could be pinned by the presence of impurities; it was not. An alternate mechanism for grain boundary pinning based on the texture of the seed layer is proposed, supported by time-resolved transmission electron microscopy and transmission electron backscatter diffraction data. The suggested model posits that the seed in narrow features has no preferred orientation, which results in rapid nucleation of subsurface grains in trench regions prior to recrystallization from the overburden down. These rapidly growing grains are able to block off several trenches from the larger overburden grains, inhibiting grain growth in narrow features. With this knowledge in hand, metallic capping layers were employed to address the problematic microstructure in 70nm lines. The capping layers (chromium, nickel, zinc, and tin) were plated on the copper overburden prior to annealing to manipulate the stress gradient and microstructural development during annealing. It appeared that regardless of as-plated stress, nickel capping altered the recrystallized texture of the copper over patterned features. The nickel capping also caused a 2x increase in the number of advantageous 'bamboo' grains that span the entire trench, which effectively block electromigration pathways. These data provides a more fundamental understanding of manipulating the microstructure in copper interconnects using pre-anneal capping layers, and demonstrates a strategy to improve the microstructure beyond the capabilities of simple annealing.

Order parameter re-mapping algorithm for 3D phase field model of grain growth using FEM

DOE PAGES

Permann, Cody J.; Tonks, Michael R.; Fromm, Bradley; ...

2016-01-14

Phase field modeling (PFM) is a well-known technique for simulating microstructural evolution. To model grain growth using PFM, typically each grain is assigned a unique non-conserved order parameter and each order parameter field is evolved in time. Traditional approaches using a one-to-one mapping of grains to order parameters present a challenge when modeling large numbers of grains due to the computational expense of using many order parameters. This problem is exacerbated when using an implicit finite element method (FEM), as the global matrix size is proportional to the number of order parameters. While previous work has developed methods to reducemore » the number of required variables and thus computational complexity and run time, none of the existing approaches can be applied for an implicit FEM implementation of PFM. Here, we present a modular, dynamic, scalable reassignment algorithm suitable for use in such a system. Polycrystal modeling with grain growth and stress require careful tracking of each grain’s position and orientation which is lost when using a reduced order parameter set. In conclusion, the method presented in this paper maintains a unique ID for each grain even after reassignment, to allow the PFM to be tightly coupled to calculations of the stress throughout the polycrystal. Implementation details and comparative results of our approach are presented.« less

Two-phase nc-TiN/a-(C,CN{sub x}) nanocomposite films: A HRTEM and MC simulation study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, J.; Lu, Y. H.; Hu, X. J.

2013-06-18

The grain growth in two-phase nanocomposite Ti-C{sub x}-N{sub y} thin films grown by reactive close-field unbalanced magnetron sputtering in an Ar-N{sub 2} gas mixture with microstructures comprising of nanocrystalline (nc-) Ti(N,C) phase surrounded by amorphous (a-) (C,CN{sub x}) phase was investigated by a combination of high-resolution transmission electron microscopy (HRTEM) and Monte Carlo (MC) simulations. The HRTEM results revealed that amorphous-free solid solution Ti(C,N) thin films exhibited polycrystallites with different sizes, orientations and irregular shapes. The grain size varied in the range between several nanometers and several decade nanometers. Further increase of C content (up to {approx}19 at.% C) mademore » the amorphous phase wet nanocrystallites, which strongly hindered the growth of nanocrystallites. As a result, more regular Ti(C,N) nanocrystallites with an average size of {approx}5 nm were found to be separated by {approx}0.5-nm amorphous phases. When C content was further increased (up to {approx}48 at.% in this study), thicker amorphous matrices were produced and followed by the formation of smaller sized grains with lognormal distribution. Our MC analysis indicated that with increasing amorphous volume fraction (i.e. increasing C content), the transformation from nc/nc grain boundary (GB)-curvature-driven growth to a/nc GB-curvature-driven growth is directly responsible for the observed grain growth from great inhomogeneity to homogeneity process.« less

Evidence for Cu2-xSe platelets at grain boundaries and within grains in Cu(In,Ga)Se2 thin films

NASA Astrophysics Data System (ADS)

Simsek Sanli, E.; Ramasse, Q. M.; Mainz, R.; Weber, A.; Abou-Ras, D.; Sigle, W.; van Aken, P. A.

2017-07-01

Cu(In,Ga)Se2 (CIGS)-based solar cells reach high power-conversion efficiencies of above 22%. In this work, a three-stage co-evaporation method was used for their fabrication. During the growth stages, the stoichiometry of the absorbers changes from Cu-poor ([Cu]/([In] + [Ga]) < 1) to Cu-rich ([Cu]/([In] + [Ga]) > 1) and finally becomes Cu-poor again when the growth process is completed. It is known that, according to the Cu-In-Ga-Se phase diagram, a Cu-rich growth leads to the presence of Cu2-xSe (x = 0-0.25), which is assumed to assist in recrystallization, grain growth, and defect annihilation in the CIGS layer. So far, Cu2-xSe precipitates with spatial extensions on the order of 10-100 nm have been detected only in Cu-rich CIGS layers. In the present work, we report Cu2-xSe platelets with widths of only a few atomic planes at grain boundaries and as inclusions within grains in a polycrystalline, Cu-poor CIGS layer, as evidenced by high-resolution scanning transmission electron microscopy (STEM). The chemistry of the Cu-Se secondary phase was analyzed by electron energy-loss spectroscopy, and STEM image simulation confirmed the identification of the detected phase. These results represent additional experimental evidence for the proposed topotactical growth model for Cu-Se-assisted CIGS thin-film formation under Cu-rich conditions.

Effect of TiO2 Addition on Grain Growth, Anodic Bubble Evolution and Anodic Overvoltage of NiFe2O4-Based Composite Inert Anodes

NASA Astrophysics Data System (ADS)

Wang, Bin; Du, Jinjing; Liu, Yihan; Fang, Zhao; Hu, Ping

2017-11-01

A two-step powder compaction and sintering process was employed to fabricate TiO2-doped NiFe2O4 ceramic-based inert anodes. Grain growth during isothermal sintering was analyzed using Brook grain growth model. The bubble behavior of NiFe2O4 ceramic-based inert anodes was investigated in a two-compartment see-through quartz cell for aluminum electrolysis process. Anodic overvoltage and potential decay curves of the inert anodes were measured by using the steady state and current interruption technique. The results showed that the kinetic index of grain growth decreased with an increase in temperature. The average activation energy of grain growth for 1.0 wt.% TiO2-doped NiFe2O4 ceramic samples with a sintering temperature range from 1373 to 1673 K dropped from 675.30 to 183.47 kJ/mol. The diameter size of bubbles before releasing from the bottom surface of the anodes was reduced with increasing the current density, and the larger average releasing bubble size for carbon anode at the same current density could be obtained, which was compared to the NiFe2O4 inert anodes. Besides, the cell voltage of carbon anodes fluctuated much more violently under the same experimental conditions. After adding small amount of TiO2, a minor reduction in anodic overvoltage of NiFe2O4-based anodes can be observed.

Microstructural Indicators Of Convection In Sills And Dykes

NASA Astrophysics Data System (ADS)

Holness, M. B.; Neufeld, J. A.; Gilbert, A. J.; Macdonald, R.

2016-12-01

The question of whether or not convection occurs in crustal magma chambers is a vexed one, with some advocating vigorous convection while others argue that convection is weak and short-lived. We argue that microstructural analysis is key to determining whether crystallization took place in solidification fronts or whether crystals grew suspended in a convecting magma before settling. The 168m, composite, Shiant Isles Main Sill is dominated by a 140m unit, of which the lower 45m contains olivine phenocrysts. The phenocrysts first fine upwards, then coarsen upwards. The coarsening-upwards sequence contains clustered olivines. Both the extent of sintering and average cluster size increase upwards. The coarsening-upwards sequence is mirrored at the roof. The fining-upwards sequence formed by rapid settling of incoming cargo crystals, while the coarsening-upwards sequence represents post-emplacement growth and clustering of grains suspended in a convecting magma. Convection is also recorded by plagioclase grain shape. Well-facetted and compact plagioclase grains are platy in rapidly-cooled rocks and blocky in slowly-cooled rocks. Plagioclase grain shape varies smoothly across mafic sills, consistent with growth in solidification fronts. In contrast, grain shape is invariant across mafic dykes, consistent with growth as individual grains and clusters suspended in a convecting magma. Convection in sills occurs when the critical Rayleigh number is exceeded, but cooling at vertical walls always results in convective instabilities. That the Shiant Isles Main Sill records prolonged and vigorous convection, while other sills of comparable thickness record grain growth predominantly in solidification fronts, is most likely due to the composite nature of the Shiant. The 140m unit is underlain by 23m of picrite which intruded shortly before - the strongly asymmetric cooling and absence of a cold, stagnant basal thermal boundary layer make convection throughout the sill more likely.

Modeling of the Coupling of Microstructure and Macrosegregation in a Direct Chill Cast Al-Cu Billet

NASA Astrophysics Data System (ADS)

Heyvaert, Laurent; Bedel, Marie; Založnik, Miha; Combeau, Hervé

2017-10-01

The macroscopic multiphase flow and the growth of the solidification microstructures in the mushy zone of a direct chill (DC) casting are closely coupled. These couplings are the key to the understanding of the formation of the macrosegregation and of the non-uniform microstructure of the casting. In the present paper we use a multiphase and multiscale model to provide a fully coupled picture of the links between macrosegregation and microstructure in a DC cast billet. The model describes nucleation from inoculant particles and growth of dendritic and globular equiaxed crystal grains, fully coupled with macroscopic transport phenomena: fluid flow induced by natural convection and solidification shrinkage, heat, mass, and solute mass transport, motion of free-floating equiaxed grains, and of grain refiner particles. We compare our simulations to experiments on grain-refined and non-grain-refined industrial size billets from literature. We show that a transition between dendritic and globular grain morphology triggered by the grain refinement is the key to the explanation of the differences between the macrosegregation patterns in the two billets. We further show that the grain size and morphology are strongly affected by the macroscopic transport of free-floating equiaxed grains and of grain refiner particles.

The water kefir grain inoculum determines the characteristics of the resulting water kefir fermentation process.

PubMed

Laureys, D; De Vuyst, L

2017-03-01

To investigate the influence of the water kefir grain inoculum on the characteristics of the water kefir fermentation process. Three water kefir fermentation processes were started with different water kefir grain inocula and followed as a function of time regarding microbial species diversity, community dynamics, substrate consumption profile and metabolite production course. The inoculum determined the water kefir grain growth, the viable counts on the grains, the time until total carbohydrate exhaustion, the final metabolite concentrations and the microbial species diversity. There were always 2-10 lactic acid bacterial cells for every yeast cell and the majority of these micro-organisms was always present on the grains. Lactobacillus paracasei, Lactobacillus hilgardii, Lactobacillus nagelii and Saccharomyces cerevisiae were always present and may be the key micro-organisms during water kefir fermentation. Low water kefir grain growth was associated with small grains with high viable counts of micro-organisms, fast fermentation and low pH values, and was not caused by the absence of exopolysaccharide-producing lactic acid bacteria. The water kefir grain inoculum influences the microbial species diversity and characteristics of the fermentation process. A select group of key micro-organisms was always present during fermentation. This study allows a rational selection of a water kefir grain inoculum. © 2016 The Society for Applied Microbiology.

The origin of pallasites. A combined experimental and numerical approach.

NASA Astrophysics Data System (ADS)

Golabek, G.; Solferino, G. F. D.

2017-12-01

Pallasites are simple stony-iron meteorites made of olivine, FeNi, FeS +/- pyroxene. The presence of olivine as well-rounded grains or highly angular fragments, and occasionally both types (mixed-type pallasites) combined with the dunite-like mineralogy make is difficult to define a robust scenario for pallasite genesis. It has been suggested that mixing of Fe-Ni-S and olivine was caused by a non-destructive collision among planetesimals. Yet, this hypothesis needs to be tested and hitherto no attempt to reproduce the simultaneous presence of olivine, solid Fe(Ni) and molten FeS has been done. In this study we performed experiments with olivine plus partially molten Fe(Ni)-S, a composition most similar to those of pallasite meteorites. The main goal was to define the grain growth rate of olivine surrounded by a matrix of Fe(Ni) and FeS melt. Additionally, a 2D finite-difference numerical model was used to define a realistic scenario (e.g., time of impact, depth of intrusion of the Fe-Ni-S) for the formation of rounded- and mixed-type pallasites for the first time. Olivine grain growth rate in partially molten Fe-S follows: d n - d0n = k0 exp(-Ea/RT) t, where, d is the grain size at time t, d0 is the starting grain size, n = 3.70 (61) the growth exponent, k0 = 3.20 μmns-1 a characteristic constant, Ea = 101 (78) kJ/mol the activation energy for a specific growth process, R the gas constant, and T the absolute temperature. This is a substantially slower grain growth than in the case of olivine surrounded by FeS melt (i.e., n = 2.42), but significantly faster than for olivine+FeNi or olivine+Ni (n > 4 or 5). We concluded that the olivine grain growth limiting factor is the coarsening rate of solid Fe(Ni), which is in agreement with previous studies. Yet, we proved that the presence of FeS melt in contact with Fe(Ni) catalyzes the ripening of the latter. The overarching conclusion of this study is that all main phases known to be present during annealing of a given silicate mineral must be reproduced experimentally in order to accurately define its growth rate, with simplified systems not suited for the scope.

Growth failure and nutrition considerations in chronic childhood wasting diseases.

PubMed

Kyle, Ursula G; Shekerdemian, Lara S; Coss-Bu, Jorge A

2015-04-01

Growth failure is a common problem in many children with chronic diseases. This article is an overview of the most common causes of growth failure/growth retardation that affect children with a number of chronic diseases. We also briefly review the nutrition considerations and treatment goals. Growth failure is multifactorial in children with chronic conditions, including patients with cystic fibrosis, chronic kidney disease, chronic liver disease, congenital heart disease, human immunodeficiency virus, inflammatory bowel disease, short bowel syndrome, and muscular dystrophies. Important contributory factors to growth failure include increased energy needs, increased energy loss, malabsorption, decreased energy intake, anorexia, pain, vomiting, intestinal obstruction, and inflammatory cytokines. Various metabolic and pathologic abnormalities that are characteristic of chronic diseases further lead to significant malnutrition and growth failure. In addition to treating disease-specific abnormalities, treatment should address the energy and protein deficits, including vitamin and mineral supplements to correct deficiencies, correct metabolic and endocrinologic abnormalities, and include long-term monitoring of weight and growth. Individualized, age-appropriate nutrition intervention will minimize the malnutrition and growth failure seen in children with chronic diseases. © 2014 American Society for Parenteral and Enteral Nutrition.

Coupled Finite Element ? Potts Model Simulations of Grain Growth in Copper Interconnects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Radhakrishnan, Balasubramaniam; Gorti, Sarma B

The paper addresses grain growth in copper interconnects in the presence of thermal expansion mismatch stresses. The evolution of grain structure and texture in copper in the simultaneous presence of two driving forces, curvature and elastic stored energy difference, is modeled by using a hybrid Potts model simulation approach. The elastic stored energy is calculated by using the commercial finite element code ABAQUS, where the effect of elastic anisotropy on the thermal mismatch stress and strain distribution within a polycrystalline grain structure is modeled through a user material (UMAT) interface. Parametric studies on the effect of trench width and themore » height of the overburden were carried out. The results show that the grain structure and texture evolution are significantly altered by the presence of elastic strain energy.« less

A Cosserat crystal plasticity and phase field theory for grain boundary migration

NASA Astrophysics Data System (ADS)

Ask, Anna; Forest, Samuel; Appolaire, Benoit; Ammar, Kais; Salman, Oguz Umut

2018-06-01

The microstructure evolution due to thermomechanical treatment of metals can largely be described by viscoplastic deformation, nucleation and grain growth. These processes take place over different length and time scales which present significant challenges when formulating simulation models. In particular, no overall unified field framework exists to model concurrent viscoplastic deformation and recrystallization and grain growth in metal polycrystals. In this work a thermodynamically consistent diffuse interface framework incorporating crystal viscoplasticity and grain boundary migration is elaborated. The Kobayashi-Warren-Carter (KWC) phase field model is extended to incorporate the full mechanical coupling with material and lattice rotations and evolution of dislocation densities. The Cosserat crystal plasticity theory is shown to be the appropriate framework to formulate the coupling between phase field and mechanics with proper distinction between bulk and grain boundary behaviour.

The mechanism of grain growth in ceramics

NASA Technical Reports Server (NTRS)

Kapadia, C. M.; Leipold, M. H.

1972-01-01

The theory of grain boundary migration as a thermally activated process is reviewed, the basic mechanisms in ceramics being the same as in metals. However, porosity and non-stochiometry in ceramic materials give an added dimension to the theory and make quantitative treatment of real systems rather complex. Grain growth is a result of several simultaneous (and sometimes interacting) processes; these are most easily discussed separately, but the overall rate depends on their interaction. Sufficient insight into the nature of rate controlling diffusion mechanisms is necessary before a qualitative understanding of boundary mobility can be developed.

Nucleation and growth of WSe2: enabling large grain transition metal dichalcogenides

NASA Astrophysics Data System (ADS)

Yue, Ruoyu; Nie, Yifan; Walsh, Lee A.; Addou, Rafik; Liang, Chaoping; Lu, Ning; Barton, Adam T.; Zhu, Hui; Che, Zifan; Barrera, Diego; Cheng, Lanxia; Cha, Pil-Ryung; Chabal, Yves J.; Hsu, Julia W. P.; Kim, Jiyoung; Kim, Moon J.; Colombo, Luigi; Wallace, Robert M.; Cho, Kyeongjae; Hinkle, Christopher L.

2017-12-01

The limited grain size (<200 nm) for transition metal dichalcogenides (TMDs) grown by molecular beam epitaxy (MBE) reported in the literature thus far is unsuitable for high-performance device applications. In this work, the fundamental nucleation and growth behavior of WSe2 is investigated through a detailed experimental design combined with on-lattice, diffusion-based first principles kinetic modeling to enable large area TMD growth. A three-stage adsorption-diffusion-attachment mechanism is identified and the adatom stage is revealed to play a significant role in the nucleation behavior. To limit the nucleation density and promote 2D layered growth, it is necessary to have a low metal flux in conjunction with an elevated substrate temperature. At the same time, providing a Se-rich environment further limits the formation of W-rich nuclei which suppresses vertical growth and promotes 2D growth. The fundamental understanding gained through this investigation has enabled an increase of over one order of magnitude in grain size for WSe2 thus far, and provides valuable insight into improving the growth of other TMD compounds by MBE and other growth techniques such as chemical vapor deposition (CVD).

Creep crack growth by grain boundary cavitation under monotonic and cyclic loading

NASA Astrophysics Data System (ADS)

Wen, Jian-Feng; Srivastava, Ankit; Benzerga, Amine; Tu, Shan-Tung; Needleman, Alan

2017-11-01

Plane strain finite deformation finite element calculations of mode I crack growth under small scale creep conditions are carried out. Attention is confined to isothermal conditions and two time histories of the applied stress intensity factor: (i) a monononic increase to a plateau value subsequently held fixed; and (ii) a cyclic time variation. The crack growth calculations are based on a micromechanics constitutive relation that couples creep deformation and damage due to grain boundary cavitation. Grain boundary cavitation, with cavity growth due to both creep and diffusion, is taken as the sole failure mechanism contributing to crack growth. The influence on the crack growth rate of loading history parameters, such as the magnitude of the applied stress intensity factor, the ratio of the applied minimum to maximum stress intensity factors, the loading rate, the hold time and the cyclic loading frequency, are explored. The crack growth rate under cyclic loading conditions is found to be greater than under monotonic creep loading with the plateau applied stress intensity factor equal to its maximum value under cyclic loading conditions. Several features of the crack growth behavior observed in creep-fatigue tests naturally emerge, for example, a Paris law type relation is obtained for cyclic loading.

Grain Nucleation and Growth in Deformed NiTi Shape Memory Alloys: An In Situ TEM Study

NASA Astrophysics Data System (ADS)

Burow, J.; Frenzel, J.; Somsen, C.; Prokofiev, E.; Valiev, R.; Eggeler, G.

2017-12-01

The present study investigates the evolution of nanocrystalline (NC) and ultrafine-grained (UFG) microstructures in plastically deformed NiTi. Two deformed NiTi alloys were subjected to in situ annealing in a transmission electron microscope (TEM) at 400 and 550 °C: an amorphous material state produced by high-pressure torsion (HPT) and a mostly martensitic partly amorphous alloy produced by wire drawing. In situ annealing experiments were performed to characterize the microstructural evolution from the initial nonequilibrium states toward energetically more favorable microstructures. In general, the formation and evolution of nanocrystalline microstructures are governed by the nucleation of new grains and their subsequent growth. Austenite nuclei which form in HPT and wire-drawn microstructures have sizes close to 10 nm. Grain coarsening occurs in a sporadic, nonuniform manner and depends on the physical and chemical features of the local environment. The mobility of grain boundaries in NiTi is governed by the local interaction of each grain with its microstructural environment. Nanograin growth in thin TEM foils seems to follow similar kinetic laws to those in bulk microstructures. The present study demonstrates the strength of in situ TEM analysis and also highlights aspects which need to be considered when interpreting the results.

Application of the Prunus spp. Cyanide Seed Defense System onto Wheat: Reduced Insect Feeding and Field Growth Tests.

PubMed

Mora, Carlos A; Halter, Jonas G; Adler, Cornel; Hund, Andreas; Anders, Heidrun; Yu, Kang; Stark, Wendelin J

2016-05-11

Many crops are ill-protected against insect pests during storage. To protect cereal grains from herbivores during storage, pesticides are often applied. While pesticides have an undoubtable functionality, increasing concerns are arising about their application. In the present study, we investigated a bioinspired cyanogenic grain coating with amygdalin as cyanogenic precursor mimicking the feeding-triggered release of hydrogen cyanide (HCN) found for example in bitter almonds. The multilayer coating consisted of biodegradable polylactic acid with individual layers containing amygdalin or β-glucosidase which is capable of degrading amygdalin to HCN. This reaction occurred only when the layers were ruptured, e.g., by a herbivore attack. Upon feeding coated cyanogenic wheat grains to Tenebrio molitor (mealworm beetle), Rhizopertha dominica (lesser grain borer), and Plodia interpunctella (Indianmeal moth), their reproduction as well as consumption rate were significantly reduced, whereas germination ability increased compared to noncoated grains. In field experiments, we observed an initial growth delay compared to uncoated grains which became negligible at later growth stages. The here shown strategy to artificially apply a naturally occurring defense mechanisms could be expanded to other crops than wheat and has the potential to replace certain pesticides with the benefit of complete biodegradability and increased safety during storage.

Morphologies of tungsten nanotendrils grown under helium exposure.

PubMed

Wang, Kun; Doerner, R P; Baldwin, M J; Meyer, F W; Bannister, M E; Darbal, Amith; Stroud, Robert; Parish, Chad M

2017-02-14

Nanotendril "fuzz" will grow under He bombardment under tokamak-relevant conditions on tungsten plasma-facing materials in a magnetic fusion energy device. We have grown tungsten nanotendrils at low (50 eV) and high (12 keV) He bombardment energy, in the range 900-1000 °C, and characterized them using electron microscopy. Low energy tendrils are finer (~22 nm diameter) than high-energy tendrils (~176 nm diameter), and low-energy tendrils have a smoother surface than high-energy tendrils. Cavities were omnipresent and typically ~5-10 nm in size. Oxygen was present at tendril surfaces, but tendrils were all BCC tungsten metal. Electron diffraction measured tendril growth axes and grain boundary angle/axis pairs; no preferential growth axes or angle/axis pairs were observed, and low-energy fuzz grain boundaries tended to be high angle; high energy tendril grain boundaries were not observed. We speculate that the strong tendency to high-angle grain boundaries in the low-energy tendrils implies that as the tendrils twist or bend, strain must accumulate until nucleation of a grain boundary is favorable compared to further lattice rotation. The high-energy tendrils consisted of very large (>100 nm) grains compared to the tendril size, so the nature of the high energy irradiation must enable faster growth with less lattice rotation.

Dielectric properties of grain-grainboundary binary system

NASA Astrophysics Data System (ADS)

Cheng, Peng-Fei; Li, Sheng-Tao; Wang, Hui

2014-09-01

Dielectric properties of grain-grainboundary binary system are analyzed theoretically and compared with unary system and classical Maxwell-Wagner (MW) polarization in binary system. It is found that MW polarization appears at higher frequency compared with intrinsic polarization for grain-grainboundary binary system, which is abnormal compared with classical dielectric theory. This dielectric anomaly is premised on the existence of electronic relaxation at grainboundary. The origin of giant dielectric constant of CaCu3Ti4O12 (CCTO) ceramics is also investigated on the basis of the theoretical results. It is proposed that low frequency relaxation originates from electronic relaxation of oxygen vacancy at depletion layer, while high frequency relaxation comes from MW polarization. The results of this paper offer a quantitative identification of MW polarization from intrinsic polarization at grainboundary and a judgment of the mechanism and location of a certain polarization in grain-grainboundary binary system.

Growth performance and total tract nutrient digestion for Holstein heifers limit-fed diets high in distillers grains with different forage particle sizes

USDA-ARS?s Scientific Manuscript database

This study evaluated dairy heifer growth performance and total tract nutrient digestion when fed diets high in dried distillers grains with solubles (DDGS) with different forage particle size. An 8-wk randomized complete block design study was conducted utilizing twenty-two Holstein heifers (123 ±...

Experimental studies of nucleation and growth processes related to the formation of presolar grains

NASA Technical Reports Server (NTRS)

Berg, Otto E.

1992-01-01

An understanding was sought for the mechanisms of nucleation of refractory materials, and the relative importance of factors controlling the rate of cluster formation and growth for astrophysically important species. The structure and composition of the condensates is being studied, with the goal of characterizing the grains present in the primitive solar nebula.

Preparation and Characterization of RF Sputtered BARIUM(2) SILICON(2) Titanium OXYGEN(8) Thin Films

NASA Astrophysics Data System (ADS)

Li, Yi.

Thin films of barium titanium silicate ( Ba_2Si_2TiO_8) are grown on crystalline (100) Si at substrate temperatures raging from 750 to 955^circC by the radio-frequency triode sputtering technique. The chemical composition, microstructure, physical properties, and growth conditions of the deposited films are investigated by dc and high-frequency dielectric measurements, wavelength dispersive and energy dispersive x-ray spectrometries, x-ray diffraction spectrometry, and optical and scanning electron microscopies. The results of the x-ray diffraction analysis show that the Ba_2Si_2TiO _8 films deposited at the optimum condition of substrate temperature of 845^circ C, 4 cm source-substance distance, 50 W rf power, and 1.2 times 10^ {-3} torr pressure of Ar, are highly c -axis oriented. The as-deposited films are smooth, glossy, polycrystalline films, exhibiting a bulk resistivity range of 10^6 Omegacdotcm, and an isotropic surface resistivity of 1.5 times 10^3 Omegacdot cm. The relative dielectric constant is 0.05, and the dielectric loss is lower than 1.0, in the frequency band 9 ~ 1000 MHz. The high-frequency impedance of BST films, which is typical for piezoelectric materials, gives a minimum impedance frequency of 9.0 MHz and a series resonant frequency of 9.5 MHz. Optical and SEM observations show that the film texture is dependent on the substrate conditions. The non-liquid-like grain coalescence of the Ba_2Si_2TiO _8 grains is characteristic of a strong film -substrate interaction. The grain growth kinetics obtained from "short-time" sputtering gives an initial lateral grain growth rate of 770 nm/min at 845^circ C, which decreases with the grain size. The initial film growth rate in the direction of thickness, measured from SEM micrographs, is 1.95 nm/min, and decreases with sputtering time. The activation free energy for grain growth is 359 +/- 30 KJ/mol for the initial stage, decreasing to 148 +/- 20 KJ/mol for the final stage. The variation of the grain growth rate and the activation energy with grain size is the result of a combined nucleation and growth mechanism in the initial stage of the film growth, and a coalescence -dominated growth mechanism at longer sputtering time and at higher temperature. Film orientation is sensitive to the supersaturation adjacent to the film surface, which depends on the source-substrate distance and substrate temperature. The effect of the substrate temperature on the orientation of the film is investigated over a wide temperature range using (100) and (111) Si substrates. Several orientations for the BST films, including an amorphous state, are obtained with increasing substrate temperature. This is discussed in relation to the atomic plane density and the energetics for the deposition process.

[Correlation between growth rate of corpus callosum and neuromotor development in preterm infants].

PubMed

Liu, Rui-Ke; Sun, Jie; Hu, Li-Yan; Liu, Fang

2015-08-01

To investigate the growth rate of corpus callosum by cranial ultrasound in very low birth weight preterm infants and to provide a reference for early evaluation and improvement of brain development. A total of 120 preterm infants under 33 weeks' gestation were recruited and divided into 26-29(+6) weeks group (n=64) and 30-32(+6) weeks group (n=56) according to the gestational age. The growth rate of corpus callosum was compared between the two groups. The correlation between the corpus callosum length and the cerebellar vermis length and the relationship of the growth rate of corpus callosum with clinical factors and the neuromotor development were analyzed. The growth rate of corpus callosum in preterm infants declined since 2 weeks after birth. Compared with the 30-32(+6) weeks group, the 26-29(+6) weeks group had a significantly lower growth rate of corpus callosum at 3-4 weeks after birth, at 5-6 weeks after birth, and from 7 weeks after birth to 40 weeks of corrected gestational age. There was a positive linear correlation between the corpus callosum length and the cerebellar vermis length. Small-for-gestational age infants had a low growth rate of corpus callosum at 2 weeks after birth. The 12 preterm infants with severe abnormal intellectual development had a lower growth rate of corpus callosum compared with the 108 preterm infants with non-severe abnormal intellectual development at 3-6 weeks after birth. The 5 preterm infants with severe abnormal motor development had a significantly lower growth rate of corpus callosum compared with the 115 preterm infants with non-severe abnormal motor development at 3-6 weeks after birth. The decline of growth rate of corpus callosum in preterm infants at 2-6 weeks after birth can increase the risk of severe abnormal neuromotor development.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Edwards, Danny J.; Ermi, Ruby M.; Schemer-Kohrn, Alan L.

Twelve AFIP in-process foil samples, fabricated by either Y-12 or LANL, were shipped from LANL to PNNL for potential characterization using optical and scanning electron microscopy techniques. Of these twelve, nine different conditions were examined to one degree or another using both techniques. For this report a complete description of the results are provided for one archive foil from each source of material, and one unirradiated piece of a foil of each source that was irradiated in the Advanced Test Reactor. Additional data from two other LANL conditions are summarized in very brief form in an appendix. The characterization revealedmore » that all four characterized conditions contained a cold worked microstructure to different degrees. The Y-12 foils exhibited a higher degree of cold working compared to the LANL foils, as evidenced by the highly elongated and obscure U-Mo grain structure present in each foil. The longitudinal orientations for both of the Y-12 foils possesses a highly laminar appearance with such a distorted grain structure that it was very difficult to even offer a range of grain sizes. The U-Mo grain structure of the LANL foils, by comparison, consisted of a more easily discernible grain structure with a mix of equiaxed and elongated grains. Both materials have an inhomogenous grain structure in that all of the characterized foils possess abnormally coarse grains.« less

New MR imaging assessment tool to define brain abnormalities in very preterm infants at term.

PubMed

Kidokoro, H; Neil, J J; Inder, T E

2013-01-01

WM injury is the dominant form of injury in preterm infants. However, other cerebral structures, including the deep gray matter and the cerebellum, can also be affected by injury and/or impaired growth. Current MR imaging injury assessment scales are subjective and are challenging to apply. Thus, we developed a new assessment tool and applied it to MR imaging studies obtained from very preterm infants at term age. MR imaging scans from 97 very preterm infants (< 30 weeks' gestation) and 22 healthy term-born infants were evaluated retrospectively. The severity of brain injury (defined by signal abnormalities) and impaired brain growth (defined with biometrics) was scored in the WM, cortical gray matter, deep gray matter, and cerebellum. Perinatal variables for clinical risks were collected. In very preterm infants, brain injury was observed in the WM (n=23), deep GM (n=5), and cerebellum (n=23). Combining measures of injury and impaired growth showed moderate to severe abnormalities most commonly in the WM (n=38) and cerebellum (n=32) but still notable in the cortical gray matter (n=16) and deep gray matter (n=11). WM signal abnormalities were associated with a reduced deep gray matter area but not with cerebellar abnormality. Intraventricular and/or parenchymal hemorrhage was associated with cerebellar signal abnormality and volume reduction. Multiple clinical risk factors, including prolonged intubation, prolonged parenteral nutrition, postnatal corticosteroid use, and postnatal sepsis, were associated with increased global abnormality on MR imaging. Very preterm infants demonstrate a high prevalence of injury and growth impairment in both the WM and gray matter. This MR imaging scoring system provides a more comprehensive and objective classification of the nature and extent of abnormalities than existing measures.

Prediction of the Grain-Microstructure Evolution Within a Friction Stir Welding (FSW) Joint via the Use of the Monte Carlo Simulation Method

NASA Astrophysics Data System (ADS)

Grujicic, M.; Ramaswami, S.; Snipes, J. S.; Avuthu, V.; Galgalikar, R.; Zhang, Z.

2015-09-01

A thermo-mechanical finite element analysis of the friction stir welding (FSW) process is carried out and the evolution of the material state (e.g., temperature, the extent of plastic deformation, etc.) monitored. Subsequently, the finite-element results are used as input to a Monte-Carlo simulation algorithm in order to predict the evolution of the grain microstructure within different weld zones, during the FSW process and the subsequent cooling of the material within the weld to room temperature. To help delineate different weld zones, (a) temperature and deformation fields during the welding process, and during the subsequent cooling, are monitored; and (b) competition between the grain growth (driven by the reduction in the total grain-boundary surface area) and dynamic-recrystallization grain refinement (driven by the replacement of highly deformed material with an effectively "dislocation-free" material) is simulated. The results obtained clearly revealed that different weld zones form as a result of different outcomes of the competition between the grain growth and grain refinement processes.

Constitutive relations for determining the critical conditions for dynamic recrystallization behavior

NASA Astrophysics Data System (ADS)

Choe, J. I.

2016-04-01

A series mathematical model has been developed for the prediction of flow stress and microstructure evolution during the hot deformation of metals such as copper or austenitic steels with low stacking fault energies, involving features of both diffusional flow and dislocation motion. As the strain rate increases, multiple peaks on the stress-strain curve decrease. At a high strain rate, the stress rises to a single peak, while dynamic recrystallization causes an oscillatory behavior. At a low strain rate (when there is sufficient time for the recrystallizing grains to grow before they become saturated with high dislocation density with an increase in strain rate), the difference in stored stress between recrystallizing and old grains diminishes, resulting in reduced driving force for grain growth and rendering smaller grains in the alloy. The final average grain size at the steady stage (large strain) increases with a decrease in the strain rate. During large strain deformation, grain size reduction accompanying dislocation creep might be balanced by the grain growth at the border delimiting the ranges of realization (field boundary) of the dislocation-creep and diffusion-creep mechanisms.

Atomistic simulation of Al-graphene thin film growth on polycrystalline Al substrate

NASA Astrophysics Data System (ADS)

Zhang, Lan; Zhu, Yongchao; Li, Na; Rong, Yan; Xia, Huimin; Ma, Huizhong

2018-03-01

The growth of Al-Graphene composite coatings on polycrystalline Al substrate was investigated by using classical molecular dynamics (MD) simulations. Unlike the diffusion behaviors on single crystal surface, most of adatoms were easily bound by the steps on polycrystalline Al surface, owing to the local accelerated energy. Both Ehrlich-Schwoebel (ES) barriers and the steering effect backed up the volmer-weber growth mode, which was consistent with the dynamic growth process observed in the deposit. The morphology of composite coatings was significantly affected by graphene flakes. Enrichment of graphene flakes gave rise to an increase of the local thickness, and graphene flakes only existed in Al grain boundaries. The size of Al grains in the composite coating visibly decreased when compared with that in the pure Al coating. This grain refinement and the mechanical property can be reinforced by the increase of graphene flakes.

Capturing the Complexity of Additively Manufactured Microstructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Livescu, Veronica; Bronkhorst, Curt Allan; Vander Wiel, Scott Alan

2016-05-12

The underlying mechanisms and kinetics controlling damage nucleation and growth as a function of material microstructure and loading paths are discussed. These experiments indicate that structural features such as grain boundaries, grain size distribution, grain morphology crystallographic texture are all factors that influence mechanical behavior.

[Effects of PASP-KT-NAA on the grain-filling of maize in different accumulated temperature zones of Hilongjiang Province, Norheast China].

PubMed

Xu, Tian-Jun; Dong, Zhi-Qiang; Gao, Jiao; Chen, Chuan-Xiao; Jiao, Liu; Xie, Zhen-Xing

2013-02-01

Taking the two maize varieties Zhengdan 958 and Fengdan 3 grown on the three accumulated temperature zones (I, II and III) in Heilongjiang Provice as test materials, a field investigation was made in 2010 and 2011 to study the effects of PASP-KT-NAA (PKN), a compound of exogenous plant growth regulators, on the grain filling and yield of the varieties under different environmental temperatures. From zone I to III, the air temperature at the grain filling stage had a decreasing trend, with the average minimum temperature being 12.16, 11.40, and 9.56, respectively. The effective accumulated temperature at the mid-ate amt sae stage of grain filling was too low to be sufficient for grain filling, which severely affected the grain filling process. Applying N, P and K promoted the dry matter accumulation of maize grain and the grain filling rate in the three zones, delayed the peak time (Tmax) of the grain filling rate of Fengdan 3 but advanced that of Zhengdan 958, promoted the growth capacity at peak time of grain filling rate and the maximum grain filling rate of the two varieties, and shortened their active grain filling period. Applying N, P, and K increased the grain yield of the two varieties in the three zones obviously, and, as compared with those in zones I and II , the grain yields of Zhengdan 958 and Fengdan 3 in zone III were increased by 8.2% and 5.1% , and 3.4% and 0.8% , respectively. Therefore, applying N, P and K could help maize utilizing the limited accumulation temperature, improve the grain filling rate, decrease the grain water content, and ultimately, increase the maize yield.

Effect of thermal treatment on the bio-corrosion and mechanical properties of ultrafine-grained ZK60 magnesium alloy.

PubMed

Choi, H Y; Kim, W J

2015-11-01

The combination of solid solution heat treatments and severe plastic deformation by high-ratio differential speed rolling (HRDSR) resulted in the formation of an ultrafine-grained microstructure with high thermal stability in a Mg-5Zn-0.5Zr (ZK60) alloy. When the precipitate particle distribution was uniform in the matrix, the internal stresses and dislocation density could be effectively removed without significant grain growth during the annealing treatment (after HRDSR), leading to enhancement of corrosion resistance. When the particle distribution was non-uniform, rapid grain growth occurred in local areas where the particle density was low during annealing, leading to development of a bimodal grain size distribution. The bimodal grain size distribution accelerated corrosion by forming a galvanic corrosion couple between the fine-grained and coarse-grained regions. The HRDSR-processed ZK60 alloy with high thermal stability exhibited high corrosion resistance, high strength and high ductility, and excellent superplasticity, which allow the fabrication of biodegradable magnesium devices with complicated designs that have a high mechanical integrity throughout the service life in the human body. Copyright © 2015 Elsevier Ltd. All rights reserved.

Synthesis of Highly Uniform and Compact Lithium Zinc Ferrite Ceramics via an Efficient Low Temperature Approach.

PubMed

Xu, Fang; Liao, Yulong; Zhang, Dainan; Zhou, Tingchuan; Li, Jie; Gan, Gongwen; Zhang, Huaiwu

2017-04-17

LiZn ferrite ceramics with high saturation magnetization (4πM s ) and low ferromagnetic resonance line widths (ΔH) represent a very critical class of material for microwave ferrite devices. Many existing approaches emphasize promotion of the grain growth (average size is 10-50 μm) of ferrite ceramics to improve the gyromagnetic properties at relatively low sintering temperatures. This paper describes a new strategy for obtaining uniform and compact LiZn ferrite ceramics (average grains size is ∼2 μm) with enhanced magnetic performance by suppressing grain growth in great detail. The LiZn ferrites with a formula of Li 0.415 Zn 0.27 Mn 0.06 Ti 0.1 Fe 2.155 O 4 were prepared by solid reaction routes with two new sintering strategies. Interestingly, results show that uniform, compact, and pure spinel ferrite ceramics were synthesized at a low temperature (∼850 °C) without obvious grain growth. We also find that a fast second sintering treatment (FSST) can further improve their gyromagnetic properties, such as higher 4πM s and lower ΔH. The two new strategies are facile and efficient for densification of LiZn ferrite ceramics via suppressing grain growth at low temperatures. The sintering strategy reported in this study also provides a referential experience for other ceramics, such as soft magnetism ferrite ceramics or dielectric ceramics.

Preferential orientation relationships in Ca{sub 2}MnO{sub 4} Ruddlesden-Popper thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lacotte, M.; David, A.; Prellier, W., E-mail: wilfrid.prellier@ensicaen.fr

2015-07-28

A high-throughput investigation of local epitaxy (called combinatorial substrate epitaxy) was carried out on Ca{sub 2}MnO{sub 4} Ruddlesden-Popper thin films of six thicknesses (from 20 to 400 nm), all deposited on isostructural polycrystalline Sr{sub 2}TiO{sub 4} substrates. Electron backscatter diffraction revealed grain-over-grain local epitaxial growth for all films, resulting in a single orientation relationship (OR) for each substrate-film grain pair. Two preferred epitaxial ORs accounted for more than 90% of all ORs on 300 different microcrystals, based on analyzing 50 grain pairs for each thickness. The unit cell over unit cell OR ([100][001]{sub film} ∥ [100][001]{sub substrate}, or OR1) accounted formore » approximately 30% of each film. The OR that accounted for 60% of each film ([100][001]{sub film} ∥ [100][010]{sub substrate}, or OR2) corresponds to a rotation from OR1 by 90° about the a-axis. OR2 is strongly favored for substrate orientations in the center of the stereographic triangle, and OR1 is observed for orientations very close to (001) or to those near the edge connecting (100) and (110). While OR1 should be lower in energy, the majority observation of OR2 implies kinetic hindrances decrease the frequency of OR1. Persistent grain over grain growth and the absence of variations of the OR frequencies with thickness implies that the growth competition is finished within the first few nm, and local epitaxy persists thereafter during growth.« less

Morphological and genetic characterization of a new cytoplasmic male sterility system (oxa CMS) in stem mustard (Brassica juncea).

PubMed

Heng, Shuangping; Liu, Sansan; Xia, Chunxiu; Tang, HongYu; Xie, Fei; Fu, Tingdong; Wan, Zhengjie

2018-01-01

KEY MESSAGE: oxa CMS is a new cytoplasmic male sterility type in Brassica juncea. oxa CMS is a cytoplasmic male sterility (CMS) line that has been widely used in the production and cultivation of stem mustard in the southwestern China. In this study, different CMS-type specific mitochondrial markers were used to confirm that oxa CMS is distinct from the pol CMS, ogu CMS, nap CMS, hau CMS, tour CMS, Moricandia arvensis CMS, orf220-type CMS, etc., that have been previously reported in Brassica crops. Pollen grains of the oxa CMS line are sterile with a self-fertility rate of almost 0% and the sterility strain rate and sterility degree of oxa CMS is 100% due to a specific flower structure and flowering habit. Scanning electron microscopy revealed that most pollen grains in mature anthers of the oxa CMS line are empty, flat and deflated. Semi-thin section further showed that the abortive stage of anther development in oxa CMS is initiated at the late uninucleate stage. Abnormally vacuolated microspores caused male sterility in the oxa CMS line. This cytological study combined with marker-assisted selection showed that oxa CMS is a novel CMS type in stem mustard (Brassica juncea). Interestingly, the abortive stage of oxa CMS is later than those in other CMS types reported in Brassica crops, and there is no negative effect on the oxa CMS line growth period. This study demonstrated that this novel oxa CMS has a unique flower structure with sterile pollen grains at the late uninucleate stage. Our results may help to uncover the mechanism of oxa CMS in Brassica juncea.

Abnormal growth kinetics of h-BN epitaxial monolayer on Ru(0001) enhanced by subsurface Ar species

NASA Astrophysics Data System (ADS)

Wei, Wei; Meng, Jie; Meng, Caixia; Ning, Yanxiao; Li, Qunxiang; Fu, Qiang; Bao, Xinhe

2018-04-01

Growth kinetics of epitaxial films often follows the diffusion-limited aggregation mechanism, which shows a "fractal-to-compact" morphological transition with increasing growth temperature or decreasing deposition flux. Here, we observe an abnormal "compact-to-fractal" morphological transition with increasing growth temperature for hexagonal boron nitride growth on the Ru(0001) surface. The unusual growth process can be explained by a reaction-limited aggregation (RLA) mechanism. Moreover, introduction of the subsurface Ar atoms has enhanced this RLA growth behavior by decreasing both reaction and diffusion barriers. Our work may shed light on the epitaxial growth of two-dimensional atomic crystals and help to control their morphology.

Significantly enhanced piezoelectricity in low-temperature sintered Aurivillius-type ceramics with ultrahigh Curie temperature of 800 °C

NASA Astrophysics Data System (ADS)

Cai, Kai; Huang, Chengcheng; Guo, Dong

2017-04-01

We report an Aurivillius-type piezoelectric ceramic (Ca1-2x (LiCe) x Bi4Ti3.99Zn0.01O15) that has an ultrahigh Curie temperature (T c) around 800 °C and a significantly enhanced piezoelectric coefficient (d 33), comparable to that of textured ceramics fabricated using the complicated templating method. Surprisingly, the highest d 33 of 26 pC/N was achieved at an unexpectedly low sintering temperature (T s) of only 920 °C (~200 °C lower than usual) despite the non-ideal density. Study of different synthesized samples indicates that a relatively low T s is crucial for suppressing Bi evaporation and abnormal grain growth, which are indispensable for high resistivity and effective poling due to decreased carrier density and restricted anisotropic conduction. Because the layered structure is sensitive to lattice defects, controlled Bi loss is considered to be crucial for maintaining structural order and spontaneous polarization. This low-T s system is very promising for practical applications due to its high piezoelectricity, low cost and high reproducibility. Contrary to our usual understanding, the results reveal that a delicate balance of density, Bi loss and grain morphology achieved by adjusting the sintering temperature is crucial for the enhancing performance in Aurivillius-type high-T c ceramics.

Early Stages of Microstructure and Texture Evolution during Beta Annealing of Ti-6Al-4V

NASA Astrophysics Data System (ADS)

Pilchak, A. L.; Sargent, G. A.; Semiatin, S. L.

2018-03-01

The early stages of microstructure evolution during annealing of Ti-6Al-4V in the beta phase field were established. For this purpose, a series of short-time heat treatments was performed using sheet samples that had a noticeable degree of alpha-phase microtexture in the as-received condition. Reconstruction of the beta-grain structure from electron-backscatter-diffraction measurements of the room-temperature alpha-phase texture revealed that microstructure evolution at short times was controlled not by general grain growth, but rather by nucleation-and-growth events analogous to discontinuous recrystallization. The nuclei comprised a small subset of beta grains that were highly misoriented relative to those comprising the principal texture component of the beta matrix. From a quantitative standpoint, the transformation kinetics were characterized by an Avrami exponent of approximately unity, thus suggestive of metadynamic recrystallization. The recrystallization process led to the weakening and eventual elimination of the initial beta texture through the growth of a population of highly misoriented grains.

Evaluation of placenta in foetal demise and foetal growth restriction.

PubMed

Ch, Ujwala; Guruvare, Shyamala; Bhat, Sudha S; Rai, Lavanya; Rao, Sugandhi

2013-11-01

The study objective was to evaluate the pathological changes of the placenta in foetal death and foetal growth restriction and to find correlation of the findings with clinical causes. Prospective study at a tertiary care hospital. Gross and histopathological examinations of the placentae were carried out in pregnancies with foetal demise (IUD) and Foetal Growth Restriction (FGR). SPSS, version 11.5. Placentae of twenty seven women with foetal demise and of equal number of women with foetal growth restriction were studied. Placental weight was less than 10(th) percentile in 61.5% women in IUD group and in 93% women in the FGR group. Gross examination of placentae showed abnormalities in 12 (44%) women of IUD group and in 16 (59%) women of FGR group. Histopathological abnormalities were observed in 74.1% women of the IUD group and in 66.7% women of FGR group. Placental histopathology correlated with clinical risk factors in 60% women of IUD group and in 40% women of FGR group. Among the women with no clinically explainable cause for IUD and FGR, 86% and 57% had placental histopathological abnormalities respectively. The histopathological abnormalities of the placenta can be used to document the clinical causes of foetal demise and growth restriction; it may explain the causes in cases of clinically unexplained foetal demise and foetal growth restriction.

Fabrication of single crystal architecture in Sb-S-I glass: Transition from dot to line

DOE PAGES

Savytskii, Dmytro; Dierolf, Volkmar; Tamura, Nobumichi; ...

2017-12-08

We have investigated the occurrence of the sometimes observed grain boundaries, as initial seed is extended to form line in laser-fabricated single-crystal architecture in glass (SCAG). In particular, for Sb 2S 3 SCAG in Sb-S-I glass as a model system, grain boundaries are formed during the transition from laser-written initial seed dot to crystal line. Such grain boundaries during the growth of Sb 2S 3 crystals occur in 16SbI 3-84Sb 2S 3glass, whereas they are absent in Sb 2S 3 glass. We correlate this difference in tendency to form multiple grains with the relative glass forming ability i.e. the dynamicsmore » of nucleation and crystal growth as determined by differential scanning calorimetry (DSC). On the basis of this understanding, methods to minimize the appearance of grain boundaries in the transition region are suggested.« less

Fabrication of single crystal architecture in Sb-S-I glass: Transition from dot to line

DOE Office of Scientific and Technical Information (OSTI.GOV)

Savytskii, Dmytro; Dierolf, Volkmar; Tamura, Nobumichi

We have investigated the occurrence of the sometimes observed grain boundaries, as initial seed is extended to form line in laser-fabricated single-crystal architecture in glass (SCAG). In particular, for Sb 2S 3 SCAG in Sb-S-I glass as a model system, grain boundaries are formed during the transition from laser-written initial seed dot to crystal line. Such grain boundaries during the growth of Sb 2S 3 crystals occur in 16SbI 3-84Sb 2S 3glass, whereas they are absent in Sb 2S 3 glass. We correlate this difference in tendency to form multiple grains with the relative glass forming ability i.e. the dynamicsmore » of nucleation and crystal growth as determined by differential scanning calorimetry (DSC). On the basis of this understanding, methods to minimize the appearance of grain boundaries in the transition region are suggested.« less

The effects of the early uterine environment on the subsequent development of embryo and fetus.

PubMed

Barnes, F L

2000-01-15

Synchrony between the embryo and the uterine endometrium is essential for the establishment of pregnancy and birth in people and livestock. When asynchronous conditions occur a variety of complication result that include failure of the embryo to implant, early embryonic mortality, retarded development and growth, and accelerated development and growth. These complications all appear to be induced within the first week of embryo development and not withstanding the immediate endpoint of large or small size at birth, may alter the course of development throughout the life of the animal. Progesterone appears to play a causative role in establishing the abnormal growth of the fetus by decelerating or accelerating embryonic development. This may act through increasing the transport of blood born growth factors into the uterine lumen or by stimulating the release of growth factors from the endometrium directly. It can not be ruled out that progesterone mediated abundance of, or absence of, appropriate nutrition may bring about the same lifelong outcome. In vitro culture situations that include serum and/or co-culture can also bring about these abnormalities of growth. It is hypothesized that exposure to growth factors "out of phase" may result in an irreversible induction of abnormal development. The described abnormalities that occur in sheep and cattle have not yet been described for children resulting from IVF.

Grain growth simulation of [001] textured YBCO films grown on (001) substrates with large lattice misfit: Prediction of misorientations of the remaining boundaries

NASA Astrophysics Data System (ADS)

Tsai, Jack W. H.; Ling, Shiun; Rodriguez, Julio C.; Mustapha, Zarina; Chan, Siu-Wai

2001-04-01

We study the effects of (1) the variation of grain boundary energy with misorientation and (2) the large lattice misfit (>3%) between the films and substrates on grain growth in films by method of Monte Carlo simulations. The results from the grain growth simulation in YBa2Cu3O7-x (YBCO) films was found to concur with previous experimental observation of preferred grain orientations for YBCO films deposited on various substrates such as (001) magnesium oxide (MgO) and (001) yttria stabilized zirconia (YSZ). The simulation has helped us to identify three factors influencing the competition of these [001] tilt boundaries. They are: (1) the relative depths of local minima in the boundary energy vs. misorientation curve, (2) the number of combinations of coincidence epitaxy (CE) orientations contributing to the exact misorientation for each of the high-angle-but-low-energy (HABLE) boundaries, and (3) the number of combinations of CE orientations within the angular ranges bracketing each of the exact HABLE boundaries. Hence, these factors can be applied to clarify the origin of special misorientations observed experimentally.

Morphology of Proeutectoid Ferrite

NASA Astrophysics Data System (ADS)

Yin, Jiaqing; Hillert, Mats; Borgenstam, Annika

2017-03-01

The morphology of grain boundary nucleated ferrite particles in iron alloys with 0.3 mass pct carbon has been classified according to the presence of facets. Several kinds of particles extend into both grains of austenite and have facets to both. It is proposed that they all belong to a continuous series of shapes. Ferrite plates can nucleate directly on the grain boundary but can also develop from edges on many kinds of particles. Feathery structures of parallel plates on both sides of a grain boundary can thus form. In sections, parallel to their main growth direction, plates have been seen to extend the whole way from the nucleation site at the grain boundary and to the growth front. This happens in the whole temperature range studied from 973 K to 673 K (700 °C to 400 °C). The plates thus grow continuously and not by subunits stopping at limited length and continuing the growth by new ones nucleating. Sometimes, the plates have ridges and in oblique sections they could be mistaken for the start of new plates. No morphological signs were observed indicating a transition between Widmanstätten ferrite and bainitic ferrite. It is proposed that there is only one kind of acicular ferrite.

Expansins expression is associated with grain size dynamics in wheat (Triticum aestivum L.)

PubMed Central

Lizana, X. Carolina; Riegel, Ricardo; Gomez, Leonardo D.; Herrera, Jaime; Isla, Adolfo; McQueen-Mason, Simon J.; Calderini, Daniel F.

2010-01-01

Grain weight is one of the most important components of cereal yield and quality. A clearer understanding of the physiological and molecular determinants of this complex trait would provide an insight into the potential benefits for plant breeding. In the present study, the dynamics of dry matter accumulation, water uptake, and grain size in parallel with the expression of expansins during grain growth in wheat were analysed. The stabilized water content of grains showed a strong association with final grain weight (r2=0.88, P <0.01). Grain length was found to be the trait that best correlated with final grain weight (r2=0.98, P <0.01) and volume (r2=0.94, P <0.01). The main events that defined final grain weight occurred during the first third of grain-filling when maternal tissues (the pericarp of grains) undergo considerable expansion. Eight expansin coding sequences were isolated from pericarp RNA and the temporal profiles of accumulation of these transcripts were monitored. Sequences showing high homology with TaExpA6 were notably abundant during early grain expansion and declined as maturity was reached. RNA in situ hybridization studies revealed that the transcript for TaExpA6 was principally found in the pericarp during early growth in grain development and, subsequently, in both the endosperm and pericarp. The signal in these images is likely to be the sum of the transcript levels of all three sequences with high similarity to the TaExpA6 gene. The early part of the expression profile of this putative expansin gene correlates well with the critical periods of early grain expansion, suggesting it as a possible factor in the final determination of grain size. PMID:20080826

Feeding fat from distillers dried grains with solubles to dairy heifers: I. Effects on growth performance and total tract digestibility of nutrients

USDA-ARS?s Scientific Manuscript database

The objective of this study was to determine if increased dietary fat from dried distillers grains with solubles (DDGS) in diets of growing heifers affected dry matter intake (DMI), average daily gain (ADG), growth performance, and nutrient digestibility. Thirty-three Holstein heifers (133 ± 18 d ol...

Thickness dependence of the electrical and thermoelectric properties of co-evaporated Sb2Te3 films

NASA Astrophysics Data System (ADS)

Shen, Haishan; Lee, Suhyeon; Kang, Jun-gu; Eom, Tae-Yil; Lee, Hoojeong; Han, Seungwoo

2018-01-01

P-type antimony telluride (Sb2Te3) films of various thicknesses (1-, 6-, 10-, and 16-μm) were deposited on an oxidized Si (100) substrate at 250 °C by effusion cell co-evaporation. Microstructural analysis using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy revealed that the grains of the films grew in a mode in which recrystallization was prevalent and grain growth subdued, in contrast to typical film growth, which is often characterized by grain growth. The resultant microstructure exhibited narrow columnar grains, the preferred orientation of which changed with film growth thickness from (1010) with the 1-μm films to (015) for the 6- and 10-μm films, and finally (110) for the 16-μm films. Carrier mobility and the overall thermoelectric properties of the Sb2Te3 films were affected significantly by changes in the film microstructure; this was attributed to the strong anisotropy of Sb2Te3 regarding electrical conductivity. The highest power factor of 3.3 mW/mK2 was observed for the 1-μm-thick Sb2Te3 film.

Induced Abnormality In Mir- and Earth-Grown Super Dwarf Wheat

NASA Technical Reports Server (NTRS)

Bubenheim, David L.; Stieber, Joseph; Campbell, William F.; Salisbury, Frank B.; Levinski, Margarita; Sytchev, Vladimir; Podolsky, Igor; Chernova, Lola; Ivanova, Irene; Kliss, Mark (Technical Monitor)

1998-01-01

Super-dwarf wheat grown on the Mir space station using the Svet "Greenhouse" exhibited morphological, metabolic and reproductive abnormalities compared with normal wheat. Of prominent importance were the abnormalities associated with reproductive ontogeny and the total absence of seed formation on Mir. Changes in the apical meristem associated with transition from the vegetative phase to floral initiation and development of the reproductive spike were all typical of 'Super Dwarf' wheat up to the point of anthesis. Observation of ruptured anthers from the Mir-grown plants revealed what appeared to be normally developed pollen. These pollen grains however, contain only one nucleus, while normal viable pollen is trinucleate. A potentially important difference in the flight experiment, compared with ground reference studies, was identified - a high level of atmospheric ethylene (1200 ppb). Ground studies conducted exposing "Super-dwarf" wheat to ethylene at just prior to anthesis resulted in manifestation of the same abnormalities observed in the space flight samples.

Effect of the Angle Between Sn Grain c-Axis and Electron Flow Direction on Cu-Reinforced Composite Solder Joints Under Current Stressing

NASA Astrophysics Data System (ADS)

Wang, Yan; Han, Jing; Wang, Yishu; Ma, Limin; Guo, Fu

2018-01-01

With a body-centered tetragonal crystal structure, Sn grains were demonstrated to have highly anisotropic behaviors in various properties. The electromigration behavior of lead-free solder was impacted by the grain orientations. In this paper, the angle between the c-axis and the electron flow direction in composite solder joints (angle θ) was proven to be an important factor during electromigration. The effects of angle θ on the electromigration of composite solder joints were investigated in this paper. Cu particle-reinforced Sn3.5Ag solder joints were stressed under a current density of 104 A/cm2 at room temperature. After 336 h current stressing time, different electromigration phenomena occurred at the two sides of the grain boundary in the composite solder joint which contained two Sn grains with different angle θ. The Sn grains with the larger angle θ had a smaller growth rate of Cu6Sn5. In addition, a composite solder joint with a single Sn grain was set as the contrast and its angle θ was smaller than that of the composite solder joint with two Sn grains. The growth rate of Cu6Sn5 in the composite solder joint with a single grain was faster than that of the composite solder joint with two Sn grains.

Head circumference and height abnormalities in autism revisited: the role of pre- and perinatal risk factors.

PubMed

Schrieken, Margo; Visser, Janne; Oosterling, Iris; van Steijn, Daphne; Bons, Daniëlle; Draaisma, Jos; van der Gaag, Rutger-Jan; Buitelaar, Jan; Donders, Rogier; Rommelse, Nanda

2013-01-01

Pre/perinatal risk factors and body growth abnormalities have been studied frequently as early risk markers in autism spectrum disorder (ASD), yet their interrelatedness in ASD has received very little research attention. This is surprising, given that pre/perinatal risk factors can have a substantial impact on growth trajectories in the first years of life. We aimed to determine which pre/perinatal factors were more prevalent in ASD children and if these factors differentially influenced body growth in ASD and control children. A total of 96 ASD and 163 control children matched for gender participated. Data of growth of head size and body length during the first 13 months of life were collected. Data on pre/perinatal risk factors were retrospectively collected through standardized questionnaires. Results indicated that after matching for SES, prematurity/low birth weight and being first born were more prevalent in the ASD versus the control group. In addition, with increasing age children with ASD tended to have a proportionally smaller head circumference compared to their height. However, the effect of prematurity/low birth weight on head growth corrected for height was significantly different in ASD and control children: premature/low birth weight control children showed a disproportionate larger head circumference in relation to height during their first year of life, whereas this effect was absent in premature/low birth weight ASD children. This may suggest that the etiology of abnormal growth is potentially different in ASD and control children: where abnormal growth in control children is related to suboptimal conditions in the uterus, abnormal growth in ASD may be more strongly related to the causal factors that also increase the risk for ASD. However, prospective studies measuring growth and ASD characteristics in both premature/low birth weight and a terme children are necessary to support this conclusion.

Grain size control of rhenium strip

NASA Technical Reports Server (NTRS)

Schuster, Gary B.

1991-01-01

Ensuring the desired grain size in the pure Re strip employed by the SP-100 space nuclear reactor design entails the establishment of an initial grain size in the as-received strip and the avoidance of excessive grain growth during subsequent fabrication. Pure Re tapered tensile specimens have been fabricated and tested in order to quantify the effects of grain-boundary migration. Grain size could be rendered fine and uniform by means of a rolling procedure that uses rather large reductions between short intermediate anneals. The critical strain regime varies inversely with annealing temperature.

Front tracking based modeling of the solid grain growth on the adaptive control volume grid

NASA Astrophysics Data System (ADS)

Seredyński, Mirosław; Łapka, Piotr

2017-07-01

The paper presents the micro-scale model of unconstrained solidification of the grain immersed in under-cooled liquid, based on the front tracking approach. For this length scale, the interface tracked through the domain is meant as the solid-liquid boundary. To prevent generation of huge meshes the energy transport equation is discretized on the adaptive control volume (c.v.) mesh. The coupling of dynamically changing mesh and moving front position is addressed. Preliminary results of simulation of a test case, the growth of single grain, are presented and discussed.

Evidence for dust grain growth in young circumstellar disks.

PubMed

Throop, H B; Bally, J; Esposito, L W; McCaughrean, M J

2001-06-01

Hundreds of circumstellar disks in the Orion nebula are being rapidly destroyed by the intense ultraviolet radiation produced by nearby bright stars. These young, million-year-old disks may not survive long enough to form planetary systems. Nevertheless, the first stage of planet formation-the growth of dust grains into larger particles-may have begun in these systems. Observational evidence for these large particles in Orion's disks is presented. A model of grain evolution in externally irradiated protoplanetary disks is developed and predicts rapid particle size evolution and sharp outer disk boundaries. We discuss implications for the formation rates of planetary systems.

Grain-dependent responses of mammalian diversity to land use and the implications for conservation set-aside.

PubMed

Wearn, Oliver R; Carbone, Chris; Rowcliffe, J Marcus; Bernard, Henry; Ewers, Robert M

2016-07-01

Diversity responses to land-use change are poorly understood at local scales, hindering our ability to make forecasts and management recommendations at scales which are of practical relevance. A key barrier in this has been the underappreciation of grain-dependent diversity responses and the role that β-diversity (variation in community composition across space) plays in this. Decisions about the most effective spatial arrangement of conservation set-aside, for example high conservation value areas, have also neglected β-diversity, despite its role in determining the complementarity of sites. We examined local-scale mammalian species richness and β-diversity across old-growth forest, logged forest, and oil palm plantations in Borneo, using intensive camera- and live-trapping. For the first time, we were able to investigate diversity responses, as well as β-diversity, at multiple spatial grains, and across the whole terrestrial mammal community (large and small mammals); β-diversity was quantified by comparing observed β-diversity with that obtained under a null model, in order to control for sampling effects, and we refer to this as the β-diversity signal. Community responses to land use were grain dependent, with large mammals showing reduced richness in logged forest compared to old-growth forest at the grain of individual sampling points, but no change at the overall land-use level. Responses varied with species group, however, with small mammals increasing in richness at all grains in logged forest compared to old-growth forest. Both species groups were significantly depauperate in oil palm. Large mammal communities in old-growth forest became more heterogeneous at coarser spatial grains and small mammal communities became more homogeneous, while this pattern was reversed in logged forest. Both groups, however, showed a significant β-diversity signal at the finest grain in logged forest, likely due to logging-induced environmental heterogeneity. The β-diversity signal in oil palm was weak, but heterogeneity at the coarsest spatial grain was still evident, likely due to variation in landscape forest cover. Our findings suggest that the most effective spatial arrangement of set-aside will involve trade-offs between conserving large and small mammals. Greater consideration in the conservation and management of tropical landscapes needs to be given to β-diversity at a range of spatial grains. © 2016 by the Ecological Society of America.

Influence of deformation on dolomite rim growth kinetics

NASA Astrophysics Data System (ADS)

Helpa, Vanessa; Rybacki, Erik; Grafulha Morales, Luiz Fernando; Dresen, Georg

2015-04-01

Using a gas-deformation apparatus stacks of oriented calcite (CaCO3) and magnesite (MgCO3) single crystals were deformed at T = 750° C and P = 400 MPa to examine the influence of stress and strain on magnesio-calcite and dolomite (CaMg[CO3]2) growth kinetics. Triaxial compression and torsion tests performed at constant stresses between 7 and 38 MPa and test durations between 4 and 171 hours resulted in bulk strains of 0.03-0.2 and maximum shear strains of 0.8-5.6, respectively. The reaction rims consist of fine-grained (2-7 μm) dolomite with palisade-shaped grains growing into magnesite reactants and equiaxed granular dolomite grains next to calcite. In between dolomite and pure calcite, magnesio-calcite grains evolved with an average grain size of 20-40 μm. Grain boundaries tend to be straighter at high bulk strains and equilibrium angles at grain triple junctions are common within the magnesio-calcite layer. Transmission electron microscopy shows almost dislocation free palisades and increasing dislocation density within granular dolomite towards the magnesio-calcite boundary. Within magnesio-calcite grains, dislocations are concentrated at grain boundaries. Variation of time at fixed stress (˜17 MPa) yields a parabolic time dependence of dolomite rim width, indicating diffusion-controlled growth, similar to isostatic rim growth behavior. In contrast, the magnesio-calcite layer growth is enhanced compared to isostatic conditions. Triaxial compression at given time shows no significant change of dolomite rim thickness (11±2 μm) and width of magnesio-calcite layers (33±5 μm) with increasing stress. In torsion experiments, reaction layer thickness and grain size decrease from the center (low stress/strain) to the edge (high strain/stress) of samples. Chemical analysis shows nearly stoichiometric composition of dolomite palisades, but enhanced Ca content within granular grains, indicating local disequilibrium with magnesio-calcite, in particular for twisted samples. The shift from local equilibrium is ˜3 mol% in triaxial compression and ˜7 mol% in torsion. Electron backscatter diffraction analysis reveals a crystallographic preferred orientation (CPO) within the reaction layers with [0001] axes parallel to the compression/rotation axis and poles of {2-1-10} and {10-10} prismatic planes parallel to the reaction interface. Compared to isostatic annealing, the CPO is more pronounced and the amount of low-angle grain boundaries is increased. At the imposed experimental conditions, most of the bulk deformation is accommodated by calcite single, which is stronger than magnesite. Application of flow laws for magnesio-calcite and dolomite suggest that the fine-grained reaction products should deform by grain boundary diffusion creep, resulting in lower flow strength than the single crystal reactants. However, microstructural observations indicate that deformation of granular dolomite and magnesio-calcite is at least partially assisted by dislocation creep, which would result in an almost similar strength to calcite. Therefore, flattening of the reaction layers during triaxial compression may be counterbalanced by enhanced reaction rates, resulting in almost constant layer thickness, independent of the applied stress. For simple shear, the reduced reaction kinetics in the high stress/strain region of twisted samples may be related to increased nucleation rates, resulting in a lower grain size and rim thickness.

Discrete statistical model of fatigue crack growth in a Ni-base superalloy, capable of life prediction

NASA Astrophysics Data System (ADS)

Boyd-Lee, Ashley; King, Julia

1992-07-01

A discrete statistical model of fatigue crack growth in a nickel base superalloy Waspaloy, which is quantitative from the start of the short crack regime to failure, is presented. Instantaneous crack growth rate distributions and persistence of arrest distributions are used to compute fatigue lives and worst case scenarios without extrapolation. The basis of the model is non-material specific, it provides an improved method of analyzing crack growth rate data. For Waspaloy, the model shows the importance of good bulk fatigue crack growth resistance to resist early short fatigue crack growth and the importance of maximizing crack arrest both by the presence of a proportion of small grains and by maximizing grain boundary corrugation.

Seed development, seed germination and seedling growth in the R50 (sym16) pea mutant are not directly linked to altered cytokinin homeostasis.

PubMed

Long, Chengli; Held, Mark; Hayward, Allison; Nisler, Jaroslav; Spíchal, Lukas; Neil Emery, R J; Moffatt, Barbara A; Guinel, Frédérique C

2012-06-01

R50 (sym16) is a pea nodulation mutant that accumulates cytokinin (CK) in its vegetative organs. Total CK content increases as the plant ages because of the low activity of the enzyme cytokinin oxidase/dehydrogenase (CKX) responsible for CK degradation. R50 exhibits a large seed with high relative water content, and its seedling establishes itself slowly. Whether these two traits are linked to abnormal CK levels was considered here. R50 was found to have a similar germination rate but a much slower epicotyl emergence than Sparkle, its wild-type (WT). At the onset of emergence, the starch grains in R50 cotyledons were larger than those of WT; furthermore, they did not degrade as fast as in WT because of low amylase activity. No differences between the pea lines were observed in the CK forms identified during seed embryogenesis. However, while CK content compared to that of WT was reduced early in R50 embryogenesis, it was elevated later on in its dry seeds where CKX activity was low, although CKX transcript abundance remained high. Transcripts of the two known PsCKX isoforms exhibited tissue- and development-specific profiles with no detectable PsCKX2 expression in cotyledons. There were more of both transcripts in R50 roots than in WT roots, but less of PsCKX2 than PsCKX1 in R50 shoots compared to WT shoots. Thus, although there is a definite CKX post-transcriptional defect in R50 dry seeds, an abnormal CK homeostasis is not the basis of the delay in R50 seedling establishment, which we linked to abnormal amylase activity early in development. Copyright © Physiologia Plantarum 2012.

A study on the influence of microstructure on small fatigue cracks

NASA Astrophysics Data System (ADS)

Castelluccio, Gustavo M.

In spite of its significance in industrial applications, the prediction of the influence of microstructure on the early stages of crack formation and growth in engineering alloys remains underdeveloped. The formation and early growth of fatigue cracks in the high cycle fatigue regime lasts for much of the fatigue life, and it is strongly influenced by microstructural features such as grain size, twins and morphological and crystallographic texture. However, most fatigue models do not predict the in uence of the microstructure on early stages of crack formation, or they employ parameters that should be calibrated with experimental data from specimens with microstructures of interest. These post facto strategies are adequate to characterize materials, but they are not fully appropriate to aid in the design of fatigue-resistant engineering alloys. This thesis considers finite element computational models that explicitly render the microstructure of selected FCC metallic systems and introduces a fatigue methodology that estimates transgranular and intergranular fatigue growth for microstructurally small cracks. The driving forces for both failure modes are assessed by means of fatigue indicators, which are used along with life correlations to estimate the fatigue life. Furthermore, cracks with meandering paths are modeled by considering crack growth on a grain-by-grain basis with a damage model embedded analytically to account for stress and strain redistribution as the cracks extend. The methodology is implemented using a crystal plasticity constitutive model calibrated for studying the effect of microstructure on early fatigue life of a powder processed Ni-base RR1000 superalloy at elevated temperature under high cycle fatigue conditions. This alloy is employed for aircraft turbine engine disks, which undergo a thermomechanical production process to produce a controlled bimodal grain size distribution. The prediction of the fatigue life for this complex microstructure presents particular challenges that are discussed and addressed. The conclusions of this work describe the mechanistic of microstructural small crack. In particular, the fatigue crack growth driving force has been characterized as it evolves within grains and crosses to other grains. Furthermore, the computational models serve as a tool to assess the effects of microstructural features on early stages of fatigue crack formation and growth, such as distributions of grain size and twins.

Morphologies of tungsten nanotendrils grown under helium exposure

DOE PAGES

Wang, Kun; Doerner, R. P.; Baldwin, Matthew J.; ...

2017-02-14

Nanotendril “fuzz” will grow under He bombardment under tokamak-relevant conditions on tungsten plasma-facing materials in a magnetic fusion energy device. We have grown tungsten nanotendrils at low (50 eV) and high (12 keV) He bombardment energy, in the range 900–1000 °C, and characterized them using electron microscopy. Low energy tendrils are finer (~22 nm diameter) than high-energy tendrils (~176 nm diameter), and low-energy tendrils have a smoother surface than high-energy tendrils. Cavities were omnipresent and typically ~5–10 nm in size. Oxygen was present at tendril surfaces, but tendrils were all BCC tungsten metal. Electron diffraction measured tendril growth axes andmore » grain boundary angle/axis pairs; no preferential growth axes or angle/axis pairs were observed, and low-energy fuzz grain boundaries tended to be high angle; high energy tendril grain boundaries were not observed. We speculate that the strong tendency to high-angle grain boundaries in the low-energy tendrils implies that as the tendrils twist or bend, strain must accumulate until nucleation of a grain boundary is favorable compared to further lattice rotation. Finally, the high-energy tendrils consisted of very large (>100 nm) grains compared to the tendril size, so the nature of the high energy irradiation must enable faster growth with less lattice rotation.« less

Morphologies of tungsten nanotendrils grown under helium exposure

PubMed Central

Wang, Kun; Doerner, R. P.; Baldwin, M. J.; Meyer, F. W.; Bannister, M. E.; Darbal, Amith; Stroud, Robert; Parish, Chad M.

2017-01-01

Nanotendril “fuzz” will grow under He bombardment under tokamak-relevant conditions on tungsten plasma-facing materials in a magnetic fusion energy device. We have grown tungsten nanotendrils at low (50 eV) and high (12 keV) He bombardment energy, in the range 900–1000 °C, and characterized them using electron microscopy. Low energy tendrils are finer (~22 nm diameter) than high-energy tendrils (~176 nm diameter), and low-energy tendrils have a smoother surface than high-energy tendrils. Cavities were omnipresent and typically ~5–10 nm in size. Oxygen was present at tendril surfaces, but tendrils were all BCC tungsten metal. Electron diffraction measured tendril growth axes and grain boundary angle/axis pairs; no preferential growth axes or angle/axis pairs were observed, and low-energy fuzz grain boundaries tended to be high angle; high energy tendril grain boundaries were not observed. We speculate that the strong tendency to high-angle grain boundaries in the low-energy tendrils implies that as the tendrils twist or bend, strain must accumulate until nucleation of a grain boundary is favorable compared to further lattice rotation. The high-energy tendrils consisted of very large (>100 nm) grains compared to the tendril size, so the nature of the high energy irradiation must enable faster growth with less lattice rotation. PMID:28195125

Multiscale Simulation and Modeling of Multilayer Heteroepitactic Growth of C60 on Pentacene.

PubMed

Acevedo, Yaset M; Cantrell, Rebecca A; Berard, Philip G; Koch, Donald L; Clancy, Paulette

2016-03-29

We apply multiscale methods to describe the strained growth of multiple layers of C60 on a thin film of pentacene. We study this growth in the presence of a monolayer pentacene step to compare our simulations to recent experimental studies by Breuer and Witte of submonolayer growth in the presence of monolayer steps. The molecular-level details of this organic semiconductor interface have ramifications on the macroscale structural and electronic behavior of this system and allow us to describe several unexplained experimental observations for this system. The growth of a C60 thin film on a pentacene surface is complicated by the differing crystal habits of the two component species, leading to heteroepitactical growth. In order to probe this growth, we use three computational methods that offer different approaches to coarse-graining the system and differing degrees of computational efficiency. We present a new, efficient reaction-diffusion continuum model for 2D systems whose results compare well with mesoscale kinetic Monte Carlo (KMC) results for submonolayer growth. KMC extends our ability to simulate multiple layers but requires a library of predefined rates for event transitions. Coarse-grained molecular dynamics (CGMD) circumvents KMC's need for predefined lattices, allowing defects and grain boundaries to provide a more realistic thin film morphology. For multilayer growth, in this particularly suitable candidate for coarse-graining, CGMD is a preferable approach to KMC. Combining the results from these three methods, we show that the lattice strain induced by heteroepitactical growth promotes 3D growth and the creation of defects in the first monolayer. The CGMD results are consistent with experimental results on the same system by Conrad et al. and by Breuer and Witte in which C60 aggregates change from a 2D structure at low temperature to 3D clusters along the pentacene step edges at higher temperatures.

Protoplanetary Disks in Multiple Star Systems

NASA Astrophysics Data System (ADS)

Harris, Robert J.

Most stars are born in multiple systems, so the presence of a stellar companion may commonly influence planet formation. Theory indicates that companions may inhibit planet formation in two ways. First, dynamical interactions can tidally truncate circumstellar disks. Truncation reduces disk lifetimes and masses, leaving less time and material for planet formation. Second, these interactions might reduce grain-coagulation efficiency, slowing planet formation in its earliest stages. I present three observational studies investigating these issues. First is a spatially resolved Submillimeter Array (SMA) census of disks in young multiple systems in the Taurus-Auriga star-forming region to study their bulk properties. With this survey, I confirmed that disk lifetimes are preferentially decreased in multiples: single stars have detectable millimeter-wave continuum emission twice as often as components of multiples. I also verified that millimeter luminosity (proportional to disk mass) declines with decreasing stellar separation. Furthermore, by measuring resolved-disk radii, I quantitatively tested tidal-truncation theories: results were mixed, with a few disks much larger than expected. I then switch focus to the grain-growth properties of disks in multiple star systems. By combining SMA, Combined Array for Research in Millimeter Astronomy (CARMA), and Jansky Very Large Array (VLA) observations of the circumbinary disk in the UZ Tau quadruple system, I detected radial variations in the grain-size distribution: large particles preferentially inhabit the inner disk. Detections of these theoretically predicted variations have been rare. I related this to models of grain coagulation in gas disks and find that our results are consistent with growth limited by radial drift. I then present a study of grain growth in the disks of the AS 205 and UX Tau multiple systems. By combining SMA, Atacama Large Millimeter/submillimeter Array (ALMA), and VLA observations, I detected radial variations of the grain-size distribution in the AS 205 A disk, but not in the UX Tau A disk. I find that some combination of radial drift and fragmentation limits growth in the AS 205 A disk. In the final chapter, I summarize my findings that, while multiplicity clearly influences bulk disk properties, it does not obviously inhibit grain growth. Other investigations are suggested.

Influence of water activity and temperature on growth and fumonisin production by Fusarium proliferatum strains on irradiated wheat grains.

PubMed

Cendoya, Eugenia; Monge, María Del Pilar; Chiacchiera, Stella Maris; Farnochi, María Cecilia; Ramirez, María Laura

2018-02-02

Wheat is the most important cereal consumed by the Argentine population. In previous studies performed in durum and common wheat grains in this country it has been observed fumonisin contamination as well as high incidence of Fusarium proliferatum. Fumonisins are toxic fungal metabolites, and consumption of fumonisin-contaminated maize has been epidemiologically associated with oesophageal cancer and neural tube defects in some human populations. Using irradiated wheat-grains, the effects of abiotic factors, temperature (15, 25, and 30°C) and water activity (a W ; 0.995, 0.98, 0.96, 0.94, 0.92, and 0.88), on mycelial growth and fumonisin biosynthesis were compared for three F. proliferatum strains isolated from wheat grains in Argentina. Although all isolates showed similar profiles of growth, the fumonisin production profiles were slightly different. Maximum growth rates were obtained at the highest a W (0.995) and 25°C, with growth decreasing as the a W of the medium was reduced. Maximum amounts of total fumonisins (FB 1 , FB 2 and FB 3 ) were produced at 0.995 a W and 15°C for 2 strains, and at 25°C and 0.995 a W for the third one. Fumonisins concentrations varied considerably depending on the a W and temperature interactions assayed. Studied strains showed different fumonisin production profiles. Two-dimensional profiles of a W by temperature interactions were developed from these data to identify areas where conditions indicate a significant risk of fumonisins accumulation on wheat. As a result, temperature and a W conditions that resulted in fumonisins production are those found during wheat grain development (especially milk and dough stages) in the field. This is the first study made using irradiated wheat grains and provides useful baseline data on conditions representing a low or a high risk for fumonisins contamination of wheat grains which is of concern because this cereal is destined mainly for human consumption. Copyright © 2017 Elsevier B.V. All rights reserved.

Microstructure of warm rolling and pearlitic transformation of ultrafine-grained GCr15 steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Jun-Jie; Lian, Fu-Liang; Liu, Hong-Ji

2014-09-15

Pearlitic transformation mechanisms have been investigated in ultra-fine grained GCr15 steel. The ultrafine-grained steel, whose grain size was less than 1 μm, was prepared by thermo-mechanical treatment at 873 K and then annealing at 923 K for 2 h. Pearlitic transformation was conducted by reheating the ultra-fine grained samples at 1073 K and 1123 K for different periods of time and then cooling in air. Scanning electron microscope observation shows that normal lamellar pearlite, instead of granular cementite and ferrite, cannot be formed when the grain size is approximately less than 4(± 0.6) μm, which yields a critical grain sizemore » for normal lamellar pearlitic transformations in this chromium alloyed steel. The result confirms that grain size has a great influence on pearlitic transformation by increasing the diffusion rate of carbon atoms in the ultra-fine grained steel, and the addition of chromium element doesn't change this pearlitic phase transformation rule. Meanwhile, the grain growth rate is reduced by chromium alloying, which is beneficial to form fine grains during austenitizing, thus it facilitating pearlitic transformation by divorced eutectoid transformation. Moreover, chromium element can form a relatively high gradient in the frontier of the undissolved carbide, which promotes carbide formation in the frontier of the undissolved carbide, i.e., chromium promotes divorced eutectoid transformation. - Highlights: • Ultrafine-grained GCr15 steel was obtained by warm rolling and annealing technology. • Reduction of grain size makes pearlite morphology from lamellar to granular. • Adding Cr does not change normal pearlitic phase transformation rule in UFG steel. • Cr carbide resists grain growth and facilitates pearlitic transformation by DET.« less

Pleiotrophin is a driver of vascular abnormalization in glioblastoma.

PubMed

Zhang, Lei; Dimberg, Anna

2016-01-01

In a recent report by Zhang et al. , pleiotrophin (PTN) was demonstrated to enhance glioma growth by promoting vascular abnormalization. PTN stimulates glioma vessels through anaplastic lymphoma kinase (Alk)-mediated perivascular deposition of vascular endothelial growth factor (VEGF). Targeting of Alk or VEGF signaling normalizes tumor vessels in PTN-expressing tumors.

Thermal Stability of Nanocrystalline Alloys by Solute Additions and A Thermodynamic Modeling

NASA Astrophysics Data System (ADS)

Saber, Mostafa

Nanocrystalline alloys show superior properties due to their exceptional microstructure. Thermal stability of these materials is a critical aspect. It is well known that grain boundaries in nanocrystalline microstructures cause a significant increase in the total free energy of the system. A driving force provided to reduce this excess free energy can cause grain growth. The presence of a solute addition within a nanocrystalline alloy can lead to the thermal stability. Kinetic and thermodynamic stabilization are the two basic mechanisms with which stability of a nanoscale grain size can be achieved at high temperatures. The basis of this thesis is to study the effect of solute addition on thermal stability of nanocrystalline alloys. The objective is to determine the effect of Zr addition on the thermal stability of mechanically alloyed nanocrysatillne Fe-Cr and Fe-Ni alloys. In Fe-Cr-Zr alloy system, nanoscale grain size stabilization was maintained up to 900 °C by adding 2 at% Zr. Kinetic pinning by intermetallic particles in the nanoscale range was identified as a primary mechanism of thermal stabilization. In addition to the grain size strengthening, intermetallic particles also contribute to strengthening mechanisms. The analysis of microhardness, XRD data, and measured grain sizes from TEM micrographs suggested that both thermodynamic and kinetic mechanisms are possible mechanisms. It was found that alpha → gamma phase transformation in Fe-Cr-Zr system does not influence the grain size stabilization. In the Fe-Ni-Zr alloy system, it was shown that the grain growth in Fe-8Ni-1Zr alloy is much less than that of pure Fe and Fe-8Ni alloy at elevated temperatures. The microstructure of the ternary Fe-8Ni-1Zr alloy remains in the nanoscale range up to 700 °C. Using an in-situ TEM study, it was determined that drastic grain growth occurs when the alpha → gamma phase transformation occurs. Accordingly, there can be a synergistic relationship between grain growth and alpha → gamma phase transformation in Fe-Ni-Zr alloys. In addition to the experimental study of thermal stabilization of nanocrystalline Fe-Cr-Zr or Fe-Ni-Zr alloys, the thesis presented here developed a new predictive model, applicable to strongly segregating solutes, for thermodynamic stabilization of binary alloys. This model can serve as a benchmark for selecting solute and evaluating the possible contribution of stabilization. Following a regular solution model, both the chemical and elastic strain energy contributions are combined to obtain the mixing enthalpy. The total Gibbs free energy of mixing is then minimized with respect to simultaneous variations in the grain boundary volume fraction and the solute concentration in the grain boundary and the grain interior. The Lagrange multiplier method was used to obtained numerical solutions. Application are given for the temperature dependence of the grain size and the grain boundary solute excess for selected binary system where experimental results imply that thermodynamic stabilization could be operative. This thesis also extends the binary model to a new model for thermodynamic stabilization of ternary nanocrystalline alloys. It is applicable to strongly segregating size-misfit solutes and uses input data available in the literature. In a same manner as the binary model, this model is based on a regular solution approach such that the chemical and elastic strain energy contributions are incorporated into the mixing enthalpy DeltaHmix, and the mixing entropy DeltaSmix is obtained using the ideal solution approximation. The Gibbs mixing free energy Delta Gmix is then minimized with respect to simultaneous variations in grain growth and solute segregation parameters. The Lagrange multiplier method is similarly used to obtain numerical solutions for the minimum Delta Gmix. The temperature dependence of the nanocrystalline grain size and interfacial solute excess can be obtained for selected ternary systems. As an example, model predictions are compared to experimental results for Fe-Cr-Zr and Fe-Ni-Zr alloy systems. Consistency between the experimental results and the present model predictions provide a more rigorous criterion for investigating thermal stabilization. However, other possible contributions for grain growth stabilization should still be considered.

The effect of microstructure on 650 C fatigue crack growth in P/M Astroloy

NASA Technical Reports Server (NTRS)

Gayda, J.; Miner, R. V.

1983-01-01

The effect of microstructure on fatigue crack propagation at 650 C has been studied in a P/M nickel-base superalloy, Astroloy. Crack propagation data were obtained in air and vacuum at 20 cpm with a modified compact tension specimen. The rate of crack growth, da/dn, was correlated with the stress intensity range. Key microstructural variables examined were grain size and the distribution and size of the strengthening gamma prime phase. A fine grain size less than 20 microns always promoted rapid, intergranular failure, while a large grain size promoted slower, transgranular failure which decreased as the size and volume fraction of aging gamma prime was manipulated so as to increase alloy strength. The rapid, intergranular mode of failure of the fine grain microstructures was suppressed in vacuum.

Recrystallization and grain growth in NiAl

NASA Technical Reports Server (NTRS)

Haff, G. R.; Schulson, E. M.

1982-01-01

Aluminide intermetallics, because of their strength, microstructural stability, and oxidation resistance at elevated temperatures, represent potential structural materials for use in advanced energy conversion systems. This inherent potential of the intermetallics can currently not be realized in connection with the general brittleness of the materials under ambient conditions. It is pointed out, however, that brittleness is not an inherent characteristic. Single crystals are ductile and polycrystals may be, too, if their grains are fine enough. The present investigation is concerned with an approach for reducing material brittleness, taking into account thermal-mechanically induced grain refinement in NiAl, a B2 aluminide which melts at 1638 C and which retains complete order to its melting point. Attention is given to the kinetics of recrystallization and grain growth of warm-worked, nickel-rich material.

Evaluation of commercially available enzymes, probiotics, or yeast on apparent total-tract nutrient digestion and growth in nursery and finishing pigs fed diets containing corn dried distillers grains with solubles

USDA-ARS?s Scientific Manuscript database

The ability of enzymes, direct fed microbials, or yeast to enhance nutrient utilization or growth performance in nursery or finishing pigs fed diets containing increased levels of corn fiber from dried distillers grains with solubles (DDGS) is largely unknown. Ten commercially available feed additiv...

Nitrogen Nutrition Improves the Potential of Wheat (Triticum aestivum L.) to Alleviate the Effects of Drought Stress during Vegetative Growth Periods.

PubMed

Abid, Muhammad; Tian, Zhongwei; Ata-Ul-Karim, Syed Tahir; Cui, Yakun; Liu, Yang; Zahoor, Rizwan; Jiang, Dong; Dai, Tingbo

2016-01-01

Efficient nitrogen (N) nutrition has the potential to alleviate drought stress in crops by maintaining metabolic activities even at low tissue water potential. This study was aimed to understand the potential of N to minimize the effects of drought stress applied/occur during tillering (Feekes stage 2) and jointing (Feekes stage 6) growth stages of wheat by observing the regulations and limitations of physiological activities, crop growth rate during drought periods as well as final grain yields at maturity. In present study, pot cultured plants of a wheat cultivar Yangmai-16 were exposed to three water levels [severe stress at 35-40% field capacity (FC), moderate stress at 55-60% FC and well-watered at 75-80% FC] under two N rates (0.24 g and 0.16 g/kg soil). The results showed that the plants under severe drought stress accompanied by low N exhibited highly downregulated photosynthesis, and chlorophyll (Chl) fluorescence during the drought stress periods, and showed an accelerated grain filling rate with shortened grain filling duration (GFD) at post-anthesis, and reduced grain yields. Severe drought-stressed plants especially at jointing, exhibited lower Chl and Rubisco contents, lower efficiency of photosystem II and greater grain yield reductions. In contrast, drought-stressed plants under higher N showed tolerance to drought stress by maintaining higher leaf water potential, Chl and Rubisco content; lower lipid peroxidation associated with higher superoxide dismutase and ascorbate peroxidase activities during drought periods. The plants under higher N showed delayed senescence, increased GFD and lower grain yield reductions. The results of the study suggested that higher N nutrition contributed to drought tolerance in wheat by maintaining higher photosynthetic activities and antioxidative defense system during vegetative growth periods.

Pharmacologic effects of grain weevil extract on isolated guinea pig tracheal smooth muscle.

PubMed

Schachter, E Neil; Zuskin, Eugenija; Arumugam, Uma; Goswami, Satindra; Castranova, Vincent; Whitmer, Mike; Chiarelli, Angelo

2008-01-01

The grain weevil, an insect (pest) that infects grain, is a frequent contaminant of processed wheat, and its presence may contribute to respiratory abnormalities in grain workers. We studied the in vitro effects of an extract of grain weevil (GWE) on airway smooth muscle. Pharmacologic studies included in vitro challenge of guinea pig trachea with GWE, in parallel organ baths, pretreated with mediator-modifying agents or a control solution. Dose-related contractions of nonsensitized guinea pig trachea (GPT) were demonstrated using this extract. Pharmacologic studies were performed by pretreating guinea pig tracheal tissue with drugs known to modulate smooth muscle contraction: atropine, indomethacin, pyrilamine, acivicin, NDGA, BPB, TMB8, captopril, and capsaicin. Atropine, pyrilamine, BPB, and capsaicin significantly reduced the contractile effects of the extract at most of the challenge doses (p < 0.01 or p < 0.05). Inhibition of GWE-induced contraction by blocking of other mediators was less complete. We suggest that GWE causes dose-related airway smooth muscle constriction of the GPT by nonimmunologic mechanisms involving a variety of airway mediators and possibly cholinergic receptors.

Endocrine Abnormalities in Patients with Chronic Kidney Disease.

PubMed

Kuczera, Piotr; Adamczak, Marcin; Wiecek, Andrzej

2015-01-01

In patients with chronic kidney disease the alterations of the endocrine system may arise from several causes. The kidney is the site of degradation as well as synthesis of many different hormones. Moreover, a number of concomitant pathological conditions such as inflammation, metabolic acidosis and malnutrition may participate in the pathogenesis of endocrine abnormalities in this group of patients. The most pronounced endocrine abnormalities in patients with chronic kidney disease are the deficiencies of: calcitriol, testosterone, insulin-like growth factor and, erythropoietin (EPO). Additionally accumulation of several hormones, such as: prolactin, growth hormone and insulin frequently also occur. The clinical consequences of the abovementioned endocrine abnormalities are among others: anemia, infertility and bone diseases.

[Effects of cropping patterns on photosynthesis characteristics of summer maize and its utilization of solar and heat resources].

PubMed

Zhu, Yuan-Gang; Dong, Shu-Ting; Zhang, Ji-Wang; Liu, Peng; Yang, Jin-Sheng; Jia, Chun-Lan; Liu, Jing-Guo; Li, Deng-Hai

2010-06-01

In order to investigate the effects of interplanting and direct seeding on the photosynthesis characteristics of summer maize and its utilization of solar and heat resources, two summer maize cultivars (Zhengdan 958 and Denghai 661) were planted in the farmlands of Denghai Seed Co. Ltd in Laizhou City of Shandong Province, with 67500 plants x hm(-2) and three sowing dates. The above-ground biomass, plant growth rate, leaf area index, and net photosynthetic rate per ear leaf were measured to reveal the photosynthesis characteristics of test cultivars. In the meantime, the characters of grain-filling were simulated by Richards' model, and the solar resource utilization efficiency of the cultivars was calculated, in combining with meteorological data. Comparing with interplanting, direct seeding increased the grain yield by 1.17%-3.33%, but decreased the thousand-grain weight significantly. Growth stages were extended under earlier sowing. The leaf area index and net photosynthetic rate from flowering to 30 d after anthesis were significantly higher under direct seeding than under interplanting, but after then, they decreased faster. Direct seeding induced a higher accumulation of dry matter and a faster plant growth rate before and after flowering. Under direct seeding, the maximum grain-filling rate reached earlier, the starting potential was higher, but the grain-filling period, active grain-filling period, and W(max) were lower, compared with those under interplanting. Also under direct seeding, the total accumulative temperature and solar radiation during growth period decreased by 150-350 degrees C x d and 200-400 MJ x m(-2), respectively, but the solar resource utilization efficiency of grain increased by 10.5%-24.7%. All the results suggested that direct seeding was superior to interplanting for the summer maize production under field condition. In order to enhance solar and heat utilization efficiency and excavate yield potential, it would be essential to improve the leaf photosynthesis efficiency and postpone leaf aging.

Structure and properties of electrodeposited nanocrystalline Ni and Ni-Fe alloy continuous foils

NASA Astrophysics Data System (ADS)

Giallonardo, Jason Derek

This research work presents the first comprehensive study on nanocrystalline materials produced in bulk quantities using a novel continuous electrodeposition process. A series of nanocrystalline Ni and Ni-Fe alloy continuous foils were produced and an intensive investigation into their structure and various properties was carried out. High-resolution transmission electron microscopy (HR-TEM) revealed the presence of local strain at high and low angle, and twin boundaries. The cause for these local strains was explained based on the interpretation of non-equilibrium grain boundary structures that result when conditions of compatibility are not satisfied. HR-TEM also revealed the presence of twin faults of the growth type, or "growth faults", which increased in density with the addition of Fe. This observation was found to be consistent with a corresponding increase in the growth fault probabilities determined quantitatively using X-ray diffraction (XRD) pattern analysis. Hardness and Young's modulus were measured by nanoindentation. Hardness followed the regular Hall-Petch behaviour down to a grain size of 20 nm after which an inverse trend was observed. Young's modulus was slightly reduced at grain sizes less than 20 nm and found to be affected by texture. Microstrain based on XRD line broadening was measured for these materials and found to increase primarily with a decrease in grain size or an increase in intercrystal defect density (i.e., grain boundaries and triple junctions). This microstrain is associated with the local strains observed at grain boundaries in the HR-TEM image analysis. A contribution to microstrain from the presence of growth faults in the nanocrystalline Ni-Fe alloys was also noted. The macrostresses for these materials were determined from strain measurements using a two-dimensional XRD technique. At grain sizes less than 20 nm, there was a sharp increase in compressive macrostresses which was also owed to the corresponding increase in intercrystal defects or interfaces in the solid.

Use of magnetic resonance imaging in short stature: data from National Cooperative Growth Study (NCGS) Substudy 8.

PubMed

Kemp, Stephen F; Alter, Craig A; Dana, Ken; Baptista, Joyce; Blethen, Sandra L

2002-05-01

The primary use of magnetic resonance imaging (MRI) in the evaluation of children with short stature (SS) is to discover lesions in the central nervous system (CNS), particularly tumors that may require intervention. MRI has a secondary role in identifying structural abnormalities responsible for growth hormone deficiency (GHD). We examined data from the National Cooperative Growth Study (NCGS) Substudy 8 to determine how American physicians are using MRI in evaluating children with SS. Of the 21,738 short children enrolled in NCGS, 5% underwent MRI during their follow-up. Children who had GH stimulation testing were more likely to have had an MRI than those in whom no GH stimulation test was performed (19% vs 2%, p <0.0001). Moreover, children diagnosed with severe GHD (maximum GH <5 ng/ml) were more likely to have an abnormal finding on MRI. Of these patients, 27% demonstrated an abnormality as compared to 12% and 12.5% in patients with partial GHD and normal GH stimulation test results (>10 ng/ml), respectively. Abnormalities unrelated to the hypothalamus or pituitary represented 30% of these findings, while disorders in pituitary anatomy, including pituitary hypoplasia, pituitary stalk interruption, and ectopic posterior pituitary, represented an additional 30% of abnormal MRI examinations. CNS tumors comprised 23% of abnormal findings in these patients. We conclude that MRI provides significant value in the evaluation of children with SS, by identifying CNS tumors associated with growth failure as well as anatomical abnormalities of the pituitary. These findings are useful in confirming the diagnosis of GHD in children and identifying potential candidates for continued GH replacement in adulthood.

Synthesis of millimeter-scale transition metal dichalcogenides single crystals

DOE PAGES

Gong, Yongji; Ye, Gonglan; Lei, Sidong; ...

2016-02-10

The emergence of semiconducting transition metal dichalcogenide (TMD) atomic layers has opened up unprecedented opportunities in atomically thin electronics. Yet the scalable growth of TMD layers with large grain sizes and uniformity has remained very challenging. Here is reported a simple, scalable chemical vapor deposition approach for the growth of MoSe2 layers is reported, in which the nucleation density can be reduced from 105 to 25 nuclei cm -2, leading to millimeter-scale MoSe 2 single crystals as well as continuous macrocrystalline films with millimeter size grains. The selective growth of monolayers and multilayered MoSe2 films with well-defined stacking orientation canmore » also be controlled via tuning the growth temperature. In addition, periodic defects, such as nanoscale triangular holes, can be engineered into these layers by controlling the growth conditions. The low density of grain boundaries in the films results in high average mobilities, around ≈42 cm 2 V -1 s -1, for back-gated MoSe 2 transistors. This generic synthesis approach is also demonstrated for other TMD layers such as millimeter-scale WSe 2 single crystals.« less

Oxygen Permeability and Grain-Boundary Diffusion Applied to Alumina Scales

NASA Technical Reports Server (NTRS)

Smialek, James L.; Jacobson, Nathan S.; Gleeson, Brian; Hovis, David B.; Heuer, Arthur H.

2013-01-01

High-temperature oxygen permeability measurements had determined grain-boundary diffusivities (deltaD(sub gb)) in bulk polycrystalline alumina (Wada, Matsudaira, and Kitaoka). They predict that oxygen deltaD(sub gb,O) varies with oxygen pressure as P(O2)(sup -1/6) at low pressure whereas aluminum deltaD(sub gb),Al varies with P(O2)(sup +3/16) at high pressure. These relations were used to evaluate alumina scale growth in terms of diffusivity and grain size. A modified Wagner treatment for dominant inward oxygen growth produces the concise solution: ?(sub i) = k(sub p,i)×G(sub i) = 12 deltaD(sub gb,O,int), where ?(sub i) is a constant and k(sub p,i) and G(sub i) refer to instantaneous values of the scale parabolic growth constant and grain size, respectively. A commercial FeCrAl(Zr) alloy was oxidized at 1100 to 1400 degC to determine k(sub p,i), interfacial grain size, ?, and thus deltaD(sub gb,O,int). The deltaD(sub gb,O,int) values predicted from oxidation at (375 kJ/mole) were about 20 times less than those obtained above (at 298 kJ/mole), but closer than extrapolations from high-temperature bulk measurements. The experimental oxidation results agree with similar FeCrAl(X) studies, especially where both k(sub p,i) and G(sub i) were characterized. This complete approach accounts for temperature-sensitive oxidation effects of grain enlargement, equilibrium interface pressure variation, and grain-boundary diffusivity.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arul Kumar, M.; Beyerlein, Irene Jane; Tomé, Carlos N.

Here we study the effect of nearest neighboring grains on the propensity for {1012} twin growth in Mg and Zr. Twin lamellae lying within one grain flanked by two neighboring grains with several orientations are considered. The fields of resolved shear stress on the twin system are calculated in the multicrystal using a three-dimensional full-field crystal plasticity Fast Fourier Transform approach. The calculations were carried out for Mg and Zr using slip threshold stresses corresponding to 300K and 76K, respectively, where twin activity is important. We show that the neighboring grain constraint tends to oppose further growth and that themore » critical applied stress needed to overcome this resistance depends on neighboring grain orientation, more strongly in Zr than in Mg. We also present results for a pair of adjacent and parallel twins at various spacings. It is found that their paired interaction increases the resistive forces for twin growth above that for an isolated twin. The critical spacing above which this enhanced resistance is removed is smaller for Zr than Mg. Our analysis reveals that these two disparate responses of Zr and Mg are both a consequence of the fact that Zr is elastically and plastically more anisotropic than Mg. Additional calculations carried out on Ti support this conclusion. Finally, these findings can help explain why, for the same grain size, more twins per grain form in Zr than in Mg, twins in Zr tend to be thinner than those in Mg, and the relationship between the thickness of the twin and its Schmid factor in Zr is not as strong as in Mg.« less

Molecular beam epitaxially grown copper indium diselenide and copper gallium diselenide films

NASA Astrophysics Data System (ADS)

Yoon, Seokhyun

2005-12-01

To eliminate the influence of grain boundaries, CuInSe2 (CIS) and CuGaSe2 (CGS) films were grown on (100) GaAs wafers. The effects of Cu to III metal ratio and dosing with Na on the growth mode and defect properties were studied at two growth temperatures. The impact of post-annealing in Se on the defect structure of CGS film was also studied. Two-dimensional simulations were used to better understand the role of grain boundary on cell performance. For growth at 360°C, the In-rich CIS films were polycrystalline, whereas the Cu-rich CIS films were epitaxial exhibiting a Stranski-Krastanov (S-K) growth mode. It is proposed that a Cu-Se secondary phase enhances the mobility of adatoms, allowing epitaxial growth to a critical thickness, at which point segregation at the nucleation sites became faster the rate of growth. Island structures, embedded in a matrix region, were oriented along the [01-1] directed edges with surface undulations apparent on the matrix surface with dominant {112} crystal planes. At the higher growth temperature of 464°C, the CIS films grew epitaxially without the need of a Cu-Se phase. Both CIS films grown at low and high temperatures were nearly relaxed. The segregation of epitaxial Cu1.5Se was also observed in the Cu-rich, Na-dosed CIS film, which is attributed to a surfactant effect of Na. At a growth temperature of 438°C, CGS films showed a S-K growth mode and nearly pseudomorphic growth. Hemispherical islands with twins were observed in the Ga-rich CGS films and epitaxial Cu1.5Se phase were identified in the top region of the island structure. From the PL analysis of Cu-rich, Na-dosed CGS film after Se-annealing, a new defect level located 20 meV above the valence band edge was identified as NaGa acceptor state. Two-dimensional simulation of the impact of grain boundaries on device performance showed that the short circuit current decreases sharply along with the other device parameters below a critical grain size due to the complete depletion. The increase of dark saturation current with decreasing grain size was predicted due to an increase in the recombination current.

Fatigue crack propagation behavior of stainless steel welds

NASA Astrophysics Data System (ADS)

Kusko, Chad S.

The fatigue crack propagation behavior of austenitic and duplex stainless steel base and weld metals has been investigated using various fatigue crack growth test procedures, ferrite measurement techniques, light optical microscopy, stereomicroscopy, scanning electron microscopy, and optical profilometry. The compliance offset method has been incorporated to measure crack closure during testing in order to determine a stress ratio at which such closure is overcome. Based on this method, an empirically determined stress ratio of 0.60 has been shown to be very successful in overcoming crack closure for all da/dN for gas metal arc and laser welds. This empirically-determined stress ratio of 0.60 has been applied to testing of stainless steel base metal and weld metal to understand the influence of microstructure. Regarding the base metal investigation, for 316L and AL6XN base metals, grain size and grain plus twin size have been shown to influence resulting crack growth behavior. The cyclic plastic zone size model has been applied to accurately model crack growth behavior for austenitic stainless steels when the average grain plus twin size is considered. Additionally, the effect of the tortuous crack paths observed for the larger grain size base metals can be explained by a literature model for crack deflection. Constant Delta K testing has been used to characterize the crack growth behavior across various regions of the gas metal arc and laser welds at the empirically determined stress ratio of 0.60. Despite an extensive range of stainless steel weld metal FN and delta-ferrite morphologies, neither delta-ferrite morphology significantly influence the room temperature crack growth behavior. However, variations in weld metal da/dN can be explained by local surface roughness resulting from large columnar grains and tortuous crack paths in the weld metal.

Monitoring fungal growth on brown rice grains using rapid and non-destructive hyperspectral imaging.

PubMed

Siripatrawan, U; Makino, Y

2015-04-16

This research aimed to develop a rapid, non-destructive, and accurate method based on hyperspectral imaging (HSI) for monitoring spoilage fungal growth on stored brown rice. Brown rice was inoculated with a non-pathogenic strain of Aspergillus oryzae and stored at 30 °C and 85% RH. Growth of A. oryzae on rice was monitored using viable colony counts, expressed as colony forming units per gram (CFU/g). The fungal development was observed using scanning electron microscopy. The HSI system was used to acquire reflectance images of the samples covering the visible and near-infrared (NIR) wavelength range of 400-1000 nm. Unsupervised self-organizing map (SOM) was used to visualize data classification of different levels of fungal infection. Partial least squares (PLS) regression was used to predict fungal growth on rice grains from the HSI reflectance spectra. The HSI spectral signals decreased with increasing colony counts, while conserving similar spectral pattern during the fungal growth. When integrated with SOM, the proposed HSI method could be used to classify rice samples with different levels of fungal infection without sample manipulation. Moreover, HSI was able to rapidly identify infected rice although the samples showed no symptoms of fungal infection. Based on PLS regression, the coefficient of determination was 0.97 and root mean square error of prediction was 0.39 log (CFU/g), demonstrating that the HSI technique was effective for prediction of fungal infection in rice grains. The ability of HSI to detect fungal infection at early stage would help to prevent contaminated rice grains from entering the food chain. This research provides scientific information on the rapid, non-destructive, and effective fungal detection system for rice grains. Copyright © 2015 Elsevier B.V. All rights reserved.

Fatigue behavior and encrustation characteristics of nanocrystalline metals

NASA Astrophysics Data System (ADS)

Lai, Li-Chung

The nanocrstalline (NC) metals have been reported to have high mechanical performance owing to it's small grain interior and a large volume fraction of grain boundary (GB) atoms. Small grain leads to the forbidden dislocation activities in grain interior while GB activities become dominant due to a higher volume fraction of GB atoms. Regarding the fatigue response to nanocrstalline metals, it has been reported that decreasing grain led to both significantly improvement on the fatigue-endurance limit and deleterious effect on the resistance to subcritical fatigue crack propagation. The increases endurance limit has been attributed to the greater resistance to fatigue crack initiation at near-surface regions. On the other hand, the less resistance to fatigue crack growth were resulted from less tortuous fatigue crack profiles supported by the deflection/closure theory. However, it has never been studied the influence of proceeding and pre-existing defects on the fatigue performance considering the difference response of NC structure from than coarse grain (CG) structure. In the present work, the influence of electrical discharge machining (EDM) and surface defects on the fatigue behavior of both conventional cold-rolled CG and electro-deposited (ED) NC Ni were investigated. The experimental results revealed considerable influence by EDM on the fatigue strength of NC Ni, while it has little or no affect on that for CG Ni. Specifically, EDM led to a 50 to 75% reduction in fatigue strength for NC Ni despite a relatively small depth of EDM affected material (˜ 1% of width). Rationale for this effect can be attributed to grain growth, microcracks, and a higher sulfur content at the GBs in the EDM affected zone. In addition, the pre-existing surface defects that appear to be due to impurity segregation near the electro-deposition substrate significantly reduced the fatigue resistance of ED NC Ni. In order to understand the fatigued behavior in NC Ni, crack tip grain structures were investigated using transmission electron microscope (TEM). Crack tip grain growth was observed at early state of crack propagation with low stress intensity factor (K ˜ 6 MPa m 1/2). As K increased, the size of grain growth zone increased exponentially in width and crack propagation behavior transmitted from interganular to transgranular. It appears that this transmission is associated with grain growth. The coalesced grains due to grain rotation/GB diffusion created larger paths for more extended dislocation movement. Dislocation activities become less forbidden and the dislocation-slip mechanism can be dominant leading to a more plastically transgranular fracture. In addition to fatigue study of ED NC Ni, encrustation on ED NC Ti was investigated. The use of materials for medical applications in the urinary tract is hampered by the formation of calcium-based crystalline deposits, generally referred to as encrustation, that act as precursors to urinary stones. Anecdotal evidence suggests that titanium can possess encrustation-resistant properties in vivo and may be useful in urologic applications. To test the utility of coating surfaces with nanostructured titanium, several forms of materials were submersed in artificial urine with saturating concentrations of calcium for a period of 14 days. The specimens were then analyzed using scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS) to determine the extent of encrustation on the surface of the various samples. Our observations indicate that nanostructured titanium offers superior resistance to encrustation when compared to polyurethane, polyvinyl chloride or conventional coarser grained titanium. Further studies investigating the use of nanostructured titanium in urologic applications are warranted.

Influence of grain size and texture prior to warm rolling on microstructure, texture and magnetic properties of Fe-6.5 wt% Si steel

NASA Astrophysics Data System (ADS)

Xu, H. J.; Xu, Y. B.; Jiao, H. T.; Cheng, S. F.; Misra, R. D. K.; Li, J. P.

2018-05-01

Fe-6.5 wt% Si steel hot bands with different initial grain size and texture were obtained through different annealing treatment. These bands were then warm rolled and annealed. An analysis on the evolution of microstructure and texture, particularly the formation of recrystallization texture was studied. The results indicated that initial grain size and texture had a significant effect on texture evolution and magnetic properties. Large initial grains led to coarse deformed grains with dense and long shear bands after warm rolling. Such long shear bands resulted in growth advantage for {1 1 3} 〈3 6 1〉 oriented grains during recrystallization. On the other hand, sharp {11 h} 〈1, 2, 1/h〉 (α∗-fiber) texture in the coarse-grained sample led to dominant {1 1 2} 〈1 1 0〉 texture after warm rolling. Such {1 1 2} 〈1 1 0〉 deformed grains provided massive nucleation sites for {1 1 3} 〈3 6 1〉 oriented grains during subsequent recrystallization. These {1 1 3} 〈3 6 1〉 grains were confirmed to exhibit an advantage on grain growth compared to γ-fiber grains. As a result, significant {1 1 3} 〈3 6 1〉 texture was developed and unfavorable γ-fiber texture was inhibited in the final annealed sheet. Both these aspects led to superior magnetic properties in the sample with largest initial grain size. The magnetic induction B8 was 1.36 T and the high frequency core loss P10/400 was 17.07 W/kg.

Rheology of ice I at low stress and elevated confining pressure

USGS Publications Warehouse

Durham, W.B.; Stern, L.A.; Kirby, S.H.

2001-01-01

Triaxial compression testing of pure, polycrystalline water ice I at conditions relevant to planetary interiors and near-surface environments (differential stresses 0.45 to 10 MPa, temperatures 200 to 250 K, confining pressure 50 MPa) reveals that a complex variety of rheologies and grain structures may exist for ice and that rheology of ice appears to depend strongly on the grain structures. The creep of polycrystalline ice I with average grain size of 0.25 mm and larger is consistent with previously published dislocation creep laws, which are now extended to strain rates as low as 2 ?? 10-8s-1. When ice I is reduced to very fine and uniform grain size by rapid pressure release from the ice II stability field, the rheology changes dramatically. At 200 and 220 K the rheology matches the grain-size-sensitive rheology measured by Goldsby and Kohlstedt [1997, this issue] at 1 atm. This finding dispels concerns that the Goldsby and Kohlstedt results were influenced by mechanisms such as microfracturing and cavitation, processes not expected to operate at elevated pressures in planetary interiors. At 233 K and above, grain growth causes the fine-grained ice to become more creep resistant. Scanning electron microscopy investigation of some of these deformed samples shows that grains have markedly coarsened and the strain hardening can be modeled by normal grain growth and the Goldsby and Kohlstedt rheology. Several samples also displayed very heterogeneous grain sizes and high aspect ratio grain shapes. Grain-size-sensitive creep and dislocation creep coincidentally contribute roughly equal amounts of strain rate at conditions of stress, temperature, and grain size that are typical of terrestrial and planetary settings, so modeling ice dynamics in these settings must include both mechanisms. Copyright 2001 by the American Geophysical Union.

Fe/Mn in olivine of carbonaceous meteorites

NASA Technical Reports Server (NTRS)

Steele, Ian M.

1993-01-01

Olivines in primitive meteorites show a range of Fe/Mn both within one grain and among grains suggesting that they have recorded changing conditions during or after growth. Because olivine should be an early forming phase, Fe/Mn is used here to infer these earliest conditions. Initial Fe/Mn in cores of isolated, euhedral forsterite in both C2 and C3 meteorites ranges from 25 to 35 but differs at grain edge. Murchison (C2) forsterites show Fe/Mn approaching 1.0 at the grain edge while Ornans Fe/Mn is near 60 at grain edge. These values are lower than the matrix Fe/Mn for both meteorites and the distinct difference in zoning profile indicates different processes operating during and after grain growth. The Fe/Mn of bulk samples from a particular source such as the Moon is nearly constant. Individual samples show variation suggesting that there is some fractionation of Mn from Fe. Minerals have their individual ranges of Fe/Mn which has been used to recognize different types of olivine within one meteorite. Extreme values of Fe/Mn below 1.0 occur in forsterite from some IDP's, UOC matrix, and C1 meteorites. There are apparently no detailed studies of Fe/Mn variation within single olivine grains. Forsterite grains in C2 and C3 carbonaceous chondrites show complex zoning, and the nearly pure forsterites (Fo greater than approximately 99.5) have high levels of some minor elements including Ti, Al, V, and Sc. There is disagreement on the original source of these grains and both chondrule and vapor growth have been proposed. In addition, there is clear evidence that diffusion has affected the outer margins but in some cases the whole grain. Within the cores, the FeO range is limited, and if growing under constant conditions, the Fe/Mn should be near constant as there is little fractionation of Mn from Fe by forsterite. Additionally, there are apparently no co-crystallizing phases as evidenced by a lack of common inclusions in the forsterites. These observations are now followed by analyses of isolated olivine grains in C2 and C3 meteorites.

Brain Growth Rate Abnormalities Visualized in Adolescents with Autism

PubMed Central

Hua, Xue; Thompson, Paul M.; Leow, Alex D.; Madsen, Sarah K.; Caplan, Rochelle; Alger, Jeffry R.; O’Neill, Joseph; Joshi, Kishori; Smalley, Susan L.; Toga, Arthur W.; Levitt, Jennifer G.

2014-01-01

Autism spectrum disorder (ASD) is a heterogeneous disorder of brain development with wide-ranging cognitive deficits. Typically diagnosed before age 3, ASD is behaviorally defined but patients are thought to have protracted alterations in brain maturation. With longitudinal magnetic resonance imaging (MRI), we mapped an anomalous developmental trajectory of the brains of autistic compared to those of typically developing children and adolescents. Using tensor-based morphometry (TBM), we created 3D maps visualizing regional tissue growth rates based on longitudinal brain MRI scans of 13 autistic and 7 typically developing boys (mean age/inter-scan interval: autism 12.0 ± 2.3 years/2.9 ± 0.9 years; control 12.3 ± 2.4/2.8 ± 0.8). The typically developing boys demonstrated strong whole-brain white matter growth during this period, but the autistic boys showed abnormally slowed white matter development (p = 0.03, corrected), especially in the parietal (p = 0.008), temporal (p = 0.03) and occipital lobes (p =0.02). We also visualized abnormal overgrowth in autism in some gray matter structures, such as the putamen and anterior cingulate cortex. Our findings reveal aberrant growth rates in brain regions implicated in social impairment, communication deficits and repetitive behaviors in autism, suggesting that growth rate abnormalities persist into adolescence. TBM revealed persisting growth rate anomalies long after diagnosis, which has implications for evaluation of therapeutic effects. PMID:22021093

The influence of diet composition upon growth and development of sandhill cranes

USGS Publications Warehouse

Serafin, J.A.

1982-01-01

Experiments were conducted to evaluate the effect of protein, metabolizable energy, and sulfur amino acid content of five diets upon growth and development of captive Florida Sandhill Crane (Grus canadensis pratensis) and Greater Sandhill Crane (G. c. tabida) chicks raised under controlled conditions. A high protein (32%) diet resulted in faster growth than that obtained when a lower protein (24%) ration was supplied. Florida Sandhill Crane chicks fed a diet containing 2,160 kcal/kg grew significantly slower than chicks fed a ration containing 2,830 kcal/kg. Reducing the sulfur amino acid content of a ration containing 24% protein from 0.88% to 0.73% significantly slowed the growth of young cranes. A 17% incidence of leg disorders and a 25% incidence of wing abnormalities occurred between 7 and 28 days of age among Greater Sandhill Cranes fed a high protein diet. Florida Sandhill Cranes grew slower than Greater Sandhill Cranes irrespective of the type of ration they were provided and did not develop leg or wing abnormalities. Abnormalities invariably developed only in the most rapidly growing Greater Sandhill Cranes. Diets that promoted slower growth reduced the incidence of abnormalities. A ration formulated to contain a low (0.73%) sulfur amino acid level appeared to be the most suitable for slowing growth rates of captive-reared Sandhill Cranes and reducing the risk of abnormaiwing or leg development.

Brain growth rate abnormalities visualized in adolescents with autism.

PubMed

Hua, Xue; Thompson, Paul M; Leow, Alex D; Madsen, Sarah K; Caplan, Rochelle; Alger, Jeffry R; O'Neill, Joseph; Joshi, Kishori; Smalley, Susan L; Toga, Arthur W; Levitt, Jennifer G

2013-02-01

Autism spectrum disorder is a heterogeneous disorder of brain development with wide ranging cognitive deficits. Typically diagnosed before age 3, autism spectrum disorder is behaviorally defined but patients are thought to have protracted alterations in brain maturation. With longitudinal magnetic resonance imaging (MRI), we mapped an anomalous developmental trajectory of the brains of autistic compared with those of typically developing children and adolescents. Using tensor-based morphometry, we created 3D maps visualizing regional tissue growth rates based on longitudinal brain MRI scans of 13 autistic and seven typically developing boys (mean age/interscan interval: autism 12.0 ± 2.3 years/2.9 ± 0.9 years; control 12.3 ± 2.4/2.8 ± 0.8). The typically developing boys demonstrated strong whole brain white matter growth during this period, but the autistic boys showed abnormally slowed white matter development (P = 0.03, corrected), especially in the parietal (P = 0.008), temporal (P = 0.03), and occipital lobes (P = 0.02). We also visualized abnormal overgrowth in autism in gray matter structures such as the putamen and anterior cingulate cortex. Our findings reveal aberrant growth rates in brain regions implicated in social impairment, communication deficits and repetitive behaviors in autism, suggesting that growth rate abnormalities persist into adolescence. Tensor-based morphometry revealed persisting growth rate anomalies long after diagnosis, which has implications for evaluation of therapeutic effects. Copyright © 2011 Wiley Periodicals, Inc.

Fine-grained zirconium-base material

DOEpatents

Van Houten, G.R.

1974-01-01

A method is described for making zirconium with inhibited grain growth characteristics, by the process of vacuum melting the zirconium, adding 0.3 to 0.5% carbon, stirring, homogenizing, and cooling. (Official Gazette)

Implications of Grain Size Evolution for the Effective Stress Exponent in Ice

NASA Astrophysics Data System (ADS)

Behn, M. D.; Goldsby, D. L.; Hirth, G.

2016-12-01

Viscous flow in ice has typically been described by the Glen law—a non-Newtonian, power-law relationship between stress and strain-rate with a stress exponent n 3. The Glen law is attributed to grain-size-insensitive dislocation creep; however, laboratory and field studies demonstrate that deformation in ice is strongly dependent on grain size. This has led to the hypothesis that at sufficiently low stresses, ice flow is controlled by grain boundary sliding [1], which explicitly incorporates the grain-size dependence of ice rheology. Yet, neither dislocation creep (n 4), nor grain boundary sliding (n 1.8), have stress exponents that match the value of n 3 for the Glen law. Thus, although the Glen law provides an approximate description of ice flow in glaciers and ice sheets, its functional form cannot be explained by a single deformation mechanism. Here we seek to understand the origin of the n 3 dependence of the Glen law through a new model for grain-size evolution in ice. In our model, grain size evolves in response to the balance between dynamic recrystallization and grain growth. To simulate these processes we adapt the "wattmeter" [2], originally developed within the solid-Earth community to quantify grain size in crustal and mantle rocks. The wattmeter posits that grain size is controlled by a balance between the mechanical work required for grain growth and dynamic grain size reduction. The evolution of grain size in turn controls the relative contributions of dislocation creep and grain boundary sliding, and thus the effective stress exponent for ice flow. Using this approach, we first benchmark our grain size evolution model on experimental data and then calculate grain size in two end-member scenarios: (1) as a function of depth within an ice-sheet, and (2) across an ice-stream margin. We show that the calculated grain sizes match ice core observations for the interior of ice sheets. Furthermore, owing to the influence of grain size on strain rate, the variation in grain size with deformation conditions results in an effective stress exponent intermediate between grain boundary sliding and dislocation creep. [1] Goldsby & Kohlstedt, JGR, 2001; [2] Austin & Evans, Geology, 1997

DOE Office of Scientific and Technical Information (OSTI.GOV)

Antonysamy, A.A., E-mail: alphons.antonysamy@GKNAerospace.com; Meyer, J., E-mail: jonathan.meyer@eads.com; Prangnell, P.B., E-mail: philip.prangnell@manchester.ac.uk

With titanium alloys, the solidification conditions in Additive Manufacturing (AM) frequently lead to coarse columnar β-grain structures. The effect of geometry on the variability in the grain structure and texture, seen in Ti-6Al-4V alloy components produced by Selective Electron Beam Melting (SEBM), has been investigated. Reconstruction of the primary β-phase, from α-phase EBSD data, has confirmed that in bulk sections where in-fill “hatching” is employed growth selection favours columnar grains aligned with an <001> {sub β} direction normal to the deposited powder layers; this results in a coarse β-grain structure with a strong < 001 > {sub β} fibre texturemore » (up 8 x random) that can oscillate between a near random distribution around the fibre axis and cube reinforcement with build height. It is proposed that this behaviour is related to the highly elongated melt pool and the raster directions alternating between two orthogonal directions every layer, which on average favours grains with cube alignment. In contrast, the outline, or “contour”, pass produces a distinctly different grain structure and texture resulting in a skin layer on wall surfaces, where nucleation occurs off the surrounding powder and growth follows the curved surface of the melt pool. This structure becomes increasingly important in thin sections. Local heterogeneities have also been found within different section transitions, resulting from the growth of skin grain structures into thicker sections. Texture simulations have shown that the far weaker α-texture (∼ 3 x random), seen in the final product, arises from transformation on cooling occurring with a near random distribution of α-plates across the 12 variants possible from the Burgers relationship. - Highlights: • Distinctly different skin and bulk structures are produced by the contour and hatching passes. • Bulk sections contain coarse β-grains with a < 001 > fibre texture in the build direction. • This oscillates between a random distribution around the axis and cube reinforcement. • In the skin layer nucleation occurs off the surrounding powder bed and growth occurs inwards. • Simulations show that a weak α-texture results from a random distribution across habit variants.« less

Maternal dietary intakes of refined grains during pregnancy and growth through the first 7 y of life among children born to women with gestational diabetes.

PubMed

Zhu, Yeyi; Olsen, Sjurdur F; Mendola, Pauline; Halldorsson, Thorhallur I; Yeung, Edwina H; Granström, Charlotta; Bjerregaard, Anne A; Wu, Jing; Rawal, Shristi; Chavarro, Jorge E; Hu, Frank B; Zhang, Cuilin

2017-07-01

Background: Refined grains, a major source of dietary carbohydrates, have been related to impaired glucose homeostasis and obesity. Emerging animal data suggest that in utero exposure to dietary refined carbohydrates may predispose offspring to an obese phenotype, indicating a potential role for nutritional programming in the early origins of obesity, but intergenerational human data are lacking. Objective: We prospectively investigated refined-grain intake during pregnancy in association with offspring growth through age 7 y among high-risk children born to women with gestational diabetes mellitus (GDM). Design: The analysis included 918 mother-singleton child dyads from the Danish National Birth Cohort. Offspring body mass index z scores (BMIZs) were calculated by using weight and length or height measured at birth, 5 and 12 mo, and 7 y. Overweight or obesity was defined by WHO cutoffs. Linear and Poisson regressions were used, with adjustment for maternal demographic, lifestyle, and dietary factors. Results: Refined-grain intake during pregnancy was positively associated with offspring BMIZ (adjusted β per serving increase per day: 0.09; 95% CI: 0.02, 0.15) and risk of overweight or obesity at age 7 y [adjusted RR (aRR) comparing the highest with the lowest quartile: 1.80; 95% CI: 1.09, 2.98; P -trend = 0.032]. The association appeared to be more pronounced among children who were breastfed <6 mo. The substitution of 1 serving refined grains/d with an equal serving of whole grains during pregnancy was related to a 10% reduced risk of offspring overweight or obesity at 7 y of age (aRR: 0.90; 95% CI: 0.82, 0.98). No associations were observed between refined-grain intake and infant growth. Conclusions: Higher maternal refined-grain intake during pregnancy was significantly related to a greater BMIZ and a higher risk of overweight or obesity at age 7 y among children born after pregnancies complicated by GDM. The findings highlight pregnancy as a potential window of susceptibility associated with offspring growth and obesity risk among this high-risk population. Data with longer follow-up are warranted. © 2017 American Society for Nutrition.

Fusion zone microstructure and porosity in electron beam welds of an α+β titanium alloy

NASA Astrophysics Data System (ADS)

Mohandas, T.; Banerjee, D.; Kutumba Rao, V. V.

1999-03-01

The effect of electron beam welding parameters on fusion zone (FZ) microstructure and porosity in a Ti -6.8 Al -3.42 Mo -1.9 Zr -0.21 Si alloy (Russian designation VT 9) has been investigated. It has been observed that the FZ grain width increased continuously with increase in heat input when the base metal was in the β heat-treated condition, while in the α+β heat-treated base metal welds, the FZ grain width increased only after a threshold energy input. The difference is attributed to both the weld thermal cycle and the pinning effect of equiaxed primary alpha on grain growth in the heat-affected zone (HAZ) of α+β heat-treated base metal. Postweld heat treatment (PWHT) in the subtransus and supertransus regions did not alter the columnar grain morphology in the FZ, possibly due to the lack of enough driving force for the formation of new grains by the breaking up of the columnar grains and grain boundary movement for grain growth. As the PWHTs were conducted in a furnace, the role of thermal gradients can be ruled out. Intragranular microstructure in the aswelded condition consisted of hexagonal martensite. The scale of the martensite laths depended on welding speed. The highest porosity was observed at intermediate welding speeds. At low speeds, a majority of pores formed at the fusion boundary, while at high speeds, occurrence of porosity was maximum at the weld center. The trends on porosity can be explained on the basis of solubility of hydrogen in titanium as a function of temperature and the influence of weld thermal cycle on nucleation, growth, and escape of hydrogen gas bubbles. The porosity at slow welding speeds is low because sufficient time exists for the nucleation, growth, and escape of hydrogen gas bubbles, while insufficient time exists for the nucleation of gas bubbles at high welding speeds. The effect of pickling of joint surface, vacuum annealing of the base metal, and successive remelting of the weld metal has also been investigated.

Transformation and precipitation in vanadium treated steels

NASA Astrophysics Data System (ADS)

Vassiliou, Andreas D.

A series of carbon manganese steels containing varying amounts of carbon, vanadium and nitrogen was investigated in relation to the solubility of VC and VN in austenite, the grain coarsening characteristics of austenite, the tempering of martensite and other structures, the transformation during continuous cooling, the effect of vanadium addition and increasing nitrogen content on the thermo-mechanical processing of austenite, and the transformation of various morphologies of austenite to ferrite.The sites for preferential nucleation and growth of ferrite were identified and the effect of ferrite grain size inhomogeneity was investigated with a view to minimising it.The C/N ratio in the V(CN) precipitates was largely controlled by C/N ratio in the steel and it was also influenced by the austenitising treatment. As expected, the solubility of VN was less than that of VC.A systematic investigation of austenitising time and temperature on the grain coarsening characteristics was carried out showing the effects of vanadium, carbon and nitrogen. It was tentatively suggested that C-C and N-N clustering in the vanadium free steels controlled the grain growth whereas in the presence of vanadium, it was shown that VN and VC pinned the austenite grain boundaries and restricted grain growth. However coarsening or solution of VC and VN allowed the grain bondaries to migrate and grain coarsening occurred. The grain coarsening temperature was controlled predominantly by VN, whilst the VC dissolved frequently below the grain coarsening temperature.In the as quenched martensite, increasing nitrogen progressively increased the as quenched hardness, and the hardness also greatly increased with increasing carbon and vanadium added together. Examining the precipitation strengthening in tempered martensite showed that in the absence of vanadium, martensite softened progressively with increasing temperature and time. Vanadium additions increased the hardness level during low temperature tempering and at higher tempering temperature introduced secondary hardening. The intensity of secondary hardening increased with increasing vanadium, whereas austenitising temperature had little or no effect. The softening after the secondary hardening was faster after austenitising at the higher temperature and when recrystallisation occurred at the highest tempering temperatures, the hardness was lower due to coarse recrystallised ferrite.Isothermal transformation studies showed that vanadium additions raised the Ar3 temperature and accelerated ferrite nucleation, whilst the growth of ferrite was delayed due to the formation of V(CN) interphase and general precipitation pinning, of the transformation front. Increasing nitrogen content in the V-steel increased the incubation period for ferrite nucleation and increasingly reduced the ferrite growth by increasing V(CN) precipitation pinning of the transformation front.Transformation during continuous cooling was examined in relation to the effect of vanadium, carbon and nitrogen together with the effect of austenitising temperature. Increasing austenitising temperature increased the austenite grain size, and it then became apparent that increasing vanadium, carbon and nitrogen increased the hardenability and raised the hardness level of the jominy curve for the non-martensitic products. (Abstract shortened by ProQuest.).

Stable Eutectoid Transformation in Nodular Cast Iron: Modeling and Validation

NASA Astrophysics Data System (ADS)

Carazo, Fernando D.; Dardati, Patricia M.; Celentano, Diego J.; Godoy, Luis A.

2017-01-01

This paper presents a new microstructural model of the stable eutectoid transformation in a spheroidal cast iron. The model takes into account the nucleation and growth of ferrite grains and the growth of graphite spheroids. Different laws are assumed for the growth of both phases during and below the intercritical stable eutectoid. At a microstructural level, the initial conditions for the phase transformations are obtained from the microstructural simulation of solidification of the material, which considers the divorced eutectic and the subsequent growth of graphite spheroids up to the initiation of the stable eutectoid transformation. The temperature field is obtained by solving the energy equation by means of finite elements. The microstructural (phase change) and macrostructural (energy balance) models are coupled by a sequential multiscale procedure. Experimental validation of the model is achieved by comparison with measured values of fractions and radius of 2D view of ferrite grains. Agreement with such experiments indicates that the present model is capable of predicting ferrite phase fraction and grain size with reasonable accuracy.

Grain Formation Processes in Oxygen-Rich Circumstellar Outflows: Testing the Metastable Eutectic Condensation Hypothesis and Measuring Atom-Grain & Grain-Grain Sticking Coefficients (A Sub-orbital Investigation)

NASA Astrophysics Data System (ADS)

Nuth, Joseph

An experimentally-based model of grain formation in oxygen-rich circumstellar outflows that includes vapor-solid nucleation, grain growth, thermal annealing and grain aggregation in sufficient detail to predict the spectral energy distribution (SED) of the shells for comparison with observations of a wide range of stellar sources still lacks critical data. In order to gather this data we propose to conduct a series of laboratory experiments using our proven experimental system and microgravity condensation, growth and grain aggregation experiments on sounding rockets with a flight-proven payload provided by Dr. Yuki Kimura of Hokkaido University. We have proposed that solids from a hydrogen-rich, supersaturated, Fe-Mg-SiO vapor condense at metastable eutectic points in this ternary phase diagram. Because the FeOMgO system is totally miscible (has no eutectic or metastable eutectic compositions), this predicts that condensates will be pure Mg-silicate or Fe-silicate grains and that no primary condensate will be a mixed Fe-Mg-silicate. We have shown that this observation leads to a logical explanation as to why pure magnesium olivine and enstatite minerals are detected in circumstellar winds rather than the mixed Mg-Fe-silicate grains that might otherwise be expected (Rietmeijer, Nuth & Karner, 1999). This simplifying hypothesis has been built into our models of circumstellar condensation and growth. However, these experimental results require confirmation and testing since they should apply to other, quite similar condensable systems. We propose to test this hypothesis by condensing solids from the Fe-Mg-AlO ternary vapor system. Since FeO-MgO miscibility also applies to this system, the primary condensates from such a vapor should consist of pure amorphous Fe-aluminates and Mg-aluminates. No mixed Fe-Mg-spinels should be detected as primary condensates if this hypothesis is correct, just as none were detected for the FeO-MgO-SiO system. Confirmation of this hypothesis would be a major step in establishing a simple, chemical kinetic model for the nucleation, growth and annealing of circumstellar oxide dust. Since strong convective flows in the terrestrial laboratory make it almost impossible to measure the growth and aggregation of freshly condensed, refractory grains, we will conduct experiments in microgravity to eliminate these flows. We propose to measure the efficiency of grain growth from simple SiO, AlO and FeO vapors and the sticking coefficients for dust coagulation via analyses of the grain morphology and size distribution of condensates collected and returned to earth during each rocket experiment. We will discuss the unique experimental systems used to produce our analog samples and the general nature of these materials. We note that these experimental systems were not designed to produce samples at equilibrium like typical petrologic systems. Indeed, they were designed to make samples that will help us to understand the properties of materials produced under highly dynamic conditions, quite far from equilibrium, that are often found in nature wherever steep temperature, pressure and/or compositional gradients result in highly unequilibrated solid systems. This design is an advantage as it presents the chance to compare and contrast samples produced at equilibrium with unequilibrated samples in order to identify distinctive traits that could be used to identify conditions under which natural samples have been formed. We will describe both the laboratory system and the rocket payload. We will present data from previous experiments in these systems and discuss why recovery of the flight payload and analyses of the particles produced is essential to build a rigorous, laboratory-based model of grain formation in astrophysical environments.

Calcium and zirconium as texture modifiers during rolling and annealing of magnesium–zinc alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bohlen, Jan, E-mail: jan.bohlen@hzg.de; Wendt, Joachim; Nienaber, Maria

2015-03-15

Rolling experiments were carried out on a ternary Mg–Zn–Ca alloy and its modification with zirconium. Short time annealing of as-rolled sheets is used to reveal the microstructure and texture development. The texture of the as-rolled sheets can be characterised by basal pole figures with split peak towards the rolling direction (RD) and a broad transverse angular spread of basal planes towards the transverse direction (TD). During annealing the RD split peaks as well as orientations in the sheet plane vanish whereas the distribution of orientations tilted towards the TD remains. It is shown in EBSD measurements that during rolling bandsmore » of twin containing structures form. During subsequent annealing basal orientations close to the sheet plane vanish based on a grain nucleation and growth mechanism of recrystallisation. Orientations with tilt towards the TD remain in grains that do not undergo such a mechanism. The addition of Zr delays texture weakening. - Highlights: • Ca in Mg–Zn-alloys contributes to a significant texture weakening during rolling and annealing. • Grain nucleation and growth in structures consisting of twins explain a texture randomisation during annealing. • Grains with transverse tilt of basal planes preferentially do not undergo a grain nucleation and growth mechanism. • Zr delays the microstructure and texture development.« less

Integrating Epitaxial-Like Pb(Zr,Ti)O3 Thin-Film into Silicon for Next-Generation Ferroelectric Field-Effect Transistor

PubMed Central

Park, Jae Hyo; Kim, Hyung Yoon; Jang, Gil Su; Seok, Ki Hwan; Chae, Hee Jae; Lee, Sol Kyu; Kiaee, Zohreh; Joo, Seung Ki

2016-01-01

The development of ferroelectric random-access memory (FeRAM) technology with control of grain boundaries would result in a breakthrough for new nonvolatile memory devices. The excellent piezoelectric and electrical properties of bulk ferroelectrics are degraded when the ferroelectric is processed into thin films because the grain boundaries then form randomly. Controlling the nature of nucleation and growth are the keys to achieving a good crystalline thin-film. However, the sought after high-quality ferroelectric thin-film has so far been thought to be impossible to make, and research has been restricted to atomic-layer deposition which is extremely expensive and has poor reproducibility. Here we demonstrate a novel epitaxial-like growth technique to achieve extremely uniform and large rectangular-shaped grains in thin-film ferroelectrics by dividing the nucleation and growth phases. With this technique, it is possible to achieve 100-μm large uniform grains, even made available on Si, which is large enough to fabricate a field-effect transistor in each grain. The electrical and reliability test results, including endurance and retention test results, were superior to other FeRAMs reported so far and thus the results presented here constitute the first step toward the development of FeRAM using epitaxial-like ferroelectric thin-films. PMID:27005886

Formation of intra-island grain boundaries in pentacene monolayers.

PubMed

Zhang, Jian; Wu, Yu; Duhm, Steffen; Rabe, Jürgen P; Rudolf, Petra; Koch, Norbert

2011-12-21

To assess the formation of intra-island grain boundaries during the early stages of pentacene film growth, we studied sub-monolayers of pentacene on pristine silicon oxide and silicon oxide with high pinning centre density (induced by UV/O(3) treatment). We investigated the influence of the kinetic energy of the impinging molecules on the sub-monolayer growth by comparing organic molecular beam deposition (OMBD) and supersonic molecular beam deposition (SuMBD). For pentacene films fabricated by OMBD, higher pentacene island-density and higher polycrystalline island density were observed on UV/O(3)-treated silicon oxide as compared to pristine silicon oxide. Pentacene films deposited by SuMBD exhibited about one order of magnitude lower island- and polycrystalline island densities compared to OMBD, on both types of substrates. Our results suggest that polycrystalline growth of single islands on amorphous silicon oxide is facilitated by structural/chemical surface pinning centres, which act as nucleation centres for multiple grain formation in a single island. Furthermore, the overall lower intra-island grain boundary density in pentacene films fabricated by SuMBD reduces the number of charge carrier trapping sites specific to grain boundaries and should thus help achieving higher charge carrier mobilities, which are advantageous for their use in organic thin-film transistors.

OsGRF4 controls grain shape, panicle length and seed shattering in rice.

PubMed

Sun, Pingyong; Zhang, Wuhan; Wang, Yihua; He, Qiang; Shu, Fu; Liu, Hai; Wang, Jie; Wang, Jianmin; Yuan, Longping; Deng, Huafeng

2016-10-01

Traits such as grain shape, panicle length and seed shattering, play important roles in grain yield and harvest. In this study, the cloning and functional analysis of PANICLE TRAITS 2 (PT2), a novel gene from the Indica rice Chuandali (CDL), is reported. PT2 is synonymous with Growth-Regulating Factor 4 (OsGRF4), which encodes a growth-regulating factor that positively regulates grain shape and panicle length and negatively regulates seed shattering. Higher expression of OsGRF4 is correlated with larger grain, longer panicle and lower seed shattering. A unique OsGRF4 mutation, which occurs at the OsmiRNA396 target site of OsGRF4, seems to be associated with high levels of OsGRF4 expression, and results in phenotypic difference. Further research showed that OsGRF4 regulated two cytokinin dehydrogenase precursor genes (CKX5 and CKX1) resulting in increased cytokinin levels, which might affect the panicle traits. High storage capacity and moderate seed shattering of OsGRF4 may be useful in high-yield breeding and mechanized harvesting of rice. Our findings provide additional insight into the molecular basis of panicle growth. © 2016 The Authors. Journal of Integrative Plant Biology Published by John Wiley & Sons Australia, Ltd on behalf of Institute of Botany, Chinese Academy of Sciences.

Coarse-grained modeling of crystal growth and polymorphism of a model pharmaceutical molecule.

PubMed

Mandal, Taraknath; Marson, Ryan L; Larson, Ronald G

2016-10-04

We describe a systematic coarse-graining method to study crystallization and predict possible polymorphs of small organic molecules. In this method, a coarse-grained (CG) force field is obtained by inverse-Boltzmann iteration from the radial distribution function of atomistic simulations of the known crystal. With the force field obtained by this method, we show that CG simulations of the drug phenytoin predict growth of a crystalline slab from a melt of phenytoin, allowing determination of the fastest-growing surface, as well as giving the correct lattice parameters and crystal morphology. By applying meta-dynamics to the coarse-grained model, a new crystalline form of phenytoin (monoclinic, space group P2 1 ) was predicted which is different from the experimentally known crystal structure (orthorhombic, space group Pna2 1 ). Atomistic simulations and quantum calculations then showed the polymorph to be meta-stable at ambient temperature and pressure, and thermodynamically more stable than the conventional orthorhombic crystal at high pressure. The results suggest an efficient route to study crystal growth of small organic molecules that could also be useful for identification of possible polymorphs as well.

Investigation of consolidation kinetics and microstructure evolution of Al alloys in direct metal laser sintering using phase field simulation

NASA Astrophysics Data System (ADS)

Bimal Satpathy, Bubloom; Nandy, Jyotirmoy; Sahoo, Seshadev

2018-03-01

Direct metal laser sintering is one of the very efficient processes which comes under the field of additive manufacturing and is capable of producing products of good mechanical and physical properties. The process parameters affect the physical and mechanical properties of the final products. Rapid solidification plays an important role in the consolidation kinetics as the powdered material sinters and forms a polycrystalline structure. In the recent times, the enormous use of computational modeling has helped in examining the utility of final products in a wide range of applications. In this study, a phase field model has been implemented to foresee the consolidation kinetics during the liquid state sintering. Temperature profiles have been used to study the densification behavior and neck growth which is caused by the surface diffusion of particles at initial stage. Later, importance of grain boundary and the volume diffusion during densification process is analyzed. It is also found that with rise in temperature, neck growth also increases rapidly due to the interaction of adjacent grains through grain boundary diffusion and stabilization of grain growth.

Enhancement effects of dietary wheat distiller's dried grains with solubles on growth, immunology, and resistance to Edwardsiella ictaluri challenge of channel catfish, Ictalurus punctatus

USDA-ARS?s Scientific Manuscript database

This study evaluated the effects of the inclusion of wheat distiller’s dried grains with solubles (WDDGS) at levels of 0 (control), 10, 20, 30 and 40% without (diets 2-5) and with (diets 6-9) lysine supplementation, as substitutes of soybean meal and corn meal mixture on growth, body composition, he...

A novel pre-sintering technique for the growth of Y-Ba-Cu-O superconducting single grains from raw metal oxides

NASA Astrophysics Data System (ADS)

Li, Jiawei; Shi, Yun-Hua; Dennis, Anthony R.; Namburi, Devendra Kumar; Durrell, John H.; Yang, Wanmin; Cardwell, David A.

2017-09-01

Most established top seeded melt growth (TSMG) processes of bulk, single grain Y-Ba-Cu-O (YBCO) superconductors are performed using a mixture of pre-reacted precursor powders. Here we report the successful growth of large, single grain YBCO samples by TSMG with good superconducting properties from a simple precursor composition consisting of a sintered mixture of the raw oxides. The elimination of the requirement to synthesize precursor powders in a separate process prior to melt processing has the potential to reduce significantly the cost of bulk superconductors, which is essential for their commercial exploitation. The growth morphology, microstructure, trapped magnetic field and critical current density, J c, at different positions within the sample and maximum levitation force of the YBCO single grains fabricated by this process are reported. Measurements of the superconducting properties show that the trapped filed can reach 0.45 T and that a zero field J c of 2.5 × 104 A cm-2 can be achieved in these samples. These values are comparable to those observed in samples fabricated using pre-reacted, high purity commercial oxide precursor powders. The experimental results are discussed and the possibility of further improving the melt process using raw oxides is outlined.

Effects of Grain Orientation on Cu6Sn5 Growth Behavior in Cu6Sn5-Reinforced Composite Solder Joints During Electromigration

NASA Astrophysics Data System (ADS)

Han, Jing; Wang, Yan; Tan, Shihai; Guo, Fu

2018-02-01

Electromigration is a major reliability problem in composite solder joints. Due to the anisotropy of the β-Sn crystal structure, the Sn grain orientations present in the solder matrix dominate the principal failure mechanism in solder joints under electric current stressing. In this work, the Cu6Sn5 growth behavior in Cu6Sn5-reinforced composite solder joints with three different Sn grain orientations was investigated at current density of 104 A/cm2 at room temperature. Micron-sized Cu particles were added to Sn-3.5Ag solder at 2% volume fraction using an in situ method. After current stressing for 528 h, the polarity effect in the composite solder joint was greatest for an angle ( θ) between the c-axis and electron flow direction of 30°, resulting in higher growth rate of Cu6Sn5 in the solder matrix compared with composite solder joints with θ of 60° or 90°. There were no noticeable changes in the composite solder joint with θ of 90°. The growth behavior of Cu6Sn5, Cu atomic motion, and Cu diffusivity in the composite solder joints with different Sn grain orientations were analyzed in detail.

Lifetime studies of high power rhodium/tungsten and molybdenum electrodes for application to AMTEC (alkali metal thermal-to-electric converter)

NASA Technical Reports Server (NTRS)

Williams, R. M.; Jeffries-Nakamura, B.; Underwood, M. L.; O'Connor, D.; Ryan, M. A.; Kikkert, S.; Bankston, C. P.

1990-01-01

A detailed and fundamental model for the electrochemical behavior of AMTEC electrodes is developed which can aid in interpreting the processes which occur during prolonged operation of these electrodes. Because the sintering and grain growth of metal particles is also a well-understood phenomenon, the changes in electrode performance which accompany its morphological evolution may be anticipated and modeled. The grain growth rate observed for porous Mo AMTEC electrodes is significantly higher than that predicted from surface diffusion data obtained at higher temperatures and incorporated into the grain growth model. The grain growth observed under AMTEC conditions is also somewhat higher than that measured for Mo films on BASE (beta-alumina solid electrolyte) substrates in vacuum or at similar temperatures. Results of modeling indicate that thin Mo electrodes may show significant performance degradation for extended operation (greater than 10,000 h) at higher operating temperatures (greater than 1150 K), whereas W/Rh and W/Pt electrodes are expected to show adequate performance at 1200 K for lifetimes greater than 10,000 h. It is pointed out that current collection grids and leads must consist of refractory metals such as Mo and W which do not accelerate sintering or metal migration.

CVD growth of large-grain graphene on Cu(111) thin films

NASA Astrophysics Data System (ADS)

Miller, David L.; Diederichsen, Kyle M.; Keller, Mark W.

2013-03-01

Chemical vapor deposition of graphene on polycrystalline Cu foils has produced high quality films with carrier mobility approaching that of exfoliated graphene. Growth on single-crystal films of Cu has received less attention, despite its potential advantages for graphene quality and its importance for eventual applications. This is likely due to the difficulty of obtaining large (>= 1 mm) grains in Cu thin films, as well as dewetting and roughening of Cu films at temperatures near the Cu melting point (1084 C). We found that 450 nm of Cu(111), epitaxially grown by sputtering onto Al2O3(0001), formed > 1 mm grains when annealed at 1065 C for 40 minutes in 40 Torr of Ar and 2.5 mTorr of H2. After this annealing, adding 3 mTorr of CH4 for 8 minutes produced a monolayer graphene film covering > 99 % of the Cu surface. Stopping growth after 4 minutes produced dendritic graphene islands with 6-fold symmetry and diameter of 20 μm to 100 μm . After growth, the Cu film remained smooth except for thermal grooving at grain boundaries and a few holes of diameter ~ 10 μm where Cu dewetted completely (~ 10 holes on each 5 mm x 6 mm chip).

Exogenous application of plant growth regulators (PGRs) induces chilling tolerance in short-duration hybrid maize.

PubMed

Waqas, Muhammad Ahmed; Khan, Imran; Akhter, Muhammad Javaid; Noor, Mehmood Ali; Ashraf, Umair

2017-04-01

Chilling stress hampers the optimal performance of maize under field conditions precipitously by inducing oxidative stress. To confer the damaging effects of chilling stress, the present study aimed to investigate the effects of some natural and synthetic plant growth regulators, i.e., salicylic acid (SA), thiourea (TU), sorghum water extract (SWE), and moringa leaf extract (MLE) on chilling stress tolerance in autumn maize hybrid. Foliar application of growth regulators at low concentrations was carried out at six leaf (V6) and tasseling stages. An increase in crop growth rate (CGR), leaf area index (LAI), leaf area duration (LAD), plant height (PH), grain yield (GY), and total dry matter accumulation (TDM) was observed in exogenously applied plants as compared to control. In addition, improved physio-biochemical, phenological, and grain nutritional quality attributes were noticed in foliar-treated maize plots as compared to non-treated ones. SA-treated plants reduced 20% electrolyte leakage in cell membrane against control. MLE and SA were proved best in improving total phenolic, relative water (19-23%), and chlorophyll contents among other applications. A similar trend was found for photosynthetic and transpiration rates, whereas MLE and SWE were found better in improving CGR, LAI, LAD, TDM, PH, GY, grains per cob, 1000 grain weight, and biological yield among all treatments including control. TU and MLE have significantly reduced the duration in phenological events of crop at the reproductive stage. MLE, TU, and SA also improved the grain protein, oil, and starch contents as compared to control. Enhanced crop water productivity was also observed in MLE-treated plants. Economic analysis suggested that MLE and SA applications were more economical in inducing chilling stress tolerance under field conditions. Although eliciting behavior of all growth regulators improved morpho-physiological attributes against suboptimal temperature stress conditions, MLE and SA acted as leading agents which proved to be better stress alleviators by improving plant physio-biochemical attributes and maize growth.

A parallelized three-dimensional cellular automaton model for grain growth during additive manufacturing

NASA Astrophysics Data System (ADS)

Lian, Yanping; Lin, Stephen; Yan, Wentao; Liu, Wing Kam; Wagner, Gregory J.

2018-05-01

In this paper, a parallelized 3D cellular automaton computational model is developed to predict grain morphology for solidification of metal during the additive manufacturing process. Solidification phenomena are characterized by highly localized events, such as the nucleation and growth of multiple grains. As a result, parallelization requires careful treatment of load balancing between processors as well as interprocess communication in order to maintain a high parallel efficiency. We give a detailed summary of the formulation of the model, as well as a description of the communication strategies implemented to ensure parallel efficiency. Scaling tests on a representative problem with about half a billion cells demonstrate parallel efficiency of more than 80% on 8 processors and around 50% on 64; loss of efficiency is attributable to load imbalance due to near-surface grain nucleation in this test problem. The model is further demonstrated through an additive manufacturing simulation with resulting grain structures showing reasonable agreement with those observed in experiments.

A parallelized three-dimensional cellular automaton model for grain growth during additive manufacturing

NASA Astrophysics Data System (ADS)

Lian, Yanping; Lin, Stephen; Yan, Wentao; Liu, Wing Kam; Wagner, Gregory J.

2018-01-01

In this paper, a parallelized 3D cellular automaton computational model is developed to predict grain morphology for solidification of metal during the additive manufacturing process. Solidification phenomena are characterized by highly localized events, such as the nucleation and growth of multiple grains. As a result, parallelization requires careful treatment of load balancing between processors as well as interprocess communication in order to maintain a high parallel efficiency. We give a detailed summary of the formulation of the model, as well as a description of the communication strategies implemented to ensure parallel efficiency. Scaling tests on a representative problem with about half a billion cells demonstrate parallel efficiency of more than 80% on 8 processors and around 50% on 64; loss of efficiency is attributable to load imbalance due to near-surface grain nucleation in this test problem. The model is further demonstrated through an additive manufacturing simulation with resulting grain structures showing reasonable agreement with those observed in experiments.

Burst Testing and Analysis of Superalloy Disks With a Dual Grain Microstructure

NASA Technical Reports Server (NTRS)

Gayda, John; Kantzos, Pete

2006-01-01

Elastic-plastic finite element analyses of room temperature burst tests on four superalloy disks were conducted and reported in this paper. Two alloys, Rene 104 (General Electric Aircraft Engines) and Alloy 10 (Honeywell Engines & Systems), were studied. For both alloys an advanced dual microstructure disk, fine grain bore and coarse grain rim, were analyzed and compared with conventional disks with uniform microstructures, coarse grain for Rene 104 and fine grain for Alloy 10. The analysis and experimental data were in good agreement up to burst. At burst, the analysis underestimated the speed and growth of the Rene 104 disks, but overestimated the speed and growth of the Alloy 10 disks. Fractography revealed that the Alloy 10 disks displayed significant surface microcracking and coalescence in comparison to Rene 104 disks. This phenomenon may help explain the differences between the Alloy 10 disks and the Rene 104 disks, as well as the observed deviations between analytical and experimental data at burst.

Effects of Laves phase particles on recovery and recrystallization behaviors of Nb-containing FeCrAl alloys

DOE PAGES

Sun, Zhiqian; Edmondson, Philip D.; Yamamoto, Yukinori

2017-11-15

The microstructures and mechanical properties of deformed and annealed Nb-containing FeCrAl alloys were investigated. Fine dispersion of Fe 2Nb-type Laves phase particles was observed in the bcc-Fe matrix after applying a thermomechanical treatment, especially along grain/subgrain boundaries, which effectively stabilized the recovered and recrystallized microstructures compared with the Nb-free FeCrAl alloy. The stability of recovered areas increased with Nb content up to 1 wt%. The recrystallized grain structure in Nb-containing FeCrAl alloys consisted of elongated grains along the rolling direction with a weak texture when annealed below 1100 °C. An abnormal relationship between recrystallized grain size and annealing temperature wasmore » found. Microstructural inhomogeneity in the deformed and annealed states was explained based on the Taylor factor. Annealed Nb-containing FeCrAl alloys showed a good combination of strength and ductility, which is desirable for their application as fuel cladding in light-water reactors.« less

EBSD characterization of the growth mechanism of SiC synthesized via direct microwave heating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jigang, E-mail: wangjigang@seu.edu.cn; Xizang Key Laboratory of Optical Information Processing and Visualization Technology, School of Information Engineering, Xizang Minzu University, Xianyang 712082; Huang, Shan

2016-04-15

Well-crystallized 3C-silicon carbide (SiC) grains/nanowires have been synthesized rapidly and conveniently via direct microwave heating, simply using silicon dioxide powders and artificial graphite as raw materials. The comprehensive characterizations have been employed to investigate the micro-structure of the obtained 3C-SiC products. Results indicated that, different from the classic screw dislocation growth mechanism, the 3C-SiC grains/nanowires synthesized via high-energy vacuum microwave irradiation were achieved through the two-dimension nucleation and laminar growth mechanism. Especially, the electron backscattered diffraction (EBSD) was employed to characterize the crystal planes of the as-grown SiC products. The calculated Euler angles suggested that the fastest-growing crystal planes (211)more » were overlapped gradually. Through the formation of the (421) transformation plane, (211) finally evolved to (220) which existed as the side face of SiC grains. The most stable crystal planes (111) became the regular hexagonal planes in the end, which could be explained by the Bravais rule. The characterization results of EBSD provided important experimental information for the evolution of crystal planes. - Graphical abstract: The formation of 3C-SiC prepared via direct microwave heating follows the mechanism of two-dimension nucleation and laminar growth. - Highlights: • 3C−SiC grains/nanowires were obtained via direct microwave heating. • 3C−SiC followed the mechanism of two-dimension nucleation and laminar growth. • In-situ EBSD analysis provided the experimental evidences of the growth.« less

Evolution of Grain Boundary Precipitates in an Al-Cu-Li Alloy During Aging

NASA Astrophysics Data System (ADS)

Ott, Noémie; Kairy, Shravan K.; Yan, Yuanming; Birbilis, Nick

2017-01-01

The grain boundary microstructure of Al-Cu-Li alloy AA2050 was investigated for different isothermal aging times to rationalize intergranular corrosion (IGC) characteristics. In the underaged condition, the dominant grain boundary precipitates are fine T1 (Al2CuLi). Extended aging revealed that grain boundaries were decorated by large T1 precipitates and S' phase (Al2CuMg), with S' growth not dimensionally constrained. Such a transition in the precipitate type at grain boundaries is a unique feature of the Al-Cu-Li system.

Endocide-Induced Abnormal Growth Forms of Invasive Giant Salvinia (Salvinia molesta).

PubMed

Li, Shiyou; Wang, Ping; Su, Zushang; Lozano, Emily; LaMaster, Olivia; Grogan, Jason B; Weng, Yuhui; Decker, Thomas; Findeisen, John; McGarrity, Monica

2018-05-22

Giant salvinia (Salvinia molesta) is one of the most noxious invasive species in the world. The fern is known to have primary, secondary, and tertiary growth forms, which are also commonly hypothesized as growth stages. The identification of these forms is primarily based on the size and folding status of the floating leaves. However, we identified 12 forms in the greenhouse and the field. Our experiments showed that the folding of floating leaves is a reversible trait dependent on water access. The floating leaves quickly fold in response to water shortage, reducing water loss and needs, decreasing growth, and avoiding trichome damage. The leaves re-open to allow trichomes repel water and enhance growth when having adequate water supply. Larger secondary or tertiary forms do not produce small-leaf primary forms without high intensity stress. These results do not support the hypothesis that three growth forms represent sequential growth stages. The abnormal small-leaf forms are the result of endocide-induced autotoxicity and some of them never grow into other forms. The development of abnormal forms and reversible leaf folding strategy in response to high stress along with rapid asexual reproduction are major adaptive traits contributing to the invasiveness of S. molesta.

The growth receptors and their role in wound healing.

PubMed

Rolfe, Kerstin J; Grobbelaar, Adriaan O

2010-11-01

Abnormal wound healing is a major problem in healthcare today, with both scarring and chronic wounds affecting large numbers of individuals worldwide. Wound healing is a complex process involving several variables, including growth factors and their receptors. Chronic wounds fail to complete the wound healing process, while scarring is considered to be an overzealous wound healing process. Growth factor receptors and their ligands are being investigated to assess their potential in the development of therapeutic strategies to improve wound healing. This review discusses potential therapeutics for manipulating growth factors and their corresponding receptors for the treatment of abnormal wound healing.

Mutant laboratory mice with abnormalities in hair follicle morphogenesis, cycling, and/or structure: an update.

PubMed

Nakamura, Motonobu; Schneider, Marlon R; Schmidt-Ullrich, Ruth; Paus, Ralf

2013-01-01

Human hair disorders comprise a number of different types of alopecia, atrichia, hypotrichosis, distinct hair shaft disorders as well as hirsutism and hypertrichosis. Their causes vary from genodermatoses (e.g. hypotrichoses) via immunological disorders (e.g. alopecia areata, autoimmune cicatrical alopecias) to hormone-dependent abnormalities (e.g. androgenetic alopecia). A large number of spontaneous mouse mutants and genetically engineered mice develop abnormalities in hair follicle morphogenesis, cycling, and/or hair shaft formation, whose analysis has proven invaluable to define the molecular regulation of hair growth, ranging from hair follicle development, and cycling to hair shaft formation and stem cell biology. Also, the accumulating reports on hair phenotypes of mouse strains provide important pointers to better understand the molecular mechanisms underlying human hair growth disorders. Since numerous new mouse mutants with a hair phenotype have been reported since the publication of our earlier review on this matter a decade ago, we present here an updated, tabulated mini-review. The updated annotated tables list a wide selection of mouse mutants with hair growth abnormalities, classified into four categories: Mutations that affect hair follicle (1) morphogenesis, (2) cycling, (3) structure, and (4) mutations that induce extrafollicular events (for example immune system defects) resulting in secondary hair growth abnormalities. This synthesis is intended to provide a useful source of reference when studying the molecular controls of hair follicle growth and differentiation, and whenever the hair phenotypes of a newly generated mouse mutant need to be compared with existing ones. Copyright © 2012 Japanese Society for Investigative Dermatology. Published by Elsevier Ireland Ltd. All rights reserved.

Study of composite thin films for applications in high density data storage

NASA Astrophysics Data System (ADS)

Yuan, Hua

Granular Co-alloy + oxide thin films are currently used as the magnetic recording layer of perpendicular media in hard disk drives. The microstructure of these films is composed mainly of fine (7--10 nm) magnetic grains physically surrounded by oxide phases, which produce magnetic isolation of the grains. As a result, the magnetic switching volume is maintained as small as the physical grain size. Consequently, ample number of magnetic switching units can be obtained in one recording bit, in other words, higher signal to noise ratios (SNR) can be achieved. Therefore, a good understanding and control of the microstructure of the films is very important for high areal density magnetic recording media. Interlayers and seedlayers play important roles in controlling the microstructure in terms of grain size, grain size distribution, oxide segregation and orientation dispersion of the crystallographic texture. Developing novel interlayers or seedlayers with smaller grain size is a key approach to produce smaller grain size in the recording layer. This study focuses on how to achieve smaller grain sizes in the recording layer through novel interlayer/seedlayer materials and processes. It also discusses the resulting microstructure in smaller-grain-size thin films. Metal + oxide (e.g. Ru + SiO2) composite thin films were chosen as interlayer and seedlayer materials due to their unique segregated microstructure. Such layers can be grown epitaxially on top of fcc metal seedlayers with good orientation. It can also provide an epitaxial growth template for the subsequent magnetic layer (recording layer). The metal and oxide phases in the composite thin films are immiscible. The final microstructure of the interlayer depends on factors, such as, sputtering pressure, oxide species, oxide volume fraction, thickness, alloy composition, temperature etc. Moreover, it has been found that the microstructure of the composite thin films is affected mostly by two important factors---oxide volume fraction and sputtering pressure. The latter affects grain size and grain segregation through surface-diffusion modification and the self-shadowing effect. The composite Ru + oxide interlayers were found to have various microstructures under various sputtering conditions. Four characteristic microstructure zones can be identified as a function of oxide volume fraction and sputtering pressure---"percolated" (A), "maze" (T), "granular" (B) and "embedded" (C), based on which, a new structural zone model (SZM) is established for composite thin films. The granular microstructure of zone B is of particular interest for recording media application. The grain size of interlayers is a strong function of pressure, oxide species and oxide volume fraction. Magnetic layers grown on top of these interlayers were found to be significantly affected by the interlayer microstructure. One-to-one grain epitaxial growth is very difficult to achieve when the grain size is too small. As a result, the magnetic properties of smaller grain size magnetic layers deteriorate due to poor growth. This presents a huge challenge to high areal density magnetic recording media. A novel approach of Ar-ion etched Ru seedlayer, which can improve epitaxy between interlayer and magnetic layer is proposed. This method produces interlayer thin films of: (1) smaller grain size and higher nucleation density due to both a rougher seedlayer surface and an oxide addition in the interlayer; (2) good (00.2) texture due to the growth on top of the low pressure deposited Ru seedlayer; (3) dome-shape grain morphology due to the high pressure deposition. Therefore, a significant Ru grain size reduction with enhanced granular morphology and improved grain-to-grain epitaxy with the magnetic layer was achieved. High resolution transmission electron microscopy (TEM) techniques, such as, electron energy loss spectroscopy (EELS), energy-filtered TEM (EFTEM), energy-dispersive X-ray spectroscopy (EDS) and mapping, and high angle annular dark field (HAADF) imaging have been utilized to investigate elemental distribution and grain morphology in composite magnetic thin films of different grain sizes. An oxygen-rich grain shell of about 0.5 ˜ 1 nm thickness is often observed for most media with different grain sizes. Reducing the grain size increases surface to volume ratio. With more surface area, smaller grains are more vulnerable to oxidization, resulting in even greater influence of the oxide on the magnetic properties of the grains.

Preliminary silvicultural recommendations and an updated annotated bibliography for birdseye sugar maple

Treesearch

Don C. Bragg

2008-01-01

The birdseye grain abnormality in sugar maple can greatly enhance its commercial appeal. However, birdseye has been opportunistically exploited, without exploring management strategies that can improve its potential. Even though the initiation and development processes of birdseye maple are still largely unknown, useful silvicultural advice can still be provided for...

Transitional grain-size-sensitive flow of milky quartz aggregates

NASA Astrophysics Data System (ADS)

Fukuda, J. I.; Holyoke, C. W., III; Kronenberg, A. K.

2014-12-01

Fine-grained (~15 μm) milky quartz aggregates exhibit reversible flow strengths in triaxial compression experiments conducted at T = 800-900oC, Pc = 1.5 GPa when strain rates are sequentially decreased (typically from 10-3.5 to 10-4.5 and 10-5.5 s-1), and then returned to the original rate (10-3.5 s-1), while samples that experience grain growth at 1000oC (to 35 μm) over the same sequence of strain rates exhibit an irreversible increase in strength. Polycrystalline quartz aggregates have been synthesized from natural milky quartz powders (ground to 5 μm) by HIP methods at T = 1000oC, Pc = 1.5 GPa and t = 24 hours, resulting in dense, fine-grained aggregates of uniform water content of ~4000 ppm (H/106Si), as indicated by a broad OH absorption band at 3400 cm-1. In experiments performed at 800o and 900oC, grain sizes of the samples are essentially constant over the duration of each experiment, though grain shapes change significantly, and undulatory extinction and deformation lamellae indicate that much of the sample shortening (to 50%) is accomplished, over the four strain-rate steps, by dislocation creep. Differential stresses measured at T = 800oC decrease from 160 to 30 MPa as strain rate is reduced from 10-4.6 to 10-5.5 s-1, and a stress of 140 MPa is measured when strain rate is returned to 10-4.5 s-1. Samples deformed at 1000o and 1100oC experience normal grain growth, with grain boundary energy-driven grain-coarsening textures superposed by undulatory extinction and deformation lamellae. Differential stresses measured at 1000oC and strain rates of 10-3.6, 10-4.6, and 10-5.5 s-1 are 185, 80, and 80 MPa, respectively, while an increased flow stress of 260 MPa is measured (following ~28 hours of prior high temperature deformation and grain growth) when strain rate is returned to 10-3.6 s-1. While all samples exhibit lattice preferred orientations, the stress exponent n inferred for the fine-grained 800oC sample is 1.5 and the stress exponent of the coarse-grained 1000oC sample is between ~3 and 4. Our value for n of fine-grained quartz samples (and previously reported values of n < 3 for quartz aggregates with added water) may attest to a component of diffusion creep and grain boundary sliding that accompanies dislocation creep.

A Pilot Study of Abnormal Growth in Autism Spectrum Disorders and Other Childhood Psychiatric Disorders

ERIC Educational Resources Information Center

Rommelse, Nanda N. J.; Peters, Cindy T. R.; Oosterling, Iris J.; Visser, Janne C.; Bons, Danielle; van Steijn, Daphne J.; Draaisma, Jos; van der Gaag, Rutger-Jan; Buitelaar, Jan. K.

2011-01-01

The aims of the current study were to examine whether early growth abnormalities are (a) comparable in autism spectrum disorders (ASD) and other childhood psychiatric disorders, and (b) specific to the brain or generalized to the whole body. Head circumference, height, and weight were measured during the first 19 months of life in 129 children…

Formation of a Martian Pyroxenite: A Comparative Study of the Nakhlite Meteorites and Theo's Flow

NASA Technical Reports Server (NTRS)

Friedman, R. C.; Taylor, G. J.; Treiman, A. H.

1999-01-01

The unusual composition of the nakhlites, a group of pyroxenitic martian meteorites with young ages, presents an opportunity to learn about nonbasaltic magmatic activity on another planet. However, the limited number of these meteorites makes unraveling their history difficult. A promising terrestrial analog for the formation of the nakhlites is Theo's Flow in Ontario, Canada. This atypical, 120 m-thick flow differentiated in place, forming distinct layered lithologies of peridotite, pyroxenite, and gabbro. Theo's pyroxenite and the nakhlites share strikingly similar petrographies, with concentrated euhedral to subhedral augite grains set in a plagioclase-rich matrix. These two suites of rocks also share specific petrologic features, mineral and whole-rock compositional features, and size and spatial distributions of cumulus grains. The numerous similarities suggest that the nakhlites formed by a similar mechanism in a surface lava flow or shallow intrusion. Their formation could have involved settling of crystals in a phenocryst-laden flow or in situ nucleation and growth of pyroxenes in an ultramafic lava flow. The latter case is more likely and requires steady-state nucleation and growth of clusters of pyroxene grains (and olivine in the nakhlites), circulating in a strongly convecting melt pool, followed by settling and continued growth in a thickening cumulate pile. Trapped pockets of intercumulus liquid in the pile gradually evolved, finally growing Fe-enriched rims on cumulus grains. With sufficient evolution, the melt reached plagioclase supersaturation, causing rapid growth of plagioclase sprays and late-stage mesostasis growth.

The proportion of nitrate in leaf nitrogen, but not changes in root growth, are associated with decreased grain protein in wheat under elevated [CO2].

PubMed

Bahrami, Helale; De Kok, Luit J; Armstrong, Roger; Fitzgerald, Glenn J; Bourgault, Maryse; Henty, Samuel; Tausz, Michael; Tausz-Posch, Sabine

2017-09-01

The atmospheric CO 2 concentration ([CO 2 ]) is increasing and predicted to reach ∼550ppm by 2050. Increasing [CO 2 ] typically stimulates crop growth and yield, but decreases concentrations of nutrients, such as nitrogen ([N]), and therefore protein, in plant tissues and grains. Such changes in grain composition are expected to have negative implications for the nutritional and economic value of grains. This study addresses two mechanisms potentially accountable for the phenomenon of elevated [CO 2 ]-induced decreases in [N]: N uptake per unit length of roots as well as inhibition of the assimilation of nitrate (NO 3 - ) into protein are investigated and related to grain protein. We analysed two wheat cultivars from a similar genetic background but contrasting in agronomic features (Triticum aestivum L. cv. Scout and Yitpi). Plants were field-grown within the Australian Grains Free Air CO 2 Enrichment (AGFACE) facility under two atmospheric [CO 2 ] (ambient, ∼400ppm, and elevated, ∼550ppm) and two water treatments (rain-fed and well-watered). Aboveground dry weight (ADW) and root length (RL, captured by a mini-rhizotron root growth monitoring system), as well as [N] and NO 3 - concentrations ([NO 3 - ]) were monitored throughout the growing season and related to grain protein at harvest. RL generally increased under e[CO 2 ] and varied between water supply and cultivars. The ratio of total aboveground N (TN) taken up per RL was affected by CO 2 treatment only later in the season and there was no significant correlation between TN/RL and grain protein concentration across cultivars and [CO 2 ] treatments. In contrast, a greater percentage of N remained as unassimilated [NO 3 - ] in the tissue of e[CO 2 ] grown crops (expressed as the ratio of NO 3 - to total N) and this was significantly correlated with decreased grain protein. These findings suggest that e[CO 2 ] directly affects the nitrate assimilation capacity of wheat with direct negative implications for grain quality. Crown Copyright © 2017. Published by Elsevier GmbH. All rights reserved.

Effect of local stress fields on twin characteristics in HCP metals

DOE PAGES

Arul Kumar, M.; Beyerlein, Irene Jane; Tomé, Carlos N.

2016-09-01

Here we study the effect of nearest neighboring grains on the propensity for {1012} twin growth in Mg and Zr. Twin lamellae lying within one grain flanked by two neighboring grains with several orientations are considered. The fields of resolved shear stress on the twin system are calculated in the multicrystal using a three-dimensional full-field crystal plasticity Fast Fourier Transform approach. The calculations were carried out for Mg and Zr using slip threshold stresses corresponding to 300K and 76K, respectively, where twin activity is important. We show that the neighboring grain constraint tends to oppose further growth and that themore » critical applied stress needed to overcome this resistance depends on neighboring grain orientation, more strongly in Zr than in Mg. We also present results for a pair of adjacent and parallel twins at various spacings. It is found that their paired interaction increases the resistive forces for twin growth above that for an isolated twin. The critical spacing above which this enhanced resistance is removed is smaller for Zr than Mg. Our analysis reveals that these two disparate responses of Zr and Mg are both a consequence of the fact that Zr is elastically and plastically more anisotropic than Mg. Additional calculations carried out on Ti support this conclusion. Finally, these findings can help explain why, for the same grain size, more twins per grain form in Zr than in Mg, twins in Zr tend to be thinner than those in Mg, and the relationship between the thickness of the twin and its Schmid factor in Zr is not as strong as in Mg.« less

Effects of feeding diets containing highly peroxidized dried distillers grains with solubles and increasing vitamin E levels to wean-finish pigs on growth performance, carcass characteristics, and pork fat composition

USDA-ARS?s Scientific Manuscript database

Lipid peroxidation in animal feed can negatively affect growth performance and meat quality. Weanling pigs (n = 432; BW = 6.6 ± 0.4 kg) were used to evaluate the effects of feeding a peroxidized dried distillers grains with solubles (DDGS) source with three levels of vitamin E (a-tocopheryl acetate)...

Responses of Rapid Viscoanalyzer Profile and Other Rice Grain Qualities to Exogenously Applied Plant Growth Regulators under High Day and High Night Temperatures

PubMed Central

Fahad, Shah; Hussain, Saddam; Saud, Shah; Hassan, Shah; Chauhan, Bhagirath Singh; Khan, Fahad; Ihsan, Muhammad Zahid; Ullah, Abid; Wu, Chao; Bajwa, Ali Ahsan; Alharby, Hesham; Amanullah; Nasim, Wajid; Shahzad, Babar; Tanveer, Mohsin; Huang, Jianliang

2016-01-01

High-temperature stress degrades the grain quality of rice; nevertheless, the exogenous application of plant growth regulators (PGRs) might alleviate the negative effects of high temperatures. In the present study, we investigated the responses of rice grain quality to exogenously applied PGRs under high day temperatures (HDT) and high night temperatures (HNT) under controlled conditions. Four different combinations of ascorbic acid (Vc), alpha-tocopherol (Ve), brassinosteroids (Br), methyl jasmonates (MeJA) and triazoles (Tr) were exogenously applied to two rice cultivars (IR-64 and Huanghuazhan) prior to the high-temperature treatment. A Nothing applied Control (NAC) was included for comparison. The results demonstrated that high-temperature stress was detrimental for grain appearance and milling qualities and that both HDT and HNT reduced the grain length, grain width, grain area, head rice percentage and milled rice percentage but increased the chalkiness percentage and percent area of endosperm chalkiness in both cultivars compared with ambient temperature (AT). Significantly higher grain breakdown, set back, consistence viscosity and gelatinization temperature, and significantly lower peak, trough and final viscosities were observed under high-temperature stress compared with AT. Thus, HNT was more devastating for grain quality than HDT. The exogenous application of PGRs ameliorated the adverse effects of high temperature in both rice cultivars, and Vc+Ve+MejA+Br was the best combination for both cultivars under high temperature stress. PMID:27472200

Postcoalescence evolution of growth stress in polycrystalline films.

PubMed

González-González, A; Polop, C; Vasco, E

2013-02-01

The growth stress generated once grains coalesce in Volmer-Weber-type thin films is investigated by time-multiscale simulations comprising complementary modules of (i) finite-element modeling to address the interactions between grains happening at atomic vibration time scales (~0.1 ps), (ii) dynamic scaling to account for the surface stress relaxation via morphology changes at surface diffusion time scales (~μs-ms), and (iii) the mesoscopic rate equation approach to simulate the bulk stress relaxation at deposition time scales (~sec-h). On the basis of addressing the main experimental evidence reported so far on the topic dealt with, the simulation results provide key findings concerning the interplay between anisotropic grain interactions at complementary space scales, deposition conditions (such as flux and mobility), and mechanisms of stress accommodation-relaxation, which underlies the origin, nature and spatial distribution, and the flux dependence of the postcoalescence growth stress.

Single crystal growth of 67%BiFeO 3 -33%BaTiO 3 solution by the floating zone method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rong, Y.; Zheng, H.; Krogstad, M. J.

The growth conditions and the resultant grain morphologies and phase purities from floating-zone growth of 67%BiFeO3-33%BaTiO3 (BF-33BT) single crystals are reported. We find two formidable challenges for the growth. First, a low-melting point constituent leads to a pre-melt zone in the feed-rod that adversely affects growth stability. Second, constitutional super-cooling (CSC), which was found to lead to dendritic and columnar features in the grain morphology, necessitates slow traveling rates during growth. Both challenges were addressed by modifications to the floating-zone furnace that steepened the temperature gradient at the melt-solid interfaces. Slow growth was also required to counter the effects ofmore » CSC. Single crystals with typical dimensions of hundreds of microns have been obtained which possess high quality and are suitable for detailed structural studies.« less

Single crystal growth of 67%BiFeO3-33%BaTiO3 solution by the floating zone method

NASA Astrophysics Data System (ADS)

Rong, Y.; Zheng, H.; Krogstad, M. J.; Mitchell, J. F.; Phelan, D.

2018-01-01

The growth conditions and the resultant grain morphologies and phase purities from floating-zone growth of 67%BiFeO3-33%BaTiO3 (BF-33BT) single crystals are reported. We find two formidable challenges for the growth. First, a low-melting point constituent leads to a pre-melt zone in the feed-rod that adversely affects growth stability. Second, constitutional super-cooling (CSC), which was found to lead to dendritic and columnar features in the grain morphology, necessitates slow traveling rates during growth. Both challenges were addressed by modifications to the floating-zone furnace that steepened the temperature gradient at the melt-solid interfaces. Slow growth was also required to counter the effects of CSC. Single crystals with typical dimensions of hundreds of microns have been obtained which possess high quality and are suitable for detailed structural studies.

Tumor Endothelial Cells

PubMed Central

Dudley, Andrew C.

2012-01-01

The vascular endothelium is a dynamic cellular “organ” that controls passage of nutrients into tissues, maintains the flow of blood, and regulates the trafficking of leukocytes. In tumors, factors such as hypoxia and chronic growth factor stimulation result in endothelial dysfunction. For example, tumor blood vessels have irregular diameters; they are fragile, leaky, and blood flow is abnormal. There is now good evidence that these abnormalities in the tumor endothelium contribute to tumor growth and metastasis. Thus, determining the biological basis underlying these abnormalities is critical for understanding the pathophysiology of tumor progression and facilitating the design and delivery of effective antiangiogenic therapies. PMID:22393533

Abnormal Canine Bone Development Associated with Hypergravity Exposure

NASA Technical Reports Server (NTRS)

Morgan, J. P.; Fisher, G. L.; McNeill, K. L.; Oyama, J.

1979-01-01

Chronic centrifugation of 85- to 92-day-old Beagles at 2.0 x g and 2.6 x g for 26 weeks during the time of active skeletal growth caused skeletal abnormalities in the radius and the ulna of ten of 11 dogs. The pattern of change mimicked that found in naturally occurring and experimentally induced premature distal ulnar physeal closure or delayed growth at this physis. Minimal changes in bone density were detected by sensitive photon absorptiometric techniques. Skeletal abnormalities also were found in five of the six cage-control dogs, although the run-control dogs were radiographically normal.

Morphology of gold and copper ion-plated coatings

NASA Technical Reports Server (NTRS)

Spalvins, T.

1978-01-01

Copper and gold films (0.2 to 2 microns thick) were ion plated onto polished 304-stainless-steel, glass, mica surfaces. These coatings were examined by SEM for defects in their morphological growth. Three types of defects were distinguished: nodular growth, abnormal or runaway growth, and spits. The cause for each type of defect was investigated. Nodular growth is due to inherent substrate microdefects, abnormal or runaway growth is due to external surface inclusions, and spits are due to nonuniform evaporation (ejection of droplets). All these defects induce stresses and produce porosity in the coatings and thus weaken their mechanical properties. During surface rubbing, large nodules are pulled out, leaving vacancies in the coatings.

Computational study of deformation mechanisms and grain size evolution in granulites - Implications for the rheology of the lower crust

NASA Astrophysics Data System (ADS)

Maierová, Petra; Lexa, Ondrej; Jeřábek, Petr; Schulmann, Karel; Franěk, Jan

2017-05-01

Most of granulite terrains worldwide are characterized by large mean grain sizes of 1 mm or more. An important exception are the high-pressure felsic granulites in the Bohemian Massif, the European Variscan belt. There, recrystallization of original coarse-grained ternary feldspar led to formation of a fine-grained (∼100 μm) mixed matrix dominated by plagioclase and K-feldspar. This change occurred at temperatures of ∼850 °C and was probably caused by chemically induced decomposition related to slight cooling and enhanced by deformation during continental collision. The resulting microstructure shows indications of diffusion creep assisted by melt-enhanced grain-boundary sliding. Further on, minor coarsening occurred associated with deformation by dislocation creep and aggregation of mineral phases. Using a thermodynamics-based model of grain size evolution we show that stability of the fine-grained microstructure crucially depends on Zener pinning in the two-phase mineral matrix. Pinning efficiently hinders grain growth, and the small grain size that resulted from the ternary feldspar decomposition can be stable even at high temperatures. The late switch from the grain-size-sensitive creep to dislocation creep is rather difficult to explain by temperature and strain rate (or stress) changes only. However, a simple incorporation of melt solidification can successfully simulate this behavior. Alternatively, the switch and the associated grain size growth can be related to mineral phase aggregation at lower pressure-temperature conditions resulting into a decrease of pinning efficiency. This study suggests that the fine grain size of the Bohemian granulites, in contrast to the common coarse-grained type, stems from abrupt recrystallization during the high-pressure high-temperature conditions, and pinning in the fine-grained matrix. Such a process may in some cases significantly and suddenly reduce the strength of the lower continental crust and allow for its efficient redistribution.

Grain Growth in Cu2ZnSnS4 Thin Films Using Sn Vapor Transport for Photovoltaic Applications

NASA Astrophysics Data System (ADS)

Toyama, Toshihiko; Konishi, Takafumi; Seo, Yuichi; Tsuji, Ryotaro; Terai, Kengo; Nakashima, Yuto; Okamoto, Hiroaki; Tsutsumi, Yasuo

2013-07-01

Cu2ZnSnS4 thin films containing grains grown using Sn vapor transport (TVT) were investigated. Structural characterization revealed that the grain sizes were equal to or larger than the film thickness (1-4 µm) and significantly larger than those in the case of growth without TVT (60 nm). Furthermore, no phase separation was detected. Photothermal diffraction spectroscopy revealed that the optical absorption coefficient was very low in the subgap region, 7×101 cm-1, suggesting the suppression of defect formation. Finally, a TVT-processed thin film was used as an absorber in a solar cell, and a conversion efficiency of 6.9% was achieved.

Grain boundary selective oxidation and intergranular stress corrosion crack growth of high-purity nickel binary alloys in high-temperature hydrogenated water

DOE PAGES

Bruemmer, S. M.; Olszta, M. J.; Toloczko, M. B.; ...

2017-11-26

The effects of alloying elements in Ni-5at%X binary alloys on intergranular (IG) corrosion and stress corrosion cracking (SCC) have been assessed in 300–360 °C hydrogenated water at the Ni/NiO stability line. Alloys with Cr or Al additions exhibited grain boundary oxidation and IGSCC, while localized degradation was not observed for pure Ni, Ni-Cu or Ni-Fe alloys. Environment-enhanced crack growth was determined by comparing the response in water and N 2 gas. Lastly, results demonstrate that selective grain boundary oxidation of Cr and Al promoted IGSCC of these Ni alloys in hydrogenated water.

Grain boundary selective oxidation and intergranular stress corrosion crack growth of high-purity nickel binary alloys in high-temperature hydrogenated water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bruemmer, S. M.; Olszta, M. J.; Toloczko, M. B.

The effects of alloying elements in Ni-5at%X binary alloys on intergranular (IG) corrosion and stress corrosion cracking (SCC) have been assessed in 300–360 °C hydrogenated water at the Ni/NiO stability line. Alloys with Cr or Al additions exhibited grain boundary oxidation and IGSCC, while localized degradation was not observed for pure Ni, Ni-Cu or Ni-Fe alloys. Environment-enhanced crack growth was determined by comparing the response in water and N 2 gas. Lastly, results demonstrate that selective grain boundary oxidation of Cr and Al promoted IGSCC of these Ni alloys in hydrogenated water.

Grain boundary selective oxidation and intergranular stress corrosion crack growth of high-purity nickel binary alloys in high-temperature hydrogenated water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bruemmer, S. M.; Olszta, M. J.; Toloczko, M. B.

The effects of alloying elements in Ni-5at%X binary alloys on intergranular (IG) corrosion and stress corrosion cracking (SCC) have been assessed in 300-360°C hydrogenated water at the Ni/NiO stability line. Alloys with Cr or Al additions exhibited grain boundary oxidation and IGSCC, while localized degradation was not observed for pure Ni, Ni-Cu or Ni-Fe alloys. Environment-enhanced crack growth was determined by comparing the response in water and N2 gas. Results demonstrate that selective grain boundary oxidation of Cr and Al promoted IGSCC of these Ni alloys in hydrogenated water.

Microstructural Damage During High-Strain Torsion Experiments on Calcite-Anhydrite Aggregates

NASA Astrophysics Data System (ADS)

Cross, A. J.; Skemer, P. A.

2016-12-01

Ductile shear zones play a critical role in localising deformation in the Earth's crust and mantle. Severe grain size reduction - a ubiquitous feature of natural mylonites - is commonly thought to cause strain weakening via a transition to grain size sensitive deformation mechanisms. Although grain size reduction is modulated by grain growth in single-phase aggregates, grain boundary pinning in well-mixed poly-phase composites can inhibit grain growth, leading to microstructural `damage' which is likely a critical element of strain localization in the lithosphere. While dynamic recrystallization has been widely explored in rock mechanics and materials science, the mechanisms behind phase-mixing remain poorly understood. In this contribution we present results from high-strain, deformation experiments on calcite-anhydrite composites. Experiments were conducted in torsion at T = 500-700°C and P 1.5 GPa, using the new Large Volume Torsion (LVT) solid-medium apparatus, to shear strains of 0.5-30. As shear strain increases, progressive thinning and necking of initially large (≤ 1 mm) calcite domains is observed, resulting in an increase in the proportion of interphase boundaries. Grain-size is negatively correlated with the fraction of interphase boundaries, such that calcite grains in well-mixed regions are significantly smaller than those in single-phase domains. Crucially, progressive deformation leads to a reduction in grain-size beyond the lower limit established by the grain size piezometer for mono-phase calcite, implying microstructural damage. These data therefore demonstrate continued microstructural evolution in two-phase composites that is not possible in single-phase aggregates. These observations mark a new `geometric' mechanism for phase mixing, complementing previous models for phase mixing involving chemical reactions, material diffusion, and/or grain boundary sliding.

Pleiotrophin promotes vascular abnormalization in gliomas and correlates with poor survival in patients with astrocytomas.

PubMed

Zhang, Lei; Kundu, Soumi; Feenstra, Tjerk; Li, Xiujuan; Jin, Chuan; Laaniste, Liisi; El Hassan, Tamador Elsir Abu; Ohlin, K Elisabet; Yu, Di; Olofsson, Tommie; Olsson, Anna-Karin; Pontén, Fredrik; Magnusson, Peetra U; Nilsson, Karin Forsberg; Essand, Magnus; Smits, Anja; Dieterich, Lothar C; Dimberg, Anna

2015-12-08

Glioblastomas are aggressive astrocytomas characterized by endothelial cell proliferation and abnormal vasculature, which can cause brain edema and increase patient morbidity. We identified the heparin-binding cytokine pleiotrophin as a driver of vascular abnormalization in glioma. Pleiotrophin abundance was greater in high-grade human astrocytomas and correlated with poor survival. Anaplastic lymphoma kinase (ALK), which is a receptor that is activated by pleiotrophin, was present in mural cells associated with abnormal vessels. Orthotopically implanted gliomas formed from GL261 cells that were engineered to produce pleiotrophin showed increased microvessel density and enhanced tumor growth compared with gliomas formed from control GL261 cells. The survival of mice with pleiotrophin-producing gliomas was shorter than that of mice with gliomas that did not produce pleiotrophin. Vessels in pleiotrophin-producing gliomas were poorly perfused and abnormal, a phenotype that was associated with increased deposition of vascular endothelial growth factor (VEGF) in direct proximity to the vasculature. The growth of pleiotrophin-producing GL261 gliomas was inhibited by treatment with the ALK inhibitor crizotinib, the ALK inhibitor ceritinib, or the VEGF receptor inhibitor cediranib, whereas control GL261 tumors did not respond to either inhibitor. Our findings link pleiotrophin abundance in gliomas with survival in humans and mice, and show that pleiotrophin promotes glioma progression through increased VEGF deposition and vascular abnormalization. Copyright © 2015, American Association for the Advancement of Science.

Deciphering the roles of specific wheat grain proteins in flour functionality, allergenic potential and the response of the grain to the growth environment

USDA-ARS?s Scientific Manuscript database

Among the wheat gluten proteins, the omega-5 gliadins show some of the most notable changes in response to post-anthesis fertilizer or high temperatures during grain development. These proteins are also associated with the serious food allergy wheat-dependent exercise-induced anaphylaxis (WDEIA). RN...

Final thickness reduction and development of Goss texture in C- and Al-free Fe-3%Si-0.1%Mn-0.012%S electrical steel

NASA Astrophysics Data System (ADS)

Oh, Eun Jee; Heo, Nam Hoe; Koo, Yang Mo

2017-11-01

The correlation between final thickness reduction and development of Goss texture has been investigated in a C- and Al-free Fe-3%Si electrical steel. During final annealing, the annealing texture is transited from {110}⊥ND to {100}⊥ND texture with increasing final thickness reduction. This is due to the decrease in primary grain size after pre-annealing with increasing final thickness reduction which accelerates the selective growth rate of the {100} grains at the expense of the other {hkl} grains. At an optimal final thickness reduction of 75.8%, the high magnetic induction of 1.95 Tesla, which arises from the sharp {110}<001> Goss texture and is comparable to that of conventional grain-oriented electrical steels, is obtained from the C- and Al-free Fe-3%Si-0.1%Mn electrical steel. Such a high magnetic property is produced through the surface-energy-induced selective grain growth of the Goss grains under the lower surface-segregated condition of sulfur which makes the surface energy of the {110} plane lowest among the {hkl} planes.

Multiscale simulation of xenon diffusion and grain boundary segregation in UO₂

DOE PAGES

Andersson, David A.; Tonks, Michael R.; Casillas, Luis; ...

2015-07-01

In light water reactor fuel, gaseous fission products segregate to grain boundaries, resulting in the nucleation and growth of large intergranular fission gas bubbles. The segregation rate is controlled by diffusion of fission gas atoms through the grains and interaction with the boundaries. Based on the mechanisms established from earlier density functional theory (DFT) and empirical potential calculations, diffusion models for xenon (Xe), uranium (U) vacancies and U interstitials in UO₂ have been derived for both intrinsic (no irradiation) and irradiation conditions. Segregation of Xe to grain boundaries is described by combining the bulk diffusion model with a model formore » the interaction between Xe atoms and three different grain boundaries in UO₂ (Σ5 tilt, Σ5 twist and a high angle random boundary), as derived from atomistic calculations. The present model does not attempt to capture nucleation or growth of fission gas bubbles at the grain boundaries. The point defect and Xe diffusion and segregation models are implemented in the MARMOT phase field code, which is used to calculate effective Xe and U diffusivities as well as to simulate Xe redistribution for a few simple microstructures.« less

Processing of high performance (LRE)-Ba Cu O large, single-grain bulk superconductors in air

NASA Astrophysics Data System (ADS)

Hari Babu, N.; Iida, K.; Shi, Y.; Cardwell, D. A.

2006-10-01

We report the fabrication of large (LRE)BCO single-grains with improved superconducting properties for LRE = Nd, Sm and Gd using a practical process via both conventional top seeded melt growth (TSMG) and seeded infiltration-growth (SIG). This process uses a new generic seed crystal that promotes heterogeneous grain nucleation in the required orientation and suppresses the formation of solid solution in a controlled manner within individual grains by the addition of excess BaO2 to the precursor powder. The spatial distribution of the superconducting properties of LRE bulk superconductors as a function of BaO2 addition for large (LRE)BCO grains fabricated in air by TSMG and SIG for LRE = Gd, Sm and Nd are compared. The optimum BaO2 content required to fabricate single-grain (LRE)BCO with high and homogeneous Tc is determined from these experiments for each LRE system. The irreversibility fields of (LRE)BCO bulk superconductors processed in air are as high as those processed in reduced PO2. Critical current densities in excess of 105 A/cm2 at 77 K and higher trapped fields have been achieved in optimized (LRE)BCO superconductors fabricated in air for the first time.

Intrinsic stress response of low and high mobility solute additions to Cu thin films

NASA Astrophysics Data System (ADS)

Kaub, Tyler; Anthony, Ryan; Thompson, Gregory B.

2017-12-01

Thin film stress is frequently controlled through adjustments applied to the processing parameters used during film deposition. In this work, we explore how the use of solutes with different intrinsic growth properties influences the residual growth stress development for a common solvent Cu film. The findings demonstrated that the addition of a high atomic mobility solute, Ag, or a low atomic mobility solute, V, results in both alloy films undergoing grain refinement that scaled with increases in the solute content. This grain refinement was associated with solute segregation and was more pronounced in the Cu(Ag) system. The grain size reduction was also associated with an increase in the tensile stresses observed in both alloy sets. These findings indicate that solutes can be used to control the grain size under the same deposition conditions, as well as alter the stress evolution of a growing thin film.

Grain growth in Class I protostar Per-emb-50: a dust continuum analysis with NOEMA & SMA .

NASA Astrophysics Data System (ADS)

Agurto-Gangas, C.; Pineda, J. E.; Testi, L.; Caselli, P.; Szucs, L.; Tazzari, M.; Dunham, M.; Stephens, I. W.; Miotello, A.

A good understanding of when dust grains grow from sub-micrometer to millimeter sizes occurs is crucial for models of planet formation. This provides the first step towards the production of pebbles and planetesimals in protoplanetary disks. Thanks to detailed studies of the spectral index in Class II disks, it is well established that Class II objects have already dust grains of millimetres sizes, however, it is not clear when in the star formation process this grain growth occurs. Here, we present interferometric data from NOEMA at 3 mm and SMA at 1.3 mm of the Class I protostar, Per-emb-50, to determine the flux density spectral index at mm-wavelengths of the unresolved disk and the surrounding envelope. We find a spectral index in the unresolved disk 30% smaller than the envelope, alpha env=2.18, comparable to values obtained toward Class 0 sources.

ISS-Experiments of Columnar-to-Equiaxed Transition in Solidification Processing

NASA Technical Reports Server (NTRS)

Sturz, Laszlo; Zimmermann, Gerhard; Gandin, Charles, Andre; Billia, Bernard; Magelinck, Nathalie; Nguyen-Thi, Henry; Browne, David John; Mirihanage, Wajira U.; Voss, Daniela; Beckermann, Christoph;

The microstructure and properties of rapidly solidified, dispersion-strengthened NiAl

NASA Technical Reports Server (NTRS)

Jha, S. C.; Ray, R.

1990-01-01

An advanced rapid solidification technology for processing reactive and refractory alloys, utilized to produce large quantities of melt-spun filaments of NiAl, is presented. The melt-spun filaments are pulverized to fine particle sizes, and subsequently consolidated by hot extrusion or hot isostatic pressing. Rapid solidification process gives rise to very fine-grained microstructures. However, exposure to elevated temperature during hot consolidation leads to grain growth. Alloying agents such as borides, carbides, and tungsten can pin the grain boundaries and retard the grain growth. Various alloy compositions are investigated. The eventual goal is to utilize the hot-extruded and forged stock to grow single-crystal NiAl blades for advanced gas-turbine engine applications. Single-crystal NiAl, containing a uniform dispersion of carbide strengthening precipitates, is expected to lead to highly creep-resistant turbine blades, and is of considerable interest to the aerospace propulsion industry.

Microstructural Evaluation of Forging Parameters for Superalloy Disks

NASA Technical Reports Server (NTRS)

Falsey, John R.

2004-01-01

Forgings of nickel base superalloy were formed under several different strain rates and forging temperatures. Samples were taken from each forging condition to find the ASTM grain size, and the as large as grain (ALA). The specimens were mounted in bakelite, polished, etched and then optical microscopy was used to determine grain size. The specimens ASTM grain sizes from each forging condition were plotted against strain rate, forging temperature, and presoak time. Grain sizes increased with increasing forging temperature. Grain sizes also increased with decreasing strain rates and increasing forging presoak time. The ALA had been determined from each forging condition using the ASTM standard method. Each ALA was compared with the ASTM grain size of each forging condition to determine if the grain sizes were uniform or not. The forging condition of a strain rate of .03/sec and supersolvus heat treatment produced non uniform grains indicated by critical grain growth. Other anomalies are noted as well.

On the competing affects of shear heating and grainsize reduction in lithospheric shear zone formation

NASA Astrophysics Data System (ADS)

Foley, B. J.

2017-12-01

Grain-size reduction is thought to play an important role in shear localization within the lithosphere, as mylonites are commonly seen in regions that have undergone intense deformation. However, flow in lithospheric shear zones can also cause heating due to the energy dissipated by deformation. As grain growth is strongly enhanced by warmer temperatures, shear heating may impede grainsize reduction and the formation of mylonite zones. I use models of simple shear, with length-scales representative of lithospheric shear zones and plate boundaries, including shear heating and grainsize evolution. Grain-damage theory is used to represent the evolution of grainsize. The models are used to determine conditions where grainsize reduction dominates versus those where shear heating dominates; if grainsize reduction dominates, then heating is held in check by the drop in viscosity brought about by small grains. On the other hand, if heating dominates then grain-reduction is prevented by fast grain-growth rates. From the numerical models, simple scaling laws are developed that give the stready-state grainsize and temperature rise as a function of strain-rate, background temperature, and parameters for grain-growth and grain-reduction. I find that for parameter ranges constrained by field observations of shear zones and rock deformation experiments, grainsize reduction dominated over shear heating. Very high strain-rates or driving stresses, above what is typically expected in natural shear zones, are needed for shear heating to dominate over grainsize reduction. Also explored is the timescale to reach steady-state grainsize and temperature conditions in a shear zone. For realistic driving stress or strain-rate, timescales to reach steady-state are often very long, on the order of hundreds of millions of years or longer. This might indicate that natural shear zones do not reach steady-state, or that additional processes are important in initiating lithospheric shear localization.

Computer modelling of grain microstructure in three dimensions

NASA Astrophysics Data System (ADS)

Narayan, K. Lakshmi

We present a program that generates the two-dimensional micrographs of a three dimensional grain microstructure. The code utilizes a novel scanning, pixel mapping technique to secure statistical distributions of surface areas, grain sizes, aspect ratios, perimeters, number of nearest neighbors and volumes of the randomly nucleated particles. The program can be used for comparing the existing theories of grain growth, and interpretation of two-dimensional microstructure of three-dimensional samples. Special features have been included to minimize the computation time and resource requirements.

Micromechanical models of delamination in aluminum-lithium alloys

NASA Astrophysics Data System (ADS)

Messner, Mark Christian

Aluminum lithium (Al-Li) alloys are lighter, stiffer, and tougher than conventional aerospace aluminum alloys. Replacing conventional aluminums with Al-Li could substantially decrease the weight and cost of aerospace structures. However, Al-Li alloys often fracture intergranularly via a mechanism called delamination cracking. While secondary delamination cracks can improve the effective toughness of a component, no current model accurately predicts the initiation and growth of intergranular cracks. Since simulations cannot incorporate delamination into a structural model, designers cannot quantify the effect of delamination cracking on a particular component. This uncertainty limits the application of Al-Li alloys. Previous experiments identify microstructural features linked to delamination. Fractography of failed surfaces indicates plastic void growth triggers intergranular failure. Furthermore, certain types of soft/stiff grain boundaries tend to localize void growth and nucleate delamination cracks. This dissertation develops a mechanism for the initiation of delamination on the microscale that accounts for these experimental observations. Microscale simulations of grain boundaries near a long primary crack explore the delamination mechanism on the mesoscale. In these simulations, a physically-based crystal plasticity (CP) model represents the constitutive response of individual grains. This CP model incorporates plastic voriticity correction terms into a standard objective stress rate integration, to accurately account for the kinematics of lattice deformation. The CP model implements slip system hardening with a modular approach to facilitate quick testing and calibration of different theories of hardening. The microscale models reveal soft/stiff grain boundaries develop elevated mean stress and plastic strain as a consequence of the mechanics of the interface. These elevated stresses and strain drive plastic void growth. The results indicate plastic void growth localizes to the grain boundaries even without the presence of material defects, such as precipitate free zones. Microscale simulations also explain the strong T-stress effect often observed in experimental fracture tests on Al-Li alloys. Finally, this dissertation develops a multiscale model of intergranular damage that incorporates the results of the microscale CP simulations. The multiscale model represents the mechanics of microscale deformation near grain boundaries with a simplified compatibility/equilibrium method. The intergranular stresses and strains from the simplified interface model drive a microscale damage index based on the physics of plastic void growth. Finally, a mesh-size independent scheme homogenizes damage on many grain boundaries into a macroscale damage index and projects the damage index to fail a plane of a macroscale structural model. The multiscale damage model, applied to 2195 Al-Li, successfully predicts delamination crack growth in a variety of standard experimental test configurations. The model correctly represents the microscale physics of delamination initiation and growth; after calibration to experimental data it can reliably predict the growth of delamination cracks in a component with any material configuration and loading. Therefore, the multiscale damage model forms the basis of a simulation method that allows designers to predict the development and net effect of delamination cracking in a structural model -- facilitating the application of lightweight Al-Li alloys in high-performance aerospace structures.

Grain boundary oxidation and its effects on high temperature fatigue life

NASA Technical Reports Server (NTRS)

Liu, H. W.; Oshida, Yoshiki

1986-01-01

Fatigue lives at elevated temperatures are often shortened by creep and/or oxidation. Creep causes grain boundary void nucleation and grain boundary cavitation. Grain boundary voids and cavities will accelerate fatigue crack nucleation and propagation, and thereby shorten fatigue life. The functional relationships between the damage rate of fatigue crack nucleation and propagation and the kinetic process of oxygen diffusion depend on the detailed physical processes. The kinetics of grain boundary oxidation penetration was investigated. The statistical distribution of grain boundary penetration depth was analyzed. Its effect on high temperature fatigue life are discussed. A model of intermittent micro-ruptures of grain boundary oxide was proposed for high temperature fatigue crack growth. The details of these studies are reported.

Selection and hydroponic growth of bread wheat cultivars for bioregenerative life support systems

NASA Astrophysics Data System (ADS)

Page, V.; Feller, U.

2013-08-01

As part of the ESA-funded MELiSSA program, the suitability, the growth and the development of four bread wheat cultivars were investigated in hydroponic culture with the aim to incorporate such a cultivation system in an Environmental Control and Life Support System (ECLSS). Wheat plants can fulfill three major functions in space: (a) fixation of CO2 and production of O2, (b) production of grains for human nutrition and (c) production of cleaned water after condensation of the water vapor released from the plants by transpiration. Four spring wheat cultivars (Aletsch, Fiorina, Greina and CH Rubli) were grown hydroponically and compared with respect to growth and grain maturation properties. The height of the plants, the culture duration from germination to harvest, the quantity of water used, the number of fertile and non-fertile tillers as well as the quantity and quality of the grains harvested were considered. Mature grains could be harvested after around 160 days depending on the varieties. It became evident that the nutrient supply is crucial in this context and strongly affects leaf senescence and grain maturation. After a first experiment, the culture conditions were improved for the second experiment (stepwise decrease of EC after flowering, pH adjusted twice a week, less plants per m2) leading to a more favorable harvest (higher grain yield and harvest index). Considerably less green tillers without mature grains were present at harvest time in experiment 2 than in experiment 1. The harvest index for dry matter (including roots) ranged from 0.13 to 0.35 in experiment 1 and from 0.23 to 0.41 in experiment 2 with modified culture conditions. The thousand-grain weight for the four varieties ranged from 30.4 to 36.7 g in experiment 1 and from 33.2 to 39.1 g in experiment 2, while market samples were in the range of 39.4-46.9 g. Calcium levels in grains of the hydroponically grown wheat were similar to those from field-grown wheat, while potassium, magnesium, phosphorus, iron, zinc, copper, manganese and nickel levels tended to be higher in the grains of experimental plants. It remains a challenge for future experiments to further adapt the nutrient supply in order to improve senescence of vegetative plant parts, harvest index and the composition of bread wheat grains.

{l_angle}110{r_angle} dendrite growth in aluminum feathery grains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Henry, S.; Rappaz, M.; Jarry, P.

1998-11-01

Automatic indexing of electron backscattered diffraction patterns, scanning electron microscopy, and optical microscopy observations have been carried out on aluminum-magnesium-silicon, aluminum-copper, and aluminum-silicon alloys directionally solidified or semicontinuously cast using the direct chill casting process. From these combined observations, it is shown that the feathery grains are made of {l_angle}110{r_angle} primary dendrite trunks (e.g., [011{bar 1}]) split in their centers by a coherent (111) twin plane. The average spacing of the dendrite trunks in the twin plane (about 10 to 20 {micro}m) is typically one order of magnitude smaller than that separating successive rows of trunks (or twin planes). Themore » [011{bar 1}] orientation of these trunks is close to the thermal gradient direction (typically within 15 deg)--a feature probably resulting from a growth competition mechanism similar to that occurring during normal <100> columnar dendrite growth. On both sides of these trunks, secondary dendrite arms also grow along {l_angle}110{r_angle} directions. Their impingement creates wavy noncoherent twin boundaries between the coherent twin planes. In the twin plane, evidence is shown that {l_angle}110{r_angle} branching mechanisms lead to the propagation of the twinned regions, to the regular arrangement of the primary dendrite trunks along a [{bar 2}11] direction, and to coherent planar twin boundaries. From these observations, it is concluded that the feathery grains are probably the result of a change from a normal <100> to a {l_angle}110{r_angle} surface tension/attachment kinetics anisotropy growth mode. Finally, the proposed mechanisms of leathery grain growth are further supported by the observation of {l_angle}110{r_angle} dendrite growth morphologies in thin aluminum-zinc coatings.« less

Processing and Characterization of NiTi Shape Memory Alloy Particle Reinforced Sn-In Solders

DTIC Science & Technology

2006-12-01

solders generally operate at a high homologous temperature. Thermally induced grain growth, mechanical stress-induced grain growth and recrystallization ...the number of I/O connects available for flip chip as compared to the wirebond chip For interconnection and packaging, Pb-Sn and eutectic 63Sn...lower melting point is desired. The maximum use temperature for this alloy is around 120°C due to the fact that the eutectic reaction happened at

Graphene templated Directional Growth of an Inorganic Nanowire

DTIC Science & Technology

2015-03-23

ammonium persulphate, (NH4)2S2O8, at room tempera- ture for 17 h (Fig. 1a). Various types of gold precursor, such as gold nanoparticles or gold...directions and grain boundaries in polycrystalline graphene using TEM or even scanning electron microscopy (SEM), as shown in Fig. 1g, h . Because the...directionGraphene Nanowire Grain boundary Nanowire axis directions g h e f i Figure 1 | Directional growth of inorganic nanowires on graphene. a

Grain boundary modification to suppress lithium penetration through garnet-type solid electrolyte

NASA Astrophysics Data System (ADS)

Hongahally Basappa, Rajendra; Ito, Tomoko; Morimura, Takao; Bekarevich, Raman; Mitsuishi, Kazutaka; Yamada, Hirotoshi

2017-09-01

Garnet-type solid electrolytes are one of key materials to enable practical usage of lithium metal anode for high-energy-density batteries. However, it suffers from lithium growth in pellets on charging, which causes short circuit. In this study, grain boundaries of Li6.5La3Zr1.5Ta0.5O12 (LLZT) pellets are modified with Li2CO3 and LiOH to investigate the influence of the microstructure of grain boundaries on lithium growth and to study the mechanism of the lithium growth. In spite of similar properties (relative density of ca. 96% and total ionic conductivity of 7 × 10-4 S cm-1 at 25 °C), the obtained pellets exhibit different tolerance on the short circuit. The LLZT pellets prepared from LiOH-modified LLZT powders exhibit rather high critical current density of 0.6 mA cm-2, at which short circuit occurs. On the other hand, the LLZT pellets without grain boundary modification short-circuited at 0.15 mA cm-2. Microstructural analyses by means of SEM, STEM and EIS suggest that lithium grows through interconnected open voids, and reveal that surface layers such as Li2CO3 and LiOH are not only plug voids but also facilitate the sintering of LLZT to suppress the lithium growth. The results indicate a strategy towards short-circuit-free lithium metal batteries.

One-step growth of thin film SnS with large grains using MOCVD.

PubMed

Clayton, Andrew J; Charbonneau, Cecile M E; Tsoi, Wing C; Siderfin, Peter J; Irvine, Stuart J C

2018-01-01

Thin film tin sulphide (SnS) films were produced with grain sizes greater than 1 μm using a one-step metal organic chemical vapour deposition process. Tin-doped indium oxide (ITO) was used as the substrate, having a similar work function to molybdenum typically used as the back contact, but with potential use of its transparency for bifacial illumination. Tetraethyltin and ditertiarybutylsulphide were used as precursors with process temperatures 430-470 °C to promote film growth with large grains. The film stoichiometry was controlled by varying the precursor partial pressure ratios and characterised with energy dispersive X-ray spectroscopy to optimise the SnS composition. X-ray diffraction and Raman spectroscopy were used to determine the phases that were present in the film and revealed that small amounts of ottemannite Sn 2 S 3 was present when SnS was deposited on to the ITO using optimised growth parameters. Interaction at the SnS/ITO interface to form Sn 2 S 3 was deduced to have resulted for all growth conditions.

Morphology transition of the primary silicon particles in a hypereutectic A390 alloy in high pressure die casting.

PubMed

Wang, J; Guo, Z; Song, J L; Hu, W X; Li, J C; Xiong, S M

2017-11-03

The microstructure of a high-pressure die-cast hypereutectic A390 alloy, including PSPs, pores, α-Al grains and Cu-rich phases, was characterized using synchrotron X-ray tomography, together with SEM, TEM and EBSD. The Cu-rich phases exhibited a net morphology and distributed at the boundaries of the α-Al grains, which in turn surrounded the PSPs. Statistical analysis of the reconstructed 1000 PSPs showed that both equivalent diameter and shape factor of the PSPs exhibited a unimodal distribution with peaks corresponding to 25 μm and 0.78, respectively.) PSPs morphology with multiple twinning were observed and morphological or growth transition of the PSPs from regular octahedral shape (with a shape factor of 0.85 was mainly caused by the constraint of the Cu-rich phases. In particular, the presence of the Cu-rich phases restricted the growth of the α-Al grains, inducing stress on the internal silicon particles, which caused multiple twinning occurrence with higher growth potential and consequently led to growth transitions of the PSPs.

Molecular Dynamics Study of High Symmetry Planar Defect Evolution during Growth of CdTe/CdS Films

DOE PAGES

Chavez, Jose Juan; Zhou, Xiao W.; Almeida, Sergio F.; ...

2017-12-15

The growth dynamics and evolution of intrinsic stacking faults, lamellar, and double positioning twin grain boundaries were explored using molecular dynamics simulations during the growth of CdTe homoepitaxy and CdTe/CdS heteroepitaxy. Initial substrate structures were created containing either stacking fault or one type of twin grain boundary, and films were subsequently deposited to study the evolution of the underlying defect. Results show that during homoepitaxy the film growth was epitaxial and the substrate’s defects propagated into the epilayer, except for the stacking fault case where the defect disappeared after the film thickness increased. In contrast, films grown on heteroepitaxy conditionsmore » formed misfit dislocations and grew with a small angle tilt (within ~5°) of the underlying substrate’s orientation to alleviate the lattice mismatch. Grain boundary proliferation was observed in the lamellar and double positioning twin cases. Finally, our study indicates that it is possible to influence the propagation of high symmetry planar defects by selecting a suitable substrate defect configuration, thereby controlling the film defect morphology.« less

Molecular Dynamics Study of High Symmetry Planar Defect Evolution during Growth of CdTe/CdS Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chavez, Jose Juan; Zhou, Xiao W.; Almeida, Sergio F.

The growth dynamics and evolution of intrinsic stacking faults, lamellar, and double positioning twin grain boundaries were explored using molecular dynamics simulations during the growth of CdTe homoepitaxy and CdTe/CdS heteroepitaxy. Initial substrate structures were created containing either stacking fault or one type of twin grain boundary, and films were subsequently deposited to study the evolution of the underlying defect. Results show that during homoepitaxy the film growth was epitaxial and the substrate’s defects propagated into the epilayer, except for the stacking fault case where the defect disappeared after the film thickness increased. In contrast, films grown on heteroepitaxy conditionsmore » formed misfit dislocations and grew with a small angle tilt (within ~5°) of the underlying substrate’s orientation to alleviate the lattice mismatch. Grain boundary proliferation was observed in the lamellar and double positioning twin cases. Finally, our study indicates that it is possible to influence the propagation of high symmetry planar defects by selecting a suitable substrate defect configuration, thereby controlling the film defect morphology.« less

Muscovite-Dehydration Melting: A Textural Study of a Key Reaction in Transforming Continental Margin Strata Into a Migmatitic Orogenic Core

NASA Astrophysics Data System (ADS)

Dyck, B. J.; St Onge, M. R.; Waters, D. J.; Searle, M. P.

2015-12-01

Metamorphosed continental margin sedimentary sequences, which comprise the dominant tectonostratigraphic assemblage exposed in orogenic hinterlands, are crucial to understanding the architecture and evolution of collisional mountain belts. This study explores the textural effect of anatexis in amphibolite-grade conditions and documents the mineral growth mechanisms that control nucleation and growth of K-feldspar, sillimanite and silicate melt. The constrained textural evolution follows four stages: 1) Nucleation - K-feldspar is documented to nucleate epitaxially on isomorphic plagioclase in quartzofeldspathic (psammitic) domains, whereas sillimanite nucleates in the Al-rich (pelitic) domain, initially on [001] mica planes. The first melt forms at the site of muscovite breakdown. 2) Chemically driven growth - In the quartzofeldspathic domain, K-feldspar progressively replaces plagioclase by a K+ - Na+ cation transfer reaction, driven by the freeing of muscovite-bound K+ during breakdown of the mica. Sillimanite forms intergrowths with the remaining hydrous melt components, contained initially in ovoid clots. 3) Merge and coarsening - With an increase in pressure, melt and sillimanite migrate away from clots along grain boundaries. A melt threshold is reached once the grain-boundary network is wetted by melt, increasing the length-scale of diffusion, resulting in grain boundary migration and grain-size coarsening. The melt threshold denotes the transition to an open-system on the lithology scale, where melt is a transient phase. 4) Residual melt crystallization - Residual melt crystallizes preferentially on existing peritectic grains as anatectic quartz, plagioclase, and K-feldspar. As the system cools and closes, grain growth forces melt into the intersections of grain-boundaries, recognized as irregular shaped melt films, or as intergrowths of the volatile-rich phases (i.e. Tur-Ms-Ap). In the Himalayan metamorphic core these processes result in the formation of: pelitic K-feldspar augen gneiss, stockwork leucogranites, and an effective strengthening of the hinterland, as evidenced by a switch in tectonic deformation style, from thin-skinned cover sequence thrust imbrication and folding to out-of-sequence basement-involved thick-skinned thrusting and folding.

Remote sensing and modelling of vegetation dynamics for early estimation and spatial analysis of grain yields in semiarid context in central Tunisia

NASA Astrophysics Data System (ADS)

Chahbi, Aicha; Zribi, Mehrez; Lili-Chabaane, Zohra

2016-04-01

In arid and semi-arid areas, population growth, urbanization, food security and climate change have an impact on agriculture in general and particular on the cereal production. Therefore to improve food security in arid countries, crop canopy monitoring and yield forecasting cereals are needed. Many models, based on the use of remote sensing or agro-meteorological models, have been developed to estimate the biomass and grain yield of cereals. Through the use of a rich database, acquired over a period of two years for more than 80 test fields, and from optical satellite SPOT/HRV images, the aim of the present study is to evaluate the feasibility of two yield prediction approaches. The first approach is based on the application of the semi-empirical growth model SAFY, developed to simulate the dynamics of the LAI and the grain yield, at the field scale. The model is able to reproduce the time evolution of the leaf area index of all fields with acceptable error. However, an inter-comparison between ground yield measurements and SAFY model simulations reveals that the yields are under-estimated by this model. We can explain the limits of the semi-empirical model SAFY by its simplicity and also by various factors that were not considered (fertilization, irrigation,...). To improve the yield estimation, a new approach is proposed: the grain yield is estimated in function of the LAI in the growth period between 25 March and 5 April. The LAI of this period is estimated by SAFY model. A linear relationship is developed between the measured grain yield and the LAI area of the maximum growth period.This approach is robust, the measured and estimated grain yields are well correlated. Following the validation of this approach, yield estimations are proposed for the entire studied site using the SPOT/HRV images.

Planetesimal formation by sweep-up coagulation

NASA Astrophysics Data System (ADS)

Windmark, Fredrik; Birnstiel, Til; Ormel, Chris W.; Dullemond, Cornelis P.

2013-07-01

The formation of planetesimals is often accredited to collisional sticking of dust grains in the protoplanetary disk. The exact process is however unknown, as collisions between larger aggregates tend to lead to fragmentation or bouncing rather than sticking. These growth barriers tend to halt the dust growth already at millimeters or centimeters in size, which is far below the kilometer-sizes that are needed for gravity to aid in the accretion. To study how far dust coagulation can proceed, we have developed a new collision model based on the latest laboratory experiments, and have used it together with a dust-size evolution code capable of resolving all grain interactions in the protoplanetary disk. We find that for the general dust population, bouncing and fragmenting collisions prevent the growth above millimeter-sizes. However, a small number of lucky particles can grow larger than the rest by only interacting at low, sticky velocities. As they grow, they become increasingly resilient to fragmentation caused by the small grains. In this way, two populations are formed: One which remains small due to the collisional barriers, and one that continues to grow by sweeping up the smaller grains around them.

Spectroscopic infrared extinction mapping as a probe of grain growth in IRDCs

NASA Astrophysics Data System (ADS)

Lim, Wanggi; Carey, Sean J.

2014-07-01

We present photometric and spectroscopic tests of MIR to FIR extinction laws toward IRDC G028.36+00.07, a potential site of massive star formation. Lim & Tan (2014, hereafter LT14) developed methods of FIR extinction mapping of this source using Spitzer-MIPS 24 micron and Herschel-PACS 70 micron images, and extending the MIR 8 micron mapping methods of (Butler & Tan 2012, hereafter BT12), finding evidence for grain growth in the highest mass surface density regions. Here we present initial results of spectroscopic infrared extinction (SIREX) mapping using Spitzer-IRS (14 to 38 micron) data of the same IRDC. These methods allow us to measure the SED of the diffuse Galactic ISM, which we compare to theoretical models of Draine & Li (2007), as well as to search for opacity law variations with mass surface density within the IRDC. By comparison with theoretical dust models, e.g., Ossenkopf & Henning (1994) and Ormel et al. (2011), we are able to search for compositional signatures of the grain ices, such as water and methanol. We find evidence for generally flatter MIR to FIR extinction laws as mass surface density increases, strengthening the evidence for grain and ice mantle growth in higher density regions.

Low-temperature formation of crystalline Si:H/Ge:H heterostructures by plasma-enhanced CVD in combination with Ni-nanodots seeding nucleation

NASA Astrophysics Data System (ADS)

Lu, Yimin; Makihara, Katsunori; Takeuchi, Daichi; Ikeda, Mitsuhisa; Ohta, Akio; Miyazaki, Seiichi

2017-06-01

Hydrogenated microcrystalline (µc) Si/Ge heterostructures were prepared on quartz substrates by plasma-enhanced chemical vapor deposition (CVD) from VHF inductively coupled plasma of SiH4 just after GeH4 employing Ni nanodots (NDs) as seeds for crystalline nucleation. The crystallinity of the films and the progress of grain growth were characterized by Raman scattering spectroscopy and atomic force microscopy (AFM), respectively. When the Ge films were grown on Ni-NDs at 250 °C, the growth of µc-Ge films with crystallinity as high as 80% was realized without an amorphous phase near the Ge film/quartz substrate interface. After the subsequent Si film deposition at 250 °C, fine grains were formed in the early stages of film growth on µc-Ge films with compositional mixing (µc-Si0.85Ge0.15:H) caused by the release of large lattice mismatch between c-Si and c-Ge. With further increase in Si:H film thickness, the formation of large grain structures accompanied by fine grains was promoted. These results suggest that crystalline Si/Ge heterojunctions can be used for efficient carrier collection in solar cell application.

Origin of a needle-like granular structure for ultrananocrystalline diamond films grown in a N2/CH4 plasma

NASA Astrophysics Data System (ADS)

Sankaran, K. J.; Kurian, J.; Chen, H. C.; Dong, C. L.; Y Lee, C.; Tai, N. H.; Lin, I. N.

2012-09-01

Microstructural evolution as a function of substrate temperature (TS) for conducting ultrananocrystalline diamond (UNCD) films is systematically studied. Variation of the sp2 graphitic and sp3 diamond content with TS in the films is analysed from the Raman and near-edge x-ray absorption fine structure spectra. Morphological and microstructural studies confirm that at TS = 700 °C well-defined acicular structures evolve. These nanowire structures comprise sp3 phased diamond, encased in a sheath of sp2 bonded graphitic phase. TS causes a change in morphology and thereby the various properties of the films. For TS = 800 °C the acicular grain growth ceases, while that for TS = 700 °C ceases only upon termination of the deposition process. The grain-growth process for the unique needle-like granular structure is proposed such that the CN species invariably occupy the tip of the nanowire, promoting an anisotropic grain-growth process and the formation of acicular structure of the grains. The electron field emission studies substantiate that the films grown at TS = 700 °C are the most conducting, with conduction mediated through the graphitic phase present in the films.

Ion induced crystallization and grain growth of hafnium oxide nano-particles in thin-films deposited by radio frequency magnetron sputtering

NASA Astrophysics Data System (ADS)

Dhanunjaya, M.; Khan, S. A.; Pathak, A. P.; Avasthi, D. K.; Nageswara Rao, S. V. S.

2017-12-01

We report on the swift heavy ion (SHI) irradiation induced crystallization and grain growth of HfO2 nanoparticles (NPs) within the HfO2 thin-films deposited by radio frequency (RF) magnetron sputtering technique. As grown films consisted of amorphous clusters of non-spherical HfO2 NPs. These amorphous clusters are transformed to crystalline grains under 100 MeV Ag ion irradiation. These crystallites are found to be spherical in shape and are well dispersed within the films. The average size of these crystallites is found to increase with fluence. Pristine and irradiated films have been characterized by high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), grazing incident x-ray diffraction (GIXRD) and photo luminescence (PL) measurements. The PL measurements suggested the existence of different types of oxygen related defects in pristine and irradiated samples. The observed results on crystallization and grain growth under the influence of SHI are explained within the framework of thermal spike model. The results are expected to provide useful information for understanding the electronic excitation induced crystallization of nanoparticles and can lead to useful applications in electronic and photonic devices.

Short-term treatment with VEGF receptor inhibitors induces retinopathy of prematurity-like abnormal vascular growth in neonatal rats.

PubMed

Nakano, Ayuki; Nakahara, Tsutomu; Mori, Asami; Ushikubo, Hiroko; Sakamoto, Kenji; Ishii, Kunio

2016-02-01

Retinal arterial tortuosity and venous dilation are hallmarks of plus disease, which is a severe form of retinopathy of prematurity (ROP). In this study, we examined whether short-term interruption of vascular endothelial growth factor (VEGF) signals leads to the formation of severe ROP-like abnormal retinal blood vessels. Neonatal rats were treated subcutaneously with the VEGF receptor (VEGFR) tyrosine kinase inhibitors, KRN633 (1, 5, or 10 mg/kg) or axitinib (10 mg/kg), on postnatal day (P) 7 and P8. The retinal vasculatures were examined on P9, P14, or P21 in retinal whole-mounts stained with an endothelial cell marker. Prevention of vascular growth and regression of some preformed capillaries were observed on P9 in retinas of rats treated with KRN633. However, on P14 and P21, density of capillaries, tortuosity index of arterioles, and diameter of veins significantly increased in KRN633-treated rats, compared to vehicle (0.5% methylcellulose)-treated animals. Similar observations were made with axitinib-treated rats. Expressions of VEGF and VEGFR-2 were enhanced on P14 in KRN633-treated rat retinas. The second round of KRN633 treatment on P11 and P12 completely blocked abnormal retinal vascular growth on P14, but thereafter induced ROP-like abnormal retinal blood vessels by P21. These results suggest that an interruption of normal retinal vascular development in neonatal rats as a result of short-term VEGFR inhibition causes severe ROP-like abnormal retinal vascular growth in a VEGF-dependent manner. Rats treated postnatally with VEGFR inhibitors could serve as an animal model for studying the mechanisms underlying the development of plus disease. Copyright © 2015 Elsevier Ltd. All rights reserved.

TEM Study of Internal Crystals in Supernova Graphites

NASA Astrophysics Data System (ADS)

Croat, T. K.; Bernatowicz, T.; Stadermann, F. J.; Messenger, S.; Amari, S.

2003-03-01

A coordinated TEM and isotopic study of ten supernova (SN) graphites from the Murchison meteorite has revealed many internal grains, mostly titanium carbides (TiCs) and TiC-kamacite composite grains, which were accreted during the graphite growth.

Whole-Plant Dynamic System of Nitrogen Use for Vegetative Growth and Grain Filling in Rice Plants (Oryza sativa L.) as Revealed through the Production of 350 Grains from a Germinated Seed Over 150 Days: A Review and Synthesis

PubMed Central

Yoneyama, Tadakatsu; Tanno, Fumio; Tatsumi, Jiro; Mae, Tadahiko

2016-01-01

A single germinated rice (Oryza sativa L) seed can produce 350 grains with the sequential development of 15 leaves on the main stem and 7–10 leaves on four productive tillers (forming five panicles in total), using nitrogen (N) taken up from the environment over a 150-day growing season. Nitrogen travels from uptake sites to the grain through growing organ-directed cycling among sequentially developed organs. Over the past 40 years, the dynamic system for N allocation during vegetative growth and grain filling has been elucidated through studies on N and 15N transport as well as enzymes and transporters involved. In this review, we synthesize the information obtained in these studies along the following main points: (1) During vegetative growth before grain-filling, about half of the total N in the growing organs, including young leaves, tillers, root tips and differentiating panicles is supplied via phloem from mature source organs such as leaves and roots, after turnover and remobilization of proteins, whereas the other half is newly taken up and supplied via xylem, with an efficient xylem-to-phloem transfer at stem nodes. Thus, the growth of new organs depends equally on both N sources. (2) A large fraction (as much as 80%) of the grain N is derived largely from mature organs such as leaves and stems by degradation, including the autophagy pathway of chloroplast proteins (e.g., Rubisco). (3) Mobilized proteinogenic amino acids (AA), including arginine, lysine, proline and valine, are derived mainly from protein degradation, with AA transporters playing a role in transferring these AAs across cell membranes of source and sink organs, and enabling their efficient reutilization in the latter. On the other hand, AAs such as glutamine, glutamic acid, γ-amino butyric acid, aspartic acid, and alanine are produced by assimilation of newly taken up N by roots and and transported via xylem and phloem. The formation of 350 filled grains over 50 days during the reproductive stage is ascribed mainly to degradation and remobilization of the reserves, previously accumulated over 100 days in the sequentially developed vegetative organs. PMID:27536309

Exploring Niches for Short-Season Grain Legumes in Semi-Arid Eastern Kenya - Coping with the Impacts of Climate Variability.

PubMed

Sennhenn, Anne; Njarui, Donald M G; Maass, Brigitte L; Whitbread, Anthony M

2017-01-01

Climate variability is the major risk to agricultural production in semi-arid agroecosystems and the key challenge to sustain farm livelihoods for the 500 million people who inhabit these areas worldwide. Short-season grain legumes have great potential to address this challenge and help to design more resilient and productive farming systems. However, grain legumes display a great diversity and differ widely in growth, development, and resource use efficiency. Three contrasting short season grain legumes common bean ( Phaseolus vulgaris L.), cowpea ( Vigna unguiculata (L.) Walp.] and lablab [ Lablab purpureus (L.) Sweet] were selected to assess their agricultural potential with respect to climate variability and change along the Machakos-Makueni transect in semi-arid Eastern Kenya. This was undertaken using measured data [a water response trial conducted during 2012/13 and 2013/14 in Machakos, Kenya] and simulated data using the Agricultural Production System sIMulator (APSIM). The APSIM crop model was calibrated and validated to simulate growth and development of short-season grain legumes in semi-arid environments. Water use efficiency (WUE) was used as indicator to quantify the production potential. The major traits of adaptation include early flowering and pod and seed set before the onset of terminal drought. Early phenology together with adapted canopy architecture allowed more optimal water use and greater partitioning of dry matter into seed (higher harvest index). While common bean followed a comparatively conservative strategy of minimizing water loss through crop transpiration, the very short development time and compact growth habit limited grain yield to rarely exceed 1,000 kg ha -1 . An advantage of this strategy was relatively stable yields independent of in-crop rainfall or season length across the Machakos-Makueni transect. The growth habit of cowpea in contrast minimized water loss through soil evaporation with rapid ground cover and dry matter production, reaching very high grain yields at high potential sites (3,000 kg ha -1 ) but being highly susceptible to in-season drought. Lablab seemed to be best adapted to dry environments. Its canopy architecture appeared to be best in compromising between the investment in biomass as a prerequisite to accumulate grain yield by minimizing water loss through soil evaporation and crop transpiration. This lead to grain yields of up to 2,000 kg ha -1 at high potential sites and >1,000 kg ha -1 at low potential sites. The variance of observed and simulated WUE was high and no clear dependency on total rainfall alone was observed for all three short-season grain legumes, highlighting that pattern of water use is also important in determining final WUE biomass and WUE grain . Mean WUE grain was lowest for cowpea (1.5-3.5 kg grain ha -1 mm -1 ) and highest for lablab (5-7 kg grain ha -1 mm -1 ) reflecting the high susceptibility to drought of cowpea and the good adaptation to dry environments of lablab. Results highlight that, based on specific morphological, phonological, and physiological characteristics, the three short-season grain legumes follow different strategies to cope with climate variability. The climate-smart site-specific utilization of the three legumes offers promising options to design more resilient and productive farming systems in semi-arid Eastern Kenya.

Growth of single crystals of BaFe12O19 by solid state crystal growth

NASA Astrophysics Data System (ADS)

Fisher, John G.; Sun, Hengyang; Kook, Young-Geun; Kim, Joon-Seong; Le, Phan Gia

2016-10-01

Single crystals of BaFe12O19 are grown for the first time by solid state crystal growth. Seed crystals of BaFe12O19 are buried in BaFe12O19+1 wt% BaCO3 powder, which are then pressed into pellets containing the seed crystals. During sintering, single crystals of BaFe12O19 up to ∼130 μm thick in the c-axis direction grow on the seed crystals by consuming grains from the surrounding polycrystalline matrix. Scanning electron microscopy-energy dispersive spectroscopy analysis shows that the single crystal and the surrounding polycrystalline matrix have the same chemical composition. Micro-Raman scattering shows the single crystal to have the BaFe12O19 structure. The optimum growth temperature is found to be 1200 °C. The single crystal growth behavior is explained using the mixed control theory of grain growth.

Modeling Nucleation and Grain Growth in the Solar Nebula: Initial Progress Report

NASA Technical Reports Server (NTRS)

Nuth, Joseph A.; Paquette, J. A.; Ferguson, F. T.

2010-01-01

The primitive solar nebula was a violent and chaotic environment where high energy collisions, lightning, shocks and magnetic re-connection events rapidly vaporized some fraction of nebular dust, melted larger particles while leaving the largest grains virtually undisturbed. At the same time, some tiny grains containing very easily disturbed noble gas signatures (e.g., small, pre-solar graphite or SiC particles) never experienced this violence, yet can be found directly adjacent to much larger meteoritic components (chondrules or CAIs) that did. Additional components in the matrix of the most primitive carbonaceous chondrites and in some chondritic porous interplanetary dust particles include tiny nebular condensates, aggregates of condensates and partially annealed aggregates. Grains formed in violent transient events in the solar nebula did not come to equilibrium with their surroundings. To understand the formation and textures of these materials as well as their nebular abundances we must rely on Nucleation Theory and kinetic models of grain growth, coagulation and annealing. Such models have been very uncertain in the past: we will discuss the steps we are taking to increase their reliability.

The fatigue response of the aluminium-lithium alloy, 8090

NASA Technical Reports Server (NTRS)

Birt, M. J.; Beevers, C. J.

1989-01-01

The fatigue response of an Al-Li-Cu-Mg-Zr (8090) alloy has been studied at room temperature. The initiation and growth of small and long cracks has been examined at R = 0.1 and at a frequency of 100 Hz. Initiation was observed to occur dominantly at sub-grain boundaries. The growth of the small cracks was crystallographic in character and exhibited little evidence of retardation or arrest at the grain boundaries. The long crack data showed the alloy to have a high resistance to fatigue crack growth with underaging providing the optimum heat treatment for fatigue crack growth resistance. In general, this can be attributed to high levels of crack closure which resulted from the presence of extensive microstructurally related asperities.

Effects of polycrystallinity in nano patterning by ion-beam sputtering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoon, Sun Mi; Kim, J.-S., E-mail: jskim@sm.ac.kr; Yoon, D.

Employing graphites with distinctly different mean grain sizes, we study the effects of polycrystallinity on the pattern formation by ion-beam sputtering. The grains influence the growth of the ripples in a highly anisotropic fashion; both the mean uninterrupted ripple length along the ridges and the surface width depend on the mean size of the grains, which is attributed to the large sputter yield at the grain boundary compared with that on the terrace. In contrast, the ripple wavelength does not depend on the mean size of the grains, indicating that the mass transport across the grain boundaries should efficiently proceedmore » by both thermal diffusion and ion-induced processes.« less

Process development for producing fine-grain casting in space

NASA Technical Reports Server (NTRS)

Gelles, S. H.; Malik, R. K.

1975-01-01

Assessment of grain growth kinetics at temperatures near the melting point and investigation into the use of potential nucleating agents in combination with the naturally occurring BeO led to the definition of critical low-g experiments which would help to determine whether one or both of these possibilities are valid and whether space processing would be able to yield fine grain ingot beryllium.

Airway responsiveness to methacholine, respiratory symptoms, and dust exposure levels in grain and flour mill workers in eastern France.

PubMed

Massin, N; Bohadana, A B; Wild, P; Kolopp-Sarda, M N; Toamain, J P

1995-06-01

Our goal was to assess the relation between dust exposure levels and the respiratory health status of workers in grain and flour mills in eastern France. We studied 118 male workers from 11 mills and 164 unexposed male controls. Dust concentration was measured by personal sampling methods. Outcome variables included respiratory symptoms, routine pulmonary function tests, and indices of airway responsiveness to methacholine. A great within- and between-area variability of inhalable dust concentration was found in all mills. A dose-response relationship was observed between dust exposure levels and chronic respiratory symptoms, suggesting that exposure to grain and flour dust may lead to chronic bronchitis. A significant relation was found between dust exposure and airway hyper-responsiveness; this finding is important since it has been hypothesized that the latter abnormality may lead to or be a predisposing factor in subsequent chronic, irreversible airflow obstruction.

Molecular microelectrostatic view on electronic states near pentacene grain boundaries

NASA Astrophysics Data System (ADS)

Verlaak, Stijn; Heremans, Paul

2007-03-01

Grain boundaries are the most inevitable and pronounced structural defects in pentacene films. To study the effect of those structural defects on the electronic state distribution, the energy levels of a hole on molecules at and near the defect have been calculated using a submolecular self-consistent-polarization-field approach in combination with atomic charge-quadrupole interaction energy calculations. This method has been benchmarked prior to application on four idealized grain boundaries: a grain boundary void, a void with molecules squeezed in between two grains, a boundary between two grains with different crystallographic orientations, and a grain boundary void in which a permanent dipole (e.g., a water molecule) has nested. While idealized, those views highlight different aspects of real grain boundaries. Implications on macroscopic charge transport models are discussed, as well as some relation between growth conditions and the formation of the grain boundary.

Growth of Ca{sub 2}MnO{sub 4} Ruddlesden-Popper structured thin films using combinatorial substrate epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lacotte, M.; David, A.; Pravarthana, D.

2014-12-28

The local epitaxial growth of pulsed laser deposited Ca{sub 2}MnO{sub 4} films on polycrystalline spark plasma sintered Sr{sub 2}TiO{sub 4} substrates was investigated to determine phase formation and preferred epitaxial orientation relationships (ORs) for isostructural Ruddlesden-Popper (RP) heteroepitaxy, further developing the high-throughput synthetic approach called Combinatorial Substrate Epitaxy (CSE). Both grazing incidence X-ray diffraction and electron backscatter diffraction patterns of the film and substrate were indexable as single-phase RP-structured compounds. The optimal growth temperature (between 650 °C and 800 °C) was found to be 750 °C using the maximum value of the average image quality of the backscattered diffraction patterns. Films grew inmore » a grain-over-grain pattern such that each Ca{sub 2}MnO{sub 4} grain had a single OR with the Sr{sub 2}TiO{sub 4} grain on which it grew. Three primary ORs described 47 out of 49 grain pairs that covered nearly all of RP orientation space. The first OR, found for 20 of the 49, was the expected RP unit-cell over RP unit-cell OR, expressed as [100][001]{sub film}||[100][001]{sub sub}. The other two ORs were essentially rotated from the first by 90°, with one (observed for 17 of 49 pairs) being rotated about the [100] and the other (observed for 10 of 49 pairs) being rotated about the [110] (and not exactly by 90°). These results indicate that only a small number of ORs are needed to describe isostructural RP heteroepitaxy and further demonstrate the potential of CSE in the design and growth of a wide range of complex functional oxides.« less

1300 K Compressive Properties of Directionally Solidified Ni-33Al-33Cr-1Mo

NASA Technical Reports Server (NTRS)

Whittenberger, J. Daniel; Raj, S. V.; Locci, Ivan E.

2000-01-01

The Ni-33Al-33Cr-1Mo eutectic has been directionally solidified by a modified Bridgeman technique at growth rates ranging from 7.6 to 508 mm/h to produce grain/cellular microstructures, containing alternating plates of NiAl and Cr alloyed with Mo. The grains had sharp boundaries for slower growth rates (< 12.7 mm/h), while faster growth rates (> 25.4 mm/h) lead to cells bounded by intercellular regions. Compressive testing at 1300 K indicated that alloys DS'ed at rates between 25.4 to 254 mm/h possessed the best strengths which exceed that for the as-cast alloy.

Cell-free fetal DNA concentration in plasma of patients with abnormal uterine artery Doppler waveform and intrauterine growth restriction--a pilot study.

PubMed

Caramelli, Elisabetta; Rizzo, Nicola; Concu, Manuela; Simonazzi, Giuliana; Carinci, Paolo; Bondavalli, Corrado; Bovicelli, Luciano; Farina, Antonio

2003-05-01

To evaluate if an increased amount of fetal DNA concentration can be found in women screened positive for intrauterine growth restriction because of abnormal uterine artery Doppler waveforms. We enrolled eight pregnant women (each bearing a male fetus), with the evidence of abnormal uterine artery Doppler waveforms, and 16 control patients for a case-control study matched for gestational age (1 : 2). Uterine artery Doppler was carried out at 20 to 35 weeks' gestation (median 29). The mean uterine artery resistance index (RI) was subsequently calculated, and a value >0.6 was considered positive for the clinical features of pre-eclampsia. The SRY locus was used to determine the amount of male fetal DNA in the maternal plasma at the time of Doppler analysis. Two controls (normal Doppler) were excluded from the final analysis because they had a pre-term delivery. One case (abnormal Doppler) had evidence of intrauterine growth restriction at the time of enrolment. In four out of eight cases (abnormal Doppler), intrauterine growth restriction was subsequently observed. Multiples of median (MoM) conversion of the fetal DNA values showed an increase of 1.81 times in the cases when compared to the controls. An increase of 2.16 times was instead observed for the cases with a growth-restricted fetus (5 cases out of 8) in comparison with the controls (14 cases). In subjects positive to uterine artery Doppler velocimetry analysis (Doppler analysis for pre-eclampsia screening), the fetal DNA concentration is higher than expected, in the absence of any other clinical feature. Since the increase in fetal DNA seems to be related to the presence or to the future development of intrauterine growth restriction, this paper suggests a possible integration between ultrasound and molecular markers for predicting the disease in some cases. Copyright 2003 John Wiley & Sons, Ltd.

Pediatric obstructive sleep apnea and the critical role of oral-facial growth: evidences.

PubMed

Huang, Yu-Shu; Guilleminault, Christian

2012-01-01

Review of evidence in support of an oral-facial growth impairment in the development of pediatric sleep apnea in non-obese children. Review of experimental data from infant monkeys with experimentally induced nasal resistance. Review of early historical data in the orthodontic literature indicating the abnormal oral-facial development associated with mouth breathing and nasal resistance. Review of the progressive demonstration of sleep-disordered-breathing (SDB) in children who underwent incomplete treatment of OSA with adenotonsillectomy, and demonstration of abnormal oral-facial anatomy that must often be treated in order for the resolution of OSA. Review of data of long-term recurrence of OSA and indication of oral-facial myofunctional dysfunction in association with the recurrence of OSA. Presentation of prospective data on premature infants and SDB-treated children, supporting the concept of oral-facial hypotonia. Presentation of evidence supporting hypotonia as a primary element in the development of oral-facial anatomic abnormalities leading to abnormal breathing during sleep. Continuous interaction between oral-facial muscle tone, maxillary-mandibular growth and development of SDB. Role of myofunctional reeducation with orthodontics and elimination of upper airway soft tissue in the treatment of non-obese SDB children. Pediatric OSA in non-obese children is a disorder of oral-facial growth.

The ultraviolet extinction properties of the 30 Dor Nebula

NASA Astrophysics Data System (ADS)

De Marchi, Guido; Panagia, Nino

2018-01-01

Recent investigation of the extinction law in 30 Dor and the Tarantula Nebula, at optical and near infrared wavelengths, has revealed a ratio of total to selective extinction RV=AV/E(B-V) of about 4.5. This indicates a larger proportion of large grains than in the Galactic diffuse interstellar medium. Possible origins include coalescence of small grains, grain growth, selective destruction of small grains, and fresh injection of large grains. From a study of the ultraviolet extinction properties of three Wolf-Rayet stars in 30 Dor (R 139, R 140, R 145), observed with the International Ultraviolet Explorer, we show that the excess of large grains does not come at the expense of small grains, which are still present. Fresh injection of large grains by supernova explosions appears to be the dominant mechanism.

Disturbance of light-absorbing aerosols on the albedo in a winter snowpack of Central Tibet.

PubMed

Ming, Jing; Wang, Pengling; Zhao, Shuyu; Chen, Pengfei

2013-08-01

A field observation on the albedo of the snowpack in Central Tibet was conducted in the Nam Co region in the winter of 2011. Snow properties, including grain size and density, were measured in the field, and surface-layer snow samples (down to 5 cm) were collected. The average concentrations of black carbon and dust were 72 ppbm (close to that in the glaciers of Mt. Nyainqentanglha) and 120 ppmm, respectively. Inverse trends were found to exist between the albedo of the snowpack and light-absorbing aerosols (LAAs) as well as grain size growth. Modeling showed that black carbon, dust, and grain growth in the winter snowpack can reduce the broadband albedo by 11%, 28%, and 61%, respectively.

Effects of Na and secondary phases on physical properties of SnS thin film after sulfurization process

NASA Astrophysics Data System (ADS)

Kawano, Yu; Kodani, Yuto; Chantana, Jakapan; Minemoto, Takashi

2016-09-01

2.48%-efficient SnS thin film solar cell is obtained under thermal evaporation method by optimizing growth temperature. The method to fabricate SnS films is limited by growth temperature, which should not be over 200 °C to prevent re-evaporation of SnS. To further enhance SnS grains, SnS films were annealed in H2S gas from 200 to 500 °C, namely sulfurization process. SnS grain size was increased with sulfurization temperature of above 400 °C however, secondary phase grains on film’s surface were observed owing to the accumulated Na, diffused from soda-lime glass substrate into the film, thus deteriorating film’s quality, implied by Urbach energy.

Principal component greenness transformation in multitemporal agricultural Landsat data

NASA Technical Reports Server (NTRS)

Abotteen, R. A.

1978-01-01

A data compression technique for multitemporal Landsat imagery which extracts phenological growth pattern information for agricultural crops is described. The principal component greenness transformation was applied to multitemporal agricultural Landsat data for information retrieval. The transformation was favorable for applications in agricultural Landsat data analysis because of its physical interpretability and its relation to the phenological growth of crops. It was also found that the first and second greenness eigenvector components define a temporal small-grain trajectory and nonsmall-grain trajectory, respectively.

The evolution of grain mantles and silicate dust growth at high redshift

NASA Astrophysics Data System (ADS)

Ceccarelli, Cecilia; Viti, Serena; Balucani, Nadia; Taquet, Vianney

2018-05-01

In dense molecular clouds, interstellar grains are covered by mantles of iced molecules. The formation of the grain mantles has two important consequences: it removes species from the gas phase and promotes the synthesis of new molecules on the grain surfaces. The composition of the mantle is a strong function of the environment that the cloud belongs to. Therefore, clouds in high-zeta galaxies, where conditions - like temperature, metallicity, and cosmic ray flux - are different from those in the Milky Way, will have different grain mantles. In the last years, several authors have suggested that silicate grains might grow by accretion of silicon-bearing species on smaller seeds. This would occur simultaneously with the formation of the iced mantles and be greatly affected by its composition as a function of time. In this work, we present a numerical study of the grain mantle formation in high-zeta galaxies, and we quantitatively address the possibility of silicate growth. We find that the mantle thickness decreases with increasing redshift, from about 120 to 20 layers for z varying from 0 to 8. Furthermore, the mantle composition is also a strong function of the cloud redshift, with the relative importance of CO, CO2, ammonia, methane, and methanol highly varying with z. Finally, being Si-bearing species always a very minor component of the mantle, the formation of silicates in molecular clouds is practically impossible.

Comparison of alternative beef production systems based on forage finishing or grain-forage diets with or without growth promotants: 2. Meat quality, fatty acid composition, and overall palatability.

PubMed

Faucitano, L; Chouinard, P Y; Fortin, J; Mandell, I B; Lafrenière, C; Girard, C L; Berthiaume, R

2008-07-01

Five beef cattle management regimens were evaluated for their effect on meat quality, fatty acid composition, and overall palatability of the longis-simus dorsi (LD) muscle in Angus cross steers. A 98-d growing phase was conducted using grass silage with or without supplementation of growth promotants (Revalor G and Rumensin) or soybean meal. Dietary treatments in the finishing phase were developed with or without supplementation of growth promotants based on exclusive feeding of forages with no grain supplementation, or the feeding of grain:forage (70:30) diets. Growth promotants increased (P < 0.01) shear force and tended (P = 0.06) to increase toughness of the LD muscle due to limited postmortem proteolytic activity (lower myofibrillar fragmentation index value; P = 0.02). Grain feeding increased DM and intramuscular fat content (P = 0.03 and P = 0.05, respectively) in the LD but decreased the sensory panel tenderness score (P = 0.01). Growth promotants increased (P

Cyclic Stable-Unstable Slip Preserved along an Appalachian Fault

NASA Astrophysics Data System (ADS)

Wells, R. K.; Newman, J.; Holyoke, C. W., III; Wojtal, S. F.

2017-12-01

The inactive Copper Creek thrust, southern Appalachians, TN, preserves evidence suggesting cyclic aseismic and unstable slip. The Copper Creek thrust is a low-temperature (4-6 km burial depth) foreland thrust with an estimated net slip of 15-20 km. Immediately below the 2 cm thick calcite-shale fault zone, the footwall is composed of shale with cross-cutting calcite veins and is separated from the fault zone by a 300 µm thick layered calcite vein. Optical and electron microscopy indicates that this complex vein layer experienced grain size reduction by plasticity-induced fracturing followed by aseismic diffusion creep. The fault zone calcite exhibits interpenetrating grain boundaries and four-grain junctions suggesting diffusion creep, but also contains nanoscale grains (7 nm), vesicular calcite, and partially-coated clasts indicating unstable, possibly seismic, slip. Well-preserved clasts of deformed calcite vein layer material within the fault zone indicate repeated cycle(s) of aseismic diffusion creep. In addition, nanoscale calcite grains, 30 nm, with straight grain boundaries that form triple junctions, may represent earlier nanoscale grains formed during unstable slip that have experienced grain growth during periods of aseismic creep. Based on the spatial and temporal relations of these preserved microstructures, we propose a sequence of deformation processes consistent with cyclic episodes of unstable slip separated by intervals of aseismic creep. Formation of calcite-filled veins is followed by grain size reduction in vein calcite by plasticity-induced fracturing and aseismic grain-size sensitive diffusion creep deformation in fine-grained calcite. During aseismic creep, the combination of grain growth, resulting in fault strengthening, and an increase in pore fluid pressure, reducing the effective fault strength, leads to new fractures and/or an unstable slip event. During unstable slip, nanograins and vesicular calcite form as a result of thermal decomposition and coated clasts form as a result of fluidization of the fault zone, and are then incorporated within ductilely deforming calcite during a new interval of aseismic creep.

The Formation, Transport Properties and Microstructure of 45 Degrees (001) Tilt Grain Boundaries in Yttrium BARIUM(2) COPPER(3) OXYGEN(7-X) Thin Films

NASA Astrophysics Data System (ADS)

Vuchic, Boris Vukan

1995-01-01

Most high angle grain boundaries in high-T _{c} superconductors exhibit weak link behavior. The Josephson-like properties of these grain boundaries can be used for many device applications such as superconducting quantum interference devices (SQUIDs). The structure-property relationship of different types of 45 ^circ (001) YBa_2 Cu_3O_{7-x} thin film grain boundary junctions are examined to study their weak link nature. A technique, termed sputter-induced epitaxy, is developed to form 45^circ (001) tilt grain boundaries in YBa_2Cu _3O_{7-x} thin films on (100) MgO substrates. A low voltage ion bombardment pre-growth substrate treatment is used to modify the epitaxial orientation relationship between the thin film and the substrate in selected regions. By modifying the orientation of the thin film, grain boundary junctions can be placed in any configuration on the substrate. A variety of pre-growth sputtering conditions in conjunction with atomic force microscopy and Rutherford backscatter spectrometry are used to determine the role of the ions in modifying the substrate surface. Sputter-induced epitaxy is extended to a multilayer MgO/LaAlO_3 substrate, allowing integration of the sputter -induced epitaxy junctions into multilayer structures. The low temperature transport properties of the sputter-induced epitaxy junctions and a set of bi-epitaxial grain boundaries are studied. Individual grain boundaries are isolated and characterized for resistance vs. temperature, current vs. voltage as a function of temperature and magnetic field behavior. Resistive and superconducting grain boundaries are compared. Microstructural analysis is performed using scanning electron microscopy, transmission electron microscopy and high resolution electron microscopy (HREM). Marked differences are observed in the microstructure of resistive and superconducting grain boundaries. HREM studies suggest the importance of the local atomic scale structure of the grain boundary in transport properties. A phenomenological grain boundary model is proposed to describe the structure -property relationship of the boundaries.

Grain-size-induced weakening of H2O ices I and II and associated anisotropic recrystallization

USGS Publications Warehouse

Stern, L.A.; Durham, W.B.; Kirby, S.H.

1997-01-01

Grain-size-dependent flow mechanisms tend to be favored over dislocation creep at low differential stresses and can potentially influence the rheology of low-stress, low-strain rate environments such as those of planetary interiors. We experimentally investigated the effect of reduced grain size on the solid-state flow of water ice I, a principal component of the asthenospheres of many icy moons of the outer solar system, using techniques new to studies of this deformation regime. We fabricated fully dense ice samples of approximate grain size 2 ?? 1 ??m by transforming "standard" ice I samples of 250 ?? 50 ??m grain size to the higher-pressure phase ice II, deforming them in the ice II field, and then rapidly releasing the pressure deep into the ice I stability field. At T ??? 200 K, slow growth and rapid nucleation of ice I combine to produce a fine grain size. Constant-strain rate deformation tests conducted on these samples show that deformation rates are less stress sensitive than for standard ice and that the fine-grained material is markedly weaker than standard ice, particularly during the transient approach to steady state deformation. Scanning electron microscope examination of the deformed fine-grained ice samples revealed an unusual microstructure dominated by platelike grains that grew normal to the compression direction, with c axes preferentially oriented parallel to compression. In samples tested at T ??? 220 K the elongation of the grains is so pronounced that the samples appear finely banded, with aspect ratios of grains approaching 50:1. The anisotropic growth of these crystallographically oriented neoblasts likely contributes to progressive work hardening observed during the transient stage of deformation. We have also documented remarkably similar microstructural development and weak mechanical behavior in fine-grained ice samples partially transformed and deformed in the ice II field.

Grain size effect on the permittivity of La1.5Sr0.5NiO4 nanoparticles

NASA Astrophysics Data System (ADS)

Dang Thanh, Tran; Van Hong, Le

2009-09-01

Using the annealing at different temperatures the La1.5Sr0.5NiO4 ceramic samples with different mean grain size were manufactured. Mean grain size () of the samples was evaluated by Warren-Averbach method and their SEM images. The obtained results of both methods are almost the same, changing from 16.2 to 95 nm in dependence on the annealing temperature. The frequency dependence of dielectric constant in the frequency range of (1-13 MHz) was recorded for all samples. The real (ɛ') and the imaginary parts (ɛ") of the permittivity of La1.5Sr0.5NiO4 samples abnormally depend on the frequency, exhibiting a dielectric resonance around 500 kHz. R-L-C in series equivalent-circuit fitted well for the obtained result. It was supposed that there exists magnetic contribution in material that suggests the material is a multiferroic one. Dependence of the (ɛ') on the mean grain size supposed that the colossal dielectric property is an intrinsic behaviour of La1.5Sr0.5NiO4 material.

Molecular dynamic simulations of the intergranular films between alumina and silicon nitride crystal grains

NASA Astrophysics Data System (ADS)

Zhang, Shenghong

The intergranular films (IGFs) between the ceramics grains have very important effects on the structure and mechanical properties on the whole ceramics and have been studied for many decades. In the thesis, molecular dynamic (MD) computer simulations were applied to study the IGFs between the alumina and silicon nitride ceramic grains. Preferential adsorption of specific ions from the IGFs to the contacting surfaces of the alumina crystals was observed in the study of calcium-alumino-silicate glassy (CAS) IGFs formed between the combined basal and prism orientations of alpha-Al2O3 crystals. This segregation of specific ions to the interface enables formation of localized, ordered structures between the IGF and the crystals. However, the segregation behavior of the ions is anisotropic, depending on the orientation of the alpha-Al2O 3 crystals. Self-diffusion of calcium ions between these CAS IGFs was also carried out by MD simulations. The results show that the diffusion coefficients adjacent to the interfaces are smaller and the activation energies are much higher than those in the interior of the IGF and in bulk glasses. It was also suggested that Ca transport is mainly though the interior of the IGF and implies that diffusion would be significantly inhibited by sufficiently thin IGFs. The growth of the alumina ceramic grains was simulated in the contacting with IGFs containing high concentrations of aluminum ions. Five different compositions in the IGFs were studied. Results show preferential growth along the [1120] of the (1120) surface in comparison to growth along the [0001] direction on the (0001) surface for compositions near a Ca/Al ratio of 0.5. The simulations also show the mechanism by which Ca ions in the IGF inhibit growth on the basal surface. The simulations provide an atomistic view of attachment onto crystal surfaces, affecting grain growth in alumina. The dissolution of the alumina crystal grains in the silicate melts is another important issue in the application of alumina ceramics. The simulations results showed that alumina grains dissolved into the melts homogeneously at very high temperatures. The orientation of the crystals and the compositions of the melts only take effect at some intermediate temperatures, to make the alumina grains dissolution anisotropic. The fracture phenomena of the pure silica IGFs between the basal silicon nitride crystals were studied by applying the constant tensile strain on the simulated IGF system, as well as for the bulk silica glass for the comparison. The data indicated that the fracture was happened in the interior of the IGFs and the thickness of the IGFs has important effect on the fracture stress/strain relationships.

Global gene expression profiling related to temperature-sensitive growth abnormalities in interspecific crosses between tetraploid wheat and Aegilops tauschii

PubMed Central

Sakaguchi, Kouhei; Ohno, Ryoko; Yoshida, Kentaro

2017-01-01

Triploid wheat hybrids between tetraploid wheat and Aegilops tauschii sometimes show abnormal growth phenotypes, and the growth abnormalities inhibit generation of wheat synthetic hexaploids. In type II necrosis, one of the growth abnormalities, necrotic cell death accompanied by marked growth repression occurs only under low temperature conditions. At normal temperature, the type II necrosis lines show grass-clump dwarfism with no necrotic symptoms, excess tillers, severe dwarfism and delayed flowering. Here, we report comparative expression analyses to elucidate the molecular mechanisms of the temperature-dependent phenotypic plasticity in the triploid wheat hybrids. We compared gene and small RNA expression profiles in crown tissues to characterize the temperature-dependent phenotypic plasticity. No up-regulation of defense-related genes was observed under the normal temperature, and down-regulation of wheat APETALA1-like MADS-box genes, considered to act as flowering promoters, was found in the grass-clump dwarf lines. Some microRNAs, including miR156, were up-regulated, whereas the levels of transcripts of the miR156 target genes SPLs, known to inhibit tiller and branch number, were reduced in crown tissues of the grass-clump dwarf lines at the normal temperature. Unusual expression of the miR156/SPLs module could explain the grass-clump dwarf phenotype. Dramatic alteration of gene expression profiles, including miRNA levels, in crown tissues is associated with the temperature-dependent phenotypic plasticity in type II necrosis/grass-clump dwarf wheat hybrids. PMID:28463975

High Temperature Burst Testing of a Superalloy Disk With a Dual Grain Structure

NASA Technical Reports Server (NTRS)

Gayda, J.; Kantzos, P.

2004-01-01

Elevated temperature burst testing of a disk with a dual grain structure made from an advanced nickel-base superalloy, LSHR, was conducted. The disk had a fine grain bore and coarse grain rim, produced using NASA's low cost DMHT technology. The results of the spin testing showed the disk burst at 42 530 rpm in line with predictions based on a 2-D finite element analysis. Further, significant growth of the disk was observed before failure which was also in line with predictions.

Cellular interface morphologies in directional solidification. II - The effect of grain boundaries

NASA Technical Reports Server (NTRS)

Ungar, Lyle H.; Brown, Robert A.

1984-01-01

A singular perturbation analysis valid for small grain-boundary slopes is used with the one-sided model for solidification to show that grain boundaries introduce imperfections into the symmetry of the developing cellular interfaces which rupture the junction between the family of planar shapes and the bifurcating cellular families. Undulating interfaces are shown to develop first near grain boundaries, and to evolve with decreasing temperature gradient either by a smooth transition from the almost planar family or by a sudden jump to moderate-amplitude cellular forms, depending on the growth rate.

Role of high microwave power on growth and microstructure of thick nanocrystalline diamond films: A comparison with large grain polycrystalline diamond films

NASA Astrophysics Data System (ADS)

Tang, C. J.; Fernandes, A. J. S.; Girão, A. V.; Pereira, S.; Shi, Fa-Nian; Soares, M. R.; Costa, F.; Neves, A. J.; Pinto, J. L.

2014-03-01

In this work, we study the growth habit of nanocrystalline diamond (NCD) films by exploring the very high power regime, up to 4 kW, in a 5 kW microwave plasma chemical vapour deposition (MPCVD) reactor, through addition of a small amount of nitrogen and oxygen (0.24%) into 4% CH4 in H2 plasma. The coupled effect of high microwave power and substrate temperature on NCD growth behaviour is systematically investigated by varying only power, while fixing the remaining operating parameters. When the power increases from 2 kW to 4 kW, resulting also in rise of the Si substrate temperature higher than 150 °C, the diamond films obtained maintain the NCD habit, while the growth rate increases significantly. The highest growth rate of 4.6 μm/h is achieved for the film grown at 4 kW, which represents a growth rate enhancement of about 15 times compared with that obtained when using 2 kW power. Possible factors responsible for such remarkable growth rate enhancement of the NCD films are discussed. The evolution of NCD growth characteristics such as morphology, microstructure and texture is studied by growing thick films and comparing it with that of large grain polycrystalline (PCD) films. One important characteristic of the NCD films obtained, in contrast to PCD films, is that irrespective of deposition time (i.e. film thickness), their grain size and surface roughness remain in the nanometer range throughout the growth. Finally, based on our present and previous experimental results, a potential parameter window is established for fast growth of NCD films under high power conditions.

Co-production of Nitrogen-15 and Oxygen-18 in Explosive Helium Burning and Implications for Supernova Graphite Grains

NASA Astrophysics Data System (ADS)

Bojazi, Michael

My Masters research involves simulations of a supernova whereby a shock wave of constant Mach number is sent through a 15-solar-mass star evolved to the point of core-collapse. The resulting nucleosynthesis is examined with the intent of explaining the overproduction, relative to solar values, of nitrogen-15 and oxygen-18 abundances in supernova presolar graphite grains, as experimentally determined by Groopman et al. via a NanoSIMS analysis. We find such overabundances to be present in the helium-rich zone. Oxygen-18 is leftover from presupernova helium burning while nitrogen-15 is produced by explosive helium burning. Interestingly, anomalous excesses in molybdenum-95 and molybdenum-97 abundances in SiC X grains, discovered by Pellin et al. using the CHARISMA instrument, probably arise from explosive helium burning as well. These results signal the importance of the helium-rich zone for supernova presolar grain growth. We suggest that matter deep from the supernova, which is rich in iron-peak elements, gets injected into the helium-rich zone. Small TiC grains form in this material. These subgrains then traverse the helium-rich zone and serve as seeds for the growth of the graphite or SiC X grains.

Recrystallization and grain growth behavior of rolled tungsten under VDE-like short pulse high heat flux loads

NASA Astrophysics Data System (ADS)

Yuan, Y.; Greuner, H.; Böswirth, B.; Krieger, K.; Luo, G.-N.; Xu, H. Y.; Fu, B. Q.; Li, M.; Liu, W.

2013-02-01

Short pulse heat loads expected for vertical displacement events (VDEs) in ITER were applied in the high heat flux (HHF) test facility GLADIS at IPP-Garching onto samples of rolled W. Pulsed neutral beams with the central heat flux of 23 MW/m2 were applied for 0.5, 1.0 and 1.5 s, respectively. Rapid recrystallization of the adiabatically loaded 3 mm thick samples was observed when the pulse duration was up to 1.0 s. Grains grew markedly following recrystallization with increasing pulse length. The recrystallization temperature and temperature dependence of the recrystallized grain size were also investigated. The results showed that the recrystallization temperature of the W grade was around 2480 °C under the applied heat loading condition, which was nearly 1150 °C higher than the conventional recrystallization temperature, and the grains were much finer. A linear relationship between the logarithm of average grain size (ln d) and the inverse of maximum surface temperature (1/Tmax) was found and accordingly the activation energy for grain growth in temperature evolution up to Tmax in 1.5 s of the short pulse HHF load was deduced to be 4.1 eV. This provided an effective clue to predict the structure evolution under short pulse HHF loads.

Prunus necrotic ringspot virus Early Invasion and Its Effects on Apricot Pollen Grain Performance.

PubMed

Amari, Khalid; Burgos, Lorenzo; Pallas, Vicente; Sanchez-Pina, María Amelia

2007-08-01

ABSTRACT The route of infection and the pattern of distribution of Prunus necrotic ringspot virus (PNRSV) in apricot pollen were studied. PNRSV was detected both within and on the surface of infected pollen grains. The virus invaded pollen during its early developmental stages, being detected in pollen mother cells. It was distributed uniformly within the cytoplasm of uni- and bicellular pollen grains and infected the generative cell. In mature pollen grains, characterized by their triangular shape, the virus was located mainly at the apertures, suggesting that PNRSV distribution follows the same pattern as the cellular components required for pollen tube germination and cell wall tube synthesis. PNRSV also was localized inside pollen tubes, especially in the growth zone. In vitro experiments demonstrated that infection with PNRSV decreases the germination percentage of pollen grains by more than half and delays the growth of pollen tubes by approximately 24 h. However, although PNRSV infection affected apricot pollen grain performance during germination, the presence of the virus did not completely prevent fertilization, because the infected apricot pollen tubes, once germinated, were able to reach the apricot embryo sacs, which, in the climatic conditions of southeastern Spain, mature later than in other climates. Thus, infected pollen still could play an important role in the vertical transmission of PNRSV in apricot.

Kinetic model for dependence of thin film stress on growth rate, temperature, and microstructure

NASA Astrophysics Data System (ADS)

Chason, E.; Shin, J. W.; Hearne, S. J.; Freund, L. B.

2012-04-01

During deposition, many thin films go through a range of stress states, changing from compressive to tensile and back again. In addition, the stress depends strongly on the processing and material parameters. We have developed a simple analytical model to describe the stress evolution in terms of a kinetic competition between different mechanisms of stress generation and relaxation at the triple junction where the surface and grain boundary intersect. The model describes how the steady state stress scales with the dimensionless parameter D/LR where D is the diffusivity, R is the growth rate, and L is the grain size. It also explains the transition from tensile to compressive stress as the microstructure evolves from isolated islands to a continuous film. We compare calculations from the model with measurements of the stress dependence on grain size and growth rate in the steady state regime and of the evolution of stress with thickness for different temperatures.

High density of (pseudo) periodic twin-grain boundaries in molecular beam epitaxy-grown van der Waals heterostructure: MoTe{sub 2}/MoS{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Diaz, Horacio Coy; Ma, Yujing; Chaghi, Redhouane

2016-05-09

Growth of transition metal dichalcogenide heterostructures by molecular beam epitaxy (MBE) promises synthesis of artificial van der Waals materials with controllable layer compositions and separations. Here, we show that MBE growth of 2H-MoTe{sub 2} monolayers on MoS{sub 2} substrates results in a high density of mirror-twins within the films. The grain boundaries are tellurium deficient, suggesting that Te-deficiency during growth causes their formation. Scanning tunneling microscopy and spectroscopy reveal that the grain boundaries arrange in a pseudo periodic “wagon wheel” pattern with only ∼2.6 nm repetition length. Defect states from these domain boundaries fill the band gap and thus give themore » monolayer an almost metallic property. The band gap states pin the Fermi-level in MoTe{sub 2} and thus determine the band-alignment in the MoTe{sub 2}/MoS{sub 2} interface.« less

Topotaxial growth of α-Fe{sub 2}O{sub 3} nanowires on iron substrate in thermal annealing method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Srivastava, Himanshu, E-mail: himsri@rrcat.gov.in; Srivastava, A. K.; Babu, Mahendra

2016-06-28

A detail cross-sectional transmission electron microscopy of as-grown α-Fe{sub 2}O{sub 3} nanowire sample, synthesized on iron substrate by thermal annealing method, was carried out to understand the mechanism of growth in this system. Iron undergoes sequential oxidation to form a layered structure of Fe/FeO/Fe{sub 3}O{sub 4}/α-Fe{sub 2}O{sub 3}. α-Fe{sub 2}O{sub 3} nanowires grow on to the top of α-Fe{sub 2}O{sub 3} layer. It was found that subsequent oxide layers grow topotaxially on the grains of iron, which results in a direct orientation relationship between the α-Fe{sub 2}O{sub 3} nanowire and the parent grain of iron. The results also showed thatmore » the grains of α-Fe{sub 2}O{sub 3} layer, which were uniquely oriented in [110] direction, undergo highly anisotropic growth to form the nanowire. This anisotropic growth occurs at a twin interface, given by (−11−1), in the α-Fe{sub 2}O{sub 3} layer. It was concluded that the growth at twin interface could be the main driving factor for such anisotropic growth. These observations are not only helpful in understanding the growth mechanism of α-Fe{sub 2}O{sub 3} nanowires, but it also demonstrates a way of patterning the nanowires by controlling the texture of iron substrate.« less

SEM Characterization of Extinguished Grains from Plasma-Ignited M30 Charges

NASA Technical Reports Server (NTRS)

Kinkennon, A.; Birk, A.; DelGuercio, M.; Kaste, P.; Lieb, R.; Newberry, J.; Pesce-Rodriguez, R.; Schroeder, M.

2000-01-01

M30 propellant grains that had been ignited in interrupted closed bomb experiments were characterize by scanning electron microscopy (SEM). Previous chemical analysis of extinguished grains had given no indications of plasma-propellant chemical interactions that could explain the increased burning rates that had been previously observed in full-pressure closed bomb experiments. (This does not mean that there is no unique chemistry occurring with plasma ignition. It may occur very early in the ignition event and then become obscured by the burning chemistry.) In this work, SEM was used to look at grain morphologies to determine if there were increases in the surface areas of the plasma-ignited grains which would contribute to the apparent increase in the burning rate. Charges were made using 30 propellant grains (approximately 32 grams) stacked in two tiers and in two concentric circles around a plastic straw. Each grain was notched so that, when the grains were expelled from the bomb during extinguishment, it could be determined in which tier and which circle each grain was originally packed. Charges were ignited in a closed bomb by either a nickel wire/Mylar-capillary plasma or black powder. The bomb contained a blowout disk that ruptured when the pressure reached 35 MPa, and the propellant was vented into a collection chamber packed with polyurethane foam. SEM analysis of the grains fired with a conventional black powder igniter showed no signs of unusual burning characteristics. The surfaces seemed to be evenly burned on the exteriors of the grains and in the perforations. Grains that had been subjected to plasma ignition, however, had pits, gouges, chasms, and cracks in the surfaces. The sides of the grains closest to the plasma had the greatest amount of damage, but even surfaces facing the outer wall of the bomb had small pits. The perforations contained gouges and abnormally burned regions (wormholes) that extended into the web. The SEM photos indicated that a grain from the top tier, which was farther away from the plasma ignition source, sustained more plasma-induced damage to the perforations and the web than did the grains on the bottom tier.

Light response of sunflower and canola as affected by plant density, plant genotype and N fertilization.

PubMed

Soleymani, A

2017-08-01

Crop response to light is an important parameter determining crop growth. Three field (split plots) experiments were conducted to investigate the effects of plant density, plant genotype and N fertilization on the light absorption and light extinction of sunflower (Helianthus annuus L.) and canola (Brassica napus L.). A detailed set of plant growth, light absorption and crop yield and oil related parameters were determined. Light was measured at noon during the sunny days with clear sky. In experiment I, although the plant density (PD) of 14 resulted in the highest rate of sunflower light absorption (31.37%) and light extinction (0.756), the highest rate of grain yield and grain oil yield was resulted at PD12 at 3639 and 1457.9kg/ha, respectively; as well as by genotype SUP.A. In experiment II (canola), PD80 resulted in the highest rate of light absorption (13.13%), light extinction (0.63), grain yield (2189.4kg/ha) and grain oil yield (556.54kg/ha). This was also the case for Genotype H. In experiment III (canola), although N150 resulted in the highest rate of light absorption (10.74%) and light extinction (0.48), the highest rate of grain yield (3413.6kg/ha) and grain oil yield (891.86kg/ha) was resulted at N100 as well as by Genotype H401. Results indicate how light properties, crop growth and yield of sunflower and canola can be affected by plant and environmental parameters, which are also of practical use by farmers. Copyright © 2017 Elsevier B.V. All rights reserved.

Effect on the growth and development and induction of abnormalities by a glyphosate commercial formulation and its active ingredient during two developmental stages of the South-American Creole frog, Leptodactylus latrans.

PubMed

Bach, Nadia Carla; Natale, Guillermo Sebastián; Somoza, Gustavo Manuel; Ronco, Alicia Estela

2016-12-01

We evaluated the acute lethal and sublethal effects of technical-grade glyphosate (GLY) and the GLY-based commercial formulation Roundup ULTRA MAX® (RU) on two Gosner stages (Gss) 25 and 36 of the South-American Creole frog, Leptodactylus latrans. Bioassays were performed following standardized methods within a wide range of concentrations (0.0007-9.62 mg of acid equivalents per liter-a.e./L-of RU and 3-300 mg/L of GLY). The endpoints evaluated were mortality, swimming activity, growth, development, and the presence of morphologic abnormalities, especially in the mouthparts. No lethal effects were observed on larvae exposed to GLY during either Gs-25 or Gs-36. The concentrations inducing 50 % lethality in RU-exposed larvae at different exposure times and Gss ranged from 3.26 to 9.61 mg a.e./L. Swimming activity was affected by only RU. Effects on growth and development and the induction of morphologic abnormalities-like oral abnormalities and edema-were observed after exposure to either GLY or RU. Gs-25 was the most sensitive stage to both forms of the herbicide. The commercial formulation was much more toxic than the active ingredient on all the endpoints assessed. Effects on growth, development, and the induction of morphologic abnormalities observed in the range of environmental concentrations reported for agroecosystems of Argentina constitute an alert to the potential detrimental effects of the herbicide that could be affecting the fitness and survival of anurans in agroecosystems.

The role of angiogenic factors in fibroid pathogenesis: potential implications for future therapy

PubMed Central

Tal, Reshef; Segars, James H.

2014-01-01

Background It is well established that tumors are dependent on angiogenesis for their growth and survival. Although uterine fibroids are known to be benign tumors with reduced vascularization, recent work demonstrates that the vasculature of fibroids is grossly and microscopically abnormal. Accumulating evidence suggests that angiogenic growth factor dysregulation may be implicated in these vascular and other features of fibroid pathophysiology. Methods Literature searches were performed in PubMed and Google Scholar for articles with content related to angiogenic growth factors and myometrium/leiomyoma. The findings are hereby reviewed and discussed. Results Multiple growth factors involved in angiogenesis are differentially expressed in leiomyoma compared with myometrium. These include epidermal growth factor (EGF), heparin-binding-EGF, vascular endothelial growth factor, basic fibroblast growth factor, platelet-derived growth factor, transforming growth factor-β and adrenomedullin. An important paradox is that although leiomyoma tissues are hypoxic, leiomyoma feature down-regulation of key molecular regulators of the hypoxia response. Furthermore, the hypoxic milieu of leiomyoma may contribute to fibroid development and growth. Notably, common treatments for fibroids such as GnRH agonists and uterine artery embolization (UAE) are shown to work at least partly via anti-angiogenic mechanisms. Conclusions Angiogenic growth factors play an important role in mechanisms of fibroid pathophysiology, including abnormal vasculature and fibroid growth and survival. Moreover, the fibroid's abnormal vasculature together with its aberrant hypoxic and angiogenic response may make it especially vulnerable to disruption of its vascular supply, a feature which could be exploited for treatment. Further experimental studies are required in order to gain a better understanding of the growth factors that are involved in normal and pathological myometrial angiogenesis, and to assess the potential of anti-angiogenic treatment strategies for uterine fibroids. PMID:24077979

Animal model of grain worker's lung.

PubMed Central

Stepner, N; Broder, I; Baumal, R

1986-01-01

We examined the light microscopic changes in the lungs of rabbits exposed to grain dust for variable periods of time, to determine whether an animal model of grain worker's lung could be developed. Experimental animals were exposed to grain dust at a concentration of 20 mg/m3 for 7 hr/day, 5 days/week, for up to 6 months. The lungs of these rabbits demonstrated a granulomatous interstitial pneumonitis associated with exudation of mononuclear cells into the alveoli and conducting airways. These changes appeared within 5 days of the onset of exposure and reached a peak at 3 weeks but were sustained through the longest exposure interval. No abnormalities were observed in the lungs of control rabbits. These results show three points of consistency with those obtained in epidemiologic studies of grain elevator workers. First, the rapid appearance of the experimental changes suggests that the mechanism of tissue injury may not be immunologic. Second, the occurrence of the histopathologic alterations in the interstitium, alveoli, and airways corresponds with the combined restrictive and obstructive ventilatory defect described in the human epidemiologic studies. Third, the absence of lung fibrosis in rabbits exposed to dust for 6 months suggests that the pneumonitis is reversible. Thus this experimental model shows promise of helping to clarify the nature and mechanism of the adverse pulmonary effects of grain dust. Images FIGURE 1. FIGURE 2. PMID:3709485

Phase and microstructural development in alumina sol-gel coatings on CoCr alloy.

PubMed

Bae, I J; Standard, O C; Roger, G J; Brazil, D

2004-09-01

Phase transformation of gamma-Al(2)O(3) to alpha-Al(2)O(3) in alumina sol gel coatings on biomedical CoCr alloy was studied as function of heat treatment temperature and time. Transformation in unseeded coatings was significant only above approximately 1200 degrees C. Addition of alpha-Al(2)O(3) seed particles having an average size of approximately 40 nm lowered the phase transformation temperature to around 800 degrees C. These particles were considered to act as heterogeneous nucleation sites for epitaxial growth of the alpha-Al(2)O(3) phase. The kinetics and activation energy (420 kJ/mol) for the phase transformation in the seeded coatings were similar to those reported for seeded monolithic alumina gels indicating that the transformation mechanism is the same in the two material configurations. Avrami growth parameters indicated that the mechanism was diffusion controlled and invariant over the temperature range studied but that growth was possibly constrained by the finite size of the seed particles and/or coating thickness. The phase transformation occurred by the growth of alpha-Al(2)O(3) grains at the expense of the precursor fine-grained gamma-Al(2)O(3) matrix and near-complete transformation coincided with physical impingement of the growing grains. The grain size at impingement was approximately 100 nm which agreed well with that predicted from the theoretical linear spacing of seed particles in the initial sol.

The structural and photosynthetic characteristics of the exposed peduncle of wheat (Triticum aestivum L.): an important photosynthate source for grain-filling.

PubMed

Kong, Lingan; Wang, Fahong; Feng, Bo; Li, Shengdong; Si, Jisheng; Zhang, Bin

2010-07-11

In wheat (Triticum aestivum L), the flag leaf has been thought of as the main source of assimilates for grain growth, whereas the peduncle has commonly been thought of as a transporting organ. The photosynthetic characteristics of the exposed peduncle have therefore been neglected. In this study, we investigated the anatomical traits of the exposed peduncle during wheat grain ontogenesis, and we compared the exposed peduncle to the flag leaf with respect to chloroplast ultrastructure, photosystem II (PSII) quantum yield, and phosphoenolpyruvate carboxylase (PEPCase; EC 4.1.1.31) activity. Transmission electron microscope observations showed well-developed chloroplasts with numerous granum stacks at grain-filling stages 1, 2 and 3 in both the flag leaf and the exposed peduncle. In the exposed peduncle, the membranes constituting the thylakoids were very distinct and plentiful, but in the flag leaf, there was a sharp breakdown at stage 4 and complete disintegration of the thylakoid membranes at stage 5. PSII quantum yield assays revealed that the photosynthetic efficiency remained constant at stages 1, 2 and 3 and then declined in both organs. However, the decline occurred more dramatically in the flag leaf than in the exposed peduncle. An enzyme assay showed that at stages 1 and 2 the PEPCase activity was lower in the exposed peduncle than in the flag leaf; but at stages 3, 4 and 5 the value was higher in the exposed peduncle, with a particularly significant difference observed at stage 5. Subjecting the exposed part of the peduncle to darkness following anthesis reduced the rate of grain growth. Our results suggest that the exposed peduncle is a photosynthetically active organ that produces photosynthates and thereby makes a crucial contribution to grain growth, particularly during the late stages of grain-filling.

Compositional inhomogeneityand segregation in (K 0.5Na 0.5)NbO 3 ceramics

DOE PAGES

Chen, Kepi; Tang, Jing; Chen, Yan

2016-03-11

The effects of the calcination temperature of (K 0.5Na 0.5)NbO 3 (KNN) powder on the sintering and piezoelectric properties of KNN ceramics have been investigated in this report. KNN powders are synthesized via the solid-state approach. Scanning electron microscopy and X-ray diffraction characterizations indicate that the incomplete reaction at 700 °C and 750 °C calcination results in the compositional inhomogeneity of the K-rich and Na-rich phases while the orthorhombic single phase is obtained after calcination at 900 °C. During the sintering, the presence of the liquid K-rich phase due to the lower melting point has a significant impact on themore » densification, the abnormal grain growth and the deteriorated piezoelectric properties. From the standpoint of piezoelectric properties, the optimal calcination temperature obtained for KNN ceramics calcined at this temperature is determined to be 800 °C, with piezoelectric constant d 33=128.3 pC/N, planar electromechanical coupling coefficient k p=32.2%, mechanical quality factor Q m=88, and dielectric loss tan δ=2.1%.« less

Development of early communication skills in the first two years of life.

PubMed

Beuker, Karin T; Rommelse, Nanda N J; Donders, Rogier; Buitelaar, Jan K

2013-02-01

The first two years of life is a crucially important period for the development of communication skills. In this study joint attention and language development were monthly assessed between 8 and 24 months of age in a sample of 23 typically developing children to establish the developmental trajectory of specific joint attention skills, to investigate the developmental interrelations of these different joint attention skills with vocabulary size, and to examine whether the order of development of following and directing attention influences the development of other early communication skills such as language. All joint attention skills emerged between 8 and 15 months of age and responsive joint attention skills tend to emerge before initiative joint attention. Early joint attention skills influenced later language development, but not the other way around. Children in whom directing attention with gaze alternation developed early (in age or order) showed a relatively larger early vocabulary growth. A fine grained mapping of the normal development of early communication skills can be helpful in the early detection of abnormalities in these skills. Copyright © 2012 Elsevier Inc. All rights reserved.

MORPHOLOGICAL AND CYTOLOGICAL CHANGES IN CENTURY PATNA 231 AND BLUEBONNET 50 RICE RESULTING FROM X-RAY AND THERMAL NEUTRON IRRADIATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shah, H.M.; Beachell, H.M.; Atkins, I.M.

1961-03-01

Morphological and cytological studies of one X/sub 2/ (maintained vegetatively) and 20 X/sub 5/ lines of Bluebonnet 50 and Century Patna 231 rice varieties obtained from seeds exposed to different dosages of x rays and thermal neutrons revealed a number of interesting and valuable mutant types. These included mutations of leaf size and color, growth habit, plant height and straw strength, particles, spikelets, flowering habit, and fertility. Some of the short-stature and other plants may have considerable economic value in breeding lodging resistant varieties. Cytological studies revealed that one plant was a tetraploid. Most plants studied were diploid but oftenmore » had abnormal chromosome numbers or association. Univalents, trivalents, and quadrivalents were common but fragments. asynapsis, knot formations, irregular division, bridge formations, and differences in pollen grain size were observed. There was a positive correIation hetween quadrivalents in P.M.C. and pollen sterility and between pollen and spikelet sterility, although there were some unusual exceptions to this. (auth)« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Kepi; Tang, Jing; Chen, Yan

The effects of the calcination temperature of (K 0.5Na 0.5)NbO 3 (KNN) powder on the sintering and piezoelectric properties of KNN ceramics have been investigated in this report. KNN powders are synthesized via the solid-state approach. Scanning electron microscopy and X-ray diffraction characterizations indicate that the incomplete reaction at 700 °C and 750 °C calcination results in the compositional inhomogeneity of the K-rich and Na-rich phases while the orthorhombic single phase is obtained after calcination at 900 °C. During the sintering, the presence of the liquid K-rich phase due to the lower melting point has a significant impact on themore » densification, the abnormal grain growth and the deteriorated piezoelectric properties. From the standpoint of piezoelectric properties, the optimal calcination temperature obtained for KNN ceramics calcined at this temperature is determined to be 800 °C, with piezoelectric constant d 33=128.3 pC/N, planar electromechanical coupling coefficient k p=32.2%, mechanical quality factor Q m=88, and dielectric loss tan δ=2.1%.« less

Seismic wave velocity of hydrate-bearing fine-grained sediments sampled from the Ulleung basin in East Sea, Korea

NASA Astrophysics Data System (ADS)

Kim, H.; Kwon, T.; Cho, G.

2012-12-01

Synthesizing gas hydrate in a fine-grained natural seabed sediment sample, mainly composed of silty-to-clayey soils, has been hardly attempted due to the low permeability. It has been known that hydrate loci in pore spaces and heterogeneity of hydrate growth in core-scale play a critical role in determining physical properties of hydrate-bearing sediments. In the presented study, we attempted to identify the effect of hydrate growth morphology on seismic velocities in natural fine-grained sediments sampled from the Ulleung Basin in East Sea. We synthesized CO2 hydrate in clayey silt sediments in an instrumented oedometric cell and measured seismic velocities during hydrate formation and loading processes. Herein, we present the experiment results on P-wave and S-wave velocities of gas hydrate-bearing fine-grained sediments. It is found that the geophysical properties of gas hydrate-bearing sediments are governed by hydrate saturation and effective stress as well as morphological feature of hydrate formation in sediments.

Irradiation effects on multilayered W/ZrO2 film under 4 MeV Au ions

NASA Astrophysics Data System (ADS)

Wang, Hongwei; Gao, Yuan; Fu, Engang; Yang, Tengfei; Xue, Jianming; Yan, Sha; Chu, Paul K.; Wang, Yugang

2014-12-01

Irradiation induced structural changes in multilayered W/ZrO2 nanocomposites with periodic bilayer thicknesses of (7/14 nm) and (70/140 nm) were investigated following Au+ ion irradiation. The samples were irradiated by 4 MeV Au ions with fluences ranging from 6 × 1014 to 1 × 1016 ions/cm2. The immiscible W/ZrO2 interfaces remained unchanged without intermixing of the layers upon the irradiation. No voids were observed in the samples with different periodic layer thicknesses. The XRD and XTEM studies reveal thickness dependent microstructural changes in the samples. W and ZrO2 grains in the thinner (7/14 nm) bilayer sample exhibit significant resistance to grain growth compared to the thicker (70/140 nm) bilayer sample as well as a W monolayer film. The high fraction of flat interfaces as well as grain boundaries in multilayer films plays a role in suppressing ion irradiation-induced grain growth and void formation.

In vitro and in vivo assessment of the effect of initial moisture content and drying temperature on the feeding value of maize grain.

PubMed

Huart, F; Malumba, P; Odjo, S; Al-Izzi, W; Béra, F; Beckers, Y

2018-06-11

1. This study assessed the impact of drying temperature (54, 90, and 130°C) and maize grain moisture content at harvest (36% and 29%) on in vitro digestibility, the growth performance and ileal digestibility of broiler chickens. 2. In contrast to the results from the in vitro digestibility, apparent ileal digestibility of starch and energy decreased when the drying temperature was raised from 54 to 130°C, and this effect was more pronounced in maize grain harvested at high initial moisture content (36%). Ileal protein digestibility of maize grain decreased significantly when dried at the intermediate temperature (90°C) and with a high harvest moisture content (36%). Drying temperature and initial moisture content did not significantly affect AMEn. 3. When maize was dried at 130°C, the particle sizes of flour recovered after standard milling procedures decreased significantly, which would influence animal growth performance and in vivo digestibility through animal feed selection.

Synthesis of large single-crystal hexagonal boron nitride grains on Cu-Ni alloy

NASA Astrophysics Data System (ADS)

Lu, Guangyuan; Wu, Tianru; Yuan, Qinghong; Wang, Huishan; Wang, Haomin; Ding, Feng; Xie, Xiaoming; Jiang, Mianheng

2015-01-01

Hexagonal boron nitride (h-BN) has attracted significant attention because of its superior properties as well as its potential as an ideal dielectric layer for graphene-based devices. The h-BN films obtained via chemical vapour deposition in earlier reports are always polycrystalline with small grains because of high nucleation density on substrates. Here we report the successful synthesis of large single-crystal h-BN grains on rational designed Cu-Ni alloy foils. It is found that the nucleation density can be greatly reduced to 60 per mm2 by optimizing Ni ratio in substrates. The strategy enables the growth of single-crystal h-BN grains up to 7,500 μm2, approximately two orders larger than that in previous reports. This work not only provides valuable information for understanding h-BN nucleation and growth mechanisms, but also gives an effective alternative to exfoliated h-BN as a high-quality dielectric layer for large-scale nanoelectronic applications.

The Role of Grain Size on Neutron Irradiation Response of Nanocrystalline Copper

PubMed Central

Mohamed, Walid; Miller, Brandon; Porter, Douglas; Murty, Korukonda

2016-01-01

The role of grain size on the developed microstructure and mechanical properties of neutron irradiated nanocrystalline copper was investigated by comparing the radiation response of material to the conventional micrograined counterpart. Nanocrystalline (nc) and micrograined (MG) copper samples were subjected to a range of neutron exposure levels from 0.0034 to 2 dpa. At all damage levels, the response of MG-copper was governed by radiation hardening manifested by an increase in strength with accompanying ductility loss. Conversely, the response of nc-copper to neutron irradiation exhibited a dependence on the damage level. At low damage levels, grain growth was the primary response, with radiation hardening and embrittlement becoming the dominant responses with increasing damage levels. Annealing experiments revealed that grain growth in nc-copper is composed of both thermally-activated and irradiation-induced components. Tensile tests revealed minimal change in the source hardening component of the yield stress in MG-copper, while the source hardening component was found to decrease with increasing radiation exposure in nc-copper. PMID:28773270