Application of Image Analysis for Characterization of Spatial Arrangements of Features in Microstructure

NASA Technical Reports Server (NTRS)

Louis, Pascal; Gokhale, Arun M.

1995-01-01

A number of microstructural processes are sensitive to the spatial arrangements of features in microstructure. However, very little attention has been given in the past to the experimental measurements of the descriptors of microstructural distance distributions due to the lack of practically feasible methods. We present a digital image analysis procedure to estimate the micro-structural distance distributions. The application of the technique is demonstrated via estimation of K function, radial distribution function, and nearest-neighbor distribution function of hollow spherical carbon particulates in a polymer matrix composite, observed in a metallographic section.

Evolution and Control of 2219 Aluminum Microstructural Features Through Electron Beam Freeform Fabrication

NASA Technical Reports Server (NTRS)

Taminger, Karen M.; Hafley, Robert A.; Domack, Marcia S.

2006-01-01

The layer-additive nature of the electron beam freeform fabrication (EBF3) process results in a tortuous thermal path producing complex microstructures including: small homogeneous equiaxed grains; dendritic growth contained within larger grains; and/or pervasive dendritic formation in the interpass regions of the deposits. Several process control variables contribute to the formation of these different microstructures, including translation speed, wire feed rate, beam current and accelerating voltage. In electron beam processing, higher accelerating voltages embed the energy deeper below the surface of the substrate. Two EBF3 systems have been established at NASA Langley, one with a low-voltage (10-30kV) and the other a high-voltage (30-60 kV) electron beam gun. Aluminum alloy 2219 was processed over a range of different variables to explore the design space and correlate the resultant microstructures with the processing parameters. This report is specifically exploring the impact of accelerating voltage. Of particular interest is correlating energy to the resultant material characteristics to determine the potential of achieving microstructural control through precise management of the heat flux and cooling rates during deposition.

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.

Microstructure Analysis of Bismuth Absorbers for Transition-Edge Sensor X-ray Microcalorimeters

NASA Astrophysics Data System (ADS)

Yan, Daikang; Divan, Ralu; Gades, Lisa M.; Kenesei, Peter; Madden, Timothy J.; Miceli, Antonino; Park, Jun-Sang; Patel, Umeshkumar M.; Quaranta, Orlando; Sharma, Hemant; Bennett, Douglas A.; Doriese, William B.; Fowler, Joseph W.; Gard, Johnathon D.; Hays-Wehle, James P.; Morgan, Kelsey M.; Schmidt, Daniel R.; Swetz, Daniel S.; Ullom, Joel N.

2018-03-01

Given its large X-ray stopping power and low specific heat capacity, bismuth (Bi) is a promising absorber material for X-ray microcalorimeters and has been used with transition-edge sensors (TESs) in the past. However, distinct X-ray spectral features have been observed in TESs with Bi absorbers deposited with different techniques. Evaporated Bi absorbers are widely reported to have non-Gaussian low-energy tails, while electroplated ones do not show this feature. In this study, we fabricated Bi absorbers with these two methods and performed microstructure analysis using scanning electron microscopy and X-ray diffraction microscopy. The two types of material showed the same crystallographic structure, but the grain size of the electroplated Bi was about 40 times larger than that of the evaporated Bi. This distinction in grain size is likely to be the cause of their different spectral responses.

MUTLI-OBJECTIVE OPTIMIZATION OF MICROSTRUCTURE IN WROUGHT MAGNESIUM ALLOYS

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

Radhakrishnan, Balasubramaniam; Gorti, Sarma B; Simunovic, Srdjan

2013-01-01

The microstructural features that govern the mechanical properties of wrought magnesium alloys include grain size, crystallographic texture, and twinning. Several processes based on shear deformation have been developed that promote grain refinement, weakening of the basal texture, as well as the shift of the peak intensity away from the center of the basal pole figure - features that promote room temperature ductility in Mg alloys. At ORNL, we are currently exploring the concept of introducing nano-twins within sub-micron grains as a possible mechanism for simultaneously improving strength and ductility by exploiting a potential dislocation glide along the twin-matrix interface amore » mechanism that was originally proposed for face-centered cubic materials. Specifically, we have developed an integrated modeling and optimization framework in order to identify the combinations of grain size, texture and twin spacing that can maximize strength-ductility combinations. A micromechanical model that relates microstructure to material strength is coupled with a failure model that relates ductility to a critical shear strain and a critical hydrostatic stress. The micro-mechanical model is combined with an optimization tool based on genetic algorithm. A multi-objective optimization technique is used to explore the strength-ductility space in a systematic fashion and identify optimum combinations of the microstructural parameters that will simultaneously maximize the strength-ductility in the alloy.« less

Microstructure design for fast oxygen conduction

DOE PAGES

Aidhy, Dilpuneet S.; Weber, William J.

2015-11-11

Research from the last decade has shown that in designing fast oxygen conducting materials for electrochemical applications has largely shifted to microstructural features, in contrast to material-bulk. In particular, understanding oxygen energetics in heterointerface materials is currently at the forefront, where interfacial tensile strain is being considered as the key parameter in lowering oxygen migration barriers. Nanocrystalline materials with high densities of grain boundaries have also gathered interest that could possibly allow leverage over excess volume at grain boundaries, providing fast oxygen diffusion channels similar to those previously observed in metals. In addition, near-interface phase transformations and misfit dislocations aremore » other microstructural phenomenon/features that are being explored to provide faster diffusion. In this review, the current understanding on oxygen energetics, i.e., thermodynamics and kinetics, originating from these microstructural features is discussed. Moreover, our experimental observations, theoretical predictions and novel atomistic mechanisms relevant to oxygen transport are highlighted. In addition, the interaction of dopants with oxygen vacancies in the presence of these new microstructural features, and their future role in the design of future fast-ion conductors, is outlined.« less

Advanced Steel Microstructural Classification by Deep Learning Methods.

PubMed

Azimi, Seyed Majid; Britz, Dominik; Engstler, Michael; Fritz, Mario; Mücklich, Frank

2018-02-01

The inner structure of a material is called microstructure. It stores the genesis of a material and determines all its physical and chemical properties. While microstructural characterization is widely spread and well known, the microstructural classification is mostly done manually by human experts, which gives rise to uncertainties due to subjectivity. Since the microstructure could be a combination of different phases or constituents with complex substructures its automatic classification is very challenging and only a few prior studies exist. Prior works focused on designed and engineered features by experts and classified microstructures separately from the feature extraction step. Recently, Deep Learning methods have shown strong performance in vision applications by learning the features from data together with the classification step. In this work, we propose a Deep Learning method for microstructural classification in the examples of certain microstructural constituents of low carbon steel. This novel method employs pixel-wise segmentation via Fully Convolutional Neural Network (FCNN) accompanied by a max-voting scheme. Our system achieves 93.94% classification accuracy, drastically outperforming the state-of-the-art method of 48.89% accuracy. Beyond the strong performance of our method, this line of research offers a more robust and first of all objective way for the difficult task of steel quality appreciation.

Microornamentation of leaf chameleons (Chamaeleonidae: Brookesia, Rhampholeon, and Rieppeleon)--with comments on the evolution of microstructures in the Chamaeleonidae.

PubMed

Riedel, Jendrian; Böhme, Wolfgang; Bleckmann, Horst; Spinner, Marlene

2015-02-01

Chameleons (Chamaeleonidae) feature many adaptations to their arboreal lifestyle, including zygodactylous feet, a prehensile tail, and epidermal microstructures. In arboreal tree chameleons, the substrate-contacting site of the feet and tail is covered by microscopic hair-like structures (setae) of 6-20 µm length. Their friction enhancing function has been shown in recent studies. Leaf chameleons and one representative of the tree chameleons (Chamaeleo namaquensis) secondarily have become ground-dwelling. Because leaf chameleons are paraphyletic, one could expect that in the three leaf chameleon genera Brookesia, Rhampholeon, and Rieppeleon and the tree chameleon Ch. namaquensis, epidermis has adapted independently to terrestrial locomotion. Using scanning electron microscopy, we investigated the substrate-contacting surfaces of the feet (subdigital) of 17 leaf chameleon species and five tree chameleon species that have not yet been examined. Additionally, surfaces not involved in locomotion, the flanks (dorsolateral), and scale interstices, were examined. Although the subdigital microstructures in leaf chameleons are more diverse than in tree chameleons, we found some features across the genera. The subdigital microornamentation of Rhampholeon spinosus consists of long thin setae and spines, comparable to those of tree chameleons. All other Rhampholeon species have spines or short but broad setae. Rh. spectrum had tooth-like structures instead of setae. Subdigital scales of Brookesia have either thorns or conical scale-tops in the center and feature honeycomb microstructures. In Rieppeleon, subdigital scales have a thorn. Scale surfaces are covered by honeycombs and short hair-like structures (spines). As subdigital scales with a thorn in the center and honeycomb microstructures were also found in the terrestrial tree chameleon Ch. namaquensis, one can assume that this geometry is a convergent adaptation to terrestrial locomotion. Despite the great number of genus-specific traits, the convergent evolution of honey-comb structures in Brookesia, Rieppeleon, and Ch. namaquensis and the high variability of spines and setae in Rhampholeon suggests a rapid adaptation of subdigital microornamentation in Chamaeleonidae. © 2014 Wiley Periodicals, Inc.

Temporal association tracts and the breakdown of episodic memory in mild cognitive impairment

PubMed Central

Metzler-Baddeley, Claudia; Hunt, Sarah; Jones, Derek K.; Leemans, Alexander; Aggleton, John P.

2012-01-01

Objective: To examine the pattern of association between microstructure of temporal lobe connections and the breakdown of episodic memory that is a core feature of mild cognitive impairment (MCI). Methods: Twenty-five individuals with MCI and 20 matched controls underwent diffusion MRI and cognitive assessment. Three temporal pathways were reconstructed by tractography: fornix, parahippocampal cingulum (PHC), and uncinate fasciculus. Tissue volume fraction—a tract-specific measure of atrophy—and microstructural measures were derived for each tract. To test specificity of associations, a comparison tract (corticospinal tract) and control cognitive domains were also examined. Results: In MCI, tissue volume fraction was reduced in the fornix. Axial and radial diffusivity were increased in uncinate and PHC implying more subtle microstructural change. In controls, tissue volume fraction in the fornix was the predominant correlate of free recall. In contrast, in MCI, the strongest relationship was with left PHC. Microstructure of uncinate and PHC also correlated with recognition memory, and recognition confidence, in MCI. Conclusions: Episodic memory in MCI is related to the structure of multiple temporal association pathways. These associations are not confined to the fornix, as they are in healthy young and older adults. In MCI, because of a compromised fornix, alternative pathways may contribute disproportionally to episodic memory performance. PMID:23175726

Three-dimensional microstructural characterization of bulk plutonium and uranium metals using focused ion beam technique

NASA Astrophysics Data System (ADS)

Chung, Brandon W.; Erler, Robert G.; Teslich, Nick E.

2016-05-01

Nuclear forensics requires accurate quantification of discriminating microstructural characteristics of the bulk nuclear material to identify its process history and provenance. Conventional metallographic preparation techniques for bulk plutonium (Pu) and uranium (U) metals are limited to providing information in two-dimension (2D) and do not allow for obtaining depth profile of the material. In this contribution, use of dual-beam focused ion-beam/scanning electron microscopy (FIB-SEM) to investigate the internal microstructure of bulk Pu and U metals is demonstrated. Our results demonstrate that the dual-beam methodology optimally elucidate microstructural features without preparation artifacts, and the three-dimensional (3D) characterization of inner microstructures can reveal salient microstructural features that cannot be observed from conventional metallographic techniques. Examples are shown to demonstrate the benefit of FIB-SEM in improving microstructural characterization of microscopic inclusions, particularly with respect to nuclear forensics.

Three-dimensional microstructural characterization of bulk plutonium and uranium metals using focused ion beam technique

DOE PAGES

Chung, Brandon W.; Erler, Robert G.; Teslich, Nick E.

2016-03-03

Nuclear forensics requires accurate quantification of discriminating microstructural characteristics of the bulk nuclear material to identify its process history and provenance. Conventional metallographic preparation techniques for bulk plutonium (Pu) and uranium (U) metals are limited to providing information in two-dimension (2D) and do not allow for obtaining depth profile of the material. In this contribution, use of dual-beam focused ion-beam/scanning electron microscopy (FIB-SEM) to investigate the internal microstructure of bulk Pu and U metals is demonstrated. Our results demonstrate that the dual-beam methodology optimally elucidate microstructural features without preparation artifacts, and the three-dimensional (3D) characterization of inner microstructures can revealmore » salient microstructural features that cannot be observed from conventional metallographic techniques. As a result, examples are shown to demonstrate the benefit of FIB-SEM in improving microstructural characterization of microscopic inclusions, particularly with respect to nuclear forensics.« less

Microstructure Imaging of Crossing (MIX) White Matter Fibers from diffusion MRI

PubMed Central

Farooq, Hamza; Xu, Junqian; Nam, Jung Who; Keefe, Daniel F.; Yacoub, Essa; Georgiou, Tryphon; Lenglet, Christophe

2016-01-01

Diffusion MRI (dMRI) reveals microstructural features of the brain white matter by quantifying the anisotropic diffusion of water molecules within axonal bundles. Yet, identifying features such as axonal orientation dispersion, density, diameter, etc., in complex white matter fiber configurations (e.g. crossings) has proved challenging. Besides optimized data acquisition and advanced biophysical models, computational procedures to fit such models to the data are critical. However, these procedures have been largely overlooked by the dMRI microstructure community and new, more versatile, approaches are needed to solve complex biophysical model fitting problems. Existing methods are limited to models assuming single fiber orientation, relevant to limited brain areas like the corpus callosum, or multiple orientations but without the ability to extract detailed microstructural features. Here, we introduce a new and versatile optimization technique (MIX), which enables microstructure imaging of crossing white matter fibers. We provide a MATLAB implementation of MIX, and demonstrate its applicability to general microstructure models in fiber crossings using synthetic as well as ex-vivo and in-vivo brain data. PMID:27982056

Specific features of direct formation of graphite-like microstructures in polycarbonate samples by single femtosecond laser pulses

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

Ganin, D V; Lapshin, K E; Obidin, A Z

2015-11-30

We present the result of the experiments on producing graphite-like cylindrical microstructures by focusing single femtosecond laser pulses into the bulk of a transparent polymer (polycarbonate). The microstructures are embedded in a cladding with a modified refractive index, possessing waveguide properties. In the experiments with nontransparent screens and diaphragms, placed in the laser beam in front of the entrance pupil of the objective with a large numerical aperture, we have found that the paraxial rays are blocked by the peripheral ones, which reduces the length of the destruction region in the pre-focal zone. In the experiments with transparent screens andmore » diaphragms, introducing optical delays τ{sub d} between the paraxial and peripheral rays, the quantitative dependence of the destruction region length in the pre-focal zone on the value of τ{sub d} is determined. (interaction of laser radiation with matter. laser plasma)« less

Effect of microstructure on the elasto-viscoplastic deformation of dual phase titanium structures

NASA Astrophysics Data System (ADS)

Ozturk, Tugce; Rollett, Anthony D.

2018-02-01

The present study is devoted to the creation of a process-structure-property database for dual phase titanium alloys, through a synthetic microstructure generation method and a mesh-free fast Fourier transform based micromechanical model that operates on a discretized image of the microstructure. A sensitivity analysis is performed as a precursor to determine the statistically representative volume element size for creating 3D synthetic microstructures based on additively manufactured Ti-6Al-4V characteristics, which are further modified to expand the database for features of interest, e.g., lath thickness. Sets of titanium hardening parameters are extracted from literature, and The relative effect of the chosen microstructural features is quantified through comparisons of average and local field distributions.

TRADITIONAL METALLURGY, NANOTECHNOLOGIES AND STRUCTURAL MATERIALS: A SORBY AWARD LECTURE

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

Louthan, M

2007-07-17

Traditional metallurgical processes are among the many ''old fashion'' practices that use nanoparticles to control the behavior of materials. Many of these practices were developed long before microscopy could resolve nanoscale features, yet the practitioners learned to manipulate and control microstructural elements that they could neither see nor identify. Furthermore, these early practitioners used that control to modify microstructures and develop desired material properties. Centuries old colored glass, ancient high strength steels and medieval organ pipes derived many of their desirable features through control of nanoparticles in their microstructures. Henry Sorby was among the first to recognize that the propertiesmore » of rocks, minerals, metals and organic materials were controlled by microstructure. However, Mr. Sorby was accused of the folly of trying to study mountains with a microscope. Although he could not resolve nanoscale microstructural features, Mr. Sorby's observations revolutionized the study of materials. The importance of nanoscale microstructural elements should be emphasized, however, because the present foundation for structural materials was built by manipulating those features. That foundation currently supports several multibillion dollar industries but is not generally considered when the nanomaterials revolution is discussed. This lecture demonstrates that using nanotechnologies to control the behavior of metallic materials is almost as old as the practice of metallurgy and that many of the emergent nanomaterials technologists are walking along pathways previously paved by traditional metallurgists.« less

Crystal plasticity assisted prediction on the yield locus evolution and forming limit curves

NASA Astrophysics Data System (ADS)

Lian, Junhe; Liu, Wenqi; Shen, Fuhui; Münstermann, Sebastian

2017-10-01

The aim of this study is to predict the plastic anisotropy evolution and its associated forming limit curves of bcc steels purely based on their microstructural features by establishing an integrated multiscale modelling approach. Crystal plasticity models are employed to describe the micro deformation mechanism and correlate the microstructure with mechanical behaviour on micro and mesoscale. Virtual laboratory is performed considering the statistical information of the microstructure, which serves as the input for the phenomenological plasticity model on the macroscale. For both scales, the microstructure evolution induced evolving features, such as the anisotropic hardening, r-value and yield locus evolution are seamlessly integrated. The predicted plasticity behaviour by the numerical simulations are compared with experiments. These evolutionary features of the material deformation behaviour are eventually considered for the prediction of formability.

Effect of local void morphology on the reaction initiation mechanism in the case of pressed HMX

NASA Astrophysics Data System (ADS)

Roy, Sidhartha; Rai, Nirmal; Udaykumar, H. S.

2017-06-01

The microstructural characteristics of pressed HMX has a significant effect on its sensitivity under shock loading. The microstructure of pressed HMX contains voids of various orientation and aspect ratio. Subject to shock loading, these voids can collapse forming hotspots and initiate chemical reaction. This work shows how the ignition and growth of chemical reaction is dependent on the local microstructural features of the voids. Morphological quantities like size, aspect ratio and orientations are extracted from the real microstructural images of Class III and Class V pressed HMX. These morphological quantities are correlated with the ignition and growth rates of the chemical reaction. The dependency of the sensitivity of a given HMX sample on the local morphological features shows that these local features can create a mocroscale physical response.

Three sets of crystallographic sub-planar structures in quartz formed by tectonic deformation

NASA Astrophysics Data System (ADS)

Derez, Tine; Pennock, Gill; Drury, Martyn; Sintubin, Manuel

2016-05-01

In quartz, multiple sets of fine planar deformation microstructures that have specific crystallographic orientations parallel to planes with low Miller-Bravais indices are commonly considered as shock-induced planar deformation features (PDFs) diagnostic of shock metamorphism. Using polarized light microscopy, we demonstrate that up to three sets of tectonically induced sub-planar fine extinction bands (FEBs), sub-parallel to the basal, γ, ω, and π crystallographic planes, are common in vein quartz in low-grade tectonometamorphic settings. We conclude that the observation of multiple (2-3) sets of fine scale, closely spaced, crystallographically controlled, sub-planar microstructures is not sufficient to unambiguously distinguish PDFs from tectonic FEBs.

Artificial Microstructures to Investigate Microstructure-Property Relationships in Metallic Glasses

NASA Astrophysics Data System (ADS)

Sarac, Baran

Technology has evolved rapidly within the last decade, and the demand for higher performance materials has risen exponentially. To meet this demand, novel materials with advanced microstructures have been developed and are currently in use. However, the already complex microstructure of technological relevant materials imposes a limit for currently used development strategies for materials with optimized properties. For this reason, a strategy to correlate microstructure features with properties is still lacking. Computer simulations are challenged due to the computing size required to analyze multi-scale characteristics of complex materials, which is orders of magnitude higher than today's state of the art. To address these challenges, we introduced a novel strategy to investigate microstructure-property relationships. We call this strategy "artificial microstructure approach", which allows us to individually and independently control microstructural features. By this approach, we defined a new way of analyzing complex microstructures, where microstructural second phase features were precisely varied over a wide range. The artificial microstructures were fabricated by the combination of lithography and thermoplastic forming (TPF), and subsequently characterized under different loading conditions. Because of the suitability and interesting properties of metallic glasses, we proposed to use this toolbox to investigate the different deformation modes in cellular structures and toughening mechanism in metallic glass (MG) composites. This study helped us understand how to combine the unique properties of metallic glasses such as high strength, elasticity, and thermoplastic processing ability with plasticity generated from heterostructures of metallic glasses. It has been widely accepted that metallic glass composites are very complex, and a broad range of contributions have been suggested to explain the toughening mechanism. This includes the shear modulus, morphology, size, spacing, volume fraction of the second phase, and strength and toughness of the interface. Previous studies suggest these contributions, however, do not provide quantitative experimental evidence. Within this thesis, we paid tribute to the complexity of the toughening mechanism by revealing the correlation between plastic zone size (Rp) and second phase spacing (s ), and the results guided us how to design elasticity through the second phase morphology (AB pore stacking) in MG heterostructures. The second phase elasticity and shear modulus were also found to be contributing to the overall elasticity. We identified the pores' ratio of diameter to spacing (d/s) as one of the major factors controlling the mechanical properties of MG hetero structures, which is most efficient when d/s ≈ 1. Effectiveness of MG heterostructures also depends on the size of the sample, w, in comparison to s. Our experimental findings illuminate the complexity in MG composites, which can be resolved with our artificial microstructure approach. Another subject where we use artificial microstructures is to identify the effect of length scales on structural properties of MG heterostructures. MG structures can be fabricated over 7 orders of magnitude length scale (nm to cm), where the effect of the feature size determines whether the deformation will be homogenous throughout the sample, it will be localized into shear bands, or it will not show any shear bands (no plasticity) during bending and tension. We investigated the deformation modes of Zr-based MGs in hexagonal cellular structures controlled by the relative density, and revealed three distinctive deformation regions: collective buckling, local failure, and global failure which originate from size effects in metallic glasses. The relative density of ˜25.0% was determined as the ideal relative density for energy absorption, strength and plasticity in MG cellular structures. Besides two specific examples studied in detail here, the artificial microstructure concept can be applied to a wide range of problems in microstructures and micro structural architectures of porous and natural materials. Furthermore, it can be used to determine the flaw tolerance, and to investigate the sensitivity of microstructures to imperfections. For example, a mechanistic understanding of shear localization would help address the major shortcoming of metallic glasses and enable predictive models to be developed which would permit one to intelligently design microstructures to exhibit desirable properties.

Interpreting U-Pb data from primary and secondary features in lunar zircon

NASA Astrophysics Data System (ADS)

Grange, M. L.; Pidgeon, R. T.; Nemchin, A. A.; Timms, N. E.; Meyer, C.

2013-01-01

In this paper, we describe primary and secondary microstructures and textural characteristics found in lunar zircon and discuss the relationships between these features and the zircon U-Pb isotopic systems and the significance of these features for understanding lunar processes. Lunar zircons can be classified according to: (i) textural relationships between zircon and surrounding minerals in the host breccias, (ii) the internal microstructures of the zircon grains as identified by optical microscopy, cathodoluminescence (CL) imaging and electron backscattered diffraction (EBSD) mapping and (iii) results of in situ ion microprobe analyses of the Th-U-Pb isotopic systems. Primary zircon can occur as part of a cogenetic mineral assemblage (lithic clast) or as an individual mineral clast and is unzoned, or has sector and/or oscillatory zoning. The age of primary zircon is obtained when multiple ion microprobe analyses across the polished surface of the grain give reproducible and essentially concordant data. A secondary set of microstructures, superimposed on primary zircon, include localised recrystallised domains, localised amorphous domains, crystal-plastic deformation, planar deformation features and fractures, and are associated with impact processes. The first two secondary microstructures often yield internally consistent and close to concordant U-Pb ages that we interpret as dating impact events. Others secondary microstructures such as planar deformation features, crystal-plastic deformation and micro-fractures can provide channels for Pb diffusion and result in partial resetting of the U-Pb isotopic systems.

Monitoring In-Vivo the Mammary Gland Microstructure during Morphogenesis from Lactation to Post-Weaning Using Diffusion Tensor MRI.

PubMed

Nissan, Noam; Furman-Haran, Edna; Shapiro-Feinberg, Myra; Grobgeld, Dov; Degani, Hadassa

2017-09-01

Lactation and the return to the pre-conception state during post-weaning are regulated by hormonal induced processes that modify the microstructure of the mammary gland, leading to changes in the features of the ductal / glandular tissue, the stroma and the fat tissue. These changes create a challenge in the radiological workup of breast disorder during lactation and early post-weaning. Here we present non-invasive MRI protocols designed to record in vivo high spatial resolution, T 2 -weighted images and diffusion tensor images of the entire mammary gland. Advanced imaging processing tools enabled tracking the changes in the anatomical and microstructural features of the mammary gland from the time of lactation to post-weaning. Specifically, by using diffusion tensor imaging (DTI) it was possible to quantitatively distinguish between the ductal / glandular tissue distention during lactation and the post-weaning involution. The application of the T 2 -weighted imaging and DTI is completely safe, non-invasive and uses intrinsic contrast based on differences in transverse relaxation rates and water diffusion rates in various directions, respectively. This study provides a basis for further in-vivo monitoring of changes during the mammary developmental stages, as well as identifying changes due to malignant transformation in patients with pregnancy associated breast cancer (PABC).

Structure of anodized Al-Zr sputter deposited coatings and effect on optical appearance

NASA Astrophysics Data System (ADS)

Gudla, Visweswara Chakravarthy; Canulescu, Stela; Shabadi, Rajashekhara; Rechendorff, Kristian; Dirscherl, Kai; Ambat, Rajan

2014-10-01

The mechanism of interaction of light with the microstructure of anodized layer giving specific optical appearance is investigated using Al-Zr sputter deposited coating as a model system on an AA6060 substrate. Differences in the oxidative nature of various microstructural components result in the evolution of typical features in the anodized layer, which are investigated as a function of microstructure and correlated with its optical appearance. The Zr concentration in the coating was varied from 6 wt.% to 23 wt.%. Heat treatment of the coated samples was carried out at 550 °C for 4 h in order to evolve Al-Zr based second phase precipitates in the microstructure. Anodizing was performed using 20 wt.% sulphuric acid at 18 °C with an intention to study the effect of anodizing on the Al-Zr based precipitates in the coating. Detailed microstructural characterization of the coating and anodized layer was carried out using high resolution scanning and transmission electron microscopy, grazing incidence X-ray diffraction analysis, glow discharge optical emission spectroscopy, and optical appearance using spectrophotometry. The evolution of microstructure in the anodized layer as a function of anodizing parameters and their influence on the interaction of light is investigated and the results in general are applicable to discolouration of anodized layer on recycled aluminium alloys due to intermetallics.

Multi-length Scale Material Model Development for Armorgrade Composites

DTIC Science & Technology

2014-05-02

various microstructural features and processes , at different length- scales, to the macroscopic-level ballistic-penetration resistance of PPTA-based...fabric or PPTA-fiber-reinforced polymer-matrix composites. Specifically, the role of various material-synthesis-/fiber- processing -induced defects, as...well as defects induced during the weaving process , was investigated. The results obtained clearly revealed that 1. REPORT DATE (DD-MM-YYYY) 4. TITLE

A study on the effects of temperature and substrate structure on the templated two-phase film growth via a hybrid model

NASA Astrophysics Data System (ADS)

Lu, Xiao; Li, Jia; Zhu, Jian-Gang; Laughlin, David E.; Zhu, Jingxi

2018-06-01

Templated growth of two-phase thin films can achieve desirably ordered microstructures. In such cases, the microstructure of the growing films follows the topography of the template. By combining the Potts model Monte Carlo simulation and the "level set" method, an attempt was previously made to understand the physical mechanism behind the templated growth process. In the current work, this model is further used to study the effect of two parameters within the templated growth scenario, namely, the temperature and the geometric features of the template. The microstructure of the thin film grown with different lattice temperatures and domes is analyzed. It is found that within a moderate temperature range, the effect of geometric features took control of the ordering of the microstructure by its influence on the surface energy gradient. Interestingly, within this temperature range, as the temperature is increased, an ordered microstructure forms on a template without the optimal geometric features, which seems to be a result of competition between the kinetics and the thermodynamics during deposition. However, when the temperature was either above or below this temperature range, the template provided no guide to the whole deposition so that no ordered microstructure formed.

Changes of the water-holding capacity and microstructure of panga and tilapia surimi gels using different stabilizers and processing methods.

PubMed

Filomena-Ambrosio, Annamaria; Quintanilla-Carvajal, María Ximena; Ana-Puig; Hernando, Isabel; Hernández-Carrión, María; Sotelo-Díaz, Indira

2016-01-01

Surimi gel is a food product traditionally manufactured from marine species; it has functional features including a specific texture and a high protein concentration. The objective of this study was to evaluate and compare the effect of the ultrasound extraction protein method and different stabilizers on the water-holding capacity (WHC), texture, and microstructure of surimi from panga and tilapia to potentially increase the value of these species. For this purpose, WHC was determined and texture profile analysis, scanning electron microscopy, and texture image analysis were carried out. The results showed that the ultrasound method and the sodium citrate can be used to obtain surimi gels from panga and tilapia with optimal textural properties such as the hardness and chewiness. Moreover, image analysis is recommended as a quantitative and non-invasive technique to evaluate the microstructure and texture image properties of surimis prepared using different processing methods and stabilizers. © The Author(s) 2015.

Review of the Effects of Microstructure on Fatigue in Aluminum Alloys. Ph.D. Thesis - Cincinnati Univ.

NASA Technical Reports Server (NTRS)

Telesman, J.

1984-01-01

Literature survey was conducted to determine the effects of different microstructural features and different load histories on fatigue crack initiation and propagation of aluminum alloys. Comparison of microstructure and monotonic and cyclic properties between powder metallurgy (P/M) and ingot metallurgy (I/M) alloys is presented. The two alloys that are representative of each process on which the comparison is focused are X7091 and 7050. Included is a detailed description of the microstructure produced through the P/M and I/M proesses. The effect of each pertinent microstructural feature on monotonic and cyclic properties, such as yield strength, toughness, crack initiation and propagation is discussed. Also discussed are the proposed mechanisms for crack initiation and propagation, as well as the effects of aggressive environments on these cyclic properties. The effects of variable amplitude loadin on fatigue crack propagation and the various models proposed to predict load interaction effects are discussed.

Shock induced damage in copper: A before and after, three-dimensional study

NASA Astrophysics Data System (ADS)

Menasche, David B.; Lind, Jonathan; Li, Shiu Fai; Kenesei, Peter; Bingert, John F.; Lienert, Ulrich; Suter, Robert M.

2016-04-01

We report on the microstructural features associated with the formation of incipient spall and damage in a fully recrystallized, high purity copper sample. Before and after ballistic shock loading, approximately 0.8 mm3 of the sample's crystal lattice orientation field is mapped using non-destructive near-field High Energy Diffraction Microscopy. Absorption contrast tomography is used to image voids after loading. This non-destructive interrogation of damage initiation allows for novel characterization of spall points vis-a-vis microstructural features and a fully 3D examination of microstructural topology and its influence on incipient damage. The spalled region is registered with and mapped back onto the pre-shock orientation field. As expected, the great majority of voids occur at grain boundaries and higher order microstructural features; however, we find no statistical preference for particular grain boundary types. The damaged region contains a large volume of Σ-3 (60 °<111 >) connected domains with a large area fraction of incoherent Σ-3 boundaries.

On the Specific Role of Microstructure in Governing Cyclic Fatigue, Deformation, and Fracture Behavior of a High-Strength Alloy Steel

NASA Astrophysics Data System (ADS)

Manigandan, K.; Srivatsan, T. S.

2015-06-01

In this paper, the results of an experimental study that focused on evaluating the conjoint influence of microstructure and test specimen orientation on fully reversed strain-controlled fatigue behavior of the high alloy steel X2M are presented and discussed. The cyclic stress response of this high-strength alloy steel revealed initial hardening during the first few cycles followed by gradual softening for most of fatigue life. Cyclic strain resistance exhibited a linear trend for the variation of elastic strain amplitude with reversals to failure, and plastic strain amplitude with reversals to failure. Fracture morphology was the same at the macroscopic level over the entire range of cyclic strain amplitudes examined. However, at the fine microscopic level, the alloy steel revealed fracture to be essentially ductile with features reminiscent of predominantly "locally" ductile and isolated brittle mechanisms. The mechanisms governing stress response at the fine microscopic level, fatigue life, and final fracture behavior are presented and discussed in light of the mutually interactive influences of intrinsic microstructural effects, deformation characteristics of the microstructural constituents during fully reversed strain cycling, cyclic strain amplitude, and resultant response stress.

TEM Characterization of High Burn-up Microstructure of U-7Mo Alloy

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

Jian Gan; Brandon Miller; Dennis Keiser

2014-04-01

As an essential part of global nuclear non-proliferation effort, the RERTR program is developing low enriched U-Mo fuels (< 20% U-235) for use in research and test reactors that currently employ highly enriched uranium fuels. One type of fuel being developed is a dispersion fuel plate comprised of U-7Mo particles dispersed in Al alloy matrix. Recent TEM characterizations of the ATR irradiated U-7Mo dispersion fuel plates include the samples with a local fission densities of 4.5, 5.2, 5.6 and 6.3 E+21 fissions/cm3 and irradiation temperatures of 101-136?C. The development of the irradiated microstructure of the U-7Mo fuel particles consists ofmore » fission gas bubble superlattice, large gas bubbles, solid fission product precipitates and their association to the large gas bubbles, grain subdivision to tens or hundreds of nanometer size, collapse of bubble superlattice, and amorphisation. This presentation will describe the observed microstructures specifically focusing on the U-7Mo fuel particles. The impact of the observed microstructure on the fuel performance and the comparison of the relevant features with that of the high burn-up UO2 fuels will be discussed.« less

Prediction of cognitive and motor development in preterm children using exhaustive feature selection and cross-validation of near-term white matter microstructure.

PubMed

Schadl, Kornél; Vassar, Rachel; Cahill-Rowley, Katelyn; Yeom, Kristin W; Stevenson, David K; Rose, Jessica

2018-01-01

Advanced neuroimaging and computational methods offer opportunities for more accurate prognosis. We hypothesized that near-term regional white matter (WM) microstructure, assessed on diffusion tensor imaging (DTI), using exhaustive feature selection with cross-validation would predict neurodevelopment in preterm children. Near-term MRI and DTI obtained at 36.6 ± 1.8 weeks postmenstrual age in 66 very-low-birth-weight preterm neonates were assessed. 60/66 had follow-up neurodevelopmental evaluation with Bayley Scales of Infant-Toddler Development, 3rd-edition (BSID-III) at 18-22 months. Linear models with exhaustive feature selection and leave-one-out cross-validation computed based on DTI identified sets of three brain regions most predictive of cognitive and motor function; logistic regression models were computed to classify high-risk infants scoring one standard deviation below mean. Cognitive impairment was predicted (100% sensitivity, 100% specificity; AUC = 1) by near-term right middle-temporal gyrus MD, right cingulate-cingulum MD, left caudate MD. Motor impairment was predicted (90% sensitivity, 86% specificity; AUC = 0.912) by left precuneus FA, right superior occipital gyrus MD, right hippocampus FA. Cognitive score variance was explained (29.6%, cross-validated Rˆ2 = 0.296) by left posterior-limb-of-internal-capsule MD, Genu RD, right fusiform gyrus AD. Motor score variance was explained (31.7%, cross-validated Rˆ2 = 0.317) by left posterior-limb-of-internal-capsule MD, right parahippocampal gyrus AD, right middle-temporal gyrus AD. Search in large DTI feature space more accurately identified neonatal neuroimaging correlates of neurodevelopment.

Microstructural imaging of the human brain with a 'super-scanner': 10 key advantages of ultra-strong gradients for diffusion MRI.

PubMed

Jones, D K; Alexander, D C; Bowtell, R; Cercignani, M; Dell'Acqua, F; McHugh, D J; Miller, K L; Palombo, M; Parker, G J M; Rudrapatna, U S; Tax, C M W

2018-05-22

The key component of a microstructural diffusion MRI 'super-scanner' is a dedicated high-strength gradient system that enables stronger diffusion weightings per unit time compared to conventional gradient designs. This can, in turn, drastically shorten the time needed for diffusion encoding, increase the signal-to-noise ratio, and facilitate measurements at shorter diffusion times. This review, written from the perspective of the UK National Facility for In Vivo MR Imaging of Human Tissue Microstructure, an initiative to establish a shared 300 mT/m-gradient facility amongst the microstructural imaging community, describes ten advantages of ultra-strong gradients for microstructural imaging. Specifically, we will discuss how the increase of the accessible measurement space compared to a lower-gradient systems (in terms of Δ, b-value, and TE) can accelerate developments in the areas of 1) axon diameter distribution mapping; 2) microstructural parameter estimation; 3) mapping micro-vs macroscopic anisotropy features with gradient waveforms beyond a single pair of pulsed-gradients; 4) multi-contrast experiments, e.g. diffusion-relaxometry; 5) tractography and high-resolution imaging in vivo and 6) post mortem; 7) diffusion-weighted spectroscopy of metabolites other than water; 8) tumour characterisation; 9) functional diffusion MRI; and 10) quality enhancement of images acquired on lower-gradient systems. We finally discuss practical barriers in the use of ultra-strong gradients, and provide an outlook on the next generation of 'super-scanners'. Copyright © 2018. Published by Elsevier Inc.

Method to fabricate multi-level silicon-based microstructures via use of an etching delay layer

DOEpatents

Manginell, Ronald P.; Schubert, W. Kent; Shul, Randy J.

2005-08-16

New methods for fabrication of silicon microstructures have been developed. In these methods, an etching delay layer is deposited and patterned so as to provide differential control on the depth of features being etched into a substrate material. Structures having features with different depth can be formed thereby in a single etching step.

Microstructure characterization via stereological relations — A shortcut for beginners

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

Pabst, Willi, E-mail: pabstw@vscht.cz; Gregorová, Eva; Uhlířová, Tereza

Stereological relations that can be routinely applied for the quantitative characterization of microstructures of heterogeneous single- and two-phase materials via global microstructural descriptors are reviewed. It is shown that in the case of dense, single-phase polycrystalline materials (e.g., transparent yttrium aluminum garnet ceramics) two quantities have to be determined, the interface density (or, equivalently, the mean chord length of the grains) and the mean curvature integral density (or, equivalently, the Jeffries grain size), while for two-phase materials (e.g., highly porous, cellular alumina ceramics), one additional quantity, the volume fraction (porosity), is required. The Delesse–Rosiwal law is recalled and size measuresmore » are discussed. It is shown that the Jeffries grain size is based on the triple junction line length density, while the mean chord length of grains is based on the interface density (grain boundary area density). In contrast to widespread belief, however, these two size measures are not alternative, but independent (and thus complementary), measures of grain size. Concomitant with this fact, a clear distinction between linear and planar grain size numbers is proposed. Finally, based on our concept of phase-specific quantities, it is shown that under certain conditions it is possible to define a Jeffries size also for two-phase materials and that the ratio of the mean chord length and the Jeffries size has to be considered as an invariant number for a certain type of microstructure, i.e., a characteristic value that is independent of the absolute size of the microstructural features (e.g., grains, inclusions or pores). - Highlights: • Stereology-based image analysis is reviewed, including error considerations. • Recipes are provided for measuring global metric microstructural descriptors. • Size measures are based on interface density and mean curvature integral density. • Phase-specific quantities and a generalized Jeffries size are introduced. • Linear and planar grain size numbers are clearly distinguished and explained.« less

Verifying the functional ability of microstructured surfaces by model-based testing

NASA Astrophysics Data System (ADS)

Hartmann, Wito; Weckenmann, Albert

2014-09-01

Micro- and nanotechnology enables the use of new product features such as improved light absorption, self-cleaning or protection, which are based, on the one hand, on the size of functional nanostructures and the other hand, on material-specific properties. With the need to reliably measure progressively smaller geometric features, coordinate and surface-measuring instruments have been refined and now allow high-resolution topography and structure measurements down to the sub-nanometre range. Nevertheless, in many cases it is not possible to make a clear statement about the functional ability of the workpiece or its topography because conventional concepts of dimensioning and tolerancing are solely geometry oriented and standardized surface parameters are not sufficient to consider interaction with non-geometric parameters, which are dominant for functions such as sliding, wetting, sealing and optical reflection. To verify the functional ability of microstructured surfaces, a method was developed based on a parameterized mathematical-physical model of the function. From this model, function-related properties can be identified and geometric parameters can be derived, which may be different for the manufacturing and verification processes. With this method it is possible to optimize the definition of the shape of the workpiece regarding the intended function by applying theoretical and experimental knowledge, as well as modelling and simulation. Advantages of this approach will be discussed and demonstrated by the example of a microstructured inking roll.

Characterizing the Effects of Washing by Different Detergents on the Wavelength-Scale Microstructures of Silk Samples Using Mueller Matrix Polarimetry.

PubMed

Dong, Yang; He, Honghui; He, Chao; Zhou, Jialing; Zeng, Nan; Ma, Hui

2016-08-10

Silk fibers suffer from microstructural changes due to various external environmental conditions including daily washings. In this paper, we take the backscattering Mueller matrix images of silk samples for non-destructive and real-time quantitative characterization of the wavelength-scale microstructure and examination of the effects of washing by different detergents. The 2D images of the 16 Mueller matrix elements are reduced to the frequency distribution histograms (FDHs) whose central moments reveal the dominant structural features of the silk fibers. A group of new parameters are also proposed to characterize the wavelength-scale microstructural changes of the silk samples during the washing processes. Monte Carlo (MC) simulations are carried out to better understand how the Mueller matrix parameters are related to the wavelength-scale microstructure of silk fibers. The good agreement between experiments and simulations indicates that the Mueller matrix polarimetry and FDH based parameters can be used to quantitatively detect the wavelength-scale microstructural features of silk fibers. Mueller matrix polarimetry may be used as a powerful tool for non-destructive and in situ characterization of the wavelength-scale microstructures of silk based materials.

Characterizing the Effects of Washing by Different Detergents on the Wavelength-Scale Microstructures of Silk Samples Using Mueller Matrix Polarimetry

PubMed Central

Dong, Yang; He, Honghui; He, Chao; Zhou, Jialing; Zeng, Nan; Ma, Hui

2016-01-01

Silk fibers suffer from microstructural changes due to various external environmental conditions including daily washings. In this paper, we take the backscattering Mueller matrix images of silk samples for non-destructive and real-time quantitative characterization of the wavelength-scale microstructure and examination of the effects of washing by different detergents. The 2D images of the 16 Mueller matrix elements are reduced to the frequency distribution histograms (FDHs) whose central moments reveal the dominant structural features of the silk fibers. A group of new parameters are also proposed to characterize the wavelength-scale microstructural changes of the silk samples during the washing processes. Monte Carlo (MC) simulations are carried out to better understand how the Mueller matrix parameters are related to the wavelength-scale microstructure of silk fibers. The good agreement between experiments and simulations indicates that the Mueller matrix polarimetry and FDH based parameters can be used to quantitatively detect the wavelength-scale microstructural features of silk fibers. Mueller matrix polarimetry may be used as a powerful tool for non-destructive and in situ characterization of the wavelength-scale microstructures of silk based materials. PMID:27517919

EBSD Analysis of Relationship Between Microstructural Features and Toughness of a Medium-Carbon Quenching and Partitioning Bainitic Steel

NASA Astrophysics Data System (ADS)

Li, Qiangguo; Huang, Xuefei; Huang, Weigang

2017-12-01

A multiphase microstructure of bainite, martensite and retained austenite in a 0.3C bainitic steel was obtained by a novel bainite isothermal transformation plus quenching and partitioning (B-QP) process. The correlations between microstructural features and toughness were investigated by electron backscatter diffraction (EBSD), and the results showed that the multiphase microstructure containing approximately 50% bainite exhibits higher strength (1617 MPa), greater elongation (18.6%) and greater impact toughness (103 J) than the full martensite. The EBSD analysis indicated that the multiphase microstructure with a smaller average local misorientation (1.22°) has a lower inner stress concentration possibility and that the first formed bainitic ferrite plates in the multiphase microstructure can refine subsequently generated packets and blocks. The corresponding packet and block average size decrease from 11.9 and 2.3 to 8.4 and 1.6 μm, respectively. A boundary misorientation analysis indicated that the multiphase microstructure has a higher percentage of high-angle boundaries (67.1%) than the full martensite (57.9%) because of the larger numbers and smaller sizes of packets and blocks. The packet boundary obstructs crack propagation more effectively than the block boundary.

Castable high-temperature Ce-modified Al alloys

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

Rios, Orlando; King, Alexander H.; McCall, Scott K.

2018-05-08

A cast alloy includes aluminum and from about 5 to about 30 weight percent of at least one material selected from the group consisting of cerium, lanthanum, and mischmetal. The cast alloy has a strengthening Al 11X 3 intermetallic phase in an amount in the range of from about 5 to about 30 weight percent, wherein X is at least one of cerium, lanthanum, and mischmetal. The Al 11X 3 intermetallic phase has a microstructure that includes at least one of lath features and rod morphological features. The morphological features have an average thickness of no more than 700 ummore » and an average spacing of no more than 10 um, the microstructure further comprising an eutectic microconstituent that comprises more than about 10 volume percent of the microstructure.« less

Laser-Based Surface Modification of Microstructure for Carbon Fiber-Reinforced Plastics

NASA Astrophysics Data System (ADS)

Yang, Wenfeng; Sun, Ting; Cao, Yu; Li, Shaolong; Liu, Chang; Tang, Qingru

2018-05-01

Bonding repair is a powerful feature of carbon fiber-reinforced plastics (CFRP). Based on the theory of interface bonding, the interface adhesion strength and reliability of the CFRP structure will be directly affected by the microscopic features of the CFRP surface, including the microstructure, physical, and chemical characteristics. In this paper, laser-based surface modification was compared to Peel-ply, grinding, and polishing to comparatively evaluate the surface microstructure of CFRP. The surface microstructure, morphology, fiber damage, height and space parameters were investigated by scanning electron microscopy (SEM) and laser confocal microscopy (LCM). Relative to the conventional grinding process, laser modification of the CFRP surface can result in more uniform resin removal and better processing control and repeatability. This decreases the adverse impact of surface fiber fractures and secondary damage. The surface properties were significantly optimized, which has been reflected such things as the obvious improvement of surface roughness, microstructure uniformity, and actual area. The improved surface microstructure based on laser modification is more conducive to interface bonding of CFRP structure repair. This can enhance the interfacial adhesion strength and reliability of repair.

Microstructure-Tensile Properties Correlation for the Ti-6Al-4V Titanium Alloy

NASA Astrophysics Data System (ADS)

Shi, Xiaohui; Zeng, Weidong; Sun, Yu; Han, Yuanfei; Zhao, Yongqing; Guo, Ping

2015-04-01

Finding the quantitative microstructure-tensile properties correlations is the key to achieve performance optimization for various materials. However, it is extremely difficult due to their non-linear and highly interactive interrelations. In the present investigation, the lamellar microstructure features-tensile properties correlations of the Ti-6Al-4V alloy are studied using an error back-propagation artificial neural network (ANN-BP) model. Forty-eight thermomechanical treatments were conducted to prepare the Ti-6Al-4V alloy with different lamellar microstructure features. In the proposed model, the input variables are microstructure features including the α platelet thickness, colony size, and β grain size, which were extracted using Image Pro Plus software. The output variables are the tensile properties, including ultimate tensile strength, yield strength, elongation, and reduction of area. Fourteen hidden-layer neurons which can make ANN-BP model present the most excellent performance were applied. The training results show that all the relative errors between the predicted and experimental values are within 6%, which means that the trained ANN-BP model is capable of providing precise prediction of the tensile properties for Ti-6Al-4V alloy. Based on the corresponding relations between the tensile properties predicted by ANN-BP model and the lamellar microstructure features, it can be found that the yield strength decreases with increasing α platelet thickness continuously. However, the α platelet thickness exerts influence on the elongation in a more complicated way. In addition, for a given α platelet thickness, the yield strength and the elongation both increase with decreasing β grain size and colony size. In general, the β grain size and colony size play a more important role in affecting the tensile properties of Ti-6Al-4V alloy than the α platelet thickness.

Shell microstructures of mussels (Bivalvia: Mytilidae: Bathymodiolinae) from deep-sea chemosynthetic sites: Do they have a phylogenetic significance?

NASA Astrophysics Data System (ADS)

Génio, Luciana; Kiel, Steffen; Cunha, Marina R.; Grahame, John; Little, Crispin T. S.

2012-06-01

The increasing number of bathymodiolin mussel species being described from deep-sea chemosynthetic environments worldwide has raised many questions about their evolutionary history, and their systematics is still being debated. Mussels are also abundant in fossil chemosynthetic assemblages, but their identification is problematic due to conservative shell morphology within the group and preservation issues. Potential resolution of bathymodiolin taxonomy requires new character sets, including morphological features that are likely to be preserved in fossil specimens. To investigate the phylogenetic significance of shell microstructural features, we studied the shell microstructure and mineralogy of 10 mussel species from hydrothermal vents and hydrocarbon seeps, and 15 taxa from sunken wood and bone habitats, and compared these observations with current molecular phylogenies of the sub-family Bathymodiolinae. In addition, we analyzed the shell microstructure in Adipicola chickubetsuensis from fossil whale carcasses, and in Bathymodiolus cf. willapaensis and “Modiola exbrocchii” from fossil cold seeps, and discussed the usefulness of these characters for identification of fossil chemosymbiotic mussels. Microstructural shell features are quite uniform among vent, seep, wood and bone mussel taxa, and therefore established bathymodiolin lineages cannot be discriminated, nor can the relations between fossil and modern species be determined with these characters. Nevertheless, the uniformity of shell microstructures observed among chemosymbiotic mussels and the similarity with its closest relative, Modiolus modiolus, does not challenge the monophyly of the group. Slight differences are found between the large vent and seep mussels and the small mytilids commonly found in habitats enriched in organic matter. Together with previous data, these results indicate that a repeated pattern of paedomorphism characterizes the evolutionary history of deep-sea mussels, and the occurrence of neotenous features should be considered in the taxonomic revision of this group.

Juniper wood structure under the microscope.

PubMed

Bogolitsyn, Konstantin G; Zubov, Ivan N; Gusakova, Maria A; Chukhchin, Dmitry G; Krasikova, Anna A

2015-05-01

The investigations confirm the physicochemical nature of the structure and self-assembly of wood substance and endorse its application in plant species. The characteristic morphological features, ultra-microstructure, and submolecular structure of coniferous wood matrix using junipers as the representative tree were investigated by scanning electron (SEM) and atomic-force microscopy (AFM). Novel results on the specific composition and cell wall structure features of the common juniper (Juniperus Communis L.) were obtained. These data confirm the possibility of considering the wood substance as a nanobiocomposite. The cellulose nanofibrils (20-50 nm) and globular-shaped lignin-carbohydrate structures (diameter of 5-60 nm) form the base of such a nanobiocomposite.

Microstructure and Hardness Profiles of Bifocal Laser-Welded DP-HSLA Steel Overlap Joints

NASA Astrophysics Data System (ADS)

Grajcar, A.; Matter, P.; Stano, S.; Wilk, Z.; Różański, M.

2017-04-01

The article presents results related to the bifocal laser welding of overlap joints made of HSLA and DP high-strength steels. The joints were made using a disk laser and a head enabling the 50-50% distribution of laser power. The effects of the laser welding rates and the distance between laser spots on morphological features and hardness profiles were analyzed. It was established that the positioning of beams at angles of 0° or 90° determined the hardness of the individual zones of the joints, without causing significant differences in microstructures of the steels. Microstructural features were inspected using scanning electron microscopy. Both steels revealed primarily martensitic-bainitic microstructures in the fusion zone and in the heat-affected zone. Mixed multiphase microstructures were revealed in the inter-critical heat-affected zone of the joint. The research involved the determination of parameters making it possible to reduce the hardness of joints and prevent the formation of the soft zone in the dual-phase steel.

Non-destructive and three-dimensional measurement of local strain development during tensile deformation in an aluminium alloy

NASA Astrophysics Data System (ADS)

Kobayashi, M.; Miura, H.; Toda, H.

2015-08-01

Anisotropy of mechanical responses depending on crystallographic orientation causes inhomogeneous deformation on the mesoscopic scale (grain size scale). Investigation of the local plastic strain development is important for discussing recrystallization mechanisms, because the sites with higher local plastic strain may act as potential nucleation sites for recrystallization. Recently, high-resolution X-ray tomography, which is non-destructive inspection method, has been utilized for observation of the materials structure. In synchrotron radiation X-ray tomography, more than 10,000 microstructural features, like precipitates, dispersions, compounds and hydrogen pores, can be observed in aluminium alloys. We have proposed employing these microstructural features as marker gauges to measure local strains, and then have developed a method to calculate the three-dimensional strain distribution by tracking the microstructural features. In this study, we report the development of local plastic strain as a function of the grain microstructure in an aluminium alloy by means of this three-dimensional strain measurement technique. Strongly heterogeneous strain development was observed during tensile loading to 30%. In other words, some parts of the sample deform little whereas another deforms a lot. However, strain in the whole specimen was keeping harmony. Comparing the microstructure with the strain concentration that is obtained by this method has a potential to reveal potential nucleation sites of recrystallization.

Peculiar Features of Microstructure Formation and Microhardness Variations During Torsional Straining of Tantalum Specimens in Bridgman Anvils

NASA Astrophysics Data System (ADS)

Ditenberg, I. A.; Tymentsev, A. N.; Korznikov, A. V.

2015-04-01

Using the method of transmission electron microscopy, peculiar features of evolution of microstructure and variations in microhardness of Та are investigated under torsional loading in the Bridgman anvil as a function of plastic deformation at room temperature. A quantitative examination of grain and defect's structure of the material under study and the values of local internal stresses is performed in different loading stages. The mechanisms of formation of submicrocrystalline and nanostructured states are analyzed and so is the microstructure variation as a function of the defect-structure characteristics, strain level, and spacing from the axis of torsion.

Effect of screw threading dislocations and inverse domain boundaries in GaN on the shape of reciprocal-space maps.

PubMed

Barchuk, Mykhailo; Motylenko, Mykhaylo; Lukin, Gleb; Pätzold, Olf; Rafaja, David

2017-04-01

The microstructure of polar GaN layers, grown by upgraded high-temperature vapour phase epitaxy on [001]-oriented sapphire substrates, was studied by means of high-resolution X-ray diffraction and transmission electron microscopy. Systematic differences between reciprocal-space maps measured by X-ray diffraction and those which were simulated for different densities of threading dislocations revealed that threading dislocations are not the only microstructure defect in these GaN layers. Conventional dark-field transmission electron microscopy and convergent-beam electron diffraction detected vertical inversion domains as an additional microstructure feature. On a series of polar GaN layers with different proportions of threading dislocations and inversion domain boundaries, this contribution illustrates the capability and limitations of coplanar reciprocal-space mapping by X-ray diffraction to distinguish between these microstructure features.

Tubular inverse opal scaffolds for biomimetic vessels

NASA Astrophysics Data System (ADS)

Zhao, Ze; Wang, Jie; Lu, Jie; Yu, Yunru; Fu, Fanfan; Wang, Huan; Liu, Yuxiao; Zhao, Yuanjin; Gu, Zhongze

2016-07-01

There is a clinical need for tissue-engineered blood vessels that can be used to replace or bypass damaged arteries. The success of such grafts depends strongly on their ability to mimic native arteries; however, currently available artificial vessels are restricted by their complex processing, controversial integrity, or uncontrollable cell location and orientation. Here, we present new tubular scaffolds with specific surface microstructures for structural vessel mimicry. The tubular scaffolds are fabricated by rotationally expanding three-dimensional tubular inverse opals that are replicated from colloidal crystal templates in capillaries. Because of the ordered porous structure of the inverse opals, the expanded tubular scaffolds are imparted with circumferentially oriented elliptical pattern microstructures on their surfaces. It is demonstrated that these tailored tubular scaffolds can effectively make endothelial cells to form an integrated hollow tubular structure on their inner surface and induce smooth muscle cells to form a circumferential orientation on their outer surface. These features of our tubular scaffolds make them highly promising for the construction of biomimetic blood vessels.There is a clinical need for tissue-engineered blood vessels that can be used to replace or bypass damaged arteries. The success of such grafts depends strongly on their ability to mimic native arteries; however, currently available artificial vessels are restricted by their complex processing, controversial integrity, or uncontrollable cell location and orientation. Here, we present new tubular scaffolds with specific surface microstructures for structural vessel mimicry. The tubular scaffolds are fabricated by rotationally expanding three-dimensional tubular inverse opals that are replicated from colloidal crystal templates in capillaries. Because of the ordered porous structure of the inverse opals, the expanded tubular scaffolds are imparted with circumferentially oriented elliptical pattern microstructures on their surfaces. It is demonstrated that these tailored tubular scaffolds can effectively make endothelial cells to form an integrated hollow tubular structure on their inner surface and induce smooth muscle cells to form a circumferential orientation on their outer surface. These features of our tubular scaffolds make them highly promising for the construction of biomimetic blood vessels. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr03173k

Metallurgical Mechanisms Controlling Mechanical Properties of Aluminum Alloy 2219 Produced by Electron Beam Freeform Fabrication

NASA Technical Reports Server (NTRS)

Domack, Marcia S.; Tainger, Karen M.

2006-01-01

The electron beam freeform fabrication (EBF3) layer-additive manufacturing process has been developed to directly fabricate complex geometry components. EBF3 introduces metal wire into a molten pool created on the surface of a substrate by a focused electron beam. Part geometry is achieved by translating the substrate with respect to the beam to build the part one layer at a time. Tensile properties demonstrated for electron beam deposited aluminum and titanium alloys are comparable to wrought products, although the microstructures of the deposits exhibit cast features. Understanding the metallurgical mechanisms controlling mechanical properties is essential to maximizing application of the EBF3 process. Tensile mechanical properties and microstructures were examined for aluminum alloy 2219 fabricated over a range of EBF3 process variables. Unique microstructures were observed within the deposited layers and at interlayer boundaries, which varied within the deposit height due to microstructural evolution associated with the complex thermal history experienced during subsequent layer deposition. Microstructures exhibited irregularly shaped grains with interior dendritic structures, described based on overall grain size, morphology, distribution, and dendrite spacing, and were correlated with deposition parameters. Fracture features were compared with microstructural elements to define fracture paths and aid in definition of basic processing-microstructure-property correlations.

A Constitutive Equation Relating Composition and Microstructure to Properties in Ti-6Al-4V: As Derived Using a Novel Integrated Computational Approach

NASA Astrophysics Data System (ADS)

Ghamarian, Iman; Samimi, Peyman; Dixit, Vikas; Collins, Peter C.

2015-11-01

While it is useful to predict properties in metallic materials based upon the composition and microstructure, the complexity of real, multi-component, and multi-phase engineering alloys presents difficulties when attempting to determine constituent-based phenomenological equations. This paper applies an approach based upon the integration of three separate modeling approaches, specifically artificial neural networks, genetic algorithms, and Monte Carlo simulations to determine a mechanism-based equation for the yield strength of α+ β processed Ti-6Al-4V (all compositions in weight percent) which consists of a complex multi-phase microstructure with varying spatial and morphological distributions of the key microstructural features. Notably, this is an industrially important alloy yet an alloy for which such an equation does not exist in the published literature. The equation ultimately derived in this work not only can accurately describe the properties of the current dataset but also is consistent with the limited and dissociated information available in the literature regarding certain parameters such as intrinsic yield strength of pure hexagonal close-packed alpha titanium. In addition, this equation suggests new interesting opportunities for controlling yield strength by controlling the relative intrinsic strengths of the two phases through solid solution strengthening.

On the determination of the origin of linear anomaly in the macrostructure of VPPA welded 2219-T87 aluminum alloy

NASA Technical Reports Server (NTRS)

Jemian, W. A.

1986-01-01

The objective was to determine the cause and significance of the weld radiograph enigma, which is a linear anomaly in the features of the X-ray film. By observing features on available radiographs and in studying published reports of similar features it was possible to conclude that there are many manifestations of the enigma, and that they are all specific features of fine structure in radiographs due to natural processes connected with welding and to specific X-ray absorption and diffraction phenomena. These processes include the thermal distribution and liquid metal flow in welding, the development of microstructure, morpohology, second phase particles and porosity due to the solidification process and to the pattern of residual stresses after the weld metal has cooled to the ambient temperature. Microdensitometer traces were made across weld radiographs of standard and enigmatic types. Similar patterns were produced by computer simulation. These show that the enigma is a relatively low contrast feature compared to real weld defects, such as undercuts or centerline cracks. The enigma can be distinguished from weld defects by these microdensitometer traces. The enigma effect on weld properties is not known but is expected to be minor.

On the determination of the origin of linear anomaly in the macrostructure of VPPA welded 2219-T87 aluminum alloy: Preliminary report

NASA Technical Reports Server (NTRS)

Jemian, W. A.

1986-01-01

The cause and significance of the weld radiograph enigma, which is a linear anomaly in the features of the X-ray film is examined. By observing features on available radiographs and in studying published reports of similar features, it was possible to conclude that there are many manifestations of the enigma, and that they are all specific features of fine structure in radiographs due to natural processes connected with welding and to specific X-ray absorption and diffraction phenomena. These processes include the thermal distribution and liquid metal flow in welding, the development of microstructure, morphology, second phase particles and porosity due to the solidification process, and to the pattern of residual stresses after the weld metal has cooled to the ambient temperature. Microdensitometer traces were made across weld radiographs of standard enigmatic types. Similar patterns were produced by computer simulation. These show that the enigma is a relatively low contrast feature compared to real weld defects, such as undercuts or centerline cracks. The enigma can be distinguished from weld defects by these microdensitometer traces. The enigma effect on weld properties is not known but is expected to be minor.

A Mass Diffusion Model for Dry Snow Utilizing a Fabric Tensor to Characterize Anisotropy

NASA Astrophysics Data System (ADS)

Shertzer, Richard H.; Adams, Edward E.

2018-03-01

A homogenization algorithm for randomly distributed microstructures is applied to develop a mass diffusion model for dry snow. Homogenization is a multiscale approach linking constituent behavior at the microscopic level—among ice and air—to the macroscopic material—snow. Principles of continuum mechanics at the microscopic scale describe water vapor diffusion across an ice grain's surface to the air-filled pore space. Volume averaging and a localization assumption scale up and down, respectively, between microscopic and macroscopic scales. The model yields a mass diffusivity expression at the macroscopic scale that is, in general, a second-order tensor parameterized by both bulk and microstructural variables. The model predicts a mass diffusivity of water vapor through snow that is less than that through air. Mass diffusivity is expected to decrease linearly with ice volume fraction. Potential anisotropy in snow's mass diffusivity is captured due to the tensor representation. The tensor is built from directional data assigned to specific, idealized microstructural features. Such anisotropy has been observed in the field and laboratories in snow morphologies of interest such as weak layers of depth hoar and near-surface facets.

Altered tract-specific white matter microstructure is related to poorer cognitive performance: The Rotterdam Study.

PubMed

Cremers, Lotte G M; de Groot, Marius; Hofman, Albert; Krestin, Gabriel P; van der Lugt, Aad; Niessen, Wiro J; Vernooij, Meike W; Ikram, M Arfan

2016-03-01

White matter microstructural integrity has been related to cognition. Yet, the potential role of specific white matter tracts on top of a global white matter effect remains unclear, especially when considering specific cognitive domains. Therefore, we determined the tract-specific effect of white matter microstructure on global cognition and specific cognitive domains. In 4400 nondemented and stroke-free participants (mean age 63.7 years, 55.5% women), we obtained diffusion magnetic resonance imaging parameters (fractional anisotropy and mean diffusivity) in 14 white matter tracts using probabilistic tractography and assessed cognitive performance with a cognitive test battery. Tract-specific white matter microstructure in all supratentorial tracts was associated with poorer global cognition. Lower fractional anisotropy in association tracts, primarily the inferior fronto-occipital fasciculus, and higher mean diffusivity in projection tracts, in particular the posterior thalamic radiation, most strongly related to poorer cognition. Altered white matter microstructure related to poorer information processing speed, executive functioning, and motor speed, but not to memory. Tract-specific microstructural changes may aid in better understanding the mechanism of cognitive impairment and neurodegenerative diseases. Copyright © 2016 Elsevier Inc. All rights reserved.

Laparoscopic optical coherence tomography imaging of human ovarian cancer

PubMed Central

Hariri, Lida P.; Bonnema, Garret T.; Schmidt, Kathy; Winkler, Amy M.; Korde, Vrushali; Hatch, Kenneth D.; Davis, John R.; Brewer, Molly A.; Barton, Jennifer K.

2011-01-01

Objectives Ovarian cancer is the fourth leading cause of cancer-related death among women in the US largely due to late detection secondary to unreliable symptomology and screening tools without adequate resolution. Optical coherence tomography (OCT) is a recently emerging imaging modality with promise in ovarian cancer diagnostics, providing non-destructive subsurface imaging at imaging depths up to 2 mm with near-histological grade resolution (10–20 μm). In this study, we developed the first ever laparoscopic OCT (LOCT) device, evaluated the safety and feasibility of LOCT, and characterized the microstructural features of human ovaries in vivo. Methods A custom LOCT device was fabricated specifically for laparoscopic imaging of the ovaries in patients undergoing oophorectomy. OCT images were compared with histopathology to identify preliminary architectural imaging features of normal and pathologic ovarian tissue. Results Thirty ovaries in 17 primarily peri or post-menopausal women were successfully imaged with LOCT: 16 normal, 5 endometriosis, 3 serous cystadenoma, and 4 adenocarcinoma. Preliminary imaging features developed for each category reveal qualitative differences in the homogeneous character of normal post-menopausal ovary, the ability to image small subsurface inclusion cysts, and distinguishable features for endometriosis, cystadenoma, and adenocarcinoma. Conclusions We present the development and successful implementation of the first laparoscopic OCT probe. Comparison of OCT images and corresponding histopathology allowed for the description of preliminary microstructural features for normal ovary, endometriosis, and benign and malignant surface epithelial neoplasms. These results support the potential of OCT both as a diagnostic tool and imaging modality for further evaluation of ovarian cancer pathogenesis. PMID:19481241

Detection of Chorus Elements and other Wave Signatures Using Geometric Computational Techniques in the Van Allen radiation belts

NASA Astrophysics Data System (ADS)

Sengupta, A.; Kletzing, C.; Howk, R.; Kurth, W. S.

2017-12-01

An important goal of the Van Allen Probes mission is to understand wave particle interactions that can energize relativistic electron in the Earth's Van Allen radiation belts. The EMFISIS instrumentation suite provides measurements of wave electric and magnetic fields of wave features such as chorus that participate in these interactions. Geometric signal processing discovers structural relationships, e.g. connectivity across ridge-like features in chorus elements to reveal properties such as dominant angles of the element (frequency sweep rate) and integrated power along the a given chorus element. These techniques disambiguate these wave features against background hiss-like chorus. This enables autonomous discovery of chorus elements across the large volumes of EMFISIS data. At the scale of individual or overlapping chorus elements, topological pattern recognition techniques enable interpretation of chorus microstructure by discovering connectivity and other geometric features within the wave signature of a single chorus element or between overlapping chorus elements. Thus chorus wave features can be quantified and studied at multiple scales of spectral geometry using geometric signal processing techniques. We present recently developed computational techniques that exploit spectral geometry of chorus elements and whistlers to enable large-scale automated discovery, detection and statistical analysis of these events over EMFISIS data. Specifically, we present different case studies across a diverse portfolio of chorus elements and discuss the performance of our algorithms regarding precision of detection as well as interpretation of chorus microstructure. We also provide large-scale statistical analysis on the distribution of dominant sweep rates and other properties of the detected chorus elements.

Mueller matrix polarimetry for characterizing microstructural variation of nude mouse skin during tissue optical clearing.

PubMed

Chen, Dongsheng; Zeng, Nan; Xie, Qiaolin; He, Honghui; Tuchin, Valery V; Ma, Hui

2017-08-01

We investigate the polarization features corresponding to changes in the microstructure of nude mouse skin during immersion in a glycerol solution. By comparing the Mueller matrix imaging experiments and Monte Carlo simulations, we examine in detail how the Mueller matrix elements vary with the immersion time. The results indicate that the polarization features represented by Mueller matrix elements m22&m33&m44 and the absolute values of m34&m43 are sensitive to the immersion time. To gain a deeper insight on how the microstructures of the skin vary during the tissue optical clearing (TOC), we set up a sphere-cylinder birefringence model (SCBM) of the skin and carry on simulations corresponding to different TOC mechanisms. The good agreement between the experimental and simulated results confirm that Mueller matrix imaging combined with Monte Carlo simulation is potentially a powerful tool for revealing microscopic features of biological tissues.

Characterization of X80 and X100 Microalloyed Pipeline Steel Using Quantitative X-ray Diffraction

NASA Astrophysics Data System (ADS)

Wiskel, J. B.; Li, X.; Ivey, D. G.; Henein, H.

2018-06-01

Quantitative X-ray diffraction characterization of four (4) X80 and three (3) X100 microalloyed steels was undertaken. The effect of through-thickness position, processing parameters, and composition on the measured crystallite size, microstrain, and J index (relative magnitude of crystallographic texture) was determined. Microstructure analysis using optical microscopy, scanning electron microscopy, transmission electron microscopy, and electron-backscattered diffraction was also undertaken. The measured value of microstrain increased with increasing alloy content and decreasing cooling interrupt temperature. Microstructural features corresponding to crystallite size in the X80 steels were both above and below the detection limit for quantitative X-ray diffraction. The X100 steels consistently exhibited microstructure features below the crystallite size detection limit. The yield stress of each steel increased with increasing microstrain. The increase in microstrain from X80 to X100 is also associated with a change in microstructure from predominantly polygonal ferrite to bainitic ferrite.

Microstructure-property relationships in directionally solidified single crystal nickel-base superalloys

NASA Technical Reports Server (NTRS)

Mackay, R. A.; Nathal, M. V.

1986-01-01

Some of the microstructural features which influence the creep properties of directionally solidified and single crystal nickel-base superalloys are discussed. Gamma precipitate size and morphology, gamma-gamma lattice mismatch, phase instability, alloy composition, and processing variations are among the factors considered. Recent experimental results are reviewed and related to the operative deformation mechanisms and to the corresponding mechanical properties. Special emphasis is placed on the creep behavior of single crystal superalloys at high temperatures, where directional gamma coarsening is prominent, and at lower temperatures, where gamma coarsening rates are significantly reduced. It can be seen that very subtle changes in microstructural features can have profound effects on the subsequent properties of these materials.

In vivo, label-free, three-dimensional quantitative imaging of liver surface using multi-photon microscopy

NASA Astrophysics Data System (ADS)

Zhuo, Shuangmu; Yan, Jie; Kang, Yuzhan; Xu, Shuoyu; Peng, Qiwen; So, Peter T. C.; Yu, Hanry

2014-07-01

Various structural features on the liver surface reflect functional changes in the liver. The visualization of these surface features with molecular specificity is of particular relevance to understanding the physiology and diseases of the liver. Using multi-photon microscopy (MPM), we have developed a label-free, three-dimensional quantitative and sensitive method to visualize various structural features of liver surface in living rat. MPM could quantitatively image the microstructural features of liver surface with respect to the sinuosity of collagen fiber, the elastic fiber structure, the ratio between elastin and collagen, collagen content, and the metabolic state of the hepatocytes that are correlative with the pathophysiologically induced changes in the regions of interest. This study highlights the potential of this technique as a useful tool for pathophysiological studies and possible diagnosis of the liver diseases with further development.

In vivo, label-free, three-dimensional quantitative imaging of liver surface using multi-photon microscopy

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

Zhuo, Shuangmu, E-mail: shuangmuzhuo@gmail.com, E-mail: hanry-yu@nuhs.edu.sg; Institute of Laser and Optoelectronics Technology, Fujian Normal University, Fuzhou 350007; Yan, Jie

2014-07-14

Various structural features on the liver surface reflect functional changes in the liver. The visualization of these surface features with molecular specificity is of particular relevance to understanding the physiology and diseases of the liver. Using multi-photon microscopy (MPM), we have developed a label-free, three-dimensional quantitative and sensitive method to visualize various structural features of liver surface in living rat. MPM could quantitatively image the microstructural features of liver surface with respect to the sinuosity of collagen fiber, the elastic fiber structure, the ratio between elastin and collagen, collagen content, and the metabolic state of the hepatocytes that are correlativemore » with the pathophysiologically induced changes in the regions of interest. This study highlights the potential of this technique as a useful tool for pathophysiological studies and possible diagnosis of the liver diseases with further development.« less

Monitoring temporal microstructural variations of skeletal muscle tissues by multispectral Mueller matrix polarimetry

NASA Astrophysics Data System (ADS)

Dong, Yang; He, Honghui; He, Chao; Ma, Hui

2017-02-01

Mueller matrix polarimetry is a powerful tool for detecting microscopic structures, therefore can be used to monitor physiological changes of tissue samples. Meanwhile, spectral features of scattered light can also provide abundant microstructural information of tissues. In this paper, we take the 2D multispectral backscattering Mueller matrix images of bovine skeletal muscle tissues, and analyze their temporal variation behavior using multispectral Mueller matrix parameters. The 2D images of the Mueller matrix elements are reduced to the multispectral frequency distribution histograms (mFDHs) to reveal the dominant structural features of the muscle samples more clearly. For quantitative analysis, the multispectral Mueller matrix transformation (MMT) parameters are calculated to characterize the microstructural variations during the rigor mortis and proteolysis processes of the skeletal muscle tissue samples. The experimental results indicate that the multispectral MMT parameters can be used to judge different physiological stages for bovine skeletal muscle tissues in 24 hours, and combining with the multispectral technique, the Mueller matrix polarimetry and FDH analysis can monitor the microstructural variation features of skeletal muscle samples. The techniques may be used for quick assessment and quantitative monitoring of meat qualities in food industry.

SEM stereo-section fractography (SSF) observations

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

Zhang, X.J.; Tregoning, R.L.; Armstrong, R.W.

1997-12-31

Cleavage initiation in engineering materials is governed by local microstructural inhomogeneities. These features are often the principal reason for the large scatter evident in fracture toughness measurements which, in extreme cases, can mask the fundamental relationship between cracking resistance and global material properties. The SEM stereo-section fractography (SSF) technique can be used to carefully evaluate these local inhomogeneities through simultaneous observation of both the fracture surface and the underlying microstructure. By sectioning the fracture surface close to the cleavage initiation site (within 10 {micro}m), and perpendicular to both the fracture surface and the precrack front, a direct correspondence between initiationmore » and the local microstructure can be established. Information obtained from this technique can provide quantitative input about important, local microstructural features which can then be used to calibrate or create realistic micromechanical models. A compendium of SSF results is presented herein for cleavage cracking in disparate materials (A533B steel plates, MIL-70S multi-pass weldments, and Ti6A14V forgings), under various testing conditions. In each case, the SSF technique was able to unambiguously identify the dominant, local features which triggered cleavage initiation.« less

SEM stereo-section fractography observations. Final report

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

Zhang, X.J.; Tregoning, R.L.; Armstrong, R.W.

1998-05-01

Cleavage initiation in engineering materials is governed by local microstructural inhomogeneities. These features are often the principal reason for the large scatter evident in fracture toughness measurements which, in extreme cases, can mask the fundamental relationship between cracking resistance and global material properties. The SEM stereo-section fractography (SSF) technique can be used to carefully evaluate these local inhomogeneities through simultaneous observation of both the fracture surface and the underlying microstructure. By sectioning the fracture surface close to the cleavage initiation site (within 10 microns), and perpendicular to both the fracture surface and the pre crack front, a direct correspondence betweenmore » initiation and the local microstructure can be established. Information obtained from this technique can provide quantitative input about important, local microstructural features which can then be used to calibrate or create realistic micromechanical models. A compendium of SSF results is presented herein for cleavage cracking in disparate materials (A533B steel plates, MIL-70S multi-pass weldments, and Ti6A14V forgings), under various testing conditions. In each case, the SSF technique was able to unambiguously identify the dominant, local features which triggered cleavage initiation.« less

Formation of microstructural features in hot-dip aluminized AISI 321 stainless steel

NASA Astrophysics Data System (ADS)

Huilgol, Prashant; Rajendra Udupa, K.; Udaya Bhat, K.

2018-02-01

Hot-dip aluminizing (HDA) is a proven surface coating technique for improving the oxidation and corrosion resistance of ferrous substrates. Although extensive studies on the HDA of plain carbon steels have been reported, studies on the HDA of stainless steels are limited. Because of the technological importance of stainless steels in high-temperature applications, studies of their microstructural development during HDA are needed. In the present investigation, the HDA of AISI 321 stainless steel was carried out in a pure Al bath. The microstructural features of the coating were studied using scanning electron microscopy and transmission electron microscopy. These studies revealed that the coating consists of two regions: an Al top coat and an aluminide layer at the interface between the steel and Al. The Al top coat was found to consist of intermetallic phases such as Al7Cr and Al3Fe dispersed in an Al matrix. Twinning was observed in both the Al7Cr and the Al3Fe phases. Furthermore, the aluminide layer comprised a mixture of nanocrystalline Fe2Al5, Al7Cr, and Al. Details of the microstructural features are presented, and their formation mechanisms are discussed.

Influence of Size on the Microstructure and Mechanical Properties of an AISI 304L Stainless Steel—A Comparison between Bulk and Fibers

PubMed Central

Baldenebro-Lopez, Francisco J.; Gomez-Esparza, Cynthia D.; Corral-Higuera, Ramon; Arredondo-Rea, Susana P.; Pellegrini-Cervantes, Manuel J.; Ledezma-Sillas, Jose E.; Martinez-Sanchez, Roberto; Herrera-Ramirez, Jose M.

2015-01-01

In this work, the mechanical properties and microstructural features of an AISI 304L stainless steel in two presentations, bulk and fibers, were systematically studied in order to establish the relationship among microstructure, mechanical properties, manufacturing process and effect on sample size. The microstructure was analyzed by XRD, SEM and TEM techniques. The strength, Young’s modulus and elongation of the samples were determined by tensile tests, while the hardness was measured by Vickers microhardness and nanoindentation tests. The materials have been observed to possess different mechanical and microstructural properties, which are compared and discussed. PMID:28787949

Effect of porosity on ductility variation in investment cast 17-4PH.

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

Wright, Robert D.; Kilgo, Alice C.; Grant, Richard P.

2005-02-01

The stainless steel alloy 17-4PH contains a martensitic microstructure and second phase delta ({delta}) ferrite. Strengthening of 17-4PH is attributed to Cu-rich precipitates produced during age hardening treatments at 900-1150 F (H900-H1150). For wrought 17-4PH, the effects of heat treatment and microstructure on mechanical properties are well-documented [for example, Ref. 1]. Fewer studies are available on cast 17-4PH, although it has been a popular casting alloy for high strength applications where moderate corrosion resistance is needed. Microstructural features and defects particular to castings may have adverse effects on properties, especially when the alloy is heat treated to high strength. Themore » objective of this work was to outline the effects of microstructural features specific to castings, such as shrinkage/solidification porosity, on the mechanical behavior of investment cast 17-4PH. Besides heat treatment effects, the results of metallography and SEM studies showed that the largest effect on mechanical properties is from shrinkage/solidification porosity. Figure 1a shows stress-strain curves obtained from samples machined from castings in the H925 condition. The strength levels were fairly similar but the ductility varied significantly. Figure 1b shows an example of porosity on a fracture surface from a room-temperature, quasi-static tensile test. The rounded features represent the surfaces of dendrites which did not fuse or only partially fused together during solidification. Some evidence of local areas of fracture is found on some dendrite surfaces. The shrinkage pores are due to inadequate backfilling of liquid metal and simultaneous solidification shrinkage during casting. A summary of percent elongation results is displayed in Figure 2a. It was found that higher amounts of porosity generally result in lower ductility. Note that the porosity content was measured on the fracture surfaces. The results are qualitatively similar to those found by Gokhale et al. and Surappa et al. in cast A356 Al and by Gokhale et al. for a cast Mg alloys. The quantitative fractography and metallography work by Gokhale et al. illustrated the strong preference for fracture in regions of porosity in cast material. That is, the fracture process is not correlated to the average microstructure in the material but is related to the extremes in microstructure (local regions of high void content). In the present study, image analysis on random cross-sections of several heats indicated an overall porosity content of 0.03%. In contrast, the area % porosity was as high as 16% when measured on fracture surfaces of tensile specimens using stereology techniques. The results confirm that the fracture properties of cast 17-4PH cannot be predicted based on the overall 'average' porosity content in the castings.« less

In situ ESEM imaging of the vapor-pressure-dependent sublimation-induced morphology of ice

NASA Astrophysics Data System (ADS)

Nair, Malavika; Husmann, Anke; Cameron, Ruth E.; Best, Serena M.

2018-04-01

Sublimation is a fundamental phase transition that has a profound impact on both natural phenomena and advanced manufacturing technologies. Although great strides have been made in the study of ice growth from melt and vapor, little consideration has been given to the effect of sublimation on the morphological features that develop in the ice microstructure. In this experimental study, we demonstrate the effect of vapor pressure on the mesoscopic faceting observed and show that a vapor-pressure-specific wavelength characterizes the periodic features that arise during sublimation. The ability to control the length scale of these features not only provides us with new insights into the mesoscopic roughness of ice crystals, but also presents the potential to exploit this effect in a plethora of applications from comet dating to ice-templated tissue engineering scaffolds.

Clinical feasibility of using mean apparent propagator (MAP) MRI to characterize brain tissue microstructure.

PubMed

Avram, Alexandru V; Sarlls, Joelle E; Barnett, Alan S; Özarslan, Evren; Thomas, Cibu; Irfanoglu, M Okan; Hutchinson, Elizabeth; Pierpaoli, Carlo; Basser, Peter J

2016-02-15

Diffusion tensor imaging (DTI) is the most widely used method for characterizing noninvasively structural and architectural features of brain tissues. However, the assumption of a Gaussian spin displacement distribution intrinsic to DTI weakens its ability to describe intricate tissue microanatomy. Consequently, the biological interpretation of microstructural parameters, such as fractional anisotropy or mean diffusivity, is often equivocal. We evaluate the clinical feasibility of assessing brain tissue microstructure with mean apparent propagator (MAP) MRI, a powerful analytical framework that efficiently measures the probability density function (PDF) of spin displacements and quantifies useful metrics of this PDF indicative of diffusion in complex microstructure (e.g., restrictions, multiple compartments). Rotation invariant and scalar parameters computed from the MAP show consistent variation across neuroanatomical brain regions and increased ability to differentiate tissues with distinct structural and architectural features compared with DTI-derived parameters. The return-to-origin probability (RTOP) appears to reflect cellularity and restrictions better than MD, while the non-Gaussianity (NG) measures diffusion heterogeneity by comprehensively quantifying the deviation between the spin displacement PDF and its Gaussian approximation. Both RTOP and NG can be decomposed in the local anatomical frame for reference determined by the orientation of the diffusion tensor and reveal additional information complementary to DTI. The propagator anisotropy (PA) shows high tissue contrast even in deep brain nuclei and cortical gray matter and is more uniform in white matter than the FA, which drops significantly in regions containing crossing fibers. Orientational profiles of the propagator computed analytically from the MAP MRI series coefficients allow separation of different fiber populations in regions of crossing white matter pathways, which in turn improves our ability to perform whole-brain fiber tractography. Reconstructions from subsampled data sets suggest that MAP MRI parameters can be computed from a relatively small number of DWIs acquired with high b-value and good signal-to-noise ratio in clinically achievable scan durations of less than 10min. The neuroanatomical consistency across healthy subjects and reproducibility in test-retest experiments of MAP MRI microstructural parameters further substantiate the robustness and clinical feasibility of this technique. The MAP MRI metrics could potentially provide more sensitive clinical biomarkers with increased pathophysiological specificity compared to microstructural measures derived using conventional diffusion MRI techniques. Published by Elsevier Inc.

Bridging the gap between atomic microstructure and electronic properties of alloys: The case of (In,Ga)N

NASA Astrophysics Data System (ADS)

Chan, J. A.; Liu, J. Z.; Zunger, Alex

2010-07-01

The atomic microstructure of alloys is rarely perfectly random, instead exhibiting differently shaped precipitates, clusters, zigzag chains, etc. While it is expected that such microstructural features will affect the electronic structures (carrier localization and band gaps), theoretical studies have, until now, been restricted to investigate either perfectly random or artificial “guessed” microstructural features. In this paper, we simulate the alloy microstructures in thermodynamic equilibrium using the static Monte Carlo method and study their electronic structures explicitly using a pseudopotential supercell approach. In this way, we can bridge atomic microstructures with their electronic properties. We derive the atomic microstructures of InGaN using (i) density-functional theory total energies of ˜50 ordered structures to construct a (ii) multibody cluster expansion, including strain effects to which we have applied (iii) static Monte Carlo simulations of systems consisting of over 27000 atoms to determine the equilibrium atomic microstructures. We study two types of alloy thermodynamic behavior: (a) under lattice incoherent conditions, the formation enthalpies are positive and thus the alloy system phase-separates below the miscibility-gap temperature TMG , (b) under lattice coherent conditions, the formation enthalpies can be negative and thus the alloy system exhibits ordering tendency. The microstructure is analyzed in terms of structural motifs (e.g., zigzag chains and InnGa4-nN tetrahedral clusters). The corresponding electronic structure, calculated with the empirical pseudopotentials method, is analyzed in terms of band-edge energies and wave-function localization. We find that the disordered alloys have no electronic localization but significant hole localization, while below the miscibility gap under the incoherent conditions, In-rich precipitates lead to strong electron and hole localization and a reduction in the band gap.

[Strategy of molecular design of drugs: the unification of macro-properties and micro-structures of a molecule].

PubMed

Guo, Zong-Ru

2008-03-01

The interaction of a drug with the organism involves both the disposition of a drug by the organism and the action of a drug on the organism. The disposition of various exogenous substances, including drugs, complies with general rules. The underlying physical and chemical changes to different drugs in view of time and space, i. e. pharmacokinetics, share common characteristics, that is the tout ensemble of a molecule and its macroscopic properties convey direct effect on the pharmacokinetic behavior as the tendency and consequence of biological evolution. The action of a drug on the organism, on the other hand, implicates the physico-chemical binding of a drug molecule to the target protein, which induces pharmacological and toxicological effects. The biological reactions, no matter beneficial or adverse, are all specific and individual manifestation of the drug molecule and determined by the interactive binding between definitive atoms or groups of the drug molecule and the macromolecular target in three-dimension. Such critical atoms, groups, or fragments responsible for the interaction reflect the microscopic structures of drug molecules and are called pharmacophore. In this context, a drug molecule is presumed as an assembly of macroscopic property and microscopic structure, with the macroscopic properties determining the absorption, distribution, metabolism and elimination of drugs and the microscopic structure coining pharmacological action. The knowledge of the internal relationship between macroscopy/microscopy and PK/PD conduces to comprehension of drug action and guides molecular drug design, because this conception facilitates the identification of structural features necessary for biological response, and the determination of factors modulating the physico-chemical and pharmacokinetic properties. The factors determining macro-properties include molecular weight, solubility, charge, lipophilicity (partition), and polar surface area, etc., which are destined by molecular scaffolds and/or side chain(s) apart from pharmacophore. The features of micro-structures contributing to specific activity contain hydrogen bonding donor and acceptor, positive and negative charge centers, hydrophobic centers and centers of aromatic rings. Different combinations and spacial arrangements of these features determine the distinct activity presented. The macro-property and micro-structure are integrated into a single molecule, and are inseparable. The macro-property reflects overall contribution of atoms and groups in the micro-structure. On the other hand, structural changes aimed to adjust macroscopic property usually alter the relative position of the microscopic structure. The goal of molecular drug design is to integrate the macroscopic and microscopic factors in optimized manner. In the early stage of molecular design, both macroscopic property and microscopic structure should be considered to make pharmacodynamics, pharmacokinetics, and physico-chemical properties in optimal match. Therefore, it required the existence of structural overlapping among acceptable pharmacokinetics, visible developing potential and specific pharmacodynamics. The larger the scope of overlapping, the higher the possibility to be a drug.

Key Factors Influencing the Energy Absorption of Dual-Phase Steels: Multiscale Material Model Approach and Microstructural Optimization

NASA Astrophysics Data System (ADS)

Belgasam, Tarek M.; Zbib, Hussein M.

2018-06-01

The increase in use of dual-phase (DP) steel grades by vehicle manufacturers to enhance crash resistance and reduce body car weight requires the development of a clear understanding of the effect of various microstructural parameters on the energy absorption in these materials. Accordingly, DP steelmakers are interested in predicting the effect of various microscopic factors as well as optimizing microstructural properties for application in crash-relevant components of vehicle bodies. This study presents a microstructure-based approach using a multiscale material and structure model. In this approach, Digimat and LS-DYNA software were coupled and employed to provide a full micro-macro multiscale material model, which is then used to simulate tensile tests. Microstructures with varied ferrite grain sizes, martensite volume fractions, and carbon content in DP steels were studied. The impact of these microstructural features at different strain rates on energy absorption characteristics of DP steels is investigated numerically using an elasto-viscoplastic constitutive model. The model is implemented in a multiscale finite-element framework. A comprehensive statistical parametric study using response surface methodology is performed to determine the optimum microstructural features for a required tensile toughness at different strain rates. The simulation results are validated using experimental data found in the literature. The developed methodology proved to be effective for investigating the influence and interaction of key microscopic properties on the energy absorption characteristics of DP steels. Furthermore, it is shown that this method can be used to identify optimum microstructural conditions at different strain-rate conditions.

Key Factors Influencing the Energy Absorption of Dual-Phase Steels: Multiscale Material Model Approach and Microstructural Optimization

NASA Astrophysics Data System (ADS)

Belgasam, Tarek M.; Zbib, Hussein M.

2018-03-01

The increase in use of dual-phase (DP) steel grades by vehicle manufacturers to enhance crash resistance and reduce body car weight requires the development of a clear understanding of the effect of various microstructural parameters on the energy absorption in these materials. Accordingly, DP steelmakers are interested in predicting the effect of various microscopic factors as well as optimizing microstructural properties for application in crash-relevant components of vehicle bodies. This study presents a microstructure-based approach using a multiscale material and structure model. In this approach, Digimat and LS-DYNA software were coupled and employed to provide a full micro-macro multiscale material model, which is then used to simulate tensile tests. Microstructures with varied ferrite grain sizes, martensite volume fractions, and carbon content in DP steels were studied. The impact of these microstructural features at different strain rates on energy absorption characteristics of DP steels is investigated numerically using an elasto-viscoplastic constitutive model. The model is implemented in a multiscale finite-element framework. A comprehensive statistical parametric study using response surface methodology is performed to determine the optimum microstructural features for a required tensile toughness at different strain rates. The simulation results are validated using experimental data found in the literature. The developed methodology proved to be effective for investigating the influence and interaction of key microscopic properties on the energy absorption characteristics of DP steels. Furthermore, it is shown that this method can be used to identify optimum microstructural conditions at different strain-rate conditions.

BISON Investigation of the Effect of the Fuel- Cladding Contact Irregularities on the Peak Cladding Temperature and FCCI Observed in AFC-3A Rodlet 4

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

Medvedev, Pavel G.

2016-09-01

The primary objective of this report is to document results of BISON analyses supporting Fuel Cycle Research and Development (FCRD) activities. Specifically, the present report seeks to provide explanation for the microstructural features observed during post irradiation examination of the helium-bonded annular U-10Zr fuel irradiated during the AFC-3A experiment. Post irradiation examination of the AFC-3A rodlet revealed microstructural features indicative of the fuel-cladding chemical interaction (FCCI) at the fuel-cladding interface. Presence of large voids was also observed in the same locations. BISON analyses were performed to examine stress and temperature profiles and to investigate possible correlation between the voids andmore » FCCI. It was found that presence of the large voids lead to a formation of circumferential temperature gradients in the fuel that may have redirected migrating lanthanides to the locations where fuel and cladding are in contact. Resulting localized increase of lanthanide concentration is expected to accelerate FCCI. The results of this work provide important guidance to the post irradiation examination studies. Specifically, the hypothesis of lanthanides being redirected from the voids to the locations where the fuel and the cladding are in contact should be verified by conducting quantitative electron microscopy or Electron Probe Micro-Analyzer (EPMA). The results also highlight the need for computer models capable of simulating lanthanide diffusion in metallic fuel and establish a basis for validation of such models.« less

Amygdala and hippocampus volumetry and diffusivity in relation to dreaming.

PubMed

De Gennaro, Luigi; Cipolli, Carlo; Cherubini, Andrea; Assogna, Francesca; Cacciari, Claudia; Marzano, Cristina; Curcio, Giuseppe; Ferrara, Michele; Caltagirone, Carlo; Spalletta, Gianfranco

2011-09-01

Microstructural analyses by MRI brain scans and by DTI analysis of MR images were used to investigate the possible relationship between deep gray matter structures (amygdala and hippocampus) and dreaming in healthy subjects. Thirty-four subjects ranging in age 20s to 70s underwent to a MRI protocol for the assessment of volume and mean diffusivity (MD) in the amygdala and hippocampus and were asked to fill out a dream diary via audiotape recording upon morning awakening for two weeks. Multiple regression analyses evaluated the relationships between anatomical measures and quantitative and qualitative measures of the reported dreams. The main result points to a dissociation between some quantitative and qualitative aspects of dream reports. While the mean number of dreams recalled per day did not show any significant relationship with the neuroanatomical measures, significant associations with some qualitative features of the recalled dreams (emotional load, bizarreness, and vividness) and, to some extent, with the length of dream reports were observed. Particularly, a higher MD of the left amygdala, reflecting a decreased microstructural integrity, was associated with shorter dream reports and lower scores on emotional load. Bizarreness of dream reports was negatively correlated with the left amygdala volume and positively correlated with the right amygdala MD. Some specific, although weaker, relationships were also found between bizarreness and hippocampal measures. These findings indicate some direct relationships between volumetric and ultrastructural measures of the hippocampus-amygdala complex and specific qualitative features of dreaming. Copyright © 2010 Wiley-Liss, Inc.

Characterization of Novel Plasmonic, Photonic, and Semiconductor Microstructures

NASA Astrophysics Data System (ADS)

Sears, Jasmine Soria

The fields of telecommunications and optoelectronics are under constant pressure to shrink devices and reduce power consumption. Micro-scale photonic and plasmonic structures can trap light and enhance the brightness of active emitters; thus, these types of structures are promising avenues to accomplishing the goals of miniaturization and efficiency. A deeper understanding of specific structures is important in order to gauge their suitability for specific applications. In this dissertation, two types of microstructures are explored: one-dimensional silicon photonic crystals and self-assembled indium islands. This dissertation will provide novel characterization of these structures and a description of how to utilize or compensate for the observed features. A photonic crystal can act as a tiny resonator for certain wavelengths, making it a promising structure for applications that require extremely small lasers. However, because of silicon’s indirect bandgap, a silicon photonic crystal cavity would require the addition of an active emitter to function as a light source. Attempts to incorporate erbium into these cavities, and the observation of an unusual coupling phenomenon, will be discussed. Self-assembled indium islands are plasmonic structures that can be grown via molecular beam epitaxy. In theory, these islands should be pure indium nanoantennas on top of a smooth gallium arsenide substrate. In practice, the component materials are less segregated than predicted, giving rise to unexpected hollow dome shapes and a sub-surface indium layer. Although these features were not an intended result of indium island growth, they provide information regarding the island formation process and potentially contribute additional applications.

Chinese wine classification system based on micrograph using combination of shape and structure features

NASA Astrophysics Data System (ADS)

Wan, Yi

2011-06-01

Chinese wines can be classification or graded by the micrographs. Micrographs of Chinese wines show floccules, stick and granule of variant shape and size. Different wines have variant microstructure and micrographs, we study the classification of Chinese wines based on the micrographs. Shape and structure of wines' particles in microstructure is the most important feature for recognition and classification of wines. So we introduce a feature extraction method which can describe the structure and region shape of micrograph efficiently. First, the micrographs are enhanced using total variation denoising, and segmented using a modified Otsu's method based on the Rayleigh Distribution. Then features are extracted using proposed method in the paper based on area, perimeter and traditional shape feature. Eight kinds total 26 features are selected. Finally, Chinese wine classification system based on micrograph using combination of shape and structure features and BP neural network have been presented. We compare the recognition results for different choices of features (traditional shape features or proposed features). The experimental results show that the better classification rate have been achieved using the combinational features proposed in this paper.

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.

A phase-field approach to model multi-axial and microstructure dependent fracture in nuclear grade graphite

DOE PAGES

Chakraborty, Pritam; Sabharwall, Piyush; Carroll, Mark C.

2016-04-07

The fracture behavior of nuclear grade graphites is strongly influenced by underlying microstructural features such as the character of filler particles, and the distribution of pores and voids. These microstructural features influence the crack nucleation and propagation behavior, resulting in quasi-brittle fracture with a tortuous crack path and significant scatter in measured bulk strength. This paper uses a phase-field method to model the microstructural and multi-axial fracture in H-451, a historic variant of nuclear graphite that provides the basis for an idealized study on a legacy grade. The representative volume elements are constructed from randomly located pores with random sizemore » obtained from experimentally determined log-normal distribution. The representative volume elements are then subjected to simulated multi-axial loading, and a reasonable agreement of the resulting fracture stress with experiments is obtained. Finally, quasi-brittle stress-strain evolution with a tortuous crack path is also observed from the simulations and is consistent with experimental results.« less

Texture and microstructure evolution in single-phase Ti{sub x}Ta{sub 1-x}N alloys of rocksalt structure

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

Koutsokeras, L. E.; Department of Materials Science and Engineering, University of Ioannina, GR-45100 Ioannina; Abadias, G.

2011-08-15

The mechanisms controlling the structural and morphological features (texture and microstructure) of ternary transition metal nitride thin films of the Ti{sub x}Ta{sub 1-x}N system, grown by various physical vapor deposition techniques, are reported. Films deposited by pulsed laser deposition, dual cathode magnetron sputtering, and dual ion beam sputtering have been investigated by means of x-ray diffraction in various geometries and scanning electron microscopy. We studied the effects of composition, energetic, and kinetics in the evolution of the microstructure and texture of the films. We obtain films with single and mixed texture as well as films with columnar ''zone-T'' and globularmore » type morphology. The results have shown that the texture evolution of ternary transition metal nitrides as well as the microstructural features of such films can be well understood in the framework of the kinetic mechanisms proposed for their binary counterparts, thus giving these mechanisms a global application.« less

Influence of Solution Treatment Duration on Microstructural Features of an Industrial Forged UNS S32750/1.4410/F53 Super Duplex Stainless Steel (SDSS) Alloy

NASA Astrophysics Data System (ADS)

Cojocaru, Vasile Dănuţ; Răducanu, Doina; Angelescu, Mariana Lucia; Vintilă, Adrian Nicolae; Şerban, Nicolae; Dan, Ioan; Cojocaru, Elisabeta Mirela; Cinca, Ion

2017-08-01

The microstructural changes induced by solution treatment of an industrial forged F53 Super Duplex Stainless Steel alloy were studied, in order to emphasize how component phases are influenced by heat treatment temperature and duration. The solution treatment was done at a temperature of 1100°C, with variable holding times: 0.6 ks (10 min), 3.6 ks (60 min) and 10.8 ks (180 min). Scanning electron microscopy-electron backscattered diffraction was used as main characterization technique, to obtain and analyse data referring to microstructural features, such as: nature and morphology of constituent phases, average grain-size and grain misorientation. It was shown that in all studied cases the microstructure consisted of a mixture of about 45% δ-Fe (ferrite) and 55% γ-Fe (austenite). Besides δ-Fe and γ-Fe phases, other phases were also identified, such as τ-phase (chromium-iron carbide), σ-phase (chromium-iron) and δ-(Cr-Fe) (ferrite).

Deformational Features and Microstructure Evolution of Copper Fabricated by a Single Pass of the Elliptical Cross-Section Spiral Equal-Channel Extrusion (ECSEE) Process

NASA Astrophysics Data System (ADS)

Wang, Chengpeng; Li, Fuguo; Liu, Juncheng

2018-04-01

The objectives of this work are to study the deformational feature, textures, microstructures, and dislocation configurations of ultrafine-grained copper processed by the process of elliptical cross-section spiral equal-channel extrusion (ECSEE). The deformation patterns of simple shear and pure shear in the ECSEE process were evaluated with the analytical method of geometric strain. The influence of the main technical parameters of ECSEE die on the effective strain distribution on the surface of ECSEE-fabricated samples was examined by the finite element simulation. The high friction factor could improve the effective strain accumulation of material deformation. Moreover, the pure copper sample fabricated by ECSEE ion shows a strong rotated cube shear texture. The refining mechanism of the dislocation deformation is dominant in copper processed by a single pass of ECSEE. The inhomogeneity of the micro-hardness distribution on the longitudinal section of the ECSEE-fabricated sample is consistent with the strain and microstructure distribution features.

Metallurgical Mechanisms Controlling Mechanical Properties of Aluminum Alloy 2219 Produced By Electron Beam Freeform Fabrication

NASA Technical Reports Server (NTRS)

Domack, Marcia S.; Taminger, Karen M. B.; Begley, Matthew

2006-01-01

The electron beam freeform fabrication (EBF3) layer-additive manufacturing process has been developed to directly fabricate complex geometry components. EBF3 introduces metal wire into a molten pool created on the surface of a substrate by a focused electron beam. Part geometry is achieved by translating the substrate with respect to the beam to build the part one layer at a time. Tensile properties have been demonstrated for electron beam deposited aluminum and titanium alloys that are comparable to wrought products, although the microstructures of the deposits exhibit features more typical of cast material. Understanding the metallurgical mechanisms controlling mechanical properties is essential to maximizing application of the EBF3 process. In the current study, mechanical properties and resulting microstructures were examined for aluminum alloy 2219 fabricated over a range of EBF3 process variables. Material performance was evaluated based on tensile properties and results were compared with properties of Al 2219 wrought products. Unique microstructures were observed within the deposited layers and at interlayer boundaries, which varied within the deposit height due to microstructural evolution associated with the complex thermal history experienced during subsequent layer deposition. Microstructures exhibited irregularly shaped grains, typically with interior dendritic structures, which were described based on overall grain size, morphology, distribution, and dendrite spacing, and were correlated with deposition parameters. Fracture features were compared with microstructural elements to define fracture paths and aid in definition of basic processing-microstructure-property correlations.

Mapping axonal density and average diameter using non-monotonic time-dependent gradient-echo MRI

NASA Astrophysics Data System (ADS)

Nunes, Daniel; Cruz, Tomás L.; Jespersen, Sune N.; Shemesh, Noam

2017-04-01

White Matter (WM) microstructures, such as axonal density and average diameter, are crucial to the normal function of the Central Nervous System (CNS) as they are closely related with axonal conduction velocities. Conversely, disruptions of these microstructural features may result in severe neurological deficits, suggesting that their noninvasive mapping could be an important step towards diagnosing and following pathophysiology. Whereas diffusion based MRI methods have been proposed to map these features, they typically entail the application of powerful gradients, which are rarely available in the clinic, or extremely long acquisition schemes to extract information from parameter-intensive models. In this study, we suggest that simple and time-efficient multi-gradient-echo (MGE) MRI can be used to extract the axon density from susceptibility-driven non-monotonic decay in the time-dependent signal. We show, both theoretically and with simulations, that a non-monotonic signal decay will occur for multi-compartmental microstructures - such as axons and extra-axonal spaces, which were here used as a simple model for the microstructure - and that, for axons parallel to the main magnetic field, the axonal density can be extracted. We then experimentally demonstrate in ex-vivo rat spinal cords that its different tracts - characterized by different microstructures - can be clearly contrasted using the MGE-derived maps. When the quantitative results are compared against ground-truth histology, they reflect the axonal fraction (though with a bias, as evident from Bland-Altman analysis). As well, the extra-axonal fraction can be estimated. The results suggest that our model is oversimplified, yet at the same time evidencing a potential and usefulness of the approach to map underlying microstructures using a simple and time-efficient MRI sequence. We further show that a simple general-linear-model can predict the average axonal diameters from the four model parameters, and map these average axonal diameters in the spinal cords. While clearly further modelling and theoretical developments are necessary, we conclude that salient WM microstructural features can be extracted from simple, SNR-efficient multi-gradient echo MRI, and that this paves the way towards easier estimation of WM microstructure in vivo.

Mapping axonal density and average diameter using non-monotonic time-dependent gradient-echo MRI.

PubMed

Nunes, Daniel; Cruz, Tomás L; Jespersen, Sune N; Shemesh, Noam

2017-04-01

White Matter (WM) microstructures, such as axonal density and average diameter, are crucial to the normal function of the Central Nervous System (CNS) as they are closely related with axonal conduction velocities. Conversely, disruptions of these microstructural features may result in severe neurological deficits, suggesting that their noninvasive mapping could be an important step towards diagnosing and following pathophysiology. Whereas diffusion based MRI methods have been proposed to map these features, they typically entail the application of powerful gradients, which are rarely available in the clinic, or extremely long acquisition schemes to extract information from parameter-intensive models. In this study, we suggest that simple and time-efficient multi-gradient-echo (MGE) MRI can be used to extract the axon density from susceptibility-driven non-monotonic decay in the time-dependent signal. We show, both theoretically and with simulations, that a non-monotonic signal decay will occur for multi-compartmental microstructures - such as axons and extra-axonal spaces, which were here used as a simple model for the microstructure - and that, for axons parallel to the main magnetic field, the axonal density can be extracted. We then experimentally demonstrate in ex-vivo rat spinal cords that its different tracts - characterized by different microstructures - can be clearly contrasted using the MGE-derived maps. When the quantitative results are compared against ground-truth histology, they reflect the axonal fraction (though with a bias, as evident from Bland-Altman analysis). As well, the extra-axonal fraction can be estimated. The results suggest that our model is oversimplified, yet at the same time evidencing a potential and usefulness of the approach to map underlying microstructures using a simple and time-efficient MRI sequence. We further show that a simple general-linear-model can predict the average axonal diameters from the four model parameters, and map these average axonal diameters in the spinal cords. While clearly further modelling and theoretical developments are necessary, we conclude that salient WM microstructural features can be extracted from simple, SNR-efficient multi-gradient echo MRI, and that this paves the way towards easier estimation of WM microstructure in vivo. Copyright © 2017 Elsevier Inc. All rights reserved.

Rabbit cornea microstructure response to changes in intraocular pressure visualized by using nonlinear optical microscopy.

PubMed

Wu, Qiaofeng; Yeh, Alvin T

2008-02-01

To characterize the microstructural response of the rabbit cornea to changes in intraocular pressure (IOP) by using nonlinear optical microscopy (NLOM). Isolated rabbit corneas were mounted on an artificial anterior chamber in series with a manometer and were hydrostatically pressurized by a reservoir. The chamber was mounted on an upright microscope stage of a custom-built NLOM system for corneal imaging without using exogenous stains or dyes. Second harmonic generation in collagen was used to image through the full thickness of the central corneal stroma at IOPs between 5 and 20 mm Hg. Microstructural morphology changes as a function of IOP were used to characterize the depth-dependent response of the central cornea. Regional collagen lamellae architecture through the full thickness of the stroma was specifically imaged as a function of IOP. Hypotensive corneas showed gaps between lamellar structures that decreased in size with increasing IOP. These morphologic features appear to result from interwoven lamellae oriented along the anterior-posterior axis and parallel to the cornea surface. They appear throughout the full thickness and disappear with tension in the anterior but persist in the posterior central cornea, even at hypertensive IOP. NLOM reveals interwoven collagen lamellae sheets through the full thickness of the rabbit central cornea oriented along the anterior-posterior axis and parallel to the surface. The nondestructive nature of NLOM allows 3-dimensional imaging of stromal architecture as a function of IOP in situ. Collagen morphologic features were used as an indirect measure of depth-dependent mechanical response to changes in IOP.

Quantitatively characterizing microstructural variations of skin tissues during ultraviolet radiation damaging process based on Mueller matrix polarimetry

NASA Astrophysics Data System (ADS)

Sheng, Wei; He, Honghui; Dong, Yang; Ma, Hui

2018-02-01

As one of the most fundamental features of light, polarization can be used to develop imaging techniques which can provide insight into the optical and structural properties of tissues. Especially, the Mueller matrix polarimetry is suitable to detect the changes in collagen and elastic fibres, which are the main compositions of skin tissue. Here we demonstrate a novel quantitative, non-contact and in situ technique to monitor the microstructural variations of skin tissue during ultraviolet radiation (UVR) induced photoaging based on Mueller matrix polarimetry. Specifically, we measure the twodimensional (2D) backscattering Mueller matrices of nude mouse skin samples, then calculate and analyze the Mueller matrix derived parameters during the skin photoaging and self-repairing processes. To induce three-day skin photoaging, the back skin of each mouse is irradiated with UVR (0.05J/cm2) for five minutes per day. After UVR, the microstructures of the nude mouse skin are damaged. During the process of UV damage, we measure the backscattering Mueller matrices of the mouse skin samples and examine the relationship between the Mueller matrix parameters and the microstructural variations of skin tissue quantitatively. The comparisons between the UVR damaged groups with and without sunscreens show that the Mueller matrix derived parameters are potential indicators for fibrous microstructure variation in skin tissue. The pathological examinations and Monte Carlo simulations confirm the relationship between the values of Mueller matrix parameters and the changes of fibrous structures. Combined with smart phones or wearable devices, this technique may have a good application prospect in the fields of cosmetics and dermatological health.

The effects of behavioral and structural assumptions in artificial stock market

NASA Astrophysics Data System (ADS)

Liu, Xinghua; Gregor, Shirley; Yang, Jianmei

2008-04-01

Recent literature has developed the conjecture that important statistical features of stock price series, such as the fat tails phenomenon, may depend mainly on the market microstructure. This conjecture motivated us to investigate the roles of both the market microstructure and agent behavior with respect to high-frequency returns and daily returns. We developed two simple models to investigate this issue. The first one is a stochastic model with a clearing house microstructure and a population of zero-intelligence agents. The second one has more behavioral assumptions based on Minority Game and also has a clearing house microstructure. With the first model we found that a characteristic of the clearing house microstructure, namely the clearing frequency, can explain fat tail, excess volatility and autocorrelation phenomena of high-frequency returns. However, this feature does not cause the same phenomena in daily returns. So the Stylized Facts of daily returns depend mainly on the agents’ behavior. With the second model we investigated the effects of behavioral assumptions on daily returns. Our study implicates that the aspects which are responsible for generating the stylized facts of high-frequency returns and daily returns are different.

Effects of the Tempering and High-Pressure Torsion Temperatures on Microstructure of Ferritic/Martensitic Steel Grade 91

PubMed Central

Ganeev, Artur; Nikitina, Marina; Sitdikov, Vil; Islamgaliev, Rinat; Hoffman, Andrew; Wen, Haiming

2018-01-01

Grade 91 (9Cr-1Mo) steel was subjected to various heat treatments and then to high-pressure torsion (HPT) at different temperatures. Its microstructure was studied using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Effects of the tempering temperature and the HPT temperature on the microstructural features and microhardness in the ultrafine-grained (UFG) Grade 91 steel were researched. The study of the UFG structure formation takes into account two different microstructures observed: before HPT in both samples containing martensite and in fully ferritic samples. PMID:29671761

The effect of wall thickness distribution on mechanical reliability and strength in unidirectional porous ceramics.

PubMed

Seuba, Jordi; Deville, Sylvain; Guizard, Christian; Stevenson, Adam J

2016-01-01

Macroporous ceramics exhibit an intrinsic strength variability caused by the random distribution of defects in their structure. However, the precise role of microstructural features, other than pore volume, on reliability is still unknown. Here, we analyze the applicability of the Weibull analysis to unidirectional macroporous yttria-stabilized-zirconia (YSZ) prepared by ice-templating. First, we performed crush tests on samples with controlled microstructural features with the loading direction parallel to the porosity. The compressive strength data were fitted using two different fitting techniques, ordinary least squares and Bayesian Markov Chain Monte Carlo, to evaluate whether Weibull statistics are an adequate descriptor of the strength distribution. The statistical descriptors indicated that the strength data are well described by the Weibull statistical approach, for both fitting methods used. Furthermore, we assess the effect of different microstructural features (volume, size, densification of the walls, and morphology) on Weibull modulus and strength. We found that the key microstructural parameter controlling reliability is wall thickness. In contrast, pore volume is the main parameter controlling the strength. The highest Weibull modulus ([Formula: see text]) and mean strength (198.2 MPa) were obtained for the samples with the smallest and narrowest wall thickness distribution (3.1 [Formula: see text]m) and lower pore volume (54.5%).

The effect of wall thickness distribution on mechanical reliability and strength in unidirectional porous ceramics

NASA Astrophysics Data System (ADS)

Seuba, Jordi; Deville, Sylvain; Guizard, Christian; Stevenson, Adam J.

2016-01-01

Macroporous ceramics exhibit an intrinsic strength variability caused by the random distribution of defects in their structure. However, the precise role of microstructural features, other than pore volume, on reliability is still unknown. Here, we analyze the applicability of the Weibull analysis to unidirectional macroporous yttria-stabilized-zirconia (YSZ) prepared by ice-templating. First, we performed crush tests on samples with controlled microstructural features with the loading direction parallel to the porosity. The compressive strength data were fitted using two different fitting techniques, ordinary least squares and Bayesian Markov Chain Monte Carlo, to evaluate whether Weibull statistics are an adequate descriptor of the strength distribution. The statistical descriptors indicated that the strength data are well described by the Weibull statistical approach, for both fitting methods used. Furthermore, we assess the effect of different microstructural features (volume, size, densification of the walls, and morphology) on Weibull modulus and strength. We found that the key microstructural parameter controlling reliability is wall thickness. In contrast, pore volume is the main parameter controlling the strength. The highest Weibull modulus (?) and mean strength (198.2 MPa) were obtained for the samples with the smallest and narrowest wall thickness distribution (3.1 ?m) and lower pore volume (54.5%).

Characterizing microstructural features of biomedical samples by statistical analysis of Mueller matrix images

NASA Astrophysics Data System (ADS)

He, Honghui; Dong, Yang; Zhou, Jialing; Ma, Hui

2017-03-01

As one of the salient features of light, polarization contains abundant structural and optical information of media. Recently, as a comprehensive description of polarization property, the Mueller matrix polarimetry has been applied to various biomedical studies such as cancerous tissues detections. In previous works, it has been found that the structural information encoded in the 2D Mueller matrix images can be presented by other transformed parameters with more explicit relationship to certain microstructural features. In this paper, we present a statistical analyzing method to transform the 2D Mueller matrix images into frequency distribution histograms (FDHs) and their central moments to reveal the dominant structural features of samples quantitatively. The experimental results of porcine heart, intestine, stomach, and liver tissues demonstrate that the transformation parameters and central moments based on the statistical analysis of Mueller matrix elements have simple relationships to the dominant microstructural properties of biomedical samples, including the density and orientation of fibrous structures, the depolarization power, diattenuation and absorption abilities. It is shown in this paper that the statistical analysis of 2D images of Mueller matrix elements may provide quantitative or semi-quantitative criteria for biomedical diagnosis.

Incorporating physically-based microstructures in materials modeling: Bridging phase field and crystal plasticity frameworks

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

Lim, Hojun; Abdeljawad, Fadi; Owen, Steven J.

Here, the mechanical properties of materials systems are highly influenced by various features at the microstructural level. The ability to capture these heterogeneities and incorporate them into continuum-scale frameworks of the deformation behavior is considered a key step in the development of complex non-local models of failure. In this study, we present a modeling framework that incorporates physically-based realizations of polycrystalline aggregates from a phase field (PF) model into a crystal plasticity finite element (CP-FE) framework. Simulated annealing via the PF model yields ensembles of materials microstructures with various grain sizes and shapes. With the aid of a novel FEmore » meshing technique, FE discretizations of these microstructures are generated, where several key features, such as conformity to interfaces, and triple junction angles, are preserved. The discretizations are then used in the CP-FE framework to simulate the mechanical response of polycrystalline α-iron. It is shown that the conformal discretization across interfaces reduces artificial stress localization commonly observed in non-conformal FE discretizations. The work presented herein is a first step towards incorporating physically-based microstructures in lieu of the overly simplified representations that are commonly used. In broader terms, the proposed framework provides future avenues to explore bridging models of materials processes, e.g. additive manufacturing and microstructure evolution of multi-phase multi-component systems, into continuum-scale frameworks of the mechanical properties.« less

DETECTION OF POLARIZED QUASI-PERIODIC MICROSTRUCTURE EMISSION IN MILLISECOND PULSARS

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

De, Kishalay; Sharma, Prateek; Gupta, Yashwant, E-mail: kde@caltech.edu

Microstructure emission, involving short timescale, often quasi-periodic, intensity fluctuations in subpulse emission, is well known in normal period pulsars. In this Letter, we present the first detections of quasi-periodic microstructure emission from millisecond pulsars (MSPs), from Giant Metrewave Radio Telescope observations of two MSPs at 325 and 610 MHz. Similar to the characteristics of microstructure observed in normal period pulsars, we find that these features are often highly polarized and exhibit quasi-periodic behavior on top of broader subpulse emission, with periods of the order of a few μ s. By measuring their widths and periodicities from single pulse intensity profilesmore » and their autocorrelation functions, we extend the microstructure timescale–rotation period relationship by more than an order of magnitude down to rotation periods ∼5 ms, and find it to be consistent with the relationship derived earlier for normal pulsars. The similarity of behavior is remarkable, given the significantly different physical properties of MSPs and normal period pulsars, and rules out several previous speculations about the possible different characteristics of microstructure in MSP radio emission. We discuss the possible reasons for the non-detection of these features in previous high time resolution MSP studies along with the physical implications of our results, both in terms of a geometric beam sweeping model and temporal modulation model for micropulse production.« less

Incorporating physically-based microstructures in materials modeling: Bridging phase field and crystal plasticity frameworks

DOE PAGES

Lim, Hojun; Abdeljawad, Fadi; Owen, Steven J.; ...

2016-04-25

Here, the mechanical properties of materials systems are highly influenced by various features at the microstructural level. The ability to capture these heterogeneities and incorporate them into continuum-scale frameworks of the deformation behavior is considered a key step in the development of complex non-local models of failure. In this study, we present a modeling framework that incorporates physically-based realizations of polycrystalline aggregates from a phase field (PF) model into a crystal plasticity finite element (CP-FE) framework. Simulated annealing via the PF model yields ensembles of materials microstructures with various grain sizes and shapes. With the aid of a novel FEmore » meshing technique, FE discretizations of these microstructures are generated, where several key features, such as conformity to interfaces, and triple junction angles, are preserved. The discretizations are then used in the CP-FE framework to simulate the mechanical response of polycrystalline α-iron. It is shown that the conformal discretization across interfaces reduces artificial stress localization commonly observed in non-conformal FE discretizations. The work presented herein is a first step towards incorporating physically-based microstructures in lieu of the overly simplified representations that are commonly used. In broader terms, the proposed framework provides future avenues to explore bridging models of materials processes, e.g. additive manufacturing and microstructure evolution of multi-phase multi-component systems, into continuum-scale frameworks of the mechanical properties.« less

Atomistic Simulation of Interfaces in Materials of Solid State Ionics

NASA Astrophysics Data System (ADS)

Ivanov-Schitz, A. K.; Mazo, G. N.

2018-01-01

The possibilities of describing correctly interfaces of different types in solids within a computer experiment using molecular statics simulation, molecular dynamics simulation, and quantum chemical calculations are discussed. Heterophase boundaries of various types, including grain boundaries and solid electrolyte‒solid electrolyte and ionic conductor‒electrode material interfaces, are considered. Specific microstructural features and mechanisms of the ion transport in real heterophase structures (cationic conductor‒metal anode and anionic conductor‒cathode) existing in solid state ionics devices (such as solid-state batteries and fuel cells) are discussed.

Stable aqueous based Cu nanoparticle ink for printing well-defined highly conductive features on a plastic substrate.

PubMed

Jeong, Sunho; Song, Hae Chun; Lee, Won Woo; Lee, Sun Sook; Choi, Youngmin; Son, Wonil; Kim, Eui Duk; Paik, Choon Hoon; Oh, Seok Heon; Ryu, Beyong-Hwan

2011-03-15

With the aim of inkjet printing highly conductive and well-defined Cu features on plastic substrates, aqueous based Cu ink is prepared for the first time using water-soluble Cu nanoparticles with a very thin surface oxide layer. Owing to the specific properties, high surface tension and low boiling point, of water, the aqueous based Cu ink endows a variety of advantages over conventional Cu inks based on organic solvents in printing narrow conductive patterns without irregular morphologies. It is demonstrated how the design of aqueous based ink affects the basic properties of printed conductive features such as surface morphology, microstructure, conductivity, and line width. The long-term stability of aqueous based Cu ink against oxidation is analyzed through an X-ray photoelectron spectroscopy (XPS) based investigation on the evolution of the surface oxide layer in the aqueous based ink.

Microstructure evolution of heat treated NiTi alloys

NASA Astrophysics Data System (ADS)

Losertová, M.; Štencek, M.; Matýsek, D.; Štefek, O.; Drápala, J.

2017-11-01

Superelastic behavior of off-stoichiometric NiTi alloys is significantly affected by microstructure changes due to heat treatment. Applying appropriate thermal treatments important effects on microstructural changes, transformation temperatures and thermomechanical properties of final NiTi products can be achieved. The experimental samples of NiTi alloy with 55.8 wt.% Ni were submitted to heat treatment and the microstructures before and after the treatment were observed. The thermal regimes consisted of annealing treatment at 600 °C for 1 hour followed by water quenching and of ageing at eight different temperatures (250, 270, 290, 300, 350, 400, 450 and 500 °C) for 30 minutes. Microstructure features studied by means of optical and scanning electron microscopies, EDX microanalyses, X-ray diffraction analyses and microhardness measurement, have shown that higher ageing temperatures led to microstructure changes and corresponding increase in microhardness.

Multi-scale invertigation of the relationship between the microstructure and mechanical properties in dual phase steels

NASA Astrophysics Data System (ADS)

Zhang, Fan

Dual phase steel alloys belong to the first generation of advanced high strength steels that are widely used in the automotive industry to form body structure and closure panels of vehicles. A deeper understanding of the microstructural features, such as phase orientation and morphology are needed in order to establish their effect on the mechanical performance and to design a material with optimized attributes. In this work, our goal is to establish what kind of relationship exist between the mechanical properties and the microstructural representation of dual phase steels obtained from experimental observations. Microstructure in different specimens are characterized with advanced experimental techniques as optical microscopy, scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction pattern, scanning probe microscopy, and nanoindentation. Nanoindentation, Vickers hardness and tensile testing are conducted to reveal a multi-scale mechanical performance on original material and also specimens under a variety combinations of temperatures, cooling rates, and rolling conditions. To quantify the single phase properties in each sample, an inverse method is adopted using experimental nanoindentation load-depth curves to obtain tensile stress-strain curves for each phase, and the inverse results were verified with the true stress-strain curves from tensile tests. This work also provides the insight on spatial phase distribution of different phases through a 2-point correlation statistical methodology and relate to material strength and formability. The microstructure information is correlated with the results of mechanical tests. The broken surfaces from tensile testing are analyzed to discover the fracture mechanism in relation to martensite morphology and distribuion. Viscoplastic self-consistent fast Fourier Transformation simulations is also used to compute efficiently the local and the homogenized viscoplastic response of the polycrystalline microstructure. The specific objectives of this work are 1) the development of etching techniques and electron backscatter diffraction strategies to characterize ferrite and martensite phases in steel; 2) the uncovering of a relationship between strength/ductility and material microstructure, 3) a statistical description to quantify the spatial distributions of these phases; and finally 4) the simulation of the microstructural evolution using parameters obtained from the experiments.

Investigations on the Mechanical Properties of Conducting Polymer Coating-Substrate Structures and Their Influencing Factors

PubMed Central

Wang, Xi-Shu; Tang, Hua-Ping; Li, Xu-Dong; Hua, Xin

2009-01-01

This review covers recent advances and work on the microstructure features, mechanical properties and cracking processes of conducting polymer film/coating- substrate structures under different testing conditions. An attempt is made to characterize and quantify the relationships between mechanical properties and microstructure features. In addition, the film cracking mechanism on the micro scale and some influencing factors that play a significant role in the service of the film-substrate structure are presented. These investigations cover the conducting polymer film/coating nucleation process, microstructure-fracture characterization, translation of brittle-ductile fractures, and cracking processes near the largest inherent macromolecule defects under thermal-mechanical loadings, and were carried out using in situ scanning electron microscopy (SEM) observations, as a novel method for evaluation of interface strength and critical failure stress. PMID:20054470

Step-by-step growth of complex oxide microstructures

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

Datskos, Panos G.; Cullen, David A.; Sharma, Jaswinder K.

The synthesis of complex and hybrid oxide microstructures is of fundamental interest and practical applications. However, the design and synthesis of such structures is a challenging task. A solution-phase process to synthesize complex silica and silica-titania hybrid microstructures was developed by exploiting the emulsion-droplet-based step-by-step growth featuring shape control. Lastly, the strategy is robust and can be extended to the preparation of complex hybrid structures consisting of two or more materials, with each having its own shape.

Step-by-step growth of complex oxide microstructures

DOE PAGES

Datskos, Panos G.; Cullen, David A.; Sharma, Jaswinder K.

2015-06-10

The synthesis of complex and hybrid oxide microstructures is of fundamental interest and practical applications. However, the design and synthesis of such structures is a challenging task. A solution-phase process to synthesize complex silica and silica-titania hybrid microstructures was developed by exploiting the emulsion-droplet-based step-by-step growth featuring shape control. Lastly, the strategy is robust and can be extended to the preparation of complex hybrid structures consisting of two or more materials, with each having its own shape.

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.

3D Microstructures for Materials and Damage Models

DOE PAGES

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

2017-02-01

Many challenges exist with regard to understanding and representing complex physical processes involved with ductile damage and failure in polycrystalline metallic materials. Currently, the ability to accurately predict the macroscale ductile damage and failure response of metallic materials is lacking. Research at Los Alamos National Laboratory (LANL) is aimed at building a coupled experimental and computational methodology that supports the development of predictive damage capabilities by: capturing real distributions of microstructural features from real material and implementing them as digitally generated microstructures in damage model development; and, distilling structure-property information to link microstructural details to damage evolution under a multitudemore » of loading states.« less

Quantifying the effect of 3D spatial resolution on the accuracy of microstructural distributions

NASA Astrophysics Data System (ADS)

Loughnane, Gregory; Groeber, Michael; Uchic, Michael; Riley, Matthew; Shah, Megna; Srinivasan, Raghavan; Grandhi, Ramana

The choice of spatial resolution for experimentally-collected 3D microstructural data is often governed by general rules of thumb. For example, serial section experiments often strive to collect at least ten sections through the average feature-of-interest. However, the desire to collect high resolution data in 3D is greatly tempered by the exponential growth in collection times and data storage requirements. This paper explores the use of systematic down-sampling of synthetically-generated grain microstructures to examine the effect of resolution on the calculated distributions of microstructural descriptors such as grain size, number of nearest neighbors, aspect ratio, and Ω3.

Morphology and microstructure of composite materials

NASA Technical Reports Server (NTRS)

Tiwari, S. N.; Srinivansan, K.

1991-01-01

Lightweight continuous carbon fiber based polymeric composites are currently enjoying increasing acceptance as structural materials capable of replacing metals and alloys in load bearing applications. As with most new materials, these composites are undergoing trials with several competing processing techniques aimed at cost effectively producing void free consolidations with good mechanical properties. As metallic materials have been in use for several centuries, a considerable database exists on their morphology - microstructure; and the interrelationships between structure and properties have been well documented. Numerous studies on composites have established the crucial relationship between microstructure - morphology and properties. The various microstructural and morphological features of composite materials, particularly those accompanying different processing routes, are documented.

The effect orientation of features in reconstructed atom probe data on the resolution and measured composition of T1 plates in an A2198 aluminium alloy.

PubMed

Mullin, Maria A; Araullo-Peters, Vicente J; Gault, Baptiste; Cairney, Julie M

2015-12-01

Artefacts in atom probe tomography can impact the compositional analysis of microstructure in atom probe studies. To determine the integrity of information obtained, it is essential to understand how the positioning of features influences compositional analysis. By investigating the influence of feature orientation within atom probe data on measured composition in microstructural features within an AA2198 Al alloy, this study shows differences in the composition of T1 (Al2CuLi) plates that indicates imperfections in atom probe reconstructions. The data fits a model of an exponentially-modified Gaussian that scales with the difference in evaporation field between solutes and matrix. This information provides a guide for obtaining the most accurate information possible. Copyright © 2015 Elsevier B.V. All rights reserved.

Method to control artifacts of microstructural fabrication

DOEpatents

Shul, Randy J.; Willison, Christi G.; Schubert, W. Kent; Manginell, Ronald P.; Mitchell, Mary-Anne; Galambos, Paul C.

2006-09-12

New methods for fabrication of silicon microstructures have been developed. In these methods, an etching delay layer is deposited and patterned so as to provide differential control on the depth of features being etched into a substrate material. Compensation for etching-related structural artifacts can be accomplished by proper use of such an etching delay layer.

Representation of microstructural features and magnetic anisotropy of electrical steels in an energy-based vector hysteresis model

NASA Astrophysics Data System (ADS)

Jacques, Kevin; Steentjes, Simon; Henrotte, François; Geuzaine, Christophe; Hameyer, Kay

2018-04-01

This paper demonstrates how the statistical distribution of pinning fields in a ferromagnetic material can be identified systematically from standard magnetic measurements, Epstein frame or Single Sheet Tester (SST). The correlation between the pinning field distribution and microstructural parameters of the material is then analyzed.

Prediction of Continuous Cooling Transformation Diagrams for Dual-Phase Steels from the Intercritical Region

NASA Astrophysics Data System (ADS)

Colla, V.; Desanctis, M.; Dimatteo, A.; Lovicu, G.; Valentini, R.

2011-09-01

The purpose of the present work is the implementation and validation of a model able to predict the microstructure changes and the mechanical properties in the modern high-strength dual-phase steels after the continuous annealing process line (CAPL) and galvanizing (Galv) process. Experimental continuous cooling transformation (CCT) diagrams for 13 differently alloying dual-phase steels were measured by dilatometry from the intercritical range and were used to tune the parameters of the microstructural prediction module of the model. Mechanical properties and microstructural features were measured for more than 400 dual-phase steels simulating the CAPL and Galv industrial process, and the results were used to construct the mechanical model that predicts mechanical properties from microstructural features, chemistry, and process parameters. The model was validated and proved its efficiency in reproducing the transformation kinetic and mechanical properties of dual-phase steels produced by typical industrial process. Although it is limited to the dual-phase grades and chemical compositions explored, this model will constitute a useful tool for the steel industry.

Quantitatively differentiating microstructural variations of skeletal muscle tissues by multispectral Mueller matrix imaging

NASA Astrophysics Data System (ADS)

Dong, Yang; He, Honghui; He, Chao; Ma, Hui

2016-10-01

Polarized light is sensitive to the microstructures of biological tissues and can be used to detect physiological changes. Meanwhile, spectral features of the scattered light can also provide abundant microstructural information of tissues. In this paper, we take the backscattering polarization Mueller matrix images of bovine skeletal muscle tissues during the 24-hour experimental time, and analyze their multispectral behavior using quantitative Mueller matrix parameters. In the processes of rigor mortis and proteolysis of muscle samples, multispectral frequency distribution histograms (FDHs) of the Mueller matrix elements can reveal rich qualitative structural information. In addition, we analyze the temporal variations of the sample using the multispectral Mueller matrix transformation (MMT) parameters. The experimental results indicate that the different stages of rigor mortis and proteolysis for bovine skeletal muscle samples can be judged by these MMT parameters. The results presented in this work show that combining with the multispectral technique, the FDHs and MMT parameters can characterize the microstructural variation features of skeletal muscle tissues. The techniques have the potential to be used as tools for quantitative assessment of meat qualities in food industry.

Sulfur Impurities and the Microstructure of Alumina Scales

NASA Technical Reports Server (NTRS)

Smialek, James L.

1997-01-01

The relationship between the microstructure of alumina scales, adhesion, and sulfur content was examined through a series of nickel alloys oxidized in 1100 to 1200 deg. C cyclic or isothermal exposures in air. In cyclic tests of undoped NiCrAl, adhesion was produced when the sulfur content was reduced, without any change in scale microstructure. Although interfacial voids were not observed in cyclic tests of NiCrAl, they were promoted by long-term isothermal exposures, by sulfur doping, and in most exposures of NiAl. Two single crystal superalloys, PWA 1480 and Rene' N5, were also tested, either in the as-received condition or after the sulfur content had been reduced to less than 1 ppmw by hydrogen annealing. The unannealed alloys always exhibited spalling to bare metal, but interfacial voids were not observed consistently. Desulfurized PWA 1480 and Rene' N5 exhibited remarkable adhesion and no voidage for either isothermal or cyclic exposures. The most consistent microstructural feature was that, for the cases where voids did form, the scale undersides exhibited corresponding areas with ridged oxide grain boundaries. Voids were not required for spallation nor were other microstructural features essential for adhesion. These observations are consistent with the model whereby scale spallation is controlled primarily by interfacial sulfur segregation and the consequent degradation of oxide-metal bonding.

Night sleep influences white matter microstructure in bipolar depression.

PubMed

Benedetti, Francesco; Melloni, Elisa M T; Dallaspezia, Sara; Bollettini, Irene; Locatelli, Clara; Poletti, Sara; Colombo, Cristina

2017-08-15

Alteration of circadian rhythms and sleep disruption are prominent trait-like features of bipolar disorder (BD). Diffusion tensor imaging (DTI) measures suggest a widespread alteration of white matter (WM) microstructure in patients with BD. Sleep promotes myelination and oligodendrocyte precursor cells proliferation. We hypothesized a possible association between DTI measures of WM microstructure and sleep quantity measures in BD. We studied 69 inpatients affected by a depressive episode in course of type I BD. We used whole brain tract-based spatial statistics on DTI measures of WM microstructure: axial, radial, and mean diffusivity (AD, RD, MD), and fractional anisotropy (FA). Self-assessed measures of time asleep (TA) and total sleep time (TST) were extracted from the Pittsburgh Sleep Quality Index (PSQI). Actigraphic recordings were performed on a subsample of 23 patients. We observed a positive correlation of DTI measures of FA with actigraphic measures of TA and TST, and with PSQI measure of TA. DTI measures of RD inversely associated with actigraphic measure of TA, and with PSQI measures of TA and TST. Several WM tracts were involved, including corpus callosum, cyngulate gyrus, uncinate fasciculus, left superior and inferior longitudinal and fronto-occipital fasciculi, thalamic radiation, corona radiata, retrolenticular part of internal capsule and corticospinal tract. The study is correlational in nature, and no conclusion about a causal connection can be drawn. Reduced FA with increased RD and MD indicate higher water diffusivity associated with less organized myelin and/or axonal structures. Our findings suggest an association between sleep disruption and these measures of brain microstructure in specific tracts contributing to the functional connectivity in BD. Copyright © 2017 Elsevier B.V. All rights reserved.

Evolution and Control of 2219 Aluminum Microstructural Features through Electron Beam Freeform Fabrication

NASA Technical Reports Server (NTRS)

Taminger, Karen M.; Hafley, Robert A.; Domack, Marcia S.

2006-01-01

Electron beam freeform fabrication (EBF3) is a new layer-additive process that has been developed for near-net shape fabrication of complex structures. EBF3 uses an electron beam to create a molten pool on the surface of a substrate. Wire is fed into the molten pool and the part translated with respect to the beam to build up a 3-dimensional structure one layer at a time. Unlike many other freeform fabrication processes, the energy coupling of the electron beam is extremely well suited to processing of aluminum alloys. The layer-additive nature of the EBF3 process results in a tortuous thermal path producing complex microstructures including: small homogeneous equiaxed grains; dendritic growth contained within larger grains; and/or pervasive dendritic formation in the interpass regions of the deposits. Several process control variables contribute to the formation of these different microstructures, including translation speed, wire feed rate, beam current and accelerating voltage. In electron beam processing, higher accelerating voltages embed the energy deeper below the surface of the substrate. Two EBF3 systems have been established at NASA Langley, one with a low-voltage (10-30kV) and the other a high-voltage (30-60 kV) electron beam gun. Aluminum alloy 2219 was processed over a range of different variables to explore the design space and correlate the resultant microstructures with the processing parameters. This report is specifically exploring the impact of accelerating voltage. Of particular interest is correlating energy to the resultant material characteristics to determine the potential of achieving microstructural control through precise management of the heat flux and cooling rates during deposition.

Microstructural and mineral analysis on the fault gouge in the coseismic shear zone of the 2008 M w 7.9 Wenchuan earthquake

NASA Astrophysics Data System (ADS)

Yuan, Ren-mao; Zhang, Bing-liang; Xu, Xi-wei; Lin, Chuan-yong; Han, Zhu-jun

2015-07-01

The 2008 M w 7.9 Wenchuan earthquake formed two coseismic surface rupture zones with the trend of N35°E, known as the Beichuan-Yingxiu rupture and the Pengguan rupture. The Beichuan-Yingxiu rupture is the principle one with abundant fault gouge development along its length. In the exploratory trench at the Saba village along the Beichuan-Yingxiu rupture, the new fault gouge zone is only ~3 mm wide, which suggests that fault slip was constrained in a very narrow zone. In this study, we thus carried out detailed microstructural and mineral component analysis on the oriented fault gouge samples from the Saba exploratory trench to understand their features and geological implication. The results show that different microstructures of localized brittle deformation can be observed in the fault gouges, including Y-shear, R1-shear, R2-shear, P-shear as well as tension fracture, bookshelf glided structure and so on. These microstructures are commonly recognized as the product of seismic fault slipping. Furthermore, within the area between two parallel Y-shears of the fault gouge, a few of microstructures of distributed ductile deformations were developed, such as P-foliation, elongation and asymmetrical trailing structure of detrital particles. The microstructure features of fault gouges implicate the thrust movement of the fault during the Wenchuan earthquake. In addition, the fault gouge has less quartz and feldspar and more clay than the surrounding rocks, which indicates that some quartz and feldspar in the surrounding rocks were transformed into clay, whereas the fault gouge has more illite and less illite/montmorillonite mixed layers than the surrounding rocks, which shows that the illite/montmorillonite mixed layer was partly converted into illite due to temperature increasing induced by coseismic fault slipping friction (also being affected partly by the chemical action of solutions). Such microstructures features and mineral component changes recorded the information of fault slip and provide criterions for discussing the genesis of fault gouge and recognition of the direction of fault movement.

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.

Development of high-temperature Kolsky compression bar techniques for recrystallization investigation

NASA Astrophysics Data System (ADS)

Song, B.; Antoun, B. R.; Boston, M.

2012-05-01

We modified the design originally developed by Kuokkala's group to develop an automated high-temperature Kolsky compression bar for characterizing high-rate properties of 304L stainless steel at elevated temperatures. Additional features have been implemented to this high-temperature Kolsky compression bar for recrystallization investigation. The new features ensure a single loading on the specimen and precise time and temperature control for quenching to the specimen after dynamic loading. Dynamic compressive stress-strain curves of 304L stainless steel were obtained at 21, 204, 427, 649, and 871 °C (or 70, 400, 800, 1200, and 1600 °F) at the same constant strain rate of 332 s-1. The specimen subjected to specific time and temperature control for quenching after a single dynamic loading was preserved for investigating microstructure recrystallization.

Microstructural development during solidification of stainless steel alloys

NASA Astrophysics Data System (ADS)

Elmer, J. W.; Allen, S. M.; Eagar, T. W.

1989-10-01

The microstructures that develop during the solidification of stainless steel alloys are related to the solidification conditions and the specific alloy composition. The solidification conditions are determined by the processing method, i.e., casting, welding, or rapid solidification, and by parametric variations within each of these techniques. One variable that has been used to characterize the effects of different processing conditions is the cooling rate. This factor and the chemical composition of the alloy both influence (1) the primary mode of solidification, (2) solute redistribution and second-phase formation during solidification, and (3) the nucleation and growth behavior of the ferrite-to-austenite phase transformation during cooling. Consequently, the residual ferrite content and the microstructural morphology depend on the cooling rate and are governed by the solidification process. This paper investigates the influence of cooling rate on the microstructure of stainless steel alloys and describes the conditions that lead to the many microstructural morphologies that develop during solidification. Experiments were performed on a series of seven high-purity Fe-Ni-Cr alloys that spanned the line of twofold saturation along the 59 wt pct Fe isopleth of the ternary alloy system. High-speed electron-beam surface-glazing was used to melt and resolidify these alloys at scan speeds up to 5 m/s. The resulting cooling rates were shown to vary from 7°C/s to 7.5×106°C/s, and the resolidified melts were analyzed by optical metallographic methods. Five primary modes of solidification and 12 microstructural morphologies were characterized in the resolidified alloys, and these features appear to be a complete “set” of the possible microstructures for 300-series stainless steel alloys. The results of this study were used to create electron-beam scan speed vs composition diagrams, which can be used to predict the primary mode of solidification and the microstructural morphology for different processing conditions. Furthermore, changes in the primary solidification mode were observed in alloys that lie on the chromium-rich side of the line of twofold saturation when they are cooled at high rates. These changes were explained by the presence of metastable austenite, which grows epitaxially and can dominate the solidification microstructure throughout the resolidified zone at high cooling rates.

Laser-induced patterns on metals and polymers for biomimetic surface engineering

NASA Astrophysics Data System (ADS)

Kietzig, Anne-Marie; Lehr, Jorge; Matus, Luke; Liang, Fang

2014-03-01

One common feature of many functional surfaces found in nature is their modular composition often exhibiting several length scales. Prominent natural examples for extreme behaviors can be named in various plant leaf (rose, peanut, lotus) or animal toe surfaces (Gecko, tree frog). Influence factors of interest are the surface's chemical composition, its microstructure, its organized or random roughness and hence the resulting surface wetting and adhesion character. Femtosecond (fs) laser micromachining offers a possibility to render all these factors in one single processing step on metallic and polymeric surfaces. Exemplarily, studies on Titanium and PTFE are shown, where the dependence of the resulting feature sizes on lasing intensity is investigated. While Ti surfaces show rigid surface patterns of micrometer scaled features with superimposed nanostructures, PTFE exhibits elastic hairy structures of nanometric diameter, which upon a certain threshold tend to bundle to larger features. Both surface patterns can be adjusted to mimic specific wetting and flow behaviour as seen on natural examples. Therefore, fs-laser micromachining is suggested as an interesting industrially scalable technique to pattern and fine-tune the surface wettability of a surface to the desired extends in one process step. Possible applications can be seen with surfaces, which require specific wetting, fouling, icing, friction or cell adhesion behaviour.

Understanding the Interdependencies Between Composition, Microstructure, and Continuum Variables and Their Influence on the Fracture Toughness of α/β-Processed Ti-6Al-4V

NASA Astrophysics Data System (ADS)

Collins, P. C.; Koduri, S.; Dixit, V.; Fraser, H. L.

2018-03-01

The fracture toughness of a material depends upon the material's composition and microstructure, as well as other material properties operating at the continuum level. The interrelationships between these variables are complex, and thus difficult to interpret, especially in multi-component, multi-phase ductile engineering alloys such as α/β-processed Ti-6Al-4V (nominal composition, wt pct). Neural networks have been used to elucidate how variables such as composition and microstructure influence the fracture toughness directly ( i.e., via a crack initiation or propagation mechanism)—and independent of the influence of the same variables influence on the yield strength and plasticity of the material. The variables included in the models and analysis include (i) alloy composition, specifically, Al, V, O, and Fe; (ii) materials microstructure, including phase fractions and average sizes of key microstructural features; (iii) the yield strength and reduction in area obtained from uniaxial tensile tests; and (iv) an assessment of the degree to which plane strain conditions were satisfied by including a factor related to the plane strain thickness. Once trained, virtual experiments have been conducted which permit the determination of each variable's functional dependency on the resulting fracture toughness. Given that the database includes both K 1 C and K Q values, as well as the in-plane component of the stress state of the crack tip, it is possible to quantitatively assess the effect of sample thickness on K Q and the degree to which the K Q and K 1 C values may vary. These interpretations drawn by comparing multiple neural networks have a significant impact on the general understanding of how the microstructure influences the fracture toughness in ductile materials, as well as an ability to predict the fracture toughness of α/β-processed Ti-6Al-4V.

Textural analysis of optical coherence tomography skin images: quantitative differentiation between healthy and cancerous tissues

NASA Astrophysics Data System (ADS)

Adabi, Saba; Conforto, Silvia; Hosseinzadeh, Matin; Noe, Shahryar; Daveluy, Steven; Mehregan, Darius; Nasiriavanaki, Mohammadreza

2017-02-01

Optical Coherence Tomography (OCT) offers real-time high-resolution three-dimensional images of tissue microstructures. In this study, we used OCT skin images acquired from ten volunteers, neither of whom had any skin conditions addressing the features of their anatomic location. OCT segmented images are analyzed based on their optical properties (attenuation coefficient) and textural image features e.g., contrast, correlation, homogeneity, energy, entropy, etc. Utilizing the information and referring to their clinical insight, we aim to make a comprehensive computational model for the healthy skin. The derived parameters represent the OCT microstructural morphology and might provide biological information for generating an atlas of normal skin from different anatomic sites of human skin and may allow for identification of cell microstructural changes in cancer patients. We then compared the parameters of healthy samples with those of abnormal skin and classified them using a linear Support Vector Machines (SVM) with 82% accuracy.

Modeling of Casting Defects in an Integrated Computational Materials Engineering Approach

NASA Astrophysics Data System (ADS)

Sabau, Adrian S.

To accelerate the introduction of new cast alloys the modeling and simulation of multiphysical phenomena needs to be considered in the design and optimization of mechanical properties of cast components. The required models related to casting defects, such as microporosity and hot tears are reviewed. Three aluminum alloys are considered A356, 356 and 319. The data on calculated solidification shrinkage is presented and its effects on microporosity levels discussed. Examples are given for predicting microporosity defects and microstructure distribution for a plate casting. Models to predict fatigue life and yield stress are briefly highlighted here for the sake of completion and to illustrate how the length scales of the microstructure features as well as porosity defects are taken into account for modeling the mechanical properties. The data on casting defects including microstructure features, is crucial for evaluating the final performance-related properties of the component.

Analysis of Radiation Damage in Light Water Reactors: Comparison of Cluster Analysis Methods for the Analysis of Atom Probe Data.

PubMed

Hyde, Jonathan M; DaCosta, Gérald; Hatzoglou, Constantinos; Weekes, Hannah; Radiguet, Bertrand; Styman, Paul D; Vurpillot, Francois; Pareige, Cristelle; Etienne, Auriane; Bonny, Giovanni; Castin, Nicolas; Malerba, Lorenzo; Pareige, Philippe

2017-04-01

Irradiation of reactor pressure vessel (RPV) steels causes the formation of nanoscale microstructural features (termed radiation damage), which affect the mechanical properties of the vessel. A key tool for characterizing these nanoscale features is atom probe tomography (APT), due to its high spatial resolution and the ability to identify different chemical species in three dimensions. Microstructural observations using APT can underpin development of a mechanistic understanding of defect formation. However, with atom probe analyses there are currently multiple methods for analyzing the data. This can result in inconsistencies between results obtained from different researchers and unnecessary scatter when combining data from multiple sources. This makes interpretation of results more complex and calibration of radiation damage models challenging. In this work simulations of a range of different microstructures are used to directly compare different cluster analysis algorithms and identify their strengths and weaknesses.

Comprehensive study of the abrasive wear and slurry erosion behavior of an expanded system of high chromium cast iron and microstructural modification for enhanced wear resistance

NASA Astrophysics Data System (ADS)

Chung, Reinaldo Javier

High chromium cast irons (HCCIs) have been demonstrated to be an effective material for a wide range of applications in aggressive environments, where resistances to abrasion, erosion and erosion-corrosion are required. For instance, machinery and facilities used in mining and extraction in Alberta's oil sands suffer from erosion and erosion-corrosion caused by silica-containing slurries, which create challenges for the reliability and maintenance of slurry pumping systems as well as other processing and handling equipment. Considerable efforts have been made to determine and understand the relationship between microstructural features of the HCCIs and their wear performance, in order to guide the material selection and development for specific service conditions with optimal performance. The focus was previously put on a narrow group of compositions dictated by ASTM A532. However, with recent advances in casting technology, the HCCI compositional range can be significantly expanded, which potentially brings new alloys that can be superior to those which are currently employed. This work consists of three main aspects of study. The first one is the investigation of an expanded system of white irons with their composition ranging from 1 to 6 wt.% C and 5 to 45 wt.% Cr, covering 53 alloys. This work has generated wear and corrosion maps and established correlation between the performance and microstructural features for the alloys. The work was conducted in collaboration with the Materials Development Center of Weir Minerals in Australia, and the results have been collected in a database that is used by the company to guide materials selection for slurry pump components in Alberta oil sands and in other mining operations throughout the world. The second part consists of three case studies on effects of high chromium and high carbon, respectively, on the performance of the HCCIs. The third aspect is the development of an approach to enhance the wear resistance of HCCIs by microstructural modification through addition of strong carbide-forming elements to produce eutectic microstructures reinforced with in-situ formed foreign carbides. Very promising results have been obtained in lab, which demonstrates that the approach is feasible and effective in tailoring HCCIs for improved performance.

The effect of strain rate on the evolution of microstructure in aluminium alloys.

PubMed

Leszczyńska-Madej, B; Richert, M

2010-03-01

Intensive deformations influence strongly microstructure. The very well-known phenomenon is the diminishing dimension of grain size by the severe plastic deformation (SPD) methods. The nanometric features of microstructure were discovered after the SPD deformation of various materials, such as aluminium alloys, iron and others. The observed changes depended on the kind of the deformed material, amount of deformation, strain rate, existence of different phases and stacking fault energy. The influence of the strain and strain rate on the microstructure is commonly investigated nowadays. It was found that the high strain rates activate deformation in shear bands, microbands and adiabatic shear bands. It was observed that bands were places of the nucleation of nanograins in the material deformed by SPD methods. In the work, the refinement of microstructure of the aluminium alloys influenced by the high strain rate was investigated. The samples were compressed by a specially designed hammer to the deformation of phi= 0/0.62 with the strain rate in the range of [Formula in text]. The highest reduction of microbands width with the increase of the strain was found in the AlCu4Zr alloy. The influence of the strain rate on the microstructure refinement indicated that the increase of the strain rate caused the reduction of the microbands width in the all investigated materials (Al99.5, AlCu4Zr, AlMg5, AlZn6Mg2.5CuZr). A characteristic feature of the microstructure of the compressed material was large density of the shear bands and microbands. It was found that the microbands show a large misorientation to the surrounds and, except Al99.5, the large density of dislocation.

Modeling of Microstructure Evolution During Alloy Solidification

NASA Astrophysics Data System (ADS)

Zhu, Mingfang; Pan, Shiyan; Sun, Dongke

In recent years, considerable advances have been achieved in the numerical modeling of microstructure evolution during solidification. This paper presents the models based on the cellular automaton (CA) technique and lattice Boltzmann method (LBM), which can reproduce a wide variety of solidification microstructure features observed experimentally with an acceptable computational efficiency. The capabilities of the models are addressed by presenting representative examples encompassing a broad variety of issues, such as the evolution of dendritic structure and microsegregation in two and three dimensions, dendritic growth in the presence of convection, divorced eutectic solidification of spheroidal graphite irons, and gas porosity formation. The simulations offer insights into the underlying physics of microstructure formation during alloy solidification.

Tubular inverse opal scaffolds for biomimetic vessels.

PubMed

Zhao, Ze; Wang, Jie; Lu, Jie; Yu, Yunru; Fu, Fanfan; Wang, Huan; Liu, Yuxiao; Zhao, Yuanjin; Gu, Zhongze

2016-07-14

There is a clinical need for tissue-engineered blood vessels that can be used to replace or bypass damaged arteries. The success of such grafts depends strongly on their ability to mimic native arteries; however, currently available artificial vessels are restricted by their complex processing, controversial integrity, or uncontrollable cell location and orientation. Here, we present new tubular scaffolds with specific surface microstructures for structural vessel mimicry. The tubular scaffolds are fabricated by rotationally expanding three-dimensional tubular inverse opals that are replicated from colloidal crystal templates in capillaries. Because of the ordered porous structure of the inverse opals, the expanded tubular scaffolds are imparted with circumferentially oriented elliptical pattern microstructures on their surfaces. It is demonstrated that these tailored tubular scaffolds can effectively make endothelial cells to form an integrated hollow tubular structure on their inner surface and induce smooth muscle cells to form a circumferential orientation on their outer surface. These features of our tubular scaffolds make them highly promising for the construction of biomimetic blood vessels.

Effect of the calcium to phosphorus ratio on the setting properties of calcium phosphate bone cements.

PubMed

Vlad, M D; Gómez, S; Barracó, M; López, J; Fernández, E

2012-09-01

α-Tricalcium phosphate (α-TCP) has become the main reactant of most experimental and commercial ceramic bone cements. It has calcium-to-phosphorus (Ca/P) ratio of 1.50. The present study expands and reports on the microstructures and mechanical properties of calcium phosphate (CP) cements containing sintered monolithic reactants obtained in the interval 1.29 < Ca/P < 1.77. The study focuses on their cement setting and hardening properties as well as on their microstructure and crystal phase evolution. The results showed that: (a) CP-cements made with reactants with Ca/P ratio other than 1.50 have longer setting and lower hardening properties; (b) CP-cements reactivity was clearly affected by the Ca/P ratio of the starting reactant; (c) reactants with Ca/P < 1.50 were composed of several phases, calcium pyrophosphate and α- and β-TCP. Similarly, reactants with Ca/P > 1.50 were composed of α-TCP, tetracalcium phosphate and hydroxyapatite; (d) only the reactant with Ca/P = 1.50 was monophasic and was made of α-TCP, which transformed during the setting into calcium deficient hydroxyapatite; (e) CP-cements developed different crystal microstructures with specific features depending on the Ca/P ratio of the starting reactant.

Brain white matter changes associated with urological chronic pelvic pain syndrome: multisite neuroimaging from a MAPP case-control study.

PubMed

Huang, Lejian; Kutch, Jason J; Ellingson, Benjamin M; Martucci, Katherine T; Harris, Richard E; Clauw, Daniel J; Mackey, Sean; Mayer, Emeran A; Schaeffer, Anthony J; Apkarian, A Vania; Farmer, Melissa A

2016-12-01

Clinical phenotyping of urological chronic pelvic pain syndromes (UCPPSs) in men and women have focused on end organ abnormalities to identify putative clinical subtypes. Initial evidence of abnormal brain function and structure in male pelvic pain has necessitated large-scale, multisite investigations into potential UCPPS brain biomarkers. We present the first evidence of regional white matter (axonal) abnormalities in men and women with UCPPS, compared with positive (irritable bowel syndrome, IBS) and healthy controls. Epidemiological and neuroimaging data were collected from participants with UCPPS (n = 52), IBS (n = 39), and healthy sex- and age-matched controls (n = 61). White matter microstructure, measured as fractional anisotropy (FA), was examined by diffusion tensor imaging. Group differences in regional FA positively correlated with pain severity, including segments of the right corticospinal tract and right anterior thalamic radiation. Increased corticospinal FA was specific and sensitive to UCPPS, positively correlated with pain severity, and reflected sensory (not affective) features of pain. Reduced anterior thalamic radiation FA distinguished patients with IBS from those with UCPPS and controls, suggesting greater microstructural divergence from normal tract organization. Findings confirm that regional white matter abnormalities characterize UCPPS and can distinguish between visceral diagnoses, suggesting that regional axonal microstructure is either altered with ongoing pain or predisposes its development.

Combination of experimental and numerical methods for mechanical characterization of Al-Si alloys

NASA Astrophysics Data System (ADS)

Kruglova, A.; Roland, M.; Diebels, S.; Mücklich, F.

2017-10-01

In general, mechanical properties of Al-Si alloys strongly depend on the morphology and arrangement of microconstituents, such as primary aluminium dendrites, silicon particles, etc. Therefore, a detailed characterization of morphological and mechanical properties of the alloys is necessary to better understand the relations between the underlined properties and to tailor the material’s microstructure to the specific application needs. The mechanical characterization usually implies numerical simulations and mechanical tests, which allow to investigate the influence of different microstructural aspects on different scales. In this study, the uniaxial tension and compression tests have been carried out on Al-Si alloys having different microstructures. The mechanical behavior of the alloys has been interpreted with respect to the morphology of the microconstituents and has been correlated with the results of numerical simulations. The advantages and limitations of the experimental and numerical methods have been disclosed and the importance of combining both techniques for the interpretation of the mechanical behavior of Al-Si alloys has been shown. Thereby, it has been suggested that the density of Si particles and the size of Al dendrites are more important for the strengthening of the alloys than the size-shape features of the eutectic Si induced by the modification.

Brain white matter changes associated with urological chronic pelvic pain syndrome: Multi-site neuroimaging from a MAPP case-control study

PubMed Central

Huang, Lejian; Kutch, Jason J.; Ellingson, Benjamin M.; Martucci, Katherine T.; Harris, Richard E.; Clauw, Daniel J.; Mackey, Sean; Mayer, Emeran A.; Schaeffer, Anthony J.; Apkarian, A. Vania; Farmer, Melissa A.

2016-01-01

Clinical phenotyping of urological chronic pelvic pain syndromes (UCPPS) in men and women has focused on end-organ abnormalities to identify putative clinical subtypes. Initial evidence of abnormal brain function and structure in male pelvic pain has necessitated large-scale, multi-site investigations into potential UCPPS brain biomarkers. We present the first evidence of regional white matter (axonal) abnormalities in men and women with UCPPS, compared to positive (irritable bowel syndrome, IBS) and healthy controls. Epidemiological and neuroimaging data was collected from participants with UCPPS (n=52), IBS (n=39), and healthy, sex- and age-matched controls (n=61). White matter microstructure, measured as fractional anisotropy (FA), was examined with diffusion tensor imaging (DTI). Group differences in regional FA positively correlated with pain severity, including segments of the right corticospinal tract and right anterior thalamic radiation. Increased corticospinal FA was specific and sensitive to UCPPS, positively correlated with pain severity, and reflected sensory (not affective) features of pain. Reduced anterior thalamic radiation FA distinguished IBS from UCPPS patients and controls, suggesting greater microstructural divergence from normal tract organization. Findings confirm that regional white matter abnormalities characterize UCPPS and can distinguish between visceral diagnoses, suggesting that regional axonal microstructure is either altered with ongoing pain or predisposes its development. PMID:27842046

Hierarchical microstructures in CZT

NASA Astrophysics Data System (ADS)

Sundaram, S. K.; Henager, C. H.; Edwards, D. J.; Schemer-Kohrn, A. L.; Bliss, M.; Riley, B. R.; Toloczko, M. B.; Lynn, K. G.

2011-10-01

Advanced characterization tools, such as electron backscatter diffraction and transmitted IR microscopy, are being applied to study critical microstructural features and orientation relations in as-grown CZT crystals to aid in understanding the relation between structure and properties in radiation detectors. Even carefully prepared single crystals of CZT contain regions of slight misorientation, Te-particles, and dislocation networks that must be understood for more accurate models of detector response. This paper describes initial research at PNNL into the hierarchy of microstructures observed in CZT grown via the vertical gradient freeze or vertical Bridgman method at PNNL and WSU.

Biaxial flexural strength and microstructure changes of two recycled pressable glass ceramics.

PubMed

Albakry, Mohammad; Guazzato, Massimiliano; Swain, Michael Vincent

2004-09-01

This study evaluated the biaxial flexural strength and identified the crystalline phases and the microstructural features of pressed and repressed materials of the glass ceramics, Empress 1 and Empress 2. Twenty pressed and 20 repressed disc specimens measuring 14 mm x 1 mm per material were prepared following the manufacturers' recommendations. Biaxial flexure (piston on 3-ball method) was used to assess strength. X-ray diffraction was performed to identify the crystalline phases, and a scanning electron microscope was used to disclose microstructural features. Biaxial flexural strength, for the pressed and repressed specimens, respectively, were E1 [148 (SD 18) and 149 (SD 35)] and E2 [340 (SD 40), 325 (SD 60)] MPa. There was no significant difference in strength between the pressed and the repressed groups of either material, Empress 1 and Empress 2 (p > 0.05). Weibull modulus values results were E1: (8, 4.7) and E2: (9, 5.8) for the same groups, respectively. X-ray diffraction revealed that leucite was the main crystalline phase for Empress 1 groups, and lithium disilicate for Empress 2 groups. No further peaks were observed in the X-ray diffraction patterns of either material after repressing. Dispersed leucite crystals and cracks within the leucite crystals and glass matrix were features observed in Empress 1 for pressed and repressed samples. Similar microstructure features--dense lithium disilicate crystals within a glass matrix--were observed in Empress 2 pressed and repressed materials. However, the repressed material showed larger lithium disilicate crystals than the singly pressed material. Second pressing had no significant effect on the biaxial flexural strength of Empress 1 or Empress 2; however, higher strength variations among the repressed samples of the materials may indicate less reliability of these materials after second pressing.

Fracture complexity of pressure vessel steels

NASA Astrophysics Data System (ADS)

Das, Arpan

2017-11-01

Significant volume of literatures are already available in the published domain reporting the mechanical and fracture behaviour of different pressure vessel steels under various testing conditions and other potential circumstances. There have been limited researches available in the open domain to correlate the tensile properties of these steels with their corresponding fracture features at various testing temperatures, which are primarily aimed at in the current investigation. A comprehensive literature review has been performed to realise this fact critically. There has been high probability that fracture features are the signature of the entire deformation history which was operated in the material. In order to understand this hypothesis, many tensile experiments are carried out at a constant strain rate by systematic variation in temperature of a reactor pressure vessel steel. The initial inclusion content and their distribution pattern are kept unaltered for all the specimens before tests, and temperatures are varied methodically to vary the nucleation sites of micro-voids (i.e. carbides, phase interfaces, etc.) which result in change of ductile fracture features. Conventional metallographic technique has been employed to characterise the microstructures at various temperatures. Fractographic characterisation of all broken tensile specimens is done to measure the two-dimensional fracture features (i.e. dimple geometry, extent of tearing ridge pattern and dimple number density) under secondary mode of imaging in scanning electron microscope. Quantitative fractography and image processing have been extensively employed to measure the two-dimensional fractographic features. An excellent correlation has been drawn between the ductile fractographic features, microstructures and corresponding tensile properties of the material as a function of test temperature. This study brings to the fore that from the systematic fractographic features, it is possible to determine reasonably the mechanical and fracture properties of a material, when the microstructure is known.

Pore- and micro-structural characterization of a novel structural binder based on iron carbonation

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

Das, Sumanta, E-mail: Sumanta.Das@asu.edu; Stone, David, E-mail: dajstone@gmail.com; Convey, Diana, E-mail: Diana.Convey@asu.edu

2014-12-15

The pore- and micro-structural features of a novel binding material based on the carbonation of waste metallic iron powder are reported in this paper. The binder contains metallic iron powder as the major ingredient, followed by additives containing silica and alumina to facilitate favorable reaction product formation. Compressive strengths sufficient for a majority of concrete applications are attained. The material pore structure is investigated primarily through mercury intrusion porosimetry whereas electron microscopy is used for microstructural characterization. Reduction in the overall porosity and the average pore size with an increase in carbonation duration from 1 day to 4 days ismore » noticed. The pore structure features are used in predictive models for gas and moisture transport (water vapor diffusivity and moisture permeability) through the porous medium which dictates its long-term durability when used in structural applications. Comparisons of the pore structure with those of a Portland cement paste are also provided. The morphology of the reaction products in the iron-based binder, and the distribution of constituent elements in the microstructure are also reported. - Highlights: • Carbonation of iron produces a dense microstructure. • Pore volume in iron carbonate lower, critical size higher than those in OPC pastes • Reaction product contains iron, carbon, silicon, aluminum and calcium. • Power-law for porosity-moisture permeability relationship was established.« less

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.

Deformation-Induced Microstructural Banding in TRIP Steels

NASA Astrophysics Data System (ADS)

Celotto, S.; Ghadbeigi, H.; Pinna, C.; Shollock, B. A.; Efthymiadis, P.

2018-05-01

Microstructure inhomogeneities can strongly influence the mechanical properties of advanced high-strength steels in a detrimental manner. This study of a transformation-induced plasticity (TRIP) steel investigates the effect of pre-existing contiguous grain boundary networks (CGBNs) of hard second-phases and shows how these develop into bands during tensile testing using in situ observations in conjunction with digital image correlation (DIC). The bands form by the lateral contraction of the soft ferrite matrix, which rotates and displaces the CGBNs of second-phases and the individual features within them to become aligned with the loading direction. The more extensive pre-existing CGBNs that were before the deformation already aligned with the loading direction are the most critical microstructural feature for damage initiation and propagation. They induce micro-void formation between the hard second-phases along them, which coalesce and develop into long macroscopic fissures. The hard phases, retained austenite and martensite, were not differentiated as it was found that the individual phases do not play a role in the formation of these bands. It is suggested that minimizing the presence of CGBNs of hard second-phases in the initial microstructure will increase the formability.

Fabrication and microstructures of functional gradient SiBCN–Nb composite by hot pressing

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

Sun, Min, E-mail: lcxsunmin@163.com; Fu, Ruoyu; Chen, Jun

2016-04-15

A functional gradient material with five layers composed of SiBCN ceramic and niobium (Nb) was prepared successfully by hot pressing. The phase composition, morphology features and microstructures were investigated in each layer of the gradient material. The Nb-containing compounds involving NbC, Nb{sub 6}C{sub 5}, Nb{sub 4}C{sub 3}, Nb{sub 5}Si{sub 3} and NbN increase with the volume fraction of Nb increasing in the sub-layer. They are randomly scattered (≤ 25 vol.% Nb), then strip-like, and finally distribute continuously (≥ 75 vol.% Nb). The size of BN(C) and SiC grains in Nb-containing layers is larger than in 100% SiBCN layer due tomore » the loss of the capsule-like structures. No distinct interfaces form in the transition regions indicating the gradual changes in phase composition and microstructures. - Highlights: • A functional gradient SiBCN–Nb material was prepared successfully by hot pressing. • Phase composition, morphology features and microstructures were investigated. • Thermodynamic calculation was used to aid in the phase analysis. • No distinct interfaces form typical of the functional gradient material.« less

Surface microstructure and chemistry of polyimide by single pulse ablation of picosecond laser

NASA Astrophysics Data System (ADS)

Du, Qifeng; Chen, Ting; Liu, Jianguo; Zeng, Xiaoyan

2018-03-01

Polyimide (PI) surface was ablated by the single pulse of picosecond laser, and the effects of laser wavelength (λ= 355 nm and 1064 nm) and fluence on surface microstructure and chemistry were explored. Scanning electron microscopy (SEM) analysis found that different surface microstructures, i.e., the concave of concentric ring and the convex of porous circular disk, were generated by 355 nm and 1064 nm picosecond laser ablation, respectively. X-ray photoelectron spectroscopy (XPS) characterization indicated that due to the high peak energy density of picosecond laser, oxygen and nitrogen from the ambient were incorporated into the PI surface mainly in the form of Cdbnd O and Csbnd Nsbnd C groups. Thus, both of the O/C and N/C atomic content ratios increased, but the increase caused by 1064 nm wavelength laser was larger. It inferred that the differences of PI surface microstructures and chemistry resulted from different laser parameters were related to different laser-matter interaction effects. For 355 nm picosecond laser, no obvious thermal features were observed and the probable ablation process of PI was mainly governed by photochemical effect; while for 1064 nm picosecond laser, obvious thermal feature appeared and photothermal effect was thought to be dominant.

Deformation-Induced Microstructural Banding in TRIP Steels

NASA Astrophysics Data System (ADS)

Celotto, S.; Ghadbeigi, H.; Pinna, C.; Shollock, B. A.; Efthymiadis, P.

2018-07-01

Microstructure inhomogeneities can strongly influence the mechanical properties of advanced high-strength steels in a detrimental manner. This study of a transformation-induced plasticity (TRIP) steel investigates the effect of pre-existing contiguous grain boundary networks (CGBNs) of hard second-phases and shows how these develop into bands during tensile testing using in situ observations in conjunction with digital image correlation (DIC). The bands form by the lateral contraction of the soft ferrite matrix, which rotates and displaces the CGBNs of second-phases and the individual features within them to become aligned with the loading direction. The more extensive pre-existing CGBNs that were before the deformation already aligned with the loading direction are the most critical microstructural feature for damage initiation and propagation. They induce micro-void formation between the hard second-phases along them, which coalesce and develop into long macroscopic fissures. The hard phases, retained austenite and martensite, were not differentiated as it was found that the individual phases do not play a role in the formation of these bands. It is suggested that minimizing the presence of CGBNs of hard second-phases in the initial microstructure will increase the formability.

Multiscale microstructural characterization of Sn-rich alloys by three dimensional (3D) X-ray synchrotron tomography and focused ion beam (FIB) tomography

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

Yazzie, K.E.; Williams, J.J.; Phillips, N.C.

2012-08-15

Sn-rich (Pb-free) alloys serve as electrical and mechanical interconnects in electronic packaging. It is critical to quantify the microstructures of Sn-rich alloys to obtain a fundamental understanding of their properties. In this work, the intermetallic precipitates in Sn-3.5Ag and Sn-0.7Cu, and globular lamellae in Sn-37Pb solder joints were visualized and quantified using 3D X-ray synchrotron tomography and focused ion beam (FIB) tomography. 3D reconstructions were analyzed to extract statistics on particle size and spatial distribution. In the Sn-Pb alloy the interconnectivity of Sn-rich and Pb-rich constituents was quantified. It will be shown that multiscale characterization using 3D X-ray and FIBmore » tomography enabled the characterization of the complex morphology, distribution, and statistics of precipitates and contiguous phases over a range of length scales. - Highlights: Black-Right-Pointing-Pointer Multiscale characterization by X-ray synchrotron and focused ion beam tomography. Black-Right-Pointing-Pointer Characterized microstructural features in several Sn-based alloys. Black-Right-Pointing-Pointer Quantified size, fraction, and clustering of microstructural features.« less

Transmission electron microscopy characterization of microstructural features of Al-Li-Cu alloys

NASA Technical Reports Server (NTRS)

Avalos-Borja, M.; Pizzo, P. P.; Larson, L. A.

1983-01-01

A transmission electron microscopy (TEM) examination of aluminum-lithium-copper alloys was conducted. The principal purpose is to characterize the nature, size, and distribution of stringer particles which result from the powder metallurgy (P/M) processing of these alloys. Microstructural features associated with the stringer particles are reported that help explain the stress corrosion susceptibility of the powder metallurgy-processed Al-Li-Cu alloys. In addition, matrix precipitation events are documented for a variety of heat treatments and process variations. Hot rolling is observed to significant alter the nature of matrix precipitation, and the observations are correlated with concomitant mechanical property variations.

Transmission electron microscopy characterization of microstructural features in aluminum-lithium-copper alloys

NASA Technical Reports Server (NTRS)

Avalos-Borja, M.; Larson, L. A.; Pizzo, P. P.

1984-01-01

A transmission electron microscopy (TEM) examination of aluminum-lithium-copper alloys was conducted. The principal purpose is to characterize the nature, size, and distribution of stringer particles which result from the powder metallurgy (P/M) processing of these alloys. Microstructural features associated with the stringer particles are reported that help explain the stress corrosion susceptibility of the powder metallurgy-processed Al-Li-Cu alloys. In addition, matrix precipitaton events are documented for a variety of heat treatments and process variations. Hot rolling is observed to significantly alter the nature of matrix precipitation, and the observations are correlated with concomitant mechanical property variations.

Influence of a magnetic field during directional solidification of MAR-M 246 + Hf superalloy

NASA Technical Reports Server (NTRS)

Andrews, J. Barry; Alter, Wendy; Schmidt, Dianne

1991-01-01

An area that has been almost totally overlooked in the optimization of properties in directionally solidified superalloys is the control of microstructural features through the application of a magnetic field during solidification. The influence of a magnetic field on the microstructural features of a nickel-base superalloys is investigated. Studies were performed on the dendritic MAR-M 246+Hf alloy, which was solidified under both a 5 K gauss magnetic field and under no-applied-field conditions. The possible influences of the magnetic field on the solidification process were observed by studying variations in microstructural features including volume fraction, surface area, number, and shape of the carbide particles. Stereological factors analyzed also included primary and secondary dendrite arm spacing and the volume fraction of the interdendritic eutectic constituent. Microprobe analysis was performed to determine the chemistry of the carbides, dendrites, and interdendritic constituents, and how it varied between field and no-field solidification samples. Experiments involving periodic application and removal of the magnetic field were also performed in order to permit a comparison with structural variations observed in a MAR-M 246+Hf alloy solidified during KC-135 high-g, low-g maneuvers.

Micro-mechanisms of Surface Defects Induced on Aluminum Alloys during Plastic Deformation at Elevated Temperatures

NASA Astrophysics Data System (ADS)

Gali, Olufisayo A.

Near-surface deformed layers developed on aluminum alloys significantly influence the corrosion and tribological behavior as well as reduce the surface quality of the rolled aluminum. The evolution of the near-surface microstructures induced on magnesium containing aluminum alloys during thermomechanical processing has been investigated with the aim generating an understanding of the influence of individual forming parameters on its evolution and examine the microstructure of the roll coating induced on the mating steel roll through material transfer during rolling. The micro-mechanisms related to the various features of near-surface microstructure developed during tribological conditions of the simulated hot rolling process were identified. Thermomechanical processing experiments were performed with the aid of hot rolling (operating temperature: 550 to 460 °C, 4, 10 and 20 rolling pass schedules) and hot forming (operating temperature: 350 to 545 °C, strain rate: 4 x 10-2 s-1) tribo-simulators. The surface, near-surface features and material transfer induced during the elevated temperature plastic deformation were examined and characterized employing optical interferometry, SEM/EDS, FIB and TEM. Near-surface features characterized on the rolled aluminum alloys included; cracks, fractured intermetallic particles, aluminum nano-particles, oxide decorated grain boundaries, rolled-in oxides, shingles and blisters. These features were related to various individual rolling parameters which included, the work roll roughness, which induced the formation of shingles, rolling marks and were responsible for the redistribution of surface oxide and the enhancements of the depth of the near-surface damage. The enhanced stresses and strains experienced during rolling were related to the formation and propagation of cracks, the nanocrystalline structure of the near-surface layers and aluminum nano-particles. The mechanism of the evolution of the near-surface microstructure were determined to include grain boundary sliding which induced the cracks at the surface and subsurface of the alloy, magnesium diffusion to free surfaces, crack propagation from shear stresses and the shear strains inducing the nanocrystalline grain structure, the formation of shingles by the shear deformation of micro-wedges induced by the work roll grooves, and the deformation of this oxide covered micro-wedges inducing the rolled-in oxides. Magnesium diffusion to free surfaces was identified as inducing crack healing due to the formation of MgO within cracks and was responsible for the oxide decorated grain boundaries. An examination of the roll coating revealed a complex layered microstructure that was induced through tribo-chemical and mechanical entrapment mechanisms. The microstructure of the roll coating suggested that the work roll material and the rolled aluminum alloy were essential in determining its composition and structure. Subsequent hot forming processes revealed the rich oxide-layer of the near-surface microstructure was beneficial for reducing the coefficient of friction during tribological contact with the steel die. Damage to the microstructure include cracks induced from grain boundary sliding of near-surface grains and the formation of oxide fibres within cracks of the near-surface deformed layers.

Additive manufacturing of metals: a brief review of the characteristic microstructures and properties of steels, Ti-6Al-4V and high-entropy alloys.

PubMed

Gorsse, Stéphane; Hutchinson, Christopher; Gouné, Mohamed; Banerjee, Rajarshi

2017-01-01

We present a brief review of the microstructures and mechanical properties of selected metallic alloys processed by additive manufacturing (AM). Three different alloys, covering a large range of technology readiness levels, are selected to illustrate particular microstructural features developed by AM and clarify the engineering paradigm relating process-microstructure-property. With Ti-6Al-4V the emphasis is placed on the formation of metallurgical defects and microstructures induced by AM and their role on mechanical properties. The effects of the large in-built dislocation density, surface roughness and build atmosphere on mechanical and damage properties are discussed using steels. The impact of rapid solidification inherent to AM on phase selection is highlighted for high-entropy alloys. Using property maps, published mechanical properties of additive manufactured alloys are graphically summarized and compared to conventionally processed counterparts.

Additive manufacturing of metals: a brief review of the characteristic microstructures and properties of steels, Ti-6Al-4V and high-entropy alloys

NASA Astrophysics Data System (ADS)

Gorsse, Stéphane; Hutchinson, Christopher; Gouné, Mohamed; Banerjee, Rajarshi

2017-12-01

We present a brief review of the microstructures and mechanical properties of selected metallic alloys processed by additive manufacturing (AM). Three different alloys, covering a large range of technology readiness levels, are selected to illustrate particular microstructural features developed by AM and clarify the engineering paradigm relating process-microstructure-property. With Ti-6Al-4V the emphasis is placed on the formation of metallurgical defects and microstructures induced by AM and their role on mechanical properties. The effects of the large in-built dislocation density, surface roughness and build atmosphere on mechanical and damage properties are discussed using steels. The impact of rapid solidification inherent to AM on phase selection is highlighted for high-entropy alloys. Using property maps, published mechanical properties of additive manufactured alloys are graphically summarized and compared to conventionally processed counterparts.

Optimization of the performance of the polymerase chain reaction in silicon-based microstructures.

PubMed Central

Taylor, T B; Winn-Deen, E S; Picozza, E; Woudenberg, T M; Albin, M

1997-01-01

We have demonstrated the ability to perform real-time homogeneous, sequence specific detection of PCR products in silicon microstructures. Optimal design/ processing result in equivalent performance (yield and specificity) for high surface-to-volume silicon structures as compared to larger volume reactions in polypropylene tubes. Amplifications in volumes as small as 0.5 microl and thermal cycling times reduced as much as 5-fold from that of conventional systems have been demonstrated for the microstructures. PMID:9224619

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

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

Many challenges exist with regard to understanding and representing complex physical processes involved with ductile damage and failure in polycrystalline metallic materials. Currently, the ability to accurately predict the macroscale ductile damage and failure response of metallic materials is lacking. Research at Los Alamos National Laboratory (LANL) is aimed at building a coupled experimental and computational methodology that supports the development of predictive damage capabilities by: capturing real distributions of microstructural features from real material and implementing them as digitally generated microstructures in damage model development; and, distilling structure-property information to link microstructural details to damage evolution under a multitudemore » of loading states.« less

Microstructural studies of nanocrystalline α-alumina powder produced from Al13-cluster

NASA Astrophysics Data System (ADS)

Harun Al Rashid Megat Ahmad, Megat; Aziz Mohamed, Abdul; Ibrahim, Azmi; Seman Mahmood, Che; Giri Rachman Putra, Edy; Jamro, Rafhayudi; Kasim, Razali; Rawi Muhammad Zin, Muhammad

2007-12-01

Nanocrystalline alumina powder was produced from calcinations of Al13-oxalate precipitates at 1100 °C. A nearly normal distribution of agglomerated alumina powder was obtained with an average particle size of about 1 μm. XRD measurement confirmed that the alumina produced was of high purity and crystalline α-phase. Microstructural features of both the precipitates and alumina obtained were studied using the small angle neutron scattering (SANS) technique. SANS examinations show the formation of microstructures in the alumina powder of mass fractals type with dimension of ˜2.8 indicative of low intra-granular porosity.

3D additive manufactured 316L components microstructural features and changes induced by working life cycles

NASA Astrophysics Data System (ADS)

Pace, M. L.; Guarnaccio, A.; Dolce, P.; Mollica, D.; Parisi, G. P.; Lettino, A.; Medici, L.; Summa, V.; Ciancio, R.; Santagata, A.

2017-10-01

The ability of processing through laser beams different kinds of metallic powders for direct production of 3D components with complex geometries has been gaining an impressive and growing attention for specific industrial applications. The process which can be distinguished as Selective Laser Sintering or Selective Laser Melting is even considered, more generally, as Additive Manufacturing where layer by layer material is built by the interaction between a laser beam and a powder bed. The rapid heating of the powder due to the laser beam energy transfer process followed by a rapid cooling rate induces within the manufactured material a cellular structure with fine sub-grains, which are in the range of few hundreds of micrometers. These metastable structures, which are smaller than the grain size in conventionally manufactured 316L stainless steel components, can undertake towards a recrystallization process due to either heat or mechanical treatments. For instance, when sub-grain boundaries of the cells are enriched with Mo and higher concentration of dislocation, dynamical processes occur generating local residual stresses. In these circumstances the segregation of Mo in cell boundaries is out of thermodynamic equilibrium conditions so that microstructures and phases are metastable. In the range of 1100-1400 °C heat treatments a complete dissolution of Mo in the Fe matrix with a gradual disappearance of sub-microns cell is observed feeding the growth of larger austenitic sub-grains formation. It follows a higher degree of Mo dissolution in the material matrix and a decrease of dislocation's concentration (Saeidi et al., 2015) [1]. In the work here presented we point out which are the microstructural features of stainless steel 316L components realized by Additive Manufacturing. Furthermore, the occurrence of a microstructural evolution is presented after experiencing to fatigue of 80000 cycles some door joints obtained by this technique. A decrease of dislocation's number, an increase of twinning due to the growth of grains and to the release of local stresses can be hypothesized following that an important role could be played by the presence of dislocations in cell boundaries as well as oxides nano-inclusion formed in-situ during the Additive Manufacturing process (Saeidi et al., 2015) [2]. From these outcomes it is going to be presented how the 3D components produced by Additive Manufacturing could change and improve their features for potential industrial applications during life cycles and enhance such a behavior by taking carefully into account the laser parameters and its scanning speed.

Site-Specific Colloidal Crystal Nucleation by Template-enhanced Particle Transport

NASA Astrophysics Data System (ADS)

Mishra, Chandan K.; Sood, A. K.; Ganapathy, Rajesh

The deliberate positioning of nano- and microstructures on surfaces is often a prerequisite for fabricating functional devices. While template-assisted nucleation is a promising route to self-assemble these structures, its success hinges on particles reaching target sites prior to nucleation and for nano/microscale particles, this is hampered by their small surface mobilities. We tailored surface features, which in the presence of attractive depletion interactions not only directed micrometer-sized colloids to specific sites but also subsequently guided their growth into ordered crystalline arrays of well-defined size and symmetry. By following the nucleation kinetics with single-particle resolution, we demonstrate control over nucleation density in a growth regime that has hitherto remained inaccessible. Our findings pave the way towards realizing non-trivial surface architectures composed of complex colloids/nanoparticles as well.

Effective Parameters in Axial Injection Suspension Plasma Spray Process of Alumina-Zirconia Ceramics

NASA Astrophysics Data System (ADS)

Tarasi, F.; Medraj, M.; Dolatabadi, A.; Oberste-Berghaus, J.; Moreau, C.

2008-12-01

Suspension plasma spray (SPS) is a novel process for producing nano-structured coatings with metastable phases using significantly smaller particles as compared to conventional thermal spraying. Considering the complexity of the system there is an extensive need to better understand the relationship between plasma spray conditions and resulting coating microstructure and defects. In this study, an alumina/8 wt.% yttria-stabilized zirconia was deposited by axial injection SPS process. The effects of principal deposition parameters on the microstructural features are evaluated using the Taguchi design of experiment. The microstructural features include microcracks, porosities, and deposition rate. To better understand the role of the spray parameters, in-flight particle characteristics, i.e., temperature and velocity were also measured. The role of the porosity in this multicomponent structure is studied as well. The results indicate that thermal diffusivity of the coatings, an important property for potential thermal barrier applications, is barely affected by the changes in porosity content.

Influence of heat treatment on microstructure and hot crack susceptibility of laser-drilled turbine blades made from Rene 80

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

Osterle, W.; Krause, S.; Moelders, T.

2008-11-15

Turbine components from conventionally cast nickel-base alloy Rene 80 show different hot cracking susceptibilities depending on their heat treatment conditions leading to slightly different microstructures. Electron probe micro-analysis, focused ion beam technique and analytical transmission electron microscopy were applied to reveal and identify grain boundary precipitates and the {gamma}-{gamma}'-microstructure. The distribution of borides along grain boundaries was evaluated statistically by quantitative metallography. The following features could be correlated with an increase of cracking susceptibility: i) Increasing grain size, ii) increasing fraction of grain boundaries with densely spaced borides, iii) lack of secondary {gamma}'-particles in matrix channels between the coarse cuboidalmore » {gamma}'-precipitates. The latter feature seems to be responsible for linking-up of cracked grain boundary precipitates which occurred as an additional cracking mechanism after one heat treatment, whereas decohesion at the boride-matrix-interface in the heat affected zone of laser-drilled holes was observed for both heat treatments.« less

Design and properties of 3D scaffolds for bone tissue engineering.

PubMed

Gómez, S; Vlad, M D; López, J; Fernández, E

2016-09-15

In this study, the Voronoi tessellation method has been used to design novel bone like three dimension (3D) porous scaffolds. The Voronoi method has been processed with computer design software to obtain 3D virtual isotropic porous interconnected models, exactly matching the main histomorphometric indices of trabecular bone (trabecular thickness, trabecular separation, trabecular number, bone volume to total volume ratio, bone surface to bone volume ratio, etc.). These bone like models have been further computed for mechanical (elastic modulus) and fluid mass transport (permeability) properties. The results show that the final properties of the scaffolds can be controlled during their microstructure and histomorphometric initial design stage. It is also shown that final properties can be tuned during the design stage to exactly match those of trabecular natural bone. Moreover, identical total porosity models can be designed with quite different specific bone surface area and thus, this specific microstructural feature can be used to favour cell adhesion, migration and, ultimately, new bone apposition (i.e. osteoconduction). Once the virtual models are fully characterized and optimized, these can be easily 3D printed by additive manufacturing and/or stereolitography technologies. The significance of this article goes far beyond the specific objectives on which it is focussed. In fact, it shows, in a guided way, the entire novel process that can be followed to design graded porous implants, whatever its external shape and geometry, but internally tuned to the exact histomorphometric indices needed to match natural human tissues microstructures and, consequently, their mechanical and fluid properties, among others. The significance is even more relevant nowadays thanks to the available new computing and design software that is easily linked to the 3D printing new technologies. It is this transversality, at the frontier of different disciplines, the main characteristic that gives this article a high scientific impact and interest to a broaden audience. Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Statistical scaling of geometric characteristics in stochastically generated pore microstructures

DOE PAGES

Hyman, Jeffrey D.; Guadagnini, Alberto; Winter, C. Larrabee

2015-05-21

In this study, we analyze the statistical scaling of structural attributes of virtual porous microstructures that are stochastically generated by thresholding Gaussian random fields. Characterization of the extent at which randomly generated pore spaces can be considered as representative of a particular rock sample depends on the metrics employed to compare the virtual sample against its physical counterpart. Typically, comparisons against features and/patterns of geometric observables, e.g., porosity and specific surface area, flow-related macroscopic parameters, e.g., permeability, or autocorrelation functions are used to assess the representativeness of a virtual sample, and thereby the quality of the generation method. Here, wemore » rely on manifestations of statistical scaling of geometric observables which were recently observed in real millimeter scale rock samples [13] as additional relevant metrics by which to characterize a virtual sample. We explore the statistical scaling of two geometric observables, namely porosity (Φ) and specific surface area (SSA), of porous microstructures generated using the method of Smolarkiewicz and Winter [42] and Hyman and Winter [22]. Our results suggest that the method can produce virtual pore space samples displaying the symptoms of statistical scaling observed in real rock samples. Order q sample structure functions (statistical moments of absolute increments) of Φ and SSA scale as a power of the separation distance (lag) over a range of lags, and extended self-similarity (linear relationship between log structure functions of successive orders) appears to be an intrinsic property of the generated media. The width of the range of lags where power-law scaling is observed and the Hurst coefficient associated with the variables we consider can be controlled by the generation parameters of the method.« less

Scanning electron microscopy combined with image processing technique: Analysis of microstructure, texture and tenderness in Semitendinous and Gluteus Medius bovine muscles.

PubMed

Pieniazek, Facundo; Messina, Valeria

2016-11-01

In this study the effect of freeze drying on the microstructure, texture, and tenderness of Semitendinous and Gluteus Medius bovine muscles were analyzed applying Scanning Electron Microscopy combined with image analysis. Samples were analyzed by Scanning Electron Microscopy at different magnifications (250, 500, and 1,000×). Texture parameters were analyzed by Texture analyzer and by image analysis. Tenderness by Warner-Bratzler shear force. Significant differences (p < 0.05) were obtained for image and instrumental texture features. A linear trend with a linear correlation was applied for instrumental and image features. Image texture features calculated from Gray Level Co-occurrence Matrix (homogeneity, contrast, entropy, correlation and energy) at 1,000× in both muscles had high correlations with instrumental features (chewiness, hardness, cohesiveness, and springiness). Tenderness showed a positive correlation in both muscles with image features (energy and homogeneity). Combing Scanning Electron Microscopy with image analysis can be a useful tool to analyze quality parameters in meat.Summary SCANNING 38:727-734, 2016. © 2016 Wiley Periodicals, Inc. © Wiley Periodicals, Inc.

The dimensionality of between-person differences in white matter microstructure in old age.

PubMed

Lövdén, Martin; Laukka, Erika Jonsson; Rieckmann, Anna; Kalpouzos, Grégoria; Li, Tie-Qiang; Jonsson, Tomas; Wahlund, Lars-Olof; Fratiglioni, Laura; Bäckman, Lars

2013-06-01

Between-person differences in white matter microstructure may partly generalize across the brain and partly play out differently for distinct tracts. We used diffusion-tensor imaging and structural equation modeling to investigate this issue in a sample of 260 adults aged 60-87 years. Mean fractional anisotropy and mean diffusivity of seven white matter tracts in each hemisphere were quantified. Results showed good fit of a model positing that individual differences in white matter microstructure are structured according to tracts. A general factor, although accounting for variance in the measures, did not adequately represent the individual differences. This indicates the presence of a substantial amount of tract-specific individual differences in white matter microstructure. In addition, individual differences are to a varying degree shared between tracts, indicating that general factors also affect white matter microstructure. Age-related differences in white matter microstructure were present for all tracts. Correlations among tract factors did not generally increase as a function of age, suggesting that aging is not a process with homogenous effects on white matter microstructure across the brain. These findings highlight the need for future research to examine whether relations between white matter microstructure and diverse outcomes are specific or general. Copyright © 2011 Wiley Periodicals, Inc.

Microstructural investigation of vintage pipeline steels highly susceptible to stress corrosion cracking

NASA Astrophysics Data System (ADS)

Torres, Monica

The use of pipelines for the transmission of gas offers not only efficiency, but a number of economic advantages. Nevertheless, pipelines are subject to aggressive operating conditions and environments which can lead to in-service degradation [1] and thus to failures. These failures can have catastrophic consequences, such as environmental damage and loss of life [2]. One of the most dangerous threats to pipeline integrity is stress corrosion cracking (SCC). Despite the substantial progress that has been achieved in the field, due to the complex nature of this phenomenon there is still not a complete understanding of this form of external corrosion. This makes its detection and prevention a challenge and therefore a risk to pipeline integrity, and most importantly, to the safety of the population. SCC cracks are the result of the interaction between a corrosive environment, applied stresses, and a susceptible microstructure. To date, what defines a susceptible microstructure remains ambiguous, as SCC has been observed in a range of steel grades, microstructures, chemical composition, and grain sizes. Therefore, in order to be able to accurately predict and prevent this hazardous form of corrosion, it is imperative to advance our knowledge on the subject and gain a better understanding on the microstructural features of highly susceptible pipeline materials, especially in the subsurface zone where crack nucleation must take place. Therefore, a microstructural characterization of the region near the surface layer was carried-out utilizing TEM. TEM analysis revealed the dislocation character, ferrite morphology, and apparent carbide precipitation in some grain boundaries. Furthermore, light microscopy, SEM, and hardness testing were performed to expand our knowledge on the microscopical features of highly SCC susceptible service components. This investigation presents a new approach to SCC characterization, which exposed the sub-surface region microscopical characteristics of service components with confirmed SCC.

Detecting diffusion-diffraction patterns in size distribution phantoms using double-pulsed field gradient NMR: Theory and experiments.

PubMed

Shemesh, Noam; Ozarslan, Evren; Basser, Peter J; Cohen, Yoram

2010-01-21

NMR observable nuclei undergoing restricted diffusion within confining pores are important reporters for microstructural features of porous media including, inter-alia, biological tissues, emulsions and rocks. Diffusion NMR, and especially the single-pulsed field gradient (s-PFG) methodology, is one of the most important noninvasive tools for studying such opaque samples, enabling extraction of important microstructural information from diffusion-diffraction phenomena. However, when the pores are not monodisperse and are characterized by a size distribution, the diffusion-diffraction patterns disappear from the signal decay, and the relevant microstructural information is mostly lost. A recent theoretical study predicted that the diffusion-diffraction patterns in double-PFG (d-PFG) experiments have unique characteristics, such as zero-crossings, that make them more robust with respect to size distributions. In this study, we theoretically compared the signal decay arising from diffusion in isolated cylindrical pores characterized by lognormal size distributions in both s-PFG and d-PFG methodologies using a recently presented general framework for treating diffusion in NMR experiments. We showed the gradual loss of diffusion-diffraction patterns in broadening size distributions in s-PFG and the robustness of the zero-crossings in d-PFG even for very large standard deviations of the size distribution. We then performed s-PFG and d-PFG experiments on well-controlled size distribution phantoms in which the ground-truth is well-known a priori. We showed that the microstructural information, as manifested in the diffusion-diffraction patterns, is lost in the s-PFG experiments, whereas in d-PFG experiments the zero-crossings of the signal persist from which relevant microstructural information can be extracted. This study provides a proof of concept that d-PFG may be useful in obtaining important microstructural features in samples characterized by size distributions.

Microstructural analysis of aluminum high pressure die castings

NASA Astrophysics Data System (ADS)

David, Maria Diana

Microstructural analysis of aluminum high pressure die castings (HPDC) is challenging and time consuming. Automating the stereology method is an efficient way in obtaining quantitative data; however, validating the accuracy of this technique can also pose some challenges. In this research, a semi-automated algorithm to quantify microstructural features in aluminum HPDC was developed. Analysis was done near the casting surface where it exhibited fine microstructure. Optical and Secondary electron (SE) and backscatter electron (BSE) SEM images were taken to characterize the features in the casting. Image processing steps applied on SEM and optical micrographs included median and range filters, dilation, erosion, and a hole-closing function. Measurements were done on different image pixel resolutions that ranged from 3 to 35 pixel/μm. Pixel resolutions below 6 px/μm were too low for the algorithm to distinguish the phases from each other. At resolutions higher than 6 px/μm, the volume fraction of primary α-Al and the line intercept count curves plateaued. Within this range, comparable results were obtained validating the assumption that there is a range of image pixel resolution relative to the size of the casting features at which stereology measurements become independent of the image resolution. Volume fraction within this curve plateau was consistent with the manual measurements while the line intercept count was significantly higher using the computerized technique for all resolutions. This was attributed to the ragged edges of some primary α-Al; hence, the algorithm still needs some improvements. Further validation of the code using other castings or alloys with known phase amount and size may also be beneficial.

Nanoscale microstructure effects on hydrogen behavior in rapidly solidified aluminum alloys

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

Tashlykova-Bushkevich, Iya I.

2015-12-31

The present work summarizes recent progress in the investigation of nanoscale microstructure effects on hydrogen behavior in rapidly solidified aluminum alloys foils produced at exceptionally high cooling rates. We focus here on the potential of modification of hydrogen desorption kinetics in respect to weak and strong trapping sites that could serve as hydrogen sinks in Al materials. It is shown that it is important to elucidate the surface microstructure of the Al alloy foils at the submicrometer scale because rapidly solidified microstructural features affect hydrogen trapping at nanostructured defects. We discuss the profound influence of solute atoms on hydrogen−lattice defectmore » interactions in the alloys. with emphasis on role of vacancies in hydrogen evolution; both rapidly solidified pure Al and conventionally processed aluminum samples are considered.« less

Spatial variations in a.c. susceptibility and microstructure for the YBa2Cu3O(7-x) superconductor and their correlation with room-temperature ultrasonic measurements

NASA Technical Reports Server (NTRS)

Roth, Don J.; Hepp, Aloysius F.; Deguire, Mark R.; Dolhert, Leonard E.

1991-01-01

The spatial (within-sample) uniformity of superconducting behavior and microstructure in YBa2Cu30(7-x) specimens over the pore fraction range of 0.10 to 0.25 was examined. The viability of using a room-temperature, nondestructive characterization method (ultrasonic velocity imaging) to predict spatial variability was determined. Spatial variations in superconductor properties were observed for specimens containing 0.10 pore fraction. An ultrasonic velocity image constructed from measurements at 1 mm increments across one such specimen revealed microstructural variation between edge and center locations that correlated with variations in alternating-current shielding and loss behavior. Optical quantitative image analysis on sample cross-sections revealed pore fraction to be the varying microstructural feature.

Spatial variations in ac susceptibility and microstructure for the YBa2Cu3O(7-x) superconductor and their correlation with room-temperature ultrasonic measurements

NASA Technical Reports Server (NTRS)

Roth, Don J.; Deguire, Mark R.; Dolhert, Leonard E.; Hepp, Aloysius F.

1991-01-01

The spatial (within-sample) uniformity of superconducting behavior and microstructure in YBa2Cu3O(7-x) specimens over the pore fraction range of 0.10 to 0.25 was examined. The viability of using a room-temperature, nondestructive characterization method (ultrasonic velocity imaging) to predict spatial variability was determined. Spatial variations in superconductor properties were observed for specimens containing 0.10 pore fraction. An ultrasonic velocity image constructed from measurements at 1 mm increments across one such specimen revealed microstructural variation between edge and center locations that correlated with variations in alternating-current shielding and loss behavior. Optical quantitative image analysis on sample cross-sections revealed pore fraction to be the varying microstructural feature.

Effect of friction stir welding on microstructure and corrosion behavior of LF6 aluminum alloy

NASA Astrophysics Data System (ADS)

Ghauri, Faizan Ali; Farooq, A.; Ahmad, A.; Deen, K. M.

2017-03-01

The LF6 aluminum alloy plates were joined by friction stir welding method. The tool rotational (1180 rpm) and transverse speed (0.56 mm s-1) were kept constant during welding of 4 mm thick plates. The microstructural features, hardness and tensile properties of the welded samples were determined to evaluate the structural integrity in comparison with the base metal. The electrochemical behavior of base metal (BM), thermo-mechanically affected zone (TMAZ) and weld nugget zone (WNZ) was also investigated by potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5% NaCl solution. The microstructural study revealed significant grain refinement and agglomeration of β (Mg2Al3) intermetallic precipitates in the WNZ. The relatively higher hardness and a decrease in the ductility (3%) also assured the formation of precipitates β precipitates in the WNZ welded samples. The fracture surface of welded sample also revealed the existence of β precipitates within the elongated dimples which may be considered as the crack initiation sites. The relatively lower corrosion rate (23.68 mpy) and higher charge transfer resistance (403 Ω cm2) of BM compared to WNZ could be associated with the galvanic dissolution of Al-matrix through competitive charge transfer and relaxation (adsorption/desorption of intermediate species) processes specifically at the vicinity of the β precipitates.

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

Inam, A., E-mail: aqil.ceet@pu.edu.pk; Brydson, R., E-mail: mtlrmdb@leeds.ac.uk; Edmonds, D.V., E-mail: d.v.edmonds@leeds.ac.uk

The potential for using graphite particles as an internal lubricant during machining is considered. Graphite particles were found to form during graphitisation of experimental medium-carbon steel alloyed with Si and Al. The graphite nucleation sites were strongly influenced by the starting microstructure, whether ferrite–pearlite, bainite or martensite, as revealed by light and electron microscopy. Favourable nucleation sites in the ferrite–pearlite starting microstructure were, not unexpectedly, found to be located within pearlite colonies, no doubt due to the presence of abundant cementite as a source of carbon. In consequence, the final distribution of graphite nodules in ferrite–pearlite microstructures was less uniformmore » than for the bainite microstructure studied. In the case of martensite, this study found a predominance of nucleation at grain boundaries, again leading to less uniform graphite dispersions. - Highlights: • Metallography of formation of graphite particles in experimental carbon steel. • Potential for using graphite in steel as an internal lubricant during machining. • Microstructure features expected to influence improved machinability studied. • Influence of pre-anneal starting microstructure on graphite nucleation sites. • Influence of pre-anneal starting microstructure on graphite distribution. • Potential benefit is new free-cutting steel compositions without e.g. Pb alloying.« less

A predictive machine learning approach for microstructure optimization and materials design

NASA Astrophysics Data System (ADS)

Liu, Ruoqian; Kumar, Abhishek; Chen, Zhengzhang; Agrawal, Ankit; Sundararaghavan, Veera; Choudhary, Alok

2015-06-01

This paper addresses an important materials engineering question: How can one identify the complete space (or as much of it as possible) of microstructures that are theoretically predicted to yield the desired combination of properties demanded by a selected application? We present a problem involving design of magnetoelastic Fe-Ga alloy microstructure for enhanced elastic, plastic and magnetostrictive properties. While theoretical models for computing properties given the microstructure are known for this alloy, inversion of these relationships to obtain microstructures that lead to desired properties is challenging, primarily due to the high dimensionality of microstructure space, multi-objective design requirement and non-uniqueness of solutions. These challenges render traditional search-based optimization methods incompetent in terms of both searching efficiency and result optimality. In this paper, a route to address these challenges using a machine learning methodology is proposed. A systematic framework consisting of random data generation, feature selection and classification algorithms is developed. Experiments with five design problems that involve identification of microstructures that satisfy both linear and nonlinear property constraints show that our framework outperforms traditional optimization methods with the average running time reduced by as much as 80% and with optimality that would not be achieved otherwise.

Optical anisotropy and domain structure of multiferroic Ni-Mn-Ga and Co-Ni-Ga Heusler-type alloys

NASA Astrophysics Data System (ADS)

Ivanova, A. I.; Gasanov, O. V.; Kaplunova, E. I.; Kalimullina, E. T.; Zalyotov, A. B.; Grechishkin, R. M.

2015-03-01

A study is made of the reflectance anisotropy of martensitic and magnetic domains in ferromagnetic shape memory alloys (FSMA) Ni-Mn-Ga and Co-Ni-Ga. The reflectance of metallographic sections of these alloys was measured in the visible with the aid of standard inverted polarized light microscope with a 360° rotatable specimen stage. Calculations are presented for the estimation of image contrast values between neighboring martensite twins. Qualitative and quantitative observations and angular measurements in reflected polarized light proved to be useful for the analysis of specific features of the martensite microstructure of multiferroic materials.

High-Performance Scanning Acousto-Ultrasonic System

NASA Technical Reports Server (NTRS)

Roth, Don; Martin, Richard; Kautz, Harold; Cosgriff, Laura; Gyekenyesi, Andrew

2006-01-01

A high-performance scanning acousto-ultrasonic system, now undergoing development, is designed to afford enhanced capabilities for imaging microstructural features, including flaws, inside plate specimens of materials. The system is expected to be especially helpful in analyzing defects that contribute to failures in polymer- and ceramic-matrix composite materials, which are difficult to characterize by conventional scanning ultrasonic techniques and other conventional nondestructive testing techniques. Selected aspects of the acousto-ultrasonic method have been described in several NASA Tech Briefs articles in recent years. Summarizing briefly: The acousto-ultrasonic method involves the use of an apparatus like the one depicted in the figure (or an apparatus of similar functionality). Pulses are excited at one location on a surface of a plate specimen by use of a broadband transmitting ultrasonic transducer. The stress waves associated with these pulses propagate along the specimen to a receiving transducer at a different location on the same surface. Along the way, the stress waves interact with the microstructure and flaws present between the transducers. The received signal is analyzed to evaluate the microstructure and flaws. The specific variant of the acousto-ultrasonic method implemented in the present developmental system goes beyond the basic principle described above to include the following major additional features: Computer-controlled motorized translation stages are used to automatically position the transducers at specified locations. Scanning is performed in the sense that the measurement, data-acquisition, and data-analysis processes are repeated at different specified transducer locations in an array that spans the specimen surface (or a specified portion of the surface). A pneumatic actuator with a load cell is used to apply a controlled contact force. In analyzing the measurement data for each pair of transducer locations in the scan, the total (multimode) acousto-ultrasonic response of the specimen is utilized. The analysis is performed by custom software that extracts parameters of signals in the time and frequency domains. The computer hardware and software provide both real-time and postscan processing and display options. For example, oscilloscope displays of waveforms and power spectral densities are available in real time. Images can be computed while scanning continues. Signals can be digitally preprocessed and/or post-processed by filtering, windowing, time-segmenting, and running-waveform-averaging algorithms. In addition, the software affords options for off-line simulation of the waveform-data-acquisition and scanning processes. In tests, the system has been shown to be capable of characterizing microstructural changes and defects in SiC/SiC and C/SiC ceramic-matrix composites. Delaminations, variations in density, microstructural changes attributable to infiltration by silicon, and crack-space indications (defined in the next sentence) have been revealed in images formed from several time- and frequency-domain parameters of scanning acousto-ultrasonic signals. The crack-space indications were image features that were not revealed by other nondestructive testing methods and are so named because they turned out to mark locations where cracking eventually occurred.

A Review on Konjac Glucomannan Gels: Microstructure and Application

PubMed Central

Yang, Dan; Wang, Lin; Wang, Xiaoshan; Mu, Ruojun; Pang, Jie; Zheng, Yafeng

2017-01-01

Konjac glucomannan (KGM) has attracted extensive attention because of its biodegradable, non-toxic, harmless, and biocompatible features. Its gelation performance is one of its most significant characteristics and enables wide applications of KGM gels in food, chemical, pharmaceutical, materials, and other fields. Herein, different preparation methods of KGM gels and their microstructures were reviewed. In addition, KGM applications have been theoretically modeled for future uses. PMID:29076996

Microstructural Features Controlling Ductile-to-Brittle Transition Behavior in High-Strength, Martensitic Steel Weld Metals

DTIC Science & Technology

1990-10-01

the austenite phase, suppresses transformation to ferrite and bainite, and promotes martensite transformation . This is shown in Fig. 4a by a shift of...100% martensite , or austenitized and isothermally transformed to produce varying proportions of upper bainite. Fracture toughness and cleavage fracture...predominantly martensitic microstructure. The reduction in hardness was caused by tempering of the martensite during deposition of subsequent passes and by

Mesoscale characterization of local property distributions in heterogeneous electrodes

NASA Astrophysics Data System (ADS)

Hsu, Tim; Epting, William K.; Mahbub, Rubayyat; Nuhfer, Noel T.; Bhattacharya, Sudip; Lei, Yinkai; Miller, Herbert M.; Ohodnicki, Paul R.; Gerdes, Kirk R.; Abernathy, Harry W.; Hackett, Gregory A.; Rollett, Anthony D.; De Graef, Marc; Litster, Shawn; Salvador, Paul A.

2018-05-01

The performance of electrochemical devices depends on the three-dimensional (3D) distributions of microstructural features in their electrodes. Several mature methods exist to characterize 3D microstructures over the microscale (tens of microns), which are useful in understanding homogeneous electrodes. However, methods that capture mesoscale (hundreds of microns) volumes at appropriate resolution (tens of nm) are lacking, though they are needed to understand more common, less ideal electrodes. Using serial sectioning with a Xe plasma focused ion beam combined with scanning electron microscopy (Xe PFIB-SEM), two commercial solid oxide fuel cell (SOFC) electrodes are reconstructed over volumes of 126 × 73 × 12.5 and 124 × 110 × 8 μm3 with a resolution on the order of ≈ 503 nm3. The mesoscale distributions of microscale structural features are quantified and both microscale and mesoscale inhomogeneities are found. We analyze the origin of inhomogeneity over different length scales by comparing experimental and synthetic microstructures, generated with different particle size distributions, with such synthetic microstructures capturing well the high-frequency heterogeneity. Effective medium theory models indicate that significant mesoscale variations in local electrochemical activity are expected throughout such electrodes. These methods offer improved understanding of the performance of complex electrodes in energy conversion devices.

Simulation of metal additive manufacturing microstructures using kinetic Monte Carlo

DOE PAGES

Rodgers, Theron M.; Madison, Jonathan D.; Tikare, Veena

2017-04-19

Additive manufacturing (AM) is of tremendous interest given its ability to realize complex, non-traditional geometries in engineered structural materials. But, microstructures generated from AM processes can be equally, if not more, complex than their conventionally processed counterparts. While some microstructural features observed in AM may also occur in more traditional solidification processes, the introduction of spatially and temporally mobile heat sources can result in significant microstructural heterogeneity. While grain size and shape in metal AM structures are understood to be highly dependent on both local and global temperature profiles, the exact form of this relation is not well understood. Wemore » implement an idealized molten zone and temperature-dependent grain boundary mobility in a kinetic Monte Carlo model to predict three-dimensional grain structure in additively manufactured metals. In order to demonstrate the flexibility of the model, synthetic microstructures are generated under conditions mimicking relatively diverse experimental results present in the literature. Simulated microstructures are then qualitatively and quantitatively compared to their experimental complements and are shown to be in good agreement.« less

Microstructural analysis of the 2195 aluminum-lithium alloy welds

NASA Technical Reports Server (NTRS)

Talia, George E.

1993-01-01

The principal objective of this research was to explain a tendency of 2195 Al-Li alloy to crack at elevated temperature during welding. Therefore, a study was made on the effect of welding and thermal treatment on the microstructure of Al-Li Alloy 2195. The critical roles of precipitates, boundaries, phases, and other features of the microstructure were inferred from the crack propagation paths and the morphology of fracture surface of the alloy with different microstructures. Particular emphasis was placed on the microstructures generated by the welding process and the mechanisms of crack propagation in such structures. Variation of the welding parameters and thermal treatments were used to alter the micro/macro structures, and they were characterized by optical and scanning electron microscopy. A theoretical model is proposed to explain changes in the microstructure of welded material. This model proposes a chemical reaction in which gases from the air (i.e., nitrogen) release hydrogen inside the alloy. Such a reaction could generate large internal stresses capable to induce porosity and crack-like delamination in the material.

Microstructural characterization, petrophysics and upscaling - from porous media to fractural media

NASA Astrophysics Data System (ADS)

Liu, J.; Liu, K.; Regenauer-Lieb, K.

2017-12-01

We present an integrated study for the characterization of complex geometry, fluid transport features and mechanical deformation at micro-scale and the upscaling of properties using microtomographic data: We show how to integrate microstructural characterization by the volume fraction, specific surface area, connectivity (percolation), shape and orientation of microstructures with identification of individual fractures from a 3D fractural network. In a first step we use stochastic analyses of microstructures to determine the geometric RVE (representative volume element) of samples. We proceed by determining the size of a thermodynamic RVE by computing upper/lower bounds of entropy production through Finite Element (FE) analyses on a series of models with increasing sizes. The minimum size for thermodynamic RVE's is identified on the basis of the convergence criteria of the FE simulations. Petrophysical properties (permeability and mechanical parameters, including plastic strength) are then computed numerically if thermodynamic convergence criteria are fulfilled. Upscaling of properties is performed by means of percolation theory. The percolation threshold is detected by using a shrinking/expanding algorithm on static micro-CT images of rocks. Parameters of the scaling laws can be extracted from quantitative analyses and/or numerical simulations on a series of models with similar structures but different porosities close to the percolation threshold. Different rock samples are analyzed. Characterizing parameters of porous/fractural rocks are obtained. Synthetic derivative models of the microstructure are used to estimate the relationships between porosity and mechanical properties. Results obtained from synthetic sandstones show that yield stress, cohesion and the angle of friction are linearly proportional to porosity. Our integrated study shows that digital rock technology can provide meaningful parameters for effective upscaling if thermodynamic volume averaging satisfies the convergence criteria. For strongly heterogeneous rocks, however, thermodynamic convergence criteria may not meet; a continuum approach cannot be justified in this case.

Effects of Pore Distributions on Ductility of Thin-Walled High Pressure Die-Cast Magnesium

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

Choi, Kyoo Sil; Li, Dongsheng; Sun, Xin

2013-06-01

In this paper, a microstructure-based three-dimensional (3D) finite element modeling method is adopted to investigate the effects of porosity in thin-walled high pressure die-cast (HPDC) Magnesium alloys on their ductility. For this purpose, the cross-sections of AM60 casting samples are first examined using optical microscope and X-ray tomography to obtain the general information on the pore distribution features. The experimentally observed pore distribution features are then used to generate a series of synthetic microstructure-based 3D finite element models with different pore volume fractions and pore distribution features. Shear and ductile damage models are adopted in the finite element analyses tomore » induce the fracture by element removal, leading to the prediction of ductility. The results in this study show that the ductility monotonically decreases as the pore volume fraction increases and that the effect of ‘skin region’ on the ductility is noticeable under the condition of same local pore volume fraction in the center region of the sample and its existence can be beneficial for the improvement of ductility. The further synthetic microstructure-based 3D finite element analyses are planned to investigate the effects of pore size and pore size distribution.« less

Characterization of nitrogen effects in high energy density weldments of Nitronic 40 stainless steel

NASA Astrophysics Data System (ADS)

Pfeif, Erik Andrew

Variation in the welding environment for laser beam welding and electron beam welding can alter the resulting weld chemical composition, microstructure and therefore the mechanical properties. The room temperature mechanical properties of Nitronic 40 stainless steel weld metal from three different heats containing 0.24, 0.28, and 0.31 wt. pct. nitrogen were evaluated for continuous mode Ytterbium doped Fiber laser welds conducted with argon and nitrogen shielding gases, and for electron beam welds. The bulk nitrogen contents were monitored and the resulting properties were then related to microstructural features measured using Electron BackScatter Diffraction (EBSD). Traditional tensile testing of weld metal is conducted on composite tensile bars consisting of base metal and weld metal often leading to failure in the region adjacent to the weld due to strength mismatch at the weld interface. These tests provide composite strength but do not specifically determine the mechanical properties of the heterogeneous weld metal. In this research, microtensile testing was conducted to characterize the properties of the different regions of the weld. The microtensile testing procedures were developed using two geometries of tensile bars measuring the properties through the thickness of 3 mm full penetration welds. In all cases an increase in the strength of the weld metal was found to occur, though the electron beam welds exhibited a higher strength than the laser welds. Standard predictive equations were found to under-predict the strength of the laser welds, even when average grain size or intercept distances were measured. The contribution of nitrogen solid solution strengthening was consistent at approximately 513 MPa per wt. pct. nitrogen. Similar cooling rates and heat inputs allow for a comparison across high energy density welding techniques. Though microstructural differences through the depth of the weld metal were observed as nitrogen vaporization decreased and cooling rates increased. Vermicular ferrite, lacy ferrite and intercellular ferrite were identified as predicted in prior research done on high nitrogen austenitic stainless steels. The resulting laser weld metal microstructures were analyzed with EBSD for grain size and ferrite content measurements, while grain boundary character was determined for a Hansen model used for multi-scale mechanical property measurements. It was found that the low angle grain boundaries were the predominant microstructural feature responsible for strengthening within the weld metal and that this contribution must be accounted for when predicting yield strength of the weld metal.

A grain boundary damage model for delamination

NASA Astrophysics Data System (ADS)

Messner, M. C.; Beaudoin, A. J.; Dodds, R. H.

2015-07-01

Intergranular failure in metallic materials represents a multiscale damage mechanism: some feature of the material microstructure triggers the separation of grain boundaries on the microscale, but the intergranular fractures develop into long cracks on the macroscale. This work develops a multiscale model of grain boundary damage for modeling intergranular delamination—a failure of one particular family of grain boundaries sharing a common normal direction. The key feature of the model is a physically-consistent and mesh independent, multiscale scheme that homogenizes damage at many grain boundaries on the microscale into a single damage parameter on the macroscale to characterize material failure across a plane. The specific application of the damage framework developed here considers delamination failure in modern Al-Li alloys. However, the framework may be readily applied to other metals or composites and to other non-delamination interface geometries—for example, multiple populations of material interfaces with different geometric characteristics.

A novel route for processing cobalt–chromium–molybdenum orthopaedic alloys

PubMed Central

Patel, Bhairav; Inam, Fawad; Reece, Mike; Edirisinghe, Mohan; Bonfield, William; Huang, Jie; Angadji, Arash

2010-01-01

Spark plasma sintering has been used for the first time to prepare the ASTM F75 cobalt–chromium–molybdenum (Co–Cr–Mo) orthopaedic alloy composition using nanopowders. In the preliminary work presented in this report, the effect of processing variables on the structural features of the alloy (phases present, grain size and microstructure) has been investigated. Specimens of greater than 99.5 per cent theoretical density were obtained. Carbide phases were not detected in the microstructure but oxides were present. However, harder materials with finer grains were produced, compared with the commonly used cast/wrought processing methods, probably because of the presence of oxides in the microstructure. PMID:20200035

Ultrasound finite element simulation sensitivity to anisotropic titanium microstructures

NASA Astrophysics Data System (ADS)

Freed, Shaun; Blackshire, James L.; Na, Jeong K.

2016-02-01

Analytical wave models are inadequate to describe complex metallic microstructure interactions especially for near field anisotropic property effects and through geometric features smaller than the wavelength. In contrast, finite element ultrasound simulations inherently capture microstructure influences due to their reliance on material definitions rather than wave descriptions. To better understand and quantify heterogeneous crystal orientation effects to ultrasonic wave propagation, a finite element modeling case study has been performed with anisotropic titanium grain structures. A parameterized model has been developed utilizing anisotropic spheres within a bulk material. The resulting wave parameters are analyzed as functions of both wavelength and sphere to bulk crystal mismatch angle.

Fe-Mn(Al, Si) TWIP steel - strengthening characteristics and weldability

NASA Astrophysics Data System (ADS)

Podany, P.; Koukolikova, M.; Kubina, T.; Prochazka, R.; Franc, A.

2017-02-01

Twinning Induced Plasticity steel, or TWIP steel, has had increased interest in recent years from various industry sectors. This is due to it being lightweight, strong, and ductile; which are all properties that are useful in the automotive and aerospace industries. These steels potentially can offer lighter weight vehicles and parts with increased strength and other mechanical properties. This combination could offer greater fuel efficiency and performance while at the same time improving the safety features of the vehicle. This steel is characterised by being a high alloy steel, specifically having a high manganese content. It also has a fully austenitic microstructure at room temperature, which is a unique characteristic. But, for TWIP steel to be useful in various industrial sectors, it must have good weldability. This paper deals with the description of the strengthening due to the cold rolling on experimental heats of manganese steel with TRIP/TWIP effect. Impacts on microstructure, yield strength and tensile strength are described. Also, the weldability of experimental TWIP steel by studying the properties of weld joints after laser welding is described.

Linguistic Feature Development Across Grades and Genre in Elementary Writing.

PubMed

Hall-Mills, Shannon; Apel, Kenn

2015-07-01

As children develop skills in writing across academic contexts, clinicians and educators need to have a fundamental understanding of typical writing development as well as valid and reliable assessment methods. The purpose of this study was to examine the progression of linguistic elements in school-age children's narrative and expository writing development. Narrative and expository writing samples produced by 89 children in Grades 2 through 4 were analyzed at the microstructure and macrostructure levels. Measures of receptive vocabulary, word-level reading, and reading comprehension were obtained. Exploratory factor analyses revealed 4 microstructure factors (e.g., productivity, grammatical complexity, grammatical accuracy, and lexical density) and 1 macrostructure factor (e.g., a combination of organization, text structure, and cohesion). Multivariate analyses of covariance with reading comprehension as a covariate showed that productivity and macrostructure were sensitive to grade-level and genre differences and that expository grammatical complexity was sensitive to grade-level differences. Findings are discussed in light of grade-level standards for narrative and expository writing and current practices in writing assessment. Multiple suggestions are offered for clinical and educational implications, and specific directions are provided for future research.

Effect of Brass Interlayer Sheet on Microstructure and Joint Performance of Ultrasonic Spot-Welded Copper-Steel Joints

NASA Astrophysics Data System (ADS)

Satpathy, Mantra Prasad; Kumar, Abhishek; Sahoo, Susanta Kumar

2017-07-01

Solid-state ultrasonic spot welding (USW) inevitably offers a potential solution for joining dissimilar metal combination like copper (Cu) and steel (SS). In this study, the USW has been performed on Cu (UNS C10100) and SS (AISI 304) with brass interlayer by varying various welding parameters, aiming to identify the interfacial reaction, changes in microstructure and weld strength. The highest tensile shear and T-peel failure loads of 1277 and 174 N are achieved at the optimum conditions like 68 µm of vibration amplitude, 0.42 MPa of weld pressure and 1 s of weld time. The fractured surface analysis of brass interlayer and AISI 304 stainless steel samples reveals the features like swirls, voids and intermetallic compounds (IMCs). These IMCs are composed of CuZn and FeZn composite-like structures with 1.0 μm thickness. This confirms that the weld quality is specifically sensitive to the levels of input parameter combinations as well as the type of material present on the sonotrode side.

Linking Initial Microstructure to ORR Related Property Degradation in SOFC Cathode: A Phase Field Simulation

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

Lei, Y.; Cheng, T. -L.; Wen, Y. H.

Microstructure evolution driven by thermal coarsening is an important factor for the loss of oxygen reduction reaction rates in SOFC cathode. In this work, the effect of an initial microstructure on the microstructure evolution in SOFC cathode is investigated using a recently developed phase field model. Specifically, we tune the phase fraction, the average grain size, the standard deviation of the grain size and the grain shape in the initial microstructure, and explore their effect on the evolution of the grain size, the density of triple phase boundary, the specific surface area and the effective conductivity in LSM-YSZ cathodes. Itmore » is found that the degradation rate of TPB density and SSA of LSM is lower with less LSM phase fraction (with constant porosity assumed) and greater average grain size, while the degradation rate of effective conductivity can also be tuned by adjusting the standard deviation of grain size distribution and grain aspect ratio. The implication of this study on the designing of an optimal initial microstructure of SOFC cathodes is discussed.« less

Linking Initial Microstructure to ORR Related Property Degradation in SOFC Cathode: A Phase Field Simulation

DOE PAGES

Lei, Y.; Cheng, T. -L.; Wen, Y. H.

2017-07-05

Microstructure evolution driven by thermal coarsening is an important factor for the loss of oxygen reduction reaction rates in SOFC cathode. In this work, the effect of an initial microstructure on the microstructure evolution in SOFC cathode is investigated using a recently developed phase field model. Specifically, we tune the phase fraction, the average grain size, the standard deviation of the grain size and the grain shape in the initial microstructure, and explore their effect on the evolution of the grain size, the density of triple phase boundary, the specific surface area and the effective conductivity in LSM-YSZ cathodes. Itmore » is found that the degradation rate of TPB density and SSA of LSM is lower with less LSM phase fraction (with constant porosity assumed) and greater average grain size, while the degradation rate of effective conductivity can also be tuned by adjusting the standard deviation of grain size distribution and grain aspect ratio. The implication of this study on the designing of an optimal initial microstructure of SOFC cathodes is discussed.« less

A tissue-like culture system using microstructures: influence of extracellular matrix material on cell adhesion and aggregation.

PubMed

Knedlitschek, G; Schneider, F; Gottwald, E; Schaller, T; Eschbach, E; Weibezahn, K F

1999-02-01

Special microenvironmental conditions are required to induce and/or maintain specific qualities of differentiated cells. An important parameter is the three-dimensional tissue architecture that cannot be reproduced in conventional monolayer systems. Advanced tissue culture systems will meet many of these demands, but may reach their limits, especially when gradients of specific substances over distinct tissue layers must be established for long-term culture. These limitations may be overcome by incorporating microstructures into tissue-like culture systems. The microstructured cell support presented consists of a flat array of 625 cubic microcontainers with porous bottoms, in which cells can be supplied with specific media from both sides of the tissue layer. Permanent cell lines and primary rat hepatocytes have been used to test the culture system. In order to define reproducible conditions for tissue formation and for cell adherence to the structure, several ECM (extracellular matrix) components were tested for coating of microstructured substrata. The described tissue culture system offers great flexibility in adapting the cell support to specific needs.

Software for Demonstration of Features of Chain Polymerization Processes

ERIC Educational Resources Information Center

Sosnowski, Stanislaw

2013-01-01

Free software for the demonstration of the features of homo- and copolymerization processes (free radical, controlled radical, and living) is described. The software is based on the Monte Carlo algorithms and offers insight into the kinetics, molecular weight distribution, and microstructure of the macromolecules formed in those processes. It also…

Alloy Microstructure Dictates Corrosion Modes in THA Modular Junctions.

PubMed

Pourzal, Robin; Hall, Deborah J; Ehrich, Jonas; McCarthy, Stephanie M; Mathew, Mathew T; Jacobs, Joshua J; Urban, Robert M

2017-12-01

Adverse local tissue reactions (ALTRs) triggered by corrosion products from modular taper junctions are a known cause of premature THA failure. CoCrMo devices are of particular concern because cobalt ions and chromium-orthophosphates were shown to be linked to ALTRs, even in metal-on-polyethylene THAs. The most common categories of CoCrMo alloy are cast and wrought alloy, which exhibit fundamental microstructural differences in terms of grain size and hard phases. The impact of implant alloy microstructure on the occurring modes of corrosion and subsequent metal ion release is not well understood. The purpose of this study was to determine whether (1) the microstructure of cast CoCrMo alloy varies broadly between manufacturers and can dictate specific corrosion modes; and whether (2) the microstructure of wrought CoCrMo alloy is more consistent between manufacturers and has low implications on the alloy's corrosion behavior. The alloy microstructure of four femoral-stem and three femoral-head designs from four manufacturers was metallographically and electrochemically characterized. Three stem designs were made from cast alloy; all three head designs and one stem design were made from wrought alloy. Alloy samples were sectioned from retrieved components and then polished and etched to visualize grain structure and hard phases such as carbides (eg, M 23 C 6 ) or intermetallic phases (eg, σ phase). Potentiodynamic polarization (PDP) tests were conducted to determine the corrosion potential (E corr ), corrosion current density (I corr ), and pitting potential (E pit ) for each alloy. Four devices were tested within each group, and each measurement was repeated three times to ensure repeatable results. Differences in PDP metrics between manufacturers and between alloys with different hard phase contents were compared using one-way analysis of variance and independent-sample t-tests. Microstructural features such as twin boundaries and slip bands as well as corrosion damage features were viewed and qualitatively assessed in a scanning electron microscope. We found broad variability in implant alloy microstructure for both cast and wrought alloy between manufacturers, but also within the same implant design. In cast alloys, there was no difference in PDP metrics between manufacturers. However, coarse hard phases and clusters of hard phases (mainly intermetallic phases) were associated with severe phase boundary corrosion and pitting corrosion. Furthermore, cast alloys with hard phases had a lower E pit than those without (0.46 V, SD 0.042; 0.53 V, SD 0.03, respectively; p = 0.015). Wrought alloys exhibited either no hard phases or numerous carbides (M 23 C 6 ). However, the corrosion behavior was mainly affected by lattice defects and banded structures indicative of segregations that appear to be introduced during bar stock manufacturing. Alloys with banding had a lower E corr (p = 0.008) and higher I corr (p = 0.028) than alloys without banding (-0.76 V, SD 0.003; -0.73 V, SD 0.009; and 1.14 × 10 -4 mA/cm 2 , SD 1.47 × 10 -5 ; 5.2 × 10 -5 mA/cm 2 , SD 2.57 × 10 -5 , respectively). Alloys with carbides had a slightly higher E corr (p = 0.046) than those without (-0.755 V, SD 0.005; -0.761 V, SD 0.004); however, alloys with carbides exhibited more severe corrosion damage as a result of phase boundary corrosion, hard phase detachment, and subsequent local crevice corrosion. The observed variability in CoCrMo alloy microstructure of both cast and wrought components in this study appears to be an important issue to address, perhaps through better standards, to minimize in vivo corrosion. The finding of the banded structures within wrought alloys is especially concerning because it unfavorably influences the corrosion behavior independent of the manufacturer. The findings suggest that a homogeneous alloy microstructure with a minimal hard phase fraction exhibits more favorable corrosion behavior within the in vivo environment of modular taper junctions, thus lowering metal ion release and subsequently the risk of ALTRs to corrosion products. Also, the question arises if hard phases fulfill a useful purpose in metal-on-polyethylene bearings, because they may come with a higher risk of phase boundary corrosion and pitting corrosion and the benefit they provide by adding strength is not needed (unlike in metal-on-metal bearings). Implant failure resulting from corrosion processes within modular junctions is a major concern in THA. Our results suggest that implant alloy microstructure is not sufficiently standardized and may also dictate specific corrosion modes and subsequent metal ion release.

Competing mechanisms in the wear resistance behavior of biomineralized rod-like microstructures

NASA Astrophysics Data System (ADS)

Escobar de Obaldia, Enrique; Herrera, Steven; Grunenfelder, Lessa Kay; Kisailus, David; Zavattieri, Pablo

2016-11-01

The remarkable mechanical properties observed in biological composite materials relative to those of their individual constituents distinguish them from common engineering materials. Some naturally occurring high-performance ceramics, like the external veneer of the Chiton (Cryptochiton stelleri) tooth, have been shown to have superior hardness and impressive abrasion resistance properties. The mechanical performance of the chiton tooth has been attributed to a hierarchical arrangement of nanostructured magnetite rods surrounded with organic material. While nanoindentation tests provide useful information about the overall performance of this biological composite, understanding the key microstructural features and energy dissipation mechanisms at small scales remains a challenging task. We present a combined experimental/numerical approach to elucidate the role of material deformation in the rods, debonding at the rod interfaces and the influence of energy dissipation mechanisms on the ability of the microstructure to distribute damage under extreme loading conditions. We employ a 3D finite element-based micromechanical model to simulate the nanoindentation tests performed in geological magnetite and cross-sections of the chiton tooth. This proposed model is capable of capturing the inelastic deformation of the rods and the failure of their interfaces, while damage, fracture and fragmentation of the mineralized rods is assessed using a probabilistic function. Our results show that these natural materials achieve their abrasion resistant properties by controlling the interface strength between rods, alleviating the tensile stress on the rods near the indentation tip and therefore decreasing the probability of catastrophic failure without significantly sacrificing resistance to penetration. The understanding of these competing energy dissipating mechanisms provides a path to the prediction of new combination of materials. In turns, these results suggest certain guidelines for abrasion resistance rod-like microstructures in composites with high volume fraction of brittle minerals or ceramics with tailored performance for specific applications.

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

Rodgers, Theron M.; Madison, Jonathan D.; Tikare, Veena

Additive manufacturing (AM) is of tremendous interest given its ability to realize complex, non-traditional geometries in engineered structural materials. But, microstructures generated from AM processes can be equally, if not more, complex than their conventionally processed counterparts. While some microstructural features observed in AM may also occur in more traditional solidification processes, the introduction of spatially and temporally mobile heat sources can result in significant microstructural heterogeneity. While grain size and shape in metal AM structures are understood to be highly dependent on both local and global temperature profiles, the exact form of this relation is not well understood. Wemore » implement an idealized molten zone and temperature-dependent grain boundary mobility in a kinetic Monte Carlo model to predict three-dimensional grain structure in additively manufactured metals. In order to demonstrate the flexibility of the model, synthetic microstructures are generated under conditions mimicking relatively diverse experimental results present in the literature. Simulated microstructures are then qualitatively and quantitatively compared to their experimental complements and are shown to be in good agreement.« less

Analyses of microstructural and elastic properties of porous SOFC cathodes based on focused ion beam tomography

NASA Astrophysics Data System (ADS)

Chen, Zhangwei; Wang, Xin; Giuliani, Finn; Atkinson, Alan

2015-01-01

Mechanical properties of porous SOFC electrodes are largely determined by their microstructures. Measurements of the elastic properties and microstructural parameters can be achieved by modelling of the digitally reconstructed 3D volumes based on the real electrode microstructures. However, the reliability of such measurements is greatly dependent on the processing of raw images acquired for reconstruction. In this work, the actual microstructures of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathodes sintered at an elevated temperature were reconstructed based on dual-beam FIB/SEM tomography. Key microstructural and elastic parameters were estimated and correlated. Analyses of their sensitivity to the grayscale threshold value applied in the image segmentation were performed. The important microstructural parameters included porosity, tortuosity, specific surface area, particle and pore size distributions, and inter-particle neck size distribution, which may have varying extent of effect on the elastic properties simulated from the microstructures using FEM. Results showed that different threshold value range would result in different degree of sensitivity for a specific parameter. The estimated porosity and tortuosity were more sensitive than surface area to volume ratio. Pore and neck size were found to be less sensitive than particle size. Results also showed that the modulus was essentially sensitive to the porosity which was largely controlled by the threshold value.

Impact of Defects in Powder Feedstock Materials on Microstructure of 304L and 316L Stainless Steel Produced by Additive Manufacturing

NASA Astrophysics Data System (ADS)

Morrow, Benjamin M.; Lienert, Thomas J.; Knapp, Cameron M.; Sutton, Jacob O.; Brand, Michael J.; Pacheco, Robin M.; Livescu, Veronica; Carpenter, John S.; Gray, George T.

2018-05-01

Recent work in both 304L and 316L stainless steel produced by additive manufacturing (AM) has shown that in addition to the unique, characteristic microstructures formed during the process, a fine dispersion of sub-micron particles, with a chemistry different from either the powder feedstock or the expected final material, are evident in the final microstructure. Such fine-scale features can only be resolved using transmission electron microscopy (TEM) or similar techniques. The present work uses electron microscopy to study both the initial powder feedstock and microstructures in final AM parts. Special attention is paid to the chemistry and origin of these nanoscale particles in several different metal alloys, and their impact on the final build. Comparisons to traditional, wrought material will be made.

Identification of distinct topographical surface microstructures favoring either undifferentiated expansion or differentiation of murine embryonic stem cells.

PubMed

Markert, Lotte D'Andrea; Lovmand, Jette; Foss, Morten; Lauridsen, Rune Hoff; Lovmand, Michael; Füchtbauer, Ernst-Martin; Füchtbauer, Annette; Wertz, Karin; Besenbacher, Flemming; Pedersen, Finn Skou; Duch, Mogens

2009-11-01

The potential of embryonic stem (ES) cells for both self-renewal and differentiation into cells of all three germ layers has generated immense interest in utilizing these cells for tissue engineering or cell-based therapies. However, the ability to culture undifferentiated ES cells without the use of feeder cells as well as means to obtain homogeneous, differentiated cell populations devoid of residual pluripotent ES cells still remain major challenges. Here we have applied murine ES cells to topographically microstructured surface libraries, BioSurface Structure Arrays (BSSA), and investigated whether these could be used to (i) identify topographically microstructured growth supports alleviating the need for feeder cells for expansion of undifferentiated ES cells and (ii) identify specific types of microstructures enforcing differentiation of ES cells. The BSSA surfaces arrays consisted of 504 different topographical microstructures each located in a tester field of 3 x 3 mm. The murine ES cell lines CJ7 and KH2 were seeded upon the BSSA libraries and specific topographical structures facilitating either undifferentiated ES cell growth or enhancing spreading indicative of differentiation of the ES cells were identified. Secondly serial passage of undifferentiated CJ7 ES cells on selected microstructures, identified in the screening of these BSSA libraries, showed that these cells had retained germ-line potential. These results indicate that one specific type of topographical surface microstructures, identified by the BSSA technology, can substitute for feeder cells and that another subset may be used to eliminate undifferentiated ES cells from a population of differentiated ES cells.

Validation of a freshwater Otolith microstructure pattern for Nisqually Chinook Salmon (Oncorhynchus tshawytscha)

USGS Publications Warehouse

Lind-Null, Angie; Larsen, Kim

2011-01-01

The Nisqually Fall Chinook salmon (Oncorhynchus tshawytscha) population is one of 27 stocks in the Puget Sound (Washington) evolutionarily significant unit listed as threatened under the federal Endangered Species Act (ESA). Extensive restoration of the Nisqually River delta ecosystem has taken place to assist in recovery of the stock since estuary habitat is a critical transition zone for juvenile fall Chinook salmon. A pre-restoration baseline that includes the characterization of life history strategies, estuary residence times, growth rates and habitat use is needed to evaluate the potential response of hatchery and natural origin Chinook salmon to restoration efforts and to determine restoration success. Otolith microstructure analysis was selected as a tool to examine Chinook salmon life history, growth and residence in the Nisqually River estuary. The purpose of the current study is to incorporate microstructural analysis from the otoliths of juvenile Nisqually Chinook salmon collected at the downstream migrant trap within true freshwater (FW) habitat of the Nisqually River. The results from this analysis confirmed the previously documented Nisqually-specific FW microstructure pattern and revealed a Nisqually-specific microstructure pattern early in development (“developmental pattern”). No inter-annual variation in the microstructure pattern was visually observed when compared to samples from previous years. Furthermore, the Nisqually-specific “developmental pattern” and the FW microstructure pattern used in combination during analysis will allow us to recognize and separate with further confidence future unmarked Chinook salmon otolith collections into Nisqually-origin (natural or unmarked hatchery) and non-Nisqually origin categories. Freshwater mean increment width, growth rate and residence time were also calculated.

Microstructural evolution of neutron irradiated 3C-SiC

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

Sprouster, David J.; Koyanagi, Takaaki; Dooryhee, Eric

The microstructural response of neutron irradiated 3C-SiC have been investigated over a wide irradiation temperature and fluence range via qualitative and quantitative synchrotron-based X-ray diffraction characterization. Here, we identify several neutron fluence- and irradiation temperature-dependent changes in the microstructure, and directly highlight the specific defects introduced through the course of irradiation. By quantifying the microstructure, we aim to develop a more detailed understanding of the radiation response of SiC. Such studies are important to build mechanistic models of material performance and to understand the susceptibility of various microstructures to radiation damage for advanced energy applications.

Microstructural evolution of neutron irradiated 3C-SiC

DOE PAGES

Sprouster, David J.; Koyanagi, Takaaki; Dooryhee, Eric; ...

2017-03-18

The microstructural response of neutron irradiated 3C-SiC have been investigated over a wide irradiation temperature and fluence range via qualitative and quantitative synchrotron-based X-ray diffraction characterization. Here, we identify several neutron fluence- and irradiation temperature-dependent changes in the microstructure, and directly highlight the specific defects introduced through the course of irradiation. By quantifying the microstructure, we aim to develop a more detailed understanding of the radiation response of SiC. Such studies are important to build mechanistic models of material performance and to understand the susceptibility of various microstructures to radiation damage for advanced energy applications.

Detecting the Extent of Cellular Decomposition after Sub-Eutectoid Annealing in Rolled UMo Foils

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

Kautz, Elizabeth J.; Jana, Saumyadeep; Devaraj, Arun

2017-07-31

This report presents an automated image processing approach to quantifying microstructure image data, specifically the extent of eutectoid (cellular) decomposition in rolled U-10Mo foils. An image processing approach is used here to be able to quantitatively describe microstructure image data in order to relate microstructure to processing parameters (time, temperature, deformation).

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.

The effects of magnetic and mechanical microstructures on the twinning stress in Ni-Mn-Ga

NASA Astrophysics Data System (ADS)

Faran, Eilon; Benichou, Itamar; Givli, Sefi; Shilo, Doron

2015-12-01

The ferromagnetic 10M Ni-Mn-Ga alloy exhibits complex magnetic and mechanical microstructures, which are expected to form barriers for motion of macro twin boundaries. Here, the contributions of both microstructures to the magnitude of the twinning stress property are investigated experimentally. A series of uniaxial loading-unloading curves are taken under different orientation angles of a constant magnetic field. The different 180 ° magnetic domains microstructures that are formed across the twin boundary in each case are visualised using a magneto optical film. Analysis of the different loading curves and the corresponding magnetic microstructures show that the latter does not contribute to the barriers for twin boundary motion. In accordance, the internal resisting stress for twin boundary motion under any magnetic field can be taken as the twinning stress measured in the absence of an external field. In addition, a statistical analysis of the fine features in the loading profiles reveals that the barrier for twinning is associated with a μ m sized characteristic length scale. This length scale corresponds to the typical thickness of micro-twinning laminates that constitute a mechanical microstructure. These findings indicate that the magnitude of the twinning stress in 10M Ni-Mn-Ga is determined by the characteristic fine twinned mechanical microstructure of this alloy.

A predictive machine learning approach for microstructure optimization and materials design

DOE PAGES

Liu, Ruoqian; Kumar, Abhishek; Chen, Zhengzhang; ...

2015-06-23

This paper addresses an important materials engineering question: How can one identify the complete space (or as much of it as possible) of microstructures that are theoretically predicted to yield the desired combination of properties demanded by a selected application? We present a problem involving design of magnetoelastic Fe-Ga alloy microstructure for enhanced elastic, plastic and magnetostrictive properties. While theoretical models for computing properties given the microstructure are known for this alloy, inversion of these relationships to obtain microstructures that lead to desired properties is challenging, primarily due to the high dimensionality of microstructure space, multi-objective design requirement and non-uniquenessmore » of solutions. These challenges render traditional search-based optimization methods incompetent in terms of both searching efficiency and result optimality. In this paper, a route to address these challenges using a machine learning methodology is proposed. A systematic framework consisting of random data generation, feature selection and classification algorithms is developed. In conclusion, experiments with five design problems that involve identification of microstructures that satisfy both linear and nonlinear property constraints show that our framework outperforms traditional optimization methods with the average running time reduced by as much as 80% and with optimality that would not be achieved otherwise.« less

Microstructures and Mechanical Properties of Commercially Pure Ti Processed by Rotationally Accelerated Shot Peening

PubMed Central

Huang, Zhaowen; Cao, Yang; Nie, Jinfeng; Zhou, Hao; Li, Yusheng

2018-01-01

Gradient structured materials possess good combinations of strength and ductility, rendering the materials attractive in industrial applications. In this research, a surface nanocrystallization (SNC) technique, rotationally accelerated shot peening (RASP), was employed to produce a gradient nanostructured pure Ti with a deformation layer that had a thickness of 2000 μm, which is thicker than those processed by conventional SNC techniques. It is possible to fabricate a gradient structured Ti workpiece without delamination. Moreover, based on the microstructural features, the microstructure of the processed sample can be classified into three regions, from the center to the surface of the RASP-processed sample: (1) a twinning-dominated core region; (2) a “twin intersection”-dominated twin transition region; and (3) the nanostructured region, featuring nanograins. A microhardness gradient was detected from the RASP-processed Ti. The surface hardness was more than twice that of the annealed Ti sample. The RASP-processed Ti sample exhibited a good combination of yield strength and uniform elongation, which may be attributed to the high density of deformation twins and a strong back stress effect. PMID:29498631

Simulating Thermal Cycling and Isothermal Deformation Response of Polycrystalline NiTi

NASA Technical Reports Server (NTRS)

Manchiraju, Sivom; Gaydosh, Darrell J.; Noebe, Ronald D.; Anderson, Peter M.

2011-01-01

A microstructure-based FEM model that couples crystal plasticity, crystallographic descriptions of the B2-B19' martensitic phase transformation, and anisotropic elasticity is used to simulate thermal cycling and isothermal deformation in polycrystalline NiTi (49.9at% Ni). The model inputs include anisotropic elastic properties, polycrystalline texture, DSC data, and a subset of isothermal deformation and load-biased thermal cycling data. A key experimental trend is captured.namely, the transformation strain during thermal cycling is predicted to reach a peak with increasing bias stress, due to the onset of plasticity at larger bias stress. Plasticity induces internal stress that affects both thermal cycling and isothermal deformation responses. Affected thermal cycling features include hysteretic width, two-way shape memory effect, and evolution of texture with increasing bias stress. Affected isothermal deformation features include increased hardening during loading and retained martensite after unloading. These trends are not captured by microstructural models that lack plasticity, nor are they all captured in a robust manner by phenomenological approaches. Despite this advance in microstructural modeling, quantitative differences exist, such as underprediction of open loop strain during thermal cycling.

Three Dimensional Characterization of Tin Crystallography and Cu6Sn5 Intermetallics in Solder Joints by Multiscale Tomography

NASA Astrophysics Data System (ADS)

Kirubanandham, A.; Lujan-Regalado, I.; Vallabhaneni, R.; Chawla, N.

2016-11-01

Decreasing pitch size in electronic packaging has resulted in a drastic decrease in solder volumes. The Sn grain crystallography and fraction of intermetallic compounds (IMCs) in small-scale solder joints evolve much differently at the smaller length scales. A cross-sectional study limits the morphological analysis of microstructural features to two dimensions. This study utilizes serial sectioning technique in conjunction with electron backscatter diffraction to investigate the crystallographic orientation of both Sn grains and Cu6Sn5 IMCs in Cu/Pure Sn/Cu solder joints in three dimensional (3D). Quantification of grain aspect ratio is affected by local cooling rate differences within the solder volume. Backscatter electron imaging and focused ion beam serial sectioning enabled the visualization of morphology of both nanosized Cu6Sn5 IMCs and the hollow hexagonal morphology type Cu6Sn5 IMCs in 3D. Quantification and visualization of microstructural features in 3D thus enable us to better understand the microstructure and deformation mechanics within these small scale solder joints.

Myocardial architecture and patient variability in clinical patterns of atrial fibrillation

NASA Astrophysics Data System (ADS)

Manani, Kishan A.; Christensen, Kim; Peters, Nicholas S.

2016-10-01

Atrial fibrillation (AF) increases the risk of stroke by a factor of 4-5 and is the most common abnormal heart rhythm. The progression of AF with age, from short self-terminating episodes to persistence, varies between individuals and is poorly understood. An inability to understand and predict variation in AF progression has resulted in less patient-specific therapy. Likewise, it has been a challenge to relate the microstructural features of heart muscle tissue (myocardial architecture) with the emergent temporal clinical patterns of AF. We use a simple model of activation wave-front propagation on an anisotropic structure, mimicking heart muscle tissue, to show how variation in AF behavior arises naturally from microstructural differences between individuals. We show that the stochastic nature of progressive transversal uncoupling of muscle strands (e.g., due to fibrosis or gap junctional remodeling), as occurs with age, results in variability in AF episode onset time, frequency, duration, burden, and progression between individuals. This is consistent with clinical observations. The uncoupling of muscle strands can cause critical architectural patterns in the myocardium. These critical patterns anchor microreentrant wave fronts and thereby trigger AF. It is the number of local critical patterns of uncoupling as opposed to global uncoupling that determines AF progression. This insight may eventually lead to patient-specific therapy when it becomes possible to observe the cellular structure of a patient's heart.

Method for the fabrication of three-dimensional microstructures by deep X-ray lithography

DOEpatents

Sweatt, William C.; Christenson, Todd R.

2005-04-05

A method for the fabrication of three-dimensional microstructures by deep X-ray lithography (DXRL) comprises a masking process that uses a patterned mask with inclined mask holes and off-normal exposures with a DXRL beam aligned with the inclined mask holes. Microstructural features that are oriented in different directions can be obtained by using multiple off-normal exposures through additional mask holes having different orientations. Various methods can be used to block the non-aligned mask holes from the beam when using multiple exposures. A method for fabricating a precision 3D X-ray mask comprises forming an intermediate mask and a master mask on a common support membrane.

Effect of convection on the dendrite growth kinetics in undercooled melts of D2 tool steels

NASA Astrophysics Data System (ADS)

Valloton, J.; Herlach, D. M.; Henein, H.

2016-03-01

Rapid solidification of D2 tool steel is investigated experimentally using the electromagnetic levitation technique under terrestrial and reduced gravity conditions. The microstructures of samples covering a broad range of undercoolings (40 K ≤ ΔT ≤ 280 K) are analysed. At low undercooling coarse grained dendritic microstructure is observed, while at higher undercoolings this dendritic feature disappears in favour of a grain refined equiaxed structure. In the latter case, the eutectic carbides are more evenly dispersed throughout the microstructure. The sample solidified in microgravity during parabolic flight experiment exhibits only a few very large grains with twinning relationship. This highlights the effect of convection on grain refinement in this system.

Processing, Microstructures, and Properties of Nb-Based Metal/Silicide Alloys

DTIC Science & Technology

2003-07-01

Fig 15. (a) Fracture features at 800°C also indicated brittle failure, (b) indication of limited microplasticity in the Nbss phase...magnification, Fig. 15(b), there are some indication of microplasticity of the Nbss phase (arrows) but it was not sufficient to provide macroscopic...features at 800°C also indicated brittle failure, (b) indication of limited microplasticity in the Nbss phase (bright features) at

Effect of Production Process on Microstructure and Mechanical Properties of Copper Coatings of Jet Charges

NASA Astrophysics Data System (ADS)

Gleener, R. E.; Cheerova, M. N.; Shadiev, B. Sh.; Katyukhin, E. B.

2017-07-01

Special features of formation of the grain structure and mechanical properties of copper during recrystallization annealing after cold deformation with a wide range of reduction are studied. The constants of the Hall-Petch equation are determined for copper, the microstructure of which forms in the course of plastic deformation and subsequent heat treatment. The results of the study are allowed for in the process of production of claddings for jet charges.

Microstructural Characterization of Polymers with Positrons

NASA Technical Reports Server (NTRS)

Singh, Jag J.

1997-01-01

Positrons provide a versatile probe for monitoring microstructural features of molecular solids. In this paper, we report on positron lifetime measurements in two different types of polymers. The first group comprises polyacrylates processed on earth and in space. The second group includes fully-compatible and totally-incompatible Semi-Interpenetrating polymer networks of thermosetting and thermoplastic polyimides. On the basis of lifetime measurements, it is concluded that free volumes are a direct reflection of physical/electromagnetic properties of the host polymers.

Electrokinetic pump

DOEpatents

Hencken, Kenneth R.; Sartor, George B.

2004-08-03

An electrokinetic pump in which the porous dielectric medium of conventional electrokinetic pumps is replaced by a patterned microstructure. The patterned microstructure is fabricated by lithographic patterning and etching of a substrate and is formed by features arranged so as to create an array of microchannels. The microchannels have dimensions on the order of the pore spacing in a conventional porous dielectric medium. Embedded unitary electrodes are vapor deposited on either end of the channel structure to provide the electric field necessary for electroosmotic flow.

Multi-Scale Microstructure and Mechanical Properties of High Carbon Eutectic Tantalum Carbide Reinforced with Carbon Nanotubes

DTIC Science & Technology

2012-07-02

more effective grain growth inhibitors. Transverse Rupture Strength of TaC reinforced with shorter CNTs displayed highest strength/density ratio with...microstructural features. 6. Strength to density ratio of CNT reinforced TaC increased from 17 to 28, which is an increase of ~ 65%. 7. Oxidation behavior of... reinforced with carbon fibers for space applications [15,16]. In recent years, Spark Plasma Sintering (SPS) also known as Electric Field Assisted Sintering

Applying neutron transmission physics and 3D statistical full-field model to understand 2D Bragg-edge imaging

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

Xie, Qingge; Song, Gian; Gorti, Sarma B.

Bragg-edge imaging, which is also known as neutron radiography, has recently emerged as a novel crystalline characterization technique. Modelling of this novel technique by incorporating various features of the underlying microstructure (including the crystallographic texture, the morphological texture, and the grain size) of the material remains a subject of considerable research and development. In this paper, Inconel 718 samples made by additive manufacturing were investigated by neutron diffraction and neutron radiography techniques. The specimen features strong morphological and crystallographic textures and a highly heterogeneous microstructure. A 3D statistical full-field model is introduced by taking details of the microstructure into accountmore » to understand the experimental neutron radiography results. The Bragg-edge imaging and the total cross section were calculated based on the neutron transmission physics. A good match was obtained between the model predictions and experimental results at different incident beam angles with respect to the sample build direction. The current theoretical approach has the ability to incorporate 3D spatially resolved microstructural heterogeneity information and shows promise in understanding the 2D neutron radiography of bulk samples. With further development to incorporate the heterogeneity in lattice strain in the model, it can be used as a powerful tool in the future to better understand the neutron radiography data.« less

Applying neutron transmission physics and 3D statistical full-field model to understand 2D Bragg-edge imaging

DOE PAGES

Xie, Qingge; Song, Gian; Gorti, Sarma B.; ...

2018-02-21

Bragg-edge imaging, which is also known as neutron radiography, has recently emerged as a novel crystalline characterization technique. Modelling of this novel technique by incorporating various features of the underlying microstructure (including the crystallographic texture, the morphological texture, and the grain size) of the material remains a subject of considerable research and development. In this paper, Inconel 718 samples made by additive manufacturing were investigated by neutron diffraction and neutron radiography techniques. The specimen features strong morphological and crystallographic textures and a highly heterogeneous microstructure. A 3D statistical full-field model is introduced by taking details of the microstructure into accountmore » to understand the experimental neutron radiography results. The Bragg-edge imaging and the total cross section were calculated based on the neutron transmission physics. A good match was obtained between the model predictions and experimental results at different incident beam angles with respect to the sample build direction. The current theoretical approach has the ability to incorporate 3D spatially resolved microstructural heterogeneity information and shows promise in understanding the 2D neutron radiography of bulk samples. With further development to incorporate the heterogeneity in lattice strain in the model, it can be used as a powerful tool in the future to better understand the neutron radiography data.« less

Application of morphological synthesis for understanding electrode microstructure evolution as a function of applied charge/discharge cycles

DOE PAGES

Glazoff, Michael V.; Dufek, Eric J.; Shalashnikov, Egor V.

2016-09-15

Morphological analysis and synthesis operations were employed for analysis of electrode microstructure transformations and evolution accompanying the application of charge/discharge cycles to electrochemical storage systems (batteries). Using state-of-the-art morphological algorithms, it was possible to predict microstructure evolution in porous Si electrodes for Li-ion batteries with sufficient accuracy. Algorithms for image analyses (segmentation, feature extraction, and 3D-reconstructions using 2D-images) were also developed. Altogether, these techniques could be considered supplementary to phase-field mesoscopic approach to microstructure evolution that is based upon clear and definitive changes in the appearance of microstructure. However, unlike in phase-field, the governing equations for morphological approach are geometry-,more » not physics-based. Similar non-physics based approach to understanding different phenomena was attempted with the introduction of cellular automata. It is anticipated that morphological synthesis and analysis will represent a useful supplementary tool to phase-field and will render assistance to unraveling the underlying microstructure-property relationships. The paper contains data on electrochemical characterization of different electrode materials that was conducted in parallel to morphological study.« less

Molecular modeling of the microstructure evolution during carbon fiber processing

NASA Astrophysics Data System (ADS)

Desai, Saaketh; Li, Chunyu; Shen, Tongtong; Strachan, Alejandro

2017-12-01

The rational design of carbon fibers with desired properties requires quantitative relationships between the processing conditions, microstructure, and resulting properties. We developed a molecular model that combines kinetic Monte Carlo and molecular dynamics techniques to predict the microstructure evolution during the processes of carbonization and graphitization of polyacrylonitrile (PAN)-based carbon fibers. The model accurately predicts the cross-sectional microstructure of the fibers with the molecular structure of the stabilized PAN fibers and physics-based chemical reaction rates as the only inputs. The resulting structures exhibit key features observed in electron microcopy studies such as curved graphitic sheets and hairpin structures. In addition, computed X-ray diffraction patterns are in good agreement with experiments. We predict the transverse moduli of the resulting fibers between 1 GPa and 5 GPa, in good agreement with experimental results for high modulus fibers and slightly lower than those of high-strength fibers. The transverse modulus is governed by sliding between graphitic sheets, and the relatively low value for the predicted microstructures can be attributed to their perfect longitudinal texture. Finally, the simulations provide insight into the relationships between chemical kinetics and the final microstructure; we observe that high reaction rates result in porous structures with lower moduli.

Creating physically-based three-dimensional microstructures: Bridging phase-field and crystal plasticity models.

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

Lim, Hojun; Owen, Steven J.; Abdeljawad, Fadi F.

In order to better incorporate microstructures in continuum scale models, we use a novel finite element (FE) meshing technique to generate three-dimensional polycrystalline aggregates from a phase field grain growth model of grain microstructures. The proposed meshing technique creates hexahedral FE meshes that capture smooth interfaces between adjacent grains. Three dimensional realizations of grain microstructures from the phase field model are used in crystal plasticity-finite element (CP-FE) simulations of polycrystalline a -iron. We show that the interface conformal meshes significantly reduce artificial stress localizations in voxelated meshes that exhibit the so-called "wedding cake" interfaces. This framework provides a direct linkmore » between two mesoscale models - phase field and crystal plasticity - and for the first time allows mechanics simulations of polycrystalline materials using three-dimensional hexahedral finite element meshes with realistic topological features.« less

Silicon-containing polymer-derived ceramic nanocomposites (PDC-NCs): preparative approaches and properties.

PubMed

Ionescu, Emanuel; Kleebe, Hans-Joachim; Riedel, Ralf

2012-08-07

Composites consist by definition of at least two materials (Gibbsian phases) with rather different properties. They exhibit a heterogeneous microstructure and possess improved properties with respect to their components. Furthermore, the design of their microstructure allows for tailoring their overall properties. In the last decades, intense work was performed on the synthesis of nanocomposites, which have the feature that at least one of their components is nanoscaled. However, the microstructure-property relationship of nanocomposite materials is still a challenging topic. This tutorial review paper deals with a special class of nanocomposites, i.e. polymer-derived ceramic nanocomposites (PDC-NCs), which have been shown to be promising materials for various structural and functional applications. Within this context, different preparative approaches for PDC-NCs as well as some of their properties will be presented and discussed. Furthermore, recent results concerning the relationship between the nano/microstructure of PDC-NCs and their properties will be highlighted.

Additive manufacturing of metals: a brief review of the characteristic microstructures and properties of steels, Ti-6Al-4V and high-entropy alloys

PubMed Central

Gorsse, Stéphane; Hutchinson, Christopher; Gouné, Mohamed; Banerjee, Rajarshi

2017-01-01

Abstract We present a brief review of the microstructures and mechanical properties of selected metallic alloys processed by additive manufacturing (AM). Three different alloys, covering a large range of technology readiness levels, are selected to illustrate particular microstructural features developed by AM and clarify the engineering paradigm relating process–microstructure–property. With Ti-6Al-4V the emphasis is placed on the formation of metallurgical defects and microstructures induced by AM and their role on mechanical properties. The effects of the large in-built dislocation density, surface roughness and build atmosphere on mechanical and damage properties are discussed using steels. The impact of rapid solidification inherent to AM on phase selection is highlighted for high-entropy alloys. Using property maps, published mechanical properties of additive manufactured alloys are graphically summarized and compared to conventionally processed counterparts. PMID:28970868

A crystal plasticity-based study of the relationship between microstructure and ultra-high-cycle fatigue life in nickel titanium alloys

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

Moore, John A.; Frankel, Dana; Prasannavenkatesan, Rajesh

Nickel Titanium (NiTi) alloys are often used in biomedical devices where failure due to mechanical fatigue is common. For other alloy systems, computational models have proven an effective means of determining the relationship between microstructural features and fatigue life. This work will extend the subset of those models which were based on crystal plasticity to examine the relationship between microstructure and fatigue life in NiTi alloys. It will explore the interaction between a spherical inclusion and the material’s free surface along with several NiTi microstructures reconstructed from 3D imaging. This work will determine the distance at which the free surfacemore » interacts with an inclusion and the effect of applied strain of surface-inclusion interaction. The effects of inclusion-inclusion interaction, matrix voiding, and matrix strengthening are explored and ranked with regards to their influence on fatigue life.« less

A crystal plasticity-based study of the relationship between microstructure and ultra-high-cycle fatigue life in nickel titanium alloys

DOE PAGES

Moore, John A.; Frankel, Dana; Prasannavenkatesan, Rajesh; ...

2016-06-06

Nickel Titanium (NiTi) alloys are often used in biomedical devices where failure due to mechanical fatigue is common. For other alloy systems, computational models have proven an effective means of determining the relationship between microstructural features and fatigue life. This work will extend the subset of those models which were based on crystal plasticity to examine the relationship between microstructure and fatigue life in NiTi alloys. It will explore the interaction between a spherical inclusion and the material’s free surface along with several NiTi microstructures reconstructed from 3D imaging. This work will determine the distance at which the free surfacemore » interacts with an inclusion and the effect of applied strain of surface-inclusion interaction. The effects of inclusion-inclusion interaction, matrix voiding, and matrix strengthening are explored and ranked with regards to their influence on fatigue life.« less

Electromagnetic nondestructive evaluation of tempering process in AISI D2 tool steel

NASA Astrophysics Data System (ADS)

Kahrobaee, Saeed; Kashefi, Mehrdad

2015-05-01

The present paper investigates the potential of using eddy current technique as a reliable nondestructive tool to detect microstructural changes during the different stages of tempering treatment in AISI D2 tool steel. Five stages occur in tempering of the steel: precipitation of ɛ carbides, formation of cementite, retained austenite decomposition, secondary hardening effect and spheroidization of carbides. These stages were characterized by destructive methods, including dilatometry, differential scanning calorimetry, X-ray diffraction, scanning electron microscopic observations, and hardness measurements. The microstructural changes alter the electrical resistivity/magnetic saturation, which, in turn, influence the eddy current signals. Two EC parameters, induced voltage sensed by pickup coil and impedance point detected by excitation coil, were evaluated as a function of tempering temperature to characterize the microstructural features, nondestructively. The study revealed that a good correlation exists between the EC parameters and the microstructural changes.

Segmentation-free image processing and analysis of precipitate shapes in 2D and 3D

NASA Astrophysics Data System (ADS)

Bales, Ben; Pollock, Tresa; Petzold, Linda

2017-06-01

Segmentation based image analysis techniques are routinely employed for quantitative analysis of complex microstructures containing two or more phases. The primary advantage of these approaches is that spatial information on the distribution of phases is retained, enabling subjective judgements of the quality of the segmentation and subsequent analysis process. The downside is that computing micrograph segmentations with data from morphologically complex microstructures gathered with error-prone detectors is challenging and, if no special care is taken, the artifacts of the segmentation will make any subsequent analysis and conclusions uncertain. In this paper we demonstrate, using a two phase nickel-base superalloy microstructure as a model system, a new methodology for analysis of precipitate shapes using a segmentation-free approach based on the histogram of oriented gradients feature descriptor, a classic tool in image analysis. The benefits of this methodology for analysis of microstructure in two and three-dimensions are demonstrated.

The features of self-assembling organic bilayers important to the formation of anisotropic inorganic materials in microgravity conditions

NASA Technical Reports Server (NTRS)

Talham, Daniel R.; Adair, James H.

2005-01-01

Materials with directional properties are opening new horizons in a variety of applications including chemistry, electronics, and optics. Structural, optical, and electrical properties can be greatly augmented by the fabrication of composite materials with anisotropic microstructures or with anisotropic particles uniformly dispersed in an isotropic matrix. Examples include structural composites, magnetic and optical recording media, photographic film, certain metal and ceramic alloys, and display technologies including flat panel displays. The new applications and the need for model particles in scientific investigations are rapidly out-distancing the ability to synthesize anisotropic particles with specific chemistries and narrowly distributed physical characteristics (e.g. size distribution, shape, and aspect ratio).

Effect of Thermochemical Synthetic Conditions on the Structure and Dielectric Properties of Ga1.9Fe0.1O3 Compounds.

PubMed

Roy, Swadipta; Ramana, C V

2018-02-05

We report on the tunable and controlled dielectric properties of iron (Fe)-doped gallium oxide (Ga 2 O 3 ; Ga 1.9 Fe 0.1 O 3 , referred to as GFO) inorganic compounds. The GFO materials were synthesized using a standard high-temperature, solid-state chemical reaction method by varying the thermochemical processing conditions, namely, different calcination and sintering environments. Structural characterization by X-ray diffraction revealed that GFO compounds crystallize in the β-Ga 2 O 3 phase. The Fe doping has induced slight lattice strain in GFO, which is evident in structural analysis. The effect of the sintering temperature (T sint ), which was varied in the range of 900-1200 °C, is significant, as revealed by electron microscopy analysis. T sint influences the grain size and microstructure evolution, which, in turn, influences the dielectric and electrical properties of GFO compounds. The energy-dispersive X-ray spectrometry and mapping data demonstrate the uniform distribution of the elemental composition over the microstructure. The temperature- and frequency-dependent dielectric measurements indicate the characteristic features that are specifically due to Fe doping in Ga 2 O 3 . The spreading factor and relaxation time, calculated using Cole-Cole plots, are in the ranges of 0.65-0.76 and 10 -4 s, respectively. The results demonstrate that densification and control over the microstructure and properties of GFO can be achieved by optimizing T sint .

Investigation of the laser engineered net shaping process for nanostructured cermets

NASA Astrophysics Data System (ADS)

Xiong, Yuhong

Laser Engineered Net Shaping (LENSRTM) is a solid freeform fabrication (SFF) technology that combines high power laser deposition and powder metallurgy technologies. The LENSRTM technology has been used to fabricate a number of metallic alloys with improved physical and mechanical material properties. The successful application provides a motivation to also apply this method to fabricate non-metallic alloys, such as tungsten carbide-cobalt (WC-Co) cermets in a timely and easy way. However, reports on this topic are very limited. In this work, the LENSRTM technology was used to investigate its application to nanostructured WC-Co cermets, including processing conditions, microstructural evolution, thermal behavior, mechanical properties, and environmental and economic benefits. Details of the approaches are described as follows. A comprehensive analysis of the relationships between process parameters, microstructural evolution and mechanical properties was conducted through various analytical techniques. Effects of process parameters on sample profiles and microstructures were analyzed. Dissolution, shape change and coarsening of WC particles were investigated to study the mechanisms of microstructural evolution. The thermal features were correlated with the microstructure and mechanical properties. The special thermal behavior during this process and its relevant effects on the microstructure have been experimentally studied and numerically simulated. A high-speed digital camera was applied to study the temperature profile, temperature gradient and cooling rate in and near the molten pool. Numerical modeling was employed for 3D samples using finite element method with ADINA software for the first time. The validated modeling results were used to interpret microstructural evolution and thermal history. In order to fully evaluate the capability of the LENSRTM technology for the fabrication of cermets, material properties of WC-Co cermets produced by different powder metallurgy technologies were compared. In addition, another cermet system, nanostructured titanium/tungsten carbide-nickel ((Ti,W)C-Ni) powder, prepared using high-energy ball milling process, was also deposited by the LENSRTM technology. Because of the near net shape feature of the LENSRTM process, special emphasis was also placed on its potential environmental and economic benefits by applying life cycle assessment (LCA) and technical cost modeling (TCM). Comparisons were conducted between the conventional powder metallurgy processes and the LENSRTM process.

Processing, Microstructure, and Mechanical Properties of Interpenetrating Biomorphic Graphite/Copper Composites

NASA Astrophysics Data System (ADS)

Childers, Amanda Esther Sall

Composite properties can surpass those of the individual phases, allowing for the development of advanced, high-performance materials. Bio-inspired and naturally-derived materials have garnered attention as composite constituents due to their inherently efficient and complex structures. Wood-derived ceramics, produced by converting a wood precursor into a ceramic scaffold, can exhibit a wide range of microstructures depending on the wood species, including porosity, pore size and distribution, and connectivity. The focus of this work was to investigate the processing, microstructure, and properties of graphite/copper composites produced using wood-derived graphite scaffolds. Graphite/copper composites combine low specific gravity, high thermal conductivity, and tailorable thermal expansion properties, and due to the non-wetting behavior of copper to graphite, offer a unique system in which mechanically bonded interfaces in composites can be studied. Graphite scaffolds were produced from red oak, beech, and pine precursors using a catalytic pyrolyzation method, resulting in varying types of pore networks. Two infiltration methods were investigated to overcome challenges associated with non-wetting systems: copper electrodeposition and pressure-assisted melt infiltration. The phase distributions, constituent properties, interfacial characteristics, mechanical behavior, and load partitioning of these biomorphic graphite/copper composites were investigated, and were correlated to the wood species. The multi-domain feature sizes in the graphite scaffolds resulted in composites with copper relegated not only to the large, connected channels produced from the transport features in the wood, but also within the smaller, lower aspect ratio fibrous regions of the scaffold. Both features contributed to the mechanical behavior of the composites to varying degrees depending on the wood species. A multi-component predictive model also was developed and used to guide the additive-assisted electroplating of the graphitized scaffold, and helped illuminate the roles of plating additives in macro-sized channels. The model can be adapted for many material systems, sample geometries, and plating conditions to investigate the use of metal electrodeposition as a means of scaffold infiltration. Additionally, X-ray diffraction tomography was used to resolve position-dependent strain in a composite. The results of this nascent capability were discussed with respect to a two-component system under increasing uniaxial load, and compared to the results of conventional volume-averaged measurements.

A novel pit pattern identifies the precursor of colorectal cancer derived from sessile serrated adenoma.

PubMed

Kimura, Tomoaki; Yamamoto, Eiichiro; Yamano, Hiro-O; Suzuki, Hiromu; Kamimae, Seiko; Nojima, Masanori; Sawada, Takeshi; Ashida, Masami; Yoshikawa, Kenjiro; Takagi, Ryo; Kato, Ryusuke; Harada, Taku; Suzuki, Ryo; Maruyama, Reo; Kai, Masahiro; Imai, Kohzoh; Shinomura, Yasuhisa; Sugai, Tamotsu; Toyota, Minoru

2012-03-01

Sessile serrated adenomas (SSAs) are known to be precursors of sporadic colorectal cancers (CRCs) with microsatellite instability (MSI), and to be tightly associated with BRAF mutation and the CpG island methylator phenotype (CIMP). Consequently, colonoscopic identification of SSAs has important implications for preventing CRCs, but accurate endoscopic diagnosis is often difficult. Our aim was to clarify which endoscopic findings are specific to SSAs. The morphological, histological and molecular features of 261 specimens from 226 colorectal tumors were analyzed. Surface microstructures were analyzed using magnifying endoscopy. Mutation in BRAF and KRAS was examined by pyrosequencing. Methylation of p16, IGFBP7, MLH1 and MINT1, -2, -12 and -31 was analyzed using bisulfite pyrosequencing. Through retrospective analysis of a training set (n=145), we identified a novel surface microstructure, the Type II open-shape pit pattern (Type II-O), which was specific to SSAs with BRAF mutation and CIMP. Subsequent prospective analysis of an independent validation set (n=116) confirmed that the Type II-O pattern is highly predictive of SSAs (sensitivity, 65.5%; specificity, 97.3%). BRAF mutation and CIMP occurred with significant frequency in Type II-O-positive serrated lesions. Progression of SSAs to more advanced lesions was associated with further accumulation of aberrant DNA methylation and additional morphological changes, including the Type III, IV and V pit patterns. Our results suggest the Type II-O pit pattern is a useful hallmark of the premalignant stage of CRCs with MSI and CIMP, which could serve to improve the efficacy of colonoscopic surveillance.

Use of fractography and sectioning techniques to study fracture mechanisms

NASA Technical Reports Server (NTRS)

Van Stone, R. H.; Cox, T. B.

1976-01-01

Recent investigations of the effect of microstructure on the fracture mechanisms and fracture toughness of steels, aluminum alloys, and titanium alloys have used standard fractographic techniques and a sectioning technique on specimens plastically deformed to various strains up to fracture. The specimens are prepared metallographically for observation in both optical and electron beam instruments. This permits observations to be made about the fracture mechanism as it occurs in thick sections and helps remove speculation from the interpretation of fractographic features. This technique may be used in conjunction with other standard techniques such as extraction replicas and microprobe analyses. Care must be taken to make sure that the microstructural features which are observed to play a role in the fracture process using the sectioning technique can be identified with fractography.

Technical and economic advantages of making lead-acid battery grids by continuous electroforming

NASA Astrophysics Data System (ADS)

Warlimont, H.; Hofmann, T.

A new continuous electroforming process to manufacture lead grids for automotive and industrial lead-acid batteries has been developed. A galvanic cell comprising a drum cathode for electroforming and a subsequent series of galvanic cells which form a strip galvanizing line are operating in a single, fully continuous, automatic process. Virgin lead or lead scrap may be used as the anode material. The product is grid strip of any specified thickness and design which can be fed into existing strip-pasting equipment. The composition and microstructure of the grid material can be varied to provide increased corrosion resistance and increased paste adherence. A unique feature of the material is its inherent layered composite structure that allows optimization of the properties according to particular functional requirements. Thus, both the specific power and the specific energy of the battery can be increased by reducing weight. The material properties increase the calendar life of the battery by increasing the corrosion resistance of the grid, and increase the cycle-life of the battery by improved adherence of the positive active material. The technical and economic features and competitive advantages of this new technology and product are presented in quantitative terms.

A thermodynamic framework for the study of crystallization in polymers

NASA Astrophysics Data System (ADS)

Rao, I. J.; Rajagopal, K. R.

In this paper, we present a new thermodynamic framework within the context of continuum mechanics, to predict the behavior of crystallizing polymers. The constitutive models that are developed within this thermodynamic setting are able to describe the main features of the crystallization process. The model is capable of capturing the transition from a fluid like behavior to a solid like behavior in a rational manner without appealing to any adhoc transition criterion. The anisotropy of the crystalline phase is built into the model and the specific anisotropy of the crystalline phase depends on the deformation in the melt. These features are incorporated into a recent framework that associates different natural configurations and material symmetries with distinct microstructural features within the body that arise during the process under consideration. Specific models are generated by choosing particular forms for the internal energy, entropy and the rate of dissipation. Equations governing the evolution of the natural configurations and the rate of crystallization are obtained by maximizing the rate of dissipation, subject to appropriate constraints. The initiation criterion, marking the onset of crystallization, arises naturally in this setting in terms of the thermodynamic functions. The model generated within such a framework is used to simulate bi-axial extension of a polymer film that is undergoing crystallization. The predictions of the theory that has been proposed are consistent with the experimental results (see [28] and [7]).

Effects of Microstructure on CVN Impact Toughness in Thermomechanically Processed High Strength Microalloyed Steel

NASA Astrophysics Data System (ADS)

Jia, Tao; Zhou, Yanlei; Jia, Xiaoxiao; Wang, Zhaodong

2017-02-01

Investigation on the correlation between microstructure and CVN impact toughness is of practical importance for the microstructure design of high strength microalloyed steels. In this work, three steels with characteristic microstructures were produced by cooling path control, i.e., steel A with granular bainite (GB), steel B with polygonal ferrite (PF) and martensite-austenite (M-A) constituent, and steel C with the mixture of bainitic ferrite (BF), acicular ferrite (AF), and M-A constituent. Under the same alloy composition and controlled rolling, similar ductile-to-brittle transition temperatures were obtained for the three steels. Steel A achieved the highest upper shelf energy (USE), while large variation of impact absorbed energy has been observed in the ductile-to-brittle transition region. With apparently large-sized PF and M-A constituent, steel B shows the lowest USE and delamination phenomenon in the ductile-to-brittle transition region. Steel C exhibits an extended upper shelf region, intermediate USE, and the fastest decrease of impact absorbed energy in the ductile-to-brittle transition region. The detailed CVN impact behavior is studied and then linked to the microstructural features.

COLLABORATIVE RESEARCH AND DEVELOPMENT (CR&D) Delivery Order 0043: Deformation and Texture Development During Hot Working of Titanium

DTIC Science & Technology

2008-04-01

Hot Working of Titanium 5a. CONTRACT NUMBER F33615-03-D-5801-0043 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 61202F 6 . AUTHOR(S) A.A...micrographs and thus to correlate microstructural features and texture data [3- 6 ]. For instance, Germain, et al. [3, 4 ] linked local orientations...microstructures can be developed in alpha/beta titanium alloys by TMP [2- 4 ], namely, fully lamellar, fully equiaxed, and duplex (bi-modal). A mixture

A Coupled EBSD/EDS Method to Determine the Primary- and Secondary-Alpha Textures in Titanium Alloys With Duplex Microstructures (Preprint)

DTIC Science & Technology

2007-07-01

primary and secondary alpha in micrographs and thus to correlate microstructural features and texture data [3- 6 ]. For instance, Germain, et al. [3, 4 ...Following electropolishing , the sample was mounted 7/3/2007 6 on the tilting stage inside an XL30 field-emission-gun scanning-electron-microscope (FEG...AFRL-RX-WP-TP-2008-4338 A COUPLED EBSD/EDS METHOD TO DETERMINE THE PRIMARY–AND SECONDARY–ALPHA TEXTURES IN TITANIUM ALLOYS WITH DUPLEX

Compressing random microstructures via stochastic Wang tilings.

PubMed

Novák, Jan; Kučerová, Anna; Zeman, Jan

2012-10-01

This Rapid Communication presents a stochastic Wang tiling-based technique to compress or reconstruct disordered microstructures on the basis of given spatial statistics. Unlike the existing approaches based on a single unit cell, it utilizes a finite set of tiles assembled by a stochastic tiling algorithm, thereby allowing to accurately reproduce long-range orientation orders in a computationally efficient manner. Although the basic features of the method are demonstrated for a two-dimensional particulate suspension, the present framework is fully extensible to generic multidimensional media.

Microstructural Characterization of Polymers by Positron Lifetime Spectroscopy

NASA Technical Reports Server (NTRS)

Singh, Jag J.

1996-01-01

Positrons provide a versatile probe for monitoring microstructural features of molecular solids. In this paper, we report on positron lifetime measurements in two different types of polymers. The first group comprises polyacrylates processed on earth and in space. The second group includes fully-compatible and totally-incompatible Semi-Interpenetrating polymer networks of thermosetting and thermoplastic polyimides. On the basis of lifetime measurements, it is concluded that free volumes are a direct reflection of physical/electromagnetic properties of the host polymers.

Effects of Hofmeister salt series on gluten network formation: Part II. Anion series.

PubMed

Tuhumury, H C D; Small, D M; Day, L

2016-12-01

Different anion salts from the Hofmeister series were used to investigate their effects on gluten network formation. The effects of these anion salts on the mixing properties of the dough and the rheological and chemical properties of gluten samples extracted from the dough with these respective salts were compared. The aim of this work was to determine how different anion salts influence the formation of the gluten structure during dough mixing. It was found that the Hofmeister anion salts affected the gluten network formation by interacting directly with specific amino acid residues that resulted in changes in gluten protein composition, specifically the percentage of the unextractable polymeric protein fractions (%UPP). These changes consequently led to remarkable differences in the mixing profiles and microstructural features of the dough, small deformation rheological properties of the gluten and a strain hardening behaviour of both dough and gluten samples. Copyright © 2016 Elsevier Ltd. All rights reserved.

Periodically microstructured composite films made by electric- and magnetic-directed colloidal assembly

PubMed Central

Demirörs, Ahmet Faik; Courty, Diana; Libanori, Rafael; Studart, André R.

2016-01-01

Living organisms often combine soft and hard anisotropic building blocks to fabricate composite materials with complex microstructures and outstanding mechanical properties. An optimum design and assembly of the anisotropic components reinforces the material in specific directions and sites to best accommodate multidirectional external loads. Here, we fabricate composite films with periodic modulation of the soft–hard microstructure by simultaneously using electric and magnetic fields. We exploit forefront directed-assembly approaches to realize highly demanded material microstructural designs and showcase a unique example of how one can bridge colloidal sciences and composite technology to fabricate next-generation advanced structural materials. In the proof-of-concept experiments, electric fields are used to dictate the position of the anisotropic particles through dielectrophoresis, whereas a rotating magnetic field is used to control the orientation of the particles. By using such unprecedented control over the colloidal assembly process, we managed to fabricate ordered composite microstructures with up to 2.3-fold enhancement in wear resistance and unusual site-specific hardness that can be locally modulated by a factor of up to 2.5. PMID:27071113

Anisotropic and Hierarchical Porosity in Multifunctional Ceramics

NASA Astrophysics Data System (ADS)

Lichtner, Aaron Zev

The performance of multifunctional porous ceramics is often hindered by the seemingly contradictory effects of porosity on both mechanical and non-structural properties and yet a sufficient body of knowledge linking microstructure to these properties does not exist. Using a combination of tailored anisotropic and hierarchical materials, these disparate effects may be reconciled. In this project, a systematic investigation of the processing, characterization and properties of anisotropic and isotropic hierarchically porous ceramics was conducted. The system chosen was a composite ceramic intended as the cathode for a solid oxide fuel cell (SOFC). Comprehensive processing investigations led to the development of approaches to make hierarchical, anisotropic porous microstructures using directional freeze-casting of well dispersed slurries. The effect of all the important processing parameters was investigated. This resulted in an ability to tailor and control the important microstructural features including the scale of the microstructure, the macropore size and total porosity. Comparable isotropic porous ceramics were also processed using fugitive pore formers. A suite of characterization techniques including x-ray tomography and 3-D sectional scanning electron micrographs (FIB-SEM) was used to characterize and quantify the green and partially sintered microstructures. The effect of sintering temperature on the microstructure was quantified and discrete element simulations (DEM) were used to explain the experimental observations. Finally, the comprehensive mechanical properties, at room temperature, were investigated, experimentally and using DEM, for the different microstructures.

Mesoscale modeling of solute precipitation and radiation damage

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

Zhang, Yongfeng; Schwen, Daniel; Ke, Huibin

2015-09-01

This report summarizes the low length scale effort during FY 2014 in developing mesoscale capabilities for microstructure evolution in reactor pressure vessels. During operation, reactor pressure vessels are subject to hardening and embrittlement caused by irradiation-induced defect accumulation and irradiation-enhanced solute precipitation. Both defect production and solute precipitation start from the atomic scale, and manifest their eventual effects as degradation in engineering-scale properties. To predict the property degradation, multiscale modeling and simulation are needed to deal with the microstructure evolution, and to link the microstructure feature to material properties. In this report, the development of mesoscale capabilities for defect accumulationmore » and solute precipitation are summarized. Atomic-scale efforts that supply information for the mesoscale capabilities are also included.« less

Confocal arthroscopy-based patient-specific constitutive models of cartilaginous tissues - II: prediction of reaction force history of meniscal cartilage specimens.

PubMed

Taylor, Zeike A; Kirk, Thomas B; Miller, Karol

2007-10-01

The theoretical framework developed in a companion paper (Part I) is used to derive estimates of mechanical response of two meniscal cartilage specimens. The previously developed framework consisted of a constitutive model capable of incorporating confocal image-derived tissue microstructural data. In the present paper (Part II) fibre and matrix constitutive parameters are first estimated from mechanical testing of a batch of specimens similar to, but independent from those under consideration. Image analysis techniques which allow estimation of tissue microstructural parameters form confocal images are presented. The constitutive model and image-derived structural parameters are then used to predict the reaction force history of the two meniscal specimens subjected to partially confined compression. The predictions are made on the basis of the specimens' individual structural condition as assessed by confocal microscopy and involve no tuning of material parameters. Although the model does not reproduce all features of the experimental curves, as an unfitted estimate of mechanical response the prediction is quite accurate. In light of the obtained results it is judged that more general non-invasive estimation of tissue mechanical properties is possible using the developed framework.

Evaluating Kurtosis-based Diffusion MRI Tissue Models for White Matter with Fiber Ball Imaging

PubMed Central

Jensen, Jens H.; McKinnon, Emilie T.; Glenn, G. Russell; Helpern, Joseph A.

2018-01-01

In order to quantify well-defined microstructural properties of brain tissue from diffusion MRI (dMRI) data, tissue models are typically employed that relate biological features, such as cell morphology and cell membrane permeability, to the diffusion dynamics. A variety of such models have been proposed for white matter, and their validation is a topic of active interest. In this paper, three different tissue models are tested by comparing their predictions for a specific microstructural parameter to the value measured independently with a recently proposed dMRI method known as fiber ball imaging (FBI). The three tissue models are all constructed with the diffusion and kurtosis tensors, and they are hence compatible with diffusional kurtosis imaging (DKI). Nevertheless, the models differ significantly in their details and predictions. For voxels with fractional anisotropies (FA) exceeding 0.5, all three are reasonably consistent with FBI. However, for lower FA values, one of these, called the white matter tract integrity (WMTI) model, is found to be in much better accord with FBI than the other two, suggesting that the WMTI model has a broader range of applicability. PMID:28085211

A cross-shear deformation for optimizing the strength and ductility of AZ31 magnesium alloys

PubMed Central

Hamad, Kotiba; Ko, Young Gun

2016-01-01

Magnesium alloys have recently attracted great interest due their lightweight and high specific strength. However, because of their hexagonal close-packed structure, they have few active slip systems, resulting in poor ductility and high mechanical anisotropy at room temperature. In the present work, we used a cross-shear deformation imposed by a differential speed rolling (DSR) technique to improve the room temperature strength and ductility of AZ31 magnesium alloy sheets. To introduce the cross-shear deformation, the sheets were rotated 180° around their longitudinal axis between the adjacent passes of DSR. The sheets of the AZ31 alloy subjected to the cross-shear deformation showed a uniform fine microstructure (1.2 ± 0.1 μm) with weak basal textures. The fabricated sheets showed a simultaneous high ultimate tensile strength and elongation-to-failure, i.e., ~333 MPa and ~21%, respectively. These were explained based on the structural features evolved due to the cross-shear deformation by DSR. The high strength was attributed to the uniform fine microstructure, whereas the high ductility was explained based on the basal texture weakening. PMID:27406685

Hypoparathyroidism: clinical features, skeletal microstructure and parathyroid hormone replacement

PubMed Central

Rubin, Mishaela R.; Bilezikian, John P.

2013-01-01

Objective Hypoparathyroidism is a disorder in which parathyroid hormone is deficient in the circulation due most often to immunological destruction of the parathyroids or to their surgical removal. The objective of this work was to define the abnormalities in skeletal microstructure as well as to establish the potential efficacy of PTH(1-84) replacement in this disorder. Subjects and methods Standard histomorphometric and μCT analyses were performed on iliac crest bone biopsies obtained from patients with hypoparathyroidism. Participants were treated with PTH(1-84) for two years. Results Bone density was increased and skeletal features reflected the low turnover state with greater BV/TV, Tb. Wi and Ct. Wi as well as suppressed MS and BFR/BS as compared to controls. With PTH(1-84), bone turnover and bone mineral density increased in the lumbar spine. Requirements for calcium and vitamin D fell while serum and urinary calcium concentrations did not change. Conclusion Abnormal microstructure of the skeleton in hypoparathyroidism reflects the absence of PTH. Replacement therapy with PTH has the potential to correct these abnormalities as well as to reduce the requirements for calcium and vitamin D. PMID:20485912

The role of tissue microstructure and water exchange in biophysical modelling of diffusion in white matter.

PubMed

Nilsson, Markus; van Westen, Danielle; Ståhlberg, Freddy; Sundgren, Pia C; Lätt, Jimmy

2013-08-01

Biophysical models that describe the outcome of white matter diffusion MRI experiments have various degrees of complexity. While the simplest models assume equal-sized and parallel axons, more elaborate ones may include distributions of axon diameters and axonal orientation dispersions. These microstructural features can be inferred from diffusion-weighted signal attenuation curves by solving an inverse problem, validated in several Monte Carlo simulation studies. Model development has been paralleled by microscopy studies of the microstructure of excised and fixed nerves, confirming that axon diameter estimates from diffusion measurements agree with those from microscopy. However, results obtained in vivo are less conclusive. For example, the amount of slowly diffusing water is lower than expected, and the diffusion-encoded signal is apparently insensitive to diffusion time variations, contrary to what may be expected. Recent understandings of the resolution limit in diffusion MRI, the rate of water exchange, and the presence of microscopic axonal undulation and axonal orientation dispersions may, however, explain such apparent contradictions. Knowledge of the effects of biophysical mechanisms on water diffusion in tissue can be used to predict the outcome of diffusion tensor imaging (DTI) and of diffusion kurtosis imaging (DKI) studies. Alterations of DTI or DKI parameters found in studies of pathologies such as ischemic stroke can thus be compared with those predicted by modelling. Observations in agreement with the predictions strengthen the credibility of biophysical models; those in disagreement could provide clues of how to improve them. DKI is particularly suited for this purpose; it is performed using higher b-values than DTI, and thus carries more information about the tissue microstructure. The purpose of this review is to provide an update on the current understanding of how various properties of the tissue microstructure and the rate of water exchange between microenvironments are reflected in diffusion MRI measurements. We focus on the use of biophysical models for extracting tissue-specific parameters from data obtained with single PGSE sequences on clinical MRI scanners, but results obtained with animal MRI scanners are also considered. While modelling of white matter is the central theme, experiments on model systems that highlight important aspects of the biophysical models are also reviewed.

Interpersonal traits of psychopathy linked to reduced integrity of the uncinate fasciculus.

PubMed

Wolf, Richard C; Pujara, Maia S; Motzkin, Julian C; Newman, Joseph P; Kiehl, Kent A; Decety, Jean; Kosson, David S; Koenigs, Michael

2015-10-01

Psychopathy is a personality disorder characterized by callous lack of empathy, impulsive antisocial behavior, and criminal recidivism. Here, we performed the largest diffusion tensor imaging (DTI) study of incarcerated criminal offenders to date (N = 147) to determine whether psychopathy severity is linked to the microstructural integrity of major white matter tracts in the brain. Consistent with the results of previous studies in smaller samples, we found that psychopathy was associated with reduced fractional anisotropy in the right uncinate fasciculus (UF; the major white matter tract connecting ventral frontal and anterior temporal cortices). We found no such association in the left UF or in adjacent frontal or temporal white matter tracts. Moreover, the right UF finding was specifically related to the interpersonal features of psychopathy (glib superficial charm, grandiose sense of self-worth, pathological lying, manipulativeness), rather than the affective, antisocial, or lifestyle features. These results indicate a neural marker for this key dimension of psychopathic symptomatology. © 2015 Wiley Periodicals, Inc.

Interpersonal traits of psychopathy linked to reduced integrity of the uncinate fasciculus

PubMed Central

Wolf, Richard C.; Pujara, Maia S.; Motzkin, Julian C.; Newman, Joseph P.; Kiehl, Kent A.; Decety, Jean; Kosson, David S.; Koenigs, Michael

2015-01-01

Psychopathy is a personality disorder characterized by callous lack of empathy, impulsive antisocial behavior, and criminal recidivism. Here we performed the largest diffusion tensor imaging (DTI) study of incarcerated criminal offenders to date (N = 147) to determine whether psychopathy severity is linked to the microstructural integrity of major white matter tracts in the brain. Consistent with the results of previous studies in smaller samples, we found that psychopathy was associated with reduced fractional anisotropy in the right uncinate fasciculus (the major white matter tract connecting ventral frontal and anterior temporal cortices). We found no such association in the left uncinate fasciculus or in adjacent frontal or temporal white matter tracts. Moreover, the right uncinate fasciculus finding was specifically related to the interpersonal features of psychopathy (glib superficial charm, grandiose sense of self-worth, pathological lying, manipulativeness), rather than the affective, antisocial, or lifestyle features. These results indicate a neural marker for this key dimension of psychopathic symptomatology. PMID:26219745

Accurate reconstruction in digital holographic microscopy using Fresnel dual-tree complex wavelet transform

NASA Astrophysics Data System (ADS)

Zhang, Xiaolei; Zhang, Xiangchao; Yuan, He; Zhang, Hao; Xu, Min

2018-02-01

Digital holography is a promising measurement method in the fields of bio-medicine and micro-electronics. But the captured images of digital holography are severely polluted by the speckle noise because of optical scattering and diffraction. Via analyzing the properties of Fresnel diffraction and the topographies of micro-structures, a novel reconstruction method based on the dual-tree complex wavelet transform (DT-CWT) is proposed. This algorithm is shiftinvariant and capable of obtaining sparse representations for the diffracted signals of salient features, thus it is well suited for multiresolution processing of the interferometric holograms of directional morphologies. An explicit representation of orthogonal Fresnel DT-CWT bases and a specific filtering method are developed. This method can effectively remove the speckle noise without destroying the salient features. Finally, the proposed reconstruction method is compared with the conventional Fresnel diffraction integration and Fresnel wavelet transform with compressive sensing methods to validate its remarkable superiority on the aspects of topography reconstruction and speckle removal.

The continuing battle against defects in nickel-base superalloys

NASA Technical Reports Server (NTRS)

Dreshfield, R. L.

1986-01-01

In the six decades since the identification of age hardenable nickel-base superalloys their compositions and microstructures have changed markedly. Current alloys are tailored for specific applications. Thus their microstructures are defined for that application. This paper briefly reviews the evolution of superalloy microstructures and comments on the appearance and implications of microstructural defects in high performance superalloys. It is seen that new alloys and proceses have generated new types of defects. Thus as the industry continues to develop new alloys and processes it must remain vigilant toward the identification and control of new types of defects.

Detecting PHG frames in wireless capsule endoscopy video by integrating rough global dominate-color with fine local texture features

NASA Astrophysics Data System (ADS)

Liu, Xiaoqi; Wang, Chengliang; Bai, Jianying; Liao, Guobin

2018-02-01

Portal hypertensive gastropathy (PHG) is common in gastrointestinal (GI) diseases, and a severe stage of PHG (S-PHG) is a source of gastrointestinal active bleeding. Generally, the diagnosis of PHG is made visually during endoscopic examination; compared with traditional endoscopy, (wireless capsule endoscopy) WCE with noninvasive and painless is chosen as a prevalent tool for visual observation of PHG. However, accurate measurement of WCE images with PHG is a difficult task due to faint contrast and confusing variations in background gastric mucosal tissue for physicians. Therefore, this paper proposes a comprehensive methodology to automatically detect S-PHG images in WCE video to help physicians accurately diagnose S-PHG. Firstly, a rough dominatecolor-tone extraction approach is proposed for better describing global color distribution information of gastric mucosa. Secondly, a hybrid two-layer texture acquisition model is designed by integrating co-occurrence matrix into local binary pattern to depict complex and unique gastric mucosal microstructure local variation. Finally, features of mucosal color and microstructure texture are merged into linear support vector machine to accomplish this automatic classification task. Experiments were implemented on an annotated data set including 1,050 SPHG and 1,370 normal images collected from 36 real patients of different nationalities, ages and genders. By comparison with three traditional texture extraction methods, our method, combined with experimental results, performs best in detection of S-PHG images in WCE video: the maximum of accuracy, sensitivity and specificity reach 0.90, 0.92 and 0.92 respectively.

The ASMEx snow slab experiment: snow microwave radiative transfer (SMRT) model evaluation

NASA Astrophysics Data System (ADS)

Sandells, Melody; Löwe, Henning; Picard, Ghislain; Dumont, Marie; Essery, Richard; Floury, Nicolas; Kontu, Anna; Lemmetyinen, Juha; Maslanka, William; Mätzler, Christian; Morin, Samuel; Wiesmann, Andreas

2017-04-01

A major uncertainty in snow microwave modelling to date has been the treatment of the snow microstructure. Although observations of microstructural parameters such as the optical grain diameter, specific surface area and correlation length have improved drastically over the last few years, scale factors have been used to derive the parameters needed in microwave emission models from these observations. Previous work has shown that a major difference between electromagnetic models of scattering coefficients is due to the specific snow microstructure models used. The snow microwave radiative transfer model (SMRT) is a new model developed to advance understanding of the role of microstructure and isolate different assumptions in existing microwave models that collectively hinder interpretation of model intercomparison studies. SMRT is implemented in Python and is modular, thus allows switching between different representations in its various components. Here, the role of microstructure is examined with the Improved Born Approximation electromagnetic model. The model is evaluated against scattering and absorption coefficients derived from radiometer measurements of snow slabs taken as part of the Arctic Snow Microstructure Experiment (ASMEx), which took place in Sodankylä, Finland over two seasons. Microtomography observations of slab samples were used to determine parameters for five microstructure models: spherical, exponential, sticky hard sphere, Teubner-Strey and Gaussian random field. SMRT brightness temperature simulations are also compared with radiometric observations of the snow slabs over a reflector plate and an absorber substrate. Agreement between simulations and observations is generally good except for slabs that are highly anisotropic.

3D Representative Volume Element Reconstruction of Fiber Composites via Orientation Tensor and Substructure Features

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

Li, Yi; Chen, Wei; Xu, Hongyi

To provide a seamless integration of manufacturing processing simulation and fiber microstructure modeling, two new stochastic 3D microstructure reconstruction methods are proposed for two types of random fiber composites: random short fiber composites, and Sheet Molding Compounds (SMC) chopped fiber composites. A Random Sequential Adsorption (RSA) algorithm is first developed to embed statistical orientation information into 3D RVE reconstruction of random short fiber composites. For the SMC composites, an optimized Voronoi diagram based approach is developed for capturing the substructure features of SMC chopped fiber composites. The proposed methods are distinguished from other reconstruction works by providing a way ofmore » integrating statistical information (fiber orientation tensor) obtained from material processing simulation, as well as capturing the multiscale substructures of the SMC composites.« less

Computer Vision and Machine Learning for Autonomous Characterization of AM Powder Feedstocks

NASA Astrophysics Data System (ADS)

DeCost, Brian L.; Jain, Harshvardhan; Rollett, Anthony D.; Holm, Elizabeth A.

2017-03-01

By applying computer vision and machine learning methods, we develop a system to characterize powder feedstock materials for metal additive manufacturing (AM). Feature detection and description algorithms are applied to create a microstructural scale image representation that can be used to cluster, compare, and analyze powder micrographs. When applied to eight commercial feedstock powders, the system classifies powder images into the correct material systems with greater than 95% accuracy. The system also identifies both representative and atypical powder images. These results suggest the possibility of measuring variations in powders as a function of processing history, relating microstructural features of powders to properties relevant to their performance in AM processes, and defining objective material standards based on visual images. A significant advantage of the computer vision approach is that it is autonomous, objective, and repeatable.

Fatigue crack growth in an aluminum alloy-fractographic study

NASA Astrophysics Data System (ADS)

Salam, I.; Muhammad, W.; Ejaz, N.

2016-08-01

A two-fold approach was adopted to understand the fatigue crack growth process in an Aluminum alloy; fatigue crack growth test of samples and analysis of fractured surfaces. Fatigue crack growth tests were conducted on middle tension M(T) samples prepared from an Aluminum alloy cylinder. The tests were conducted under constant amplitude loading at R ratio 0.1. The stress applied was from 20,30 and 40 per cent of the yield stress of the material. The fatigue crack growth data was recorded. After fatigue testing, the samples were subjected to detailed scanning electron microscopic (SEM) analysis. The resulting fracture surfaces were subjected to qualitative and quantitative fractographic examinations. Quantitative fracture analysis included an estimation of crack growth rate (CGR) in different regions. The effect of the microstructural features on fatigue crack growth was examined. It was observed that in stage II (crack growth region), the failure mode changes from intergranular to transgranular as the stress level increases. In the region of intergranular failure the localized brittle failure was observed and fatigue striations are difficult to reveal. However, in the region of transgranular failure the crack path is independent of the microstructural features. In this region, localized ductile failure mode was observed and well defined fatigue striations were present in the wake of fatigue crack. The effect of interaction of growing fatigue crack with microstructural features was not substantial. The final fracture (stage III) was ductile in all the cases.

Synchrotron X-ray fluorescence spectroscopy of salts in natural sea ice

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

Obbard, Rachel W.; Lieb-Lappen, Ross M.; Nordick, Katherine V.

We describe the use of synchrotron-based X-ray fluorescence spectroscopy to examine the microstructural location of specific elements, primarily salts, in sea ice. This work was part of an investigation of the location of bromine in the sea ice-snowpack-blowing snow system, where it plays a part in the heterogeneous chemistry that contributes to tropospheric ozone depletion episodes. We analyzed samples at beamline 13-ID-E of the Advanced Photon Source at Argonne National Laboratory. Using an 18 keV incident energy beam, we produced elemental maps of salts for sea ice samples from the Ross Sea, Antarctica. The distribution of salts in sea icemore » depends on ice type. In our columnar ice samples, Br was located in parallel lines spaced roughly 0.5 mm apart, corresponding to the spacing of lamellae in the skeletal region during initial ice growth. The maps revealed concentrations of Br in linear features in samples from all but the topmost and bottommost depths. For those samples, the maps revealed rounded features. Calibration of the Br elemental maps showed bulk concentrations to be 5–10 g/m 3, with concentrations ten times larger in the linear features. Through comparison with horizontal thin sections, we could verify that these linear features were brine sheets or layers.« less

Synchrotron X-ray fluorescence spectroscopy of salts in natural sea ice

DOE PAGES

Obbard, Rachel W.; Lieb-Lappen, Ross M.; Nordick, Katherine V.; ...

2016-10-23

We describe the use of synchrotron-based X-ray fluorescence spectroscopy to examine the microstructural location of specific elements, primarily salts, in sea ice. This work was part of an investigation of the location of bromine in the sea ice-snowpack-blowing snow system, where it plays a part in the heterogeneous chemistry that contributes to tropospheric ozone depletion episodes. We analyzed samples at beamline 13-ID-E of the Advanced Photon Source at Argonne National Laboratory. Using an 18 keV incident energy beam, we produced elemental maps of salts for sea ice samples from the Ross Sea, Antarctica. The distribution of salts in sea icemore » depends on ice type. In our columnar ice samples, Br was located in parallel lines spaced roughly 0.5 mm apart, corresponding to the spacing of lamellae in the skeletal region during initial ice growth. The maps revealed concentrations of Br in linear features in samples from all but the topmost and bottommost depths. For those samples, the maps revealed rounded features. Calibration of the Br elemental maps showed bulk concentrations to be 5–10 g/m 3, with concentrations ten times larger in the linear features. Through comparison with horizontal thin sections, we could verify that these linear features were brine sheets or layers.« less

Formation of Foam-like Microstructural Carbon Material by Carbonization of Porous Coordination Polymers through a Ligand-Assisted Foaming Process.

PubMed

Kongpatpanich, Kanokwan; Horike, Satoshi; Fujiwara, Yu-Ichi; Ogiwara, Naoki; Nishihara, Hirotomo; Kitagawa, Susumu

2015-09-14

Porous carbon material with a foam-like microstructure has been synthesized by direct carbonization of porous coordination polymer (PCP). In situ generation of foaming agents by chemical reactions of ligands in PCP during carbonization provides a simple way to create lightweight carbon material with a foam-like microstructure. Among several substituents investigated, the nitro group has been shown to be the key to obtain the unique foam-like microstructure, which is due to the fast kinetics of gas evolution during carbonization. Foam-like microstructural carbon materials showed higher pore volume and specific capacitance compared to a microporous carbon. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Microstructural Effects on SCC Initiation PWR Primary Water Cold-Worked Alloy 600

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

Zhai, Ziqing; Toloczko, Mychailo B.; Bruemmer, Stephen M.

SCC initiation behavior of one mill annealed alloy 600 plate heat was investigated in simulated PWR primary water under constant load at yield stress with in-situ direct current potential drop (DCPD) monitoring for crack initiation. Twelve specimens were tested at similar cold work levels among which three showed much shorter SCC initiation times (<400 hrs) than the others (>1200 hrs). Post-test examinations revealed that these three specimens all feature an inhomogeneous microstructure where the primary crack always nucleated along the boundary of large elongated grains protruding normally into the gauge. In contrast, such microstructure was either not observed or didmore » not extend deep enough into the gauge in the other specimens exhibiting ~3-6X longer initiation times. In order to better understand the role of this microstructural inhomogeneity in SCC initiation, high-resolution microscopy was performed to compare carbide morphology and strain distribution between the long grains and normal grains, and their potential effects on SCC initiation are discussed in this paper.« less

Micropillar compression study of the influence of size and internal boundary on the strength of HT9 tempered martensitic steel

NASA Astrophysics Data System (ADS)

Lim, Sangyeob; Shin, Chansun; Heo, Jungwoo; Kim, Sangeun; Jin, Hyung-Ha; Kwon, Junhyun; Guim, Hwanuk; Jang, Dongchan

2018-05-01

HT9, a ferritic/martensitic steel, is a candidate structural material for next-generation advanced reactors. Its microstructure is a typical tempered martensite showing a hierarchical lath-block-and-packet structure. We investigate the specimen size effect and strengthening contribution of various microstructural boundaries manifested in the compression tests of micropillars with diameters ranging from 0.5 to 17 μm. It is observed that micropillars with diameters larger than 3 μm show uniform deformation and plastic flow curves comparable to the bulk flow curve. Localized deformation by a few pronounced slip bands occurs in micropillars with diameters smaller than 1 μm, and the yield strength is reduced. Careful examination of the sizes of the microstructural features and cross-sections of the micropillars shows that the block boundaries are the most effective strengthening boundaries in tempered martensitic microstructure. The bulk mechanical properties of HT9 can be evaluated from a micropillar with diameter as low as 3 μm.

Microstructural characterization in dissimilar friction stir welding between 304 stainless steel and st37 steel

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

Jafarzadegan, M.; State Key Laboratory of Advanced Welding Production Technology, School of Materials Science and Eng., Harbin Institute of Technology, P.O. Box: 150001, Harbin; Feng, A.H.

2012-12-15

In the present study, 3 mm-thick plates of 304 stainless steel and st37 steel were welded together by friction stir welding at a welding speed of 50 mm/min and tool rotational speed of 400 and 800 rpm. X-ray diffraction test was carried out to study the phases which might be formed in the welds. Metallographic examinations, and tensile and microhardness tests were used to analyze the microstructure and mechanical properties of the joint. Four different zones were found in the weld area except the base metals. In the stir zone of the 304 stainless steel, a refined grain structure withmore » some features of dynamic recrystallization was evidenced. A thermomechanically-affected zone was characterized on the 304 steel side with features of dynamic recovery. In the other side of the stir zone, the hot deformation of the st37 steel in the austenite region produced small austenite grains and these grains transformed to fine ferrite and pearlite and some products of displacive transformations such as Widmanstatten ferrite and martensite by cooling the material after friction stir welding. The heat-affected zone in the st37 steel side showed partially and fully refined microstructures like fusion welding processes. The recrystallization in the 304 steel and the transformations in the st37 steel enhanced the hardness of the weld area and therefore, improved the tensile properties of the joint. - Highlights: Black-Right-Pointing-Pointer FSW produced sound welds between st37 low carbon steel and 304 stainless steel. Black-Right-Pointing-Pointer The SZ of the st37 steel contained some products of allotropic transformation. Black-Right-Pointing-Pointer The material in the SZ of the 304 steel showed features of dynamic recrystallization. Black-Right-Pointing-Pointer The finer microstructure in the SZ increased the hardness and tensile strength.« less

Nonequilibrium Phase Chemistry in High Temperature Structure Alloys

NASA Technical Reports Server (NTRS)

Wang, R.

1991-01-01

Titanium and nickel aluminides of nonequilibrium microstructures and in thin gauge thickness were identified, characterized and produced for potential high temperature applications. A high rate sputter deposition technique for rapid surveillance of the microstructures and nonequilibrium phase is demonstrated. Alloys with specific compositions were synthesized with extended solid solutions, stable dispersoids, and specific phase boundaries associated with different heat treatments. Phase stability and mechanical behavior of these nonequilibrium alloys were investigated and compared.

Accelerated Microstructure Imaging via Convex Optimization (AMICO) from diffusion MRI data.

PubMed

Daducci, Alessandro; Canales-Rodríguez, Erick J; Zhang, Hui; Dyrby, Tim B; Alexander, Daniel C; Thiran, Jean-Philippe

2015-01-15

Microstructure imaging from diffusion magnetic resonance (MR) data represents an invaluable tool to study non-invasively the morphology of tissues and to provide a biological insight into their microstructural organization. In recent years, a variety of biophysical models have been proposed to associate particular patterns observed in the measured signal with specific microstructural properties of the neuronal tissue, such as axon diameter and fiber density. Despite very appealing results showing that the estimated microstructure indices agree very well with histological examinations, existing techniques require computationally very expensive non-linear procedures to fit the models to the data which, in practice, demand the use of powerful computer clusters for large-scale applications. In this work, we present a general framework for Accelerated Microstructure Imaging via Convex Optimization (AMICO) and show how to re-formulate this class of techniques as convenient linear systems which, then, can be efficiently solved using very fast algorithms. We demonstrate this linearization of the fitting problem for two specific models, i.e. ActiveAx and NODDI, providing a very attractive alternative for parameter estimation in those techniques; however, the AMICO framework is general and flexible enough to work also for the wider space of microstructure imaging methods. Results demonstrate that AMICO represents an effective means to accelerate the fit of existing techniques drastically (up to four orders of magnitude faster) while preserving accuracy and precision in the estimated model parameters (correlation above 0.9). We believe that the availability of such ultrafast algorithms will help to accelerate the spread of microstructure imaging to larger cohorts of patients and to study a wider spectrum of neurological disorders. Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.

Large area ultraviolet photodetector on surface modified Si:GaN layers

NASA Astrophysics Data System (ADS)

Anitha, R.; R., Ramesh; Loganathan, R.; Vavilapalli, Durga Sankar; Baskar, K.; Singh, Shubra

2018-03-01

Unique features of semiconductor based heterostructured photoelectric devices have drawn considerable attention in the recent past. In the present work, large area UV photodetector has been fabricated utilizing interesting Zinc oxide microstructures on etched Si:GaN layers. The surface of Si:GaN layer grown by metal organic chemical vapor deposition method on sapphire has been modified by chemical etching to control the microstructure. The photodetector exhibits response to Ultraviolet light only. Optimum etching of Si:GaN was required to exhibit higher responsivity (0.96 A/W) and detectivity (∼4.87 × 109 Jones), the two important parameters for a photodetector. Present method offers a tunable functionality of photodetector through modification of top layer microstructure. A comparison with state of art materials has also been presented.

Liquid Phase Miscibility Gap Materials

NASA Technical Reports Server (NTRS)

Gelles, S. H.; Markworth, A. J.

1985-01-01

The manner in which the microstructural features of liquid-phase miscibility gap alloys develop was determined. This will allow control of the microstructures and the resultant properties of these alloys. The long-duration low gravity afforded by the shuttle will allow experiments supporting this research to be conducted with minimal interference from buoyancy effects and gravitationally driven convection currents. Ground base studies were conducted on Al-In, Cu-Pb, and Te-Tl alloys to determine the effect of cooling rate, composition, and interfacial energies on the phase separation and solidification processes that influence the development of microstructure in these alloys. Isothermal and directional cooling experiments and simulations are conducted. The ground based activities are used as a technological base from which flight experiments formulated and to which these flight experiments are compared.

Microstructure characterisation of Ti-6Al-4V from different additive manufacturing processes

NASA Astrophysics Data System (ADS)

Neikter, M.; Åkerfeldt, P.; Pederson, R.; Antti, M.-L.

2017-10-01

The focus of this work has been microstructure characterisation of Ti-6Al-4V manufactured by five different additive manufacturing (AM) processes. The microstructure features being characterised are the prior β size, grain boundary α and α lath thickness. It was found that material manufactured with powder bed fusion processes has smaller prior β grains than the material from directed energy deposition processes. The AM processes with fast cooling rate render in thinner α laths and also thinner, and in some cases discontinuous, grain boundary α. Furthermore, it has been observed that material manufactured with the directed energy deposition processes has parallel bands, except for one condition when the parameters were changed, while the powder bed fusion processes do not have any parallel bands.

High resolution projection micro stereolithography system and method

DOEpatents

Spadaccini, Christopher M.; Farquar, George; Weisgraber, Todd; Gemberling, Steven; Fang, Nicholas; Xu, Jun; Alonso, Matthew; Lee, Howon

2016-11-15

A high-resolution P.mu.SL system and method incorporating one or more of the following features with a standard P.mu.SL system using a SLM projected digital image to form components in a stereolithographic bath: a far-field superlens for producing sub-diffraction-limited features, multiple spatial light modulators (SLM) to generate spatially-controlled three-dimensional interference holograms with nanoscale features, and the integration of microfluidic components into the resin bath of a P.mu.SL system to fabricate microstructures of different materials.

Creep deformation in near-γ TiAl: Part 1. the influence of microstructure on creep deformation in Ti-49Al-1V

NASA Astrophysics Data System (ADS)

Worth, Brian D.; Jones, J. Wayne; Allison, John E.

1995-11-01

The influence of microstructure on creep deformation was examined in the near-y TiAl alloy Ti-49A1-1V. Specifically, microstructures with varying volume fractions of lamellar constituent were produced through thermomechanical processing. Creep studies were conducted on these various microstructures under constant load in air at temperatures between 760 °C and 870 °C and at stresses ranging from 50 to 200 MPa. Microstructure significantly influences the creep behavior of this alloy, with a fully lamellar microstructure yielding the highest creep resistance of the microstructures examined. Creep resistance is dependent on the volume fraction of lamellar constituent, with the lowest creep resistance observed at intermediate lamellar volume fractions. Examination of the creep deformation structure revealed planar slip of dislocations in the equiaxed y microstructure, while subboundary formation was observed in the duplex microstructure. The decrease in creep resistance of the duplex microstructure, compared with the equiaxed y microstructure, is attributed to an increase in dislocation mobility within the equiaxed y constituent, that results from partitioning of oxygen from the γ phase to the α2 phase. Dislocation motion in the fully lamellar microstructure was confined to the individual lamellae, with no evidence of shearing of γ/γ or γ/α2 interfaces. This suggests that the high creep resistance of the fully lamellar microstructure is a result of the fine spacing of the lamellar structure, which results in a decreased effective slip length for dislocation motion over that found in the duplex and equiaxed y microstructures.

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

Laguna, O.; Collar, E.P.; Taranco, J.

Observations are made about microstructural aspects from HDPE and LDPE homopolymers and their blends as virgin materials and also from urban plastic wastes. Micrographs were taken by SEM. Micrographs corresponding to the fracture surface from specimens tested in an impact test clearly show different microstructural features due to polymer which is more than 50%. Parts were injection molded. A discussion is given about crystallization behavior of those materials obtained by DSC. For all blends the same results have been found, i.e., two peaks owing to each of the two polymers which are present in the blends.

Biomimetic Materials by Freeze Casting

NASA Astrophysics Data System (ADS)

Porter, Michael M.; Mckittrick, Joanna; Meyers, Marc A.

2013-06-01

Natural materials, such as bone and abalone nacre, exhibit exceptional mechanical properties, a product of their intricate microstructural organization. Freeze casting is a relatively simple, inexpensive, and adaptable materials processing method to form porous ceramic scaffolds with controllable microstructural features. After infiltration of a second polymeric phase, hybrid ceramic-polymer composites can be fabricated that closely resemble the architecture and mechanical performance of natural bone and nacre. Inspired by the narwhal tusk, magnetic fields applied during freeze casting can be used to further control architectural alignment, resulting in freeze-cast materials with enhanced mechanical properties.

Highly birefringent polymer microstructured optical fibers embedded in composite materials

NASA Astrophysics Data System (ADS)

Lesiak, P.; SzelÄ g, M.; Kuczkowski, M.; Domański, A. W.; Woliński, T. R.

2013-05-01

Composite structures are made from two or more constituent materials with significantly different physical or chemical properties and they remain separate and distinct in a macroscopic level within the finished structure. This feature allows for introducing highly birefringent polymer microstructured optical fibers into the composite material. These new fibers can consist of only two polymer materials (PMMA and PC) with similar value of the Young modulus as the composite material so any stresses induced in the composite material can be easily measured by the proposed embedded fiber optic sensors.

The use of cold sprayed alloys for metallic stents

NASA Astrophysics Data System (ADS)

AL-Mangour, Bandar

With the invention of the coronary stent, which is a wire metal mesh tube designed to keep the arteries open in the treatment of heart diseases, promising clinical outcomes were generated. However, the long term successes of stents have been delayed by significant in-stent restenosis (blockages) and stent fracture. In this research work, it has been proposed to use Cold Gas Dynamic Spraying (CGDS) coating material as an alternative choice to manufacture metallic stent. In CGDS, fine particles are accelerated to a high velocity and undergo solid-state plastic deformation upon impact on the substrate, which leads to particle-particle bonding. The feature of CGDS distinct from other thermal spray techniques is that the processing gas temperature is below the melting point of the feedstock. Therefore, unwanted effects of high temperatures, such as oxidation, grain growth and thermal stresses, are absent. In response to the fact that the majority of stents are made from stainless steel (316L) or Co-Cr alloy (L605), this study specifically addresses the development and characterization of 316L and 316L mixed with L605 coatings produced by the CGDS process. Scanning electron microscopy and electron backscatter diffraction were used to investigate the microstructural changes of these coatings before and after annealing. The effect of gas type on the microstructure of 316L coatings and the role of post-heat treatment in the microstructure and properties are also studied. Of particular interest are grain refinement, heat treatment, mechanical properties and corrosion behavior of the cold sprayed material.

Microstructure Evolution and Composition Control During the Processing of Thin-Gage Metallic Foil

NASA Astrophysics Data System (ADS)

Semiatin, S. L.; Gross, M. E.; Matson, D. W.; Bennett, W. D.; Bonham, C. C.; Ustinov, A. I.; Ballard, D. L.

2012-12-01

The manufacture of thin-gage superalloy and gamma-titanium-aluminide foil products via near-conventional thermomechanical processing and two different vapor-deposition methods was investigated. Thermomechanical processing was based on hot-pack rolling of plate and sheet. Foils of the superalloy LSHR and the near-gamma titanium aluminide Ti-45.5Al-2Cr-2Nb made by this approach exhibited excellent gage control and fine two-phase microstructures. The vapor-phase techniques used magnetron sputtering (MS) of a target of the desired product composition or electron-beam physical vapor deposition (EBPVD) of separate targets of the specific alloying elements. Thin deposits of LSHR and Ti-48Al-2Cr-2Nb made by MS showed uniform thickness/composition and an ultrafine microstructure. However, systematic deviations from the specific target composition were found. During subsequent heat treatment, the microstructure of the MS samples showed various degrees of grain growth and coarsening. Foils of Ti-43Al and Ti-51Al-1V fabricated by EBPVD were fully dense. The microstructures developed during EBPVD were interpreted in terms of measured phase equilibria and the dependence of evaporant flux on temperature.

Reducing the orientation influence of Mueller matrix measurements for anisotropic scattering media

NASA Astrophysics Data System (ADS)

Sun, Minghao; He, Honghui; Zeng, Nan; Du, E.; He, Yonghong; Ma, Hui

2014-09-01

Mueller matrix polarimetry techniques contain rich micro-structural information of samples, such as the sizes and refractive indices of scatterers. Recently, Mueller matrix imaging methods have shown great potentials as powerful tools for biomedical diagnosis. However, the orientations of anisotropic fibrous structures in tissues have prominent influence on Mueller matrix measurements, resulting in difficulties for extracting micro-structural information effectively. In this paper, we apply the backscattering Mueller matrix imaging technique to biological samples with different microstructures, such as chicken heart muscle, bovine skeletal muscle, porcine liver and fat tissues. Experimental results show that the directions of the muscle fibers have prominent influence on the Mueller matrix elements. In order to reduce the orientation influence, we adopt the rotation-independent MMT and RLPI parameters, which were proposed in our previous studies, to the tissue samples. Preliminary results in this paper show that the orientation-independent parameters and their statistic features are helpful for analyzing the tissues to obtain their micro-structural properties. Since the micro-structure variations are often related to the pathological changes, the method can be applied to microscope imaging techniques and used to detect abnormal tissues such as cancer and other lesions for diagnosis purposes.

Imaging of Scleral Collagen Deformation Using Combined Confocal Raman Microspectroscopy and Polarized Light Microscopy Techniques.

PubMed

Chakraborty, Nilay; Wang, Mian; Solocinski, Jason; Kim, Wonsuk; Argento, Alan

2016-01-01

This work presents an optospectroscopic characterization technique for soft tissue microstructure using site-matched confocal Raman microspectroscopy and polarized light microscopy. Using the technique, the microstructure of soft tissue samples is directly observed by polarized light microscopy during loading while spatially correlated spectroscopic information is extracted from the same plane, verifying the orientation and arrangement of the collagen fibers. Results show the response and orientation of the collagen fiber arrangement in its native state as well as during tensile and compressive loadings in a porcine sclera model. An example is also given showing how the data can be used with a finite element program to estimate the strain in individual collagen fibers. The measurements demonstrate features that indicate microstructural reorganization and damage of the sclera's collagen fiber arrangement under loading. The site-matched confocal Raman microspectroscopic characterization of the tissue provides a qualitative measure to relate the change in fibrillar arrangement with possible chemical damage to the collagen microstructure. Tests and analyses presented here can potentially be used to determine the stress-strain behavior, and fiber reorganization of the collagen microstructure in soft tissue during viscoelastic response.

Effect of milling time on microstructure and mechanical properties of Cu-Ni-graphite composites

NASA Astrophysics Data System (ADS)

Wang, Yiran; Gao, Yimin; Li, Yefei; Zhang, Chao; Huang, Xiaoyu; Zhai, Wenyan

2017-09-01

Cu-Ni-graphite composites are intended for application in switch slide baseplate materials. The microstructure of the composites depends strongly on the ball milling time, and a suitable time can significantly improve the properties of the Cu-Ni-graphite composites. In this study, a two-step milling method was employed. The morphology evolution and microstructural features of the powder was characterized at different milling times. Afterwards, the Cu-Ni-graphite composites were prepared in the process of cold pressing, sintering, re-pressing and re-sintering as a function of the different milling times. Finally, both the microstructure and mechanical properties of the Cu-Ni-graphite composites are discussed. The results show that no new phase was generated during the milling process. The morphology evolution of the mixture of Cu/Ni powder changed from spherical-like to cubic-like, plate-like and flake-like with an increasing milling time. The microstructure of the composites consisted of α-phase and graphite. The boundary area and quantity of pores changed as the milling time increased. The relative density, hardness and flexural strength reached maximum values at 15 h of milling time.

Altered Sputum Microstructure as a Marker of Airway Obstruction in Cystic Fibrosis Patients

NASA Astrophysics Data System (ADS)

Duncan, Gregg; Jung, James; West, Natalie; Boyle, Michael; Suk, Jung Soo; Hanes, Justin

In the lungs of cystic fibrosis (CF) patients, highly viscoelastic mucus remains stagnant in the lung leading to obstructed airways prone to recurrent infections. Bulk-fluid rheological measurement is primarily used to assess the pathological features of mucus. However, this approach is limited in detecting microscopic properties on the length scale of pathogens and immune cells. We have shown in prior work based on the transport of muco-inert nanoparticles (MIP) in CF sputum that patients can carry significantly different microstructural properties. In this study, we aimed to determine the factors leading to variations between patients in sputum microstructure and their clinical implications. The microrheological properties of CF sputum were measured using multi-particle tracking experiments of MIP. MIP were made by grafting polyethylene glycol onto the surface of polystyrene nanoparticles which prior work has shown prevents adhesion to CF sputum. Biochemical analyses show that sputum microstructure was significantly altered by elevated mucin and DNA content. Reduction in sputum pore size is characteristic of patients with obstructed airways as indicated by measured pulmonary function tests. Our microstructural read-out may serve as a novel biomarker for CF.

Microstructural characterization of pressed HMX material sets at differing densities

NASA Astrophysics Data System (ADS)

Molek, C. D.; Welle, E. J.; Wixom, R. R.; Ritchey, M. B.; Samuels, P.; Horie, Y.

2017-01-01

The detonation physics community has embraced the idea that initiation of high explosives (HE) proceeds from an ignition event through subsequent growth to steady detonation. A weakness of all the commonly used ignition and growth models is the microstructural characteristics of the HE are not explicitly incorporated in their ignition and growth terms. This is the case in spite of a demonstrated, but not well-understood, empirical link between particle morphology and initiation of HE. Morphological effects have been parametrically studied in many ways, the majority of efforts focus on establishing a tie between bulk powder metrics and initiation of the pressed beds. More recently, there has been a shift toward characterizing the microstructure of pressed beds in order to understand the underlying mechanisms governing initiation behavior. In this work, we have characterized the microstructures of two HMX classes pressed at three densities using ion bombardment techniques. We find more significant compaction associated with the larger crystalline material - Class 3 - than the smaller fluid energy milled material. The Class 3 material exhibits evidence of crystal cracking. Finally, we discuss this evidence and our attempt to correlate microstructural features to observed changes in continuum level initiation behavior.

Quantification of diagenetic overprint processes deduced from fossil carbonate shells and laboratory-based hydrothermal alteration experiments

NASA Astrophysics Data System (ADS)

Griesshaber, Erika; Casella, Laura; Mavromatis, Vasileios; Dietzel, Martin; Immenhauser, Adrian; Schmahl, Wolfgang

2016-04-01

Benthic and nektonic marine biogenic carbonate archives represent the foundation of numerous studies aiming at reconstructions of past climate dynamics and environmental change. However, living organisms are not in thermodynamic equilibrium and create local chemical environments where physiologic processes such as biomineralization takes place. After the death of the organism the former physiologic disequilibrium conditions are not sustained any more and all biological tissues are altered by equilibration according to the surrounding environment: diagenesis. With increasing diagenetic alteration, the biogenic structure and fingerprint fades away and is replaced by inorganic features. Thus, recrystallization of organism-specific microstructure is a clear indicator for diagenetic overprint. Microstructural data, which mirror recrystallization, are of great value for interpreting geochemical proxies for paleo-environment reconstruction. Despite more than a century of research dealing with carbonate diagenesis, many of the controlling processes and factors are only understood in a qualitative manner. One of the main issues is that diagenetically altered carbonates are usually present as the product of a complex preceding diagenetic pathway with an unknown number of intermediate steps. In this contribution we present and discuss laboratory based alteration experiments with the aim to investigate time-series data sets in a controlled manner. We conducted hydrothermal alteration experiments with modern Arctica islandica (bivalvia) and Notosaria nigricans (brachiopoda) in order to mimic diagenetic overprint. We explore first the potential of electron backscattered diffraction (EBSD) measurements together with statistical data evaluation as a tool to quantify diagenetic alteration of carbonate skeletons. Subsequently, we compare microstructural patterns obtained from experimentally altered shell material with those of fossil specimens that have undergone variable degrees of diagenetic overprint. We intend to come up with a process-oriented understanding of alteration parameters and products as the change in microstructure, texture and mineral phase needs a careful action when it comes to the interpretation of paleoclimate reconstruction data.

Radiopaque Resists for Two-Photon Lithography To Enable Submicron 3D Imaging of Polymer Parts via X-ray Computed Tomography

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

Saha, Sourabh K.; Oakdale, James S.; Cuadra, Jefferson A.

Two-photon lithography (TPL) is a high-resolution additive manufacturing (AM) technique capable of producing arbitrarily complex three-dimensional (3D) microstructures with features 2–3 orders of magnitude finer than human hair. This process finds numerous applications as a direct route toward the fabrication of novel optical and mechanical metamaterials, miniaturized optics, microfluidics, biological scaffolds, and various other intricate 3D parts. As TPL matures, metrology and inspection become a crucial step in the manufacturing process to ensure that the geometric form of the end product meets design specifications. X-ray-based computed tomography (CT) is a nondestructive technique that can provide this inspection capability for themore » evaluation of complex internal 3D structure. However, polymeric photoresists commonly used for TPL, as well as other forms of stereolithography, poorly attenuate X-rays due to the low atomic number (Z) of their constituent elements and therefore appear relatively transparent during imaging. We present the development of optically clear yet radiopaque photoresists for enhanced contrast under X-ray CT. We have synthesized iodinated acrylate monomers to formulate high-Z photoresist materials that are capable of forming 3D microstructures with sub-150 nm features. In addition, we have developed a formulation protocol to match the refractive index of the photoresists to the immersion medium of the objective lens so as to enable dip-in laser lithography, a direct laser writing technique for producing millimeter-tall structures. Our radiopaque photopolymer then resists increase X-ray attenuation by a factor of more than 10 times without sacrificing the sub-150 nm feature resolution or the millimeter-scale part height. Thus, our resists can successfully replace existing photopolymers to generate AM parts that are suitable for inspection via X-ray CT. By providing the “feedstock” for radiopaque AM parts, our resist formulation is expected to play a critical role in enabling fabrication of functional polymer parts to tight design tolerances.« less

Radiopaque Resists for Two-Photon Lithography To Enable Submicron 3D Imaging of Polymer Parts via X-ray Computed Tomography

DOE PAGES

Saha, Sourabh K.; Oakdale, James S.; Cuadra, Jefferson A.; ...

2017-11-24

Two-photon lithography (TPL) is a high-resolution additive manufacturing (AM) technique capable of producing arbitrarily complex three-dimensional (3D) microstructures with features 2–3 orders of magnitude finer than human hair. This process finds numerous applications as a direct route toward the fabrication of novel optical and mechanical metamaterials, miniaturized optics, microfluidics, biological scaffolds, and various other intricate 3D parts. As TPL matures, metrology and inspection become a crucial step in the manufacturing process to ensure that the geometric form of the end product meets design specifications. X-ray-based computed tomography (CT) is a nondestructive technique that can provide this inspection capability for themore » evaluation of complex internal 3D structure. However, polymeric photoresists commonly used for TPL, as well as other forms of stereolithography, poorly attenuate X-rays due to the low atomic number (Z) of their constituent elements and therefore appear relatively transparent during imaging. We present the development of optically clear yet radiopaque photoresists for enhanced contrast under X-ray CT. We have synthesized iodinated acrylate monomers to formulate high-Z photoresist materials that are capable of forming 3D microstructures with sub-150 nm features. In addition, we have developed a formulation protocol to match the refractive index of the photoresists to the immersion medium of the objective lens so as to enable dip-in laser lithography, a direct laser writing technique for producing millimeter-tall structures. Our radiopaque photopolymer then resists increase X-ray attenuation by a factor of more than 10 times without sacrificing the sub-150 nm feature resolution or the millimeter-scale part height. Thus, our resists can successfully replace existing photopolymers to generate AM parts that are suitable for inspection via X-ray CT. By providing the “feedstock” for radiopaque AM parts, our resist formulation is expected to play a critical role in enabling fabrication of functional polymer parts to tight design tolerances.« less

Effect of food microstructure on growth dynamics of Listeria monocytogenes in fish-based model systems.

PubMed

Verheyen, Davy; Bolívar, Araceli; Pérez-Rodríguez, Fernando; Baka, Maria; Skåra, Torstein; Van Impe, Jan F

2018-06-01

Traditionally, predictive growth models for food pathogens are developed based on experiments in broth media, resulting in models which do not incorporate the influence of food microstructure. The use of model systems with various microstructures is a promising concept to get more insight into the influence of food microstructure on microbial dynamics. By means of minimal variation of compositional and physicochemical factors, these model systems can be used to study the isolated effect of certain microstructural aspects on microbial growth, survival and inactivation. In this study, the isolated effect on microbial growth dynamics of Listeria monocytogenes of two food microstructural aspects and one aspect influenced by food microstructure were investigated, i.e., the nature of the food matrix, the presence of fat droplets, and microorganism growth morphology, respectively. To this extent, fish-based model systems with various microstructures were used, i.e., a liquid, a second more viscous liquid system containing xanthan gum, an emulsion, an aqueous gel, and a gelled emulsion. Growth experiments were conducted at 4 and 10 °C, both using homogeneous and surface inoculation (only for the gelled systems). Results regarding the influence of the growth morphology indicated that the lag phase of planktonic cells in the liquid system was similar to the lag phase of submerged colonies in the xanthan system. The lag phase of submerged colonies in each gelled system was considerably longer than the lag phase of surface colonies on these respective systems. The maximum specific growth rate of planktonic cells in the liquid system was significantly lower than for submerged colonies in the xanthan system at 10 °C, while no significant differences were observed at 4 °C. The maximum cell density was higher for submerged colonies than for surface colonies. The nature of the food matrix only exerted an influence on the maximum specific growth rate, which was significantly higher in the viscous systems than in the gelled systems. The presence of a small amount of fat droplets improved the growth of L. monocytogenes at 4 °C, resulting in a shorter lag phase and a higher maximum specific growth rate. The obtained results could be useful in the determination of a set of suitable microstructural parameters for future predictive models that incorporate the influence of food microstructure on microbial dynamics. Copyright © 2018. Published by Elsevier B.V.

The Relationships Between Microstructure, Tensile Properties and Fatigue Life in Ti-5Al-5V-5Mo-3Cr-0.4Fe (Ti-5553)

NASA Astrophysics Data System (ADS)

Foltz, John W., IV

beta-titanium alloys are being increasingly used in airframes as a way to decrease the weight of the aircraft. As a result of this movement, Ti-5Al-5V-5Mo-3Cr-0.4Fe (Timetal 555), a high-strength beta titanium alloy, is being used on the current generation of landing gear. This alloy features good combinations of strength, ductility, toughness and fatigue life in alpha+beta processed conditions, but little is known about beta-processed conditions. Recent work by the Center for the Accelerated Maturation of Materials (CAMM) research group at The Ohio State University has improved the tensile property knowledge base for beta-processed conditions in this alloy, and this thesis augments the aforementioned development with description of how microstructure affects fatigue life. In this work, beta-processed microstructures have been produced in a Gleeble(TM) thermomechanical simulator and subsequently characterized with a combination of electron and optical microscopy techniques. Four-point bending fatigue tests have been carried out on the material to characterize fatigue life. All the microstructural conditions have been fatigue tested with the maximum test stress equal to 90% of the measured yield strength. The subsequent results from tensile tests, fatigue tests, and microstructural quantification have been analyzed using Bayesian neural networks in an attempt to predict fatigue life using microstructural and tensile inputs. Good correlation has been developed between lifetime predictions and experimental results using microstructure and tensile inputs. Trained Bayesian neural networks have also been used in a predictive fashion to explore functional dependencies between these inputs and fatigue life. In this work, one section discusses the thermal treatments that led to the observed microstructures, and the possible sequence of precipitation that led to these microstructures. The thesis then describes the implications of microstructure on fatigue life and implications of tensile properties on fatigue life. Several additional experiments are then described that highlight possible causes for the observed dependence of microstructure on fatigue life, including fractographic evidence to provide support of microstructural dependencies.

Multi-scale Microstructure Characterization for Improved Understanding of Microstructure-Property Relationship in Additive Manufacturing

NASA Astrophysics Data System (ADS)

Song, Hye Yun

Additive manufacturing (AM) is the process for making 3-D objects by adding materials layer by layer. It can result in a marked reduction of the time and cost associated with designing and producing highly complex parts. Over the past decade, significant progress has been made in machine hardware and control software for process development to achieve dimensional accuracy and mitigate defects. On the other hand, the knowledge on microstructure-property relationship in the additively manufactured builds is still being established. In additive manufacturing, the interactions between the heat source and the material lead to a series of physical phenomena including localized heating, melting, solidification and micro-segregation, and cooling. Far-from-equilibrium microstructure can form as the material experiences a large number of repeated, rapid heating and cooling cycles (i.e. temperature gyrations) during depositions. The mechanical properties of additively manufactured parts are significantly influenced by their final microstructure. The overarching goal of the present research is to improve the fundamental understanding of microstructure-property relationship for AM parts. Specially, it is investigated the high-temperature creep strength of InconelRTM 718 (abbreviated as IN718 thereafter) fabricated by laser-powder bed fusion (L-PBF) AM. The specific objectives include (1) effect of support on the local microstructure, (2) microstructure evolution during post-built heat treatment, and (3) creep strength. Detailed microstructure characterization is performed using a multitude of tools including micro-hardness mapping, scanning electron microscope (SEM) along with electron backscatter diffraction (EBSD), and transmission electron microscope (TEM) for selected area diffraction (SAD) analysis and energy-dispersive X-ray spectroscopy (EDS). The characterized microstructure is correlated to the mechanical properties. Highlights of the research findings are discussed in the following. A support is a "temporary" structure typically built in-situ with the primary part to provide the structural support to the mass of overhanging features; it is subsequently removed after fabrication. During the building process, the existence of such support can affect the local heat flow from the build to the substrate, which in turn may influence the local microstructure. The first objective of this research is to develop a fundamental understanding of the effect of the support on the microstructure fabricated by L-PBF AM. Two groups of as-built samples, with support and without support, are studied. SEM along with EBSD is used to analyze the microstructure characteristics including the growth of the microstructures, the fraction of different microstructure and the misorientation among the microstructure grains. At the nano-scale resolution, TEM is used to identify the precipitate phases. In addition, the micro-hardness values are also measured for samples built with and without support. As a precipitation-strengthened alloy, the heat treatment is critical for IN718, since the desired mechanical properties, such as high-temperature tensile and creep strength, are only acquired by the formation of the strengthening precipitates, namely gamma' prime and gamma''. Currently, the industrial standards for the heat treatment of IN718 are developed for cast and wrought cases and not specifically for AM builds. Thus, it is essential to evaluate the effect of the heat treatment on the formation of the strengthening precipitates in IN718 builds fabricated by L-PBF AM, which is the focus of the second objective. Particularly, a modification to the industry standard heat treatment is developed to maximize the fraction of the strengthening precipitates in the IN718 builds. The microstructural characterizations are performed for several modified heat treatment cases including a homogenization step, solution annealing step and aging step. The micro-hardness values are measured for as-built conditions and several heat-treated conditions including the modified homogenization, solution anneal and aging steps. Finally, the oxidation behavior during the heat treatment is also discussed and compared to that for a piece of actual cast. The third objective of the present study is the evaluation of the mechanical properties of heat-treated IN718 builds produced by L-PBF AM. Particularly, creep test are performed to quantify the mechanical properties of the heat-treated IN718 builds. The creep samples are heat-treated using the following condition: homogenization at 1100 °C for 2 hours followed by air cooling (AC), and aging at 760 °C for 10 hours also followed by AC. For the creep test, the samples are loaded at a constant stress (690 MPa or 100 ksi) at 649 °C (1200 °F) in accordance to Aerospace Material Standards (AMS) 5663. The creep rate of the heat-treated AM sample is compared with the literature data for wrought cases. The relationship of creep strength to the characteristic of the microstructures in the heat-treated IN718 builds is discussed. In summary, the research results provide insights into the microstructure-creep-strength relationship for IN718 fabricated by additive manufacturing. Particularly, a modified post-built heat treatment is developed to maximize the formation of strengthening precipitates and achieve large grains in IN718, resulting in a markedly higher creep strength when compared to the literature data for wrought cases. Taken as a whole, the new knowledge generated in this dissertation is essential to ensure the performance of additively manufactured parts in structural applications.

Geometry segmentation of voxelized representations of heterogeneous microstructures using betweenness centrality

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

Yuan, Rui; Singh, Sudhanshu S.; Chawla, Nikhilesh

2016-08-15

We present a robust method for automating removal of “segregation artifacts” in segmented tomographic images of three-dimensional heterogeneous microstructures. The objective of this method is to accurately identify and separate discrete features in composite materials where limitations in imaging resolution lead to spurious connections near close contacts. The method utilizes betweenness centrality, a measure of the importance of a node in the connectivity of a graph network, to identify voxels that create artificial bridges between otherwise distinct geometric features. To facilitate automation of the algorithm, we develop a relative centrality metric to allow for the selection of a threshold criterionmore » that is not sensitive to inclusion size or shape. As a demonstration of the effectiveness of the algorithm, we report on the segmentation of a 3D reconstruction of a SiC particle reinforced aluminum alloy, imaged by X-ray synchrotron tomography.« less

Dynamic deformation of volcanic ejecta from the Toba caldera: possible relevance to Cretaceous/Tertiary boundary phenomena

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

Carter, N.L.; Officer, C.B.; Chesner, C.A.

1986-05-01

Plagioclase and biotite phenocrysts in ignimbrites erupted from the Toba caldera, Sumatra, show microstructures and textures indicative of shock stress levels higher than 10 GPa. Strong dynamic deformation has resulted in intense kinking in biotite and, with increasing shock intensity, the development of plagioclase of planar features, shock mosaicism, incipient recrystallization, and possible partial melting. Microstructures in quartz indicative of strong shock deformation are rare, however, and many shock lamellae, if formed, may have healed during post-shock residence in the hot ignimbrite; they might be preserved in ash falls. Peak shock stresses from explosive silicic volcanism and other endogenous processesmore » may be high and if so would obviate the need for extraterrestrial impacts to produce all dynamically deformed structures, possibly including shock features observed near the Cretaceous/Tertiary boundary. 38 references, 3 figures.« less

Temperature rise due to mechanical energy dissipation in undirectional thermoplastic composites(AS4/PEEK)

NASA Technical Reports Server (NTRS)

Georgious, I. T.; Sun, C. T.

1992-01-01

The history of temperature rise due to internal dissipation of mechanical energy in insulated off-axis uniaxial specimens of the unidirectional thermoplastic composite (AS4/PEEK) has been measured. The experiment reveals that the rate of temperature rise is a polynomial function of stress amplitude: It consists of a quadratic term and a sixth power term. This fact implies that the specific heat of the composite depends on the stretching its microstructure undergoes during deformation. The Einstein theory for specific heat is used to explain the dependence of the specific heat on the stretching of the microstructure.

A neural network technique for remeshing of bone microstructure.

PubMed

Fischer, Anath; Holdstein, Yaron

2012-01-01

Today, there is major interest within the biomedical community in developing accurate noninvasive means for the evaluation of bone microstructure and bone quality. Recent improvements in 3D imaging technology, among them development of micro-CT and micro-MRI scanners, allow in-vivo 3D high-resolution scanning and reconstruction of large specimens or even whole bone models. Thus, the tendency today is to evaluate bone features using 3D assessment techniques rather than traditional 2D methods. For this purpose, high-quality meshing methods are required. However, the 3D meshes produced from current commercial systems usually are of low quality with respect to analysis and rapid prototyping. 3D model reconstruction of bone is difficult due to the complexity of bone microstructure. The small bone features lead to a great deal of neighborhood ambiguity near each vertex. The relatively new neural network method for mesh reconstruction has the potential to create or remesh 3D models accurately and quickly. A neural network (NN), which resembles an artificial intelligence (AI) algorithm, is a set of interconnected neurons, where each neuron is capable of making an autonomous arithmetic calculation. Moreover, each neuron is affected by its surrounding neurons through the structure of the network. This paper proposes an extension of the growing neural gas (GNN) neural network technique for remeshing a triangular manifold mesh that represents bone microstructure. This method has the advantage of reconstructing the surface of a genus-n freeform object without a priori knowledge regarding the original object, its topology, or its shape.

Microstructural white matter alterations in preclinical Alzheimer’s disease detected using free water elimination diffusion tensor imaging

PubMed Central

Ly, Martina; Carlsson, Cynthia M.; Okonkwo, Ozioma C.; Zetterberg, Henrik; Blennow, Kaj; Sager, Mark A.; Asthana, Sanjay; Johnson, Sterling C.; Alexander, Andrew L.; Bendlin, Barbara B.

2017-01-01

Brain changes associated with Alzheimer’s disease (AD) begin decades before disease diagnosis. While β-amyloid plaques and neurofibrillary tangles are defining features of AD, neuronal loss and synaptic pathology are closely related to the cognitive dysfunction. Brain imaging methods that are tuned to assess degeneration of myelinated nerve fibers in the brain (collectively called white matter) include diffusion tensor imaging (DTI) and related techniques, and are expected to shed light on disease-related loss of structural connectivity. Participants (N = 70, ages 47–76 years) from the Wisconsin Registry for Alzheimer’s Prevention study underwent DTI and hybrid diffusion imaging to determine a free-water elimination (FWE-DTI) model. The study assessed the extent to which preclinical AD pathology affects brain white matter. Preclinical AD pathology was determined using cerebrospinal fluid (CSF) biomarkers. The sample was enriched for AD risk (APOE ε4 and parental history of AD). AD pathology assessed by CSF analyses was significantly associated with altered microstructure on both DTI and FWE-DTI. Affected regions included frontal, parietal, and especially temporal white matter. The f-value derived from the FWE-DTI model appeared to be the most sensitive to the relationship between the CSF AD biomarkers and microstructural alterations in white matter. These findings suggest that white matter degeneration is an early pathological feature of AD that may have utility both for early disease detection and as outcome measures for clinical trials. More complex models of microstructural diffusion properties including FWE-DTI may provide increased sensitivity to early brain changes associated with AD over standard DTI. PMID:28291839

The co-evolution of microstructure features in self-ion irradiated HT9 at very high damage levels

NASA Astrophysics Data System (ADS)

Getto, E.; Vancoevering, G.; Was, G. S.

2017-02-01

Understanding the void swelling and phase evolution of reactor structural materials at very high damage levels is essential to maintaining safety and longevity of components in Gen IV fast reactors. A combination of ion irradiation and modeling was utilized to understand the microstructure evolution of ferritic-martensitic alloy HT9 at high dpa. Self-ion irradiation experiments were performed on alloy HT9 to determine the co-evolution of voids, dislocations and precipitates up to 650 dpa at 460 °C. Modeling of microstructure evolution was conducted using the modified Radiation Induced Microstructure Evolution (RIME) model, which utilizes a mean field rate theory approach with grouped cluster dynamics. Irradiations were performed with 5 MeV raster-scanned Fe2+ ions on samples pre-implanted with 10 atom parts per million He. The swelling, dislocation and precipitate evolution at very high dpa was determined using Analytical Electron Microscopy in Scanning Transmission Electron Microscopy (STEM) mode. Experimental results were then interpreted using the RIME model. A microstructure consisting only of dislocations and voids is insufficient to account for the swelling evolution observed experimentally at high damage levels in a complicated microstructure such as irradiated alloy HT9. G phase was found to have a minimal effect on either void or dislocation evolution. M2X played two roles; a variable biased sink for defects, and as a vehicle for removal of carbon from solution, thus promoting void growth. When accounting for all microstructure interactions, swelling at high damage levels is a dynamic process that continues to respond to other changes in the microstructure as long as they occur.

Investigating pianists' individuality in the performance of five timbral nuances through patterns of articulation, touch, dynamics, and pedaling

PubMed Central

Bernays, Michel; Traube, Caroline

2014-01-01

Timbre is an essential expressive feature in piano performance. Concert pianists use a vast palette of timbral nuances to color their performances at the microstructural level. Although timbre is generally envisioned in the pianistic community as an abstract concept carried through an imaged vocabulary, performers may share some common strategies of timbral expression in piano performance. Yet there may remain further leeway for idiosyncratic processes in the production of piano timbre nuances. In this study, we examined the patterns of timbral expression in performances by four expert pianists. Each pianist performed four short pieces, each with five different timbral intentions (bright, dark, dry, round, and velvety). The performances were recorded with the high-accuracy Bösendorfer CEUS system. Fine-grained performance features of dynamics, touch, articulation and pedaling were extracted. Reduced PCA performance spaces and descriptive performance portraits confirmed that pianists exhibited unique, specific profiles for different timbral intentions, derived from underlying traits of general individuality, while sharing some broad commonalities of dynamics and articulation for each timbral intention. These results confirm that pianists' abstract notions of timbre correspond to reliable patterns of performance technique. Furthermore, these effects suggest that pianists can express individual styles while complying with specific timbral intentions. PMID:24624099

Lower Length Scale Model Development for Embrittlement of Reactor Presure Vessel Steel

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

Zhang, Yongfeng; Schwen, Daniel; Chakraborty, Pritam

2016-09-01

This report summarizes the lower-length-scale effort during FY 2016 in developing mesoscale capabilities for microstructure evolution, plasticity and fracture in reactor pressure vessel steels. During operation, reactor pressure vessels are subject to hardening and embrittlement caused by irradiation induced defect accumulation and irradiation enhanced solute precipitation. Both defect production and solute precipitation start from the atomic scale, and manifest their eventual effects as degradation in engineering scale properties. To predict the property degradation, multiscale modeling and simulation are needed to deal with the microstructure evolution, and to link the microstructure feature to material properties. In this report, the development ofmore » mesoscale capabilities for defect accumulation and solute precipitation are summarized. A crystal plasticity model to capture defect-dislocation interaction and a damage model for cleavage micro-crack propagation is also provided.« less

A study of spectrum fatigue crack propagation in two aluminum alloys. 2: Influence of microstructures

NASA Technical Reports Server (NTRS)

Telesman, J.; Antolovich, S. D.

1985-01-01

The important metallurgical factors that influence both constant amplitude and spectrum crack growth behavior in aluminum alloys were investigated. The effect of microstructural features such as grain size, inclusions, and dispersoids was evaluated. It was shown that a lower stress intensities, the I/M 7050 alloy showed better fatigue crack propagation (FCP) resistance than P/M 7091 alloy for both constant amplitude and spectrum testing. It was suggested that the most important microstructural variable accounting for superior FCP resistance of 7050 alloy is its large grain size. It was further postulated that the inhomogenous planar slip and large grain size of 7050 limit dislocation interactions and thus increase slip reversibility which improves FCP performance. The hypothesis was supported by establishing that the cyclic strain hardening exponent for the 7091 alloy is higher than that of 7050.

Data on processing of Ti-25Nb-25Zr β-titanium alloys via powder metallurgy route: Methodology, microstructure and mechanical properties.

PubMed

Ueda, D; Dirras, G; Hocini, A; Tingaud, D; Ameyama, K; Langlois, P; Vrel, D; Trzaska, Z

2018-04-01

The data presented in this article are related to the research article entitled "Cyclic Shear behavior of conventional and harmonic structure-designed Ti-25Nb-25Zr β-titanium alloy: Back-stress hardening and twinning inhibition" (Dirras et al., 2017) [1]. The datasheet describes the methods used to fabricate two β-titanium alloys having conventional microstructure and so-called harmonic structure (HS) design via a powder metallurgy route, namely the spark plasma sintering (SPS) route. The data show the as-processed unconsolidated powder microstructures as well as the post-SPS ones. The data illustrate the mechanical response under cyclic shear loading of consolidated alloy specimens. The data show how electron back scattering diffraction(EBSD) method is used to clearly identify induced deformation features in the case of the conventional alloy.

Microstructure and mechanical properties of heat-resistant 12% Cr ferritic-martensitic steel EK-181 after thermomechanical treatment

NASA Astrophysics Data System (ADS)

Polekhina, N. A.; Litovchenko, I. Yu.; Tyumentsev, A. N.; Astafurova, E. G.; Chernov, V. M.; Leontyeva-Smirnova, M. V.

2015-10-01

The effect of high-temperature thermomechanical treatment (TMT) with the deformation in the austenitic region on the features of microstructure, phase transformations and mechanical properties of low-activation 12% Cr ferritic-martensitic steel EK-181 is investigated. It is established, that directly after thermomechanical treatment (without tempering) the sizes and density of V(CN) particles are comparable with those after a traditional heat treatment (air quenching and tempering at 720°C, 3 h), where these particles are formed only during tempering. It causes the increasing of the yield strength of the steel up to ≈1450 MPa at room temperature and up to ≈430 MPa at the test temperature T = 650°C. The potential of microstructure modification by this treatment aimed at improving heat resistance of steel is discussed.

Effect of lattice-mismatch-induced strains on coupled diffusive and displacive phase transformations

NASA Astrophysics Data System (ADS)

Bouville, Mathieu; Ahluwalia, Rajeev

2007-02-01

Materials which can undergo slow diffusive transformations as well as fast displacive transformations are studied using the phase-field method. The model captures the essential features of the time-temperature-transformation (TTT) diagrams, continuous cooling transformation (CCT) diagrams, and microstructure formation of these alloys. In some material systems there can exist an intrinsic volume change associated with these transformations. We show that these coherency strains can stabilize mixed microstructures (such as retained austenite-martensite and pearlite-martensite mixtures) by an interplay between diffusive and displacive mechanisms, which can alter TTT and CCT diagrams. Depending on the conditions there can be competitive or cooperative nucleation of the two kinds of phases. The model also shows that small differences in volume changes can have noticeable effects on the early stages of martensite formation and on the resulting microstructures.

The role of grain size and shape in strengthening of dispersion hardened nickel alloys.

NASA Technical Reports Server (NTRS)

Wilcox, B. A.; Clauer, A. H.

1972-01-01

Thermomechanical processing was used to develop various microstructures in Ni, Ni-2ThO2, Ni-20Cr, Ni-20Cr-2ThO2, Ni-20Cr-10W and Ni-20Cr-10W-2ThO2, and the influence of microstructure on room temperature and elevated temperature strength was investigated. The yield strength at 25 C increased with substructure refinement according to the Hall-Petch relation. It was found that substructure refinement was a much more potent means of strengthening at room temperature than was dispersion hardening. At elevated temperature (1093 C), the most important microstructural feature affecting strength of dispersion hardened nickel alloys was the grain aspect ratio, i.e. grain length, L, divided by grain width,l. The yield strength and creep strength increased linearly with increasing L/l.

Effect of microstructural features on the laser efficiency of Nd{sup 3+}:Y{sub 3}Al{sub 5}O{sub 12} ceramics

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

Vorona, I O; Yavetskiy, R P; Tolmachev, A V

2015-09-30

The optical properties and microstructure of transparent Nd{sup 3+}:Y{sub 3}Al{sub 5}O{sub 12} ceramics synthesised by different reactive sintering routes are studied. It is found that the residual porosity of optical ceramics is directly related to the homogeneity of the microstructure of initial compacts, which can be estimated by the existence of particle agglomerates larger than 1 mm in initial nanopowders. A qualitative correlation is established between the residual porosity, the optical losses and the lasing slope efficiency of Nd{sup 3+}:Y{sub 3}Al{sub 5}O{sub 12} ceramics. The maximum laser efficiency (η = 49%) was observed in the samples with the lowest porositymore » (2.3 × 10{sup -3} vol %). (lasers)« less

Tensile Deformation Temperature Impact on Microstructure and Mechanical Properties of AISI 316LN Austenitic Stainless Steel

NASA Astrophysics Data System (ADS)

Xiong, Yi; He, Tiantian; Lu, Yan; Ren, Fengzhang; Volinsky, Alex A.; Cao, Wei

2018-03-01

Uniaxial tensile tests were conducted on AISI 316LN austenitic stainless steel from - 40 to 300 °C at a rate of 0.5 mm/min. Microstructure and mechanical properties of the deformed steel were investigated by optical, scanning and transmission electron microscopies, x-ray diffraction, and microhardness testing. The yield strength, ultimate tensile strength, elongation, and microhardness increase with the decrease in the test temperature. The tensile fracture morphology has the dimple rupture feature after low-temperature deformations and turns to a mixture of transgranular fracture and dimple fracture after high-temperature ones. The dominating deformation microstructure evolves from dislocation tangle/slip bands to large deformation twins/slip bands with temperature decrease. The deformation-induced martensite transformation can only be realized at low temperature, and its quantity increases with the decrease in the temperature.

On the influence of manufacturing practices on the SCC behavior of Alloy 690 steam generator tubing

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

Doherty, P.E.; Doyle, D.M.; Sarver, J.M.

1996-12-31

Thermally treated (TT) Alloy 690 is the tubing materials of choice for replacement steam generators (RSGs) throughout the world. It is manufactured using a variety of processing methods with regards to melt practice and thermomechanical forming. Studies assessing the IGSCC resistance of Alloy 690 TT SG tubing have identified a variability in the corrosion performance of nominally identical alloys. While tubing of comparable bulk chemistry may exhibit variations in microchemistry as a result of different melt practice, the correlation between melt practice and SCC resistance is difficult to assess due to other contributing factors. The other contributing factors are identifiedmore » in this investigation as microstructural features whose generation is dependent on features of particular strain-anneal forming methods by which SG tubes are fabricated. In this study the microstructural characteristics which appear to affect inservice corrosion performance of Alloy 690 TT SG tubes were evaluated. The studies included extensive microstructural examinations in addition to CERT tests performed on actual Alloy 690 TT nuclear SG tubing. The CERT test results indicate that Alloy 690 TT tubing processed at higher mill anneal temperatures display the highest degree of stress corrosion cracking (SCC) resistance. This observation is discussed with reference to carbide distributions, textural aspects and grain boundary orientation character.« less

Anomaly detection of microstructural defects in continuous fiber reinforced composites

NASA Astrophysics Data System (ADS)

Bricker, Stephen; Simmons, J. P.; Przybyla, Craig; Hardie, Russell

2015-03-01

Ceramic matrix composites (CMC) with continuous fiber reinforcements have the potential to enable the next generation of high speed hypersonic vehicles and/or significant improvements in gas turbine engine performance due to their exhibited toughness when subjected to high mechanical loads at extreme temperatures (2200F+). Reinforced fiber composites (RFC) provide increased fracture toughness, crack growth resistance, and strength, though little is known about how stochastic variation and imperfections in the material effect material properties. In this work, tools are developed for quantifying anomalies within the microstructure at several scales. The detection and characterization of anomalous microstructure is a critical step in linking production techniques to properties, as well as in accurate material simulation and property prediction for the integrated computation materials engineering (ICME) of RFC based components. It is desired to find statistical outliers for any number of material characteristics such as fibers, fiber coatings, and pores. Here, fiber orientation, or `velocity', and `velocity' gradient are developed and examined for anomalous behavior. Categorizing anomalous behavior in the CMC is approached by multivariate Gaussian mixture modeling. A Gaussian mixture is employed to estimate the probability density function (PDF) of the features in question, and anomalies are classified by their likelihood of belonging to the statistical normal behavior for that feature.

Electrochemical Corrosion Behavior of Spray-Formed Boron-Modified Supermartensitic Stainless Steel

NASA Astrophysics Data System (ADS)

Zepon, Guilherme; Nogueira, Ricardo P.; Kiminami, Claudio S.; Botta, Walter J.; Bolfarini, Claudemiro

2017-04-01

Spray-formed boron-modified supermartensitic stainless steel (SMSS) grades are alloys developed to withstand severe wear conditions. The addition of boron to the conventional chemical composition of SMSS, combined with the solidification features promoted by the spray forming process, leads to a microstructure composed of low carbon martensitic matrix reinforced by an eutectic network of M2B-type borides, which considerably increases the wear resistance of the stainless steel. Although the presence of borides in the microstructure has a very beneficial effect on the wear properties of the alloy, their effect on the corrosion resistance of the stainless steel was not comprehensively evaluated. The present work presents a study of the effect of boron addition on the corrosion resistance of the spray-formed boron-modified SMSS grades by means of electrochemical techniques. The borides fraction seems to have some influence on the repassivation kinetics of the spray-formed boron-modified SMSS. It was shown that the Cr content of the martensitic matrix is the microstructural feature deciding the corrosion resistance of this sort of alloys. Therefore, if the Cr content in the alloy is increased to around 14 wt pct to compensate for the boron consumed by the borides formation, the corrosion resistance of the alloy is kept at the same level of the alloy without boron addition.

Grain boundary engineering: fatigue fracture

NASA Astrophysics Data System (ADS)

Das, Arpan

2017-04-01

Grain boundary engineering has revealed significant enhancement of material properties by modifying the populations and connectivity of different types of grain boundaries within the polycrystals. The character and connectivity of grain boundaries in polycrystalline microstructures control the corrosion and mechanical behaviour of materials. A comprehensive review of the previous researches has been carried out to understand this philosophy. Present research thoroughly explores the effect of total strain amplitude on phase transformation, fatigue fracture features, grain size, annealing twinning, different grain connectivity and grain boundary network after strain controlled low cycle fatigue deformation of austenitic stainless steel under ambient temperature. Electron backscatter diffraction technique has been used extensively to investigate the grain boundary characteristics and morphologies. The nominal variation of strain amplitude through cyclic plastic deformation is quantitatively demonstrated completely in connection with the grain boundary microstructure and fractographic features to reveal the mechanism of fatigue fracture of polycrystalline austenite. The extent of boundary modifications has been found to be a function of the number of applied loading cycles and strain amplitudes. It is also investigated that cyclic plasticity induced martensitic transformation strongly influences grain boundary characteristics and modifications of the material's microstructure/microtexture as a function of strain amplitudes. The experimental results presented here suggest a path to grain boundary engineering during fatigue fracture of austenite polycrystals.

Effect of microstructure and surface features on wetting angle of a Fe-3.2 wt%C.E. cast iron with water

NASA Astrophysics Data System (ADS)

Riahi, Samira; Niroumand, Behzad; Dorri Moghadam, Afsaneh; Rohatgi, Pradeep K.

2018-05-01

In the present study, variation in surface wetting behavior of a hypoeutectic cast iron with its microstructural features and surface roughness was investigated. Samples with an identical composition, i.e. Fe-3.2 wt%C.E., and different microstructures (a gray cast iron with A-type flake graphite and a white cast iron) were fabricated by gravity casting of molten cast iron in a chill mold at different cooling rates. A variation of surface roughness was also developed by polishing, a four-stage electroetching and a four-stage mechanical abrading on the samples. Roughness and water contact angles of all surfaces were then measured. The surface roughness factor and the solid fraction in contact with water by the Wenzel and Cassie-Baxter contact models were also calculated and compared with the corresponding measured contact angles to find out which regime was active. Results indicated that the surface microstructure and the type of constituents present at the surface influenced the cast iron surface wettability and that it was possible to change the surface contact angle by modification of the surface microstructure. The mechanically abraded gray cast iron followed the Wenzel-type regime while the electroetched surfaces of gray cast iron exhibited a transition from Wenzel to Cassie-Baxter type regime. In white cast iron, the results indicated Wenzel type behavior in the electroetched samples while for the mechanically abraded samples, none of these two models could predict the wetting behavior. Furthermore, the wetting angles of both gray and white cast irons were measured after 1, 2, 3 and 4 weeks of air exposure. The results showed that the wetting angles of both samples increased to above 90° after one week of air exposure which was likely due to adsorption of low surface energy hydrocarbons on the surfaces.

Development of High Toughness Sheet and Extruded Products for Airplane Fuselage Structures

NASA Astrophysics Data System (ADS)

Magnusen, P. E.; Mooy, D. C.; Yocum, L. A.; Rioja, R. J.

High specific ultimate strength and high plane stress fracture toughness are primary requirements of aircraft fuselage skins. The performance of alloys/products used in high performance fuselage applications is first reviewed. The specific fracture toughness for products such as 2017-T3, 2024-T3, 2524-T3 and 6013-T6, is discussed as a function of their composition and microstructure. Then the performance of modern Al-Li alloys/products such as 2199 and 2060 sheet and 2099 and 2055 extrusions is examined. It is concluded that the performance of Li containing alloys/products offer significant improvements over non-Li containing conventional fuselage products because of the optimization of strengthening precipitates and grain microstructures. The role of chemical composition on resulting microstructures is discussed.

Features of plastic deformation and fracture of dispersion-strengthened V–Cr–Zr–W alloy depending on temperature of tension

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

Ditenberg, Ivan A.; Grinyaev, Konstantin V.; Tyumentsev, Alexander N.

2015-10-27

Influence of tension temperature on features of plastic deformation and fracture of V–4.23Cr–1.69Zr–7.56W alloy was investigated by scanning and transmission electron microscopy. It is shown that temperature increase leads to activation of the recovery processes, which manifests in the coarsening of microstructure elements, reducing the dislocation density, relaxation of continuous misorientations.

Impact of Exposure to Pressure of 50 MPa on the Specific Surface Area of Clay

NASA Astrophysics Data System (ADS)

Koszela-Marek, Ewa

2017-12-01

The paper presents results of laboratory tests conducted to determine the impact of pressure of 50 MPa on specific surface area of clay. These tests were carried out in an original, high-pressure test stand. The specific surface area of clay extracted directly from an open pit mine was compared with the specific surface area of the same clay subjected to the pressure of 50 MPa in a high-pressure chamber. The study found that the specific surface area of the clay subjected to the pressure of 50 MPa increased distinctly by over 35 %. The increase in specific surface can be a result of changes in the microstructure of clay particles and microstructural alteration in the soil skeleton, caused by the pressure.

Phase-field based Multiscale Modeling of Heterogeneous Solid Electrolytes: Applications to Nanoporous Li 3 PS 4

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

Hu, Jia-Mian; Wang, Bo; Ji, Yanzhou

Modeling the effective ion conductivities of heterogeneous solid electrolytes typically involves the use of a computer-generated microstructure consisting of randomly or uniformly oriented fillers in a matrix. But, the structural features of the filler/matrix interface, which critically determine the interface ion conductivity and the microstructure morphology, have not been considered during the microstructure generation. In using nanoporous β-Li 3PS 4 electrolyte as an example, we develop a phase-field model that enables generating nanoporous microstructures of different porosities and connectivity patterns based on the depth and the energy of the surface (pore/electrolyte interface), both of which are predicted through density functionalmore » theory (DFT) calculations. Room-temperature effective ion conductivities of the generated microstructures are then calculated numerically, using DFT-estimated surface Li-ion conductivity (3.14×10 -3 S/cm) and experimentally measured bulk Li-ion conductivity (8.93×10 -7 S/cm) of β-Li 3PS 4 as the inputs. We also use the generated microstructures to inform effective medium theories to rapidly predict the effective ion conductivity via analytical calculations. Furthemore, when porosity approaches the percolation threshold, both the numerical and analytical methods predict a significantly enhanced Li-ion conductivity (1.74×10 -4 S/cm) that is in good agreement with experimental data (1.64×10 -4 S/cm). The present phase-field based multiscale model is generally applicable to predict both the microstructure patterns and the effective properties of heterogeneous solid electrolytes.« less

Studying microstructure and microstructural changes in plant tissues by advanced diffusion magnetic resonance imaging techniques

PubMed Central

Morozov, Darya; Tal, Iris; Pisanty, Odelia; Shani, Eilon

2017-01-01

Abstract As sessile organisms, plants must respond to the environment by adjusting their growth and development. Most of the plant body is formed post-embryonically by continuous activity of apical and lateral meristems. The development of lateral adventitious roots is a complex process, and therefore the development of methods that can visualize, non-invasively, the plant microstructure and organ initiation that occur during growth and development is of paramount importance. In this study, relaxation-based and advanced diffusion magnetic resonance imaging (MRI) methods including diffusion tensor (DTI), q-space diffusion imaging (QSI), and double-pulsed-field-gradient (d-PFG) MRI, at 14.1 T, were used to characterize the hypocotyl microstructure and the microstructural changes that occurred during the development of lateral adventitious roots in tomato. Better contrast was observed in relaxation-based MRI using higher in-plane resolution but this also resulted in a significant reduction in the signal-to-noise ratio of the T2-weighted MR images. Diffusion MRI revealed that water diffusion is highly anisotropic in the vascular cylinder. QSI and d-PGSE MRI showed that in the vascular cylinder some of the cells have sizes in the range of 6–10 μm. The MR images captured cell reorganization during adventitious root formation in the periphery of the primary vascular bundles, adjacent to the xylem pole that broke through the cortex and epidermis layers. This study demonstrates that MRI and diffusion MRI methods allow the non-invasive study of microstructural features of plants, and enable microstructural changes associated with adventitious root formation to be followed. PMID:28398563

Phase-field based Multiscale Modeling of Heterogeneous Solid Electrolytes: Applications to Nanoporous Li 3 PS 4

DOE PAGES

Hu, Jia-Mian; Wang, Bo; Ji, Yanzhou; ...

2017-09-07

Modeling the effective ion conductivities of heterogeneous solid electrolytes typically involves the use of a computer-generated microstructure consisting of randomly or uniformly oriented fillers in a matrix. But, the structural features of the filler/matrix interface, which critically determine the interface ion conductivity and the microstructure morphology, have not been considered during the microstructure generation. In using nanoporous β-Li 3PS 4 electrolyte as an example, we develop a phase-field model that enables generating nanoporous microstructures of different porosities and connectivity patterns based on the depth and the energy of the surface (pore/electrolyte interface), both of which are predicted through density functionalmore » theory (DFT) calculations. Room-temperature effective ion conductivities of the generated microstructures are then calculated numerically, using DFT-estimated surface Li-ion conductivity (3.14×10 -3 S/cm) and experimentally measured bulk Li-ion conductivity (8.93×10 -7 S/cm) of β-Li 3PS 4 as the inputs. We also use the generated microstructures to inform effective medium theories to rapidly predict the effective ion conductivity via analytical calculations. Furthemore, when porosity approaches the percolation threshold, both the numerical and analytical methods predict a significantly enhanced Li-ion conductivity (1.74×10 -4 S/cm) that is in good agreement with experimental data (1.64×10 -4 S/cm). The present phase-field based multiscale model is generally applicable to predict both the microstructure patterns and the effective properties of heterogeneous solid electrolytes.« less

Corpus callosum vasculature predicts white matter microstructure abnormalities following pediatric mild traumatic brain injury.

PubMed

Wendel, Kara M; Lee, Jeong Bin; Affeldt, Bethann; Hamer, Mary; Harahap-Carrillo, Indira S; Pardo, Andrea C; Obenaus, Andre

2018-05-09

Emerging data suggest that pediatric traumatic brain injury (TBI) is associated with impaired developmental plasticity and poorer neuropsychological outcomes than adults with similar head injuries. Unlike adult mild TBI (mTBI), the effects of mTBI on white matter (WM) microstructure and vascular supply are not well-understood in the pediatric population. The cerebral vasculature plays an important role providing necessary nutrients and removing waste. To address this critical element, we examined the microstructure of the corpus callosum (CC) following pediatric mTBI using diffusion tensor imaging (DTI), and investigated myelin, oligodendrocytes, and vasculature of WM with immunohistochemistry. We hypothesized that pediatric mTBI leads to abnormal WM microstructure and impacts the vasculature within the CC, and that these alterations to WM vasculature contribute to the long-term altered microstructure. We induced a closed head injury mTBI at postnatal day 14, then at 4, 14, and 60 days post injury (DPI) mice were sacrificed for analysis. We observed persistent changes in apparent diffusion coefficient (ADC) within the ipsilateral CC following mTBI, indicating microstructural changes, but surprisingly changes in myelin and oligodendrocyte densities were minimal. However, vasculature features of the ipsilateral CC such as vessel density, length, and number of junctions were persistently altered following mTBI. Correlative analysis showed a strong inverse relationship between ADC and vessel density at 60 DPI, suggesting increased vessel density following mTBI may restrict WM diffusion characteristics. Our findings suggest that WM vasculature contributes to the long-term microstructural changes within the ipsilateral CC following mTBI.

Additive Manufacturing of 17-4 PH Stainless Steel: Post-processing Heat Treatment to Achieve Uniform Reproducible Microstructure

NASA Astrophysics Data System (ADS)

Cheruvathur, Sudha; Lass, Eric A.; Campbell, Carelyn E.

2016-03-01

17-4 precipitation hardenable (PH) stainless steel is a useful material when a combination of high strength and good corrosion resistance up to about 315°C is required. In the wrought form, this steel has a fully martensitic structure that can be strengthened by precipitation of fine Cu-rich face-centered cubic phase upon aging. When fabricated via additive manufacturing (AM), specifically laser powder-bed fusion, 17-4 PH steel exhibits a dendritic structure containing a substantial fraction of nearly 50% of retained austenite along with body centered cubic/martensite and fine niobium carbides preferentially aligned along interdendritic boundaries. The effect of post-build thermal processing on the material microstructure is studied in comparison to that of conventionally produced wrought 17-4 PH with the intention of creating a more uniform, fully martensitic microstructure. The recommended stress relief heat treatment currently employed in industry for post-processing of AM 17-4 PH steel is found to have little effect on the as-built dendritic microstructure. It is found that, by implementing the recommended homogenization heat treatment regimen of Aerospace Materials Specification 5355 for CB7Cu-1, a casting alloy analog to 17-4 PH, the dendritic solidification structure is eliminated, resulting in a microstructure containing about 90% martensite with 10% retained austenite.

Research on non-direct reflection columnar microstructure

NASA Astrophysics Data System (ADS)

Wu, B. Q.; Wang, X. Z.; Dong, L. H.

2015-10-01

To minimize the risk of laser accidents, especially those involving eye and skin injuries, it is crucial to pay more attention to laser safety. To control the risk of injury, depending on the laser power and wavelength, a number of required safety measures have been put forward, such as specific protection walls, and wearing safety goggles when operating lasers. The direct reflection columnar microstructure can also be used for laser safety. Based on mathematical foundations , a columnar microstructure is designed by the optical design software LightTools. Simulation showed that there is a tilt angle between the emergent and incident light, the incident light being perpendicular to the microstructure, as well as the phenomenon of no direct reflection happened. A novel testing platform was built for the columnar microstructure after it was machined. The applied testing method can measure the angle between the emergent and incident light. The method lays the condition for the further research. It is shown that the columnar microstructure with no direct reflection can be utilized in laser protection systems.

Microstructure and corrosion behavior of shielded metal arc-welded dissimilar joints comprising duplex stainless steel and low alloy steel

NASA Astrophysics Data System (ADS)

Srinivasan, P. Bala; Muthupandi, V.; Sivan, V.; Srinivasan, P. Bala; Dietzel, W.

2006-12-01

This work describes the results of an investigation on a dissimilar weld joint comprising a boiler-grade low alloy steel and duplex stainless steel (DSS). Welds produced by shielded metal arc-welding with two different electrodes (an austenitic and a duplex grade) were examined for their microstructural features and properties. The welds were found to have overmatching mechanical properties. Although the general corrosion resistance of the weld metals was good, their pitting resistance was found to be inferior when compared with the DSS base material.

Structural features and mechanical properties of austenitic Hadfield steel after high-pressure torsion and subsequent high-temperature annealing

NASA Astrophysics Data System (ADS)

Tukeeva, M. S.; Melnikov, E. V.; Maier, H. J.; Astafurova, E. G.

2012-06-01

Mechanisms of structure fragmentation and strengthening of single crystals of a Hadfield steel after warm torsion under high-pressure torsion (HPT) and subsequent annealing in a temperature range of 400-800°C have been studied. Multiple twinning and formation of ultrafine carbides upon HPT at 400°C ( P = 5 GPa) promote rapid fragmentation of the microstructure. They are responsible for the high mechanical properties of the steel after HPT and the thermal stability of the microstructure up to an annealing temperature of 500°C.

Properties of RBSN and RBSN-SiC composites. [Reaction Bonded Silicon Nitride

NASA Technical Reports Server (NTRS)

Lightfoot, A.; Ker, H. L.; Haggerty, J. S.; Ritter, J. E.

1990-01-01

Strengths, fracture toughnesses, hardnesses, and dimensional changes have been measured for RBSN and RBSN/SiC composites. Samples were made from mixtures of Si and either Si- or C-rich SiC powders. For pure, 75 pct dense RBSN dispersed with octanol, strengths up to 858 MPa have been achieved. Improved strengths result from a combination of microstructural perfection and increased fracture toughness. The mechanical properties of the composites were approximately equal to those of methanol processed RBSN but not quite equal to those of the octanol-processed RBSN. Results are discussed in terms of observed microstructural features.

Enhanced Coalescence-Induced Droplet-Jumping on Nanostructured Superhydrophobic Surfaces in the Absence of Microstructures.

PubMed

Zhang, Peng; Maeda, Yota; Lv, Fengyong; Takata, Yasuyuki; Orejon, Daniel

2017-10-11

Superhydrophobic surfaces are receiving increasing attention due to the enhanced condensation heat transfer, self-cleaning, and anti-icing properties by easing droplet self-removal. Despite the extensive research carried out on this topic, the presence or absence of microstructures on droplet adhesion during condensation has not been fully addressed yet. In this work we, therefore, study the condensation behavior on engineered superhydrophobic copper oxide surfaces with different structural finishes. More specifically, we investigate the coalescence-induced droplet-jumping performance on superhydrophobic surfaces with structures varying from the micro- to the nanoscale. The different structural roughness is possible due to the specific etching parameters adopted during the facile low-cost dual-scale fabrication process. A custom-built optical microscopy setup inside a temperature and relative humidity controlled environmental chamber was used for the experimental observations. By varying the structural roughness, from the micro- to the nanoscale, important differences on the number of droplets involved in the jumps, on the frequency of the jumps, and on the size distribution of the jumping droplets were found. In the absence of microstructures, we report an enhancement of the droplet-jumping performance of small droplets with sizes in the same order of magnitude as the microstructures. Microstructures induce further droplet adhesion, act as a structural barrier for the coalescence between droplets growing on the same microstructure, and cause the droplet angular deviation from the main surface normal. As a consequence, upon coalescence, there is a decrease in the net momentum in the out-of-plane direction, and the jump does not ensue. We demonstrate that the absence of microstructures has therefore a positive impact on the coalescence-induced droplet-jumping of micrometer droplets for antifogging, anti-icing, and condensation heat transfer applications.

Solidification of undercooled liquids

NASA Technical Reports Server (NTRS)

Perepezko, J. H.; Shiohara, Y.; Paik, J. S.; Flemmings, M. C.

1982-01-01

During rapid solidification processing (RSP) the amount of liquid undercooling is an important factor in determining microstructural development by controlling phase selection during nucleation and morphological evolution during crystal growth. While undercooling is an inherent feature of many techniques of RSP, the deepest undercoolings and most controlled studies have been possible in carefully prepared fine droplet samples. From past work and recent advances in studies of nucleation kinetics it has become clear that the initiation of crystallization during RSP is governed usually by heterogeneous sites located at surfaces. With known nucleant sites, it has been possible to identify specific pathways of metastable phase formation and microstructural development in alloys. These advances have allowed for a clearer assessment of the interplay between undercooling, cooling rate and particle size statistics in structure formation. New approaches to the examination of growth processes have been developed to follow the thermal behavior and morphology in small samples in the period of rapid crystallization and recalescence. Based upon the new experimental information from these studies, useful models can be developed for the overall solidification process to include nucleation behavior, thermodynamic constraints, thermal history, growth kinetics, solute redistribution and resulting structures. From the refinement of knowledge concerning the underlying factors that govern RSP a basis is emerging for an effective alloy design and processing strategy.

Membrane-on-a-chip: microstructured silicon/silicon-dioxide chips for high-throughput screening of membrane transport and viral membrane fusion.

PubMed

Kusters, Ilja; van Oijen, Antoine M; Driessen, Arnold J M

2014-04-22

Screening of transport processes across biological membranes is hindered by the challenge to establish fragile supported lipid bilayers and the difficulty to determine at which side of the membrane reactants reside. Here, we present a method for the generation of suspended lipid bilayers with physiological relevant lipid compositions on microstructured Si/SiO2 chips that allow for high-throughput screening of both membrane transport and viral membrane fusion. Simultaneous observation of hundreds of single-membrane channels yields statistical information revealing population heterogeneities of the pore assembly and conductance of the bacterial toxin α-hemolysin (αHL). The influence of lipid composition and ionic strength on αHL pore formation was investigated at the single-channel level, resolving features of the pore-assembly pathway. Pore formation is inhibited by a specific antibody, demonstrating the applicability of the platform for drug screening of bacterial toxins and cell-penetrating agents. Furthermore, fusion of H3N2 influenza viruses with suspended lipid bilayers can be observed directly using a specialized chip architecture. The presented micropore arrays are compatible with fluorescence readout from below using an air objective, thus allowing high-throughput screening of membrane transport in multiwell formats in analogy to plate readers.

A laboratory means to produce tough aluminum sheet from powder

NASA Technical Reports Server (NTRS)

Singleton, O. R.; Royster, D. M.; Thomas, J. R.

1990-01-01

The rapid solidification of aluminum alloys as powder and the subsequent fabrication processes can be used to develop and tailor alloys to satisfy specific aerospace design requirements, including high strength and toughness. Laboratory procedures to produce aluminum powder-metallurgy (PM) materials are efficient but require evidence that the laboratory methods used can produce a product with superior properties. This paper describes laboratory equipment and procedures which can be used to produce tough aluminum PM sheet. The processing of a 2124 + 0.9 percent Zr aluminum alloy powder is used as an example. The fully hardened sheet product is evaluated in terms of properties and microstructure. The key features of the vacuum hot press pressing operation used to consolidate the powder are described. The 2124 + 0.9 percent Zr - T8 temper aluminum sheet produced was both strong (460-490 MPa yield strength) and tough (Kahn Tear unit-propagation- energy values over three times those typical for ingot metallurgy 2024-T81). Both the longitudinal and longitudinal-transverse directions of the sheet were tested. The microstructure was well refined with subgrains of one or two micrometers. Fine dispersoids of Al3Zr in the precipitate free regions adjacent to boundaries are believed to contribute to the improved toughness.

Non-destructive thermo-mechanical behavior assessment of glass-ceramics for dental applications

NASA Astrophysics Data System (ADS)

Kordatos, E. Z.; Abdulkadhim, Z.; Feteira, A. M.

2017-05-01

Every year millions of people seek dental treatment to either repair damaged, unaesthetic and dysfunctional teeth or replace missing natural teeth. Several dental materials have been developed to meet the stringent requirements in terms of mechanical properties, aesthetics and chemical durability in the oral environment. Glass-ceramics exhibit a suitable combination of these properties for dental restorations. This research is focused on the assessment of the thermomechanical behavior of bio-ceramics and particularly lithium aluminosilicate glass-ceramics (LAS glass-ceramics). Specifically, methodologies based on Infrared Thermography (IRT) have been applied in order the structure - property relationship to be evaluated. Non-crystallized, partially crystallized and fully crystallized glass-ceramic samples have been non-destructively assessed in order their thermo-mechanical behavior to be associated with their micro-structural features.

Microstructure Formation in Dissimilar Metal Welds: Electron Beam Welding of Ti/Ni

NASA Astrophysics Data System (ADS)

Chatterjee, Subhradeep; Abinandanan, T. A.; Reddy, G. Madhusudhan; Chattopadhyay, Kamanio

2016-02-01

We present results for electron beam welding of a binary Ti/Ni dissimilar metal couple. The difference in physical properties of the base metals and metallurgical features (thermodynamics and kinetics) of the system influence both macroscopic transport and microstructure development in the weld. Microstructures near the fusion interfaces are markedly different from those inside the weld region. At the Ti side, Ti2Ni dendrites are observed to grow toward the fusion interface, while in the Ni side, layered growth of γ-Ni, Ni3Ti, and Ni3Ti + NiTi eutectic is observed. Different morphologies of the latter eutectic constitute the predominant microstructure inside the weld metal region. These results are compared and contrasted with those from laser welding of the same binary couple, and a scheme of solidification is proposed to explain the observations. This highlights notable departures from welding of similar and other dissimilar metals such as a significant asymmetry in heat transport that governs progress of solidification from each side of the couple, and a lack of unique liquidus isotherm characterizing the liquid-solid front.

Grain Cluster Microstructure and Grain Boundary Character Distribution in Alloy 690

NASA Astrophysics Data System (ADS)

Xia, Shuang; Zhou, Bangxin; Chen, Wenjue

2009-12-01

The effects of thermal-mechanical processing (TMP) on microstructure evolution during recrystallization and grain boundary character distribution (GBCD) in aged Alloy 690 were investigated by the electron backscatter diffraction (EBSD) technique and optical microscopy. The original grain boundaries of the deformed microstructure did not play an important role in the manipulation of the proportion of the Σ3 n ( n = 1, 2, 3…) type boundaries. Instead, the grain cluster formed by multiple twinning starting from a single nucleus during recrystallization was the key microstructural feature affecting the GBCD. All of the grains in this kind of cluster had Σ3 n mutual misorientations regardless of whether they were adjacent. A large grain cluster containing 91 grains was found in the sample after a small-strain (5 pct) and a high-temperature (1100 °C) recrystallization anneal, and twin relationships up to the ninth generation (Σ39) were found in this cluster. The ratio of cluster size over grain size (including all types of boundaries as defining individual grains) dictated the proportion of Σ3 n boundaries.

Microstructures, Mechanical Properties, and Strain Hardening Behavior of an Ultrahigh Strength Dual Phase Steel Developed by Intercritical Annealing of Cold-Rolled Ferrite/Martensite

NASA Astrophysics Data System (ADS)

Mazaheri, Y.; Kermanpur, A.; Najafizadeh, A.

2015-07-01

A dual phase (DP) steel was produced by a new process utilizing an uncommon cold-rolling and subsequent intercritical annealing of a martensite-ferrite duplex starting structure. Ultrafine grained DP steels with an average grain size of about 2 μm and chain-networked martensite islands were achieved by short intercritical annealing of the 80 pct cold-rolled duplex microstructure. The strength of the low carbon steel with the new DP microstructure was reached about 1300 MPa (140 pct higher than that of the as-received state, e.g., 540 MPa), without loss of ductility. Tensile testing revealed good strength-elongation balance for the new DP steels (UTS × UE ≈ 11,000 to 15,000 MPa pct) in comparison with the previous works and commercially used high strength DP steels. Two strain hardening stages with comparable exponents were observed in the Holloman analysis of all DP steels. The variations of hardness, strength, elongation, and strain hardening behavior of the specimens with thermomechanical parameters were correlated to microstructural features.

Fast and cheap fabrication of molding tools for polymer replication

NASA Astrophysics Data System (ADS)

Richter, Christiane; Kirschner, Nadine; Worgull, Matthias; Rapp, Bastian E.

2017-02-01

Polymer replication is a prerequisite for low-cost microstructure components for consumer and end user market. The production of cost-effective microstructure in polymers requires metal molding tools which are often fabricated by direct structuring methods like milling or laser machining both of which are time-consuming and cost-intensive. We present an alternative fabrication method based on replication processes which allows the cheap ( 50 €) and fast ( 12 h) replication of complex microstructures into metal. The process comprises three steps: 1. Generation of the microstructure in a photoresist via lithography. 2. Casting of the structure into a high-temperature silicone which serves as original mold for creation of the metal molding tool. 3. Melting of an eutectic alloy of Sn, Ag and Cu under light pressure directly inside of the silicone within an oven. After cooling to room temperature the metal molding tool can be used for polymer replication into conventional thermoplastic polymers. As a first example we structured polymethylmethacrylate (PMMA) foils with a thickness of 1 mm via hot embossing and feature sizes of 100 μm could be replicated with high fidelity.

Influence of Cu Content on the Microstructure and Mechanical Properties of Cr-Cu-N Coatings

PubMed Central

Ding, Ji Cheng; Zhang, Teng Fei; Wan, Zhi Xin; Mei, Hai Juan; Kang, Myung Chang

2018-01-01

The Cr-Cu-N coatings with various Cu contents (0–25.18 (±0.17) at.%) were deposited on Si wafer and stainless steel (SUS 304) substrates in reactive Ar+N2 gas mixture by a hybrid coating system combining pulsed DC and RF magnetron sputtering techniques. The influence of Cu content on the coating composition, microstructure, and mechanical properties was investigated. The microstructure of the coatings was significantly altered by the introduction of Cu. The deposited coatings exhibit solid solution structure with different compositions in all of the samples. Addition of Cu is intensively favored for preferred orientation growth along (200) direction by restricting in (111) direction. With increasing Cu content, the surface and cross-sectional morphology of coatings were changed from triangle cone-shaped, columnar feature to broccoli-like and compact glassy microstructure, respectively. The mechanical properties including the residual stress, nanohardness, and toughness of the coatings were explored on the basis of Cu content. The highest hardness was obtained at the Cu content of 1.49 (±0.10) at.%. PMID:29552269

Microstructure and degradation performance of biodegradable Mg-Si-Sr implant alloys.

PubMed

Gil-Santos, Andrea; Marco, Iñigo; Moelans, Nele; Hort, Norbert; Van der Biest, Omer

2017-02-01

In this work the microstructure and degradation behavior of several as-cast alloy compositions belonging to the Mg rich corner of the Mg-Si-Sr system are presented and related. The intermetallic phases are identified and analyzed describing the microstructure evolution during solidification. It is intended in this work to obtain insight in the behavior of the ternary alloys in in vitro tests and to analyze the degradation behavior of the alloys under physiologically relevant conditions. The as-cast specimens have been exposed to immersion tests, both mass loss (ML) and potentiodynamic polarization (PDP). The degradation rate (DR) have been assessed and correlated to microstructure features, impurity levels and alloy composition. The initial reactions resulted to be more severe while the degradation stabilizes with time. A higher DR is related with a high content of the Mg 17 Sr 2 phase and with the presence of coarse particles of the intermetallics Mg 2 Si, MgSiSr and MgSi 2 Sr. Specimens with a higher DR typically have higher levels of impurities and alloy contents. Copyright © 2016 Elsevier B.V. All rights reserved.

New Development in Selective Laser Melting of Ti-6Al-4V: A Wider Processing Window for the Achievement of Fully Lamellar α + β Microstructures

NASA Astrophysics Data System (ADS)

Lui, E. W.; Xu, W.; Pateras, A.; Qian, M.; Brandt, M.

2017-12-01

Recent progress has shown that Ti-6Al-4V fabricated by selective laser melting (SLM) can achieve a fully lamellar α + β microstructure using 60 µm layer thickness in the as-built state via in situ martensite decomposition by manipulating the processing parameters. The potential to broaden the processing window was explored in this study by increasing the layer thickness to the less commonly used 90 µm. Fully lamellar α + β microstructures were produced in the as-built state using inter-layer times in the range of 1-12 s. Microstructural features such as the α-lath thickness and morphology were sensitive to both build height and inter-layer time. The α-laths produced using the inter-layer time of 1 s were much coarser than those produced with the inter-layer time of 12 s. The fine fully lamellar α + β structure resulted in tensile ductility of 11% and yield strength of 980 MPa. The tensile properties can be further improved by minimizing the presence of process-induced defects.

Influence of Cu Content on the Microstructure and Mechanical Properties of Cr-Cu-N Coatings.

PubMed

Ding, Ji Cheng; Zhang, Teng Fei; Wan, Zhi Xin; Mei, Hai Juan; Kang, Myung Chang; Wang, Qi Min; Kim, Kwang Ho

2018-01-01

The Cr-Cu-N coatings with various Cu contents (0-25.18 (±0.17) at.%) were deposited on Si wafer and stainless steel (SUS 304) substrates in reactive Ar+N 2 gas mixture by a hybrid coating system combining pulsed DC and RF magnetron sputtering techniques. The influence of Cu content on the coating composition, microstructure, and mechanical properties was investigated. The microstructure of the coatings was significantly altered by the introduction of Cu. The deposited coatings exhibit solid solution structure with different compositions in all of the samples. Addition of Cu is intensively favored for preferred orientation growth along (200) direction by restricting in (111) direction. With increasing Cu content, the surface and cross-sectional morphology of coatings were changed from triangle cone-shaped, columnar feature to broccoli-like and compact glassy microstructure, respectively. The mechanical properties including the residual stress, nanohardness, and toughness of the coatings were explored on the basis of Cu content. The highest hardness was obtained at the Cu content of 1.49 (±0.10) at.%.

Improving microstructural quantification in FIB/SEM nanotomography.

PubMed

Taillon, Joshua A; Pellegrinelli, Christopher; Huang, Yi-Lin; Wachsman, Eric D; Salamanca-Riba, Lourdes G

2018-01-01

FIB/SEM nanotomography (FIB-nt) is a powerful technique for the determination and quantification of the three-dimensional microstructure in subsurface features. Often times, the microstructure of a sample is the ultimate determiner of the overall performance of a system, and a detailed understanding of its properties is crucial in advancing the materials engineering of a resulting device. While the FIB-nt technique has developed significantly in the 15 years since its introduction, advanced nanotomographic analysis is still far from routine, and a number of challenges remain in data acquisition and post-processing. In this work, we present a number of techniques to improve the quality of the acquired data, together with easy-to-implement methods to obtain "advanced" microstructural quantifications. The techniques are applied to a solid oxide fuel cell cathode of interest to the electrochemistry community, but the methodologies are easily adaptable to a wide range of material systems. Finally, results from an analyzed sample are presented as a practical example of how these techniques can be implemented. Copyright © 2017 Elsevier B.V. All rights reserved.

Optical and Calorimetric Studies of Cholesterol-Rich Filamentous, Helical Ribbon and Crystal Microstructures

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

Miroshnikova, Y. A.; Elsenbeck, M.; Zastavker, Y. V.

2009-04-19

Formation of biological self-assemblies at all scales is a focus of studies in fields ranging from biology to physics to biomimetics. Understanding the physico-chemical properties of these self-assemblies may lead to the design of bio-inspired structures and technological applications. Here we examine self-assembled filamentous, helical ribbon, and crystal microstructures formed in chemically defined lipid concentrate (CDLC), a model system for cholesterol crystallization in gallbladder bile. CDLC consists of cholesterol, bilayer-forming amphiphiles, micelle-forming amphiphiles, and water. Phase contrast and differential interference contrast (DIC) microscopy indicate the presence of three microstructure types in all samples studied, and allow for an investigation ofmore » the structures' unique geometries. Additionally, confocal microscopy is used for qualitative assessment of surface and internal composition. To complement optical observations, calorimetric (differential-scanning and modulation) experiments, provide the basis for an in-depth understanding of collective and individual thermal behavior. Observed ''transition'' features indicate clustering and ''straightening'' of helical ribbons into short, increasingly thickening, filaments that dissolve with increasing temperature. These results suggest that all microstructures formed in CDLC may coexist in a metastable chemical equilibrium. Further investigation of the CDLC thermal profile should uncover the process of cholesterol crystallization as well as the unique design and function of microstructures formed in this system.« less

Continuum understanding of twin formation near grain boundaries of FCC metals with low stacking fault energy

NASA Astrophysics Data System (ADS)

Jung, Jaimyun; Yoon, Jae Ik; Kim, Jung Gi; Latypov, Marat I.; Kim, Jin You; Kim, Hyoung Seop

2017-12-01

Deformation twinning from grain boundaries is often observed in face-centered cubic metals with low stacking fault energy. One of the possible factors that contribute to twinning origination from grain boundaries is the intergranular interactions during deformation. Nonetheless, the influence of mechanical interaction among grains on twin evolution has not been fully understood. In spite of extensive experimental and modeling efforts on correlating microstructural features with their twinning behavior, a clear relation among the large aggregate of grains is still lacking. In this work, we characterize the micromechanics of grain-to-grain interactions that contribute to twin evolution by investigating the mechanical twins near grain boundaries using a full-field crystal plasticity simulation of a twinning-induced plasticity steel deformed in uniaxial tension at room temperature. Microstructures are first observed through electron backscatter diffraction technique to obtain data to reconstruct a statistically equivalent microstructure through synthetic microstructure building. Grain-to-grain micromechanical response is analyzed to assess the collective twinning behavior of the microstructural volume element under tensile deformation. Examination of the simulated results reveal that grain interactions are capable of changing the local mechanical behavior near grain boundaries by transferring strain across grain boundary or localizing strain near grain boundary.

An Investigation of TIG welding parameters on microhardness and microstructure of heat affected zone of HSLA steel

NASA Astrophysics Data System (ADS)

Musa, M. H. A.; Maleque, M. A.; Ali, M. Y.

2018-01-01

Nowadays a wide variety of metal joining methods are used in fabrication industries. In this study, the effect of various welding parameters of the TIG welding process on microhardness, depth, and microstructure of the heat-affected zone (HAZ) of L450 HSLA steel and optimizing these process parameters following Taguchi experimental design was investigated. The microhardness tended to increase significantly with the increase of welding speed from 1.0 to 2.5 mm/s whereas the width of HAZ decreased. The current and arc voltage was found to be less significant in relative comparison. Microstructures of the welded samples were also studied to analyze the changes in the microstructure of the material in terms of ferrite, pearlite, bainite, and martensite formations. Welding speed was found to be the most significant factors leading to changes in microhardness and metallurgical properties. The increase of welding heat input caused an increase in width (depth) of HAZ and the growth of prior austenite grains and then enlarged the grain size of coarse grain heat affected zone (CGHAZ). However, the amount of martensite in the HAZ decreased accompanied by an opposite change of paint. It was observed that the hardness properties and the microstructural feature of HAZ area was strongly affected by the welding parameters.

In-situ Observation of Cross-Sectional Microstructural Changes and Stress Distributions in Fracturing TiN Thin Film during Nanoindentation.

PubMed

Zeilinger, Angelika; Todt, Juraj; Krywka, Christina; Müller, Martin; Ecker, Werner; Sartory, Bernhard; Meindlhumer, Michael; Stefenelli, Mario; Daniel, Rostislav; Mitterer, Christian; Keckes, Jozef

2016-03-07

Load-displacement curves measured during indentation experiments on thin films depend on non-homogeneous intrinsic film microstructure and residual stress gradients as well as on their changes during indenter penetration into the material. To date, microstructural changes and local stress concentrations resulting in plastic deformation and fracture were quantified exclusively using numerical models which suffer from poor knowledge of size dependent material properties and the unknown intrinsic gradients. Here, we report the first in-situ characterization of microstructural changes and multi-axial stress distributions in a wedge-indented 9 μm thick nanocrystalline TiN film volume performed using synchrotron cross-sectional X-ray nanodiffraction. During the indentation, needle-like TiN crystallites are tilted up to 15 degrees away from the indenter axis in the imprint area and strongly anisotropic diffraction peak broadening indicates strain variation within the X-ray nanoprobe caused by gradients of giant compressive stresses. The morphology of the multiaxial stress distributions with local concentrations up to -16.5 GPa correlate well with the observed fracture modes. The crack growth is influenced decisively by the film microstructure, especially by the micro- and nano-scopic interfaces. This novel experimental approach offers the capability to interpret indentation response and indenter imprint morphology of small graded nanostructured features.

Sensitivity of Austempering Heat Treatment of Ductile Irons to Changes in Process Parameters

NASA Astrophysics Data System (ADS)

Boccardo, A. D.; Dardati, P. M.; Godoy, L. A.; Celentano, D. J.

2018-06-01

Austempered ductile iron (ADI) is frequently obtained by means of a three-step austempering heat treatment. The parameters of this process play a crucial role on the microstructure of the final product. This paper considers the influence of some process parameters ( i.e., the initial microstructure of ductile iron and the thermal cycle) on key features of the heat treatment (such as minimum required time for austenitization and austempering and microstructure of the final product). A computational simulation of the austempering heat treatment is reported in this work, which accounts for a coupled thermo-metallurgical behavior in terms of the evolution of temperature at the scale of the part being investigated (the macroscale) and the evolution of phases at the scale of microconstituents (the microscale). The paper focuses on the sensitivity of the process by looking at a sensitivity index and scatter plots. The sensitivity indices are determined by using a technique based on the variance of the output. The results of this study indicate that both the initial microstructure and the thermal cycle parameters play a key role in the production of ADI. This work also provides a guideline to help selecting values of the appropriate process parameters to obtain parts with a required microstructural characteristic.

Elucidating doping driven microstructure evolution and optical properties of lead sulfide thin films grown from a chemical bath

NASA Astrophysics Data System (ADS)

Mohanty, Bhaskar Chandra; Bector, Keerti; Laha, Ranjit

2018-03-01

Doping driven remarkable microstructural evolution of PbS thin films grown by a single-step chemical bath deposition process at 60 °C is reported. The undoped films were discontinuous with octahedral-shaped crystallites after 30 min of deposition, whereas Cu doping led to a distinctly different surface microstructure characterized by densely packed elongated crystallites. A mechanism, based on the time sequence study of microstructural evolution of the films, and detailed XRD and Raman measurements, has been proposed to explain the contrasting microstructure of the doped films. The incorporation of Cu forms an interface layer, which is devoid of Pb. The excess Cu ions in this interface layer at the initial stages of film growth strongly interact and selectively stabilize the charged {111} faces containing either Pb or S compared to the uncharged {100} faces that contain both Pb and S. This interaction interferes with the natural growth habit resulting in the observed surface features of the doped films. Concurrently, the Cu-doping potentially changed the optical properties of the films: A significant widening of the bandgap from 1.52 eV to 1.74 eV for increase in Cu concentration from 0 to 20% was observed, making it a highly potential absorber layer in thin film solar cells.

The Microstructural Evolution of Fatigue Cracks in FCC Metals

NASA Astrophysics Data System (ADS)

Gross, David William

The microstructural evolution during fatigue crack propagation was investigated in a variety of planar and wavy slip FCC metals. The planar materials included Haynes 230, Nitronic 40, and 316 stainless steel, and the wavy materials included pure nickel and pure copper. Three different sets of experiments were performed to fully characterize the microstructural evolution. The first, performed on Haynes 230, mapped the strain field ahead a crack tip using digital image correlation and electron backscatter diffraction techniques. Focused ion beam (FIB) lift-out techniques were then utilized to extract transmission electron microscopy (TEM) samples at specific distances from the crack tip. TEM investigations compared the measured strain to the microstructure. Overall, the strain measured via DIC and EBSD was only weakly correlated to the density of planar slip bands in the microstructure. The second set of experiments concerned the dislocation structure around crack tips. This set of experiments was performed on all the materials. The microstructure at arrested fatigue cracks on the free surface was compared to the microstructure found beneath striations on the fracture surfaces by utilizing FIB micromachining to create site-specific TEM samples. The evolved microstructure depended on the slip type. Strong agreement was found between the crack tip microstructure at the free surface and the fracture surface. In the planar materials, the microstructure in the plastic zone consisted of bands of dislocations or deformation twins, before transitioning to a refined sub-grain microstructure near the crack flank. The sub-grain structure extended 300-500 nm away from the crack flank in all the planar slip materials studied. In contrast, the bulk structure in the wavy slip material consisted of dislocation cells and did not transition to a different microstructure as the crack tip was approached. The strain in wavy slip was highest near the crack tip, as the misorientations between the dislocation cells increased and the cell size decreased as the crack flank was approached. The final set of experiments involved reloading the arrested crack tips in monotonic tension. This was performed on both the Haynes 230 and 316 stainless steel. This technique exposed the fracture surface and location of the arrested crack tip away from the free surface, allowing for a sample to be extracted via FIB micromachining and TEM evaluation of the microstructure. This permitted the crack tip microstructure to be investigated without exposing the microstructure to crack closure or free surface effects. These experiments confirmed what was inferred from the earlier experiments, namely that the banded structure was a product of the crack tip plastic zone and the refined structure was a product of the strain associated with crack advance. Overall the microstructural complexity presented in this work was much higher than would be predicted by current models of fatigue crack propagation. It is recommended that future models attempt to simulate interactions between the dislocations emitted during fatigue crack growth and the pre-existing microstructure to more accurately simulate the processes occurring at the crack tip during crack growth.

Decreased consumption of sweet fluids in mu opioid receptor knockout mice: a microstructural analysis of licking behavior

PubMed Central

Ostlund, Sean B.; Kosheleff, Alisa; Maidment, Nigel T.; Murphy, Niall P.

2013-01-01

Summary Rationale Evidence suggests that the palatability of food (i.e., the hedonic impact produced by its sensory features) can promote feeding and may underlie compulsive eating, leading to obesity. Pharmacological studies implicate opioid transmission in the hedonic control of feeding, though these studies often rely on agents lacking specificity for particular opioid receptors. Objectives Here, we investigated the role of mu opioid receptors (MORs) specifically in determining hedonic responses to palatable sweet stimuli. Methods In Experiment 1, licking microstructure when consuming sucrose solution (2 to 20 %) was compared in MOR knockout and wildtype mice as a function of sucrose concentration and level of food deprivation. In Experiment 2, a similar examination was conducted using the palatable but calorie-free stimulus sucralose (0.001 to 1%), allowing study of licking behavior independent of homeostatic variables. Results In Experiment 1, MOR knockout mice exhibited several alterations in sucrose licking. Although wildtype mice exhibited a two-fold increase in the burst length when food deprived, relative to the nondeprived test, this aspect of sucrose licking was generally insensitive to manipulations of food deprivation for MOR knockout mice. Furthermore, during concentration testing, their rate of sucrose licking was less than half that of wildtype mice. During sucralose testing (Experiment 2), MOR knockout mice licked at approximately half the wildtype rate, providing more direct evidence that MOR knockout mice were impaired in processing stimulus palatability. Conclusions These results suggest that transmission through MORs mediates hedonic responses to palatable stimuli, and therefore likely contributes to normal and pathological eating. PMID:23568577

Microstructure Optimization of Dual-Phase Steels Using a Representative Volume Element and a Response Surface Method: Parametric Study

NASA Astrophysics Data System (ADS)

Belgasam, Tarek M.; Zbib, Hussein M.

2017-12-01

Dual-phase (DP) steels have received widespread attention for their low density and high strength. This low density is of value to the automotive industry for the weight reduction it offers and the attendant fuel savings and emission reductions. Recent studies on developing DP steels showed that the combination of strength/ductility could be significantly improved when changing the volume fraction and grain size of phases in the microstructure depending on microstructure properties. Consequently, DP steel manufacturers are interested in predicting microstructure properties and in optimizing microstructure design. In this work, a microstructure-based approach using representative volume elements (RVEs) was developed. The approach examined the flow behavior of DP steels using virtual tension tests with an RVE to identify specific mechanical properties. Microstructures with varied martensite and ferrite grain sizes, martensite volume fractions, carbon content, and morphologies were studied in 3D RVE approaches. The effect of these microstructure parameters on a combination of strength/ductility of DP steels was examined numerically using the finite element method by implementing a dislocation density-based elastic-plastic constitutive model, and a Response surface methodology to determine the optimum conditions for a required combination of strength/ductility. The results from the numerical simulations are compared with experimental results found in the literature. The developed methodology proves to be a powerful tool for studying the effect and interaction of key microstructural parameters on strength and ductility and thus can be used to identify optimum microstructural conditions.

Microstructure effects on the recrystallization of low-symmetry alpha-uranium

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

McCabe, Rodney James; Richards, Andrew Walter; Coughlin, Daniel Robert

2015-10-01

We employ electron backscatter diffraction (EBSD) to investigate microstructural evolution of uranium during recrystallization. To understand the relationship between microstructure and recrystallization, we use measures of intra-granular misorientation within grains and near grain boundaries in both deformed (non-recrystallized) uranium and recrystallizing uranium. The data show that the level of intra-granular misorientation depends on crystallographic orientation. However, contrary to expectation, this relationship does not significantly affect the recrystallization texture. Rather, the analysis suggests that recrystallization nucleation occurs along high angle grain boundaries in the deformed microstructure. Specifically, we show that the nucleation of recrystallized grains correlates well with the spatially heterogeneousmore » distribution of high angle boundaries. Due to the inhomogeneous distribution of high angle boundaries, the recrystallized microstructure after long times exhibits clustered distributions of small and large grains. Twin boundaries do not appear to act as recrystallization nucleation sites.« less

Location-dependent correlation between tissue structure and the mechanical behaviour of the urinary bladder.

PubMed

Morales-Orcajo, Enrique; Siebert, Tobias; Böl, Markus

2018-05-25

The mechanical properties of the urinary bladder wall are important to understand its filling-voiding cycle in health and disease. However, much remains unknown about its mechanical properties, especially regarding regional heterogeneities and wall microstructure. The present study aimed to assess the regional differences in the mechanical properties and microstructure of the urinary bladder wall. Ninety (n=90) samples of porcine urinary bladder wall (ten samples from nine different locations) were mechanically and histologically analysed. Half of the samples (n=45) were equibiaxially tested within physiological conditions, and the other half, matching the sample location of the mechanical tests, was frozen, cryosectioned, and stained with Picro-Sirius red to differentiate smooth muscle cells, extracellular matrix, and fat. The bladder wall shows a non-linear stress-stretch relationship with hysteresis and softening effects. Regional differences were found in the mechanical response and in the microstructure. The trigone region presents higher peak stresses and thinner muscularis layer compared to the rest of the bladder. Furthermore, the ventral side of the bladder presents anisotropic characteristics, whereas the dorsal side features perfect isotropic behaviour. This response matches the smooth muscle fibre bundle orientation within the tunica muscularis. This layer, comprising approximately 78% of the wall thickness, is composed of two fibre bundle arrangements that are cross-oriented, one with respect to the other, varying the angle between them across the organ. That is, the ventral side presents a 60°/120° cross-orientation structure, while the muscle bundles were oriented perpendicular in the dorsal side. In the present study, we demonstrate that the mechanical properties and the microstructure of the urinary bladder wall are heterogeneous across the organ. The mechanical properties and the microstructure of the urinary bladder wall within nine specific locations matching explicitly the mechanical and structural variations have been examined. On the one hand, the results of this study contribute to the understanding of bladder mechanics and thus to their functional understanding of bladder filling and voiding. On the other hand, they are relevant to the fields of constitutive formulation of bladder tissue, whole bladder mechanics, and bladder-derived scaffolds i.e., tissue-engineering grafts. Copyright © 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Influence of Starting Powders on Hydroxyapatite Coatings Fabricated by Room Temperature Spraying Method.

PubMed

Seo, Dong Seok; Lee, Jong Kook; Hwang, Kyu Hong; Hahn, Byung Dong; Yoon, Seog Young

2015-08-01

Three types of raw materials were used for the fabrication of hydroxyapatite coatings by using the room temperature spraying method and their influence on the microstructure and in vitro characteristics were investigated. Starting hydroxyapatite powders for coatings on titanium substrate were prepared by a heat treatment at 1100 °C for 2 h of bovine bone, bone ash, and commercial hydroxyapatite powders. The phase compositions and Ca/P ratios of the three hydroxyapatite coatings were similar to those of the raw materials without decomposition or formation of a new phase. All hydroxyapatite coatings showed a honeycomb structure, but their surface microstructures revealed different features in regards to surface morphology and roughness, based on the staring materials. All coatings consisted of nano-sized grains and had dense microstructure. Inferred from in vitro experiments in pure water, all coatings have a good dissolution-resistance and biostability in water.

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

Xu, Pei-quan; Li, Leijun, E-mail: leijun.li@ualberta.ca; Zhang, Chunbo

The as-welded microstructure of laser-welded Ti-6Al-4V is characterized as a function of CO2 key-hole mode laser welding speed. Martensitic α′ is the predominant phase, with some α and retained β. Phase transformation is affected by the cooling rate through laser welding speed. A higher welding speed of 1.6 to 2.0 m/min produced more martensite α′ and less retained β in the welds. 1.4 m/min welding speed produced small amounts of α, besides the martensite α′. A trace of δ titanium hydride phase seems to have formed in the weld fusion zone. Moiré fringes are a common feature in the TEMmore » microstructure, due to abundance of multi-phase interfaces. Tensile twins and clusters of dislocations indicate that plastic deformation has happened in the as-welded microstructure, indicating the local stress levels to be approaching the yield stress on-cooling during laser welding.« less

Dynamic Analysis of Recalescence Process and Interface Growth of Eutectic Fe82B17Si1 Alloy

NASA Astrophysics Data System (ADS)

Fan, Y.; Liu, A. M.; Chen, Z.; Li, P. Z.; Zhang, C. H.

2018-03-01

By employing the glass fluxing technique in combination with cyclical superheating, the microstructural evolution of the undercooled Fe82B17Si1 alloy in the obtained undercooling range was studied. With increase in undercooling, a transition of cooling curves was detected from one recalescence to two recalescences, followed by one recalescence. The two types of cooling curves were fitted by the break equation and the Johnson-Mehl-Avrami-Kolmogorov model. Based on the cooling curves at different undercoolings, the recalescence rate was calculated by the multi-logistic growth model and the Boettinger-Coriel-Trivedi model. Both the recalescence features and the interface growth kinetics of the eutectic Fe82B17Si1 alloy were explored. The fitting results that were obtained using TEM (SAED), SEM and XRD were consistent with the changing rule of microstructures. Finally, the relationship between the microstructure and hardness was also investigated.

On flaw tolerance of nacre: a theoretical study

PubMed Central

Shao, Yue; Zhao, Hong-Ping; Feng, Xi-Qiao

2014-01-01

As a natural composite, nacre has an elegant staggered ‘brick-and-mortar’ microstructure consisting of mineral platelets glued by organic macromolecules, which endows the material with superior mechanical properties to achieve its biological functions. In this paper, a microstructure-based crack-bridging model is employed to investigate how the strength of nacre is affected by pre-existing structural defects. Our analysis demonstrates that owing to its special microstructure and the toughening effect of platelets, nacre has a superior flaw-tolerance feature. The maximal crack size that does not evidently reduce the tensile strength of nacre is up to tens of micrometres, about three orders higher than that of pure aragonite. Through dimensional analysis, a non-dimensional parameter is proposed to quantify the flaw-tolerance ability of nacreous materials in a wide range of structural parameters. This study provides us some inspirations for optimal design of advanced biomimetic composites. PMID:24402917

Synthesis and microstructure of electrodeposited and sputtered nanotwinned face-centered-cubic metals

DOE PAGES

Bufford, Daniel C.; Wang, Morris; Liu, Yue; ...

2016-04-01

The remarkable properties of nanotwinned (NT) face-centered-cubic (fcc) metals arise directly from twin boundaries, the structures of which can be initially determined by growth twinning during the deposition process. When we understand the synthesis process and its relation to the resulting microstructure, and ultimately to material properties, we realize how key it is to understanding and utilizing these materials. Furthermore, our article presents recent studies on electrodeposition and sputtering methods that produce a high density of nanoscale growth twins in fcc metals. Nanoscale growth twins tend to form spontaneously in monolithic and alloyed fcc metals with lower stacking-fault energies, whilemore » engineered approaches are necessary for fcc metals with higher stacking-fault energies. Finally, growth defects and other microstructural features that influence nanotwin behavior and stability are introduced here, and future challenges in fabricating NT materials are highlighted.« less

The effect of forging history on the strength and microstructure of TDNiCr /Ni-20Cr-2ThO2/

NASA Technical Reports Server (NTRS)

Filippi, A. M.

1975-01-01

Forging variables were evaluated to determine their influence on the elevated temperature strength and microstructure of TDNiCr. Grain size was the principal microstructural feature related to elevated temperature strength and was controlled primarily by the thermomechanical variables of forging temperature and final annealing condition. Tests at 1366 K revealed a factor of eight increase in tensile strength as grain size increased from 1 to 150 microns, while stress-rupture strength improved by three to five times as grain size increased from 15 to 150 microns. Forged material of grain size greater than or equal to about 150 microns displayed a level of elevated temperature strength comparable to that of optimized TDNiCr sheet. The presence of a preponderance of small twins and a strong preferred orientation may have also been factors contributing to the excellent high temperature strength of large grain forged material.

Predicting Deformation Limits of Dual-Phase Steels Under Complex Loading Paths

DOE PAGES

Cheng, G.; Choi, K. S.; Hu, X.; ...

2017-04-05

Here in this study, the deformation limits of various DP980 steels are examined with the deformation instability theory. Under uniaxial tension, overall stress–strain curves of the material are estimated based on a simple rule of mixture (ROM) with both iso-strain and iso-stress assumptions. Under complex loading paths, an actual microstructure-based finite element (FE) method is used to resolve the deformation compatibilities explicitly between the soft ferrite and hard martensite phases. The results show that, for uniaxial tension, the deformation instability theory with iso-strain-based ROM can be used to provide the lower bound estimate of the uniform elongation (UE) for themore » various DP980 considered. Under complex loading paths, the deformation instability theory with microstructure-based FE method can be used in examining the effects of various microstructural features on the deformation limits of DP980 steels.« less

Characterization of the tensile and microstructural properties of an aluminum metal matrix composite

NASA Technical Reports Server (NTRS)

Birt, M. J.; Johnson, W. S.

1990-01-01

This study examines a powder metallurgy aluminum alloy in the unreinforced state and with a discontinuous reinforcement of 15 v/o or 30 v/o SiC whisker or 15 v/o SiC particulate. The materials were extruded and then hot-rolled to three plate thicknesses of 6.35, 3.18 and 1.8 mm and were investigated in the as-fabricated and peak aged conditions. The influence of mechanical working on the reinforcement morphology and distribution were examined. A comparison of the mechanical properties was made and the elastic moduli of the reinforced materials were predicted using a micromechanics model. Fractography of tensile specimens revealed that the fracture process was dominated by the presence of microstructural inhomogeneities which were related to both the matrix alloy and to the reinforcement type. An analysis of these microstructural features and a description of the micromechanics model are presented in the paper.

A Comparative study of two RVE modelling methods for chopped carbon fiber SMC

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

Chen, Zhangxing; Li, Yi; Shao, Yimin

To achieve vehicle light-weighting, the chopped carbon fiber sheet molding compound (SMC) is identified as a promising material to replace metals. However, there are no effective tools and methods to predict the mechanical property of the chopped carbon fiber SMC due to the high complexity in microstructure features and the anisotropic properties. In this paper, the Representative Volume Element (RVE) approach is used to model the SMC microstructure. Two modeling methods, the Voronoi diagram-based method and the chip packing method, are developed for material RVE property prediction. The two methods are compared in terms of the predicted elastic modulus andmore » the predicted results are validated using the Digital Image Correlation (DIC) tensile test results. Furthermore, the advantages and shortcomings of these two methods are discussed in terms of the required input information and the convenience of use in the integrated processing-microstructure-property analysis.« less

Synthesis and microstructure of electrodeposited and sputtered nanotwinned face-centered-cubic metals

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

Bufford, Daniel C.; Wang, Morris; Liu, Yue

The remarkable properties of nanotwinned (NT) face-centered-cubic (fcc) metals arise directly from twin boundaries, the structures of which can be initially determined by growth twinning during the deposition process. When we understand the synthesis process and its relation to the resulting microstructure, and ultimately to material properties, we realize how key it is to understanding and utilizing these materials. Furthermore, our article presents recent studies on electrodeposition and sputtering methods that produce a high density of nanoscale growth twins in fcc metals. Nanoscale growth twins tend to form spontaneously in monolithic and alloyed fcc metals with lower stacking-fault energies, whilemore » engineered approaches are necessary for fcc metals with higher stacking-fault energies. Finally, growth defects and other microstructural features that influence nanotwin behavior and stability are introduced here, and future challenges in fabricating NT materials are highlighted.« less

Predicting Deformation Limits of Dual-Phase Steels Under Complex Loading Paths

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

Cheng, G.; Choi, K. S.; Hu, X.

The deformation limits of various DP980 steels are examined in this study with deformation instability theory. Under uniaxial tension, overall stress-strain curves of the material are estimated based on simple rule of mixture (ROM) with both iso-strain and iso-stress assumptions. Under complex loading paths, actual microstructure-based finite element (FE) method is used to explicitly resolve the deformation incompatibilities between the soft ferrite and hard martensite phases. The results show that, for uniaxial tension, the deformation instability theory with iso-strain-based ROM can be used to provide the lower bound estimate of the uniform elongation (UE) for the various DP980 considered. Undermore » complex loading paths, the deformation instability theory with microstructure-based FE method can be used in examining the effects of various microstructural features on the deformation limits of DP980 steels.« less

Predicting Deformation Limits of Dual-Phase Steels Under Complex Loading Paths

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

Cheng, G.; Choi, K. S.; Hu, X.

Here in this study, the deformation limits of various DP980 steels are examined with the deformation instability theory. Under uniaxial tension, overall stress–strain curves of the material are estimated based on a simple rule of mixture (ROM) with both iso-strain and iso-stress assumptions. Under complex loading paths, an actual microstructure-based finite element (FE) method is used to resolve the deformation compatibilities explicitly between the soft ferrite and hard martensite phases. The results show that, for uniaxial tension, the deformation instability theory with iso-strain-based ROM can be used to provide the lower bound estimate of the uniform elongation (UE) for themore » various DP980 considered. Under complex loading paths, the deformation instability theory with microstructure-based FE method can be used in examining the effects of various microstructural features on the deformation limits of DP980 steels.« less

Predicting the constitutive behavior of semi-solids via a direct finite element simulation: application to AA5182

NASA Astrophysics Data System (ADS)

Phillion, A. B.; Cockcroft, S. L.; Lee, P. D.

2009-07-01

The methodology of direct finite element (FE) simulation was used to predict the semi-solid constitutive behavior of an industrially important aluminum-magnesium alloy, AA5182. Model microstructures were generated that detail key features of the as-cast semi-solid: equiaxed-globular grains of random size and shape, interconnected liquid films, and pores at the triple-junctions. Based on the results of over fifty different simulations, a model-based constitutive relationship which includes the effects of the key microstructure features—fraction solid, grain size and fraction porosity—was derived using regression analysis. This novel constitutive equation was then validated via comparison with both the FE simulations and experimental stress/strain data. Such an equation can now be used to incorporate the effects of microstructure on the bulk semi-solid flow stress within a macro- scale process model.

Characterization of microstructural, mechanical and thermophysical properties of Th-52U alloy

NASA Astrophysics Data System (ADS)

Das, Santanu; Kaity, S.; Kumar, R.; Banerjee, J.; Roy, S. B.; Chaudhari, G. P.; Daniel, B. S. S.

2016-11-01

Th-52 wt.% U alloy has a microstructure featuring interspersed networks of uranium rich and thorium rich phases. Room temperature hardness of the alloy is more than twice that of unalloyed thorium. The alloy age hardens (550 °C) only slightly (peak hardness/hardness of solution heated and quenched = 1.05). Room temperature thermal conductivity (25.6 W m-1 °C-1) is close to that of uranium and most of the binary and ternary metallic alloy fuel materials. Average linear coefficient of thermal expansion (CTE) of Th-52 wt.% U alloy [11.2 × 10-06 °C-1 (27-290 °C) and 16.75 × 10-06 °C-1 (27-600 °C)] are comparable with that of many metallic alloy fuel candidates. Th-52 wt.% U alloy with non-age hardenable microstructure, appreciable thermal conductivity, moderate thermal expansion may find metallic fuel applications in nuclear reactors.

Preparation and Characterization of New Geopolymer-Epoxy Resin Hybrid Mortars

PubMed Central

Colangelo, Francesco; Roviello, Giuseppina; Ricciotti, Laura; Ferone, Claudio; Cioffi, Raffaele

2013-01-01

The preparation and characterization of metakaolin-based geopolymer mortars containing an organic epoxy resin are presented here for the first time. The specimens have been prepared by means of an innovative in situ co-reticulation process, in mild conditions, of commercial epoxy based organic resins and geopolymeric slurry. In this way, geopolymer based hybrid mortars characterized by a different content of normalized sand (up to 66% in weight) and by a homogeneous dispersion of the organic resin have been obtained. Once hardened, these new materials show improved compressive strength and toughness in respect to both the neat geopolymer and the hybrid pastes since the organic polymer provides a more cohesive microstructure, with a reduced amount of microcracks. The microstructural characterization allows to point out the presence of an Interfacial Transition Zone similar to that observed in cement based mortars and concretes. A correlation between microstructural features and mechanical properties has been studied too. PMID:28811418

Effect of Low-Dose MDCT and Iterative Reconstruction on Trabecular Bone Microstructure Assessment.

PubMed

Kopp, Felix K; Holzapfel, Konstantin; Baum, Thomas; Nasirudin, Radin A; Mei, Kai; Garcia, Eduardo G; Burgkart, Rainer; Rummeny, Ernst J; Kirschke, Jan S; Noël, Peter B

2016-01-01

We investigated the effects of low-dose multi detector computed tomography (MDCT) in combination with statistical iterative reconstruction algorithms on trabecular bone microstructure parameters. Twelve donated vertebrae were scanned with the routine radiation exposure used in our department (standard-dose) and a low-dose protocol. Reconstructions were performed with filtered backprojection (FBP) and maximum-likelihood based statistical iterative reconstruction (SIR). Trabecular bone microstructure parameters were assessed and statistically compared for each reconstruction. Moreover, fracture loads of the vertebrae were biomechanically determined and correlated to the assessed microstructure parameters. Trabecular bone microstructure parameters based on low-dose MDCT and SIR significantly correlated with vertebral bone strength. There was no significant difference between microstructure parameters calculated on low-dose SIR and standard-dose FBP images. However, the results revealed a strong dependency on the regularization strength applied during SIR. It was observed that stronger regularization might corrupt the microstructure analysis, because the trabecular structure is a very small detail that might get lost during the regularization process. As a consequence, the introduction of SIR for trabecular bone microstructure analysis requires a specific optimization of the regularization parameters. Moreover, in comparison to other approaches, superior noise-resolution trade-offs can be found with the proposed methods.

Bone tissue heterogeneity is associated with fracture toughness: a polarization Raman spectroscopy study

NASA Astrophysics Data System (ADS)

Makowski, Alexander J.; Granke, Mathilde; Uppuganti, Sasidhar; Mahadevan-Jansen, Anita; Nyman, Jeffry S.

2015-02-01

Polarization Raman Spectroscopy has been used to demonstrate microstructural features and collagen fiber orientation in human and mouse bone, concurrently measuring both organization and composition; however, it is unclear as to what extent these measurements explain the mechanical quality of bone. In a cohort of age and gender matched cadaveric cortical bone samples (23-101 yr.), we show homogeneity of both composition and structure are associated with the age related decrease in fracture toughness. 64 samples were machined into uniform specimens and notched for mechanical fracture toughness testing and polished for Raman Spectroscopy. Fingerprint region spectra were acquired on wet bone prior to mechanical testing by sampling nine different microstructural features spaced in a 750x750 μm grid in the region of intended crack propagation. After ASTM E1820 single edge notched beam fracture toughness tests, the sample was dried in ethanol and the osteonal-interstitial border of one osteon was samples in a 32x32 grid of 2μm2 pixels for two orthogonal orientations relative to the long bone axis. Standard peak ratios from the 9 separate microstructures show heterogeneity between structures but do not sufficiently explain fracture toughness; however, peak ratios from mapping highlight both lamellar contrast (ν1Phos/Amide I) and osteon-interstitial contrast (ν1Phos/Proline). Combining registered orthogonal maps allowed for multivariate analysis of underlying biochemical signatures. Image entropy and homogeneity metrics of single principal components significantly explain resistance to crack initiation and propagation. Ultimately, a combination of polarization content and multivariate Raman signatures allowed for the association of microstructural tissue heterogeneity with fracture resistance.

Long bone histology of the subterranean rodent Bathyergus suillus (Bathyergidae): ontogenetic pattern of cortical bone thickening.

PubMed

Montoya-Sanhueza, Germán; Chinsamy, Anusuya

2017-02-01

Patterns of bone development in mammals are best known from terrestrial and cursorial groups, but there is a considerable gap in our understanding of how specializations for life underground affect bone growth and development. Likewise, studies of bone microstructure in wild populations are still scarce, and they often include few individuals and tend to be focused on adults. For these reasons, the processes generating bone microstructural variation at intra- and interspecific levels are not fully understood. This study comprehensively examines the bone microstructure of an extant population of Cape dune molerats, Bathyergus suillus (Bathyergidae), the largest subterranean mammal endemic to the Western Cape of South Africa. The aim of this study is to investigate the postnatal bone growth of B. suillus using undecalcified histological sections (n = 197) of the femur, humerus, tibia-fibula, ulna and radius, including males and females belonging to different ontogenetic and reproductive stages (n = 42). Qualitative histological features demonstrate a wide histodiversity with thickening of the cortex mainly resulting from endosteal and periosteal bone depositions, whilst there is scarce endosteal resorption and remodeling throughout ontogeny. This imbalanced bone modeling allows the tissues deposited during ontogeny to remain relatively intact, thus preserving an excellent record of growth. The distribution of the different bone tissues observed in the cortex depends on ontogenetic status, anatomical features (e.g. muscle attachment structures) and location on the bone (e.g. anterior or lateral). The type of bone microstructure and modeling is discussed in relation to digging behavior, reproduction and physiology of this species. This study is the first histological assessment describing the process of cortical thickening in long bones of a fossorial mammal. © 2016 Anatomical Society.

Biological Response of Human Bone Marrow-Derived Mesenchymal Stem Cells to Commercial Tantalum Coatings with Microscale and Nanoscale Surface Topographies

NASA Astrophysics Data System (ADS)

Skoog, Shelby A.; Kumar, Girish; Goering, Peter L.; Williams, Brian; Stiglich, Jack; Narayan, Roger J.

2016-06-01

Tantalum is a promising orthopaedic implant coating material due to its robust mechanical properties, corrosion resistance, and excellent biocompatibility. Previous studies have demonstrated improved biocompatibility and tissue integration of surface-treated tantalum coatings compared to untreated tantalum. Surface modification of tantalum coatings with biologically inspired microscale and nanoscale features may be used to evoke optimal tissue responses. The goal of this study was to evaluate commercial tantalum coatings with nanoscale, sub-microscale, and microscale surface topographies for orthopaedic and dental applications using human bone marrow-derived mesenchymal stem cells (hBMSCs). Tantalum coatings with different microscale and nanoscale surface topographies were fabricated using a diffusion process or chemical vapor deposition. Biological evaluation of the tantalum coatings using hBMSCs showed that tantalum coatings promote cellular adhesion and growth. Furthermore, hBMSC adhesion to the tantalum coatings was dependent on surface feature characteristics, with enhanced cell adhesion on sub-micrometer- and micrometer-sized surface topographies compared to hybrid nano-/microstructures. Nanostructured and microstructured tantalum coatings should be further evaluated to optimize the surface coating features to promote osteogenesis and enhance osseointegration of tantalum-based orthopaedic implants.

Direct visualization of soliton stripes in the Cu O2 plane and oxygen interstitials in B i2(S r2 -xL ax) Cu O6 +δ superconductors

NASA Astrophysics Data System (ADS)

Guo, C.; Tian, H. F.; Yang, H. X.; Zhang, B.; Sun, K.; Sun, X.; Peng, Y. Y.; Zhou, X. J.; Li, J. Q.

2017-11-01

Microstructure features in correlation with the incommensurate modulation and oxygen interstitials in B i2(S r2 -xL ax) Cu O6 +δ superconducting materials were studied by Cs-corrected scanning transmission electron microscopy. Atomic displacements following the modulation wave were well characterized by a sinusoidal wave for each atomic layer, which highlighted clear changes resulting from increases in the La concentration. Careful investigations of the alterations in the local atomic structure revealed that remarkable microstructural features, i.e., notable soliton lines, which arise from the prominent interplay between incommensurate modulation and the basic lattice, appear at the Cu O2 sheets yielding visible structural anomalies for x ranging from 0.40 to 0.85. The interstitial oxygen atoms between the SrO-BiO layers became clearly visible for X ≥0.73 and showed well-defined ordered states in the x =1.10 sample. These structural features, in particular the strong structural effects of the soliton lines on the Cu O2 sheets, could evidently affect the physical properties of layered La-Bi2201 systems.

Applying a foil queue micro-electrode in micro-EDM to fabricate a 3D micro-structure

NASA Astrophysics Data System (ADS)

Xu, Bin; Guo, Kang; Wu, Xiao-yu; Lei, Jian-guo; Liang, Xiong; Guo, Deng-ji; Ma, Jiang; Cheng, Rong

2018-05-01

Applying a 3D micro-electrode in a micro electrical discharge machining (micro-EDM) can fabricate a 3D micro-structure with an up and down reciprocating method. However, this processing method has some shortcomings, such as a low success rate and a complex process for fabrication of 3D micro-electrodes. By focusing on these shortcomings, this paper proposed a novel 3D micro-EDM process based on the foil queue micro-electrode. Firstly, a 3D micro-electrode was discretized into several foil micro-electrodes and these foil micro-electrodes constituted a foil queue micro-electrode. Then, based on the planned process path, foil micro-electrodes were applied in micro-EDM sequentially and the micro-EDM results of each foil micro-electrode were able to superimpose the 3D micro-structure. However, the step effect will occur on the 3D micro-structure surface, which has an adverse effect on the 3D micro-structure. To tackle this problem, this paper proposes to reduce this adverse effect by rounded corner wear at the end of the foil micro-electrode and studies the impact of machining parameters on rounded corner wear and the step effect on the micro-structure surface. Finally, using a wire cutting voltage of 80 V, a current of 0.5 A and a pulse width modulation ratio of 1:4, the foil queue micro-electrode was fabricated by wire electrical discharge machining. Also, using a pulse width of 100 ns, a pulse interval of 200 ns, a voltage of 100 V and workpiece material of 304# stainless steel, the foil queue micro-electrode was applied in micro-EDM for processing of a 3D micro-structure with hemispherical features, which verified the feasibility of this process.

Universal Spatial Correlation Functions for Describing and Reconstructing Soil Microstructure

PubMed Central

Skvortsova, Elena B.; Mallants, Dirk

2015-01-01

Structural features of porous materials such as soil define the majority of its physical properties, including water infiltration and redistribution, multi-phase flow (e.g. simultaneous water/air flow, or gas exchange between biologically active soil root zone and atmosphere) and solute transport. To characterize soil microstructure, conventional soil science uses such metrics as pore size and pore-size distributions and thin section-derived morphological indicators. However, these descriptors provide only limited amount of information about the complex arrangement of soil structure and have limited capability to reconstruct structural features or predict physical properties. We introduce three different spatial correlation functions as a comprehensive tool to characterize soil microstructure: 1) two-point probability functions, 2) linear functions, and 3) two-point cluster functions. This novel approach was tested on thin-sections (2.21×2.21 cm2) representing eight soils with different pore space configurations. The two-point probability and linear correlation functions were subsequently used as a part of simulated annealing optimization procedures to reconstruct soil structure. Comparison of original and reconstructed images was based on morphological characteristics, cluster correlation functions, total number of pores and pore-size distribution. Results showed excellent agreement for soils with isolated pores, but relatively poor correspondence for soils exhibiting dual-porosity features (i.e. superposition of pores and micro-cracks). Insufficient information content in the correlation function sets used for reconstruction may have contributed to the observed discrepancies. Improved reconstructions may be obtained by adding cluster and other correlation functions into reconstruction sets. Correlation functions and the associated stochastic reconstruction algorithms introduced here are universally applicable in soil science, such as for soil classification, pore-scale modelling of soil properties, soil degradation monitoring, and description of spatial dynamics of soil microbial activity. PMID:26010779

Universal spatial correlation functions for describing and reconstructing soil microstructure.

PubMed

Karsanina, Marina V; Gerke, Kirill M; Skvortsova, Elena B; Mallants, Dirk

2015-01-01

Structural features of porous materials such as soil define the majority of its physical properties, including water infiltration and redistribution, multi-phase flow (e.g. simultaneous water/air flow, or gas exchange between biologically active soil root zone and atmosphere) and solute transport. To characterize soil microstructure, conventional soil science uses such metrics as pore size and pore-size distributions and thin section-derived morphological indicators. However, these descriptors provide only limited amount of information about the complex arrangement of soil structure and have limited capability to reconstruct structural features or predict physical properties. We introduce three different spatial correlation functions as a comprehensive tool to characterize soil microstructure: 1) two-point probability functions, 2) linear functions, and 3) two-point cluster functions. This novel approach was tested on thin-sections (2.21×2.21 cm2) representing eight soils with different pore space configurations. The two-point probability and linear correlation functions were subsequently used as a part of simulated annealing optimization procedures to reconstruct soil structure. Comparison of original and reconstructed images was based on morphological characteristics, cluster correlation functions, total number of pores and pore-size distribution. Results showed excellent agreement for soils with isolated pores, but relatively poor correspondence for soils exhibiting dual-porosity features (i.e. superposition of pores and micro-cracks). Insufficient information content in the correlation function sets used for reconstruction may have contributed to the observed discrepancies. Improved reconstructions may be obtained by adding cluster and other correlation functions into reconstruction sets. Correlation functions and the associated stochastic reconstruction algorithms introduced here are universally applicable in soil science, such as for soil classification, pore-scale modelling of soil properties, soil degradation monitoring, and description of spatial dynamics of soil microbial activity.

A semi-empirical model relating micro structure to acoustic properties of bimodal porous material

NASA Astrophysics Data System (ADS)

Mosanenzadeh, Shahrzad Ghaffari; Doutres, Olivier; Naguib, Hani E.; Park, Chul B.; Atalla, Noureddine

2015-01-01

Complex morphology of open cell porous media makes it difficult to link microstructural parameters and acoustic behavior of these materials. While morphology determines the overall sound absorption and noise damping effectiveness of a porous structure, little is known on the influence of microstructural configuration on the macroscopic properties. In the present research, a novel bimodal porous structure was designed and developed solely for modeling purposes. For the developed porous structure, it is possible to have direct control on morphological parameters and avoid complications raised by intricate pore geometries. A semi-empirical model is developed to relate microstructural parameters to macroscopic characteristics of porous material using precise characterization results based on the designed bimodal porous structures. This model specifically links macroscopic parameters including static airflow resistivity ( σ ) , thermal characteristic length ( Λ ' ) , viscous characteristic length ( Λ ) , and dynamic tortuosity ( α ∞ ) to microstructural factors such as cell wall thickness ( 2 t ) and reticulation rate ( R w ) . The developed model makes it possible to design the morphology of porous media to achieve optimum sound absorption performance based on the application in hand. This study makes the base for understanding the role of microstructural geometry and morphological factors on the overall macroscopic parameters of porous materials specifically for acoustic capabilities. The next step is to include other microstructural parameters as well to generalize the developed model. In the present paper, pore size was kept constant for eight categories of bimodal foams to study the effect of secondary porous structure on macroscopic properties and overall acoustic behavior of porous media.

3D/4D analyses of damage and fracture behaviours in structural materials via synchrotron X-ray tomography.

PubMed

Toda, Hiroyuki

2014-11-01

X-ray microtomography has been utilized for the in-situ observation of various structural metals under external loading. Recent advances in X-ray microtomography provide remarkable tools to image the interior of materials. In-situ X-ray microtomography provides a unique possibility to access the 3D character of internal microstructure and its time evolution behaviours non-destructively, thereby enabling advanced techniques for measuring local strain distribution. Local strain mapping is readily enabled by processing such high-resolution tomographic images either by the particle tracking technique or the digital image correlation technique [1]. Procedures for tracking microstructural features which have been developed by the authors [2], have been applied to analyse localised deformation and damage evolution in a material [3]. Typically several tens of thousands of microstructural features, such as particles and pores, are tracked in a tomographic specimen (0.2 - 0.3 mm(3) in volume). When a sufficient number of microstructural features is dispersed in 3D space, the Delaunay tessellation algorithm is used to obtain local strain distribution. With these techniques, 3D strain fields can be measured with reasonable accuracy. Even local crack driving forces, such as local variations in the stress intensity factor, crack tip opening displacement and J integral along a crack front line, can be measured from discrete crack tip displacement fields [4]. In the present presentation, complicated crack initiation and growth behaviour and the extensive formation of micro cracks ahead of a crack tip are introduced as examples.A novel experimental method has recently been developed by amalgamating a pencil beam X-Ray diffraction (XRD) technique with the microstructural tracking technique [5]. The technique provides information about individual grain orientations and 1-micron-level grain morphologies in 3D together with high-density local strain mapping. The application of this technique to the deformation behavior of a polycrystalline aluminium alloy will be demonstrated in the presentation [6].The synchrotron-based microtomography has been mainly utilized to light materials due to their good X-ray transmission. In the present talk, the application of the synchrotron-based microtomography to steels will be also introduced. Degradation of contrast and spatial resolution due to forward scattering could be avoided by selecting appropriate experimental conditions in order to obtain superior spatial resolution close to the physical limit even in ferrous materials [7]. © The Author 2014. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Microstructural characterization of pipe bomb fragments

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

Gregory, Otto, E-mail: gregory@egr.uri.edu; Oxley, Jimmie; Smith, James

2010-03-15

Recovered pipe bomb fragments, exploded under controlled conditions, have been characterized using scanning electron microscopy, optical microscopy and microhardness. Specifically, this paper examines the microstructural changes in plain carbon-steel fragments collected after the controlled explosion of galvanized, schedule 40, continuously welded, steel pipes filled with various smokeless powders. A number of microstructural changes were observed in the recovered pipe fragments: deformation of the soft alpha-ferrite grains, deformation of pearlite colonies, twin formation, bands of distorted pearlite colonies, slip bands, and cross-slip bands. These microstructural changes were correlated with the relative energy of the smokeless powder fillers. The energy of themore » smokeless powder was reflected in a reduction in thickness of the pipe fragments (due to plastic strain prior to fracture) and an increase in microhardness. Moreover, within fragments from a single pipe, there was a radial variation in microhardness, with the microhardness at the outer wall being greater than that at the inner wall. These findings were consistent with the premise that, with the high energy fillers, extensive plastic deformation and wall thinning occurred prior to pipe fracture. Ultimately, the information collected from this investigation will be used to develop a database, where the fragment microstructure and microhardness will be correlated with type of explosive filler and bomb design. Some analyses, specifically wall thinning and microhardness, may aid in field characterization of explosive devices.« less

Influence of inductive heating on microstructure and material properties in roll forming processes

NASA Astrophysics Data System (ADS)

Guk, Anna; Kunke, Andreas; Kräusel, Verena; Landgrebe, Dirk

2017-10-01

The increasing demand for sheet metal parts and profiles with enhanced mechanical properties by using high and ultra-high-strength (UHS) steels for the automotive industry must be covered by increasing flexibility of tools and machines. This can be achieved by applying innovative technologies such as roll forming with integrated inductive heating. This process is similar to indirect press hardening and can be used for the production of hardened profiles and profiles with graded properties in longitudinal and traverse direction. The advantage is that the production of hardened components takes place in a continuous process and the integration of heating and quenching units in the profiling system increases flexibility, accompanied by shortening of the entire process chain and minimizing the springback risk. The features of the mentioned process consists of the combination of inhomogeneous strain distribution over the stripe width by roll forming and inhomogeneity of microstructure by accelerated inductive heating to austenitizing temperature. Therefore, these two features have a direct influence on the mechanical properties of the material during forming and hardening. The aim of this work is the investigation of the influence of heating rates on microstructure evolution and mechanical properties to determine the process window. The results showed that heating rate should be set at 110 K/s for economic integration of inductive heating into the roll forming process.

Single-photon-multi-layer-interference lithography for high-aspect-ratio and three-dimensional SU-8 micro-/nanostructures.

PubMed

Ghosh, Siddharth; Ananthasuresh, G K

2016-01-04

We report microstructures of SU-8 photo-sensitive polymer with high-aspect-ratio, which is defined as the ratio of height to in-plane feature size. The highest aspect ratio achieved in this work exceeds 250. A multi-layer and single-photon lithography approach is used in this work to expose SU-8 photoresist of thickness up to 100 μm. Here, multi-layer and time-lapsed writing is the key concept that enables nanometer localised controlled photo-induced polymerisation. We use a converging monochromatic laser beam of 405 nm wavelength with a controllable aperture. The reflection of the converging optics from the silicon substrate underneath is responsible for a trapezoidal edge profile of SU-8 microstructure. The reflection induced interfered point-spread-function and multi-layer-single-photon exposure helps to achieve sub-wavelength feature sizes. We obtained a 75 nm tip diameter on a pyramid shaped microstructure. The converging beam profile determines the number of multiple optical focal planes along the depth of field. These focal planes are scanned and exposed non-concurrently with varying energy dosage. It is notable that an un-automated height axis control is sufficient for this method. All of these contribute to realising super-high-aspect-ratio and 3D micro-/nanostructures using SU-8. Finally, we also address the critical problems of photoresist-based micro-/nanofabrication and their solutions.

Stress Dependence of Microstructures in Experimentally Deformed Calcite

NASA Astrophysics Data System (ADS)

Platt, J. P.; De Bresser, J. H. P.

2017-12-01

Measurements of dynamically recrystallized grain size (Dr), subgrain size (Sg), minimum bulge size (Blg), and the maximum scale length for surface-energy driven grain-boundary migration (γGBM) in experimentally deformed Cararra marble help define the dependence of these microstructural features on stress and temperature. Measurements were made optically on ultra-thin sections in order to allow these features to be defined during measurement on the basis of microstructural setting and geometry. Taken together with previously published data Dr defines a paleopiezometer with a stress exponent of -1.09. There is no discernible temperature dependence over the 500°C temperature range of the experiments. Recrystallization occured mainly by bulging and subgrain rotation, and the two processes operated together, so that it is not possible to separate grains nucleated by the two mechanisms. Sg and Dr measured in the same samples are closely similar in size, suggesting that new grains do not grow significantly after nucleation, and that subgrain size is likely to be the primary control on recrystallized grain size. Blg and γGBM measured on each sample define a relationship to stress with an exponent of approximately -1.6, which helps define the boundary in stress - grain-size space between a region of dominant strain-energy-driven grain-boundary migration at high stress, from a region of dominant surface-energy-driven grain-boundary migration at low stress.

Thermoelectric properties of In and I doped PbTe

NASA Astrophysics Data System (ADS)

Bali, Ashoka; Chetty, Raju; Sharma, Amit; Rogl, Gerda; Heinrich, Patrick; Suwas, Satyam; Misra, Dinesh Kumar; Rogl, Peter; Bauer, Ernst; Mallik, Ramesh Chandra

2016-11-01

A systematic study of structural, microstructural, and thermoelectric properties of bulk PbTe doped with indium (In) alone and co-doped with both indium and iodine (I) has been done. X-ray diffraction results showed all the samples to be of single phase. Scanning electron microscopy (SEM) results revealed the particle sizes to be in the range of micrometers, while high resolution transmission electron microscopy was used to investigate distinct microstructural features such as interfaces, grain boundaries, and strain field domains. Hall measurement at 300 K revealed the carrier concentration ˜1019 cm-3 showing the degenerate nature which was further seen in the electrical resistivity of samples, which increased with rising temperature. Seebeck coefficient indicated that all samples were n-type semiconductors with electrons as the majority carriers throughout the temperature range. A maximum power factor ˜25 μW cm-1 K-2 for all In doped samples and Pb0.998In0.003Te1.000I0.003 was observed at 700 K. Doping leads to a reduction in the total thermal conductivity due to enhanced phonon scattering by mass fluctuations and distinct microstructure features such as interfaces, grain boundaries, and strain field domains. The highest zT of 1.12 at 773 K for In doped samples and a zT of 1.1 at 770 K for In and I co-doped samples were obtained.

Microstructural Analysis of Rat Ethanol and Water Drinking Patterns Using a Modified Operant Self-administration Model

PubMed Central

Robinson, Stacey L.; McCool, Brian A.

2015-01-01

Background Ethanol drinking pattern has emerged as an important factor in the development, maintenance, and health consequences of alcohol use disorders in humans. The goal of these studies was to further our understanding of this important factor through refinement of an operant rodent model of ethanol consumption capable of drinking pattern microstructural analysis. We evaluated measures of total consumption, appetitive behavior, and drinking microstructure for ethanol and water at baseline and assessed alterations induced by two treatments previously shown to significantly alter gross ethanol appetitive and consummatory behaviors in opposing directions. Methods Male Long Evans rats were trained on an FR1 operant paradigm which allowed for continuous liquid access until an 8 second pause in consumption resulted in termination of liquid access. Total appetitive and consummatory behaviors were assessed in addition to microstructural drinking pattern for both ethanol and water during a five day baseline drinking period, after chronic intermittent ethanol vapor exposure, and following administration of a cannabinoid receptor antagonist SR141716a. Results As in previous operant studies, ethanol vapor exposure resulted in increases in ethanol-directed responding, total consumption, and rate of intake. Further, striking differential alterations to ethanol and water bout size, duration, and lick pattern occurred consistent with alterations in hedonic evaluation. Vapor additionally specifically reduced the number of ethanol-directed lever presses which did not result in subsequent consumption. SR141716a administration reversed many of these effects. Conclusions The addition of microstructural analysis to operant self-administration by rodents provides a powerful and translational tool for the detection of specific alterations in ethanol drinking pattern which may enable insights into neural mechanisms underlying specific components of drug consumption. PMID:26037631

Microstructural analysis of rat ethanol and water drinking patterns using a modified operant self-administration model.

PubMed

Robinson, Stacey L; McCool, Brian A

2015-10-01

Ethanol drinking pattern has emerged as an important factor in the development, maintenance, and health consequences of alcohol use disorders in humans. The goal of these studies was to further our understanding of this important factor through refinement of an operant rodent model of ethanol consumption capable of drinking pattern microstructural analysis. We evaluated measures of total consumption, appetitive behavior, and drinking microstructure for ethanol and water at baseline and assessed alterations induced by two treatments previously shown to significantly alter gross ethanol appetitive and consummatory behaviors in opposing directions. Male Long-Evans rats were trained on an FR1 operant paradigm which allowed for continuous liquid access until an 8 second pause in consumption resulted in termination of liquid access. Total appetitive and consummatory behaviors were assessed in addition to microstructural drinking pattern for both ethanol and water during a five day baseline drinking period, after chronic intermittent ethanol vapor exposure, and following administration of a cannabinoid receptor antagonist SR141716a. As in previous operant studies, ethanol vapor exposure resulted in increases in ethanol-directed responding, total consumption, and rate of intake. Further, striking differential alterations to ethanol and water bout size, duration, and lick pattern occurred consistent with alterations in hedonic evaluation. Vapor additionally specifically reduced the number of ethanol-directed lever presses which did not result in subsequent consumption. SR141716a administration reversed many of these effects. The addition of microstructural analysis to operant self-administration by rodents provides a powerful and translational tool for the detection of specific alterations in ethanol drinking pattern which may enable insights into neural mechanisms underlying specific components of drug consumption. Copyright © 2015 Elsevier Inc. All rights reserved.

Right Fronto-Subcortical White Matter Microstructure Predicts Cognitive Control Ability on the Go/No-go Task in a Community Sample.

PubMed

Hinton, Kendra E; Lahey, Benjamin B; Villalta-Gil, Victoria; Boyd, Brian D; Yvernault, Benjamin C; Werts, Katherine B; Plassard, Andrew J; Applegate, Brooks; Woodward, Neil D; Landman, Bennett A; Zald, David H

2018-01-01

Go/no-go tasks are widely used to index cognitive control. This construct has been linked to white matter microstructure in a circuit connecting the right inferior frontal gyrus (IFG), subthalamic nucleus (STN), and pre-supplementary motor area. However, the specificity of this association has not been tested. A general factor of white matter has been identified that is related to processing speed. Given the strong processing speed component in successful performance on the go/no-go task, this general factor could contribute to task performance, but the general factor has often not been accounted for in past studies of cognitive control. Further, studies on cognitive control have generally employed small unrepresentative case-control designs. The present study examined the relationship between go/no-go performance and white matter microstructure in a large community sample of 378 subjects that included participants with a range of both clinical and subclinical nonpsychotic psychopathology. We found that white matter microstructure properties in the right IFG-STN tract significantly predicted task performance, and remained significant after controlling for dimensional psychopathology. The general factor of white matter only reached statistical significance when controlling for dimensional psychopathology. Although the IFG-STN and general factor tracts were highly correlated, when both were included in the model, only the IFG-STN remained a significant predictor of performance. Overall, these findings suggest that while a general factor of white matter can be identified in a young community sample, white matter microstructure properties in the right IFG-STN tract show a specific relationship to cognitive control. The findings highlight the importance of examining both specific and general correlates of cognition, especially in tasks with a speeded component.

Correlation between microstructural characteristics and weight loss of natural stones exposed to simulated acid rain.

PubMed

Franzoni, Elisa; Sassoni, Enrico

2011-12-15

The correlation between stone microstructural characteristics and material degradation (in terms of weight loss), in given environmental conditions, was investigated. Seven lithotypes, having very different microstructural characteristics, were used. Four acidic aqueous solutions were prepared to simulate acid rain (two adding H(2)SO(4) and two adding HNO(3) to deionized water, in order to reach, for each acid, pH values of 5.0 and 4.0), and deionized water at pH=5.6 was used to simulate clean rain. Stone samples were then immersed in such aqueous solutions, the surface alteration being periodically inspected and the weight loss periodically measured. After 14 days of immersion, a good correlation was found between weight loss and the product of carbonate content and specific surface area in the starting materials. This was explained considering that this product accounts for the weight loss owing to the sample's fraction actually composed of calcite (the most soluble fraction) and the effective surface area exposed to dissolving solution (which depends on stone porosity and pore size distribution). Such correlation between stone microstructure and degradation may be useful for comparing the durability of different lithotypes, in given environmental conditions, and quantitatively predicting the weight loss of a lithotype, compared to another one. Hence, the correlation found in this study may be used to specifically tailor to various stone types, with different microstructural characteristics, some results that have been calculated in literature for specific stone types and then proposed as possibly representative for a broad category of stones with similar characteristics. Copyright © 2011 Elsevier B.V. All rights reserved.

Numerical Analysis for Relevant Features in Intrusion Detection (NARFid)

DTIC Science & Technology

2009-03-01

Rosenblatt, Frank. Principles of Neurodynamics : Perceptrons and the Theory of Brain Mechanisms. Spartan Books, Washington DC, 1961. 74. Rossey, Lee M., Robert...editors), Parallel distributed process- ing: Explorations in the microstructure of cognition , Volume 1: Foundations. MIT Press, 1986. 76. Russel, Stuart and

Modulating laser intensity profile ellipticity for microstructural control during metal additive manufacturing

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

Roehling, Tien T.; Wu, Sheldon S. Q.; Khairallah, Saad A.

Additively manufactured (AM) metals are often highly textured, containing large columnar grains that initiate epitaxially under steep temperature gradients and rapid solidification conditions. These unique microstructures partially account for the massive property disparity existing between AM and conventionally processed alloys. Although equiaxed grains are desirable for isotropic mechanical behavior, the columnar-to-equiaxed transition remains difficult to predict for conventional solidification processes, and much more so for AM. In this study, the effects of laser intensity profile ellipticity on melt track macrostructures and microstructures were studied in 316L stainless steel. Experimental results were supported by temperature gradients and melt velocities simulated usingmore » the ALE3D multi-physics code. As a general trend, columnar grains preferentially formed with increasing laser power and scan speed for all beam profiles. However, when conduction mode laser heating occurs, scan parameters that result in coarse columnar microstructures using Gaussian profiles produce equiaxed or mixed equiaxed-columnar microstructures using elliptical profiles. Furthermore, by modulating spatial laser intensity profiles on the fly, site-specific microstructures and properties can be directly engineered into additively manufactured parts.« less

Modulating laser intensity profile ellipticity for microstructural control during metal additive manufacturing

DOE PAGES

Roehling, Tien T.; Wu, Sheldon S. Q.; Khairallah, Saad A.; ...

2017-02-12

Additively manufactured (AM) metals are often highly textured, containing large columnar grains that initiate epitaxially under steep temperature gradients and rapid solidification conditions. These unique microstructures partially account for the massive property disparity existing between AM and conventionally processed alloys. Although equiaxed grains are desirable for isotropic mechanical behavior, the columnar-to-equiaxed transition remains difficult to predict for conventional solidification processes, and much more so for AM. In this study, the effects of laser intensity profile ellipticity on melt track macrostructures and microstructures were studied in 316L stainless steel. Experimental results were supported by temperature gradients and melt velocities simulated usingmore » the ALE3D multi-physics code. As a general trend, columnar grains preferentially formed with increasing laser power and scan speed for all beam profiles. However, when conduction mode laser heating occurs, scan parameters that result in coarse columnar microstructures using Gaussian profiles produce equiaxed or mixed equiaxed-columnar microstructures using elliptical profiles. Furthermore, by modulating spatial laser intensity profiles on the fly, site-specific microstructures and properties can be directly engineered into additively manufactured parts.« less

Snow Micro-Structure Model

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

Micah Johnson, Andrew Slaughter

PIKA is a MOOSE-based application for modeling micro-structure evolution of seasonal snow. The model will be useful for environmental, atmospheric, and climate scientists. Possible applications include application to energy balance models, ice sheet modeling, and avalanche forecasting. The model implements physics from published, peer-reviewed articles. The main purpose is to foster university and laboratory collaboration to build a larger multi-scale snow model using MOOSE. The main feature of the code is that it is implemented using the MOOSE framework, thus making features such as multiphysics coupling, adaptive mesh refinement, and parallel scalability native to the application. PIKA implements three equations:more » the phase-field equation for tracking the evolution of the ice-air interface within seasonal snow at the grain-scale; the heat equation for computing the temperature of both the ice and air within the snow; and the mass transport equation for monitoring the diffusion of water vapor in the pore space of the snow.« less

Microstructural and geometric influences in the protective scales of Atractosteus spatula

PubMed Central

Sherman, Vincent R.; Yaraghi, Nicholas A.; Kisailus, David

2016-01-01

Atractosteus spatula has been described as a living fossil (having existed for 100 Myr), retaining morphological characteristics of early ancestors such as the ability to breathe air and survive above water for hours. Its highly effective armour consists of ganoid scales. We analyse the protective function of the scales and identify key features which lead to their resistance to failure. Microstructural features include: a twisted cross-plied mineral arrangement that inhibits crack propagation in the external ganoine layer, mineral crystals that deflect cracks in the bony region in order to activate the strength of mineralized collagen fibrils, and saw-tooth ridges along the interface between the two scale layers which direct cracks away from the intrinsically weak interface. The macroscale geometry is additionally evaluated and it is shown that the scales retain full coverage in spite of minimal overlap between adjacent scales while conforming to physiologically required strain and maintaining flexibility via a process in which adjacent rows of scales slide and concurrently reorient. PMID:27974575

Microstructural and geometric influences in the protective scales of Atractosteus spatula.

PubMed

Sherman, Vincent R; Yaraghi, Nicholas A; Kisailus, David; Meyers, Marc A

2016-12-01

Atractosteus spatula has been described as a living fossil (having existed for 100 Myr), retaining morphological characteristics of early ancestors such as the ability to breathe air and survive above water for hours. Its highly effective armour consists of ganoid scales. We analyse the protective function of the scales and identify key features which lead to their resistance to failure. Microstructural features include: a twisted cross-plied mineral arrangement that inhibits crack propagation in the external ganoine layer, mineral crystals that deflect cracks in the bony region in order to activate the strength of mineralized collagen fibrils, and saw-tooth ridges along the interface between the two scale layers which direct cracks away from the intrinsically weak interface. The macroscale geometry is additionally evaluated and it is shown that the scales retain full coverage in spite of minimal overlap between adjacent scales while conforming to physiologically required strain and maintaining flexibility via a process in which adjacent rows of scales slide and concurrently reorient. © 2016 The Author(s).

Stress dependence of microstructures in experimentally deformed calcite

NASA Astrophysics Data System (ADS)

Platt, John P.; De Bresser, J. H. P.

2017-12-01

Optical measurements of microstructural features in experimentally deformed Carrara marble help define their dependence on stress. These features include dynamically recrystallized grain size (Dr), subgrain size (Sg), minimum bulge size (Lρ), and the maximum scale length for surface-energy driven grain-boundary migration (Lγ). Taken together with previously published data Dr defines a paleopiezometer over the range 15-291 MPa and temperature over the range 500-1000 °C, with a stress exponent of -1.09 (CI -1.27 to -0.95), showing no detectable dependence on temperature. Sg and Dr measured in the same samples are closely similar in size, suggesting that the new grains did not grow significantly after nucleation. Lρ and Lγ measured on each sample define a relationship to stress with an exponent of approximately -1.6, which helps define the boundary between a region of dominant strain-energy-driven grain-boundary migration at high stress, from a region of dominant surface-energy-driven grain-boundary migration at low stress.

Quantitatively characterizing the microstructural features of breast ductal carcinoma tissues in different progression stages by Mueller matrix microscope.

PubMed

Dong, Yang; Qi, Ji; He, Honghui; He, Chao; Liu, Shaoxiong; Wu, Jian; Elson, Daniel S; Ma, Hui

2017-08-01

Polarization imaging has been recognized as a potentially powerful technique for probing the microstructural information and optical properties of complex biological specimens. Recently, we have reported a Mueller matrix microscope by adding the polarization state generator and analyzer (PSG and PSA) to a commercial transmission-light microscope, and applied it to differentiate human liver and cervical cancerous tissues with fibrosis. In this paper, we apply the Mueller matrix microscope for quantitative detection of human breast ductal carcinoma samples at different stages. The Mueller matrix polar decomposition and transformation parameters of the breast ductal tissues in different regions and at different stages are calculated and analyzed. For more quantitative comparisons, several widely-used image texture feature parameters are also calculated to characterize the difference in the polarimetric images. The experimental results indicate that the Mueller matrix microscope and the polarization parameters can facilitate the quantitative detection of breast ductal carcinoma tissues at different stages.

Investigation of Microstructural Features Determining the Toughness of 980 MPa Bainitic Weld Metal

NASA Astrophysics Data System (ADS)

Cao, R.; Zhang, X. B.; Wang, Z.; Peng, Y.; Du, W. S.; Tian, Z. L.; Chen, J. H.

2014-02-01

The microstructural features that control the impact toughness of weld metals of a 980 MPa 8 pct Ni high-strength steel are investigated using instrumented Charpy V tester, optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), electron back-scattered diffraction (EBSD), and finite-element method (FEM) calculation. The results show that the critical event for cleavage fracture in this high-strength steel and weld metals is the propagation of a bainite packet-sized crack across the packet boundary into contiguous packets, and the bainitic packet sizes control the impact toughness. The high-angle misorientation boundaries detected in a bainite packet by EBSD form fine tear ridges on fracture surfaces. However, they are not the decisive factors controlling the cleavage fracture. The effects of Ni content are essential factors for improving the toughness. The extra large cleavage facets seriously deteriorate the toughness, which are formed on the interfaces of large columnar crystals growing in welding pools with high heat input.

Effect of Heat Input on Inclusion Evolution Behavior in Heat-Affected Zone of EH36 Shipbuilding Steel

NASA Astrophysics Data System (ADS)

Sun, Jincheng; Zou, Xiaodong; Matsuura, Hiroyuki; Wang, Cong

2018-03-01

The effects of heat input parameters on inclusion and microstructure characteristics have been investigated using welding thermal simulations. Inclusion features from heat-affected zones (HAZs) were profiled. It was found that, under heat input of 120 kJ/cm, Al-Mg-Ti-O-(Mn-S) composite inclusions can act effectively as nucleation sites for acicular ferrites. However, this ability disappears when the heat input is increased to 210 kJ/cm. In addition, confocal scanning laser microscopy (CSLM) was used to document possible inclusion-microstructure interactions, shedding light on how inclusions assist beneficial transformations toward property enhancement.

Analysis of the ceramic layer microstructure influence on plasma spray thermal barrier coating performance

NASA Astrophysics Data System (ADS)

Bogdanovich, V. I.; Giorbelidze, M. G.

2017-12-01

This paper outlines the results of analysis and describes the structure of the thermal protection coatings formed by atomic ion stream deposition in vacuum, and plasma thermal spraying method. Crystallite structure features are considered along with the crystallite dimensions, spatial orientation, and position of the boundaries between separate crystallites. Discontinuity, volume, and morphology of the pores has been evaluated. Experimental studies have been accomplished using various fractions of the powder-like material ZrO2 - 8%Y2O3. The influence of the coating microstructure on the coating performance has been analyzed, such as adhesive strength, thermal stability, and thermal conductivity.

Effect of Heat Input on Inclusion Evolution Behavior in Heat-Affected Zone of EH36 Shipbuilding Steel

NASA Astrophysics Data System (ADS)

Sun, Jincheng; Zou, Xiaodong; Matsuura, Hiroyuki; Wang, Cong

2018-06-01

The effects of heat input parameters on inclusion and microstructure characteristics have been investigated using welding thermal simulations. Inclusion features from heat-affected zones (HAZs) were profiled. It was found that, under heat input of 120 kJ/cm, Al-Mg-Ti-O-(Mn-S) composite inclusions can act effectively as nucleation sites for acicular ferrites. However, this ability disappears when the heat input is increased to 210 kJ/cm. In addition, confocal scanning laser microscopy (CSLM) was used to document possible inclusion-microstructure interactions, shedding light on how inclusions assist beneficial transformations toward property enhancement.

Dynamic shaping of cellular membranes by phospholipids and membrane-deforming proteins.

PubMed

Suetsugu, Shiro; Kurisu, Shusaku; Takenawa, Tadaomi

2014-10-01

All cellular compartments are separated from the external environment by a membrane, which consists of a lipid bilayer. Subcellular structures, including clathrin-coated pits, caveolae, filopodia, lamellipodia, podosomes, and other intracellular membrane systems, are molded into their specific submicron-scale shapes through various mechanisms. Cells construct their micro-structures on plasma membrane and execute vital functions for life, such as cell migration, cell division, endocytosis, exocytosis, and cytoskeletal regulation. The plasma membrane, rich in anionic phospholipids, utilizes the electrostatic nature of the lipids, specifically the phosphoinositides, to form interactions with cytosolic proteins. These cytosolic proteins have three modes of interaction: 1) electrostatic interaction through unstructured polycationic regions, 2) through structured phosphoinositide-specific binding domains, and 3) through structured domains that bind the membrane without specificity for particular phospholipid. Among the structured domains, there are several that have membrane-deforming activity, which is essential for the formation of concave or convex membrane curvature. These domains include the amphipathic helix, which deforms the membrane by hemi-insertion of the helix with both hydrophobic and electrostatic interactions, and/or the BAR domain superfamily, known to use their positively charged, curved structural surface to deform membranes. Below the membrane, actin filaments support the micro-structures through interactions with several BAR proteins as well as other scaffold proteins, resulting in outward and inward membrane micro-structure formation. Here, we describe the characteristics of phospholipids, and the mechanisms utilized by phosphoinositides to regulate cellular events. We then summarize the precise mechanisms underlying the construction of membrane micro-structures and their involvements in physiological and pathological processes. Copyright © 2014 the American Physiological Society.

Concurrent white and gray matter degeneration of disease-specific networks in early-stage Alzheimer's disease and behavioral variant frontotemporal dementia.

PubMed

Steketee, Rebecca M E; Meijboom, Rozanna; de Groot, Marius; Bron, Esther E; Niessen, Wiro J; van der Lugt, Aad; van Swieten, John C; Smits, Marion

2016-07-01

This study investigates regional coherence between white matter (WM) microstructure and gray matter (GM) volume and perfusion measures in Alzheimer's disease (AD) and behavioral variant frontotemporal dementia (bvFTD) using a correlational approach. WM-GM coherence, compared with controls, was stronger between cingulum WM and frontotemporal GM in AD, and temporoparietal GM in bvFTD. In addition, in AD compared with controls, coherence was stronger between inferior fronto-occipital fasciculus WM microstructure and occipital GM perfusion. In this first study assessing regional WM-GM coherence in AD and bvFTD, we show that WM microstructure and GM volume and perfusion measures are coherent, particularly in regions implicated in AD and bvFTD pathology. This indicates concurrent degeneration in disease-specific networks. Our methodology allows for the detection of incipient abnormalities that go undetected in conventional between-group analyses. Copyright © 2016 Elsevier Inc. All rights reserved.

Analysis of New Composite Architectures

NASA Technical Reports Server (NTRS)

Whitcomb, John D.

1996-01-01

Efficient and accurate specialty finite elements methods to analyze textile composites were developed and are described. Textile composites present unique challenges to the analyst because of the large, complex 'microstructure'. The geometry of the microstructure is difficult to model and it introduces unusual free surface effects. The size of the microstructure complicates the use of traditional homogenization methods. The methods developed constitute considerable progress in addressing the modeling difficulties. The details of the methods and attended results obtained therefrom, are described in the various chapters included in Part 1 of the report. Specific conclusions and computer codes generated are included in Part 2 of the report.

Modeling transmission parameters of polymer microstructured fibers for applications in FTTH networks

NASA Astrophysics Data System (ADS)

Gdula, P.; Welikow, K.; Szczepański, P.; Buczyński, R.; Piramidowicz, R.

2011-10-01

This paper is focused on selected aspects of designing and modeling of transmission parameters of plastic optical fibers (POFs), considered in the context of their potential applications in optical access networks and, specifically, in Fiber-To- The-Home (FTTH) systems. The survey of state-of-the-art solutions is presented and possibility of improving transmission properties of POFs by microstructurization is discussed on the basis of the first results of numerical modeling. In particular, the microstructured POF was designed supporting propagation of limited number of modes while keeping relatively large mode area and, simultaneously, significantly lowered bending losses.

High-rate production of micro- and nanostructured surfaces: Injection molding and novel process for metal tooling manufacturing

NASA Astrophysics Data System (ADS)

De Jesus Vega, Marisely

Devices containing micro and nanostructured surfaces are developing and constantly finding new applications, especially for medical diagnostics, point-of-care applications, and microneedles. They are also employed in the functionalization of surfaces for superhydrophobicity, drag reduction, or reversible adhesion by mimicking bio-inspired surfaces. This research provides a thorough investigation on the effects of different polymeric materials and processing conditions on the replication of micro and nanostructured surfaces via injection molding. In addition, this dissertation also presents a novel approach for the production of durable microstructured metal tooling to be used for the production of surfaces with microchannels via injection molding. Materials such as thermoplastic vulcanizates are substituting regular thermoplastic materials and vulcanized elastomers in many applications due to their outstanding properties and ease of processability. These material properties broaden the scope of applications for microstructured surfaces. However, there is a need for understanding how these materials behave in microinjection molding since thermoplastic elastomers' behavior during injection molding have been shown to differ from that of the widely understood behavior of thermoplastics. Replication of microstructured surfaces using thermoplastic vulcanizates (TPV) was studied in the first part of this thesis. TPVs with different hardness's were molded using microinjection molding with various processing conditions and the replication and surface details of 20 microm pillars (aspect ratio of 1:1) were characterized. In the second part of this research liquid silicone rubber (LSR) was studied as a material for the production of micro and nanostructured surfaces. LSR is a silicone based material such as polydimethylsiloxane (PDMS), which is widely used for research and development of micro and nanostructured devices, and thus provides all the benefits of PDMS but can be rapidly processed via liquid injection molding. LSR with its excellent mechanical properties, transparency, non-toxicity and rapid molding capabilities can bring the production of micro and nanostructured surfaces from laboratory research facilities to high-rate manufacturing. However, previous research on microstructured surfaces made off LSR does not focus on the processing aspect of this material. Therefore, there is a lack of understanding of how different processing conditions affect the replication of microstructures. Additionally, there are no reports molding nanostructures of LSR. Features between 115 microm and 0.250 microm were molded in this work and the effect of different processing conditions and features sizes were studied. For the last part of this work, a novel metal additive manufacturing technique was used for the production of microstructured surfaces to be used as tooling for injection molding. The printing method consists of metal pastes printed through a tip onto a steel substrate. Prior work has shown spreading and swelling of features when metal pastes extrude out of the printing tip. PDMS was studied as a binder material to minimize spreading and swelling of the features by curing right after printing. In addition, prior work has shown durability of this metal printed tool up to 5000 injection molding cycles. This work compares this durability to durability of commercially available selective laser sintering metal tools. Furthermore, surface roughness was studied as this is one of the most important things to consider when molding microchannels for certain applications.

In-situ Observation of Cross-Sectional Microstructural Changes and Stress Distributions in Fracturing TiN Thin Film during Nanoindentation

PubMed Central

Zeilinger, Angelika; Todt, Juraj; Krywka, Christina; Müller, Martin; Ecker, Werner; Sartory, Bernhard; Meindlhumer, Michael; Stefenelli, Mario; Daniel, Rostislav; Mitterer, Christian; Keckes, Jozef

2016-01-01

Load-displacement curves measured during indentation experiments on thin films depend on non-homogeneous intrinsic film microstructure and residual stress gradients as well as on their changes during indenter penetration into the material. To date, microstructural changes and local stress concentrations resulting in plastic deformation and fracture were quantified exclusively using numerical models which suffer from poor knowledge of size dependent material properties and the unknown intrinsic gradients. Here, we report the first in-situ characterization of microstructural changes and multi-axial stress distributions in a wedge-indented 9 μm thick nanocrystalline TiN film volume performed using synchrotron cross-sectional X-ray nanodiffraction. During the indentation, needle-like TiN crystallites are tilted up to 15 degrees away from the indenter axis in the imprint area and strongly anisotropic diffraction peak broadening indicates strain variation within the X-ray nanoprobe caused by gradients of giant compressive stresses. The morphology of the multiaxial stress distributions with local concentrations up to −16.5 GPa correlate well with the observed fracture modes. The crack growth is influenced decisively by the film microstructure, especially by the micro- and nano-scopic interfaces. This novel experimental approach offers the capability to interpret indentation response and indenter imprint morphology of small graded nanostructured features. PMID:26947558

Review of beetle forewing structures and their biomimetic applications in China: (I) On the structural colors and the vertical and horizontal cross-sectional structures.

PubMed

Chen, Jinxiang; Xie, Juan; Wu, Zhishen; Elbashiry, Elsafi Mohamed Adam; Lu, Yun

2015-10-01

This paper discusses the progress made in China in terms of the structural colors, microstructure and mechanical properties of the beetle forewing. 1) The forewing microstructures can be classified into six phases, the first three of which are characterized by sandwich, multilayer and fiber layer structures, respectively. The fracture behaviors resulting from these three phases suggest that different scale microstructures or coupled adjacent scale microstructures can determine the macroscopic mechanical behavior of the forewing. 2) The forewing colors are derived from three features: regulation of the structural parameters of the internal optical structures, i.e., a sculpted multilayer composite two-dimensional nanopillar structure grating system; scattering on the three-dimensional surface of the bowl-shaped structure; and reversible color changes due to changes in the physical microstructure of fluffs. Their formation mechanisms were clarified, and fibers with ecological biomimetic structural colors have been developed. 3) Beetles exhibit a lightweight sectional frame structure with a trabecular core structure. Both of the joints on the left and right are concave-convex butt-joint structures with burrs, which provide an efficient docking mechanism with high intensity. The forewing of dichotoma exhibits a non-equiangular layered structure, which results in anisotropy in its tensile strength. Finally, the authors propose potential new research directions for the next 20 years. Copyright © 2015 Elsevier B.V. All rights reserved.

Direct Numerical Simulations of Microstructure Effects During High-Rate Loading of Additively Manufactured Metals

NASA Astrophysics Data System (ADS)

Battaile, Corbett; Owen, Steven; Moore, Nathan

2017-06-01

The properties of most engineering materials depend on the characteristics of internal microstructures and defects. In additively manufactured (AM) metals, these can include polycrystalline grains, impurities, phases, and significant porosity that qualitatively differ from conventional engineering materials. The microscopic details of the interactions between these internal defects, and the propagation of applied loads through the body, act in concert to dictate macro-observable properties like strength and compressibility. In this work, we used Sandia's ALEGRA finite element software to simulate the high-strain-rate loading of AM metals from laser engineered net shaping (LENS) and thermal spraying. The microstructural details of the material were represented explicitly, such that internal features like second phases and pores are captured and meshed as individual entities in the computational domain. We will discuss the dependence of the high-strain-rate mechanical properties on microstructural characteristics such as the shapes, sizes, and volume fractions of second phases and pores. In addition, we will examine how the details of the microstructural representation affect the microscopic material response to dynamic loads, and the effects of using ``stair-step'' versus conformal interfaces smoothed via the SCULPT tool in Sandia's CUBIT software. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US DOE NNSA under contract DE-AC04-94AL85000.

Chemical vapor deposition of low reflective cobalt (II) oxide films

NASA Astrophysics Data System (ADS)

Amin-Chalhoub, Eliane; Duguet, Thomas; Samélor, Diane; Debieu, Olivier; Ungureanu, Elisabeta; Vahlas, Constantin

2016-01-01

Low reflective CoO coatings are processed by chemical vapor deposition from Co2(CO)8 at temperatures between 120 °C and 190 °C without additional oxygen source. The optical reflectivity in the visible and near infrared regions stems from 2 to 35% depending on deposition temperature. The combination of specific microstructural features of the coatings, namely a fractal ⿿cauliflower⿿ morphology and a grain size distribution more or less covering the near UV and IR wavelength ranges enhance light scattering and gives rise to a low reflectivity. In addition, the columnar morphology results in a density gradient in the vertical direction that we interpret as a refractive index gradient lowering reflectivity further down. The coating formed at 180 °C shows the lowest average reflectivity (2.9%), and presents an interesting deep black diffuse aspect.

Orientational anisotropy and interfacial transport in polycrystals

NASA Astrophysics Data System (ADS)

Moghadam, M. M.; Rickman, J. M.; Harmer, M. P.; Chan, H. M.

2016-04-01

Interfacial diffusion is governed to a large degree by geometric parameters that are determined by crystallographic orientation. In this study, we assess the impact of orientational anisotropy on mass transport at internal interfaces, focusing on the role of preferred crystallographic orientation (i.e., texture) on mass diffusion in a polycrystal. More specifically, we perform both numerical and analytical studies of steady-state diffusion for polycrystals having various grain-orientation distributions. By relating grain misorientation to grain-boundary energies and, via the Borisov relation, to the diffusivity, we link microstructure variability to kinetics. Our aim is to correlate shape features of the orientation distribution, such as the location and shapes of peaks, with the calculated effective diffusivity. Finally, we discuss the role of crystallographic constraints, such as those associated with grain junctions, in determining the effective diffusivity of a polycrystal.

Effect of Cold Rolling and Heat Treatment on Microstructure and Mechanical Properties of Ti-4Al-1Mn Titanium Alloy

NASA Astrophysics Data System (ADS)

Gaur, Rishi; Gupta, R. K.; AnilKumar, V.; Banwait, S. S.

2018-05-01

Mechanical behavior of Ti-4Al-1Mn titanium alloy has been studied in annealed, cold-rolled and heat-treated conditions. Room temperature tensile strength as well as % elongation has been found to be low with increasing amount of cold rolling. Lowering of strength in cold worked condition is attributed to premature failure. However, the same has been mitigated after heat treatment. Significant effect of cooling media (air and water) from heat treatment temperature on microstructure was not found except for the degree of fineness of α plates. Optimum properties (strength as well as ductility) were exhibited by samples subjected to 15% cold rolling and heat treatment below β transus temperature, which can be attributed to presence of recrystallized microstructure. In cold worked condition, the microstructure shows fine fragmented α plates/Widmanstätten morphology with high dislocation density along with a large amount of strain fields and twinning, which gets transformed to recrystallized equiaxed microstructure and with plate-like morphology after near β heat treatment. Prior cold work is found to have a significant effect on mechanical properties supported by evolution of microstructure. Twinning is found to be assisting in deformation as well as in recrystallization through the formation of deformation and annealing twins during cold working and heat treatment. Fracture analysis of the tested sample with prior cold work and heat-treated condition revealed quasi-ductile failure as compared to only ductile failure features seen for samples heat treated without prior cold work.

Microstructure and Tensile/Corrosion Properties Relationships of Directionally Solidified Al-Cu-Ni Alloys

NASA Astrophysics Data System (ADS)

Rodrigues, Adilson V.; Lima, Thiago S.; Vida, Talita A.; Brito, Crystopher; Garcia, Amauri; Cheung, Noé

2018-03-01

Al-Cu-Ni alloys are of scientific and technological interest due to high strength/high temperature applications, based on the reinforcement originated from the interaction between the Al-rich phase and intermetallic composites. The nature, morphology, size, volume fraction and dispersion of IMCs particles throughout the Al-rich matrix are important factors determining the resulting mechanical and chemical properties. The present work aims to evaluate the effect of the addition of 1wt%Ni into Al-5wt%Cu and Al-15wt%Cu alloys on the solidification rate, macrosegregation, microstructure features and the interrelations of such characteristics on tensile and corrosion properties. A directional solidification technique is used permitting a wide range of microstructural scales to be examined. Experimental growth laws relating the primary and secondary dendritic spacings to growth rate and solidification cooling rate are proposed, and Hall-Petch type equations are derived relating the ultimate tensile strength and elongation to the primary dendritic spacing. Considering a compromise between ultimate tensile strength and corrosion resistance of the examined alloys samples from both alloys castings it is shown that the samples having more refined microstructures are associated with the highest values of such properties.

Study of the Microstructure and Cracking Mechanisms of Hastelloy X Produced by Laser Powder Bed Fusion.

PubMed

Marchese, Giulio; Basile, Gloria; Bassini, Emilio; Aversa, Alberta; Lombardi, Mariangela; Ugues, Daniele; Fino, Paolo; Biamino, Sara

2018-01-11

Hastelloy X (HX) is a Ni-based superalloy which suffers from high crack susceptibility during the laser powder bed fusion (LPBF) process. In this work, the microstructure of as-built HX samples was rigorously investigated to understand the main mechanisms leading to crack formation. The microstructural features of as-built HX samples consisted of very fine dendrite architectures with dimensions typically less than 1 µm, coupled with the formation of sub-micrometric carbides, the largest ones were mainly distributed along the interdendritic regions and grain boundaries. From the microstructural analyses, it appeared that the formation of intergranular carbides provided weaker zones, which combined with high thermal residual stresses resulted in hot cracks formation along the grain boundaries. The carbides were extracted from the austenitic matrix and characterized by combining different techniques, showing the formation of various types of Mo-rich carbides, classified as M₆C, M 12 C and M n C m type. The first two types of carbides are typically found in HX alloy, whereas the last one is a metastable carbide probably generated by the very high cooling rates of the process.

Review of Relationship Between Particle Deformation, Coating Microstructure, and Properties in High-Pressure Cold Spray

NASA Astrophysics Data System (ADS)

Rokni, M. R.; Nutt, S. R.; Widener, C. A.; Champagne, V. K.; Hrabe, R. H.

2017-08-01

In the cold spray (CS) process, deposits are produced by depositing powder particles at high velocity onto a substrate. Powders deposited by CS do not undergo melting before or upon impacting the substrate. This feature makes CS suitable for deposition of a wide variety of materials, most commonly metallic alloys, but also ceramics and composites. During processing, the particles undergo severe plastic deformation and create a more mechanical and less metallurgical bond with the underlying material. The deformation behavior of an individual particle depends on multiple material and process parameters that are classified into three major groups—powder characteristics, geometric parameters, and processing parameters, each with their own subcategories. Changing any of these parameters leads to evolution of a different microstructure and consequently changes the mechanical properties in the deposit. While cold spray technology has matured during the last decade, the process is inherently complex, and thus, the effects of deposition parameters on particle deformation, deposit microstructure, and mechanical properties remain unclear. The purpose of this paper is to review the parameters that have been investigated up to now with an emphasis on the existent relationships between particle deformation behavior, microstructure, and mechanical properties of various cold spray deposits.

Study of the Microstructure and Cracking Mechanisms of Hastelloy X Produced by Laser Powder Bed Fusion

PubMed Central

Basile, Gloria; Bassini, Emilio; Ugues, Daniele; Fino, Paolo

2018-01-01

Hastelloy X (HX) is a Ni-based superalloy which suffers from high crack susceptibility during the laser powder bed fusion (LPBF) process. In this work, the microstructure of as-built HX samples was rigorously investigated to understand the main mechanisms leading to crack formation. The microstructural features of as-built HX samples consisted of very fine dendrite architectures with dimensions typically less than 1 µm, coupled with the formation of sub-micrometric carbides, the largest ones were mainly distributed along the interdendritic regions and grain boundaries. From the microstructural analyses, it appeared that the formation of intergranular carbides provided weaker zones, which combined with high thermal residual stresses resulted in hot cracks formation along the grain boundaries. The carbides were extracted from the austenitic matrix and characterized by combining different techniques, showing the formation of various types of Mo-rich carbides, classified as M6C, M12C and MnCm type. The first two types of carbides are typically found in HX alloy, whereas the last one is a metastable carbide probably generated by the very high cooling rates of the process. PMID:29324658

Dissecting the mechanism of martensitic transformation via atomic-scale observations.

PubMed

Yang, Xu-Sheng; Sun, Sheng; Wu, Xiao-Lei; Ma, Evan; Zhang, Tong-Yi

2014-08-21

Martensitic transformation plays a pivotal role in the microstructural evolution and plasticity of many engineering materials. However, so far the underlying atomic processes that accomplish the displacive transformation have been obscured by the difficulty in directly observing key microstructural signatures on atomic scale. To resolve this long-standing problem, here we examine an AISI 304 austenitic stainless steel that has a strain/microstructure-gradient induced by surface mechanical attrition, which allowed us to capture in one sample all the key interphase regions generated during the γ(fcc) → ε(hcp) → α'(bcc) transition, a prototypical case of deformation induced martensitic transformation (DIMT). High-resolution transmission electron microscopy (HRTEM) observations confirm the crucial role of partial dislocations, and reveal tell-tale features including the lattice rotation of the α' martensite inclusion, the transition lattices at the ε/α' interfaces that cater the shears, and the excess reverse shear-shuffling induced γ necks in the ε martensite plates. These direct observations verify for the first time the 50-year-old Bogers-Burgers-Olson-Cohen (BBOC) model, and enrich our understanding of DIMT mechanisms. Our findings have implications for improved microstructural control in metals and alloys.

Dissecting the Mechanism of Martensitic Transformation via Atomic-Scale Observations

PubMed Central

Yang, Xu-Sheng; Sun, Sheng; Wu, Xiao-Lei; Ma, Evan; Zhang, Tong-Yi

2014-01-01

Martensitic transformation plays a pivotal role in the microstructural evolution and plasticity of many engineering materials. However, so far the underlying atomic processes that accomplish the displacive transformation have been obscured by the difficulty in directly observing key microstructural signatures on atomic scale. To resolve this long-standing problem, here we examine an AISI 304 austenitic stainless steel that has a strain/microstructure-gradient induced by surface mechanical attrition, which allowed us to capture in one sample all the key interphase regions generated during the γ(fcc) → ε(hcp) → α′(bcc) transition, a prototypical case of deformation induced martensitic transformation (DIMT). High-resolution transmission electron microscopy (HRTEM) observations confirm the crucial role of partial dislocations, and reveal tell-tale features including the lattice rotation of the α′ martensite inclusion, the transition lattices at the ε/α′ interfaces that cater the shears, and the excess reverse shear-shuffling induced γ necks in the ε martensite plates. These direct observations verify for the first time the 50-year-old Bogers-Burgers-Olson-Cohen (BBOC) model, and enrich our understanding of DIMT mechanisms. Our findings have implications for improved microstructural control in metals and alloys. PMID:25142283

Follicle Microstructure and Innervation Vary between Pinniped Micro- and Macrovibrissae.

PubMed

Mattson, Erin E; Marshall, Christopher D

2016-01-01

Histological data from terrestrial, semiaquatic, and fully aquatic mammal vibrissa (whisker) studies indicate that follicle microstructure and innervation vary across the mystacial vibrissal array (i.e. medial microvibrissae to lateral macrovibrissae). However, comparative data are lacking, and current histological studies on pinniped vibrissae only focus on the largest ventrolateral vibrissae. Consequently, we investigated the microstructure, medial-to-lateral innervation, and morphometric trends in harp seal (Pagophilus groenlandicus) vibrissal follicle-sinus complexes (F-SCs). The F-SCs were sectioned either longitudinally or in cross-section and stained with a modified Masson's trichrome stain (microstructure) or Bodian's silver stain (innervation). All F-SCs exhibited a tripartite blood organization system. The dermal capsule thickness, the distribution of major branches of the deep vibrissal nerve, and the hair shaft design were more symmetrical in medial F-SCs, but these features became more asymmetrical as the F-SCs became more lateral. Overall, the mean axon count was 1,221 ± 422.3 axons/F-SC and mean axon counts by column ranged from 550 ± 97.4 axons/F-SC (medially, column 11) to 1,632 ± 173.2 axons/F-SC (laterally, column 2). These values indicate a total of 117,216 axons innervating the entire mystacial vibrissal array. The mean axon count of lateral F-SCs was 1,533 ± 192.9 axons/ F-SC, which is similar to values reported in the literature for other pinniped F-SCs. Our data suggest that conventional studies that only examine the largest ventrolateral vibrissae may overestimate the total innervation by ∼20%. However, our study also accounts for variation in quantification methods and shows that conventional analyses likely only overestimate innervation by ∼10%. The relationship between axon count and cross-sectional F-SC surface area was nonlinear, and axon densities were consistent across the snout. Our data indicate that harp seals exhibit microstructural and innervational differences between their microvibrissae (columns 8-11) and macrovibrissae (columns 1-7). We hypothesize that this feature is conserved among pinnipeds and may result in functional compartmentalization within their mystacial vibrissal arrays. © 2016 S. Karger AG, Basel.

Advanced imaging of the macrostructure and microstructure of bone

NASA Technical Reports Server (NTRS)

Genant, H. K.; Gordon, C.; Jiang, Y.; Link, T. M.; Hans, D.; Majumdar, S.; Lang, T. F.

2000-01-01

Noninvasive and/or nondestructive techniques are capable of providing more macro- or microstructural information about bone than standard bone densitometry. Although the latter provides important information about osteoporotic fracture risk, numerous studies indicate that bone strength is only partially explained by bone mineral density. Quantitative assessment of macro- and microstructural features may improve our ability to estimate bone strength. The methods available for quantitatively assessing macrostructure include (besides conventional radiographs) quantitative computed tomography (QCT) and volumetric quantitative computed tomography (vQCT). Methods for assessing microstructure of trabecular bone noninvasively and/or nondestructively include high-resolution computed tomography (hrCT), micro-computed tomography (muCT), high-resolution magnetic resonance (hrMR), and micromagnetic resonance (muMR). vQCT, hrCT and hrMR are generally applicable in vivo; muCT and muMR are principally applicable in vitro. Although considerable progress has been made in the noninvasive and/or nondestructive imaging of the macro- and microstructure of bone, considerable challenges and dilemmas remain. From a technical perspective, the balance between spatial resolution versus sampling size, or between signal-to-noise versus radiation dose or acquisition time, needs further consideration, as do the trade-offs between the complexity and expense of equipment and the availability and accessibility of the methods. The relative merits of in vitro imaging and its ultrahigh resolution but invasiveness versus those of in vivo imaging and its modest resolution but noninvasiveness also deserve careful attention. From a clinical perspective, the challenges for bone imaging include balancing the relative advantages of simple bone densitometry against the more complex architectural features of bone or, similarly, the deeper research requirements against the broader clinical needs. The considerable potential biological differences between the peripheral appendicular skeleton and the central axial skeleton have to be addressed further. Finally, the relative merits of these sophisticated imaging techniques have to be weighed with respect to their applications as diagnostic procedures requiring high accuracy or reliability on one hand and their monitoring applications requiring high precision or reproducibility on the other. Copyright 2000 S. Karger AG, Basel.

Corrosion and Corrosion-Fatigue Behavior of 7075 Aluminum Alloys Studied by In Situ X-Ray Tomography

NASA Astrophysics Data System (ADS)

Stannard, Tyler

7XXX Aluminum alloys have high strength to weight ratio and low cost. They are used in many critical structural applications including automotive and aerospace components. These applications frequently subject the alloys to static and cyclic loading in service. Additionally, the alloys are often subjected to aggressive corrosive environments such as saltwater spray. These chemical and mechanical exposures have been known to cause premature failure in critical applications. Hence, the microstructural behavior of the alloys under combined chemical attack and mechanical loading must be characterized further. Most studies to date have analyzed the microstructure of the 7XXX alloys using two dimensional (2D) techniques. While 2D studies yield valuable insights about the properties of the alloys, they do not provide sufficiently accurate results because the microstructure is three dimensional and hence its response to external stimuli is also three dimensional (3D). Relevant features of the alloys include the grains, subgrains, intermetallic inclusion particles, and intermetallic precipitate particles. The effects of microstructural features on corrosion pitting and corrosion fatigue of aluminum alloys has primarily been studied using 2D techniques such as scanning electron microscopy (SEM) surface analysis along with post-mortem SEM fracture surface analysis to estimate the corrosion pit size and fatigue crack initiation site. These studies often limited the corrosion-fatigue testing to samples in air or specialized solutions, because samples tested in NaCl solution typically have fracture surfaces covered in corrosion product. Recent technological advancements allow observation of the microstructure, corrosion and crack behavior of aluminum alloys in solution in three dimensions over time (4D). In situ synchrotron X-Ray microtomography was used to analyze the corrosion and cracking behavior of the alloy in four dimensions to elucidate crack initiation at corrosion pits for samples of multiple aging conditions and impurity concentrations. Additionally, chemical reactions between the 3.5 wt% NaCl solution and the crack surfaces were quantified by observing the evolution of hydrogen bubbles from the crack. The effects of the impurity particles and age-hardening particles on the corrosion and fatigue properties were examined in 4D.

Phase-field simulation of microstructure formation in technical castings - A self-consistent homoenthalpic approach to the micro-macro problem

NASA Astrophysics Data System (ADS)

Böttger, B.; Eiken, J.; Apel, M.

2009-10-01

Performing microstructure simulation of technical casting processes suffers from the strong interdependency between latent heat release due to local microstructure formation and heat diffusion on the macroscopic scale: local microstructure formation depends on the macroscopic heat fluxes and, in turn, the macroscopic temperature solution depends on the latent heat release, and therefore on the microstructure formation, in all parts of the casting. A self-consistent homoenthalpic approximation to this micro-macro problem is proposed, based on the assumption of a common enthalpy-temperature relation for the whole casting which is used for the description of latent heat production on the macroscale. This enthalpy-temperature relation is iteratively obtained by phase-field simulations on the microscale, thus taking into account the specific morphological impact on the latent heat production. This new approach is discussed and compared to other approximations for the coupling of the macroscopic heat flux to complex microstructure models. Simulations are performed for the binary alloy Al-3at%Cu, using a multiphase-field solidification model which is coupled to a thermodynamic database. Microstructure formation is simulated for several positions in a simple model plate casting, using a one-dimensional macroscopic temperature solver which can be directly coupled to the microscopic phase-field simulation tool.

Thermal Effects on Microstructural Heterogeneity of Inconel 718 Materials Fabricated by Electron Beam Melting

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

Sames, William J.; Unocic, Kinga A.; Dehoff, Ryan R.

2014-07-28

Additive manufacturing (AM) technologies, also known as 3D printing, have demonstrated the potential to fabricate complex geometrical components, but the resulting microstructures and mechanical properties of these materials are not well understood due to unique and complex thermal cycles observed during processing. The electron beam melting (EBM) process is unique because the powder bed temperature can be elevated and maintained at temperatures over 1000 °C for the duration of the process. This results in three specific stages of microstructural phase evolution: (a) rapid cool down from the melting temperature to the process temperature, (b) extended hold at the process temperature,more » and (c) slow cool down to the room temperature. In this work, the mechanisms for reported microstructural differences in EBM are rationalized for Inconel 718 based on measured thermal cycles, preliminary thermal modeling, and computational thermodynamics models. The relationship between processing parameters, solidification microstructure, interdendritic segregation, and phase precipitation (δ, γ´, and γ´´) are discussed.« less

White matter microstructure and cognitive decline in metabolic syndrome: a review of diffusion tensor imaging.

PubMed

Alfaro, Freddy J; Gavrieli, Anna; Saade-Lemus, Patricia; Lioutas, Vasileios-Arsenios; Upadhyay, Jagriti; Novak, Vera

2018-01-01

Metabolic syndrome is a cluster of cardiovascular risk factors defined by the presence of abdominal obesity, glucose intolerance, hypertension and/or dyslipidemia. It is a major public health epidemic worldwide, and a known risk factor for the development of cognitive dysfunction and dementia. Several studies have demonstrated a positive association between the presence of metabolic syndrome and worse cognitive outcomes, however, evidence of brain structure pathology is limited. Diffusion tensor imaging has offered new opportunities to detect microstructural white matter changes in metabolic syndrome, and a possibility to detect associations between functional and structural abnormalities. This review analyzes the impact of metabolic syndrome on white matter microstructural integrity, brain structure abnormalities and their relationship to cognitive function. Each of the metabolic syndrome components exerts a specific signature of white matter microstructural abnormalities. Metabolic syndrome and its components exert both additive/synergistic, as well as, independent effects on brain microstructure thus accelerating brain aging and cognitive decline. Copyright © 2017 Elsevier Inc. All rights reserved.

The effects of memory training on behavioral and microstructural plasticity in young and older adults

PubMed Central

Bråthen, Anne Cecilie Sjøli; Rohani, Darius A.; Grydeland, Håkon; Fjell, Anders M.; Walhovd, Kristine B.

2017-01-01

Abstract Age differences in human brain plasticity are assumed, but have not been systematically investigated. In this longitudinal study, we investigated changes in white matter (WM) microstructure in response to memory training relative to passive and active control conditions in 183 young and older adults. We hypothesized that (i) only the training group would show improved memory performance and microstructural alterations, (ii) the young adults would show larger memory improvement and a higher degree of microstructural alterations as compared to the older adults, and (iii) changes in memory performance would relate to microstructural alterations. The results showed that memory improvement was specific to the training group, and that both the young and older participants improved their performance. The young group improved their memory to a larger extent compared to the older group. In the older sample, the training group showed less age‐related decline in WM microstructure compared to the control groups, in areas overlapping the corpus callosum, the cortico‐spinal tract, the cingulum bundle, the superior longitudinal fasciculus, and the anterior thalamic radiation. Less microstructural decline was related to a higher degree of memory improvement. Despite individual adaptation securing sufficient task difficulty, no training‐related group differences in microstructure were found in the young adults. The observed divergence of behavioral and microstructural responses to memory training with age is discussed within a supply‐demand framework. The results demonstrate that plasticity is preserved into older age, and that microstructural alterations may be part of a neurobiological substrate for behavioral improvements in older adults. Hum Brain Mapp 38:5666–5680, 2017. © 2018 The Authors Human Brain Mapping Published byWiley Periodicals, Inc. PMID:28782901

Towards a metadata scheme for the description of materials - the description of microstructures

NASA Astrophysics Data System (ADS)

Schmitz, Georg J.; Böttger, Bernd; Apel, Markus; Eiken, Janin; Laschet, Gottfried; Altenfeld, Ralph; Berger, Ralf; Boussinot, Guillaume; Viardin, Alexandre

2016-01-01

The property of any material is essentially determined by its microstructure. Numerical models are increasingly the focus of modern engineering as helpful tools for tailoring and optimization of custom-designed microstructures by suitable processing and alloy design. A huge variety of software tools is available to predict various microstructural aspects for different materials. In the general frame of an integrated computational materials engineering (ICME) approach, these microstructure models provide the link between models operating at the atomistic or electronic scales, and models operating on the macroscopic scale of the component and its processing. In view of an improved interoperability of all these different tools it is highly desirable to establish a standardized nomenclature and methodology for the exchange of microstructure data. The scope of this article is to provide a comprehensive system of metadata descriptors for the description of a 3D microstructure. The presented descriptors are limited to a mere geometric description of a static microstructure and have to be complemented by further descriptors, e.g. for properties, numerical representations, kinetic data, and others in the future. Further attributes to each descriptor, e.g. on data origin, data uncertainty, and data validity range are being defined in ongoing work. The proposed descriptors are intended to be independent of any specific numerical representation. The descriptors defined in this article may serve as a first basis for standardization and will simplify the data exchange between different numerical models, as well as promote the integration of experimental data into numerical models of microstructures. An HDF5 template data file for a simple, three phase Al-Cu microstructure being based on the defined descriptors complements this article.

Towards a metadata scheme for the description of materials - the description of microstructures.

PubMed

Schmitz, Georg J; Böttger, Bernd; Apel, Markus; Eiken, Janin; Laschet, Gottfried; Altenfeld, Ralph; Berger, Ralf; Boussinot, Guillaume; Viardin, Alexandre

2016-01-01

The property of any material is essentially determined by its microstructure. Numerical models are increasingly the focus of modern engineering as helpful tools for tailoring and optimization of custom-designed microstructures by suitable processing and alloy design. A huge variety of software tools is available to predict various microstructural aspects for different materials. In the general frame of an integrated computational materials engineering (ICME) approach, these microstructure models provide the link between models operating at the atomistic or electronic scales, and models operating on the macroscopic scale of the component and its processing. In view of an improved interoperability of all these different tools it is highly desirable to establish a standardized nomenclature and methodology for the exchange of microstructure data. The scope of this article is to provide a comprehensive system of metadata descriptors for the description of a 3D microstructure. The presented descriptors are limited to a mere geometric description of a static microstructure and have to be complemented by further descriptors, e.g. for properties, numerical representations, kinetic data, and others in the future. Further attributes to each descriptor, e.g. on data origin, data uncertainty, and data validity range are being defined in ongoing work. The proposed descriptors are intended to be independent of any specific numerical representation. The descriptors defined in this article may serve as a first basis for standardization and will simplify the data exchange between different numerical models, as well as promote the integration of experimental data into numerical models of microstructures. An HDF5 template data file for a simple, three phase Al-Cu microstructure being based on the defined descriptors complements this article.

The Development of Combined Raman Spectroscopy-Optical Coherence Tomography and Application for Skin Cancer Diagnosis

NASA Astrophysics Data System (ADS)

Patil, Chetan

2009-11-01

Optical spectroscopy and imaging have shown promise for performing rapid, non-invasive disease detection and diagnosis in vivo. Independently, Raman Spectroscopy (RS) has demonstrated the ability to perform diagnosis of epithelial cancers such the cervix with excellent overall classification accuracy due to the inherent biochemical specificity of the technique, however relating features of tissue morphology with techniques such as Raman mapping is clinically impractical due to the weak nature of the scattering phenomena resulting in prohibitively long acquisition times. Optical Coherence Tomography (OCT), on the other hand, has demonstrated the ability to perform real-time, high-resolution, cross-sectional imaging of the microstructural characteristics of disease, but typically lacks molecularly specific information that can assist in classifying pathological lesions. We present the development of a combined Raman Spectroscopy-OCT (RS-OCT) instrument capable of compensating for the limitations of each technique individually and performing both biochemical and microstructural evaluation of tissues. We will include the design and development of benchtop RS-OCT implementations based on independent 785 nm Raman and 1310 nm time-domain OCT system backbones, as well as with a 785nm Raman / 850nm spectral-domain OCT setup employing an integrated detection arm. These systems motivated the ultimate design of a clinical RS-OCT system for application in dermatology. In order to aid in the development of our Raman spectral processing and classification methods, we conducted a simultaneous pilot study in which RS alone was used to measure basal and squamous cell carcinomas. We will present the initial results from our clinical experiences with the combined RS-OCT device, and include a discussion of spectral classification and the ultimate potential of combined RS-OCT for skin cancer diagnosis.

Lithium and GSK3-β Promoter Gene Variants Influence White Matter Microstructure in Bipolar Disorder

PubMed Central

Benedetti, Francesco; Bollettini, Irene; Barberi, Ignazio; Radaelli, Daniele; Poletti, Sara; Locatelli, Clara; Pirovano, Adele; Lorenzi, Cristina; Falini, Andrea; Colombo, Cristina; Smeraldi, Enrico

2013-01-01

Lithium is the mainstay for the treatment of bipolar disorder (BD) and inhibits glycogen synthase kinase 3-β (GSK3-β). The less active GSK3-β promoter gene variants have been associated with less detrimental clinical features of BD. GSK3-β gene variants and lithium can influence brain gray matter structure in psychiatric conditions. Diffusion tensor imaging (DTI) measures of white matter (WM) integrity showed widespred disruption of WM structure in BD. In a sample of 70 patients affected by a major depressive episode in course of BD, we investigated the effect of ongoing long-term lithium treatment and GSK3-β promoter rs334558 polymorphism on WM microstructure, using DTI and tract-based spatial statistics with threshold-free cluster enhancement. We report that the less active GSK3-β rs334558*C gene-promoter variants, and the long-term administration of the GSK3-β inhibitor lithium, were associated with increases of DTI measures of axial diffusivity (AD) in several WM fiber tracts, including corpus callosum, forceps major, anterior and posterior cingulum bundle (bilaterally including its hippocampal part), left superior and inferior longitudinal fasciculus, left inferior fronto-occipital fasciculus, left posterior thalamic radiation, bilateral superior and posterior corona radiata, and bilateral corticospinal tract. AD reflects the integrity of axons and myelin sheaths. We suggest that GSK3-β inhibition and lithium could counteract the detrimental influences of BD on WM structure, with specific benefits resulting from effects on specific WM tracts contributing to the functional integrity of the brain and involving interhemispheric, limbic, and large frontal, parietal, and fronto-occipital connections. PMID:22990942

Multifunctional Beta Ti Alloy with Improved Specific Strength

NASA Astrophysics Data System (ADS)

Park, Chan Hee; Hong, Jae-Keun; Lee, Sang Won; Yeom, Jong-Taek

2017-12-01

Gum metals feature properties such as ultrahigh strength, ultralow elastic modulus, superelasticity, and superplasticity. They are composed of elements from Groups 4 and 5 of the periodic table and exist when the valance electron concentration (\\overline{e/a}) is 4.24; the bond order (\\overline{Bo}) is 2.87; and the "d" electron-orbital energy level (\\overline{Md}) is 2.45 eV. Typical compositions include Ti-23Nb-2Zr-0.7Ta-O and Ti-12Ta-9Nb-6Zr-3 V-O, which contain large amounts of heavy Group-5 elements such as Nb and Ta. In the present study, to improve the specific strength of a multifunctional beta Ti alloy, three alloys (Ti-20Nb-5Zr-1Fe-O, Ti-12Zr-10Mo-4Nb-O, and Ti-24Zr-9Cr-3Mo-O) were designed by satisfying the above three requirements while adding Fe, Mo, and Cr, which are not only lightweight but also have strong hardening effects. Microstructural and mechanical property analyses revealed that Ti-20Nb-5Zr-1Fe-O has a 25% higher specific strength than gum metal while maintaining an ultralow elastic modulus.

Overview of urban climate

Treesearch

Roscoe R., Jr. Braham

1977-01-01

The broad features of urban climate anomalies are described and explained by combining recent METROMEX data with those from prior studies. The urban heat island is well understood, and urban effects upon cloud nuclei and cloud microstructure are clearly observed and explained in part; but the causes of urban effects upon rainfall remain speculative.

The Rock Elm meteorite impact structure, Wisconsin: Geology and shock-metamorphic effects in quartz

USGS Publications Warehouse

French, B.M.; Cordua, W.S.; Plescia, J.B.

2004-01-01

The Rock Elm structure in southwest Wisconsin is an anomalous circular area of highly deformed rocks, ???6.5 km in diameter, located in a region of virtually horizontal undeformed sedimentary rocks. Shock-produced planar microstructures (PMs) have been identified in quartz grains in several lithologies associated with the structure: sandstones, quartzite pebbles, and breccia. Two distinct types of PMs are present: P1 features, which appear identical to planar fractures (PFs or cleavage), and P2 features, which are interpreted as possible incipient planar deformation features (PDFs). The latter are uniquely produced by the shock waves associated with meteorite impact events. Both types of PMs are oriented parallel to specific crystallographic planes in the quartz, most commonly to c(0001), ??112??2, and r/z101??1. The association of unusual, structurally deformed strata with distinct shock-produced microdeformation features in their quartz-bearing rocks establishes Rock Elm as a meteorite impact structure and supports the view that the presence of multiple parallel cleavages in quartz may be used independently as a criterion for meteorite impact. Preliminary paleontological studies indicate a minimum age of Middle Ordovician for the Rock Elm structure. A similar age estimate (450-400 Ma) is obtained independently by combining the results of studies of the general morphology of complex impact structures with estimated rates of sedimentation for the region. Such methods may be applicable to dating other old and deeply eroded impact structures formed in sedimentary target rocks.

The Effects of Grain Size and Texture on Dynamic Abnormal Grain Growth in Mo

NASA Astrophysics Data System (ADS)

Noell, Philip J.; Taleff, Eric M.

2016-10-01

This is the first report of abnormal grain morphologies specific to a Mo sheet material produced from a commercial-purity arc-melted ingot. Abnormal grains initiated and grew during plastic deformation of this material at temperatures of 1793 K and 1813 K (1520 °C and 1540 °C). This abnormal grain growth during high-temperature plastic deformation is termed dynamic abnormal grain growth, DAGG. DAGG in this material readily consumes nearly all grains near the sheet center while leaving many grains near the sheet surface unconsumed. Crystallographic texture, grain size, and other microstructural features are characterized. After recrystallization, a significant through-thickness variation in crystallographic texture exists in this material but does not appear to directly influence DAGG propagation. Instead, dynamic normal grain growth, which may be influenced by texture, preferentially occurs near the sheet surface prior to DAGG. The large grains thus produced near the sheet surface inhibit the subsequent growth of the abnormal grains produced by DAGG, which preferentially consume the finer grains near the sheet center. This produces abnormal grains that span the sheet center but leave unconsumed polycrystalline microstructure near the sheet surface. Abnormal grains are preferentially oriented with the < 110rangle approximately along the tensile axis. These results provide additional new evidence that boundary curvature is the primary driving force for DAGG in Mo.

Evolution of the Specific Surface Area of Snow in a High Temperature Gradient Metamorphism

NASA Astrophysics Data System (ADS)

Wang, X.; Baker, I.

2014-12-01

The structural evolution of low-density snow under a high temperature gradient over a short period usually takes place in the surface layers during diurnal recrystallization or on a clear, cold night. To relate snow microstructures with their thermal properties, we combined X-ray computed microtomography (micro-CT) observations with numerical simulations. Different types of snow were tested over a large range of TGs (100 K m-1- 500 K m-1). The Specific Surface Area (SSA) was used to characterize the temperature gradient metamorphism (TGM). The magnitude of the temperature gradient and the initial snow type both influence the evolution of SSA. The SSA evolution under TGM was dominated by grain growth and the formation of complex surfaces. Fresh snow experienced a logarithmic decrease of SSA with time, a feature been observed previously by others [Calonne et al., 2014; Schneebeli and Sokratov, 2004; Taillandier et al., 2007]. However, for initial rounded and connected snow structures, the SSA will increase during TGM. Understanding the SSA increase is important in order to predict the enhanced uptake of chemical species by snow or increase in snow albedo. Calonne, N., F. Flin, C. Geindreau, B. Lesaffre, and S. Rolland du Roscoat (2014), Study of a temperature gradient metamorphism of snow from 3-D images: time evolution of microstructures, physical properties and their associated anisotropy, The Cryosphere Discussions, 8, 1407-1451, doi:10.5194/tcd-8-1407-2014. Schneebeli, M., and S. A. Sokratov (2004), Tomography of temperature gradient metamorphism of snow and associated changes in heat conductivity, Hydrological Processes, 18(18), 3655-3665, doi:10.1002/hyp.5800. Taillandier, A. S., F. Domine, W. R. Simpson, M. Sturm, and T. A. Douglas (2007), Rate of decrease of the specific surface area of dry snow: Isothermal and temperature gradient conditions, Journal of Geophysical Research: Earth Surface (2003-2012), 112(F3), doi: 10.1029/2006JF000514.

Three-dimensional gold nanorods-doped multicolor microstructures

NASA Astrophysics Data System (ADS)

Lien, C.-H.; Cho, K.-C.; Kuo, W.-S.; Lin, C.-Y.; Chui, C.-L.; Chen, S.-J.

2012-03-01

In this study, three-dimensional (3D) crosslinked bovine serum albumin (BSA) microstructures containing gold nanorods (AuNRs) at different absorption wavelengths were fabricated via multiphoton excited photochemistry using rose Bengal (RB) as the photoactivator. After the processing, a higher laser power, greater than the threshold of the AuNR photothermal damage at the matched wavelength for the longitudinal plasmon resonance of AuNR, is adopted to reshape the AuNRs into gold nanospheres at the designed positions of the 3D structure. As a result, 3D BSA microstructures containing different color AuNRs at the designed positions can be successfully fabricated. The AuNRs-doped BSA multicolor microstructures not only can be applied in biomedical scaffolds with plasmonic properties such as two-photon luminescence imaging and photothermal therapy but also can be a specific 3D biomaterial microdevice for plasmonic field.

Predictions and Experimental Microstructural Characterization of High Strain Rate Failure Modes in Layered Aluminum Composites

NASA Astrophysics Data System (ADS)

Khanikar, Prasenjit

Different aluminum alloys can be combined, as composites, for tailored dynamic applications. Most investigations pertaining to metallic alloy layered composites, however, have been based on quasi-static approaches. The dynamic failure of layered metallic composites, therefore, needs to be characterized in terms of strength, toughness, and fracture response. A dislocation-density based crystalline plasticity formulation, finite-element techniques, rational crystallographic orientation relations and a new fracture methodology were used to predict the failure modes associated with the high strain rate behavior of aluminum layered composites. Two alloy layers, a high strength alloy, aluminum 2195, and an aluminum alloy 2139, with high toughness, were modeled with representative microstructures that included precipitates, dispersed particles, and different grain boundary (GB) distributions. The new fracture methodology, based on an overlap method and phantom nodes, is used with a fracture criteria specialized for fracture on different cleavage planes. One of the objectives of this investigation, therefore, was to determine the optimal arrangements of the 2139 and 2195 aluminum alloys for a metallic layered composite that would combine strength, toughness and fracture resistance for high strain-rate applications. Different layer arrangements were investigated for high strain-rate applications, and the optimal arrangement was with the high toughness 2139 layer on the bottom, which provided extensive shear strain localization, and the high strength 2195 layer on the top for high strength resistance. The layer thickness of the bottom high toughness layer also affected the bending behavior of the roll-boned interface and the potential delamination of the layers. Shear strain localization, dynamic cracking and delamination were the mutually competing failure mechanisms for the layered metallic composite, and control of these failure modes can be optimized for high strain-rate applications. The second major objective of this investigation was the use of recently developed dynamic fracture formulations to model and analyze the crack nucleation and propagation of aluminum layered composites subjected to high strain rate loading conditions and how microstructural effects, such as precipitates, dispersed particles, and GB orientations affect failure evolution. This dynamic fracture approach is used to investigate crack nucleation and crack growth as a function of the different microstructural characteristics of each alloy in layered composites with and without pre-existing cracks. The zigzag nature of the crack paths were mainly due to the microstructural features, such as precipitates and dispersed particles distributions and orientations ahead of the crack front, and it underscored the capabilities of the fracture methodology. The evolution of dislocation density and the formation of localized shear slip contributed to the blunting of the propagating crack. Extensive geometrical and thermal softening due to the localized plastic slip also affected crack path orientations and directions. These softening mechanisms resulted in the switching of cleavage planes, which affected crack path orientations. Interface delamination can also have an important role in the failure and toughening of the layered composites. Different scenarios of delamination were investigated, such as planar crack growth and crack penetration into the layers. The presence of brittle surface oxide platelets in the interface region also significantly influenced the interface delamination process. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Optical Microscopy (OM) characterization provided further physical insights and validation of the predictive capabilities. The inherent microstructural features of each alloy play a significant role in the dynamic fracture, shear strain localization, and interface delamination of the layered metallic composite. These microstructural features, such as precipitates, dispersed particles, and GB orientations and distributions can be optimized for desired behavior of metallic composites.

Classification of micro-CT images using 3D characterization of bone canal patterns in human osteogenesis imperfecta

NASA Astrophysics Data System (ADS)

Abidin, Anas Z.; Jameson, John; Molthen, Robert; Wismüller, Axel

2017-03-01

Few studies have analyzed the microstructural properties of bone in cases of Osteogenenis Imperfecta (OI), or `brittle bone disease'. Current approaches mainly focus on bone mineral density measurements as an indirect indicator of bone strength and quality. It has been shown that bone strength would depend not only on composition but also structural organization. This study aims to characterize 3D structure of the cortical bone in high-resolution micro CT images. A total of 40 bone fragments from 28 subjects (13 with OI and 15 healthy controls) were imaged using micro tomography using a synchrotron light source (SRµCT). Minkowski functionals - volume, surface, curvature, and Euler characteristics - describing the topological organization of the bone were computed from the images. The features were used in a machine learning task to classify between healthy and OI bone. The best classification performance (mean AUC - 0.96) was achieved with a combined 4-dimensional feature of all Minkowski functionals. Individually, the best feature performance was seen using curvature (mean AUC - 0.85), which characterizes the edges within a binary object. These results show that quantitative analysis of cortical bone microstructure, in a computer-aided diagnostics framework, can be used to distinguish between healthy and OI bone with high accuracy.

Differentiating characteristic microstructural features of cancerous tissues using Mueller matrix microscope.

PubMed

Wang, Ye; He, Honghui; Chang, Jintao; Zeng, Nan; Liu, Shaoxiong; Li, Migao; Ma, Hui

2015-12-01

Polarized light imaging can provide rich microstructural information of samples, and has been applied to the detections of various abnormal tissues. In this paper, we report a polarized light microscope based on Mueller matrix imaging by adding the polarization state generator and analyzer (PSG and PSA) to a commercial transmission optical microscope. The maximum errors for the absolute values of Mueller matrix elements are reduced to 0.01 after calibration. This Mueller matrix microscope has been used to examine human cervical and liver cancerous tissues with fibrosis. Images of the transformed Mueller matrix parameters provide quantitative assessment on the characteristic features of the pathological tissues. Contrast mechanism of the experimental results are backed up by Monte Carlo simulations based on the sphere-cylinder birefringence model, which reveal the relationship between the pathological features in the cancerous tissues at the cellular level and the polarization parameters. Both the experimental and simulated data indicate that the microscopic transformed Mueller matrix parameters can distinguish the breaking down of birefringent normal tissues for cervical cancer, or the formation of birefringent surrounding structures accompanying the inflammatory reaction for liver cancer. With its simple structure, fast measurement and high precision, polarized light microscope based on Mueller matrix shows a good diagnosis application prospect. Copyright © 2015 Elsevier Ltd. All rights reserved.

Three-dimensional printing of freeform helical microstructures: a review.

PubMed

Farahani, R D; Chizari, K; Therriault, D

2014-09-21

Three-dimensional (3D) printing is a fabrication method that enables creation of structures from digital models. Among the different structures fabricated by 3D printing methods, helical microstructures attracted the attention of the researchers due to their potential in different fields such as MEMS, lab-on-a-chip systems, microelectronics and telecommunications. Here we review different types of 3D printing methods capable of fabricating 3D freeform helical microstructures. The techniques including two more common microfabrication methods (i.e., focused ion beam chemical vapour deposition and microstereolithography) and also five methods based on computer-controlled robotic direct deposition of ink filament (i.e., fused deposition modeling, meniscus-confined electrodeposition, conformal printing on a rotating mandrel, UV-assisted and solvent-cast 3D printings) and their advantages and disadvantages regarding their utilization for the fabrication of helical microstructures are discussed. Focused ion beam chemical vapour deposition and microstereolithography techniques enable the fabrication of very precise shapes with a resolution down to ∼100 nm. However, these techniques may have material constraints (e.g., low viscosity) and/or may need special process conditions (e.g., vacuum chamber) and expensive equipment. The five other techniques based on robotic extrusion of materials through a nozzle are relatively cost-effective, however show lower resolution and less precise features. The popular fused deposition modeling method offers a wide variety of printable materials but the helical microstructures manufactured featured a less precise geometry compared to the other printing methods discussed in this review. The UV-assisted and the solvent-cast 3D printing methods both demonstrated high performance for the printing of 3D freeform structures such as the helix shape. However, the compatible materials used in these methods were limited to UV-curable polymers and polylactic acid (PLA), respectively. Meniscus-confined electrodeposition is a flexible, low cost technique that is capable of fabricating 3D structures both in nano- and microscales including freeform helical microstructures (down to few microns) under room conditions using metals. However, the metals suitable for this technique are limited to those that can be electrochemically deposited with the use of an electrolyte solution. The highest precision on the helix geometry was achieved using the conformal printing on a rotating mandrel. This method offers the lowest shape deformation after printing but requires more tools (e.g., mandrel, motor) and the printed structure must be separated from the mandrel. Helical microstructures made of multifunctional materials (e.g., carbon nanotube nanocomposites, metallic coated polymer template) were used in different technological applications such as strain/load sensors, cell separators and micro-antennas. These innovative 3D microsystems exploiting the unique helix shape demonstrated their potential for better performance and more compact microsystems.

Modeling of microstructure evolution in direct metal laser sintering: A phase field approach

NASA Astrophysics Data System (ADS)

Nandy, Jyotirmoy; Sarangi, Hrushikesh; Sahoo, Seshadev

2017-02-01

Direct Metal Laser Sintering (DMLS) is a new technology in the field of additive manufacturing, which builds metal parts in a layer by layer fashion directly from the powder bed. The process occurs within a very short time period with rapid solidification rate. Slight variations in the process parameters may cause enormous change in the final build parts. The physical and mechanical properties of the final build parts are dependent on the solidification rate which directly affects the microstructure of the material. Thus, the evolving of microstructure plays a vital role in the process parameters optimization. Nowadays, the increase in computational power allows for direct simulations of microstructures during materials processing for specific manufacturing conditions. In this study, modeling of microstructure evolution of Al-Si-10Mg powder in DMLS process was carried out by using a phase field approach. A MATLAB code was developed to solve the set of phase field equations, where simulation parameters include temperature gradient, laser scan speed and laser power. The effects of temperature gradient on microstructure evolution were studied and found that with increase in temperature gradient, the dendritic tip grows at a faster rate.

Nonlinear optical microscopy and ultrasound imaging of human cervical structure

NASA Astrophysics Data System (ADS)

Reusch, Lisa M.; Feltovich, Helen; Carlson, Lindsey C.; Hall, Gunnsteinn; Campagnola, Paul J.; Eliceiri, Kevin W.; Hall, Timothy J.

2013-03-01

The cervix softens and shortens as its collagen microstructure rearranges in preparation for birth, but premature change may lead to premature birth. The global preterm birth rate has not decreased despite decades of research, likely because cervical microstructure is poorly understood. Our group has developed a multilevel approach to evaluating the human cervix. We are developing quantitative ultrasound (QUS) techniques for noninvasive interrogation of cervical microstructure and corroborating those results with high-resolution images of microstructure from second harmonic generation imaging (SHG) microscopy. We obtain ultrasound measurements from hysterectomy specimens, prepare the tissue for SHG, and stitch together several hundred images to create a comprehensive view of large areas of cervix. The images are analyzed for collagen orientation and alignment with curvelet transform, and registered with QUS data, facilitating multiscale analysis in which the micron-scale SHG images and millimeter-scale ultrasound data interpretation inform each other. This novel combination of modalities allows comprehensive characterization of cervical microstructure in high resolution. Through a detailed comparative study, we demonstrate that SHG imaging both corroborates the quantitative ultrasound measurements and provides further insight. Ultimately, a comprehensive understanding of specific microstructural cervical change in pregnancy should lead to novel approaches to the prevention of preterm birth.

Disparities in correlating microstructural to nanostructural preservation of dinosaur femoral bones

NASA Astrophysics Data System (ADS)

Kim, Jung-Kyun; Kwon, Yong-Eun; Lee, Sang-Gil; Lee, Ji-Hyun; Kim, Jin-Gyu; Huh, Min; Lee, Eunji; Kim, Youn-Joong

2017-03-01

Osteohistological researches on dinosaurs are well documented, but descriptions of direct correlations between the bone microstructure and corresponding nanostructure are currently lacking. By applying correlative microscopy, we aimed to verify that well-preserved osteohistological features correlate with pristine fossil bone nanostructures from the femoral bones of Koreanosaurus boseongensis. The quality of nanostructural preservation was evaluated based on the preferred orientation level of apatite crystals obtained from selected area electron diffraction (SAED) patterns and by measuring the “arcs” from the {100} and {002} diffraction rings. Unlike our expectations, our results revealed that well-preserved microstructures do not guarantee pristine nanostructures and vice versa. Structural preservation of bone from macro- to nanoscale primarily depends on original bioapatite density, and subsequent taphonomical factors such as effects from burial, pressure, influx of external elements and the rate of diagenetic alteration of apatite crystals. Our findings suggest that the efficient application of SAED analysis opens the opportunity for comprehensive nanostructural investigations of bone.

Molecular analyses of dinosaur osteocytes support the presence of endogenous molecules.

PubMed

Schweitzer, Mary Higby; Zheng, Wenxia; Cleland, Timothy P; Bern, Marshall

2013-01-01

The discovery of soft, transparent microstructures in dinosaur bone consistent in morphology with osteocytes was controversial. We hypothesize that, if original, these microstructures will have molecular features in common with extant osteocytes. We present immunological and mass spectrometry evidence for preservation of proteins comprising extant osteocytes (Actin, Tubulin, PHEX, Histone H4) in osteocytes recovered from two non-avian dinosaurs. Furthermore, antibodies to DNA show localized binding to these microstructures, which also react positively with DNA intercalating stains propidium iodide (PI) and 4',6'-diamidino-2-phenylindole dihydrochloride (DAPI). Each antibody binds dinosaur cells in patterns similar to extant cells. These data are the first to support preservation of multiple proteins and to present multiple lines of evidence for material consistent with DNA in dinosaurs, supporting the hypothesis that these structures were part of the once living animals. We propose mechanisms for preservation of cells and component molecules, and discuss implications for dinosaurian cellular biology. Copyright © 2012 Elsevier Inc. All rights reserved.

Microstructure and Corrosive Behavior of Enamel Coating Modified on Mild Steel

NASA Astrophysics Data System (ADS)

Li, Y. L.; Huang, Z. R.; Zhong, Q. D.

Due to the study of marine corrosion of mild steel, in order to simulate the corrosion conditions of enamel coatings in seawater, enamel coatings applied on mild steel were immersed in 3.5wt.% NaCl liquor and the related corrosion features and behavior of enamel were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and evaluated by electro-chemical method such as potentiodynamic polarization testing. Under the appropriate heat treatment system, the enamel coatings sintered on the same kind of mild steel at different temperatures were studied: all enamel samples were within the temperature range from 710∘C to 830∘C, the heat treating process at the microstructural level was evaluated and correlated with corrosion resistance properties. All the enamel coatings were characterized and it was observed that the enamel coatings that showed excellent corrosion resistance when sintered at a temperature of 810∘C can offer a better physical barrier than other temperatures because of their better bonding force and dense microstructure with less pores.

Microstructure and Tribological Properties of Mo–40Ni–13Si Multiphase Intermetallic Alloy

PubMed Central

Song, Chunyan; Wang, Shuhuan; Gui, Yongliang; Cheng, Zihao; Ni, Guolong

2016-01-01

Intermetallic compounds are increasingly being expected to be utilized in tribological environments, but to date their implementation is hindered by insufficient ductility at low and medium temperatures. This paper presents a novel multiphase intermetallic alloy with the chemical composition of Mo–40Ni–13Si (at %). Microstructure characterization reveals that a certain amount of ductile Mo phases formed during the solidification process of a ternary Mo–Ni–Si molten alloy, which is beneficial to the improvement of ductility of intermetallic alloys. Tribological properties of the designed alloy—including wear resistance, friction coefficient, and metallic tribological compatibility—were evaluated under dry sliding wear test conditions at room temperature. Results suggest that the multiphase alloy possesses an excellent tribological property, which is attributed to unique microstructural features and thereby a good combination in hardness and ductility. The corresponding wear mechanism is explained by observing the worn surface, subsurface, and wear debris of the alloy, which was found to be soft abrasive wear. PMID:28774106

Development of the novel ferrous-based stainless steel for biomedical applications, part I: high-temperature microstructure, mechanical properties and damping behavior.

PubMed

Wu, Ching-Zong; Chen, Shih-Chung; Shih, Yung-Hsun; Hung, Jing-Ming; Lin, Chia-Cheng; Lin, Li-Hsiang; Ou, Keng-Liang

2011-10-01

This research investigated the high-temperature microstructure, mechanical properties, and damping behavior of Fe-9 Al-30 Mn-1C-5 Co (wt.%) alloy by means of electron microscopy, experimental model analysis, and hardness and tensile testing. Subsequent microstructural transformation occurred when the alloy under consideration was subjected to heat treatment in the temperature range of 1000-1150 °C: γ → (γ+κ). The κ-phase carbides had an ordered L'1(2)-type structure with lattice parameter a = 0.385 nm. The maximum yield strength (σ(y)), hardness, elongation, and damping coefficient of this alloy are 645 MPa, Hv 292, ~54%, and 178.5 × 10(-4), respectively. These features could be useful in further understanding the relationship between the biocompatibility and the wear and corrosion resistance of the alloy, so as to allow the development of a promising biomedical material. Copyright © 2011 Elsevier Ltd. All rights reserved.

On the formation features, microstructure and microhardness of single laser tracks formed by laser cladding of a NiCrBSi self-fluxing alloy

NASA Astrophysics Data System (ADS)

Devojno, O. G.; Feldshtein, E.; Kardapolava, M. A.; Lutsko, N. I.

2018-07-01

In the present paper, the influence of laser cladding conditions on the powder flow conditions, as well as the microstructure, phases and microhardness of an Ni-based self-fluxing alloy coating are described. The optimal granulations of a self-fluxing alloy powder and the relationship between the flow of powder of various fractions and the flow rate and pressure of the transporting gas have been determined. The laser beam speed, track pitch and the distance from the nozzle to the coated surface influence the height and width of single tracks. Regularities in the formation of microstructure under different cladding conditions are defined, as well as regularity of distribution of elements over the track depth and in the transient zone. The patterns of microhardness distribution over the track depth for different cladding conditions are found. These patterns as well as the optimal laser spot pitch allowed obtaining a uniform cladding layer.

Manifestation of anharmonic resonance in the interaction of intense ultrashort laser pulses with microstructured targets

NASA Astrophysics Data System (ADS)

Dalui, Malay; Kundu, M.; Madhu Trivikram, T.; Ray, Krishanu; Krishnamurthy, M.

2016-10-01

Identification of the basic processes responsible for an efficient heating of intense laser produced plasmas is one of the important features of high intensity laser matter interaction studies. Collisionless absorption due to the anharmonicity in the self-consistent electrostatic potential of the plasma, known as anharmonic resonance (AHR), has been proposed to be a basic mechanism but a clear experimental demonstration is needed. Here, we show that microstructured targets enhance X-ray emission and the polarization dependence ascribes the enhancement to anharmonic resonance heating. It is found that p-polarized pulses of 5 ×1017 W/cm2 intensity bring in a 16-fold enhancement in the X-ray emission in the energy range 20-350 keV compared to s-polarized pulses with microstructured targets. This ratio is 2 for the case of polished targets under otherwise identical conditions. Particle-in-cell simulations clearly show that AHR is the key absorption mechanism responsible for this effect.

Manipulating Semicrystalline Polymers in Confinement.

PubMed

Shingne, Nitin; Geuss, Markus; Thurn-Albrecht, Thomas; Schmidt, Hans-Werner; Mijangos, Carmen; Steinhart, Martin; Martín, Jaime

2017-08-17

Because final properties of nanoscale polymeric structures are largely determined by the solid-state microstructure of the confined polymer, it is imperative not only to understand how the microstructure of polymers develops under nanoscale confinement but also to establish means to manipulate it. Here we present a series of processing strategies, adapted from methods used in bulk polymer processing, that allow us to control the solidification of polymer nanostructures. First, we show that supramolecular nucleating agents can be readily used to modify the crystallization kinetics of confined poly(vinylidene fluoride) (PVDF). In addition, we demonstrate that microstructural features that are not traditionally affected by nucleating agents, such as the orientation of crystals, can be tuned with the crystallization temperature applied. Interestingly, we also show that high crystallization temperatures and long annealing periods induce the formation of the γ modification of PVDF, hence enabling the simple production of ferro/piezoelectric nanostructures. We anticipate that the approaches presented here can open up a plethora of new possibilities for the processing of polymer-based nanostructures with tailored properties and functionalities.

Electron microscopy study of the iron meteorite Santa Catharina

NASA Technical Reports Server (NTRS)

Zhang, J.; Williams, D. B.; Goldstein, J. I.; Clarke, R. S., Jr.

1990-01-01

A characterization of the microstructural features of Santa Catharina (SC) from the millimeter to submicron scale is presented. The same specimen was examined using an optical microscope, a scanning electron microscope, an electron probe microanalyzer, and an analytical electron microscope. Findings include the fact that SC metal nodules may have different bulk Ni values, leading to different microstructures upon cooling; that SC USNM 6293 is the less corroded sample, as tetrataenite exists as less than 10 nm ordered domains throughout the entire fcc matrix (it is noted that this structure is the same as that of the Twin City meteorite and identical to clear taenite II in the retained taenite regions of the octahedrites); that SC USNM 3043 has a more complicated microstructure due to corrosion; and that the low Ni phase of the cloudy zone was selectively corroded in some areas and formed the dark regions, indicating that the SC meteorite corrosion process was electrochemical in nature and may involve Cl-containing akaganeite.

Magnetization reversal mechanism of magnetic tunnel junctions

NASA Astrophysics Data System (ADS)

Liu, Cun-Ye; Li, Jian; Wang, Yue; Chen, Jian-Yong; Xu, Qing-Yu; Ni, Gang; Sang, Hai; Du, You-Wei

2002-01-01

Using the ion-beam-sputtering technique, we have fabricated Fe/Al2O3/Fe magnetic tunnelling junctions (MTJs). We have observed double-peaked shapes of curves, which have a level summit and a symmetrical feature, showing the magnetoresistance of the junction as a function of applied field. We have measured the tunnel conductance of MTJs which have insulating layers of different thicknesses. We have studied the dependence of the magnetoresistance of MTJs on tunnel conductance. The microstructures of hard- and soft-magnetic layers and interfaces of ferromagnets and insulators were probed. Analysing the influence of MJT microstructures, including those having clusters or/and granules in magnetic and non-magnetic films, a magnetization reversal mechanism (MRM) is proposed, which suggests that the MRM of tunnelling junctions may be explained by using a group-by-group reversal model of magnetic moments of the mesoscopical particles. We discuss the influence of MTJ microstructures, including those with clusters or/and granules in the ferromagnetic and non-magnetic films, on the MRM.

In Situ Imaging during Compression of Plastic Bonded Explosives for Damage Modeling

NASA Astrophysics Data System (ADS)

Yeager, John; Manner, Virginia; Patterson, Brian; Walters, David; Cordes, Nikolaus; Henderson, Kevin; Tappan, Bryce; Luscher, Darby

2017-06-01

The microstructure of plastic bonded explosives (PBXs) is known to influence behavior during insults such as deformation, heating or initiation to detonation. Obtaining three-dimensional microstructural data can be difficult due in part to fragility of the material and small feature size. X-ray computed tomography (CT) is an ideal characterization technique but the explosive crystals and binder in formulations such as PBX 9501 do not have sufficient x-ray contrast to differentiate between the components. Here, we have formulated several PBXs using octahydro-1,3,5,7-tetranitro-1,3,5,7- tetrazocine (HMX) crystals and low-density binder systems. The full three-dimensional microstructure of these samples has been characterized using microscale CT during uniaxial mechanical compression in an interrupted in situ modality. The rigidity of the binder was observed to significantly influence fracture, crystal-binder delamination, and material flow. Additionally, the segmented, 3D images were meshed for finite element simulation. Initial results of the mesoscale modeling exhibit qualitatively similar delamination. Los Alamos National Laboratory - LDRD.

The nanostructure and microstructure of SiC surface layers deposited by MWCVD and ECRCVD

NASA Astrophysics Data System (ADS)

Dul, K.; Jonas, S.; Handke, B.

2017-12-01

Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) have been used to investigate ex-situ the surface topography of SiC layers deposited on Si(100) by Microwave Chemical Vapour Deposition (MWCVD) -S1,S2 layers and Electron Cyclotron Resonance Chemical Vapor Deposition (ECRCVD) - layers S3,S4, using silane, methane, and hydrogen. The effects of sample temperature and gas flow on the nanostructure and microstructure have been investigated. The nanostructure was described by three-dimensional surface roughness analysis based on digital image processing, which gives a tool to quantify different aspects of surface features. A total of 13 different numerical parameters used to describe the surface topography were used. The scanning electron image (SEM) of the microstructure of layers S1, S2, and S4 was similar, however, layer S3 was completely different; appearing like grains. Nonetheless, it can be seen that no grain boundary structure is present in the AFM images.

Microstructural stability of a self-ion irradiated lanthana-bearing nanostructured ferritic steel

NASA Astrophysics Data System (ADS)

Pasebani, Somayeh; Charit, Indrajit; Burns, Jatuporn; Alsagabi, Sultan; Butt, Darryl P.; Cole, James I.; Price, Lloyd M.; Shao, Lin

2015-07-01

Thermally stable nanofeatures with high number density are expected to impart excellent high temperature strength and irradiation stability in nanostructured ferritic steels (NFSs) which have potential applications in advanced nuclear reactors. A lanthana-bearing NFS (14LMT) developed via mechanical alloying and spark plasma sintering was used in this study. The sintered samples were irradiated by Fe2+ ions to 10, 50 and 100 dpa at 30 °C and 500 °C. Microstructural and mechanical characteristics of the irradiated samples were studied using different microscopy techniques and nanoindentation, respectively. Overall morphology and number density of the nanofeatures remained unchanged after irradiation. Average radius of nanofeatures in the irradiated sample (100 dpa at 500 °C) was slightly reduced. A notable level of irradiation hardening and enhanced dislocation activity occurred after ion irradiation except at 30 °C and ⩾50 dpa. Other microstructural features like grain boundaries and high density of dislocations also provided defect sinks to assist in defect removal.

Imaging pancreatobiliary ductal system with optical coherence tomography: A review

PubMed Central

Mahmud, Mohammad S; May, Gray R; Kamal, Mohammad M; Khwaja, Ahmed S; Sun, Carry; Vitkin, Alex; Yang, Victor XD

2013-01-01

An accurate, noninvasive and cost-effective method of in situ tissue evaluation during endoscopy would be highly advantageous for the detection of dysplasia or early cancer and for identifying different disease stages. Optical coherence tomography (OCT) is a noninvasive, high-resolution (1-10 μm) emerging optical imaging method with potential for identifying microscopic subsurface features in the pancreatic and biliary ductal system. Tissue microstructure of pancreaticobiliary ductal system has been successfully imaged by inserting an OCT probe through a standard endoscope operative channel. High-resolution OCT images and the technique’s endoscopic compatibility have allowed for the microstructural diagnostic of the pancreatobiliary diseases. In this review, we discussed currently available pancreaticobiliary ductal imaging systems to assess the pancreatobiliary tissue microstructure and to evaluate varieties of pancreaticobiliary disorders and diseases. Results show that OCT can improve the quality of images of pancreatobiliary system during endoscopic retrograde cholangiopancheatography procedure, which may be important in distinguishing between the neoplastic and non-neoplastic lesions. PMID:24255746

Compact forced simple-shear sample for studying shear localization in materials

DOE PAGES

Gray, George Thompson; Vecchio, K. S.; Livescu, Veronica

2015-11-06

In this paper, a new specimen geometry, the compact forced-simple-shear specimen (CFSS), has been developed as a means to achieve simple shear testing of materials over a range of temperatures and strain rates. The stress and strain state in the gage section is designed to produce essentially “pure” simple shear, mode II in-plane shear, in a compact-sample geometry. The 2-D plane of shear can be directly aligned along specified directional aspects of a material's microstructure of interest; i.e., systematic shear loading parallel, at 45°, and orthogonal to anisotropic microstructural features in a material such as the pancake-shaped grains typical inmore » many rolled structural metals, or to specified directions in fiber-reinforced composites. Finally, the shear-stress shear-strain response and the damage evolution parallel and orthogonal to the pancake grain morphology in 7039-Al are shown to vary significantly as a function of orientation to the microstructure.« less

Rapid prototyping of microstructures in polydimethylsiloxane (PDMS) by direct UV-lithography.

PubMed

Scharnweber, Tim; Truckenmüller, Roman; Schneider, Andrea M; Welle, Alexander; Reinhardt, Martina; Giselbrecht, Stefan

2011-04-07

Microstructuring of polydimethylsiloxane (PDMS) is a key step for many lab-on-a-chip (LOC) applications. In general, the structure is generated by casting the liquid prepolymer against a master. The production of the master in turn calls for special equipment and know how. Furthermore, a given master only allows the reproduction of the defined structure. We report on a simple, cheap and practical method to produce microstructures in already cured PDMS by direct UV-lithography followed by chemical development. Due to the available options during the lithographic process like multiple exposures, the method offers a high design flexibility granting easy access to complex and stepped structures. Furthermore, no master is needed and the use of pre-cured PDMS allows processing at ambient (light) conditions. Features down to approximately 5 µm and a depth of 10 µm can be realised. As a proof of principle, we demonstrate the feasibility of the process by applying the structures to various established soft lithography techniques.

Microstructural evolution and grain growth kinetics of GZ31 magnesium alloy

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

Roostaei, M., E-mail: miladroustaei68@ut.ac.ir

2016-08-15

Grain growth behavior of Mg–3Gd–1Zn (GZ31) magnesium alloy was studied in a wide range of annealing time and temperature to clarify the kinetics of grain growth, microstructural evolution and related metallurgical phenomena. This material exhibited typical normal grain growth mode under annealing conditions with annealing temperature of lower than 300 °C and soaking time of lower than 240 min. However, the abnormality in grain growth was also evident at annealing temperature of 400 °C and 500 °C. The dependence of abnormal grain growth (AGG) at mentioned annealing temperatures upon microstructural features such as dispersed precipitates, which were rich in Znmore » and Gd, was investigated by optical micrographs, X-ray diffraction patterns, scanning electron microscopy images, and energy dispersive X-ray analysis spectra. The bimodality in grain-size distribution histograms also signified the occurrence of AGG. Based on the experimental data on grain growth obtained by annealing treatments, the grain growth exponent and the activation energy were also figured out.« less

Investigation of the effect of aggregates' morphology on concrete creep properties by numerical simulations

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

Lavergne, F.; Sab, K., E-mail: karam.sab@enpc.fr; Sanahuja, J.

2015-05-15

Prestress losses due to creep of concrete is a matter of interest for long-term operations of nuclear power plants containment buildings. Experimental studies by Granger (1995) have shown that concretes with similar formulations have different creep behaviors. The aim of this paper is to numerically investigate the effect of size distribution and shape of elastic inclusions on the long-term creep of concrete. Several microstructures with prescribed size distribution and spherical or polyhedral shape of inclusions are generated. By using the 3D numerical homogenization procedure for viscoelastic microstructures proposed by Šmilauer and Bažant (2010), it is shown that the size distributionmore » and shape of inclusions have no measurable influence on the overall creep behavior. Moreover, a mean-field estimate provides close predictions. An Interfacial Transition Zone was introduced according to the model of Nadeau (2003). It is shown that this feature of concrete's microstructure can explain differences between creep behaviors.« less

Influence of SMAT Parameters on Microstructural and Mechanical Properties of Al-Mg-Si Alloy AA 6061

NASA Astrophysics Data System (ADS)

Anand Kumar, S.; Satish Kumar, P.; Ganesh Sundara Raman, S.; Sankara Narayanan, T. S. N.

2017-04-01

In the present work, the influence of surface mechanical attrition treatment (SMAT) parameters on the microstructural and mechanical properties of an aluminum-magnesium-silicon alloy AA 6061 was studied using design of experiment technique. Balls of three different diameters were used, and SMAT was done for three different durations. The microstructural features of the surface layer fabricated by SMAT were characterized by cross-sectional scanning electron microscopic observations, x-ray diffraction technique and transmission electron microscopy. The microindentation hardness, nanoindentation hardness and surface roughness were determined. Due to SMAT, nanocrystallites formed on the surface and near-surface regions, and hardness and surface roughness increased. The ball diameter was the most influencing SMAT parameter compared to the treatment duration. However, interaction between ball diameter and treatment duration could not be ignored. Regression equations were developed relating the process parameters to the surface properties. The ball diameter and treatment duration could thus be properly selected as per the required values of roughness and/or the hardness.

Microstructural and Microanalytical Study on Concrete Exposed to the Sulfate Environment

NASA Astrophysics Data System (ADS)

Qing, Fang; Beixing, Li; Jiangang, Yin; Xiaolu, Yuan

2017-11-01

Microstructural properties have been examined to investigate the effect of mineral admixtures on the sulfate resistance of concrete. Concrete and cement paste specimens made with ordinary Portland cement (OPC) or ordinary Portland cement incorporating 20% fly ash (FA) or 30% ground blast furnace slag (GBFS), were made and exposed to 250 cycles of the cyclic sulfate environment. Microstructural and Microanalytical study was conducted by means of x-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and mercury intrusion porosimetry (MIP). Results indicate that the pore structure of concrete after sulfate exposure possesses the fractal feature. The OPC concrete presents more complex pore internal surface, higher porosity and less micro-pores than the concrete incorporating fly ash and GBFS. Portlandite in OPC concrete and OPC-FA concrete is mainly converted to gypsum; while for OPC-GBFS concrete, both gypsum and ettringite are formed. In the cyclic sulfate environment, repeated hydration and dehydration of sulfates produce the expansive stress in pores, aggravating the demolishment of concrete structure.

Modeling defect cluster evolution in irradiated structural materials: Focus on comparing to high-resolution experimental characterization studies

DOE PAGES

Wirth, Brian D.; Hu, Xunxiang; Kohnert, Aaron; ...

2015-03-02

Exposure of metallic structural materials to irradiation environments results in significant microstructural evolution, property changes, and performance degradation, which limits the extended operation of current generation light water reactors and restricts the design of advanced fission and fusion reactors. Further, it is well recognized that these irradiation effects are a classic example of inherently multiscale phenomena and that the mix of radiation-induced features formed and the corresponding property degradation depend on a wide range of material and irradiation variables. This inherently multiscale evolution emphasizes the importance of closely integrating models with high-resolution experimental characterization of the evolving radiation-damaged microstructure. Lastly,more » this article provides a review of recent models of the defect microstructure evolution in irradiated body-centered cubic materials, which provide good agreement with experimental measurements, and presents some outstanding challenges, which will require coordinated high-resolution characterization and modeling to resolve.« less

Microstructure and Tribological Properties of Mo-40Ni-13Si Multiphase Intermetallic Alloy.

PubMed

Song, Chunyan; Wang, Shuhuan; Gui, Yongliang; Cheng, Zihao; Ni, Guolong

2016-12-06

Intermetallic compounds are increasingly being expected to be utilized in tribological environments, but to date their implementation is hindered by insufficient ductility at low and medium temperatures. This paper presents a novel multiphase intermetallic alloy with the chemical composition of Mo-40Ni-13Si (at %). Microstructure characterization reveals that a certain amount of ductile Mo phases formed during the solidification process of a ternary Mo-Ni-Si molten alloy, which is beneficial to the improvement of ductility of intermetallic alloys. Tribological properties of the designed alloy-including wear resistance, friction coefficient, and metallic tribological compatibility-were evaluated under dry sliding wear test conditions at room temperature. Results suggest that the multiphase alloy possesses an excellent tribological property, which is attributed to unique microstructural features and thereby a good combination in hardness and ductility. The corresponding wear mechanism is explained by observing the worn surface, subsurface, and wear debris of the alloy, which was found to be soft abrasive wear.

Microstructural fingerprints of phase transitions in shock-loaded iron

NASA Astrophysics Data System (ADS)

Wang, S. J.; Sui, M. L.; Chen, Y. T.; Lu, Q. H.; Ma, E.; Pei, X. Y.; Li, Q. Z.; Hu, H. B.

2013-01-01

The complex structural transformation in crystals under static pressure or shock loading has been a subject of long-standing interest to materials scientists and physicists. The polymorphic transformation is of particular importance for iron (Fe), due to its technological and sociological significance in the development of human civilization, as well as its prominent presence in the earth's core. The martensitic transformation α-->ɛ (bcc-->hcp) in iron under shock-loading, due to its reversible and transient nature, requires non-trivial detective work to uncover its occurrence. Here we reveal refined microstructural fingerprints, needle-like colonies and three sets of {112}<111> twins with a threefold symmetry, with tell-tale features that are indicative of two sequential martensitic transformations in the reversible α-->ɛ phase transition, even though no ɛ is retained in the post-shock samples. The signature orientation relationships are consistent with previously-proposed transformation mechanisms, and the unique microstructural fingerprints enable a quantitative assessment of the volume fraction transformed.

Morphological effects on sensitivity of heterogeneous energetic materials

NASA Astrophysics Data System (ADS)

Roy, Sidhartha; Rai, Nirmal; Sen, Oishik; Udaykumar, H. S.

2017-06-01

The mesoscale physical response under shock loading in heterogeneous energetics is inherently linked to the microstructural characteristics. The current work demonstrates the connection between the microstructural features of porous energetic material and its sensitivity. A unified levelset based framework is developed to characterize the microstructures of a given sample. Several morphological metrics describing the mesoscale geometry of the materials are extracted using the current tool including anisotropy, tortuosity, surface to volume, nearest neighbors, size and curvature distributions. The relevant metrics among the ones extracted are identified and correlated to the mesoscale response of the energetic materials under shock loading. Two classes of problems are considered here: (a) field of idealized voids embedded in the HMX material and (b) real samples of pressed HMX. The effects of stochasticity associated with void arrangements on the sensitivity of the energetic material samples are shown. In summary, this work demonstrates the relationship between the mesoscale morphology and shock response of heterogeneous energetic materials using a levelset based framework.

Coarsening Kinetics and Morphological Evolution in a Two-Phase Titanium Alloy During Heat Treatment

NASA Astrophysics Data System (ADS)

Xu, Jianwei; Zeng, Weidong; Jia, Zhiqiang; Sun, Xin; Zhao, Yawei

2016-03-01

The effects of alpha/beta heat treatment on microstructure evolution of Ti-17 alloy with a lamellar colony structure are established. Heat treatment experiments are conducted at 1103 or 1063 K for times ranging from 10 min to 8 h. The main features of microstructure evolution during heat treatment comprise static globularization and coarsening of primary alpha phase. Such behaviors can be accelerated by higher heat treatment temperature. Furthermore, globularization and coarsening behaviors show a faster rate at higher prestrain. In order to better understand the microstructure evolution of Ti-17 alloy during alpha/beta heat treatment, static globularization and coarsening behaviors are modeled in the theoretical frame of the Johnson-Mehl-Avarmi-Kolmogorov (JMAK) and Lifshitz-Slyozov-Wagner (LSW) theories, respectively. The JMAK and LSW kinetics parameters are derived under different experimental conditions. Agreements between measurements and predictions are found, indicating that the JMAK and LSW theories can be used to predict and trace static globularization and coarsening processes of Ti-17 alloy during alpha/beta heat treatment.

Application of Al-2La-1B Grain Refiner to Al-10Si-0.3Mg Casting Alloy

NASA Astrophysics Data System (ADS)

Jing, Lijun; Pan, Ye; Lu, Tao; Li, Chenlin; Pi, Jinhong; Sheng, Ningyue

2018-05-01

This paper reports the application and microstructure refining effect of an Al-2La-1B grain refiner in Al-10Si-0.3Mg casting alloy. Compared with the traditional Al-5Ti-1B refiner, Al-2La-1B refiner shows better performances on the grain refinement of Al-10Si-0.3Mg alloy. Transmission electron microscopy analysis suggests that the crystallite structure features of LaB6 are beneficial to the heterogeneous nucleation of α-Al grains. Regarding the mechanical performances, tensile properties of Al-10Si-0.3Mg casting alloy are prominently improved, due to the refined microstructures.

Preparation, anti-biofouling and drag-reduction properties of a biomimetic shark skin surface

PubMed Central

Pu, Xia; Li, Guangji; Huang, Hanlu

2016-01-01

ABSTRACT Shark skin surfaces show non-smoothness characteristics due to the presence of a riblet structure. In this study, biomimetic shark skin was prepared by using the polydimethylsiloxane (PDMS)-embedded elastomeric stamping (PEES) method. Scanning electron microscopy (SEM) was used to examine the surface microstructure and fine structure of shark skin and biomimetic shark skin. To analyse the hydrophobic mechanism of the shark skin surface microstructure, the effect of biomimetic shark skin surface microstructure on surface wettability was evaluated by recording water contact angle. Additionally, protein adhesion experiments and anti-algae adhesion performance testing experiments were used to investigate and evaluate the anti-biofouling properties of the surface microstructure of biomimetic shark skin. The recorded values of the water contact angle of differently microstructured surfaces revealed that specific microstructures have certain effects on surface wettability. The anti-biofouling properties of the biomimetic shark skin surface with microstructures were superior to a smooth surface using the same polymers as substrates. Moreover, the air layer fixed on the surface of the biomimetic shark skin was found to play a key role in their antibiont adhesion property. An experiment into drag reduction was also conducted. Based on the experimental results, the microstructured surface of the prepared biomimetic shark skin played a significant role in reducing drag. The maximum of drag reduction rate is 12.5%, which is higher than the corresponding maximum drag reduction rate of membrane material with a smooth surface. PMID:26941105

Preparation, anti-biofouling and drag-reduction properties of a biomimetic shark skin surface.

PubMed

Pu, Xia; Li, Guangji; Huang, Hanlu

2016-04-15

Shark skin surfaces show non-smoothness characteristics due to the presence of a riblet structure. In this study, biomimetic shark skin was prepared by using the polydimethylsiloxane (PDMS)-embedded elastomeric stamping (PEES) method. Scanning electron microscopy (SEM) was used to examine the surface microstructure and fine structure of shark skin and biomimetic shark skin. To analyse the hydrophobic mechanism of the shark skin surface microstructure, the effect of biomimetic shark skin surface microstructure on surface wettability was evaluated by recording water contact angle. Additionally, protein adhesion experiments and anti-algae adhesion performance testing experiments were used to investigate and evaluate the anti-biofouling properties of the surface microstructure of biomimetic shark skin. The recorded values of the water contact angle of differently microstructured surfaces revealed that specific microstructures have certain effects on surface wettability. The anti-biofouling properties of the biomimetic shark skin surface with microstructures were superior to a smooth surface using the same polymers as substrates. Moreover, the air layer fixed on the surface of the biomimetic shark skin was found to play a key role in their antibiont adhesion property. An experiment into drag reduction was also conducted. Based on the experimental results, the microstructured surface of the prepared biomimetic shark skin played a significant role in reducing drag. The maximum of drag reduction rate is 12.5%, which is higher than the corresponding maximum drag reduction rate of membrane material with a smooth surface. © 2016. Published by The Company of Biologists Ltd.

Modelling of deformation and recrystallisation microstructures in rocks and ice

NASA Astrophysics Data System (ADS)

Bons, Paul D.; Evans, Lynn A.; Gomez-Rivas, Enrique; Griera, Albert; Jessell, Mark W.; Lebensohn, Ricardo; Llorens, Maria-Gema; Peternell, Mark; Piazolo, Sandra; Weikusat, Ilka; Wilson, Chris J. L.

2015-04-01

Microstructures both record the deformation history of a rock and strongly control its mechanical properties. As microstructures in natural rocks only show the final "post-mortem" state, geologists have attempted to simulate the development of microstructures with experiments and later numerical models. Especially in-situ experiments have given enormous insight, as time-lapse movies could reveal the full history of a microstructure. Numerical modelling is an alternative approach to simulate and follow the change in microstructure with time, unconstrained by experimental limitations. Numerical models have been applied to a range of microstructural processes, such as grain growth, dynamic recrystallisation, porphyroblast rotation, vein growth, formation of mylonitic fabrics, etc. The numerical platform "Elle" (www.elle.ws) in particular has brought progress in the simulation of microstructural development as it is specifically designed to include the competition between simultaneously operating processes. Three developments significantly improve our capability to simulate microstructural evolution: (1) model input from the mapping of crystallographic orientation with EBSD or the automatic fabric analyser, (2) measurement of grain size and crystallographic preferred orientation evolution using neutron diffraction experiments and (3) the implementation of the full-field Fast Fourier Transform (FFT) solver for modelling anisotropic crystal-plastic deformation. The latter enables the detailed modelling of stress and strain as a function of local crystallographic orientation, which has a strong effect on strain localisation such as, for example, the formation of shear bands. These models can now be compared with the temporal evolution of crystallographic orientation distributions in in-situ experiments. In the last decade, the possibility to combine experiments with numerical simulations has allowed not only verification and refinement of the numerical simulation technique but also increased significantly the ability to predict and/or interpret natural microstructures. This contribution will present the most recent developments in in-situ and numerical modelling of deformation and recrystallisation microstructures in rocks and in ice.

A Systematic Study on Tooth Enamel Microstructures of Lambdopsalis bulla (Multituberculate, Mammalia) - Implications for Multituberculate Biology and Phylogeny

PubMed Central

Mao, Fangyuan; Wang, Yuanqing; Meng, Jin

2015-01-01

Tooth enamel microstructure is a reliable and widely used indicator of dietary interpretations and data for phylogenetic reconstruction, if all levels of variability are investigated. It is usually difficult to have a thorough examination at all levels of enamel structures for any mammals, especially for the early mammals, which are commonly represented by sparse specimens. Because of the random preservation of specimens, enamel microstructures from different teeth in various species are often compared. There are few examples that convincingly show intraspecific variation of tooth enamel microstructure in full dentition of a species, including multituberculates. Here we present a systematic survey of tooth enamel microstructures of Lambdopsalis bulla, a taeniolabidoid multituberculate from the Late Paleocene Nomogen Formation, Inner Mongolia. We examined enamel structures at all hierarchical levels. The samples are treated differently in section orientations and acid preparation and examined using different imaging methods. The results show that, except for preparation artifacts, the crystallites, enamel types, Schmelzmuster and dentition types of Lambdopsalis are relatively consistent in all permanent teeth, but the prism type, including the prism shape, size and density, may vary in different portions of a single tooth or among different teeth of an individual animal. The most common Schmelzmuster of the permanent teeth in Lambdopsalis is a combination of radial enamel in the inner and middle layers, aprismatic enamel in the outer layer, and irregular decussations in tooth crown area with great curvature. The prism seam is another comparably stable characteristic that may be a useful feature for multituberculate taxonomy. The systematic documentation of enamel structures in Lambdopsalis may be generalized for the enamel microstructure study, and thus for taxonomy and phylogenetic reconstruction, of multituberculates and even informative for the enamel study of other early mammals. PMID:26020958

Correlation of microstructure, tensile properties and hole expansion ratio in cold rolled advanced high strength steels

NASA Astrophysics Data System (ADS)

Terrazas, Oscar R.

The demand for advanced high strength steels (AHSS) with higher strengths is increasing in the automotive industry. While there have been major improvements recently in the trade-off between ductility and strength, sheared-edge formability of AHSS remains a critical issue. AHSS sheets exhibit cracking during stamping and forming operations below the predictions of forming limits. It has become important to understand the correlation between microstructure and sheared edge formability. The present work investigates the effects of shearing conditions, microstructure, and tensile properties on sheared edge formability. Seven commercially produced steels with tensile strengths of 1000 +/- 100 MPa were evaluated: five dual-phase (DP) steels with different compositions and varying microstructural features, one trip aided bainitic ferrite (TBF) steel, and one press-hardened steel tempered to a tensile strength within the desired range. It was found that sheared edge formability is influenced by the martensite in DP steels. Quantitative stereology measurements provided results that showed martensite size and distribution affect hole expansion ratio (HER). The overall trend is that HER increases with more evenly dispersed martensite throughout the microstructure. This microstructure involves a combination of martensite size, contiguity, mean free distance, and number of colonies per unit area. Additionally, shear face characterization showed that the fracture and burr region affect HER. The HER decreases with increasing size of fracture and burr region. With a larger fracture and burr region more defects and/or micro-cracks will be present on the shear surface. This larger fracture region on the shear face facilitates cracking in sheared edge formability. Finally, the sheared edge formability is directly correlated to true fracture strain (TFS). The true fracture strain from tensile samples correlates to the HER values. HER increases with increasing true fracture strain.

Defects-tolerant Co-Cr-Mo dental alloys prepared by selective laser melting.

PubMed

Qian, B; Saeidi, K; Kvetková, L; Lofaj, F; Xiao, C; Shen, Z

2015-12-01

CrCoMo alloy specimens were successfully fabricated using selective laser melting (SLM). The aim of this study was to carefully investigate microstructure of the SLM specimens in order to understand the influence of their structural features inter-grown on different length scales ranging from nano- to macro-levels on their mechanical properties. Two different sets of processing parameters developed for building the inner part (core) and the surface (skin) of dental prostheses were tested. Microstructures were characterized by SEM, EBSD and XRD analysis. The elemental distribution was assessed by EDS line profile analysis under TEM. The mechanical properties of the specimens were measured. The microstructures of both specimens were characterized showing formation of grains comprised of columnar sub-grains with Mo-enrichment at the sub-grain boundaries. Clusters of columnar sub-grains grew coherently along one common crystallographic direction forming much larger single crystal grains which are intercrossing in different directions forming an overall dendrite-like microstructure. Three types of microstructural defects were occasionally observed; small voids (<10 μm), fine cracks at grain boundaries (<10 μm) and cracks at weld line boundaries (>10 μm). Despite the presence of these defects, the yield and the ultimate tensile strength (UTS) were 870 and 430MPa and 1300MPa and 1160MPa, respectively, for the skin and core specimens which are higher than casted dental alloy. Although the formation of microstructural defects is hard to be avoided during the SLM process, the SLM CoCrMo alloys can achieve improved mechanical properties than their casted counterparts, implying they are "defect-tolerant". Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Design Issues for Using Magnetic Materials in Radiation Environments at Elevated Temperature

NASA Technical Reports Server (NTRS)

Bowman, Cheryl L.

2013-01-01

One of the challenges of designing motors and alternators for use in nuclear powered space missions is accounting for the effects of radiation. Terrestrial reactor power plants use distance and shielding to minimize radiation damage but space missions must economize volume and mass. Past studies have shown that sufficiently high radiation levels can affect the magnetic response of hard and soft magnetic materials. Theoretical models explaining the radiation-induced degradation have been proposed but not verified. This paper reviews the literature and explains the cumulative effects of temperature, magnetic-load, and radiation-level on the magnetic properties of component materials. Magnetic property degradation is very specific to alloy choice and processing history, since magnetic properties are very much entwined with specific chemistry and microstructural features. However, there is basic theoretical as well as supportive experimental evidence that the negative impact to magnetic properties will be minimal if the bulk temperature of the material is less than fifty percent of the Curie temperature, the radiation flux is low, and the demagnetization field is small. Keywords: Magnets, Permanent Magnets, Power Converters, Nuclear Electric Power Generation, Radiation Tolerance.

Behavioral and neuroanatomical abnormalities in pleiotrophin knockout mice.

PubMed

Krellman, Jason W; Ruiz, Henry H; Marciano, Veronica A; Mondrow, Bracha; Croll, Susan D

2014-01-01

Pleiotrophin (PTN) is an extracellular matrix-associated protein with neurotrophic and neuroprotective effects that is involved in a variety of neurodevelopmental processes. Data regarding the cognitive-behavioral and neuroanatomical phenotype of pleiotrophin knockout (KO) mice is limited. The purpose of this study was to more fully characterize this phenotype, with emphasis on the domains of learning and memory, cognitive-behavioral flexibility, exploratory behavior and anxiety, social behavior, and the neuronal and vascular microstructure of the lateral entorhinal cortex (EC). PTN KOs exhibited cognitive rigidity, heightened anxiety, behavioral reticence in novel contexts and novel social interactions suggestive of neophobia, and lamina-specific decreases in neuronal area and increases in neuronal density in the lateral EC. Initial learning of spatial and other associative tasks, as well as vascular density in the lateral EC, was normal in the KOs. These data suggest that the absence of PTN in vivo is associated with disruption of specific cognitive and affective processes, raising the possibility that further study of PTN KOs might have implications for the study of human disorders with similar features.

A study of microstructure, quasi-static response, fatigue, deformation and fracture behavior of high strength alloy steels

NASA Astrophysics Data System (ADS)

Kannan, Manigandan

The history of steel dates back to the 17th century and has been instrumental in the betterment of every aspect of our lives ever since, from the pin that holds the paper together to the Automobile that takes us to our destination steel touches everyone every day. Path breaking improvements in manufacturing techniques, access to advanced machinery and understanding of factors like heat treatment, corrosion resistance have aided in the advancement in the properties of steel in the last few years. In this dissertation document, the results of a study aimed at the influence of alloy chemistry, processing and influence of the quasi static and fatigue behavior of seven alloy steels is discussed. The microstructure of the as-received steel was examined and characterized for the nature and morphology of the grains and the presence of other intrinsic features in the microstructure. The tensile, cyclic fatigue and bending fatigue tests were done on a fully automated closed-loop servo-hydraulic test machine at room temperature. The failed samples of high strength steels were examined in a scanning electron microscope for understanding the fracture behavior, especially the nature of loading be it quasi static, cyclic fatigue or bending fatigue . The quasi static and cyclic fatigue fracture behavior of the steels examined coupled with various factors contributing to failure are briefly discussed in light of the conjoint and mutually interactive influences of intrinsic microstructural effects, nature of loading, and stress (load)-deformation-microstructural interactions.

Property and microstructural nonuniformity in the yttrium-barium-copper-oxide superconductor determined from electrical, magnetic, and ultrasonic measurements. Ph.D. Thesis - Case Western Reserve Univ.

NASA Technical Reports Server (NTRS)

Roth, Don J.

1991-01-01

The purpose of this dissertation was the following: (1) to characterize the effect of pore fraction on a comprehensive set of electrical and magnetic properties for the yttrium-barium-copper-oxide (YBCO) high temperature ceramic superconductor; and (2) to determine the viability of using a room-temperature, nondestructive characterization method to aid in the prediction of superconducting (cryogenic) properties. The latter involved correlating ultrasonic velocity measurements at room temperature with property-affecting pore fraction and oxygen content variations. The use of ultrasonic velocity for estimating pore fraction in YBCO is presented, and other polycrystalline materials are reviewed, modeled, and statistically analyzed. This provides the basis for using ultrasonic velocity to interrogate microstructure. The effect of pore fraction (0.10-0.25) on superconductor properties of YBCO samples was characterized. Spatial (within-sample) variations in microstructure and superconductor properties were investigated, and the effect of oxygen content on elastic behavior was examined. Experimental methods used included a.c. susceptibility, electrical, and ultrasonic velocity measurements. Superconductor properties measured included transition temperature, magnetic transition width, transport and magnetic critical current density, magnetic shielding, a.c. loss, and sharpness of the voltage-current characteristics. An ultrasonic velocity image constructed from measurements at 1mm increments across a YBCO sample revealed microstructural variations that correlated with variations in magnetic shielding and a.c. loss behavior. Destructive examination using quantitative image analysis revealed pore fraction to be the varying microstructural feature.

Anisotropic wetting of microstructured surfaces as a function of surface chemistry.

PubMed

Neuhaus, Sonja; Spencer, Nicholas D; Padeste, Celestino

2012-01-01

In order to study the influence of surface chemistry on the wetting of structured surfaces, microstructures consisting of grooves or squares were produced via hot embossing of poly(ethylene-alt-tetrafluoroethylene) ETFE substrates. The structured substrates were modified with polymer brushes, thereby changing their surface functionality and wettability. Water droplets were most strongly pinned to the structure when the surface was moderately hydrophilic, as in the case of poly(4-vinylpyridine) (P4VP) or poly(vinyl(N-methyl-2-pyridone) (PVMP) brush-modified substrates. As a result, the droplet shape was determined by the features of the microstructure. The water contact angles (CA) were considerably higher than on flat surfaces and differed, in the most extreme case, by 37° when measured on grooved substrates, parallel and perpendicular to the grooves. On hydrophobic substrates (pristine ETFE), the same effects were observed but were much less pronounced. On very hydrophilic sampes (those modified with poly(N-methyl-vinylpyridinium) (QP4VP)), the microstructure had no influence on the drop shape. These findings are explained by significant differences in apparent and real contact angles at the relatively smooth edges of the embossed structures. Finally, the highly anisotropic grooved microstructure was combined with a gradient in polymer brush composition and wettability. In the case of a parallel alignment of the gradient direction to the grooves, the directed spreading of water droplets could be observed. © 2011 American Chemical Society

Characterization of aging-induced microstructural changes in M250 maraging steel using magnetic parameters

NASA Astrophysics Data System (ADS)

Rajkumar, K. V.; Vaidyanathan, S.; Kumar, Anish; Jayakumar, T.; Raj, Baldev; Ray, K. K.

2007-05-01

The best combinations of mechanical properties (yield stress and fracture toughness) of M250 maraging steel is obtained through short-term thermal aging (3-10 h) at 755 K. This is attributed to the microstructure containing precipitation of intermetallic phases in austenite-free low-carbon martensite matrix. Over-aged microstructure, containing reverted austenite degrades the mechanical properties drastically. Hence, it necessitates identification of a suitable non-destructive evaluation (NDE) technique for detecting any reverted austenite unambiguously during aging. The influence of aging on microstructure, room temperature hardness and non-destructive magnetic parameters such as coercivity ( Hc), saturation magnetization ( Ms) and magnetic Barkhausen emission (MBE) RMS peak voltage is studied in order to derive correlations between these parameters in aged M250 maraging steel. Hardness was found to increase with precipitation of intermetallics during initial aging and decrease at longer durations due to austenite reversion. Among the different magnetic parameters studied, MBE RMS peak voltage was found to be very sensitive to austenite reversion (non-magnetic phase) as they decreased drastically up on initiation of austenite reversion. Hence, this parameter can be effectively utilized to detect and quantify the reverted austenite in maraging steel specimen. The present study clearly indicates that the combination of MBE RMS peak voltage and hardness can be used for unambiguous characterization of microstructural features of technological and practical importance (3-10 h of aging duration at 755 K) in M250 grade maraging steel.

Correlations of microstructure with dynamic and quasi-static fracture in a plain carbon steel

NASA Astrophysics Data System (ADS)

Couque, H.; Asaro, R. J.; Duffy, J.; Lee, S. H.

1988-09-01

An investigation was conducted into the effects of temperature, loading rate, and various micro-structural parameters on the initiation of plane strain fracture of a plain carbon AISI 1020 steel. Ferrite and prior austenite grain sizes were chosen as the principal microstructural features to be in-vestigated. The microstructural variations were accomplished by changing the austenitizing tempera-ture and by altering the cooling rate during normalization. Fracture toughness tests were conducted using precracked notched round bars loaded in tension to produce two stress intensity rates, viz., K 1 = 1 MPa √m s-1 and K 1 = 2 × 106 MPa √m s-1. In addition, Charpy impact tests along with quasistatic and high rate plasticity tests were conducted. The plasticity tests were done in torsion at shear strain rates ofoverline γ = 5.0 × 10^{ - 4} s^{ - 1 } and overline γ = 1.5 × 10^{3 } s^{ - 1} . Testing temperatures covered the range from -150 °C to 150 °C which encompassed fracture initiation modes involving transgranular cleavage to fully ductile fracture. Micromechanical processes involved in void and cleavage micro-crack formation were identified and quantified. For these purposes notched round tensile tests and subsequent metallographic observations along with TEM and SEM observations of the plane strain fracture toughness specimens were performed. The experimental results and quantitative micro-modeling using simple fracture models provide a means of correlating both quasistatic and dynamic fracture toughness with microstructures.

White matter biomarkers from diffusion MRI

NASA Astrophysics Data System (ADS)

Nørhøj Jespersen, Sune

2018-06-01

As part of an issue celebrating 2 decades of Joseph Ackerman editing the Journal of Magnetic Resonance, this paper reviews recent progress in one of the many areas in which Ackerman and his lab has made significant contributions: NMR measurement of diffusion in biological media, specifically in brain tissue. NMR diffusion signals display exquisite sensitivity to tissue microstructure, and have the potential to offer quantitative and specific information on the cellular scale orders of magnitude below nominal image resolution when combined with biophysical modeling. Here, I offer a personal perspective on some recent advances in diffusion imaging, from diffusion kurtosis imaging to microstructural modeling, and the connection between the two. A new result on the estimation accuracy of axial and radial kurtosis with axially symmetric DKI is presented. I moreover touch upon recently suggested generalized diffusion sequences, promising to offer independent microstructural information. We discuss the need and some methods for validation, and end with an outlook on some promising future directions.

Age-related decline in task switching is linked to both global and tract-specific changes in white matter microstructure.

PubMed

Jolly, Todd A D; Cooper, Patrick S; Rennie, Jaime L; Levi, Christopher R; Lenroot, Rhoshel; Parsons, Mark W; Michie, Patricia T; Karayanidis, Frini

2017-03-01

Task-switching performance relies on a broadly distributed frontoparietal network and declines in older adults. In this study, they investigated whether this age-related decline in task switching performance was mediated by variability in global or regional white matter microstructural health. Seventy cognitively intact adults (43-87 years) completed a cued-trials task switching paradigm. Microstructural white matter measures were derived using diffusion tensor imaging (DTI) analyses on the diffusion-weighted imaging (DWI) sequence. Task switching performance decreased with increasing age and radial diffusivity (RaD), a measure of white matter microstructure that is sensitive to myelin structure. RaD mediated the relationship between age and task switching performance. However, the relationship between RaD and task switching performance remained significant when controlling for age and was stronger in the presence of cardiovascular risk factors. Variability in error and RT mixing cost were associated with RaD in global white matter and in frontoparietal white matter tracts, respectively. These findings suggest that age-related increase in mixing cost may result from both global and tract-specific disruption of cerebral white matter linked to the increased incidence of cardiovascular risks in older adults. Hum Brain Mapp 38:1588-1603, 2017. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

in vivo quantification of white matter microstructure for use in aging: A focus on two emerging techniques

PubMed Central

Lamar, Melissa; Zhou, Xiaohong Joe; Charlton, Rebecca A.; Dean, Douglas; Little, Deborah; Deoni, Sean C

2013-01-01

Human brain imaging has seen many advances in the quantification of white matter in vivo. For example, these advances have revealed the association between white matter damage and vascular disease as well as their impact on risk for and development of dementia and depression in an aging population. Current neuroimaging methods to quantify white matter damage provide a foundation for understanding such age-related neuropathology; however, these methods are not as adept at determining the underlying microstructural abnormalities signaling at risk tissue or driving white matter damage in the aging brain. This review will begin with a brief overview of the use of diffusion tensor imaging (DTI) in understanding white matter alterations in aging before focusing in more detail on select advances in both diffusion-based methods and multi-component relaxometry techniques for imaging white matter microstructural integrity within myelin sheaths and the axons they encase. While DTI greatly extended the field of white matter interrogation, these more recent technological advances will add clarity to the underlying microstructural mechanisms that contribute to white matter damage. More specifically, the methods highlighted in this review may prove more sensitive (and specific) for determining the contribution of myelin versus axonal integrity to the aging of white matter in brain. PMID:24080382

White matter microstructure in boys with persistent depressive disorder.

PubMed

Vilgis, Veronika; Vance, Alasdair; Cunnington, Ross; Silk, Timothy J

2017-10-15

Persistent depressive symptoms in children and adolescents are considered a risk factor for the development of major depressive disorder (MDD) later in life. Previous research has shown alterations in white matter microstructure in pediatric MDD but discrepancies exist as to the specific tracts affected. The current study aimed to improve upon previous methodology and address the question whether previous findings of lower fractional anisotropy (FA) replicate in a sample of children with persistent depressive disorder characterized by mild but more chronic symptoms of depression. White matter microstructure was examined in 25 boys with persistent depressive disorder and 25 typically developing children. Tract specific analysis implemented with the Diffusion Tensor Imaging - ToolKit (DTI-TK) was used to probe fractional anisotropy (FA) in eleven major white matter tracts. Clusters within the left uncinate, inferior fronto-occipital and cerebrospinal tracts showed lower FA in the clinical group. FA in the left uncinate showed a negative association with self-reported symptoms of depression. The results demonstrate lower FA in several white matter tracts in children with persistent depressive disorder. These findings support the contention that early onset depression is associated with altered white matter microstructure, which may contribute to the maintenance and recurrence of symptoms. Copyright © 2017. Published by Elsevier B.V.

Osteonic organization of limb bones in mammals, including humans, and birds: a preliminary study.

PubMed

Castrogiovanni, Paola; Imbesi, Rosa; Fisichella, Marco; Mazzone, Venera

2011-01-01

As it is well known, bone tissue is characterized by a calcified extracellular matrix which makes this tissue suitable to support the body and protect the inner organs. Lamellar bone tissue is organized in lamellae, 3-7 microm in thickness, and arranged concentrically around vascular channels: the basic structure in this type of organization is called Haversian system or osteon and the diameter of osteons depends on the number of lamellae. Shape and regional density of osteons are related to the bone segment and the specific functional requirements to meet. Aim of this study is to correlate the compact bone tissue microstructure in various classes of mammals, including humans, and birds in order to find an adequate identification key. The results of our study show that in bone tissue samples from various classes of mammals, including humans, and birds the osteonic structure shows peculiar features, often depending on the rate of bone remodelling, different in different animal species. We conclude that a careful microscopic analysis of bone tissue and the characterization of distinctive osteonic features could give a major contribution to forensic medicine to obtain a more reliable recognition of bone findings.

Effects of Solid Solution Treatments on the Microstructure and Mechanical Properties of a Nanoscale Precipitate-Strengthened Ferritic Steel

NASA Astrophysics Data System (ADS)

Zhao, Y.; Guo, H.; Xu, S. S.; Mao, M. J.; Chen, L.; Gokhman, O.; Zhang, Z. W.

2018-05-01

Solid solution treatment (SST) and age hardening are the two main treatments used to produce nanoscale precipitation-strengthened steels. In this work, solution treatment and aging are employed to develop a nanoscale precipitation-strengthened steel displaying high degrees of strength, ductility, and toughness. The effects of SST on the microstructure and mechanical properties of the produced steel are investigated. The results show that the solution temperature strongly influences the matrix microstructure. Partial austenitization between A_{{{c}1}} and A_{{{c}3}} favors the formation of granular ferrite, while complete austenitization above A_{{{c}3}} leads to the formation of polygonal ferrite. Refined granular ferrite with a low dislocation density can effectively improve the plasticity and low-temperature toughness of steel. Precipitation strengthening is mainly related to the nature of the nano-precipitates, specifically their size and number density, independently of the matrix microstructure.

Effects of carbohydrate/protein ratio on the microstructure and the barrier and sorption properties of wheat starch-whey protein blend edible films.

PubMed

Basiak, Ewelina; Lenart, Andrzej; Debeaufort, Frédéric

2017-02-01

Starch and whey protein isolate and their mixtures were used for making edible films. Moisture sorption isotherms, water vapour permeability, sorption of aroma compounds, microstructure, water contact angle and surface properties were investigated. With increasing protein content, the microstructure changes became more homogeneous. The water vapour permeability increases with both the humidity gradient and the starch content. For all films, the hygroscopicity increases with starch content. Surface properties change according to the starch/whey protein ratio and are mainly related to the polar component of the surface tension. Films composed of 80% starch and 20% whey proteins have more hydrophobic surfaces than the other films due to specific interactions. The effect of carbohydrate/protein ratio significantly influences the microstructure, the surface wettability and the barrier properties of wheat starch-whey protein blend films. © 2016 Society of Chemical Industry. © 2016 Society of Chemical Industry.

Layered Manufacturing: Challenges and Opportunities

DTIC Science & Technology

2003-04-01

quality of the surface finish, eliminating residual stress , controlling local composition and microstructure, achieving fine feature size and...applications. Some methods have achieved commercial status, having graduated from the university level, others are in various stages of research. However...Road * Sintering * Co-firing * Shrinkage * Gas dimensions + Powder or + Resin * Residual stress precursors * Layer wire feeding infiltration * Distortion

Microstructural Effects of Multiple Passes during Friction Stir Processing of Nickel Aluminum Bronze

DTIC Science & Technology

2009-12-01

various tool steel compositions for use with aluminum, and materials such as Densimet®, a tungsten-iron composite. Additionally, various other...mixture of martensite or bainite in which Widmanstätten α ahs also formed. These features likely reflect the effect of the tool shoulder as it pulls base

Feature Extraction and Classification of FLIR Imagery Using Relative Locations of Non-Homogeneous Regions with Feedforward Neural Networks

DTIC Science & Technology

1992-04-01

Proceedings of Tri-Service Data Fusion Symposium, Johns Hopkins University, May 1989. 39. F. Rosenblatt. Principles of Neurodynamics : Perceptrons and the...104 47. David E. Rummelhart and James L. McClelland. Parallel Distributed Processing: Explorations in the Microstructure of Cognition , volume 1. The

In-situ Indentation and Correlated Precession Electron Diffraction Analysis of a Polycrystalline Cu Thin Film

NASA Astrophysics Data System (ADS)

Guo, Qianying; Thompson, Gregory B.

2018-04-01

In-situ TEM nanoindentation of a polycrystalline Cu film was cross-correlated with precession electron diffraction (PED) to quantify the microstructural evolution. The use of PED is shown to clearly reveal features, such as grain size, that are easily masked by diffraction contrast created by the deformation. Using PED, the accompanying grain refinement and change in texture as well as the preservation of specific grain boundary structures, including a ∑3 boundary, under the indent impression were quantified. The nucleation of dislocations, evident in low-angle grain boundary formations, was also observed under the indent. PED quantification of texture gradients created by the indentation process linked well to bend contours observed in the bright-field images. Finally, PED enabled generating a local orientation spread map that gave an approximate estimation of the spatial distribution of strain created by the indentation impression.

Study of the propagation of a plane turbulent jet in flow-through chamber workings

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

Laigna, K.Yu.; Potter, E.A.

1988-05-01

The purpose of this study was to determine experimentally the parameters of microstructures of confined planar jets and to investigate the specific features of turbulent diffusion of impurities in such flows for problems of mine ventilation and pollution abatement in underground workings. A confined planar jet flowing from a slot coaxially into the model of a chamber working of rectangular transverse cross section was studied. The averaged and pulsating characteristics of the jet were measured by a thermoanemometer. Transient and channel zones were identified and the movement of the jet within them was described. Results demonstrated that the turbulent diffusionmore » coefficient in the jet-affected zone was greater by two or three orders of magnitude than in the remainder of the flow and that it is therefore incorrect to use turbulent diffusion coefficients of confined flows for evaluations of the jet diffusion of impurities.« less

Redescription of Gyropus parvus (Ewing, 1924) (Insecta: Phthiraptera: Amblycera: Gyropidae) from tucos-tucos (Rodentia: Ctenomyidae: Ctenomys ) in Patagonia, Argentina.

PubMed

Martino, N S; Romero, M D; Castro, D C

2010-02-01

A detailed redescription of Gyropus parvus (Insecta: Phthiraptera: Amblycera: Gyropidae) is given based on specimens collected from the type host, Ctenomys colburni Allen 1903 , and the type locality, Estancia Huanuluán, Provincia de Rio Negro, Argentina. We expand and provide new chaetotaxy. New scanning electron microscopy images showing microstructural details of adults and eggs of G. parvus obtained from topotype specimens are included. Sexual dimorphism was mainly shown by differences in body size and abdominal chaetotaxy, with females being 17.5% larger than males and with more setae in each cluster. Significant differences between males and females were also observed in sternal plate measurements. Features described here show homogeneity within type host population. This information contributes to our knowledge of intra- and inter-specific variability for parasite populations. Our investigation constitutes the first collection of G. parvus from the type host and locality since it was described.

Wear and Reactivity Studies of Melt infiltrated Ceramic Matrix Composite

NASA Technical Reports Server (NTRS)

Jarmon, David C.; Ojard, Greg; Brewer, David N.

2013-01-01

As interest grows in the use of ceramic matrix composites (CMCs) for critical gas turbine engine components, the effects of the CMCs interaction with the adjoining structure needs to be understood. A series of CMC/material couples were wear tested in a custom elevated temperature test rig and tested as diffusion couples, to identify interactions. Specifically, melt infiltrated silicon carbide/silicon carbide (MI SiC/SiC) CMC was tested in combination with a nickel-based super alloy, Waspaloy, a thermal barrier coating, Yttria Stabilized Zirconia (YSZ), and a monolithic ceramic, silicon nitride (Si3N4). To make the tests more representative of actual hardware, the surface of the CMC was kept in the as-received state (not machined) with the full surface features/roughness present. Test results include: scanning electron microscope characterization of the surfaces, micro-structural characterization, and microprobe analysis.

Correlation of Rupture Life, Creep Rate, and Microstructure for Type 304 Stainless Steel

NASA Technical Reports Server (NTRS)

Swindeman, R. W.; Moteff, J.

1983-01-01

The stress and temperature sensitivites of the rupture life and secondary creep rate were examined in detail for a single heat of type 304 stainless steel (9T2796). Assuming that the rupture life has a power law stress dependency, relatively small differences in the stress exponent were observed over a broad range of stress and temperature. In contrast, large changes were observed for equivalent parameter for secondary creep rate. As a result of these differences, the Monkman-Grant correlation was sensitive to stress and temperature below 650 C. Metallurgical studies based on light and transmission electron microscopy suggested that the temperature and stress sensitivities of secondary creep rate at temperatures below 650 C were related to features of the substructure not present at higher temperature. Specifically, the presence of a fine dislocation network stabilized by precipitates altered the stress and temperature sensitivities relative to what might be expected from high temperature studies.

The role of cathodic current in PEO of aluminum: Influence of cationic electrolyte composition on the transient current-voltage curves and the discharges optical emission spectra

NASA Astrophysics Data System (ADS)

Rogov, A. B.; Shayapov, V. R.

2017-02-01

In this paper, the influence of cationic electrolytes composition on electrical and optical responses of plasma electrolytic oxidation process of A1050 aluminum alloy under alternating polarization is considered. The electrolytes consist of 0.1 M boric acid with addition of one of the following hydroxides: LiOH, NaOH, KOH, tetraethylammonium hydroxide, Ca(OH)2 up to pH value 9.2. Coatings microstructure, elemental and phase compositions were studied by SEM, EDS and XRD. It was shown that the hysteresis of anodic current-voltage curve (specific feature of "Soft sparking" PEO) was clear observed in the presence of sodium and potassium cations. It was found that composition of microdischarges plasma is also affected by the nature of the cations. It was shown that there are a number of reciprocal processes, which take place under anodic and cathodic polarization.

Comparison and experimental validation of two potential resonant viscosity sensors in the kilohertz range

NASA Astrophysics Data System (ADS)

Lemaire, Etienne; Heinisch, Martin; Caillard, Benjamin; Jakoby, Bernhard; Dufour, Isabelle

2013-08-01

Oscillating microstructures are well established and find application in many fields. These include force sensors, e.g. AFM micro-cantilevers or accelerometers based on resonant suspended plates. This contribution presents two vibrating mechanical structures acting as force sensors in liquid media in order to measure hydrodynamic interactions. Rectangular cross section microcantilevers as well as circular cross section wires are investigated. Each structure features specific benefits, which are discussed in detail. Furthermore, their mechanical parameters and their deflection in liquids are characterized. Finally, an inverse analytical model is applied to calculate the complex viscosity near the resonant frequency for both types of structures. With this approach it is possible to determine rheological parameters in the kilohertz range in situ within a few seconds. The monitoring of the complex viscosity of yogurt during the fermentation process is used as a proof of concept to qualify at least one of the two sensors in opaque mixtures.