Note: This page contains sample records for the topic high al stress from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: November 12, 2013.
1

Degradation mechanism of InAlN/GaN based HFETs under high electric field stress  

NASA Astrophysics Data System (ADS)

Degradation of InAlN/GaN based HFETs under stress for four bias conditions, namely, on-state high field stress (hot phonon, hot electron and self heating effect), off-state high field stress (hot electron effect), onstate low field stress (self heating effect), and reverse gate bias stress (inverse piezoelectric effect) has been examined. The degradation is characterized by monitoring electrical properties, such as, drain current reduction, gate lag, and low frequency noise. On-state high field stress has shown more than 50% reduction in the drain current and approximately 25-30 dBc/Hz increase in low frequency noise after 25 hours of stress, while other stress conditions led to much lesser degradation. It is demonstrated that the major degradation mechanism in InAlN/GaN HFETs is the hot-phonon and hot-electron effect in the realm of short term effects.

Zhu, Congyong; Wu, Mo; Kayis, Cemil; Zhang, Fan; Li, Xing; Ferreyra, Romualdo; Avrutin, Vitaliy; zgur, mit; Morko, Hadis

2012-02-01

2

Phosphorus Enhances Al Resistance in Al-resistant Lespedeza bicolor but not in Al-sensitive L. cuneata Under Relatively High Al Stress  

PubMed Central

Background and Aims Aluminium (Al) toxicity and phosphorus (P) deficiency often co-exist in acidic soils and limit crop production worldwide. Lespedeza bicolor is a leguminous forage species that grows very well in infertile, acidic soils. The objective of this study was to investigate the effects of Al and P interactions on growth of Lespedeza and the distributions of Al and P in two different Al-resistant species, and to explore whether P can ameliorate the toxic effect of Al in the two species. Methods Two species, Lespedeza bicolor and L. cuneata, were grown for 30 d with alternate Al and P treatments in a hydroponics system. Harvested roots were examined using a root-system scanner, and the contents of Al, P and other nutrient elements in the plants were determined using inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Haematoxylin staining was used to observe the distribution of Al in the roots of seedlings. After pre-culture with or without P application, organic acids in the exudates of roots exposed to Al were held in an anion-exchange resin, eluted with 2 m HCl and then analysed using high-performance liquid chromatography (HPLC). Key Results Lespedeza bicolor exhibited a stronger Al resistance than did L. cuneata; Al exclusion mechanisms may mainly be responsible for resistance. P application alleviated the toxic effect of Al on root growth in L. bicolor, while no obvious effects were observed in L. cuneata. Much less Al was accumulated in roots of L. bicolor than in L. cuneata after P application, and the P contents in both roots and shoots increased much more for L. bicolor than for L. cuneata. Lespedeza bicolor showed a higher P/Al ratio in roots and shoots than did L. cuneata. P application decreased the Al accumulation in root tips of L. bicolor but not in L. cuneata. The amount of Al-induced organic acid (citrate and malate) exudation from roots pre-cultured with P was much less than from roots without P application; no malate and citrate exudation was detected in L. cuneata. Conclusions P enhanced Al resistance in the Al-resistant L. bicolor species but not in the Al-sensitive L. cuneata under relatively high Al stress, although P in L. cuneata might also possess an alleviative potential. Enhancement of Al resistance by P in the resistant species might be associated with its more efficient P accumulation and translocation to shoots and greater Al exclusion from root tips after P application, but not with an increased exudation of organic acids from roots.

Sun, Qing Bin; Shen, Ren Fang; Zhao, Xue Qiang; Chen, Rong Fu; Dong, Xiao Ying

2008-01-01

3

Frequency and stress ratio effects in high cycle fatigue of Ti6Al4V  

Microsoft Academic Search

Experiments were conducted to determine the effects of test frequency on the high cycle fatigue (HCF) behavior of Ti-6Al-4V. Specimens were tested at a range of frequencies for three different stress ratios (0.1, 0.5, and 0.8). Results indicate a frequency dependence that varies with stress ratio (R). At low R, the fatigue strength increases with increasing frequency. As R is

R. J Morrissey; D. L McDowell; T Nicholas

1999-01-01

4

Influence of stress state on high cycle fatigue of notched Ti6Al4V specimens  

Microsoft Academic Search

The high cycle fatigue (HCF) notch size effect is investigated for Ti-6Al-4V flat dogbone specimens with two notch sizes, each having an elastic stress concentration factor of Kt=2.72. Points were generated on a constant life Haigh diagram using a step-loading technique. The notch size effect is compared with previous results obtained from circumferentially notched cylindrical specimens in terms of the

David B. Lanning; George K. Haritos; Theodore Nicholas

1999-01-01

5

Constitutive equations for high temperature flow stress prediction of Al14Cu7Ce alloy  

Microsoft Academic Search

In order to find material parameters of established ZenerHollomon constitutive equations and predict high-temperature flow stress of Al14Cu7Ce alloy, isothermal hot compression tests were conducted using a Gleeble 3500 thermomechanical simulator at constant stain rates of 0.001, 0.01, 0.1 and 1s?1 and at temperatures ranging from 300 to 550C at intervals of 50C. The effects of strain rate and temperature

Wei Li; Hai Li; Zhixiu Wang; Ziqiao Zheng

2011-01-01

6

AlGaN/GaN High Electron Mobility Transistor Degradation Under On- and Off-State Stress.  

National Technical Information Service (NTIS)

AlGaN/GaN High Electron Mobility Transistors (HEMTs) with various gate lengths have been stepstressed under both on- and off-state conditions. On- state, high power stress tests were performed on 0.17 lm gate length HEMTs and a single 5 lm spaced TLM patt...

B. P. Gila C. F. Lo C. Y. Chang D. J. Cheney E. A. Douglas

2011-01-01

7

High temperature stress relief cavitation of an Al-bearing ?-brass  

Microsoft Academic Search

High temperature stress relief intergranular cavitation and subsequent room temperature embrittlement of an aluminium-bearinga-brass has been studied metallographically. The behaviour of a cast susceptible to cavitation has been compared to one which does not exhibit intergranular cavitation during stress relief, and which is subsequently more ductile at room temperature. A number of micro-analytical techniques (SIMS and EDX) failed to reveal

L. Kjellsson; L. E. Svensson; R. Sundberg; G. L. Dunlop

1978-01-01

8

Influence of residual stresses on high cycle fatigue strength of Ti6Al4V subjected to foreign object damage  

Microsoft Academic Search

The role of residual stresses in the high cycle fatigue (HCF) strength of Ti6Al4V subjected to foreign object damage (FOD) was evaluated on simulated airfoil and rectangular geometries. Both real and simulated impacts were conducted using spherical projectiles launched at 300 m\\/s and quasi-static chisel indentation, respectively. The spheres used were 1 mm diameter glass beads while the quasi-static indentor

Steven R. Thompson; John J. Ruschau; Theodore Nicholas

2001-01-01

9

Subcritical crack growth of Ti-6Al-4V at room temperature under high stress-ratio loading  

SciTech Connect

Ti-6Al-4V is a two phase {alpha}-{beta} titanium alloy commonly used for turbine fan and compressor components. The crack growth behavior of Ti-6Al-4V and the role played by various material, mechanical, and environmental factors has been thoroughly investigated. This alloy is also susceptible to crack growth under sustained loading in air (SLC), and both hydrogen assisted cracking and low temperature creep mechanisms have been used to explain this susceptibility. Very little information is available on high R-ratio fatigue crack growth of Ti-6Al-4V and the role played by SLC on the fatigue process. In order to gain better understanding of the cracking behavior of this alloy under ripple loading conditions, room temperature, high stress-ratio (R {ge} 0.9) fatigue and SLC experiments have been conducted on a Ti-6Al-4V plate forging material in the duplex-annealed (DA) condition. The results of this investigation,namely, fatigue crack growth rates (CGR) as a function of stress intensity; SLC data; and scanning electron microscopy of the fatigue and SLC fracture surfaces are reported below.

Thomas, J.P. [Univ. of Notre Dame, IN (United States). Dept. of Aerospace and Mechanical Engineering

1998-11-13

10

Stress competition and vortex magnetic anisotropy in FeCoAlO high-frequency soft magnetic films with gradient Al-O contents  

NASA Astrophysics Data System (ADS)

A vortex magnetic anisotropy (VMA) was formed via the competition of residual stresses between radial and tangential directions in the FeCoAlO soft magnetic films (SMFs), prepared by a composition gradient sputtering (CGS) method. The VMA of the magnetic films gives rise to a rotating excitation direction of the ferromagnetic resonance. As a results, the as-deposited FeCoAlO films exhibit good high-frequency ferromagnetic properties with high permeability about 100, cut-off frequency over 2 GHz, and Qm factor over 50 along its individual excitation direction. These SMFs with the VMA are promising in the integration with the circular spiral inductors due to the geometrical match between the excitation direction of the SMFs and the circular inductor lines.

Li, Shandong; Du, Honglei; Xue, Qian; Xie, Shiming; Liu, Ming; Shao, Weiquan; Xu, Jie; Nan, Tianxiang; Sun, Nian X.; Duh, Jenq-Gong

2013-05-01

11

High frequency characteristics of FeCoAlO thin films combined the effects of stress and magnetic field  

SciTech Connect

The soft magnetic FeCoAlO thin films with different response at high frequency were prepared by using RF magnetron sputtering. Two different configurations of the sputtering targets were used: the Al{sub 2}O{sub 3} chips were placed on Fe{sub 70}Co{sub 30} disk either uniformly dispersed on the sputtering area (Target-A) or dispersed on the half side of the sputtering area (Target-B). It was found that, although, the films deposited from both of Target A and B possessed good soft magnetic properties and in-plane uniaxial magnetic anisotropy, they showed different behaviors at high frequency. The films deposited by using Target-A have mean permeability of 500 and a cut-off frequency (f{sub r}) of around 780 MHz, while the films deposited by using Target-B have mean permeability of 200 and a f{sub r} of 3.4 GHz. The higher f{sub r} of the later corresponds to the higher uniaxial anisotropic field in the films deposited by using the Target-B, which due to an extra anisotropy induced by the stress resulted from gradient of the Al-O composition. By adjusting the configuration of Target-B, the permeability and f{sub r} can be tuned to satisfy the different requirements for certain industrial applications.

Zheng Fu; Wang Xuan; Li Xu; Bai Jianmin; Wei Fulin [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China); Wei Dan [Lab of Advanced Materials, Department of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Liu Xiaoxi [Department of Information Engineering, Shinshu University, Nagano 380-8553 (Japan); Xie Wenhui [Department of Physics, East China Normal University, Shanghai 200062 (China)

2011-04-01

12

Role of Hydrogen in the Stress Corrosion Failure of High Strength Al-Zn-Mg Alloys.  

National Technical Information Service (NTIS)

Previous studies have been shown that high strength A1-Zn-Mg based alloys suffer environment assisted cracking. In the present work, room temperature constant strain rate (.0001/s - .000001/s) and constant load tensile tests on A1 6% Zn 3% Mg and copper a...

M. L. Yuen H. M. Flower

1984-01-01

13

Microstructure and Residual Stress of Alumina Scale Formed on Ti2AlC at High Temperature in Air  

SciTech Connect

Ti2AlC ternary carbide is being explored for various high temperature applications owing to its high strength at high temperatures, excellent thermal-shock resistance, and high electrical conductivity. In this study, isothermal oxidation at 1000 XC, 1200 XC, and 1400 XC for up to 25 hours, as well as 1,000 1-hour cyclic oxidation at 1200 XC were performed in air to examine the oxidation behavior of Ti2AlC. Characteristics of the oxide scale developed in air, including mass change, residual stress in the -Al2O3 scale, phase constituents and microstructure, were examined as functions of time and temperature by thermogravimetry, photostimulated luminescence, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy via focused ion beam in-situ lift-out. A continuous and adherent -Al2O3 scale underneath a discontinuous-transient rutile-TiO2 scale was identified in the oxide scale developed at 1000 XC and 1200 XC. At 1400 XC, Al2TiO5 was identified as the discontinuous-transient scale above the continuous and adherent -Al2O3 scale. The -Al2O3 scale thickened to more than 15 m after 25 hours of isothermal oxidation at 1400 XC, and after 1,000 1-hour cyclic oxidation at 1200 XC, yet remained adherent and protective. The compressive residual stress determined by photoluminescence for the -Al2O3 scale remained under 0.65 GPa for the specimens oxidized up to 1400 XC for 25 hours. The small magnitude of the compressive residual stress may impart the high spallation-resistance of the protective -Al2O3 scale developed on Ti2AlC.

Byeon, J [University of Central Florida; Liu, j [University of Central Florida; Hopkins, m [University of Central Florida; Fischer, W [University High School Orlando, FL; Park, K [University of Central Florida; Brady, Michael P [ORNL; Radovic, Miladin [ORNL; Sohn, Yong Ho [University of Central Florida

2007-01-01

14

Defect and stress relaxation in HVPE-GaN films using high temperature reactively sputtered AlN buffer  

Microsoft Academic Search

The influence of high temperature buffer layers on the structural characteristics of GaN grown by hydride vapour phase epitaxy on sapphire was investigated. Strain relaxation as well as mismatch-induced defect reduction in thick GaN layers grown on AlN buffer was microscopically identified using cathodoluminescence and micro-Raman spectroscopy in cross-section of the films. The results were correlated with photoluminescence and Hall-effect

T. Paskova; E. Valcheva; J. Birch; S. Tungasmita; P.-O. . Persson; P. P. Paskov; S. Evtimova; M. Abrashev; B. Monemar

2001-01-01

15

Localization of off-stress-induced damage in AlGaN/GaN high electron mobility transistors by means of low frequency 1/f noise measurements  

NASA Astrophysics Data System (ADS)

The location of the time dependent degradation in OFF-state stressed AlGaN/GaN high electron mobility transistors is studied using low frequency 1/f noise measurements, with additional electroluminescence analysis. The gate bias dependence of the 1/f noise is shown to be a powerful tool to illustrate that in addition to the gate edge breakdown, progressive time-dependent trap generation occurs underneath the gate area, possibly extending in the gate-drain access region due to the electric field peak associated with the gate field plate.

Silvestri, Marco; Uren, Michael J.; Killat, Nicole; Marcon, Denis; Kuball, Martin

2013-07-01

16

Stress-corrosion resistance of high-strength Al-Zn-Mg-Cu alloys with and without silver additions  

Microsoft Academic Search

The separate and combined effects of adding silver, substituting other elements for chromium, increasing zinc, or varying\\u000a the copper content on the tensile properties and resistance to stress-corrosion cracking of 7075-type alloys were investigated.\\u000a Adding silver produced no increase in strength and marginal increases in the resistance to stress-corrosion cracking. Substituting\\u000a either zirconium or manganese for chromium increased strength and

H. Y. Hunsicker; J. T. Staley; R. H. Brown

1972-01-01

17

Improved Off-State Stress Critical Voltage on AlGaN/GaN High Electron Mobility Transistors Utilizing Pt/Ti/Au Based Gate Metallization  

SciTech Connect

The critical voltage for degradation of AlGaN/GaN high electron mobility transistors (HEMTs) employed with the Pt/Ti/Au gate metallization instead of the commonly used Ni/Au was significantly increased during the off-state stress. The typical critical voltage for HEMTs with Ni/Au gate metallization was around -60V. By sharp contrast, no critical voltage was observed for the HEMTs with Pt/Ti/Au gate metallization, even up to -100V, which was the instrumental limitation in this experiment. Both Schottky forward and reverse gate characteristics of the Ni/Au degraded once the gate voltage passed the critical voltage of around -60V. There was no degradation exhibited for the HEMTs with Pt-gated HEMTs.

Lo, C. F. [University of Florida; Liu, L. [University of Florida, Gainesville; Kang, Tsung Sheng [University of Florida, Gainesville; Davies, Ryan [University of Florida; Gila, Brent P. [University of Florida, Gainesville; Pearton, S. J. [University of Florida; Kravchenko, Ivan I [ORNL; Laboutin, O. [Kopin Corporation, Taunton, MA; Cao, Yu [Kopin Corporation, Taunton, MA; Johnson, Wayne J. [Kopin Corporation, Taunton, MA; Ren, F. [University of Florida

2011-01-01

18

Improvement of Off-State Stress Critical Voltage by Using Pt-gated AlGaN/GaN High Electron Mobility Transistors  

SciTech Connect

By replacing the commonly used Ni/Au gate metallization with Pt/Ti/Au, the critical voltage for degradation of AlGaN/GaN High Electron Mobility Transistors (HEMTs) during off-state biasing stress was significantly increased. The typical critical voltage for the HEMTs with Ni/Au gate metallization was around -55V. By sharp contrast, no critical voltage was observed for the HEMTs with Pt/Ti/Au gate metallization, even up -100V, which was the instrumental limitation in this experiment. Both Schottky forward and reverse gate characteristics of the Ni/Au degraded once the gate voltage passed the critical voltage of -55V. There was no degradation exhibited for the HEMTs with Pt/Ti/Au gate metallization.

Lo, C. F. [University of Florida; Liu, L. [University of Florida, Gainesville; Kang, Tsung Sheng [University of Florida, Gainesville; Gila, Brent P. [University of Florida, Gainesville; Pearton, S. J. [University of Florida; Kravchenko, Ivan I [ORNL; Laboutin, O. [Kopin Corporation, Taunton, MA; Cao, Yu [Kopin Corporation, Taunton, MA; Johnson, Wayne J. [Kopin Corporation, Taunton, MA; Ren, F. [University of Florida

2011-01-01

19

Stress granules as crucibles of ALS pathogenesis  

PubMed Central

Amyotrophic lateral sclerosis (ALS) is a fatal human neurodegenerative disease affecting primarily motor neurons. Two RNA-binding proteins, TDP-43 and FUS, aggregate in the degenerating motor neurons of ALS patients, and mutations in the genes encoding these proteins cause some forms of ALS. TDP-43 and FUS and several related RNA-binding proteins harbor aggregation-promoting prion-like domains that allow them to rapidly self-associate. This property is critical for the formation and dynamics of cellular ribonucleoprotein granules, the crucibles of RNA metabolism and homeostasis. Recent work connecting TDP-43 and FUS to stress granules has suggested how this cellular pathway, which involves protein aggregation as part of its normal function, might be coopted during disease pathogenesis.

King, Oliver D.

2013-01-01

20

Stress granules as crucibles of ALS pathogenesis.  

PubMed

Amyotrophic lateral sclerosis (ALS) is a fatal human neurodegenerative disease affecting primarily motor neurons. Two RNA-binding proteins, TDP-43 and FUS, aggregate in the degenerating motor neurons of ALS patients, and mutations in the genes encoding these proteins cause some forms of ALS. TDP-43 and FUS and several related RNA-binding proteins harbor aggregation-promoting prion-like domains that allow them to rapidly self-associate. This property is critical for the formation and dynamics of cellular ribonucleoprotein granules, the crucibles of RNA metabolism and homeostasis. Recent work connecting TDP-43 and FUS to stress granules has suggested how this cellular pathway, which involves protein aggregation as part of its normal function, might be coopted during disease pathogenesis. PMID:23629963

Li, Yun R; King, Oliver D; Shorter, James; Gitler, Aaron D

2013-04-29

21

Influence of GaN Stress on Threshold Voltage Shift in AlGaN/GaN High-Electron-Mobility Transistors on Si under Off-State Electrical Bias  

NASA Astrophysics Data System (ADS)

The change in threshold voltage (Vth) in AlGaN/GaN high-electron-mobility transistors (HEMTs) on Si occurs during off-state bias stress. Raman spectroscopy shows that the GaN strain/stress changes with the increase in buffer and i-GaN thicknesses. Our results revealed that there is a strong correlation between the Vth shift and GaN strain/stress. The Vth shifts positively and negatively, respectively, for biaxial tensile and compressive strains. We observed minimal device degradation with the negligible Vth shift before and after off-state bias stress for the strain relieved sample. The results illustrate the importance of GaN strain/stress for the degradation and reliability of AlGaN/GaN HEMTs.

Wilson, Amalraj Frank; Wakejima, Akio; Egawa, Takashi

2013-08-01

22

Yield stress anomaly in B2 FeAl  

SciTech Connect

The studies on yield stress anomaly of B2 FeAl single crystals are reviewed in this paper. A positive temperature dependence of yield stress, so-called yield stress anomaly, is observed in B2 FeAl in which excess vacancies are fully annealed out. Associated with the anomaly, characteristic asymmetry is found between tension and compression. While the strain-rate sensitivity is almost zero in the temperature range of the yield stress anomaly, the stress relaxation becomes significant with increasing temperature, indicating that a recovery process is thermally activated. It is ascertained by the two-surface trace analysis that slip transition from <111> direction at intermediate temperature to <100> at high temperature occurs around the peak temperature. Even at the peak temperature, in addition, operative slip vector for yielding is confirmed to be predominantly <111> by TEM. Also, it is observed that <111>-type superdislocations are frequently climb-dissociated in the temperature range of the anomaly. APB formation on {l_brace}111{r_brace} plane is energetically favorable, which is in agreement with the Flinn`s calculation for the B2 superlattice that APB energy on {l_brace}111{r_brace} plane is lower than that on {l_brace}110{r_brace} plane. Such an anisotropy of APB energy would offer specific driving force for the climb dissociation on <111> superdislocations. On the basis of the observed results, the anomalous strengthening behavior of B2 FeAl single crystals is discussed.

Yoshimi, K.; Hanada, S. [Tohoku Univ., Sendai (Japan). Inst. for Materials Research; Yoo, M.H. [Oak Ridge National Lab., TN (United States). Metals and Ceramics Div.

1996-12-31

23

Stress Corrosion Cracking of Al-Mg and Mg-Al Alloys  

SciTech Connect

Aluminum and magnesium based alloys are being used for reducing the weight of automobiles. For structural applications they must have adequate stress corrosion resistance and yet, under some circumstances, stress corrosion cracking can occur in both alloy systems. Precipitation of the Mg rich Beta-phase (Al3Mg2) at grain boundaries of Al-Mg alloys and the Beta-phase (Mg17Al12) at grain boundaries of the Mg-Al alloys are critical factors in their stress corrosion performance. In Mg-Al, the Beta-phase is cathodic to the matrix while in the Al-Mg case, the Beta-phase is anodic to the matrix. These phases produce localized galvanic induced-corrosion that leads to intergranular stress corrosion cracking and cracking growth rates of 5 and 103 times faster than the solution treated condition, for Al-Mg and Mg-Al, respectively.

Jones, Russell H.; Vetrano, John S.; Windisch, Charles F.

2004-12-01

24

Short-Duration and Stress-Rupture Strength of Beta-Alloy of Ti-Mo-Cr-Fe-Al System at High Temperatures.  

National Technical Information Service (NTIS)

A beta-alloy of Ti contg. Mo 7, Cr 5.5, Fe 3, and Al 3 percent when quenched from 800 degrees and aged at 550 or 525 degrees for 15 hrs. at 500 degrees for 20 hrs., and at 450 degrees for 50 hrs. exhibits high mech. properties at elevated temps. When expo...

N. V. Ageev S. G. Glazunov L. A. Petrova G. N. Tarasenko L. P. Grankova

1969-01-01

25

Effects of Thermal Stress on the Performance of Benzocyclobutene-Passivated In0.52Al0.48As/In0.53Ga0.47As High Electron Mobility Transistors  

NASA Astrophysics Data System (ADS)

The effects of thermal stress on benzocyclobutene (BCB)-passivated In0.52Al0.48As/In0.53Ga0.47As high electron mobility transistors (HEMTs) were investigated and compared with those on silicon nitride and polyimide-passivated devices by DC, RF and microwave power characterization for the first time. In order to investigate the thermal stress effects on the devices passivated by different layers, DC and small-signal S-parameters were measured and characterized. Moreover, the variation of parameters, which are related to the RF performance of the devices, was analyzed based on small-signal parameters extracted during thermal stress. Compared to the polyimide-passivated devices, the BCB-passivated HEMTs exhibited more stable DC-gm and access resistance (Rd+Rs) as functions of thermal stress time. The BCB-passivated HEMTs also showed a device performance comparable to that of the silicon nitride-passivated HEMTs that were stabilized by stabilization bake. In addition, the BCB-passivated HEMTs demonstrated better microwave power characteristics before and after 100 h thermal stress, indicating that BCB is an attractive passivation layer for In0.52Al0.48As/In0.53Ga0.47As HEMTs.

Yoon, Myounghoon; Kim, Taeho; Kim, Daehee; Yang, Kyounghoon

2004-04-01

26

Thermal Stress Calculation and Fabrication of 6063 Al\\/60SiC35Al5Si Graded Materials by Spark Plasma Sintering  

Microsoft Academic Search

The high intensity of thermal stress was generated during fabrication of 6063 aluminum\\/60SiC-35Al-5Si double-layer material. In order to decrease the thermal stress, graded materials of Al\\/60SiC-35Al-5Si was fabricated by spark plasma sintering. The CTE in the graded layer was controlled by SiC fraction and particle sizes. The calculation results indicate that the net stress of more than 800 MPa was

Zhang Dongming; Zhang Lianmeng; Gu Xiaofeng; Chen Fei

2008-01-01

27

Effect of Stress Level on the High Temperature Deformation and Fracture Mechanisms of Ti-45Al-2Nb-2Mn-0.8 vol. pct TiB2: An In Situ Experimental Study  

NASA Astrophysics Data System (ADS)

The effect of the applied stress on the deformation and crack nucleation and propagation mechanisms of a ?-TiAl intermetallic alloy (Ti-45Al-2Nb-2Mn (at. pct)-0.8 vol. pct TiB2) was examined by means of in situ tensile (constant strain rate) and tensile-creep (constant load) experiments performed at 973 K (700 C) using a scanning electron microscope. Colony boundary cracking developed during the secondary stage in creep tests at 300 and 400 MPa and during the tertiary stage of the creep tests performed at higher stresses. Colony boundary cracking was also observed in the constant strain rate tensile test. Interlamellar ledges were only found during the tensile-creep tests at high stresses ( ? > 400 MPa) and during the constant strain rate tensile test. Quantitative measurements of the nature of the crack propagation path along secondary cracks and along the primary crack indicated that colony boundaries were preferential sites for crack propagation under all the conditions investigated. The frequency of interlamellar cracking increased with stress, but this fracture mechanism was always of secondary importance. Translamellar cracking was only observed along the primary crack.

Muoz-Moreno, Roco; Prez-Prado, M. Teresa; Llorca, Javier; Ruiz-Navas, Elisa Mara; Boehlert, Carl J.

2013-04-01

28

Degradation analysis and characterization of multifilamentary conduction patterns in high-field stressed atomic-layer-deposited TiO2/Al2O3 nanolaminates on GaAs  

NASA Astrophysics Data System (ADS)

In this paper, the effects of applying a high-field electrical stress on TiO2/Al2O3 nanolaminates grown by atomic layer deposition onto a p-type GaAs substrate are investigated. First, it is shown that the current-time (I-t) characteristic of the devices during a constant voltage stress follows the extended Curie-von Schweidler law for dielectric degradation. The application of voltage sweeps from negative to positive bias and back also reveals an hysteretic behavior of the current-voltage (I-V) characteristic typical of the resistive switching mechanism ocurring in these and others high permittivity oxide films. Second, we show that after the detection of the breakdown event the capacitors exhibit a random spot pattern on the top metal electrode (Al) associated with the generation of multifilamentary conduction paths running across the insulating film. The number of generated spots depends on the magnitude of the electrical stress and for a sufficiently large density, it is possible to demonstrate that they are spatially uncorrelated. The analysis is carried out using spatial statistics techniques such as the intensity plot, the interspot distance histogram, and the pair correlation function.

Miranda, E.; Su, J.; Das, T.; Mahata, C.; Maiti, C. K.

2012-09-01

29

Stress Development and Relaxation in Al2O3 during Early StageOxidation of beta-NiAl  

SciTech Connect

Using a glancing synchrotron X-ray beam (Advanced Photon Source, Beamline 12BM, Argonne National Laboratory), Debye-Scherrer diffraction patterns from thermally grown oxides on NiAl samples were recorded during oxidation at 1000 or 1100 C in air. The diffraction patterns were analyzed to determine strain and phase changes in the oxide scale as it developed and evolved. Strain was obtained from measurements of the elliptical distortion of the Debye-Scherrer rings, where data from several rings of a single phase were used. Results were obtained from {alpha}-Al{sub 2}O{sub 3} as well as from the transition alumina, in this case {theta}-Al{sub 2}O{sub 3}, which formed during the early stage. Compressive stress was found in the first-formed transition alumina, but the initial stress in {alpha}-Al{sub 2}O{sub 3} was tensile, with a magnitude high enough to cause Al{sub 2}O{sub 3} fracture. New {alpha}-Al{sub 2}O{sub 3} patches nucleated at the scale/alloy interface and spread laterally and upward. This transformation not only puts the alpha alumina in tension, but can also cause the transition alumina to be in tension. After a complete {alpha}-Al{sub 2}O{sub 3} layer formed at the interface, the strain level in {alpha}-Al{sub 2}O{sub 3} became compressive, reaching a steady state level around -75 MPa at 1100 C. To study a specimen's response to stress perturbation, samples with different thickness, after several hours of oxidation at 1100 C, were quickly cooled to 950 C to impose a compressive thermal stress in the scale. The rate of stress relaxation was the same for 1 and 3.5 mm thick samples, having a strain rate of {approx} 1 x 10{sup -8}/s. This behavior indicates that oxide creep is the major stress relaxation mechanism.

Hou, P.Y.; Paulikas, A.P.; Veal, B.W.

2005-04-20

30

Experimental study of through-depth residual stress in explosive welded AlCuAl multilayer  

Microsoft Academic Search

Explosive welded multi-layers sheet metals are widely used in recent years. Evaluation of residual stresses of this new merging material is necessary for better understanding of its mechanical behavior. In this paper, incremental hole-drilling (IHD) is used to measure through-depth non-uniform residual stress gradient in explosive welded AlCuAl multilayers. At first, the multilayer sheets at two different initial thicknesses were

M. Sedighi; M. Honarpisheh

31

High temperature creep behaviour of Al-rich Ti-Al alloys  

NASA Astrophysics Data System (ADS)

Compared to Ti-rich ?-TiAl-based alloys Al-rich Ti-Al alloys offer an additional reduction of in density and a better oxidation resistance which are both due to the increased Al content. Polycrystalline material was manufactured by centrifugal casting. Microstructural characterization was carried out employing light-optical, scanning and transmission electron microscopy and XRD analyses. The high temperature creep of two binary alloys, namely Al60Ti40 and Al62Ti38 was comparatively assessed with compression tests at constant true stress in a temperature range between 1173 and 1323 K in air. The alloys were tested in the cast condition (containing various amounts of the metastable phases Al5Ti3 and h-Al2Ti) and after annealing at 1223 K for 200 h which produced (thermodynamically stable) lamellar ?-TiAl + r-Al2Ti microstructures. In general, already the as-cast alloys exhibit a reasonable creep resistance at 1173 K. Compared with Al60Ti40, both, the as-cast and the annealed Al62Ti38 alloy exhibit better creep resistance up to 1323 K which can be rationalized by the reduced lamella spacing. The assessment of creep tests conducted at identical stress levels and varying temperatures yielded apparent activation energies for creep of Q = 430 kJ/mol for the annealed Al60Ti40 alloy and of Q = 383 kJ/mol for the annealed Al62Ti38 material. The latter coincides well with that of Al diffusion in ?-TiAl, whereas the former can be rationalized by the instability of the microstructure containing metastable phases.

Sturm, D.; Heilmaier, M.; Saage, H.; Aguilar, J.; Schmitz, G. J.; Drevermann, A.; Palm, M.; Stein, F.; Engberding, N.; Kelm, K.; Irsen, S.

2010-07-01

32

High cycle fatigue behaviour of microsphere Al 2O 3Al particulate metal matrix composites  

Microsoft Academic Search

The high-cycle stress-life (SN) curve and fatigue crack growth threshold (?Kth) behaviour of COMRAL-85TM, a 6061 aluminiummagnesiumsilicon alloy reinforced with 20vol.% Al2O3-based polycrystalline ceramic microspheres, and manufactured by a liquid metallurgy route, have been investigated for a stress ratio of R=?1 (fully reversed loading). Fatigue testing was conducted on both smooth round bar (SN) specimens and notched round bar (fatigue

B. G. Park; A. G. Crosky; A. K. Hellier

2008-01-01

33

Multiscale Modeling of Metal-Metal Contact Dynamics under High Electromagnetic Stress: Timescales and Mechanisms for Joule Melting of Al-Cu Asperities  

Microsoft Academic Search

An analysis and initial results from a multiscale continuum-atomistic simulation of the Joule heating and melting of Cu-Al asperity contacts is presented. An analytic expression is given for the time needed to reach the Al melting point for an asperity as a function of the voltage drop and the asperity contact area. The coupled continuum-atomistic simulations capture the initial stages

Douglas Irving; Clifford Padgett; Yin Guo; John Mintmire; Donald Brenner

2008-01-01

34

Multiscale Modeling of MetalMetal Contact Dynamics Under High Electromagnetic Stress: Timescales and Mechanisms for Joule Melting of AlCu Asperities  

Microsoft Academic Search

An analysis and initial results from a multiscale continuum-atomistic simulation of the Joule heating and melting of Cu-Al asperity contacts are presented. An analytic expression is given for the time needed to reach the Al melting point for an asperity as a function of the voltage drop and the asperity contact area. The coupled continuum-atomistic simulations capture the initial stages

Douglas L. Irving; Clifford W. Padgett; Yin Guo; John W. Mintmire; Donald W. Brenner

2009-01-01

35

Rye oxidative stress under long term Al exposure.  

PubMed

Aluminium (Al) toxicity decreases plant growth. Secale cereale L. is among the most Al-tolerant crop species. In order to study the response to Al-long term exposure, two rye genotypes with different Al sensitivity ('D. Zlote' and 'Riodeva') were exposed to 1.11 and 1.85mM Al and the antioxidant responses were followed for 2 and 3 weeks in roots and leaves. Al toxicity signals, such as a severe decrease in root growth, occurred sooner in 'Riodeva.' The antioxidant response was dependent on the genotype, the organ, Al concentration and the exposure period. Al-exposed roots of 'D. Zlote' showed earlier enhancements of APX, SOD and G-POX activities than those of 'Riodeva.' 'D. Zlote' roots showed stimulation of the AsA-GSH cycle after the second week (when root growth inhibition was less severe), while later (when severe root growth inhibition was observed), oxidation of AsA and GSH pools was observed. In leaves of both genotypes, CAT, SOD and G-POX activities increased with Al exposure. In these leaves, the effect of AsA-GSH was time dependent, with maximum oxidation at the second week, followed by recovery. We confirmed that the oxidation state of AsA and GSH pools is involved in the detoxification of Al-induced oxidative stress. Moreover, our data demonstrate that the production of ROS does not correlate with the Al-induced root growth decrease. Finally, the differences observed over time indicate that long term exposure may provide additional information on rye sensitivity to Al, and contribute to a better understanding of this species' mechanisms of Al tolerance. PMID:23537706

Silva, Snia; Pinto, Glria; Correia, Barbara; Pinto-Carnide, Olinda; Santos, Conceio

2013-03-26

36

Relationship between electrical conductivity and stress corrosion cracking susceptibility of Al 7075 and Al 7475 alloys  

SciTech Connect

A relationship between electrical conductivity and stress corrosion cracking (SCC) resistance of the 7,000-series Al-Zn-Mg alloys has been established, although only from the near-peak strength T6 temper to the overaged T73 tempered condition. The present work investigated whether this relationship exists for all periods of aging and for Al alloys with different compositions and grain structures. The materials studied were commercial 2-mm thick Al 7075 (Al-5.76% Zn-2.46% Mg-1.70% Cu-0.20% Cr-0.12% Fe-0.09% Si-0.06% Mn-0.04% Ti) and Al 7475 (Al-5.80% Zn-2.24% Mg-1.53% Cu-0.19% Cr-0.08% Fe-0.02% Si-0.01% Mn-0.02% Ti) alloy plates.

Tsai, T.C.; Chuang, T.H. [National Taiwan Univ., Taipei (Taiwan, Province of China). Inst. of Materials Science and Engineering

1996-06-01

37

High altitude and oxidative stress  

Microsoft Academic Search

Exposure to high altitude, which is associated with decreased oxygen pressure, could result in oxidative\\/reductive stress, enhanced generation of reactive oxygen and nitrogen species (RONS), and related oxidative damage to lipids, proteins, and DNA. The severity of oxidative challenge is related to the degree of altitude. A wide range of RONS generating systems are activated during exposure to high altitude,

Agoston Dosek; Hideko Ohno; Zoltan Acs; Albert W. Taylor; Zsolt Radak

2007-01-01

38

Mechanically induced residual stresses in Al/SiC composites  

SciTech Connect

Mechanically induced residual stresses are an inherent feature of permanently deformed metal-matrix composites. The presence of hard reinforcement particles promotes non-homogeneous flow in the material, resulting in residual stresses when the applied loads are removed. Several distinct approaches have been used in attempts to quantify thermally and mechanically induced residual stresses in metal-matrix composites. One approach has been to assume that the composite consist of a periodic array of whiskers embedded throughout the matrix. With this assumption, a boundary value problem can be formulated on a single unit cell and solved by use of the finite element method. A second approach uses modified techniques originally developed by Eshelby to estimate residual stresses for composites reinforced by ellipsoidal inclusions. The main objective of the present paper is to compare predicted average residual elastic strains with those measured by neutron diffraction for Al/SiC composites subjected to a rapid quench followed by different loading histories.

Povirk, G.L.; Nutt, S.R.; Needlemen, A. (Brown Univ., Providence, RI (United States). Div. of Engineering); Stout, M.G.; Bourke, M.; Goldstone, J.A.; Lawson, A.C.; Lovato, M. (Los Alamos National Lab., NM (United States)); MacEwen, S.R. (Alcan International Ltd., Kingston Research and Development Center, Kingston, Ontario K7L 5L9 (CA))

1991-08-01

39

An examination of surface stress effects and deformation mechanisms in Al Cu nanowires  

NASA Astrophysics Data System (ADS)

A molecular dynamics simulation was utilized to study AlCu and AlCu3 nanowires. The simulation results showed that surface stress can force AlCu nanowires into high-elastic states and induce slip and clusters in AlCu3 nanowires. Two distinct types of deformation mechanisms were observed. One is that the AlCu nanowires underwent the changes of elastic deformation, amorphous transition, necking and breaking. The other is because the {1 0 1} twinning and crystal region coexist, the calculated tensile curves of AlCu3 nanowires also show many yield points, and unloading can lead to elastic recovery of 4-9%. It implies that AlCu3 nanowires are usable even after external shock waves. This work indicates that changing atomic proportions in alloy nanowires can be utilized to control the deformation mechanism upon loading.

Zheng, B.; Wang, Y. N.; Qi, M.; Chen, C. L.

2008-06-01

40

Stress Control of AlN Thin Film Sputter-Deposited Using ECR Plasma  

NASA Astrophysics Data System (ADS)

AlN thin film is widely utilized for piezoelectric devices e.g. acoustic filters and sensors, since AlN has well-balanced properties such as high acoustic velocity, low loss at high frequency, moderate electro-mechanical coupling coefficient and moderate temperature coefficient, and can be deposited at relatively low temperature. The sputtering technology using ECR plasma can deposit a highly-oriented AlN thin film by the assist of low energy plasma flow. However, its residual stress is normally highly-compressive, and thus free-standing AlN MEMS are easily broken during the fabrication process. In this research, to solve this problem, we investigated the reduction of AlN compressive stress, and the full width at half maximum of the XRD rocking curve (FWHMXRD:RC) by changing various parameters such as substrate bias voltage, the gas flow ratio of Ar:N2 and substrate temperature. It was experimentally confirmed that the positive substrate bias voltage and the substrate temperature can considerably reduce AlN compressive stress to nearly zero without remarkable deterioration of FWHMXRD:RC.

Hino, Ryunosuke; Matsumura, Takeshi; Esashi, Masayoshi; Tanaka, Shuji

41

Residual stress in friction stir-welded Al sheets  

Microsoft Academic Search

Friction stir welding (FSW) is a relatively new joining technique particularly for aluminum alloys that are difficult to fusion weld. Although FSW is as a solid-state joining process which produces low-distortion welds of high quality, significant levels of residual stresses can be present in the weld after fabrication. These residual stresses can influence the service performance of the welded components

P. Staron; M. Koak; S. Williams; A. Wescott

2004-01-01

42

Thermal Relaxation of Residual Stresses in Shot Peened Surface Layer of SiCw\\/Al Composite  

Microsoft Academic Search

The residual stress relaxation of the shot peened layer on the SiCw\\/Al composite during isothermal annealing was investigated.\\u000a The results showed that the residual stresses relaxed in the whole deformation layer especially when the annealing temperature\\u000a was higher than 200C. The relaxation process during isothermal annealing could be described precisely using Zener-Wert-Avrami\\u000a function. Because of high intensity dislocation around reinforcements

Junjie Huang; Zhou Wang; Kai Bian; Chuanhai Jiang

2011-01-01

43

Stress corrosion cracking of an Al-Li alloy  

Microsoft Academic Search

Stress corrosion cracking (SCC) has been studied in an Al-Li alloy with variables of orientation of specimen, heat treatment,\\u000a and applied potentials. The distribution of the electrochemical potential resulting from precipitate clusters was measured,\\u000a and the hydrogen content on the specimen surface was detected. The results showed that the SCC susceptibility under the peakaged\\u000a (PA) condition was higher than that

Z. F. Wang; Z. Y. Zhu; Y. Zhang; W. Ke

1992-01-01

44

Thermal Relaxation of Residual Stresses in Shot Peened Surface Layer of SiCw/Al Composite  

NASA Astrophysics Data System (ADS)

The residual stress relaxation of the shot peened layer on the SiCw/Al composite during isothermal annealing was investigated. The results showed that the residual stresses relaxed in the whole deformation layer especially when the annealing temperature was higher than 200 C. The relaxation process during isothermal annealing could be described precisely using Zener-Wert-Avrami function. Because of high intensity dislocation around reinforcements producing a large amount of stored energy, the residual stress relaxation activation enthalpy of shot peened SiCw/Al was smaller than self-diffusion activation enthalpy of pure aluminum. According to the analysis of full-width at half-maximum (FWHM) of the shot peened composite in different annealing temperatures, it can be concluded the recovery and recrystallization behavior became intensely when anneal temperature was larger than 200 C. The small relaxation of residual stress in low annealing temperature was mainly due to partly recovery and recrystallization in a very low level.

Huang, Junjie; Wang, Zhou; Bian, Kai; Jiang, Chuanhai

2012-06-01

45

High temperature deformation of Ti(4648)Al2W intermetallic compounds  

Microsoft Academic Search

The high temperature deformation behavior of Ti46Al2W and Ti48Al2W intermetallic compounds have been investigated in isothermal compressive tests, performed at temperatures between 1000C and 1200C for strain rates between 10?3 and 10?1 s?1. The stressstrain curve during high temperature deformation exhibits a peak stress which is followed by a gradual decrease into a steady state stress with increasing the strain.

Hee Y. Kim; Woong H. Sohn; Soon H. Hong

1998-01-01

46

Raman Scattering Spectroscopy of Residual Stresses in Epitaxial AlN Films  

NASA Astrophysics Data System (ADS)

High-crystalline-quality epitaxial films of wurtzite AlN were grown by metalorganic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HVPE). The lattice strain of the films was analyzed by high-resolution X-ray diffraction and the E2 (high)-phonon frequency was observed by Raman scattering. Data analysis for wide ranges of lattice strains and phonon-peak shifts yielded a precise biaxial stress coefficient of this phonon mode, -4.04 0.3 cm-1/GPa. Furthermore, the deformation potential constant was accurately determined from the biaxial stress coefficient.

Yang, Shibo; Miyagawa, Reina; Miyake, Hideto; Hiramatsu, Kazumasa; Harima, Hiroshi

2011-03-01

47

High-risk stress fractures  

Microsoft Academic Search

High-risk stress fractures require precise assessment and treatment because of their propensity for delayed union, nonunion,\\u000a or complete fracture and their resulting disabling complications. Proper diagnosis necessitates a thorough clinical evaluation,\\u000a centering on the patient's diet and history, particularly the training regimen. For a definitive diagnosis, plain radiography,\\u000a ultrasound, bone scintigraphy, magnetic resonance imagery (MRI), and computed tomography (CT) are

Steven R. Murray; Michael T. Reeder; Brian E. Udermann; Robert W. Pettitt

2006-01-01

48

Fractography of Stress Corrosion Cracking of Mg-Al Alloys  

Microsoft Academic Search

Mechanisms for the stress corrosion cracking (SCC) of Mg-Al alloys have been investigated by scanning electron microscopy\\u000a (SEM) of the fracture surfaces, for the two-phase alloy AZ91 and the single-phase alloys AZ31 and AM30 in distilled water.\\u000a The mechanism for crack initiation in AZ31 and AM30 involves localized dissolution. The mechanisms for crack propagation in\\u000a AZ31 and AM30 involve microvoid

Nicholas Winzer; A. Atrens; W. Dietzel; G. Song; K. U. Kainer

2008-01-01

49

Correlation of mechanical stress and Doppler broadening of the positron annihilation line in Al and Al alloys  

NASA Astrophysics Data System (ADS)

The plastic deformation of Al samples, of the technical alloys AlMgSi0.5, and AlMg3 was studied by Doppler-broadening spectroscopy (DBS) of the positron annihilation line. First, the defect sensitive line-shape parameter S was measured after the application of axial tensile stress, and the corresponding stress-strain curves were recorded that allowed us to correlate the strain, the mechanical stress and the S -parameter values after mechanical load quantitatively. In a next step, asymmetrically deformed Al samples were investigated with a monoenergetic positron beam by DBS in order to obtain the laterally resolved information of the stress-induced defects. It is demonstrated that the resulting two-dimensional S -parameter map (scan area 1414mm2 , step width 1 mm) can be expressed quantitatively in terms of the locally acting stress which is responsible for the creation of the lattice defects.

Hugenschmidt, C.; Qi, N.; Stadlbauer, M.; Schreckenbach, K.

2009-12-01

50

Investigation for Different Peening Techniques on Residual Stress Field of SiCw/Al Composite  

NASA Astrophysics Data System (ADS)

In order to improve the residual stress field of SiCw/Al composite after conventional shot peening, modified warm peening, stress peening, and compound peening were carried out on SiCw/Al composite specimens and residual stress fields of those specimens were investigated via x-ray measurement. Results show conventional peening can improve residual stress field of SiCw/Al composite but the improvement has a limit. Compared with conventional peening, modified warm peening can increase the maximum residual stress, the depth of compressive residual stress layer and improve stability of residual stress field whereas stress peening can increase all characteristic parameters of residual stress field efficiently. Compound peening combines the positive effects of modified warm peening and stress peening, and has the most strengthening effects.

Huang, Junjie; Wang, Zhou; Bian, Kai; Jiang, Chuanhai

2013-03-01

51

The strengthening effect of Al{sub 3}Ti in high temperature deformation of Al-Al{sub 3}Ti composites  

SciTech Connect

A series of Al-Al{sub 3}Ti composites with systematic variation of Al{sub 3}Ti content were prepared by mechanical alloying. Microstructural observations have indicated that among these composites, the only distinct variable is the Al{sub 3}Ti content, while the other microstructural variables are essentially the same. The high temperature (623--773 K) deformation behavior of these composites was found to be similar to that of dispersion-hardened aluminum. By considering the presence of a threshold stress, the plastic flow in these composites can be described by lattice-diffusion controlled dislocation creep in the aluminum matrix with a constant structure. The presence of Al{sub 3}Ti particles can increase the creep strength of these alloys significantly. By considering the load-sharing effect of Al{sub 3}Ti, an analysis based on continuum mechanics approach has been conducted, which can successfully account for the creep rate of these Al-Al{sub 3}Ti composites. The threshold stress for creep in these composites was found to increase with increasing Al{sub 3}Ti content, which could be attributed to the load-shearing effect of Al{sub 3}Ti particles.

Wang, S.H.; Kao, P.W. [National Sun Yat-Sen Univ., Kaohsiung (Taiwan, Province of China). Inst. of Materials Science and Engineering

1998-05-01

52

Transverse stress effect on the critical current of jelly-roll multifilamentary Nb sub 3 Al wires  

SciTech Connect

Experiments were conducted to determine the transverse stress sensitivity of the critical current ({ital I}{sub {ital c}}) of jelly-roll multifilamentary Nb{sub 3}Al wires at 8 and 12 T. For comparison, similar experiments were conducted on bronze-process (NbTi){sub 3}Sn wires. At 12 T and under a transverse compressive stress of 150 MPa{emdash}conditions expected in fusion magnets{emdash}the {ital I}{sub {ital c}} degradation of the Nb{sub 3}Al specimen was {similar to}20% vs {similar to}65% for the (NbTi){sub 3}Sn specimen. The intrinsic superiority of Nb{sub 3}Al over (NbTi){sub 3}Sn with regard to transverse compressive stress is thus clear. There is optimism that Nb{sub 3}Al will eventually become a useful superconductor for large-scale, high-field applications.

Zeritis, D.; Ando, T.; Takahashi, Y.; Nishi, M.; Nakajima, H.; Shimamoto, S. (Naka Fusion Research Establishment, Japan Atomic Energy Research Institute, Naka-machi, Naka-gun, Ibaraki-ken 311-01 (Japan))

1990-07-30

53

AN INVESTIGATION OF THE EFFECTS OF STRESS RATIO AND CRACK CLOSURE ON THE MICROMECHANISMS OF FATIGUE CRACK GROWTH IN Ti6Al4V  

Microsoft Academic Search

The effects of positive stress ratios on the fatigue crack growth behavior of a forged, mill-annealed Ti-6Al-4V alloy (with a duplex ? + ? microstructure) are discussed. Differences between fatigue crack growth rates at low and high stress ratios are shown to be due largely to crack closure. A 1% offset procedure is shown to collapse closure corrected low stress

S. DUBEY; A. B. O. SOBOYEJO; W. O. SOBOYEJO

1997-01-01

54

Changes in antioxidant gene expression and induction of oxidative stress in pea ( Pisum sativum L.) under Al stress  

Microsoft Academic Search

Aluminium toxicity has been recognized as a primary growth-limiting factor in acid soil, resulting in a decrease in plant\\u000a growth and production. In this experiment we have studied the induction of oxidative stress and changes in antioxidant gene\\u000a expression in pea (var. ALASKA) under aluminium (Al) stress. We have found that Al treatment affected the growth of pea plant\\u000a and

Sanjib Kumar Panda; Hideki Matsumoto

2010-01-01

55

High temperature aqueous stress corrosion testing device  

DOEpatents

A description is given of a device for stressing tensile samples contained within a high temperature, high pressure aqueous environment, thereby permitting determination of stress corrosion susceptibility of materials in a simple way. The stressing device couples an external piston to an internal tensile sample via a pull rod, with stresses being applied to the sample by pressurizing the piston. The device contains a fitting/seal arrangement including Teflon and weld seals which allow sealing of the internal system pressure and the external piston pressure. The fitting/seal arrangement allows free movement of the pull rod and the piston.

Bornstein, A.N.; Indig, M.E.

1975-12-01

56

High temperature oxidation of mechanically alloyed NiAlFeAlNAl 2O 3  

Microsoft Academic Search

A new NiAlFe alloy containing uniformly distributed ultra-fine AlN and Al2O3 dispersoids was produced by mechanical alloying in a controlled atmosphere and by subsequent hot extrusion process. The new NiAlFeAlNAl2O3 alloy was oxidized in the temperature range between 1073 and 1473 K in air. The alloy displayed similar oxidation behavior with conventional NiAl alloys. As the oxidation temperature increased, the

D. B. Lee; G. Y. Kim; S. W. Park; S. C. Ur

2002-01-01

57

Superconductivity and flow stress of Al-Li alloys near 1 K  

NASA Astrophysics Data System (ADS)

Superconductivity was discovered in Al-Li, Al-Mg-Li-Zr, and Al-Cu-Li-Zr alloys, and the critical parameters of the superconductors were estimated. The sensitivity of the flow stress and serrated deformation with respect to the electron state of the sample were observed. The applied magnetic field and the temperature dependence of the flow stress change Delta(Sigma sub sn) at the superconducting transition were studied in the interval from Tc to 0.5 K.

Pustovalov, V. V.; Isaev, N. V.; Fomenko, V. S.; Shumilin, S. E.; Kolobnev, N. I.; Fridliander, I. N.

58

Superconductivity and flow stress of Al-Li alloys near 1 K  

Microsoft Academic Search

Superconductivity was discovered in Al-Li, Al-Mg-Li-Zr, and Al-Cu-Li-Zr alloys, and the critical parameters of the superconductors were estimated. The sensitivity of the flow stress and serrated deformation with respect to the electron state of the sample were observed. The applied magnetic field and the temperature dependence of the flow stress change Delta(Sigma sub sn) at the superconducting transition were studied

V. V. Pustovalov; N. V. Isaev; V. S. Fomenko; S. E. Shumilin; N. I. Kolobnev; I. N. Fridliander

1992-01-01

59

Residual stress characterization of Al/SiC nanoscale multilayers using X-ray  

SciTech Connect

Nanolayered composites are used in a variety of applications such as wear resistant coatings, thermal barrier coatings, optical and magnetic thin films, and biological coatings. Residual stresses produced in these materials during processing play an important role in controlling their microstructure and properties. In this paper, we have studied the residual stresses in model metal-ceramic Al/SiC nanoscale multilayers produced by physical vapor deposition (magnetron sputtering). X-ray synchrotron radiation was used to measure stresses in the multilayers using the sin{sup 2} {Psi} technique. The stresses were evaluated as a function of layer thicknesses of Al and SiC and also as a function of the number of layers. The stress state of Al in the multilayer was largely compressive, compared to single layer Al stresses. This is attributed to a peening mechanism due to bombardment of the Al layers by SiC and Ar neutrals during deposition. The stress evolution was numerically modeled by a simplified peening process to qualitatively explain the Al thickness-dependent residual stresses.

Singh, DRP [Arizona State University; Deng, X. [Arizona State University; Chawla, N. [Arizona State University; Bai, J. [Brookhaven National Laboratory (BNL); Hubbard, Camden R [ORNL; Tang, G [University of New Mexico, Albuquerque; Shen, Y-L [University of New Mexico, Albuquerque

2010-01-01

60

Low-energy deposition of high-strength Al(0) alloys from an ECR plasma  

SciTech Connect

Low-energy deposition of Al(O) alloys from an electron cyclotron resonance (ECR) plasma offers a scaleable method for the synthesis of thick, high-strength Al layers. This work compares alloy layers formed by an ECR-0{sub 2} plasma in conjunction with Al evaporation to 0-implanted Al (ion energies 25-200 keV); and it examines the effects of volume fraction of A1{sub 2}0{sub 3} phase and deposition temperature on the yield stress of the material. TEM showed the Al(O) alloys contain a dense dispersion of small {gamma}-Al{sub 2}0{sub 3} precipitates ({approximately}l nm) in a fine-grain (10-100 nm) fcc Al matrix when deposited at a temperature of {approximately}100C, similar to the microstructure for gigapascal-strength 0-implanted Al. Nanoindentation gave hardnesses for ECR films from 1.1 to 3.2 GPa, and finite-element modeling gave yield stresses up to 1.3 {plus_minus} 0.2 GPa with an elastic modulus of 66 GPa {plus_minus} 6 GPa (similar to pure bulk Al). The yield stress of a polycrystalline pure Al layer was only 0.19 {plus_minus} 0.02 GPa, which was increased to 0.87 {plus_minus} 0.15 GPa by implantation with 5 at. % 0.

Barbour, J.C.; Follstaedt, D.M.; Knapp, J.A.; Myers, S.M. [Sandia National Labs., Albuquerque, NM (United States); Marshall, D.A.; Lad, R.J. [Univ. of Maine, Orono, ME (United States)

1995-12-31

61

Characterization of Quench-Extracted High Pressure Stressed Microorganisms  

NASA Astrophysics Data System (ADS)

In-situ high pressure microbiology work by Sharma et al (2002) presented a unique approach with diamond anvil cells to the study of microbes under environmental stress. This study focused on high pressure exposure as the stress component and provided a technique to directly monitor microbial activity. However, it lacked the much desired biochemical and biophysical information that could reflect the state of surviving microorganisms with insights into the process of adaptation at extreme. More recent work (Sharma et al 2011) expands on the previous study by including synergistic effect of high temperature with increased pressures along variable time scale. With the cell extraction and subsequent cell growth demonstrated, Sharma et al. (2011) show that more than pressure, temperature remains the environmental variable that defines the limits of life's survival. In this study we have refined the extraction process from the diamond anvil cell such that the stressed microorganisms can be routinely available for in-depth physiological study using conventional and state-of-the-art high resolution imaging tools. Here we present some recent in-depth FESEM, AFM and optical spectroscopy data to study the effect of stress on Escherichia coli. Contrary to earlier studies where various cell membrane ruptures were reported after moderate pressure exposure, we find that most cells remain viable and except for some occasional anomalous morphology, the surviving cells were similar to the unstressed state. Preliminary results suggest that the stress response in Escherichia coli exposed to short term extreme pressures (ranging from 1 -24 hrs) seems rapidly reversible. Biophysical entities such as the cell membrane, therefore, remain intact in the whole organism (and colony of microorganisms) at significantly higher pressure conditions than 300 MPa as reported in previous biophysics literature.

Sharma, P.; Sharma, A.

2011-12-01

62

Degradation in AlGaN/GaN heterojunction field effect transistors upon electrical stress: Effects of field and temperature  

NASA Astrophysics Data System (ADS)

AlGaN/GaN heterojunction field effect transistors (HFETs) with 2 ?m gate length were subjected to on-state-high-field (high drain bias and drain current) and reverse-gate-bias (no drain current and reverse gate bias) stress at room and elevated temperatures for up to 10 h. The resulting degradation of the HFETs was studied by direct current and uniquely phase noise before and after stress. A series of drain and gate voltages was applied during the on-state-high-field and reverse-gate-bias stress conditions, respectively, to examine the effect of electric field on degradation of the HFET devices passivated with SiNx. The degradation behaviors under these two types of stress conditions were analyzed and compared. In order to isolate the effect of self-heating/temperature on device degradation, stress experiments were conducted at base plate temperatures up to 150 C. It was found that the electric field induced by reverse-gate-bias mainly generated trap(s), most likely in the AlGaN barrier, which initially were manifested as generation-recombination (G-R) peak(s) in the phase noise spectra near 103 Hz. Meanwhile electric field induced by on-state-high-field stress mainly generated hot-electron and hot-phonon effects, which result in a nearly frequency independent increase of noise spectra. The external base plate temperatures promote trap generation as evidenced by increased G-R peak intensities.

Zhu, C. Y.; Zhang, F.; Ferreyra, R. A.; Avrutin, V.; zgr, .; Morko, H.

2013-10-01

63

The strengthening effect of Al 3Ti in high temperature deformation of AlAl 3Ti composites  

Microsoft Academic Search

A series of AlAl3Ti composites with systematic variation of Al3Ti content were prepared by mechanical alloying. Microstructural observations have indicated that among these composites, the only distinct variable is the Al3Ti content, while the other microstructural variables are essentially the same. The high temperature (623773K) deformation behavior of these composites was found to be similar to that of dispersion-hardened aluminum.

S. H. Wang; P. W. Kao

1998-01-01

64

Flow stress of 2197 Al-Li alloy during hot compression deformation  

Microsoft Academic Search

The flow stress behavior of 2197 Al-Li alloy during hot compression deformation was studied in the strain rate range from 0.01 to 10 s?1 and the temperature range from 360 to 510 ? by isothermal compression test on a Gleeble-1500 thermal-mechanical simulator. The results show that the flow stress of 2197 Al-Li alloy decreases with the increase of deformation temperature

WEI Xiu-yu; ZHENG Zi-qiao; FU Xin; CHEN Qiu-ni

65

Characterisation of stress corrosion cracking (SCC) of MgAl alloys  

Microsoft Academic Search

Stress corrosion cracking (SCC) of the MgAl alloys AZ91, AZ31 and AM30 in distilled water has been characterised using constant extension rate tests (CERTs) and linearly increasing stress tests (LISTs). AZ91 consists of an ?-matrix with extensive ?-particles, whereas AZ31 and AM30 consist only of an ?-matrix with an Al-concentration similar to that in AZ91. The presence of ?-particles in

N. Winzer; A. Atrens; W. Dietzel; V. S. Raja; G. Song; K. U. Kainer

2008-01-01

66

On the Phenomenon of Stress Drop During Hot Deformation of ZrTiAlV Alloy  

NASA Astrophysics Data System (ADS)

Hot deformation behaviors of 47Zr-45Ti-5Al-3V alloys with different grain sizes were investigated by compression tests. The flow curves exhibited a pronounced stress drop at the very beginning of deformation. The magnitude of the stress drop increased with the decreasing deformation temperature and the increasing strain rate. The sudden stress drop may be associated with the disappearance of mobile dislocations in the grain boundaries. Larger initial grain size increased the flow stress, promoted the stress drop, and enhanced the activation energy of deformation.

Tan, Yuanbiao; Liu, Wenchang; Yuan, Hui; Liu, Riping; Zhang, Xiangyi

2013-09-01

67

Internal friction of ?-TiAl alloys at high temperature  

Microsoft Academic Search

Intermetallic ?-TiAl based alloys of engineering interest with respect to high temperature applications are two-phase alloys consisting of ?-TiAl (ordered face-centered tetragonal structure) and ?2-Ti3Al (ordered hexagonal structure). For this investigation a ?-TiAl based alloy with a composition of Ti-46.4 at%Al-4 at% (Cr, Nb, Ta, B) was studied utilizing a low frequency subresonance apparatus at frequencies between 0.01 and 10

M Weller; A Chatterjee; G Haneczok; H Clemens

2000-01-01

68

Stress Corrosion Cracking in Al-Zn-Mg-Cu Aluminum Alloys in Saline Environments  

NASA Astrophysics Data System (ADS)

Stress corrosion cracking of Al-Zn-Mg-Cu (AA7xxx) aluminum alloys exposed to saline environments at temperatures ranging from 293 K to 353 K (20 C to 80 C) has been reviewed with particular attention to the influences of alloy composition and temper, and bulk and local environmental conditions. Stress corrosion crack (SCC) growth rates at room temperature for peak- and over-aged tempers in saline environments are minimized for Al-Zn-Mg-Cu alloys containing less than ~8 wt pct Zn when Zn/Mg ratios are ranging from 2 to 3, excess magnesium levels are less than 1 wt pct, and copper content is either less than ~0.2 wt pct or ranging from 1.3 to 2 wt pct. A minimum chloride ion concentration of ~0.01 M is required for crack growth rates to exceed those in distilled water, which insures that the local solution pH in crack-tip regions can be maintained at less than 4. Crack growth rates in saline solution without other additions gradually increase with bulk chloride ion concentrations up to around 0.6 M NaCl, whereas in solutions with sufficiently low dichromate (or chromate), inhibitor additions are insensitive to the bulk chloride concentration and are typically at least double those observed without the additions. DCB specimens, fatigue pre-cracked in air before immersion in a saline environment, show an initial period with no detectible crack growth, followed by crack growth at the distilled water rate, and then transition to a higher crack growth rate typical of region 2 crack growth in the saline environment. Time spent in each stage depends on the type of pre-crack ("pop-in" vs fatigue), applied stress intensity factor, alloy chemistry, bulk environment, and, if applied, the external polarization. Apparent activation energies ( E a) for SCC growth in Al-Zn-Mg-Cu alloys exposed to 0.6 M NaCl over the temperatures ranging from 293 K to 353 K (20 C to 80 C) for under-, peak-, and over-aged low-copper-containing alloys (<0.2 wt pct) are typically ranging from 80 to 85 kJ/mol, whereas for high-copper-containing alloys (>~0.8 wt pct), they are typically ranging from 20 to 40 kJ/mol for under- and peak-aged alloys, and based on limited data, around 85 kJ/mol for over-aged tempers. This means that crack propagation in saline environments is most likely to occur by a hydrogen-related process for low-copper-containing Al-Zn-Mg-Cu alloys in under-, peak- and over-aged tempers, and for high-copper alloys in under- and peak-aged tempers. For over-aged high-copper-containing alloys, cracking is most probably under anodic dissolution control. Future stress corrosion studies should focus on understanding the factors that control crack initiation, and insuring that the next generation of higher performance Al-Zn-Mg-Cu alloys has similar longer crack initiation times and crack propagation rates to those of the incumbent alloys in an over-aged condition where crack rates are less than 1 mm/month at a high stress intensity factor.

Holroyd, N. J. Henry; Scamans, G. M.

2013-03-01

69

Cyclic deformation and fracture behavior of Al alloy 6061 under the action of positive mean stresses  

NASA Astrophysics Data System (ADS)

Cyclic deformation and fatigue fracture behavior of Al alloy 6061 were studied over an extensive range of positive mean stress. In the regime of low cyclic stress amplitude, both secondary stage creep rate and fracture process are retarded by decreasing mean stress, but they are accelerated if the cyclic stress ratio is smaller than 0. 75. The superimposition of cyclic compressive stress is found to decrease the creep rate, but it has no effect on the relationship between fatigue life and mean stress. Characteristic patterns on the specimen fracture surfaces, representing the interaction between creep and fatigue and also the mechanism of the fatigue-creep deformation in different mean stress ranges, are discussed analytically. Finally, the concept of equivalent creep rate is proposed and a method to predict fatigue life with positive mean stresses is established and verified using the present experimental results.

Yang, Zhi'an; Wang, Zhirui

1993-09-01

70

Stress corrosion cracking and hydrogen embrittlement of an Al-Zn-Mg-Cu alloy  

SciTech Connect

The age hardening, stress corrosion cracking (SCC) and hydrogen embrittlement (HE) of an Al-Zn-Mg-Cu 7175 alloy were investigated experimentally. There were two peak-aged states during ageing. For ageing at 413 K, the strength of the second peak-aged state was slightly higher than that of the first one, whereas the SCC susceptibility was lower, indicating that it is possible to heat treat 7175 to high strength and simultaneously to have high SCC resistance. The SCC susceptibility increased with increasing Mg segregation at the grain boundaries. Hydrogen embrittlement (HE) increased with increased hydrogen charging and decreased with increasing ageing time for the same hydrogen charging conditions. Computer simulations were carried out of (a) the Mg grain boundary segregation using the embedded atom method and (b) the effect of Mg and H segregation on the grain boundary strength using a quasi-chemical approach. The simulations showed that (a) Mg grain boundary segregation in Al-Zn-Mg-Cu alloys is spontaneous, (b) Mg segregation decreases the grain boundary strength, and (c) H embrittles the grain boundary more seriously than does Mg. Therefore, the SCC mechanism of Al-Zn-Mg-Cu alloys is attributed to the combination of HE and Mg segregation induced grain boundary embrittlement.

Song, R.G.; Dietzel, W.; Zhang, B.J.; Liu, W.J.; Tseng, M.K.; Atrens, A

2004-09-20

71

Trigger Stress for Stress-Induced Martensitic Transformation during Tensile Deformation in Ti-Al-Nb Alloys: Effect of Grain Size  

Microsoft Academic Search

The effect of ? grain size on trigger stress for stress-induced martensitic transformation during tensile deformation in Ti-Al-Nb alloys\\u000a was investigated. The trigger stress for stress-induced martensitic transformation (SIMT) in Ti-Al-Nb alloys exhibited a U-shaped\\u000a behavior with variation in grain size. The variation of trigger stress with grain size was explained qualitatively, in terms\\u000a of the contrasting change in the

Archana Paradkar; S. V. Kamat; A. K. Gogia; B. P. Kashyap

2008-01-01

72

Trigger Stress for Stress-Induced Martensitic Transformation during Tensile Deformation in Ti-Al-Nb Alloys: Effect of Grain Size  

Microsoft Academic Search

The effect of beta grain size on trigger stress for stress-induced martensitic transformation during tensile deformation in Ti-Al-Nb alloys was investigated. The trigger stress for stress-induced martensitic transformation (SIMT) in Ti-Al-Nb alloys exhibited a U-shaped behavior with variation in grain size. The variation of trigger stress with grain size was explained qualitatively, in terms of the contrasting change in the

Archana Paradkar; S. V. Kamat; A. K. Gogia; B. P. Kashyap

2008-01-01

73

Accumulation of mechanical stress in Al2O3:Cr under swift heavy ion irradiation  

Microsoft Academic Search

The build-up and accumulation of stresses in Al2O3:Cr single crystalline samples under 670MeV Bi, 167MeV Xe and 107MeV Kr ion irradiation have been studied using ion-beam-induced luminescence measurements. The stress level has been deduced from R-line luminescence spectra measured in situ on the basis of the piezospectroscopic effect. The experimental data have revealed different stages in the stress accumulation processes

G. Bujnarowski; V. A. Skuratov; K. Havancsak; Yu. S. Kovalev

2009-01-01

74

Modelling Of Residual Stresses Induced By High Speed Milling Process  

SciTech Connect

Maintenance processes used in heavy industries often include high speed milling operations. The reliability of the post-process material state has to be studied. Numerical simulation appears to be a very interesting way to supply an efficient residual stresses (RS) distribution prediction.Because the adiabatic shear band and the serrated chip shaping are features of the austenitic stainless steel high speed machining, a 2D high speed orthogonal cutting model is briefly presented. This finite element model, developed on Forge registered software, is based on data taken from Outeiro and al.'s paper [1]. A new behaviour law fully coupling Johnson-Cook's constitutive law and Latham and Cockcroft's damage model is detailed in this paper. It ensures results that fit those found in literature.Then, the numerical tools used on the 2D model are integrated to a 3D high speed milling model. Residual stresses distribution is analysed, on the surface and into the depth of the material. Various revolutions and passes of the two teeth hemispheric mill on the workpiece are simulated. Thus the sensitivity of the residual stresses generation to the cutting conditions can be discussed. In order to validate the 3D model, a comparison of the cutting forces measured by EDF R and D to those given by numerical simulations is achieved.

Desmaison, Olivier; Mocellin, Katia [Mines ParisTech, CEMEF, Centre of Material Forming, CNRS UMR 7635, BP 207, 1 rue Claude Daunesse, 06904 Sophia Antipolis Cedex (France); Jardin, Nicolas [Industrial Risks Management Dept.-EDF R and D, Chatou-78400 (France)

2011-05-04

75

Stress Annealing Induced Diffuse Scattering from Ni3 (Al, Si) Precipitates  

NASA Astrophysics Data System (ADS)

Diffuse scattering caused by L12 type Ni3 (Al, Si) precipitates after stress annealing of Ni-Al-Si alloys is studied. Peculiarities of diffuse scattering in the asymptotic region as compared to the Huang scattering region are discussed. Coupling between the stress annealing direction and the precipitate shape is demonstrated. Experimental reciprocal space maps (RSMs) are compared to theoretical ones. Oscillations of diffuse scattering due to Ni3 (Al, Sc) precipitates are observed. The strengths of the precipitates are estimated from the analysis of the diffuse scattering oscillations.

Barabash, R. I.; Ice, G. E.; Karapetrova, E. A.; Zschack, P.

2012-05-01

76

Deformation simulation of low-temperature high-speed extrusion for 6063 Al alloy  

Microsoft Academic Search

The hot compression test of 6063 Al alloy was performed on a Gleeble-1500 thermo-simulation machine, and the forming of 6063\\u000a rod extrudate in low-temperature high-speed extrusion was simulated with extrusion ratio of 25 on the platform of DEFORM 2D\\u000a successfully. From the compression experimental results, the flow stress model of this Al alloy is obtained which could be\\u000a the constitutive

Meng-jun Wang; Zhao He; Xing-xing Wu; Cai-wen Li; Guang-yao Li

2010-01-01

77

Field-Induced Defect Morphology in Ni-gate AlGaN/GaN High Electron Mobility Transistors.  

National Technical Information Service (NTIS)

AlGaN/GaN high electron mobility transistors were electrically stressed using off-state high reverse gate biases. In devices demonstrating the largest, most rapid decrease in normalized maximum drain current, defects were found at the gate/AlGaN epilayer ...

K. S. Jones M. R. Holzworth N. G. Rudawski P. G. Whiting S. J. Pearton

2013-01-01

78

High-performance nonvolatile Al/AlOx/CdTe:Sb nanowire memory device  

NASA Astrophysics Data System (ADS)

Here we demonstrate a room temperature processed nonvolatile memory device based on an Al/AlOx/CdTe:Sb nanowire (NW) heterojunction. Electrical analysis shows an echelon hysteresis composed of a high-resistance state (HRS) and a low-resistance state (LRS), which can allow it to write and erase data from the device. The conductance ratio is as high as 106, with a retention time of 3 104 s. Moreover, the SET voltages ranged from +6 to +8 V, whilst the RESET voltage ?0 V. In addition, flexible memory nano-devices on PET substrate with comparable switching performance at bending condition were fabricated. XPS analysis of the Al/AlOx/CdTe:Sb NW heterojunction after controlled Ar+ bombardment reveals that this memory behavior is associated with the presence of ultra-thin AlOx film. This Al/AlOx/CdTe:Sb NW heterojunction will open up opportunities for new memory devices with different configurations.

Xie, Chao; Nie, Biao; Zhu, Long; Zeng, Long-Hui; Yu, Yong-Qiang; Wang, Xian-He; Fang, Qun-Ling; Luo, Lin-Bao; Wu, Yu-Cheng

2013-09-01

79

TWO DIMENSIONAL SIMULATION OF DEHYDRATION OF A HIGHLY DEFORMABLEGEL : MOISTURE CONTENT, STRESS AND STRAW FIELDS  

Microsoft Academic Search

A model taking into account the simultaneous influence of mechanical and hygrometric actions (Mrani and al., 1995a, 1995b) was applied to study of the dehydration of a cylinder of highly deformable biphase gel (agar gel) (Mrani and al., 1995b). Numerical solution of the water transport equation and the mechanical equilibrium equation provided access to the water content and stresses and

I. Mrani; J. C. Bnet; G. Fras; Z. Zrikem

1997-01-01

80

Alucone interlayers to minimize stress caused by thermal expansion mismatch between Al?O? films and Teflon substrates.  

PubMed

Alucone films were employed as interlayers to minimize stress caused by thermal expansion mismatch between Al(2)O(3) films grown by atomic layer deposition (ALD) and Teflon fluorinated ethylene propylene (FEP) substrates. The alucone films were grown by molecular layer deposition (MLD) using trimethylaluminum (TMA), ethylene glycol (EG), and H(2)O. Without the alucone interlayer, the Al(2)O(3) films were susceptible to cracking resulting from the high coefficient of thermal expansion (CTE) mismatch between the Al(2)O(3) film and the Teflon FEP substrate. Cracking was observed by field emission scanning electron microscopy (FE-SEM) images of Al(2)O(3) films grown directly on Teflon FEP substrates at temperatures from 100 to 160 C and then cooled to room temperature. With an alucone interlayer, the Al(2)O(3) film had a crack density that was reduced progressively versus alucone interlayer thickness. For Al(2)O(3) film thicknesses of 48 nm deposited at 135 C, no cracks were observed for alucone interlayer thicknesses >60 nm on 50 ?m thick Teflon FEP substrates. For thinner Al(2)O(3) film thicknesses of 21 nm deposited at 135 C, no cracks were observed for alucone interlayer thicknesses >40 nm on 50 ?m thick Teflon FEP substrates. Slightly higher alucone interlayer thicknesses were required to prevent cracking on thicker Teflon FEP substrates with a thickness of 125 ?m. The alucone interlayer linearly reduced the compressive stress on the Al(2)O(3) film caused by the thermal expansion mismatch between the Al(2)O(3) coating and the Teflon FEP substrate. The average compressive stress reduction per thickness of the alucone interlayer was determined to be 8.5 2.3 MPa/nm. Comparison of critical tensile strains for alucone films on Teflon FEP and HSPEN substrates revealed that residual compressive stress in the alucone film on Teflon FEP could help offset applied tensile stress and lead to the attainment of much higher critical tensile strains. PMID:23272996

Jen, Shih-Hui; George, Steven M; McLean, Robert S; Carcia, Peter F

2013-01-31

81

The evaluation and measurement of AlGaN epitaxial layer with high Al mole fraction  

NASA Astrophysics Data System (ADS)

The epitaxial layer quality of AlxGa1-xN (x>0.6) on sapphire substrate grown by metal organic chemical vapor deposition (MOCVD) needs to be further improved. In this paper, we evaluated the properties of defects, lattice mismatch between epitaxial layer and substrate, crystal quality and conductivity for these high Al mole fraction materials from the viewpoint of fabricating high performance solar blind detectors by comprehensive utilizing various undamaged measurements. The measurement of transmission spectrum was used to evaluate the absorption edge, band gap, mole fraction of Al content, hetero-epitaxial interface, and transmissivity in the ultraviolet spectral range. X-ray diffraction (XRD) was used to measure the component of the AlGaN material, uniformity of the material and crystal quality. The conductivity of the surface layer of the AlGaN film material was obtained by using high precision current-voltage curve measurement. In short, the material quality, optical and electrical properties, and uniformity for high Al mole fraction AlGaN epitaxial layers were qualitatively or quantitatively measured and analyzed. These works lay the foundation for manufacturing high performance solar blind ultraviolet detectors based on high Al mole fraction AlGaN epitaxial materials on sapphire substrate.

Meng, Zhao; Yu, Libo; Li, Xiao; Liu, Qibin; Duan, Huiqiang; Yu, Chenhui; Chen, Changqing

2009-08-01

82

The Influence of Hydrogen on the Stress Corrosion Cracking of Low-Strength AL-MG Alloys  

SciTech Connect

There is growing evidence for hydrogen uptake in aluminum alloys and its contribution to the crack growth of high-strength aluminum alloys but less evidence for low-strength alloys. This paper summarizes the evidence for hydrogen uptake in a low-strength alloy AA5083 and its contribution to the stress corrosion cracking of this alloy. A key factor is the anodic dissolution of grain boundary b phase (Al3Mg2) and the associated hydrogen reduction that accompanies this dissolution.

Jones, Russell H.

2003-02-01

83

High temperature deformation of a submicron grained Al-12 wt% Ti alloy  

SciTech Connect

Compressive deformation behavior of a MA Al-12wt%Ti alloy has been studied at 623--773 K with strain rates from 4 {times} 10{sup {minus}5} to 1 {times} 10{sup {minus}1} s{sup {minus}1}. A high stress exponent was observed in the stress dependence of strain rate. By assuming that the presence of a threshold stress is the cause of the high stress exponent, the experimental data were analyzed and compared with existing models. The creep behavior of this alloy is found similar to the dispersion strengthened Al-Al{sub 2}O{sub 3} alloys. It is suggested that the high temperature deformation of this alloy is mainly governed by the fine carbide and oxide strengthened aluminum matrix, which can be described by lattice-diffusion controlled creep with a constant structure. In addition, a strong temperature dependence of the threshold stress was observed. It might be related to certain grain boundary processes and/or thermally activated deformation of strengthening particles.

Wang, S.H.; Kao, P.W. [National Sun Yat-Sen Univ., Kaohsiung (Taiwan, Province of China). Inst. of Materials Science and Engineering

1997-06-15

84

Response of human endothelial cells to oxidative stress on Ti6Al4V alloy.  

PubMed

Titanium and its alloys are amongst the most frequently used materials in bone and dental implantology. The good biocompatibility of titanium(-alloys) is attributed to the formation of a titanium oxide layer on the implant surface. However, implant failures do occur and this appears to be due to titanium corrosion. Thus, cells participating in the wound healing processes around an implanted material, among them endothelial cells, might be subjected to reactive oxygen species (ROS) formed by electrochemical processes during titanium corrosion. Therefore, we studied the response of endothelial cells grown on Ti6Al4V alloy to H(2)O(2) and compared this with the response of endothelial cells grown on cell culture polystyrene (PS). We could show that although the cell number was the same on both surfaces, metabolic activity of endothelial cells grown on Ti6Al4V alloy was reduced compared to the cells on PS and further decreased following prototypic oxidative stress (H(2)O(2)-treatment). The analysis of H(2)O(2)-induced oxidative stress showed a higher ROS formation in endothelial cells on Ti6Al4V than on PS. This correlated with the depletion of reduced glutathione (GSH) in endothelial cells grown on Ti6Al4V surfaces and indicated permanent oxidative stress. Thus, endothelial cells in direct contact with Ti6Al4V showed signs of oxidative stress and higher impairment of cell vitality after an additional oxidative stress. However, the exact nature of the agent of oxidative stress generated from Ti6Al4V remains unclear and requires further investigation. PMID:17049373

Tsaryk, Roman; Kalbacova, Marie; Hempel, Ute; Scharnweber, Dieter; Unger, Ronald E; Dieter, Peter; Kirkpatrick, C James; Peters, Kirsten

2006-10-16

85

Determination and Relaxation of Residual Stress in 2024 Al-30 vol.% Magnesium Borate Whisker Composites  

NASA Astrophysics Data System (ADS)

Residual stresses in 30 vol.% magnesium borate whisker-reinforced 2024 aluminum matrix composites have been determined by a nanoindentation method which takes into consideration pile-up and sink-in effects on indentation contact depth. Owing to the thermal mismatch and the large difference in elasticity modulus between the Al matrix and MBO whiskers, tensile residual stress was introduced to Al matrix material during fabrication. It was found that the solution treatment reduced the tensile residual stress by producing interfacial component and dislocations in the composites. Cryogenic cooling released the stress via reversing the tensile residual stress to compression in the matrix, which was more effective than solution treatment to release the tension stress in the composites. The combination of the solution treatment and the cryogenic cooling provided the most effective procedure to release the residual stress in the composites, which reduced the tensile residual stress from 232.6 to 56.5 MPa, i.e., 76% reduction. Meanwhile, no cracks were observed in the composite when processed with such sudden thermal shocking.

Wang, Zhijiang; Jiang, Zhaohua; Hu, Henry; Nie, Xueyuan

2013-05-01

86

Residual stresses in plasma electrolytic oxidation coatings on Al alloy produced by pulsed unipolar current  

Microsoft Academic Search

Plasma electrolytic oxidation (PEO) coatings have been produced on aluminium substrates using a pulsed unipolar current mode at different duty cycle and frequency, along with reference samples produced using direct current. Residual stresses attributed to the ?-Al2O3 constituent of the coating have been evaluated by X-ray diffraction using the Sin2? method. It is found that compressive normal and shear stresses

R. H. U. Khan; A. L. Yerokhin; T. Pilkington; A. Leyland; A. Matthews

2005-01-01

87

Low stress and superplastic creep behavior of Zn22 Pct Al eutectoid alloy  

Microsoft Academic Search

The temperature, grain size, and stress dependence of steady-state strain-rates were investigated for Zn-22 pct Al eutectoid\\u000a alloy using double shear type specimens. Tests were performed on specimens of grain size from 1.3 m to 3.7 ?m over a range of temperature from 450 to 525 K. The applied stresses were in the range between 10?1 and 4.0 x 101

A. Arieli; A. K. S. Yu; A. K. Mukherjee

1980-01-01

88

Low stress and superplastic creep behavior of Zn22 Pct Al eutectoid alloy  

Microsoft Academic Search

The temperature, grain size, and stress dependence of steady-state strain-rates were investigated for Zn-22 pct Al eutectoid alloy using double shear type specimens. Tests were performed on specimens of grain size from 1.3 m to 3.7 mu m over a range of temperature from 450 to 525 K. The applied stresses were in the range between 10-1 and 4.0 x

A. Arieli; A. K. S. Yu; A. K. Mukherjee

1980-01-01

89

Accumulation of mechanical stress in Al2O3:Cr under swift heavy ion irradiation  

Microsoft Academic Search

The build-up and accumulation of stresses in Al2O3:Cr single crystalline samples under 670 MeV Bi, 167 MeV Xe and 107 MeV Kr ion irradiation have been studied using ion-beam-induced luminescence measurements. The stress level has been deduced from R-line luminescence spectra measured in situ on the basis of the piezospectroscopic effect. The experimental data have revealed different stages in the

G. Bujnarowski; V. A. Skuratov; K. Havancsak; Yu S. Kovalev

2009-01-01

90

Reliability analysis of GaAs\\/AlGaAs HBTs under forward current\\/temperature stress  

Microsoft Academic Search

The reliability of GaAs\\/AlGaAs heterojunction bipolar transistors is investigated by accelerated life-testing of discrete devices under forward bias stress at elevated temperatures. The DC device characteristics are monitored to evaluate the effect of bias\\/temperature stress on a large number of devices fabricated on MBE (molecular beam epitaxy) grown material. The primary degradation observed in some devices is a reduction in

M. E. Hafizi; L. M. Pawlowicz; L. T. Tran; D. K. Umemoto; D. C. Streit; A. K. Oki; M. E. Kim; K. H. Yen

1990-01-01

91

Mechanical stress power measurements during high-power laser ablation  

Microsoft Academic Search

Laser-induced stresses have been studied extensively to understand macroscopic phenomenon during high-power laser ablation of solids. Recently, a norm of stress times the rate of change in stress, similar to mechanical stress power, was monitored acoustically in the target and ambient medium during high-power laser-material interactions, and compared with stress measurements. This study investigates the relationship between stress and the

Mark A. Shannon; Boris Rubinsky; Richard E. Russo

1996-01-01

92

Luminescence sensing of stress in Ti/Al{sub 2}O{sub 3} fiber reinforced composites  

SciTech Connect

The high temperature processing of fibrous metal matrix composites has been predicted to result in the development of large residual stresses because of a difference between the coefficients of thermal expansion (CTE) of the fibers and matrix. The R1 and R2 optical luminescence line shifts of single crystal {alpha}-Al{sub 2}O{sub 3} fibers embedded in a titanium matrix have been measured using a fiber optic method and related to the reinforcing fiber`s principal stresses. The fiber`s axial stress component has been found to be more than twice that predicted by a concentric cylinder`s (CTE difference) model, while the fiber`s radial (and hoop) direction stresses are smaller than expected. The authors propose that the stress in these composites is affected by two presently unmodeled effects: an elevation of composite`s residual stress due to the large CTE difference between the tooling used for processing of the composite and a relaxation of the transverse stress components by radial matrix cracking. The result has important consequences for the manufacture of metal matrix composites and for efforts to predict their mechanical properties.

Hough, H.; Demas, J.; Williams, T.O.; Wadley, H.N.G. [Univ. of Virginia, Charlottesville, VA (United States)

1995-02-01

93

Application of a method for determinations of the internal stress in polycrystalline NiAl  

SciTech Connect

The concept of the internal stress is widely accepted, however, its measurement has proven difficult. Qian and Reed-Hill have developed a simplified approach for determining [sigma][sub i] which implies a zero entropy of activation. The feasibility of this approach has been demonstrated for the commercial purity niobium data of Fries et al., the experimental Nb-O data of Park et al. and the Cu[sub 3]Sn data of Qian and Reed-Hill. In this paper, the general approach is reviewed and an attempt is made to apply it to the polycrystalline Ni-48.9 at.% Al and Ni-43.0 at.% Al data of Pascoe and Newey. The authors conclude that the approach of Qian and Reed-Hill is useful for determining the internal stress in NiAl and for modeling the strain rate sensitivity and flow stress as a function of temperature and strain provided data is available below the regime of DSA and when the strain rate dependence of the flow stress can be approximated with a power law.

Weaver, M.L.; Kaufman, M.J. (Univ. of Florida, Gainesville, FL (United States). Dept. of Materials Science and Engineering)

1994-09-15

94

On the threshold stress in mechanically alloyed NiAl  

Microsoft Academic Search

Intermetallic compounds, such as nickel, iron and titanium aluminides, have emerged as a new class of potential structural materials for high temperature applications such as gas turbine engines. However, before this material can be of practical use a number of technical problems must be overcome including lack of ductility at room temperature and poor strength at high temperatures. The authors

S. Suh; M. Dollar

1994-01-01

95

Flow stress behavior and processing map of Al-Cu-Mg-Ag alloy during hot compression  

Microsoft Academic Search

The hot deformation behavior of Al-Cu-Mg-Ag was studied by isothermal hot compression tests in the temperature range of 573773\\u000a K and strain rate range of 0.0011 s?1 on a Gleeble 1500 D thermal mechanical simulator. The results show the flow stress of Al-Cu-Mg-Ag alloy increases with strain\\u000a rate and decreases after a peak value, indicating dynamic recovery and recrystallization. A

Sheng Yang; Danqing Yi; Hong Zhang; Sujuan Yao

2008-01-01

96

[Exudation and accumulation of citric acid in common bean in response to Al toxicity stress].  

PubMed

Significant differences in the exudation and accumulation of citric acid in common bean genotypes were observed in response to Al toxicity stress by hydroponic cultural experiments. Secreted citric acid increased with increasing external concentrations of Al3+ which ranged from 0 to 50 mumol.L-1, while ranged from 50 to 80 mumol.L-1, secreted citric acid decreased with increasing external concentrations of Al3+. Among different genotypic common beans, citric acid secreted in G19842 was the largest, while Al uptake per unit dry weight in G19842 was the least. No difference in the accumulation of citric acid in leaves was found among different genotypic common beans, while the size of the content of citric acid in roots was G19842 > AFR > ZPV > G5273. The amount of citric acid exuded was smaller induced by phosphorus deficiency than that induced by Al toxicity stress. Exposure to 50 mumol.L-1 LaCl3 could not induce the exudation of citric acid, and it implied that the exudation and accumulation of citric acid in common bean was an important physiological response of resistance to Al toxicity stress. PMID:12132159

Shen, Hong; Yan, Xiaolong; Zheng, Shaoling; Wang, Xiurong

2002-03-01

97

High-temperature tribological properties of CrAlN, CrAlSiN and AlCrSiN coatings  

Microsoft Academic Search

CrAlSiN coatings with high and low Cr\\/Al ratios (CrAlSiN and AlCrSiN, respectively) were deposited on WC substrates by cathodic arc and compared with a reference CrAlN coating. The silicon content was close to 3at.%. X-ray diffraction analysis showed that CrAlN and CrAlSiN coatings exhibited the cubic Cr(Al)N structure, whereas in AlCrSiN a mixture of cubic Cr(Al)N and wurtzite-type AlN was

Tomas Polcar; Albano Cavaleiro

2011-01-01

98

The significance of acoustic emission during stressing of TiAl-based alloys. Part II: Influence of cracks induced by pre-stressing on the fatigue life  

Microsoft Academic Search

Fully lamellar samples of Ti44Al8Nb1B have been tested in tensiontension fatigue, after being pre-stressed, in order to investigate the effect on fatigue life of the cracks which are introduced by pre-stressing. It has been found that pre-stressing samples at 0.95 of the 0.2% proof stress leads to early failure when they are fatigue-tested at stress levels of about 0.65 of

X Wu; D Hu; R Botten; M. H Loretto

2001-01-01

99

Residual stress distribution in FeAl weld overlay on steel  

NASA Astrophysics Data System (ADS)

Neutron diffraction was used to measure the residual stress distribution in an FeAl weld overlay on steel. It was found that the residual stresses accumulated during welding were essentially removed by the post-weld heat treatment that was applied to the specimen; most residual stresses in the specimen developed during cooling following the post-weld heat treatment. The experimental data were compared with a plasto-elastic finite element analysis. While some disagreement exists in absolute strain values, there is satisfactory agreement in strain spatial distribution between the experimental data and the finite element analysis.

Wang, X. L.; Spooner, S.; Hubbard, C. R.; Maziasz, P. J.; Goodwin, G. M.; Feng, Z.; Zacharia, T.

1994-04-01

100

Deposition of ultrathin AlN films for high frequency electroacoustic devices  

SciTech Connect

The authors investigate the microstructure, crystal orientation, and residual stress of reactively sputtered aluminum nitride (AlN) films having thicknesses as low as 200 down to 25 nm. A two-step deposition process by the dual cathode ac (40 kHz) powered S-gun magnetron enabling better conditions for AlN nucleation on the surface of the molybdenum (Mo) bottom electrode was developed to enhance crystallinity of ultrathin AlN films. Using the two-step process, the residual in-plane stress as well as the stress gradient through the film thickness can be effectively controlled. X-ray rocking curve measurements have shown that ultrathin films grown on Mo using this technology are highly c-axis oriented with full widths at half maximum of 1.8 deg. and 3.1 deg. for 200- and 25-nm-thick films, respectively, which are equal to or even better than the results previously reported for relatively thick AlN films. High-resolution transmission electron microscopy and fast Fourier transform analyses have confirmed strong grain orientation in 25-100-nm-thick films. A fine columnar texture and a continuous lattice microstructure within a single grain from the interface with the Mo substrate through to the AlN surface have been elicited even in the 25-nm-thick film.

Felmetsger, Valery V.; Laptev, Pavel N.; Graham, Roger J. [OEM Group Incorporated, 2120 W. Guadalupe Road, Gilbert, Arizona 85233 (United States); NanoTEM Analytics Incorporated, 7620 E. McKellips Road, Suite 4109, Scottsdale, Arizona 85257 (United States)

2011-03-15

101

Effects of SiN passivation and high-electric field on AlGaN-GaN HFET degradation  

Microsoft Academic Search

The authors report on the effects of silicon nitride (SiN) surface passivation and high-electric field stress (hot electron stress) on the degradation of undoped AlGaN-GaN power HFETs. Stressed devices demonstrated a decrease in the drain current and maximum transconductance and an increase in the parasitic drain series resistance, gate leakage, and subthreshold current. The unpassivated devices showed more significant degradation

Hyungtak Kim; Richard M. Thompson; Vinayak Tilak; Thomas R. Prunty; James R. Shealy; Lester F. Eastman

2003-01-01

102

LP MOVPE growth and characterization of high Al content Al x Ga 1? x N epilayers  

Microsoft Academic Search

High quality AlxGa1?xN layers have been grown on sapphire (0001) by low pressure metalorganic vapour phase epitaxy (LP MOVPE) at 1180C. The aluminum content covers a wide composition range varying from 0 to 65%. In order to ameliore the quality of these epilayers especially for high aluminum content (XsAl >0.35), growth conditions are carefully optimized. The growth rate of AlGaN

C. Touzi; F. Omns; B. El Jani; P. Gibart

2005-01-01

103

Residual stress effect on impact properties of Gr\\/Al metal matrix composite  

Microsoft Academic Search

The effects of residual stress on the impact properties of the unidirectionally reinforced P 100 Gr\\/6061 Al metal matrix composites with different thermal histories have been investigated using an instrumented impact test method and scanning electron microscopy. The cantilever impact generally causes tensile failure at the notch and compressive loading on the opposite side of the specimen. The specimens with

Ji-Liang Doong; Shyh-Nung S. Lin; H. L. Marcus

1992-01-01

104

Effects of Al addition on high strain rate deformation of fully austenitic high Mn steels  

Microsoft Academic Search

The effects of Al addition on dynamic flow response of the fully austenitic high Mn steel were investigated by conducting high strain rate compression tests on Fe22MnxAl0.6C steels (x=0, 3, 6 in wt.%). While dynamic yield strength of the 0 Al steel and the 3 Al steel were comparable, the 6 Al steel exhibited the highest one. Meanwhile, strain hardenability

Si Woo Hwang; Jung Hoon Ji; Kyung-Tae Park

2011-01-01

105

Growth strains and stress relaxation in alumina scales during high temperature oxidation  

SciTech Connect

A novel X-ray technique was used, exploiting synchrotron radiation at the Advanced Photon Source at Argonne National Laboratory, to investigate the growth stresses in {alpha}-Al{sub 2}O{sub 3}. In-situ measurements of Debye-Scherrer diffraction patterns from the scale were recorded during oxidation and cooling, and the elliptical distortion of the diffraction rings was analyzed to yield the in-plane strain. Fe-28Al, Fe-40Al, Fe-40Al-0.2Hf, Fe-20Cr-10Al and Ni-50Al (at. %) were studied. Data were acquired in air at temperatures between 950-1100 C and during cool down. In all cases, the steady stage growth strain was relatively low (<0.1%) and was either tensile or compressive depending on the alloy. A higher tensile strain often existed during the initial oxidation period when transition alumina was present. Thermal stresses imposed on NiAl by reducing the sample temperature to 950 C for a period of time showed noticeable stress relaxation by creep. Different degrees of relaxation were also found during cooling depending on alloy composition and scale microstructure. On all Fe-based alloys, the first formed {alpha}-Al{sub 2}O{sub 3} was highly textured with the degree of texture decreasing with further oxidation. The relationships between stress development, scale wrinkling, oxide phase changes, and the effect of reactive element addition on growth stresses are discussed. Results are compared with other reports of growth stresses in Al{sub 2}O{sub 3} scales.

Hou, P.Y.; Paulikas, A.P.; Veal, B.W.

2004-03-23

106

Time-dependent stress concentration and microcrack nucleation in TiAl  

SciTech Connect

Localized stress evolution associated with the interaction of slip or twinning with an interface is treated by means of a superposition of the {open_quotes}internal loading{close_quotes} of a crystalline subsystem by dynamic dislocation pile-up and the stress relaxation by climb of interfacial dislocations. The peak value of a stress concentration factor depends on both the angular function that includes the effect of mode mixity and the ratio of characteristic times for stress relaxation and internal loading. The available experimental data on orientation and strain-rate dependences of interfacial fracture mode in polysynthetically twinned TiAl crystals are discussed in view of the theoretical concepts presented in this paper.

Yoo, M.H.

1995-07-01

107

An investigation of the effects of stress ratio and crack closure on the micromechanisms of fatigue crack growth in Ti-6Al-4V  

SciTech Connect

The effects of positive stress ratios on the fatigue crack growth behavior of a forged, mill-annealed Ti-6Al-4V alloy (with duplex {alpha} + {beta} microstructure) are discussed. Differences between fatigue crack growth rates at low and high stress ratios are shown to be due largely to crack closure. A 1% offset procedure is shown to collapse closure corrected low stress ratio data with the closure-free high stress ratio data. A three parameter multiple regression model is developed for the prediction of the fatigue crack growth rate as a function of stress ratio, crack closure and stress intensity factor range for Ti-6Al-4V. The micromechanisms of fatigue crack growth in the near-threshold and Paris regimes are elucidated via crack tip transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Crack tip TEM shows that Stage II fatigue crack growth in Ti-6Al-4V is crystallographic in nature. Stage II cracks are shown to unzip along intersecting slip bands that are induced as a result of shear localization. The unzipping crack growth mechanism observed in polycrystalline Ti-6Al-4V is shown to be consistent with Neumann`s alternating slip model for the information of striations in single crystals.

Dubey, S.; Soboyejo, A.B.O.; Soboyejo, W.O. [Ohio State Univ., Columbus, OH (United States). Dept. of Materials Science and Engineering

1997-07-01

108

Defect Band Characteristics in Mg-Al and Al-Si High-Pressure Die Castings  

Microsoft Academic Search

Bands of positive macrosegregation and porosity commonly follow the surface contour of components produced by high-pressure\\u000a die casting (HPDC). In this article, Al alloy AlSi7Mg and Mg alloys AZ91 and AM60 were cast into tensile test bars using cold-chamber\\u000a (cc) HPDC. Microstructural characterization revealed that externally solidified crystals (ESCs) are not necessary for defect\\u000a band formation, and that defect bands

C. M. Gourlay; H. I. Laukli; A. K. Dahle

2007-01-01

109

Defect Band Characteristics in Mg-Al and Al-Si High-Pressure Die Castings  

Microsoft Academic Search

Bands of positive macrosegregation and porosity commonly follow the surface contour of components produced by high-pressure die casting (HPDC). In this article, Al alloy AlSi7Mg and Mg alloys AZ91 and AM60 were cast into tensile test bars using cold-chamber (cc) HPDC. Microstructural characterization revealed that externally solidified crystals (ESCs) are not necessary for defect band formation, and that defect bands

C. M. Gourlay; H. I. Laukli; A. K. Dahle

2007-01-01

110

High-speed InGaAlAs\\/InAlAs multiple quantum well optical modulators  

Microsoft Academic Search

High-speed modulation over 22 GHz for waveguided InGaAlAs\\/InAlAs multiple quantum well (MQW) optical modulators is described. A large on\\/off ratio of over 25 dB is demonstrated with a low-drive voltage (6 V) operating in the 1.55-?m wavelength region. The design and characteristics of MQW p-i-n modulators are discussed. The causes of large-insertion loss and the required drive voltage bandwidth figure

Koichi Wakita; Isamu Kotaka; Osamu Mitomi; Hiromitsu Asai; Yuichi Kawamura; Mitsuru Naganuma

1990-01-01

111

High temperature dispersion strengthening of NiAl  

Microsoft Academic Search

A potential high temperature strengthening mechanism for alloys based on the intermetallic compound NiAl has been investigated. This study forms part of an overall program at NASA Lewis Research Center for exploring the potential of alloys based on NiAl for high temperature applications. An alloy containing 2.26 at% Nb and produced by hot extrusion of blended powders has been examined

Mark Sherman; Krishna Vedula

1986-01-01

112

Low-frequency noise measurements of electrical stress in InAlN/GaN and AlGaN/GaN heterostructure field-effect transistors  

NASA Astrophysics Data System (ADS)

We report on the low-frequency noise (LFN) measurements on GaN based heterostructure field-effect transistors (HFETs) on sapphire with InAlN and AlGaN barriers to investigate the effects of electrical stress. The HFETs with InAlN barrier undergone a DC stress at bias conditions of VDS=20V and VG= -4.5 for up to 4 hours in aggregate. These devices exhibited an LFN in the form of 1/f? and a significant increase in the noise spectrum up to 15 dB for 2 hours and then the noise saturated for further stress durations. We also monitored the LFN for the HFETs with AlGaN barriers. The devices were stressed by applying 20V DC drain bias for up to 64 hours at various gate voltages. Stressing at a gate bias (VG) of -2V showed negligible degradation. On the other hand, stressing at VG=0V surprisingly reduced the noise power by about 4 to 15 dB in the frequency range of 1 Hz-100 kHz. Additionally, the InAlN-barrier HFETs exhibited 20-25 dB lower noise power than the ones with the AlGaN layer for the tested devices within the entire frequency range. The results suggest that the trap generation increases due to electrical stress in devices with InAlN barrier, whereas the noise power decreases as a function of stress in AlGaN/GaN HFETs due to an increase in the activation energy of the excess traps.

Kayis, Cemil; Zhu, C. Y.; Wu, Mo; Li, Xing; zgr, mit; Morko, Hadis

2011-02-01

113

Piezospectroscopic Study of Residual Stresses in Al2O3-ZrO2 Directionally Solidified Eutectics  

Microsoft Academic Search

The residual thermoelastic stresses were studied in Al2O3- ZrO2 (monoclinic zirconia, m-ZrO2) and Al2O3-ZrO2(Y2O3) (tetragonal zirconia, t-ZrO2) fibrous eutectics that were pro- duced via the laser floating zone method, using different piezospectrosocopic probes. The luminescence of the R-lines of ruby (Cr31 in Al2O3 phase) was used to determine the stresses in the Al2O3 matrix, assuming that the stress state in

Rosa I. Merino; Victor M. Orera; Javier LLorca

2000-01-01

114

ALS mutant FUS disrupts nuclear localization and sequesters wild-type FUS within cytoplasmic stress granules  

PubMed Central

Mutations in the gene encoding Fused in Sarcoma (FUS) cause amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disorder. FUS is a predominantly nuclear DNA- and RNA-binding protein that is involved in RNA processing. Large FUS-immunoreactive inclusions fill the perikaryon of surviving motor neurons of ALS patients carrying mutations at post-mortem. This sequestration of FUS is predicted to disrupt RNA processing and initiate neurodegeneration. Here, we demonstrate that C-terminal ALS mutations disrupt the nuclear localizing signal (NLS) of FUS resulting in cytoplasmic accumulation in transfected cells and patient fibroblasts. FUS mislocalization is rescued by the addition of the wild-type FUS NLS to mutant proteins. We also show that oxidative stress recruits mutant FUS to cytoplasmic stress granules where it is able to bind and sequester wild-type FUS. While FUS interacts with itself directly by proteinprotein interaction, the recruitment of FUS to stress granules and interaction with PABP are RNA dependent. These findings support a two-hit hypothesis, whereby cytoplasmic mislocalization of FUS protein, followed by cellular stress, contributes to the formation of cytoplasmic aggregates that may sequester FUS, disrupt RNA processing and initiate motor neuron degeneration.

Vance, Caroline; Scotter, Emma L.; Nishimura, Agnes L.; Troakes, Claire; Mitchell, Jacqueline C.; Kathe, Claudia; Urwin, Hazel; Manser, Catherine; Miller, Christopher C.; Hortobagyi, Tibor; Dragunow, Mike; Rogelj, Boris; Shaw, Christopher E.

2013-01-01

115

The transverse stress effect on the critical current of jelly-roll multifilamentary Nb sub 3 Al wires  

SciTech Connect

This paper reports on experiments conducted to determine the effect of transverse compressive stress (TCS) on the critical current of jelly-roll multifilamentary Nb{sub 3}Al wire (0.8-mm dia.) for magnetic flux densities up to 12 T. For comparison, identical experiments were performed for bronze-process Ti-alloyed multifilamentary Nb{sub 3}Sn wire (1.0-mm dia.). Although the unstressed critical current density of Nb{sub 3}Al was inferior to that of (NbTi){sub 3}Sn at high fields, under applied TCS Nb{sub 3}Al exhibited less critical current degradation than (NbTi){sub 3}Sn. For example, at 12 T and 150 MPa, TCS-induced critical current degradation was approximately 20% for Nb{sub 3}Al, whereas it was approximately 65% for (NbTi){sub 3}Sn. There is optimism that Nb{sub 3}Al will evolve into a useful superconductor for large-scale, high-field applications.

Zeritis, D. (Booz-Allen-Hamilton, Bethesda, MD (US)); Iwasa, Y. (Massachusetts Inst. of Tech., Cambridge, MA (United States). Plasma Fusion Center); Ando, T.; Takahashi, Y.; Nishi, M.; Nakajima, H.; Shimanoto, S. (Naka Fusion Research Center, Japan Atomic Energy Research Inst., Naka-machi, Ibaraki-ken 31911 (JP))

1991-03-01

116

Characteristics of MCrAlY coatings sprayed by high velocity oxygen-fuel spraying system  

SciTech Connect

High velocity oxygen-fuel (HVOF) spraying system in open air has been established for producing the coatings that are extremely clean and dense. It is thought that the HVOF sprayed MCrAlY (M is Fe, Ni and/or Co) coatings can be applied to provide resistance against oxidation and corrosion to the hot parts of gas turbines. Also, it is well known that the thicker coating can be sprayed in comparison with any other thermal spraying systems due to improved residual stresses. However, thermal and mechanical properties of HVOF coatings have not been clarified. Especially, the characteristics of residual stress, that are the most important property from the view point of production technique, have not been made clear. In this paper, the mechanical properties of HVOF sprayed MCrAlY coatings were measured in both the case of as-sprayed and heat-treated coatings in comparison with a vacuum plasma sprayed MCrAlY coatings. It was confirmed that the mechanical properties of HVOF sprayed MCrAlY coatings could be improved by a diffusion heat treatment to equate the vacuum plasma sprayed MCrAlY coatings. Also, the residual stress characteristics were analyzed using a deflection measurement technique and a X-ray technique. The residual stress of HVOF coating was reduced by the shot-peening effect comparable to that of a plasma spray system in open air. This phenomena could be explained by the reason that the HVOF sprayed MCrAlY coating was built up by poorly melted particles.

Itoh, Y.; Saitoh, M.; Tamura, M.

2000-01-01

117

Thermal relaxation of residual stresses in shot peened surface layer of (TiB + TiC)\\/Ti6Al4V composite at elevated temperatures  

Microsoft Academic Search

As an effective and important surface treatment method, shot peening can introduce high residual compressive stress and microstructure variation at near surface deformation layers. In this work, residual stresses relaxation behaviors of the shot peened layer of (TiB+TiC)\\/Ti6Al4V composite were investigated during thermal exposure, and the microstrain was calculated according to the integral breadth after isothermal annealing. The microstrain decreased

Lechun Xie; Chuanhai Jiang; Vincent Ji

2011-01-01

118

High-temperature creep of the intermetallic alloy Ni 3 Al  

Microsoft Academic Search

Constant stress creep tests have been conducted on Ni3Al (Hf, B) single crystals in an attempt to characterize the high-temperature creep behavior of this alloy. In contrast to\\u000a intermediate temperature creep behavior, steady-state creep was observed at 1273 K. This extended steady-state region was\\u000a formed in less than 1 pct creep strain and lasted for the duration of the creep

K. J. Hemker; W. D. Nix

1993-01-01

119

High-temperature creep of the intermetallic alloy Ni[sub 3]Al  

Microsoft Academic Search

Constant stress creep tests have been conducted on Ni[sub 3]Al (Hf, B) single crystals in an attempt to characterize the high-temperature creep behavior of this alloy. In contrast to intermediate temperature creep behavior, steady-state creep was observed at 1273 K. This extended steady-state region was formed in less than 1 pct creep strain and lasted for the duration of the

K. J. Hemker; W. D. Nix

1993-01-01

120

High-temperature creep of the intermetallic alloy Ni3Al  

Microsoft Academic Search

Constant stress creep tests have been conducted on Ni3Al (Hf, B) single crystals in an attempt to characterize the high-temperature creep behavior of this alloy. In contrast to intermediate temperature creep behavior, steady-state creep was observed at 1273 K. This extended steady-state region was formed in less than 1 pct creep strain and lasted for the duration of the creep

K. J. Hemker; W. D. Nix

1993-01-01

121

Static High Pressure X-Ray Diffraction of TI-6AL-4V  

SciTech Connect

Ti-6Al-4V was examined under static-high pressure conditions using a diamond anvil cell. The angle-dispersive x-ray diffraction experiments were performed at the Advanced Photon Source, Argonne National Laboratory. Radial and axial geometry were used to examine multiple samples. The purpose of the experiment was to generate pressure-volume data at room temperature (which is non-existent in literature) and to examine deviatoric stress effects on such a hard alloy.

Chesnut, Gary N.; Velisavljevic, Nenad; Sanchez, Lilliana (LANL)

2008-01-10

122

Static high pressure X-ray diffraction of TI-6AL-4V  

SciTech Connect

Ti-6Al-4V was examined under static-high pressure conditions using a diamond anvil cell. The angle-dispersive x-ray diffraction experiments were performed at the Advanced Photon Source, Argonne National Laboratory. Radial and axial geometry were used to examine multiple samples. The purpose of the experiment was to generate pressure-volume data at room temperature (which is non-existent in literature) and to examine deviatoric stress effects on such a hard alloy.

Chesnut, Gary N.; Velisavljevic, Nenad; Sanchez, Lilliana [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

2007-12-12

123

High temperature oxidation behavior of Ti 3AlNb alloys prepared by pulse discharge sintering  

Microsoft Academic Search

Titanium aluminides have received considerable attentions as the basis for new high temperature structural materials. Several compositions based on Ti3AlNb have been developed to achieve specific strength and stress rupture properties which exceed those of Ni base alloys such as INCO 718 over temperature range 823973 K. Recently, pulse discharge sintering (PDS) process technique was successfully developed to manufacture net

Wei Fang; Se-Hyun Ko; Hitoshi Hashimoto; Toshihiko Abe; Yong-Ho Park

2002-01-01

124

Stress corrosion cracking of sensitized AA5083 (Al4.5Mg1.0Mn)  

Microsoft Academic Search

The AA5083 (Al-4.4Mg-0.7Mn-0.15Cr) alloy is a nonheat-treatable aluminum alloy known for its excellent corrosion resistance.\\u000a However, it can become susceptible to intergranular stress corrosion cracking (IGSCC) when exposed to temperatures ranging\\u000a from 50 C to 200 C for sufficient lengths of time. This IGSCC is widely believed to be associated with dissolution of the\\u000a electrochemically active ? phase, Al3Mg2, which

J. L. Searles; P. I. Gouma; R. G. Buchheit

2001-01-01

125

Particle weakening in superplastic SiC/2124 Al composites at high temperature  

SciTech Connect

High-strain-rate superplastic behavior of powder-metallurgy-processed 2124 Al matrix alloy and 10%, 20%, and 30% SiC particulate reinforced 2124 Al composites were investigated over the temperature range from 370 C to 565 C, and the strain rate range from 10{sup {minus}4}/s to 1/s. The true activation energy for the plastic flow after threshold stress compensation was close to that for lattice diffusion in aluminum for the 2124 Al alloy, while the activation energies for the 2124 composites were considerably higher than those for the unreinforced alloy, increasing with an increase in the volume fraction of SiC. The strength of the 2124 Al composites is lower than the strength of the 2124 Al alloy at high temperatures. The strength differential between the unreinforced and reinforced 2124 Al alloys is a function of temperature and is seen to decrease systematically with decrease in temperature and virtually vanishes at 460 C. Particle weakening is discussed in the light of load transfer effect, interphase diffusion, dissolution of second phase particles into matrix and the presence of liquid phase. It is proposed that interphase weakening, possibly with some liquid formation, is the principal factor contributing to the results obtained. Interphase and boundary sliding is believed to be the rate-controlling process in plastic flow of the SiC/2124 Al composites.

Kim, W.J.; Sherby, O.D.

2000-05-11

126

Stress corrosion cracking and hydrogen embrittlement of an AlZnMgCu alloy  

Microsoft Academic Search

The age hardening, stress corrosion cracking (SCC) and hydrogen embrittlement (HE) of an AlZnMgCu 7175 alloy were investigated experimentally. There were two peak-aged states during ageing. For ageing at 413 K, the strength of the second peak-aged state was slightly higher than that of the first one, whereas the SCC susceptibility was lower, indicating that it is possible to heat

R. G. Song; W. Dietzel; B. J. Zhang; W. J. Liu; M. K. Tseng; A. Atrens

2004-01-01

127

Effect of microstructure on stress corrosion cracking of an Al-Zn-Mg-Cu alloy  

Microsoft Academic Search

The susceptibility to stress corrosion cracking (SCC) of the Al-Zn-Mg-Cu French 7010 alloy of different temper has been investigated by Slow Strain Rate Testing. The tests have been carried out at strain rate ranged between 10?5 and 10?7s?1, at corrosion potential and at cathodic polarisation, in NaCl and NaCl + As2O3 solution. The lowest susceptibility to SCC of overaged alloy

M. Puiggali; A. Zielinski; J. M. Olive; E. Renauld; D. Desjardins; M. Cid

1998-01-01

128

Stress corrosion crack velocity and grain boundary precipitates in an Al-Zn-Mg alloy  

Microsoft Academic Search

The fracture kinetics of Al-5.5 Zn-2.5 Mg alloys submersed in 3 pct NaCl-H2O solutions were varied by heat treatment. The steady state velocity, on a plot of velocity vs stress intensity, was compared\\u000a with microstructure and it was found to be inversely proportional to the volume of MgZn2 in the grain boundary. This behavior suggests that grain boundary precipitates can

P. K. Poulose; J. E. Morral; A. J. McEvily

1974-01-01

129

Effect of creep stress on microstructure of a Ni-Cr-W-Al-Ti superalloy  

Microsoft Academic Search

Creep stress changes the morphology and distribution of the precipitates in the precipitation-hardened alloys. It leads to the formation of precipitate free zones (PFZs) near the grain boundaries. From the microstructural observation of the creep tested specimens of a Ni-Cr-W-Al-Ti superalloy, the relation between PFZs and the amount of plastic deformation in the creep-ruptured specimen is established and the validity

Jung-Man Doh; Kyung-Keun Yoo; Hong-Ku Baik; Ju Choi; Sung-Kang Hur

1996-01-01

130

Stress corrosion crack velocity and grain boundary precipitates in an Al-Zn-Mg alloy  

Microsoft Academic Search

The fracture kinetics of Al-5.5 Zn-2.5 Mg alloys submersed in 3 pct NaCl-H2O solutions were varied by heat treatment. The steady state velocity, on a plot of velocity vs stress intensity, was compared with microstructure and it was found to be inversely proportional to the volume of MgZn2 in the grain boundary. This behavior suggests that grain boundary precipitates can

P. K. Poulose; J. E. Morral; A. J. McEvily

1974-01-01

131

Analyses on the Flow Stress of an Al-Mg Alloy During Dynamic Recovery  

NASA Astrophysics Data System (ADS)

A comprehensive analysis on flow stress of a wrought Al-Mg alloy is performed to examine the effect of strain. For this study, hot compression tests were carried at different temperatures and strain rates. Corrections of friction and adiabatic heating effects lead to the true stress-true strain curves in the form of dynamic recovery, which reach to a steady-state condition. After correction, constitutive analysis at a constant strain is carried out using hyperbolic-sine equation. The effect of strain on each constitutive parameter is studied to derive a strain-dependent constitutive equation based on hyperbolic-sine equation. Some of constitutive parameters reach to the constant values at the specific strain values. Also, the relations between Zener-Holloman parameter and steady-state values of strain and stress are achieved. In order to develop a strong and general flow stress equation, stress-strain curves are normalized to their steady-state values, which results in an almost similar normalized stress-strain behavior for all of the studied deformation conditions (i.e., deformations at different temperatures and strain rates).

Mostafaei, M. A.; Kazeminezhad, M.

2013-03-01

132

Fatigue behavior of Fe-48 at.% Al polycrystals with B2 structure at high temperatures  

SciTech Connect

In FeAl alloys with the B2 structure, slip transition from <111> at low temperature to <001> at high temperature occurs depending on crystal orientation, alloying composition and lattice defects such as excess thermal vacancies. The slip transition strongly influences the strength, ductility and fracture mode in these alloys. According to recent results using FeAl single crystals containing a low density of excess thermal vacancies, yield stress increased with increasing temperature showing an anomalous peak between 823 and 873K. The anomalous strengthening peak corresponded to the slip transition: <111> superlattice dislocations were dominantly operative at temperatures below the peak, while <001> dislocations appeared above the peak. In this article, the authors report on the fatigue behavior of an Fe-48at.%Al polycrystalline alloy deformed at high temperatures, focusing on the effect of anomalous strengthening and the transition in slip direction.

Yasuda, H.Y.; Behgozin, A.; Umakoshi, Y. [Osaka Univ., Suita, Osaka (Japan). Dept. of Materials Science and Engineering

1998-12-18

133

Failure mechanisms of silver and aluminum on titanium nitride under high current stress  

Microsoft Academic Search

The effects of high-current stress (310 A) on single-line structures of aluminum (Al) and silver (Ag) of different widths (2.510 ?m) and on titanium nitride (TiN) as barrier are reported in this paper. As the applied current-densities were increased, the lines experienced catastrophic failure. In the cases of Al\\/TiN\\/SiO2 and Ag\\/TiN\\/Si, failure occurred at individual sites that were distributed over

E. Misra; C. Marenco; N. D. Theodore; T. L. Alford

2005-01-01

134

Energy dissipation of highly charged ions on Al oxide films  

Microsoft Academic Search

Slow highly charged ions (HCIs) carry a large amount of potential energy that can be dissipated within femtoseconds upon interaction with a surface. HCI-insulator collisions result in high sputter yields and surface nanofeature creation due to strong coupling between the solid's electronic system and lattice. For HCIs interacting with Al oxide, combined experiments and theory indicate that defect mediated desorption

R. E. Lake; J. M. Pomeroy; C. E. Sosolik

2010-01-01

135

Dislocation bending and tensile stress generation in GaN and AlGaN films  

NASA Astrophysics Data System (ADS)

The growth of GaN and AlGaN films is accompanied by dislocation bending, interaction, density reduction and tensile stress generation to varying degrees. A kinetic model involving outdiffusion of atoms at the growth surface has been adapted to rationalize all of these phenomena using a single platform. Active contribution of dislocation interaction, apart from stress and a surface chemical potential, to the driving force for outdiffusion of atoms from the growth surface has been considered. The kinetic model has then been used to explain stress evolution during growth of GaN films on Si using an AlN buffer layer, an example of a most general case. Stress-thickness relations obtained from the model have been fitted to experimental data to derive basic outdiffusion parameters. These parameters have been used to analyze experimental observations of dislocation structure evolution. The model is able to account for the varying degrees of dislocation bending and interaction observed in these films.

Raghavan, Srinivasan; Manning, Ian C.; Weng, Xiaojun; Redwing, Joan M.

2012-11-01

136

Eigenspannungen in AL2O3: Vergleich von Elektromechanischen Messungen mit Fem-Rechnungen (Residual Stresses in AL2O3: Comparison Between Electromechanical Measurements and Finite Element Method Calculations).  

National Technical Information Service (NTIS)

The thermally induced residual stresses in Al2O3 ceramics after cooling from sintering temperature were investigated. These stresses are due to the temperature difference between the fast cooling edge and the slowly cooling core. The residual stresses wer...

I. Buresch A. Dutschk H. Schubert

1990-01-01

137

Nrf2/ARE Signaling Pathway: Key Mediator in Oxidative Stress and Potential Therapeutic Target in ALS  

PubMed Central

Nrf2 (nuclear erythroid 2-related factor 2) is a basic region leucine-zipper transcription factor which binds to the antioxidant response element (ARE) and thereby regulates the expression of a large battery of genes involved in the cellular antioxidant and anti-inflammatory defence as well as mitochondrial protection. As oxidative stress, inflammation and mitochondrial dysfunctions have been identified as important pathomechanisms in amyotrophic lateral sclerosis (ALS), this signaling cascade has gained interest both with respect to ALS pathogenesis and therapy. Nrf2 and Keap1 expressions are reduced in motor neurons in postmortem ALS tissue. Nrf2-activating compounds have shown therapeutic efficacy in the ALS mouse model and other neurodegenerative disease models. Alterations in Nrf2 and Keap1 expression and dysregulation of the Nrf2/ARE signalling program could contribute to the chronic motor neuron degeneration in ALS and other neurodegenerative diseases. Therefore, Nrf2 emerges as a key neuroprotective molecule in neurodegenerative diseases. Our recent studies strongly support that the Nrf2/ARE signalling pathway is an important mediator of neuroprotection and therefore represents a promising target for development of novel therapies against ALS, Parkinson's disease (PD), Huntington's disease (HD), and Alzheimer's disease (AD).

Petri, Susanne; Korner, Sonja; Kiaei, Mahmoud

2012-01-01

138

High-current and thermal-shock testing of TaSi2-polycide\\/Al-alloy composites  

Microsoft Academic Search

High-current failure levels of TaSi2-polycide\\/Al-alloy bilevel-conductor composites were measured using 10 min increment step-stress tests. Al-alloy metallizations were Al and Al-1 percent Si; polycide and metal linewidths ranged from 2.5 to 3.0 microns; and interlevel-contact sizes ranged from 1.5 to 2.0 sq microns. In all cases, the weak links in the bilevel composite were the interlevel contacts. In units with

T. J. Faith; R. S. Irven; E. P. Bertin

1985-01-01

139

Influence of Al2O3/YSZ micro-laminated coatings on high temperature oxidation and spallation resistance of MCrAlY alloys  

NASA Astrophysics Data System (ADS)

Al2O3/YSZ micro-laminated coatings with different layers were prepared on MCrAlY alloys by magnetron sputtering and characterized by high-resolution field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). Results indicated that the laminated structures of Al2O3 and YSZ layers were observed with compact microstructure and the thickness at sub-micron level each layer. High-temperature cyclic oxidation test at 1000C in air was performed to investigate the oxidation and spallation resistance of the coatings on MCrAlY substrates. Result shows that the coatings exhibit more excellent oxidation and spallation resistance with the increase of the layers, which can be attributed to the increase of stress tolerance and fracture toughness in the laminated coatings by the thinner layers and crack deflection toughening.

Yao, Junqi; He, Yedong; Wang, Deren

2013-03-01

140

On the high-stress region stress exponent during creep  

Microsoft Academic Search

The creep behavior of pure metal and solid solution alloys has been reasonably defined. A power law in the form of ε = A ⁿ usually describes the steady state creep of these materials where the stress exponent n is between 3 to 5. Precipitation hardened alloys, however, creep quite differently. The zinc alloy used contains 1wt%Cu and 0.15wt%Ti which

Z. F. Zhou; B. A. Parker

1995-01-01

141

Energetic-particle synthesis of high-strength Al(O) alloys  

SciTech Connect

High-strength Al(O) alloys, initially discovered by ion implantation, have now been produced with electron-cyclotron resonance plasma deposition and pulsed-laser deposition. The mechanical properties of these deposited alloy layers were examined with nanoindentation, and finite element modeling of the indented layer on Si substrates was used to determine yield stresses for the alloys of {approximately} 1--5 GPa. The key to these high strengths is the high density of nanometer-size {gamma}-Al{sub 2}O{sub 3} precipitates formed when high concentrations (5--30 at.%) of oxygen are introduced into aluminum as individual atoms or molecules. The strongest alloys have precipitates as small as 1 nm, implying that such small precipitates block dislocation motion. Based upon previous studies with oxygen-implanted aluminum, improved tribological properties are expected for layers made by the two new deposition methods.

Follstaedt, D.M.; Knapp, J.A.; Barbour, J.C.; Myers, S.M.; Dugger, M.T.

1995-09-28

142

DEVELOPMENT OF THE ULTRASONIC HIGH TEMPERATURE BOLT STRESS MONITOR  

Microsoft Academic Search

A high temperature bolt stress monitor, based on the testing of the Transit Time of Longitudinal wave and Shear Wave (TTLSW for short) and on the calculation of the stress through the established stress vs TTLSW equation, has been developed and tested. Lithium Niobate was used for piezoelectric material, gold or silver films were used for coupling material and clamping

S.-M. ZHU; J. LU; M.-Z. XIAO; Y.-G. WANG; M.-A. WE

1992-01-01

143

Microstructural effects on ignition sensitivity in Ni/Al systems subjected to high strain rate impacts  

NASA Astrophysics Data System (ADS)

The effect of microstructural refinement on the sensitivity of the Ni/Al (1:1 mol%) system to ignition via high strain rate impacts is investigated. The tested microstructures include compacts of irregularly convoluted lamellar structures with nanometric features created through high-energy ball milling (HEBM) of micron size Ni/Al powders and compacts of nanometric Ni and Al powders. The test materials were subjected to high strain rate impacts through Asay shear experiments powered by a light gas gun. Muzzle velocities up to 1.1 km/s were used. It was found that the nanometric powder exhibited a greater sensitivity to ignition via impact than the HEBM material, despite greater thermal sensitivity of the HEBM. A previously unseen fast reaction mode where the reaction front traveled at the speed of the input stress wave was also observed in the nanometric mixtures at high muzzle energies. This fast mode is considered to be a mechanically induced thermal explosion mode dependent on the magnitude of the traveling stress wave, rather than a self-propagating detonation, since its propagation rate decreases rapidly across the sample. A similar mode is not exhibited by HEBM samples, although local, nonpropagating reaction zones shear bands formed during the impact event are observed.

Reeves, Robert V.; Mukasyan, Alexander S.; Son, Steven

2012-03-01

144

Microstructural effects on ignition sensitivity in Ni/Al systems subjected to high strain rate impacts  

NASA Astrophysics Data System (ADS)

The effect of microstructural refinement on the sensitivity of the Ni/Al (1:1 at%) system to ignition via high strain rate impacts is investigated. The tested microstructures include compacts of irregularly convoluted lamellar structures with nanometric features created through high-energy ball milling (HEBM) of micron size Ni/Al powders and compacts of nanometric Ni and Al powders. The test materials were subjected to high strain rate impacts through Asay shear experiments powered by a light gas gun. Muzzle velocities up to 1.1 km/s were used. It was found that the nanometric powder exhibited a greater sensitivity to ignition via impact than the HEBM material, despite greater thermal sensitivity of the HEBM. A previously unseen fast reaction mode where the reaction front traveled at the speed of the input stress wave was also observed in the nanometric mixtures at high muzzle energies. This fast mode is considered to be a mechanically induced thermal explosion mode dependent on the magnitude of the traveling stress wave, rather than a self-propagating detonation, since its propagation rate decreases rapidly across the sample. A similar mode is not exhibited by HEBM samples, although local, nonpropagating reaction zones occur in shear bands formed during the impact event.

Reeves, Robert; Mukasyan, Alexander; Son, Steven

2011-06-01

145

Structural, microstructural, and residual stress investigations of plasma-sprayed hydroxyapatite on Ti-6Al-4 V.  

PubMed

Plasma-spray (PS) is a classical technique usually employed to cover orthopaedic titanium implant surfaces with hydroxyapatite (HA - Ca(10)(PO(4))(6)(OH)(2)). The objective of the current study is to investigate the structure and microstructure of HA plasma-spray 50 mum thick coating on titanium alloy (Ti-6Al-4 V) and residual stress due to processing in the substrate and in HA coating. The structure of the coatings was determined by high-energy synchrotron X-ray diffraction in energy dispersive (HESXRD), selected area electron diffraction (saed), Scanning Electron Microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). No impurity phases in the HA were identified by HESXRD to keep away from the decomposition of HA at high temperature. hcp phase of HA substrate was detected with slight amorphous background. FTIR spectrum of a HA powder shows a typical spectrum for HA material with the characteristic phosphate peaks for HA at wavenumbers of 1090, 1052, 963, 602, and 573 cm(-1) are present. The morphology of HA powder observed by SEM exhibits grains of ca. 0.1 mum well-adapted for cell proliferation. HA/Ti-6Al-4 V interface observed by cross-section scanning and transmission electron microscopy (TEM) presents microcracks. Residual stresses were analyzed by sin(2) Psi X-ray diffraction method on titanium substrates and HA coating. Although the Ti substrates are in a slightly tensile residual state, the coated ones show a compressive state. PMID:20356205

Carrad, Adele

2010-02-01

146

Intense visible light emission from stress-activated SrMgAl6O11:Eu  

NASA Astrophysics Data System (ADS)

We have investigated deformation luminescence phenomena and the constituent phases of SrMgAl6O11:Eu. The deformation luminescence is clearly visible to the naked eye in air, and the luminescence intensity is the highest among the materials reported. Using x-ray diffraction the constituent phases of SrMgAl6O11:Eu are determined to be SrAl2O4, SrMgAl10O17, and MgAl2O4. The deformation luminescence center has been identified as the Eu2+ ion from the deformation and photoluminescence studies of the three-phase composite. The thermoluminescence glow curve of the composite indicates the trapping levels around room temperature. This result means that the three-phase structure of the composite influences the high deformation luminescence intensity.

Akiyama, Morito; Nishikubo, Keiko; Nonaka, Kazuhiro

2003-07-01

147

Modified Cu-Mn-Al high damping alloys. Technical report  

Microsoft Academic Search

Zirconium and erbium modified Cu-Mn-Al was spray formed in an effort to increase homogeneity and damping capacity and decrease impurity levels. Although the microstructure revealed that the optimum spray forming parameters have not yet been achieved, the modified alloys showed both high damping and resistance to losing that damping over time. The elemental additions also accelerated the formation of alpha

C. R. Wong; R. S. Venkatachalam

1994-01-01

148

Ab initio investigation of thermoelectric properties of AlN nanowires under axial stress  

NASA Astrophysics Data System (ADS)

Small diameter nanowires, down to a few lattice constants, are structurally and electronically different from bulk, due to the large surface-to-volume ratio and the effects of the surface states, which has consequences in the optical absorption and in the electrical/thermal transport. It has been recently established that AlN nanowires can suffer a stress induced phase transition from a wurtzite to a graphite-like phase [1]. The thermopower of atomic-sized wurtzite AlN wires coupled to Al(111) bulk contacts is investigated at low temperatures using Green-Keldysh formalism. We ?nd that the conduction of the wide bandgap semiconductor wire is essentially enhanced by the presence of surface states. We show that the evanescent coupling to the surface states is strong enough to render thermopower of a few tens of micro-V/K, which may be enhanced by controlling the position of the surface states. [2]. We also investigate the changes in the thermopower under applied axial stress, comparatively analyzing the nanowires in the wurtzite and graphite-like configurations. [1] T.L. Mitran, Adela Nicolaev, G.A. Nemnes, L. Ion, S. Antohe, Comput. Mat. Sci. 50, 2955 (2011) [2] G.A. Nemnes, C. Visan, S. Antohe, Physica E 44, 1092 (2012)

Alexandru Nemnes, George; Mitran, Tudor Luca; Nicolaev, Adela; Visan, Camelia; Ion, Lucian; Antohe, Stefan

2013-03-01

149

High-Temperature Thick Al Wire Bonding Technology for High-Power Modules  

NASA Astrophysics Data System (ADS)

In order to enhance the strength of thick Al wire bonds while eliminating damage, we have developed a new high-temperature thick Al wire bonding technology. The 300-?m-diameter Al wires were bonded to Al pads on an insulated gate bipolar transistor (IGBT) chip at varying substrate temperatures and ultrasonic powers. Al wire bonds joined at 423 K with 2.0 W ultrasonic power exhibited high bonding strength compared to those joined at room temperature with 5.0 W power. The main reason for the high bonding strength exhibited by the high-temperature bonding process with low ultrasonic power may be the ease of deformation of Al wires and Al electrode films which results in the enhancement of the true bonded area between Al wires and Al electrode films. We also confirmed that Si damage did not occur during this high temperature bonding process using low ultrasonic power. High-temperature thick Al wire bonding technology is considered to be a promising candidate for the production of reliable IGBT modules.

Komiyama, Takao; Chonan, Yasunori; Onuki, Jin; Koizumi, Masahiko; Shigemura, Tatsuya

2002-08-01

150

The ALS -- A high-brightness XUV synchrotron radiation source  

SciTech Connect

The Advanced Light Source (ALS) at the Lawrence Berkeley Laboratory is scheduled to be operational in the spring of 1993 as a US Department of Energy national user facility. The ALS will be a next-generation source of soft x-ray and ultraviolet (XUV) synchrotron radiation. Undulators will provide high-brightness radiation oat photon energies from below 10 eV to above 2 keV; wiggler and bend-magnet radiation will extend the spectral coverage with high fluxes approaching 20 keV. The ALS will support an extensive research program in which XUV radiation is used to study matter in all its varied gaseous, liquid, and solid forms. the high brightness will open new areas of research from the materials sciences, such as spatially resolved spectroscopy, to the life sciences, such as x-ray microscopy with element-specific sensitivity. Experimental facilities (insertion devices, beamlines, and end stations) will be developed and operated by participating research teams working with the ALS staff. 6 refs., 2 figs., 2 tabs.

Robinson, A.L.; Schlachter, A.S.

1991-05-01

151

Spallation in Ti-6Al-4V: Stress Measurements and Recovery  

SciTech Connect

Previous work by a number of authors has shown that the spall strength of the engineering alloy, Ti 6Al - 4V increases markedly with pulse duration. In this paper, we have reproduced those results in a low oxygen variant of the alloy, over a range of impact stresses. The microstructure consisted of a mixture of primary {alpha} grains in a matrix of transformed {beta}. Samples have also been shock loaded and recovered under conditions of one-dimensional strain, to compliment the results of the stress gauge experiments. In all the recovered samples, complete spallation occurred, but examination of damage at secondary sites showed that this occurred via nucleation and growth of pores. Ductile failure appears to be a mixture of void formation and coalescence within primary {alpha} grains and along primary {alpha} / transformed {beta} boundaries.

Tyler, C.; Bourne, N. K. [University of Manchester, Sackville Street, Manchester, M60 1QD (United Kingdom); Millett, J. C. F. [Defence Academy of the United Kingdom, Cranfield University, Shrivenham, Swindon, SN6 8LA (United Kingdom)

2006-07-28

152

Stress distributions in highly frictional granular heaps  

NASA Astrophysics Data System (ADS)

The practice of storing granular materials in stock piles occurs throughout the world in many industrial situations. As a result, there is much interest in predicting the stress distribution within a stock pile. In 1981, it was suggested from experimental work that the peak force at the base does not occur directly beneath the vertex of the pile, but at some intermediate point resulting in a ring of maximum pressure. With this in mind, any analytical solution pertaining to this problem has the potential to provide useful insight into this phenomenon. Here, we propose to utilize some recently determined exact parametric solutions of the governing equations for the continuum mechanical theory of granular materials for two and three-dimensional stock piles. These solutions are valid provided sin ? = 1, where ? is the angle of internal friction, and we term such materials as ``highly frictional''. We note that there exists materials possessing angles of internal friction around 60 to 65 degrees, resulting in values of sin ? equal to around 0.87 to 0.91. Further, the exact solutions presented here are potentially the leading terms in a perturbation solution for granular materials for which 1- sin ? is close to zero. The model assumes that the stock pile is composed of two regions, namely an inner rigid region and an outer yield region. The exact parametric solution is applied to the outer yield region, and the solution is extended continuously into the inner rigid region. The results presented here extend previous work of the authors to the case of highly frictional granular solids.

Thamwattana, Ngamta; Cox, Grant M.; Hill, James M.

153

Effect of Tensile Deformation and Heat Treatment on the Stress Corrosion Susceptibility of an Al-ZN-Mg Alloy.  

National Technical Information Service (NTIS)

The effect of a series of thermomechanical treatments on the stress corrosion susceptibility of an Al-6.86 w/o Zn-2.35 w/o Mg alloy in a 3.5 percent sodium chloride solution was studied by bent beam type stress corrosion tests. The results indicated that ...

C. R. Shastry M. Levy

1973-01-01

154

Ultrasonic and atomic force studies of the martensitic transformation induced by temperature and uniaxial stress in NiAl alloys  

Microsoft Academic Search

The single-crystal elastic constants were measured in NiAl alloys with nickel compositions between 49.4 and 63 at. %. For Ni compositions in excess of 61 at. %, the crystals undergo a martensitic transformation. The transformation was studied as a function of temperature and uniaxial stress using ultrasonic, optical, and atomic force microscopy techniques. Uniaxial stress applied along the [001] direction

T. Davenport; L. Zhou; J. Trivisonno

1999-01-01

155

Stresses in Selectively Oxidized GaAs/(AlGa){sub x}O{sub y} Structures  

SciTech Connect

Raman scattering spectroscopy is used to study the process of selective oxidation of Al{sub 0.97}Ga{sub 0.03}As layers. Stresses arising in GaAs/(AlGa){sub x}O{sub y} layers as a result of selective oxidation under different conditions are determined. The effects of local heating of the samples with laser radiation during measurements of the Raman signals, photoresist hardening resulting from the oxidation, and overoxidation are analyzed. The instrumentation and method of selective oxidation are optimized; as a result, arrays of vertical-cavity surface-emitting lasers are fabricated. The active region of these lasers is based on two InGaAs quantum wells with top oxidized and bottom semiconductor distributed Bragg reflectors.

Blokhin, S.A.; Smirnov, A.N.; Sakharov, A.V.; Gladyshev, A.G.; Kryzhanovskaya, N.V.; Maleev, N.A.; Zhukov, A.E.; Semenova, E.S.; Bedarev, D.A.; Nikitina, E.V.; Kulagina, M.M.; Maksimov, M.V.; Ledentsov, N.N.; Ustinov, V.M. [Ioffe Physicotechnical Institute, Russian Academy of Sciences, Politekhnicheskaya ul. 26, St. Petersburg, 194021 (Russian Federation)

2005-07-15

156

Very small critical current spreads in Nb\\/Al-AlOx\\/Nb integrated circuits using low-temperature and low-stress ECR PECVD silicon oxide films  

Microsoft Academic Search

We have developed a new Nb\\/Al-AlOx\\/Nb IC process with very small critical current spread. Low-temperature and low-stress ECR (Electron Cyclotron Resonance) PECVD (Plasma Enhanced Chemical Vapor Deposition) silicon oxide films have been used in the Nb IC process for all dielectric insulating layers to replace e-beam evaporated silicon monooxide films and RF reactive sputtered silicon oxide. Since ECR PECVD silicon

Xiaofan Meng; Anupama Bhat; Theodore Van Duzer

1999-01-01

157

Stress relaxation behavior of shot-peened Ti6Al4V under fretting fatigue at elevated temperature  

Microsoft Academic Search

Relaxation behavior of residual stress in a shot-peened titanium alloy, Ti6Al4V subjected to fretting fatigue was investigated at room and elevated temperatures. Constant amplitude fretting fatigue tests were conducted at several maximum stress levels, ?max ranging from 333 to 666MPa with a stress ratio of 0.1. Two heaters, placed at the front and back of specimen, were used to heat

Hyukjae Lee; Shankar Mall

2004-01-01

158

Prediction of flow stress in Ti6Al4V alloy with an equiaxed ? + ? microstructure by artificial neural networks  

Microsoft Academic Search

Flow stress during hot deformation depends mainly on the strain, strain rate and temperature, and shows a complex and nonlinear relationship with them. A number of semi-empirical models were reported by others to predict the flow stress during hot deformation. This work attempts to develop a back-propagation neural network model to predict the flow stress of Ti6Al4V alloy for any

N. S. Reddy; You Hwan Lee; Chan Hee Park; Chong Soo Lee

2008-01-01

159

Implications of tangential shear stress induced failure during transverse loading of SiC/Ti-6Al-4V composites  

SciTech Connect

During transverse loading of fiber-matrix composites, the interface is subjected to both tangential shear stresses and radial stresses. Interface failure in several carbon/carbon-rich coated SiC Ti-6Al-4V composites can occur by tangential shear stresses before the observed non-linearity in the experimental stress-strain curve due to normal interface separation. In this study, the effect of frictional sliding before normal interface separation on the stress redistribution and the stress-strain response of SiC Ti-6Al-4V composites was examined using finite element analysis. The interface was modeled by contact elements with varying coefficients of friction, representing two different types of carbon/carbon-rich composite interfaces. Results indicate that stress redistribution due to tangential shear sliding may significantly modify both interface radial stress distribution and matrix hoop stress. The matrix equivalent stresses, however, are not significantly affected by tangential shear sliding until normal interface separation occurs. A methodology and pertinent plots are provided for determining the stress concentration factor and the normal bond strength of an interface where tangential shear sliding is known to occur. Using this approach, the normal bond strengths for the Trimarc 1/Ti-6Al-4V and the SCS-6/Ti-6Al-4V interfaces were estimated as 40 MPa and 145 MPa, respectively. These values are significantly higher than those calculated without considering frictional sliding. The progression of interface failure under transverse loading and its effects on the stress-strain response is also discussed.

Warrier, S.G.; Majumdar, B.S. [UES, Inc., Dayton, OH (United States); Gundel, D.B. [Systran Corp., Dayton, OH (United States); Miracle, D.B. [Wright Lab. Materials Directorate, Wright-Patterson AFB, OH (United States)

1997-08-01

160

A high-temperature silicon-on-insulator stress sensor  

Microsoft Academic Search

A piezoresistive stress sensor is developed using silicon-on-insulator (SOI) wafers and calibrated for stress measurement for high-temperature applications. The stress sensor consists of silicon-island-like piezoresistor rosettes that are etched on the SOI layer. This eliminates leakage current and enables excellent electrical insulation at high temperature. To compensate for the measurement errors caused by the misalignment of the piezoresistor rosettes with

Zheyao Wang; Kuo Tian; Youzheng Zhou; Liyang Pan; Chaohong Hu; Litian Liu

2008-01-01

161

Lateral gradients of phases, residual stress and hardness in a laser heated Ti0.52Al0.48N coating on hard metal.  

PubMed

The influence of a local thermal treatment on the properties of Ti-Al-N coatings is not understood. In the present work, a Ti0.52Al0.48N coating on a WC-Co substrate was heated with a diode laser up to 900C for 30s and radially symmetric lateral gradients of phases, residual stress and hardness were characterized ex-situ using position-resolved synchrotron X-ray diffraction, Raman spectroscopy, transmission electron microscopy and nanoindentation. The results reveal (i) a residual stress relaxation at the edge of the irradiated area and (ii) a compressive stress increase of few GPa in the irradiated area center due to the Ti-Al-N decomposition, in particular due to the formation of small wurtzite (w) AlN domains. The coating hardness increased from 35 to 47GPa towards the center of the heated spot. In the underlying heated substrate, a residual stress change from about -200 to 500MPa down to a depth of 6?m is observed. Complementary, in-situ high-temperature X-ray diffraction analysis of stresses in a homogeneously heated Ti0.52Al0.48N coating on a WC-Co substrate was performed in the range of 25-1003C. The in-situ experiment revealed the origin of the observed thermally-activated residual stress oscillation across the laser heated spot. Finally, it is demonstrated that the coupling of laser heating to produce lateral thermal gradients and position-resolved experimental techniques opens the possibility to perform fast screening of structure-property relationships in complex materials. PMID:23471140

Bartosik, M; Daniel, R; Zhang, Z; Deluca, M; Ecker, W; Stefenelli, M; Klaus, M; Genzel, C; Mitterer, C; Keckes, J

2012-06-25

162

Highly piezoelectric AlN thin films grown on amorphous, insulating substrates  

SciTech Connect

AlN thin films were grown by reactive sputtering on amorphous SiO{sub 2} thin films. Film texture, x-ray rocking curve width, mechanical stress, and the clamped piezoelectric constant d{sub 33,f} were studied as a function of rf bias power and substrate roughness. A high d{sub 33,f} of 5.0 pm/V was achieved at low substrate roughness and low mechanical AlN film stress. Increasing substrate roughness and stress leads to a deterioration of d{sub 33,f}, which is correlated with a higher density of opposite polarity grains detected by piezoresponse force microscopy. Extrapolating to 100% uniform polarity, a d{sub 33,f} of 6.1 pm/V is derived as highest possible value, probably corresponding to the d{sub 33,f}=e{sub 33}/c{sub 33}{sup E} of perfect single crystalline material. Growth mechanisms are proposed and underlined by high resolution transmission electron microscopy to explain the observed phenomena.

Artieda, Alvaro; Sandu, Cosmin; Muralt, Paul [Laboratoire de Ceramique, Ecole Polytechnique Federale de Lausanne (EPFL), 1015 Lausanne (Switzerland)

2010-05-15

163

Defect Band Characteristics in Mg-Al and Al-Si High-Pressure Die Castings  

NASA Astrophysics Data System (ADS)

Bands of positive macrosegregation and porosity commonly follow the surface contour of components produced by high-pressure die casting (HPDC). In this article, Al alloy AlSi7Mg and Mg alloys AZ91 and AM60 were cast into tensile test bars using cold-chamber (cc) HPDC. Microstructural characterization revealed that externally solidified crystals (ESCs) are not necessary for defect band formation, and that defect bands can form both near to and relatively far from any surface layer of different microstructure. The defect bands were 140 to 240 ?m thick. In addition to defect-band-related macrosegregation, the castings also contained inverse segregation and surface segregation. Defect bands are shown to have the characteristics of the dilatant shear bands reported in past rheology studies, indicating that defect bands form due to strain localization in partially solid material during the HPDC process.

Gourlay, C. M.; Laukli, H. I.; Dahle, A. K.

2007-08-01

164

High temperature deformation behavior of physical vapor deposited Ti-6Al-4V  

SciTech Connect

A detailed study has been conducted of the high temperature creep and microstructural evolution accompanying in the creep deformation of an initially nanocrystalline Ti-6Al-4V alloy. For test temperatures of 600 and 680 C the alloy transformed from an ({alpha} + {alpha}{prime}) to a single phase {alpha} during creep testing and exhibited exceptionally low creep resistance. During testing between 760 and 900 C, the alloy transformed to a conventional ({alpha} + {beta}) microstructure and exhibited up to ten times the creep rates of conventional grain size (super-plastic) Ti-6Al-4V. Creep models based on grain boundary sliding, dislocation and diffusional creep were combined with relationships for phase evolution and grain growth to predict stress-strain rate relationships at each test temperature. The analysis indicates that in the low temperature region dislocation accommodated GBS, in conjunction with diffusional flow, are responsible for creep whilst in the high temperature region diffusion accommodated GBS is the dominant mechanism.

Warren, J.; Hsiung, L.M.; Wadley, H.N.G. [Univ. of Virginia, Charlottesville, VA (United States). Dept. of Materials Science and Engineering

1995-07-01

165

Residual stresses in high-velocity oxy-fuel metallic coatings  

NASA Astrophysics Data System (ADS)

X-ray based residual stress measurements were made on type 316 stainless steel and Fe3Al coatings that were high-velocity oxy-fuel (HVOF) sprayed onto low-carbon and stainless steel substrates. Nominal coating thicknesses varied from 250 to 1500 m. The effect of HVOF spray particle velocity on residual stress and deposition efficiency was assessed by preparing coatings at three different torch chamber pressures. The effect of substrate thickness on residual stress was determined by spraying coatings onto thick (6.4 mm) and thin (1.4 mm) substrates. Residual stresses were compressive for both coating materials and increased in magnitude with spray velocity. For coatings applied to thick substrates, near-surface residual stresses were essentially constant with increasing coating thickness. Differences in thermal expansion coefficient between low-carbon and stainless steels led to a 180 MPa difference in residual stress for Fe3Al coatings. Deposition efficiency for both materials is maximized at an intermediate (600 m/s) velocity. Considerations for X-ray measurement of residual stresses in HVOF coatings are also presented.

Totemeier, T. C.; Wright, R. N.; Swank, W. D.

2004-06-01

166

High-Temperature Creep Degradation of the AM1/NiAlPt/EBPVD YSZ System  

NASA Astrophysics Data System (ADS)

The failure mechanisms of a NiAlPt/electron beam physical vapor deposition yttria-stabilized-zirconia thermal barrier coating system deposited on the AM1 single crystalline substrate have been investigated under pure creep conditions in the temperature range from 1273 K to 1373 K (1000 C to 1100 C) and for durations up to 1000 hours. Doubly tapered specimens were used allowing for the analysis of different stress states and different accumulated viscoplastic strains for a given creep condition. Under such experiments, two kinds of damage mechanisms were observed. Under low applied stress conditions (i.e., long creep tests), microcracking is localized in the vicinity of the thermally grown oxide (TGO). Under high applied stress conditions, an unconventional failure mechanism at the substrate/bond coat interface is observed because of large creep strains and fast creep deformation, hence leading to a limited TGO growth. This unconventional failure mechanism is observed although the interfacial bond coat/top coat TGO thickening is accelerated by the mechanical applied stress beyond a given stress threshold.

Riallant, Fanny; Cormier, Jonathan; Longuet, Arnaud; Milhet, Xavier; Mendez, Jos

2013-08-01

167

Degradation of AlGaN/GaN high electron mobility transistors related to hot electrons  

NASA Astrophysics Data System (ADS)

This paper reports on an extensive analysis of the degradation of AlGaN/GaN high electron mobility transistors (HEMTs) submitted to on-state and off-state stresses. The results of this study indicate that: (i) the analyzed devices do not show any degradation when submitted to off-state stress tests up to 100 V (ii) during on-state stress, devices show a significant decrease in drain current and in the electroluminescence (EL) signal; (iii) degradation rate is strongly dependent on the intensity of the EL signal measured during stress on the devices, which is related to the concentration of hot electrons in the channel. Based on the experimental evidence collected within this paper, the on-state degradation of HEMTs is ascribed to the trapping of negative charge in the gate-drain access region, triggered by hot electrons. By considering the intensity of the EL signal as a measure of the stress acceleration factor, we have derived an acceleration law for the hot-electron induced degradation.

Meneghini, Matteo; Stocco, Antonio; Silvestri, Riccardo; Meneghesso, Gaudenzio; Zanoni, Enrico

2012-06-01

168

High temperature power performance of AlGaN/GaN high-electron-mobility transistors on high-resistivity silicon  

NASA Astrophysics Data System (ADS)

High temperature power performance of AlGaN/GaN high-electron-mobility transistor (HEMT) on high-resistivity-(HR) Si for different microwave frequencies of 3, 6, and 8 GHz was studied. The device output power density (Pout) reduction with temperature for HR-Si-based AlGaN/GaN HEMTs is almost equivalent to the Pout reduction with temperature for semi-insulating-SiC substrate based AlGaN/GaN HEMTs. After high temperature stress, very small degradation was observed in the power performance at 3 GHz. Moreover, the rate of Pout decrease with the temperature is not much affected by measurement frequencies. The conduction mechanism of trap assisted impact ionization and temperature assisted tunneling were identified on Si3N4 passivated AlGaN/GaN HEMTs. The AlGaN/GaN HEMTs on HR-Si can also be used for high-power and high-frequency applications at elevated temperatures.

Arulkumaran, S.; Ng, G. I.; Liu, Z. H.; Lee, C. H.

2007-08-01

169

The Role of PentaCoordinated Al3+ Ions in the High Temperature Phase Transformation of ?-Al2O3  

SciTech Connect

In this work, the structural stability of gamma-alumina (?-Al2O3) was investigated by a combination of XRD and high resolution solid state 27Al MAS NMR at an ultra-high magnetic field of 21.1 tesla. XRD measurements show that ?-Al2O3 undergoes a phase transition to ?-Al2O3 during calcination at 1000oC for 10hr. The formation of the ?-Al2O3 phase is further confirmed by 27Al MAS NMR; additional 27Al peaks centered at 10.5 and ~78 ppm were observed in samples calcined at this high temperature. Both the XRD and NMR results indicate that, after calcination at 1000C for 10 hrs, the ratio of the ?-Al2O3 phase to the total alumina in samples modified by either BaO or La2O3 is significantly reduced in comparison with ?-Al2O3. 27Al MAS NMR spectra revealed that the reduction in the extent of ?-Al2O3 formation was highly correlated with the reduction in the amount of penta-coordinated aluminum ions, measured after 500C calcination, in both BaO- and La2O3-modified ?-Al2O3 samples. These results strongly suggest that the penta-coordinated aluminum ions, present exclusively on the surface of ?-Al2O3, play a critical role in the phase transformation of ?-Al2O3 to ?-Al2O3. The role of the modifiers, in our case BaO or La2O3, is to convert the penta-coordinated aluminum ions into octahedral ones, thereby improving the thermal stabilities of the samples. Oxide additives, on the other hand, had no beneficial effect on preventing the specific surface area reduction that occurred during high temperature (?1000C) calcination.

Kwak, Ja Hun; Hu, Jian Zhi; Lukaski, Adrienne C.; Kim, Do Heui; Szanyi, Janos; Peden, Charles HF

2008-06-26

170

Energy dissipation of highly charged ions on Al oxide films  

NASA Astrophysics Data System (ADS)

Slow highly charged ions (HCIs) carry a large amount of potential energy that can be dissipated within femtoseconds upon interaction with a surface. HCI-insulator collisions result in high sputter yields and surface nanofeature creation due to strong coupling between the solid's electronic system and lattice. For HCIs interacting with Al oxide, combined experiments and theory indicate that defect mediated desorption can explain reasonably well preferential O atom removal and an observed threshold for sputtering due to potential energy. These studies have relied on measuring mass loss on the target substrate or probing craters left after desorption. Our approach is to extract highly charged ions onto the Al oxide barriers of metal-insulator-metal tunnel junctions and measure the increased conductance in a finished device after the irradiated interface is buried under the top metal layer. Such transport measurements constrain dynamic surface processes and provide large sets of statistics concerning the way individual HCI projectiles dissipate their potential energy. Results for Xeq + for q = 32, 40, 44 extracted onto Al oxide films are discussed in terms of postirradiation electrical device characteristics. Future work will elucidate the relationship between potential energy dissipation and tunneling phenomena through HCI modified oxides.

Lake, R. E.; Pomeroy, J. M.; Sosolik, C. E.

2010-03-01

171

High strain rate deformation of NiAl  

SciTech Connect

NiAl is a potential high temperature structural material. Applications for which NiAl is being considered (such as rotating components in jet engines) requires knowledge of mechanical properties over a wide range of strain rates. Single crystal NiAl (stoichiometric and Ni 49.75Al 0.25Fe) has been deformed in compression along [100] at strain rates of 0.001, 0.1/s and 2000/s and temperatures of 76,298 and 773K. <111> slip was observed after 76K testing at a strain rate of 0.001/s and 298K testing at a strain rate of 2000/s. Kinking was observed after deformation at 298K and a strain rate of 0.001/s and sometimes at 298 K and a strain rate of 0.1/s. Strain hardening rates of 8200 and 4000 MPa were observed after 773 and 298K testing respectively, at a strain rate of 2000/s. Results are discussed in reference to resulting dislocation substructure.

Maloy, S.A.; Gray, G.T. III [Los Alamos National Lab., NM (United States); Darolia, R. [General Electric Co., Cincinnati, OH (United States). Aircraft Engines

1994-07-01

172

Reinforcement stresses during deformation of sphere- and particulate-reinforced Al-matrix composites  

SciTech Connect

Recent experimental results showed that reinforcement fracture is very often the dominant damage mechanism during ambient temperature deformation of discontinuously reinforced Al-matrix composites (DRAC). The reinforcements are broken by cracks perpendicular to the loading axis, and the fraction of broken reinforcements increases during plastic deformation as the load transferred from the matrix to the ceramic particulates increases. This process continues until a criteria fraction of broken reinforcements is reached, and then fracture takes place suddenly by a ductile mechanism involving localized necking of the intervoid matrix. The rate of reinforcement fracture depends on the strength of the ceramic reinforcements and on the stresses acting on them, and the modeling of the processes of damage accumulation in DRAC requires the knowledge of both. In particular, the stresses acting on the reinforcements during monotonic tensile deformation are a function of the applied strain, of the matrix and reinforcement properties, and of the volume fraction and shape of the ceramic reinforcements. A parametrical study is presented in this article of the influence of these factors on the stress acting on the reinforcements. The numerical results covered the whole range of matrix strengths which are typical in DRAC and were fitted to simple analytical expressions to facilitate their use by other researchers.

Justice, I. [Oxford Univ. (United Kingdom). Dept. of Materials; Poza, P.; Martinez, J.L.; Llorca, J. [Polytechnic Univ. of Madrid (Spain). Dept. of Materials Science

1996-02-01

173

New AlGaN/GaN High Electron Mobility Transistors Employing Charge Accumulation in Multiple Al2O3/Ga2O3 Stacks  

NASA Astrophysics Data System (ADS)

We have proposed and fabricated new AlGaN/GaN high electron mobility transistors (HEMTs) employing charge accumulation in multiple Al2O3/Ga2O3 stacks by rf-sputtering in order to increase the breakdown voltage and the threshold voltage (VTH). 10-nm-thick rf-sputtered Al2O3/Ga2O3 stacks on the GaN cap, which consist of 2-nm-thick Al2O3 and 2-nm-thick Ga2O3, would induce accumulation of electrons and holes in the stacks on AlGaN/GaN HEMTs. The proposed device achieves the high breakdown voltage of 1104 V while the unpassivated one shows the low breakdown voltage of 380 V. The drain leakage current is considerably suppressed from 654 ?A/mm to 33 nA/mm. The VTH of the proposed device is -1.4 V while that of the conventional device is -2 V due to the accumulated electrons in the multiple Al2O3/Ga2O3 stacks. We have also investigated the charge accumulation phenomena by applying the negative DC stress to the proposed device with and without final SiO2 passivation, respectively.

Seok, Ogyun; Ahn, Woojin; Han, Min-Koo; Ha, Min-Woo

2012-10-01

174

Growth of High Al Concentration AlGaN for Solar Blind Photodetector Applications  

Microsoft Academic Search

The development of a metalorganic chemical vapor deposition growth process for AlxGa1- xN materials with high aluminum composition (x~0.40-0.60) on sapphire substrates is reported. Room temperature Hall measurements of Si-doped AlGaN epilayers with x~0.40 show a narrow window for efficient doping with a carrier concentration of ~1.5x1018 cm-3 and a mobility of ~35 cm2\\/V-s obtained under optimum growth conditions. AlxGa1-xN-based

Shiping Guo; Milan Pophristic; Ian Ferguson; Boris Peres; Phil Lamarre; Steve Tobin; Kwok Wong; Marion Reine; Ashok Sood

175

Through-thickness determination of phase composition and residual stresses in thermall barrier coatings using high- energy x-rays.  

SciTech Connect

High-energy X-rays were used to determine the local phase composition and residual stresses through the thickness of as-sprayed and heat-treated plasma-sprayed thermal barrier coatings consisting of a NiCoCrAlY bond coat and an yttria-stabilized zirconia (YSZ) topcoat produced with through-thickness segmentation cracks. The as-sprayed residual stresses reflected the combined influence of quenching stresses from the plasma spray process, thermal expansion mismatch between the topcoat, bond coat and substrate, and stress relief from the segmentation cracks. Heat treatments led to the formation of a thermally grown oxide (TGO) which was in compression in the plane, as well as relief of quenching stresses and development of a stress gradient in the YSZ topcoat. The high-energy X-ray technique used in this study revealed the effects that TGO and segmentation cracks have on the in-plane stress state of the entire coating.

Weyant, , C. M.; Almer, J. D.; Faber, K. T.; Stony Brook Univ.

2009-01-01

176

High-cycle fatigue of titanium-aluminum-vanadium: Investigation of mean stress sensitivity  

NASA Astrophysics Data System (ADS)

An effort has been made to achieve a better understanding of the mechanisms of fatigue crack initiation and growth that are responsible for anomalous mean stress dependence of fatigue strength in Ti-6Al-4V alloy. The high cycle fatigue properties of Ti-6Al-4V with six different microstructure/texture combinations were investigated. Only material with lamellar microstructure exhibited linear Goodman relationship on the constant fatigue life diagram. Materials with coarse bimodal and equiaxed microstructures had pronounced mean stress sensitivity, with HCF strength at intermediate mean stresses being significantly lower than predicted by Goodman relationship. Cyclic strain tests in strain control mode did not reveal any significant differences in cyclic deformation behavior between the six investigated microstructures. Investigation of fatigue crack initiation process by replication technique showed that in most cases crack first initiates in the alpha grain, resulting in formation of flat alpha facet on the fracture surface. Results of fractography analysis suggest that cleavage plays a role in the fatigue crack initiation and early stages of crack propagation in these materials, and it is argued that crack initiates at the points of localized stress concentration due to the dislocations piling-up at the alpha grains unfavorably oriented for slip. This mechanism is accelerated in Ti-6Al-4V because of the planarity of slip which leads to abnormally low fatigue strength at intermediate mean stresses.

Ivanova, Svetlana Genrievna

177

Comfort food is comforting to those most stressed: Evidence of the chronic stress response network in high stress women  

PubMed Central

Summary Chronically stressed rodents who are allowed to eat calorie-dense comfort food develop greater mesenteric fat, which in turn dampens hypothalamic-pituitary-adrenocortical (HPA) axis activity. We tested whether similar relations exist in humans, at least cross-sectionally. Fifty-nine healthy premenopausal women were exposed to a standard laboratory stressor to examine HPA response to acute stress and underwent diurnal saliva sampling for basal cortisol and response to dexamethasone administration. Based on perceived stress scores, women were divided into extreme quartiles of low vs. high stress categories. We found as hypothesized that the high stress group had significantly greater BMI and sagittal diameter, and reported greater eating after stressful events. In response to acute lab stressor, the high stress group showed a blunted cortisol response, lower diurnal cortisol levels, and greater suppression in response to dexamethasone. These cross-sectional findings support the animal model, which suggests that long-term adaptation to chronic stress in the face of dense calories result in greater visceral fat accumulation (via ingestion of calorie-dense food), which in turn modulates HPA axis response, resulting in lower cortisol levels.

Tomiyama, A. Janet; Dallman, Mary F.; Epel, Elissa S.

2012-01-01

178

Effects of Crystal Orientation on Stress Rupture Behavior of a Ni3Al-BASE Single Crystal Superalloy IC6SX  

NASA Astrophysics Data System (ADS)

The effect of the crystal orientation on the stress rupture behavior of the Ni3Al-base Single Crystal alloy IC6SX under the test condition of 1100C/120Mpa has been studied. The results showed that the stress rupture lives of the specimens with [001], [011] and [111] crystal orientations were 205.45h, 268.6h and 485h, respectively, i.e., the specimen with [111] crystal orientation had the longest stress rupture life. The results of the tests also showed the significant different of high temperature stress rupture elongation and area reduction for different crystal orientation specimens, i.e., the ruptured elongations for the specimens with [001], [011] and [111] crystal orientations were 61.9%, 22.9% and 28.8%, and the values of area reduction for the specimens with [001], [011]and [111] crystal orientations were 11.7%, 12.2%and 7.3% respectively.

Jiang, Liwu; Li, Shusuo; Wu, Meiling; Han, Yafang

179

Simulation of distortion and residual stress in high pressure die casting - modelling and experiments  

NASA Astrophysics Data System (ADS)

Two individual high-pressure die-casting geometries were developed in order to study the influence of process parameters and different alloys on the distortion behaviour of castings. These geometries were a stress lattice and a V-shaped sample tending to form residual stress due to different wall thickness respectively by a deliberate massive gating system. In the experimental castings the influence of the most important process parameters such as die temperature and die opening time and the cooling regime was examined. The time evolution of process temperatures was measured using thermal imaging. The heat transfer coefficients were adapted to the observed temperature distributions. Castings were produced from the two alloys AlSi12 and AlSi10MnMg. The distortion of the castings was measured by means of a tactile measuring device. For the alloy AlSi10MnMg thermo-physical and thermo-mechanical data were obtained using differential scanning calorimetry, laser flash technique, dilatometry and tensile testing at elevated temperatures. These data were used for modelling the material behaviour of the AlSi10MnMg alloy in the numerical model while for the alloy AlSi12(Fe) literature data were used. Process and stress simulation were conducted using the commercial FEM software ANSYS Workbench. A survey on the results of the comparison between simulation and experiment is given for both alloys.

Hofer, P.; Kaschnitz, E.; Schumacher, P.

2012-07-01

180

Design of a High Field Nb3Al Common Coil Magnet  

SciTech Connect

A high field Nb{sub 3}Al common coil magnet is under development as an R&D of 'Advanced Superconducting Magnets for the LHC Luminosity Upgrade', in the framework of the CERN-KEK cooperation program. The goal of this research is to demonstrate the feasibility of high field magnet wound with Nb{sub 3}Al cable. The common coil approach and the shell-based structure were adopted in the design of this magnet. Besides three Nb{sub 3}Al coils, two Nb{sub 3}Sn coils were included to increase the peak field of the whole magnet. The two types of coils were designed with different straight lengths to reduce the peak field of the Nb{sub 3}Sn coils. The peak fields of the Nb{sub 3}Al and Nb{sub 3}Sn coils are 13.1 T and 11.8 T respectively. An aluminum shell together with four aluminum rods applies stress to the coils to overcome the Lorenz force during excitation. Two different support structures for the superconducting coils were introduced in this paper. The development status is also presented.

Xu, Qingjin; Sasaki, Kenichi; Nakamoto, Tatsushi; Terashima, Akio; Tsuchiya, Kiyosumi; Yamamoto, Akira; Kikuchi, Akihiro; Takeuchi, Takao; Sabbi, GianLuca; Caspi, Shlomo; Ferracin, Paolo; Felice, Helene; Hafalia, Ray; Zlobin, Alexander; Barzi, Emauela; Yamada, Ryuji

2009-10-19

181

Regional aspect of highly water-stressed population estimated by world water resources under SRES scenarios  

NASA Astrophysics Data System (ADS)

Global and regional populations lived in highly water-stressed basin for a function of the temperature were estimated using the socio-economical data and the outputs of GCMs. In global, the highly water-stressed population in scenario A2 rapidly increased when the anomaly of temperature is exceeding to about +1.5 deg.. In the case of the scenario A1b, the gradient of increase of highly water-stressed population was less than that in the case of the scenario A2. When the value of temperature anomaly was exceeding to about + 1.5 deg., the gradient of increase of highly water-stressed population became loose. On the other hand, the highly water-stressed population in the scenario B1 decreased when the temperature anomaly was exceeding to about +1.2 deg.. According to the estimation of the highly water-stressed population when the effect of climate change was ignored (that is, runoff was not changed), the highly water-stressed population was almost same. This result implied that it is strongly contributed by not the climate change but the socio- economical factors (ex; an irrigated area, increase of industrial water use, increase of population itself). Parry et al. (2001) pointed out that the influence on the water risk by the climate change is serious when the anomaly of temperature is exceeding to +2 deg.. However, our assessment disagrees with their assignment. When the highly water-stressed population assessment is estimated within the social elements (ex., the increase of irrigation demand, industrial demand, and population itself), the climate change is not so effective. Part of this study was financially supported by the Global Environment Research Fund, "S-4" and "S-5", from the Japanese Ministry of the Environment.

Kiguchi, M.; Shen, Y.; Kanae, S.; Oki, T.

2008-12-01

182

Nanocrystalline Ni-Al ferrites for high frequency applications  

NASA Astrophysics Data System (ADS)

Nanocrystalline Ni0.94Co0.03Mn0.04Cu0.03Fe1.96-xAlxO4(x = 0,0.1,0.3,0.5,0.7and0.9) were synthesized using microwave hydrothermal method at 160C/40 min. The synthesized powders were characterized using XRD, TEM and FTIR. The nanopowders were sintered using microwave sintering method at 950C/30 min. The prepared samples were characterized using XRD and SEM. The substitution of Al3+ ions in place of Fe3+ ions results decrease of the density and lattice constant. The increase in D.C resistivity and reduction in the initial permeability, Ms and TC has been observed with an increase of Al3+ ions. High D.C resistivity, thereby decrease in the dielectric losses and an excellent temperature stability of Magnetization (4?Ms) are desired characteristics of ferrites used for fabrication of microwave devices.

Ramesh, T.; Bharadwaj, S.; Shinde, R. S.; Murthy, S. R.

2013-02-01

183

Fracture in stress engineered, high density, thin film interconnects  

NASA Astrophysics Data System (ADS)

The micro-contact spring is a new technology that is based on physically vapor deposited thin film cantilevers with a purposely-imposed stress gradient through the thickness of the film. These "springs" have the potential to meet the long and near term high-density packaging and probing challenges, as outlined by the International Technology Roadmap for Semiconductors. The success of this technology is, in part, dependent on the ability to create springs that are reliable against interfacial fracture during fabrication, microelectronic probing, and microelectronic packaging applications. Through this research, a framework to understand the interfacial integrity of thin film cantilevers under monotonic and cyclic loading has been established. This research has developed a modified decohesion test (MDT) that eliminates the shortcomings of current interfacial fracture toughness measurement methods for thin film interfaces. This highly flexible and robust test gives tight bounds on the fracture toughness using a single sample, generates any mode mix, creates an interface representative of microelectronic or MEMS applications, and remains in the linear elastic fracture mechanics regime. The MDT was applied to investigate the interfacial fracture toughness of two material systems relevant to micro-contact spring applications: titanium/silicon and titanium/Al 2O3. A von Karman Plate Theory (VKPT) based analytical method was applied and further enhanced in this research to analytically model the large, nonlinear behavior of intrinsically stressed, thin film, cantilever strips. The multilayer analytical approach, based on simply supported plates, was shown to predict the energy release rate of cantilevered strips during monotonic fracture remarkably well and showed the importance of bifurcation of curvature in understanding the nonlinear behavior of intrinsically stressed thin film cantilever plates. A framework for numerical modeling of micro-contact springs in fabrication, packaging, and probing applications was developed in this research. Based on the these models, the VKPT analytical framework, and the interfacial fracture toughness measured through the MDT, comprehensive design guidelines were established to achieve micro-contact spring fabrication design goals and ensure continuing reliability in subsequent probing and free-air packaging applications.

Modi, Mitul Bharat

184

First-principles characterization of the anisotropy of theoretical strength and the stress-strain relation for a TiAl intermetallic compound.  

PubMed

We perform first-principles computational tensile and compressive tests (FPCTT and FPCCT) to investigate the intrinsic bonding and mechanical properties of a ?-TiAl intermetallic compound (L 1(0) structure) using a first-principles total energy method. We found that the stress-strain relations and the corresponding theoretical tensile strengths exhibit strong anisotropy in the [001], [100] and [110] crystalline directions, originating from the structural anisotropy of ?-TiAl. Thus, ?-TiAl is a representative intermetallic compound that includes three totally different stress-strain modes. We demonstrate that all the structure transitions in the FPCTT and FPCCT result from the breakage or formation of bonds, and this can be generalized to all the structural transitions. Furthermore, based on the calculations we qualitatively show that the Ti-Al bond should be stronger than the Ti-Ti bond in ?-TiAl. Our results provide a useful reference for understanding the intrinsic bonding and mechanical properties of ?-TiAl as a high-temperature structural material. PMID:21825422

Zhou, Hong-Bo; Zhang, Ying; Liu, Yue-Lin; Kohyama, Masanori; Yin, Peng-Gang; Lu, Guang-Hong

2009-03-30

185

Quantitative spectroscopic strain analysis of AlGaAs-based high-power diode laser devices  

NASA Astrophysics Data System (ADS)

Results of quantitative spectroscopic analysis of packaging-induced strain in In{0.06}Ga{0.86}Al{0.08}As/Ga{0.7}Al{0.3}As/GaAs high-power `cm-bars' diode laser arrays are presented. Theoretically, the influence on the results of particular device structure properties, such as intrinsic strain, is analyzed. We compare these theoretical results, which are based on a unaxial stress model, with photocurrent data. For In-soldered devices on copper heatsinks, we find a strain difference of (0.050 0.015)% between edge and center of the device. Almost complete strain-relaxation toward the device edges is experimentally demonstrated. The general approach is also applicable to the analysis of all data that refer to changes of the electronic bandstructure, such as absorption and photoluminescence.

Tomm, J. W.; Gerhardt, A.; Biermann, M. L.; Holland, J. P.

2004-07-01

186

Characterization of AlGaN layer with high Al content grown by mixed-source HVPE  

Microsoft Academic Search

Using mixed-source hydride vapor-phase epitaxy (HVPE), an AlGaN layer with high Al content on GaN\\/Al2O3 substrate is obtained. The AlGaN layer grown by mixed-source HVPE is characterized by X-ray diffraction (XRD) measurements and cathodoluminescence (CL) spectra. In the mixed-source HVPE technique, the AlGaN material is compounded from the chemical reaction between NH3 and an aluminum-gallium chloride formed using HCl that

H. S. Ahn; K. H. Kim; M. Yang; J. Y. Yi; H. J. Lee; J. H. Chang; H. S. Kim; S. W. Kim; S. C. Lee; Y. Honda; M. Yamaguchi; N. Sawaki

2005-01-01

187

Alleviating Stress in Parents of High-Risk Preterm Infants.  

ERIC Educational Resources Information Center

|Possible sources of stress for parents of preterm high-risk infants are reviewed from a research perspective. Stages of parental attachment to their premature baby are spelled out. Strategies for special education teachers to use in alleviating parental stress are described. (JDD)|

Lowenthal, Barbara

1989-01-01

188

Stress Corrosion Crack Branching in High-Strength Steels.  

National Technical Information Service (NTIS)

The criteria for stress corrosion crack branching in high-strength steels are shown to be (1) a constant crack velocity and (2) attainment of a critical stress intensity K sub Ib. For the steels investigated, values of K sub Ib/K sub Iscc range from 2 to ...

C. S. Carter

1969-01-01

189

Preparation of TiAl3-Al Composite Coating by Cold Spray and Its High Temperature Oxidation Behavior  

NASA Astrophysics Data System (ADS)

A novel TiAl3-Al coating was prepared by cold spray for high temperature protection of titanium aluminum-based alloy. The substrate alloy was orthorhombic-Ti-22Al-26Nb (at.%). The composite coating was mainly composed of TiAl3 embedded in the matrix of residual aluminum. An interlayer about 10 ?m was formed between the coating and the substrate. The oxidation test indicated that this composite coating was very effective in improving the high-temperature oxidation resistance of the substrate alloy at 950 C in the tested 150 cycles without any sign of degradation. The microstructure analysis of the oxidized composite coating showed that an Al2O3 scale with a complex structure can be formed outside the interlayer during oxidation and no oxides beneath the interlayer were detected, which indicated that the complex continuous Al2O3 and the interlayer provide the protection of the substrate at high-temperature oxidation condition.

Kong, L. Y.; Shen, L.; Lu, B.; Yang, R.; Cui, X. Y.; Li, T. F.; Xiong, T. Y.

2010-12-01

190

High sea-floor stress induced by extreme hurricane waves  

NASA Astrophysics Data System (ADS)

Strong surface waves and currents generated by major hurricanes can produce extreme forces at the seabed that scour the seafloor and cause massive underwater mudslides. Our understanding of these forces is poor due to lack of concurrent measurements of waves and currents under these storms. Using unique observations collected during the passage of a category-4 hurricane, Ivan, bottom stress due to currents and waves over the outer continental shelf in the Gulf of Mexico was examined. During the passage of Ivan, the bottom stress was highly correlated with the wind with a maximum of about 40% of the wind stress. The bottom stress was dominated by the wave-induced stresses, and exceeded critical levels at depths as large as 90 m. Surprisingly, the bottom damaging stress persisted after the passage of Ivan for about a week, and was modulated by near-inertial waves.

Wijesekera, Hemantha W.; Wang, David W.; Teague, William J.; Jarosz, Ewa

2010-06-01

191

Phase-stress partition during uniaxial tensile loading of a TiC-particulate-reinforced Al composite  

SciTech Connect

Using neutron diffraction, the authors measured during in situ loading the lattice elastic mean phase (LEMP) strains in the matrix and reinforcement of a 15 vol pct TiC-particulate-reinforced 2219 Al composite. From the strain components longitudinal to and transverse to loading, the in situ normal phase stresses (average normal stresses in the constituent phases) were obtained through Hooke`s law. The internal stress partition between the matrix and reinforcement, i.e., load sharing, can then be inferred. Internal stress development was also modeled using the finite-element method (FEM), showing good agreement with the experimental results. Both indicate that the relationship between the LEMP strains/phase stresses and the applied load noticeably deviates from linearity during composite microyielding, long before the nominal 0.2 pct proof stress is reached. The nonlinearity arises (despite the linear elastic relationship between phase stresses and LEMP strains) because the applied traction is not synonymous with the phase stresses, and the ratio of phase stresses may vary during loading. Notably, the morphology of the LEMP strain development with applied load differs in the directions parallel to or perpendicular to the load. The differences are explained by considering the evolution of local matrix plasticity. Thermal residual stresses and inelastic stress relaxation, driven by interfacial diffusion, are also discussed.

Shi, N.; Bourke, M.A.M.; Roberts, J.A. [Los Alamos National Lab., NM (United States); Allison, J.E. [Ford Motor Co., Dearborn, MI (United States). Scientific Research Lab.

1997-12-01

192

Phase transitions of LiAlO{sub 2} at high pressure and high temperature  

SciTech Connect

This work presents a comprehensive study on phase transitions in LiAlO{sub 2} system at high pressures and temperatures (0.5-5.0 GPa and 300-1873 K, respectively), as well as the phase stability for polymeric phases of LiAlO{sub 2} in the studied P-T space by X-ray diffraction (XRD). Besides the previously described polymorphic hexagonal {alpha}-phase, orthorhombic {beta}-phase and tetragonal {delta}-phase, a possible new phase of LiAlO{sub 2} was observed after the tetragonal {gamma}-LiAlO{sub 2} sample was treated at 5.0 GPa and 389 K. The stable regimes of these high-pressure phases were defined through the observation of coexistence points of the polymeric phases. Our results revealed that LiAlO{sub 2} could experience structural phase transitions from {gamma}-LiAlO{sub 2} to its polymorphs at lower pressures and temperatures compared to the reported results. Hexagonal {alpha}-LiAlO{sub 2} with highly (003) preferential orientation was prepared at 5.0 GPa and 1873 K. - Graphical abstract: Constructing the pressure-temperature phase diagram for LiAlO{sub 2}.

Lei Li [Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China); He Duanwei [Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China)], E-mail: duanweihe@yahoo.com; Zou Yongtao; Zhang Wei; Wang Zhao [Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China); Jiang Ming; Du Maolu [Department of Electrical and Information Engineering, Southwest University for Nationalities, Chengdu 610041 (China)

2008-08-15

193

High temperature electron transport properties of AlGaN/GaN heterostructures with different Al-contents  

NASA Astrophysics Data System (ADS)

Electron transport properties in AlGaN/GaN heterostructures with different Al-contents have been investigated from room temperature up to 680 K. The temperature dependencies of electron mobility have been systematically measured for the samples. The electron mobility at 680 K were measured as 154 and 182 cm2/Vs for Al0.15Ga0.85N/GaN and Al0.40Ga0.60N/GaN heterostructures, respectively. It was found that the electron mobility of low Al-content Al0.15Ga0.85N/GaN heterostructure was less than that of high Al-content Al0.40Ga0.60N/GaN heterostructure at high temperature of 680 K, which is different from that at room temperature. Detailed analysis showed that electron occupations in the first subband were 75% and 82% at 700 K for Al0.15Ga0.85N/GaN and Al0.40Ga0.60N/GaN heterostructures, respectively, and the two dimensional gas (2DEG) ratios in the whole electron system were 30% and near 60%, respectively. That indicated the 2DEG was better confined in the well, and was still dominant in the whole electron system for higher Al-content AlGaN/GaN heterostructure at 700 K, while lower one was not. Thus it had a higher electron mobility. So a higher Al-content AlGaN/GaN heterostructure is more suitable for high-temperature applications.

Zhang, Zhongfen; Zhang, Jincheng; Xu, Zhihao; Duan, Huantao; Hao, Yue

2009-12-01

194

Comfort food is comforting to those most stressed: evidence of the chronic stress response network in high stress women.  

PubMed

Chronically stressed rodents who are allowed to eat calorie-dense "comfort" food develop greater mesenteric fat, which in turn dampens hypothalamic-pituitary-adrenocortical (HPA) axis activity. We tested whether similar relations exist in humans, at least cross-sectionally. Fifty-nine healthy premenopausal women were exposed to a standard laboratory stressor to examine HPA response to acute stress and underwent diurnal saliva sampling for basal cortisol and response to dexamethasone administration. Based on perceived stress scores, women were divided into extreme quartiles of low versus high stress categories. We found as hypothesized that the high stress group had significantly greater BMI and sagittal diameter, and reported greater emotional eating. In response to acute lab stressor, the high stress group showed a blunted cortisol response, lower diurnal cortisol levels, and greater suppression in response to dexamethasone. These cross-sectional findings support the animal model, which suggests that long-term adaptation to chronic stress in the face of dense calories result in greater visceral fat accumulation (via ingestion of calorie-dense food), which in turn modulates HPA axis response, resulting in lower cortisol levels. PMID:21906885

Tomiyama, A Janet; Dallman, Mary F; Epel, Elissa S

2011-09-08

195

Residual stresses in Al[sub 2]O[sub 3]-ZrO[sub 2] composites: A test of stochastic stress models  

SciTech Connect

In cooling sintered composites of Al[sub 2]O[sub 3]-ZrO[sub 2] from their fabrication temperature residual stresses are created as a result of both the difference in thermal expansion between the two phases and the crystallographically anisotropic thermal expansion of the Al[sub 2]O[sub 3] phase. In this work the first and second moments of the residual stress distribution have been measured as a function of volume fraction of zirconia from 0.01 to 0.90. The measurement technique used is piezo-spectroscopy based on the optical fluorescence from Cr[sup 3+] dopants in the alumina phase. For zirconia volume fractions up to 0.35 the average stress accurately fits the predictions given by the upper Hashin bound and this fit provides a value of the average thermal strain in the composites. Using this value, the effective medium approximation produces an excellent description of the average stress over the entire volume fraction. It is shown that the fluorescence broadening due to stress fluctuations lies close to the predicted upper and lower Hashin bounds modified by the restrictions imposed by the principle of maximum entropy. The measured moments and those predicted by stochastic stress analysis compare well suggesting that the stochastic analysis provides a reliable method of calculating residual stress in composites.

Ma, Qing; Clarke, D.R. (Univ. of California, Santa Barbara, CA (United States). Materials Dept.); Pompe, W. (Technical Univ. of Dresden (Germany). Materials Science Dept.); French, J.D. (National Inst. of Standards and Technology, Gaithersburg, MD (United States). Ceramics Div.)

1994-05-01

196

Yield Strength of Transparent MgAl2O4 Nano-Ceramic at High Pressure and Temperature  

PubMed Central

We report here experimental results of yield strength and stress relaxation measurements of transparent MgAl2O4 nano-ceramics at high pressure and temperature. During compression at ambient temperature, the differential strain deduced from peak broadening increased significantly with pressure up to 2 GPa, with no clear indication of strain saturation. However, by then, warming the sample above 400C under 4 GPa, stress relaxation was obviously observed, and all subsequent plastic deformation cycles are characterized again by peak broadening. Our results reveal a remarkable reduction in yield strength as the sintering temperature increases from 400 to 900C. The low temperature for the onset of stress relaxation has attracted attention regarding the performance of transparent MgAl2O4 nano-ceramics as an engineering material.

2010-01-01

197

Yield Strength of Transparent MgAl2O4 Nano-Ceramic at High Pressure and Temperature.  

PubMed

We report here experimental results of yield strength and stress relaxation measurements of transparent MgAl2O4 nano-ceramics at high pressure and temperature. During compression at ambient temperature, the differential strain deduced from peak broadening increased significantly with pressure up to 2 GPa, with no clear indication of strain saturation. However, by then, warming the sample above 400C under 4 GPa, stress relaxation was obviously observed, and all subsequent plastic deformation cycles are characterized again by peak broadening. Our results reveal a remarkable reduction in yield strength as the sintering temperature increases from 400 to 900C. The low temperature for the onset of stress relaxation has attracted attention regarding the performance of transparent MgAl2O4 nano-ceramics as an engineering material. PMID:20676198

Zhang, Jie; Lu, Tiecheng; Chang, Xianghui; Jiang, Shengli; Wei, Nian; Qi, Jianqi

2010-05-23

198

The stress and spalling behavior of the oxide scale formed on polycrystalline Ni{sub 3}Al  

SciTech Connect

The residual stress in the oxide scale formed on polycrystalline Ni{sub 3}Al in air in the range of 900--1,200 C was determined at room temperature using optical fluorescence piezospectroscopy. The stress was found to be almost independent of time or temperature of oxidation. In contrast, the spalling behavior was strongly dependent on the oxidation temperature, not occurring below 1,100 C and profusely at 1,200 C. In the intermediate temperature regime ({approximately}1,100 C), spallation of the oxide scale occurred preferentially in the vicinity of grain boundaries in the Ni{sub 3}Al. This is attributed to a buckling instability driven by the residual thermal mismatch stress and induced by both void formation and a non-planar interface structure resulting from preferential diffusion along the Ni{sub 3}Al grain boundaries.

Christensen, R.J.; Lipkin, D.M.; Clarke, D.R. [Univ. of California, Santa Barbara, CA (United States)

1996-09-01

199

High pressure X-ray diffraction study of LaAl2 and LaAl3  

NASA Astrophysics Data System (ADS)

LaAl2 and LaAl3 exhibit MgCu2 type (space group Fd3m) and Ni3Sn type (space group P63/mmc) structures, respectively, at NTP. High pressure X-ray diffraction studies on these two systems are carried out up to ~35 and ~30GPa, respectively, with a diamond anvil cell, mounted on a high precision Guinier diffractometer. The volume compression determined at the highest pressures are about 33% for LaAl2 and 23% for LaAl3. Neither compound shows any structural transition.

Sekar, M.; Chandra Shekar, N. V.; Sahu, P. Ch.; Sanjay Kumar, N. R.; Rajan, K. Govinda

2002-11-01

200

Optical Stress Gauge Development for Very High Stresses Piezoraman Measurements and Analysis.  

National Technical Information Service (NTIS)

Experiments and analyses were carried out to demonstrate the use of diamond crystals as very high stress, optical transducers under shock loading. Experimental methods were developed to routinely permit time-resolved measurements (10 ns resolution) of str...

Y. M. Gupta

1995-01-01

201

Life expectancy of modular Ti6Al4V hip implants: influence of stress and environment.  

PubMed

Stress dependent electrochemical dissolution is identified as one of the key mechanisms governing surface degradation in fretting and crevice corrosion of biomedical implants. The present study focuses on delineating the roles of mechanical stress and chemical conditions on the life expectancy of modular hip implants. First, material removal on a stressed surface of Ti6Al4V subjected to single asperity contact is investigated experimentally to identify the influence of contact load, in-plane stress and chemical environment on mean wear rates. A range of known stress levels are applied to the specimen while its surface is mechanically stimulated in different non-reactive to oxidizing aqueous environments. Evolution of surface degradation is monitored, and its mechanism is elucidated. This phase allows estimation of Preston Constant which is later used in the analysis. Second phase of the work is semi-analytical and computational, where, based on the estimated Preston constant and other material and process parameters, the scratch propensity (consisting of magnitude of scratch depth and their frequency per unit area) due to micro-motion in modular hip implants is estimated. The third phase views these scratches as initial notches and utilizes a mixed-mode fatigue crack propagation model to estimate the critical crack length for onset of instability. The number of loading cycles needed to reach this critical crack length is then labeled as the expected life of the implant under given mechanical and chemical conditions. Implications of different material and process conditions to life expectancy of orthopedic implants are discussed. It is observed that transverse micro-motion, compared to longitudinal micro-motion, plays a far more critical role in determining the implant life. Patient body weight, as well as proximity of the joint fluid to its iso-electric point play key roles in determining wear rates and associated life expectancies of modular hip implants. Sustained aeration of joint fluid, as well as proper tolerancing of mating surfaces, along with a proper choice of material microstructure may be utilized to extend implant life. PMID:22098898

Chandra, A; Ryu, J J; Karra, P; Shrotriya, P; Tvergaard, V; Gaisser, M; Weik, T

2011-07-03

202

Career and College Prepardness and Stress Among High School Seniors  

Microsoft Academic Search

A study of career and college preparedness and stress among high school seniors was done by a counselor education graduate student. A survey was given to 100 high school students, at least 18 years of age, at a high school in upstate New York. The results were collected and discussed. Some major areas of concerns among the high school seniors

Melissa Gilyardi

2006-01-01

203

Synchrotron XRD study of residual stress in a shot peened Al\\/SiC p composite  

Microsoft Academic Search

In the present study, residual strain profiles in shot peened specimens of 2124-T4 aluminium alloy matrix composite reinforced with 17vol% particulate silicon carbide (SiCp) were measured by means of synchrotron-based diffraction using monochromatic, high energy X-ray beams. The stress state was considered in relation with the microstructural and morphological modifications induced in the material by shot peening. Strain-induced changes in

Fabio Rotundo; Alexander M. Korsunsky

2009-01-01

204

High Stress Responsivity Predicts Later Blood Pressure Only in Combination With Positive Family History and High Life Stress  

Microsoft Academic Search

High cardiovascular responsivity to stressors has not consistently improved prediction of later blood pressure increases beyond the predictive effects of baseline pressure. Animal models suggest that genetic susceptibility to hypertension and frequent stress exposure are important modulating factors in stress-related hypertension. Thus in 103 men originally tested at age 18 to 22 years and reassessed 10 years later, interactive effects

Kathleen C. Light; Susan S. Girdler; Andrew Sherwood; Edith E. Bragdon; Kimberly A. Brownley; Sheila G. West; Alan L. Hinderliter

205

Effect of buffer structures on AlGaN/GaN high electron mobility transistor reliability  

SciTech Connect

AlGaN/GaN high electron mobility transistors (HEMTs) with three different types of buffer layers, including a GaN/AlGaN composite layer, or 1 or 2 lm GaN thick layers, were fabricated and their reliability compared. The HEMTs with the thick GaN buffer layer showed the lowest critical voltage (Vcri) during off-state drain step-stress, but this was increased by around 50% and 100% for devices with the composite AlGaN/GaN buffer layers or thinner GaN buffers, respectively. The Voff - state for HEMTs with thin GaN and composite buffers were 100 V, however, this degraded to 50 60V for devices with thick GaN buffers due to the difference in peak electric field near the gate edge. A similar trend was observed in the isolation breakdown voltage measurements, with the highest Viso achieved based on thin GaN or composite buffer designs (600 700 V), while a much smaller Viso of 200V was measured on HEMTs with the thick GaN buffer layers. These results demonstrate the strong influence of buffer structure and defect density on AlGaN/GaN HEMT performance and reliability.

Liu, L. [University of Florida, Gainesville; Xi, Y. Y. [University of Florida, Gainesville; Ren, F. [University of Florida; Pearton, S. J. [University of Florida; Laboutin, O. [Kopin Corporation, Taunton, MA; Cao, Yu [Kopin Corporation, Taunton, MA; Johnson, Wayne J. [Kopin Corporation, Taunton, MA; Kravchenko, Ivan I [ORNL

2012-01-01

206

Behavior of High-Strength Concrete Under Sustained Compressive Stress.  

National Technical Information Service (NTIS)

The behavior of plain high-strength concrete subjected to sustained compressive stress is reported. Time-dependent deformational and strength characteristics were investigated. A direct comparison was made to the behavior of normal-strength concrete subje...

A. S. Ngab

1980-01-01

207

Observation of stress-induced voiding with an ultra-high voltage electron microscope  

Microsoft Academic Search

An investigation of stress-induced voiding at temperatures 400 to 500 degrees C in passivated Al metallizations (0.5 by 1 mu m wide) with a bamboo grain structure by ultra-high voltage (2 MV) electron microscopy is discussed. Emphasis is placed on the study of nucleation and growth of voids. Conventional and in situ observations of initial stages of voiding indicate that

A. Tanikawa; H. Okabayashi; H. Mori; H. Fujita

1990-01-01

208

Effects of fretting fatigue on the residual stress of shot peened Ti6Al4V samples  

Microsoft Academic Search

X-ray diffraction residual stress measurement has been utilized as nondestructive tool for the characterization of fretting fatigue damage in shot peened samples of Ti6Al4V. Prior to fretting fatigue damage, compressive residual stresses were found to be uniform over the entire face of the sample and independent of the measurement direction. After fretting fatigue, inside and in the vicinity of the

S. A. Martinez; S. Sathish; M. P. Blodgett; S. Mall; S. Namjoshi

2005-01-01

209

High-temperature plastic behaviour of Al 2O 3Y 3Al 5O 12 directionally solidified eutectics  

Microsoft Academic Search

Al2O3Y3Al5O12 eutectic rods grown by the laser floating zone method at 25, 350 and 750mm\\/h have been studied by means of constant strain rate and constant stress compressive tests. Creep exponents were in the range n?1.93, and the activation energy was 72020kJ\\/mol for rods grown at 350mm\\/h. The experimental results indicate that to explain creep behaviour in these materials the

J. Ramrez-Rico; A. R. Pinto-Gmez; J. Martnez-Fernndez; A. R. de Arellano-Lpez; P. B. Oliete; J. I. Pea; V. M. Orera

2006-01-01

210

Probe-hole drilling: High-stress detection in coal  

Microsoft Academic Search

Coal mine bounces and bursts are major problems facing U.S. mine operators. Bounces and bursts have the potential to inflict severe injury on mining personnel, damage equipment, and cause mine closures. High-stress conditions, at or near the working face, are the common denominator in the burst problem. If mine operators can locate high-stress and potentially burst-prone zones, they can then

J. P. McDonnell; K. Y. Haramy

1988-01-01

211

Thermal-stress effect in the high-latitude ionosphere  

Microsoft Academic Search

The contribution of heat-flux gradients to the viscosity tensor of the ionospheric plasma (i.e., the thermal-stress effect) is analyzed. It is shown that this effect is manifested most strongly in structures with high ion temperature and low plasma concentration, which are observed in high-latitude ionization troughs. Experimental results indicate that the thermal-stress effect makes a significant contribution to the plasma-pressure

Iu. V. Konikov

1991-01-01

212

Highly Accelerated Temperature and Humidity Stress Test Technique (HAST)  

Microsoft Academic Search

A method for highly accelerated bias-temperature humidity stress testing is described. This method allows testing in the regime 100C\\/175C and 50% R.H.\\/85% R.H. Experimental results which demonstrate invariance of corrosion failure modes and lognormal sigmas under different high temperature-humidity conditions are presented. Acceleration factors relative to 85C\\/81% R.H. and 60C\\/81% R.H. stress tests are given.

Jeffrey E. Gunn; Sushil K. Malik; Purabi M. Mazumdar

1981-01-01

213

Stress sensing performance using mechanoluminescence of SrAl2O4:Eu (SAOE) and SrAl2O4:Eu, Dy (SAOED) under mechanical loadings  

NASA Astrophysics Data System (ADS)

In this paper, the stress sensing performance of two well-known mechanoluminescence (ML) sensing materials, (1) SrAl2O4:Eu (SAOE) and (2) SrAl2O4:Eu, Dy (SAOED), has been experimentally studied. Under the same input loadings and strain rates, changes of the light intensity have been characterized in terms of sensitivity, repeatability and linearity. Effects of the strain rate on the light intensity changes have also been investigated for both ML sensing materials. SAOED appears to perform better as an ML stress sensor than SAOE because it shows higher sensitivity and no saturation of light during the loading history. Although SAOE showed saturation of light emissions, its initial sensitivity to loading was higher than that of SAOED. Therefore, SAOE appears to be more suitable for sensors for monitoring dynamic active cracks.

Yun, Gun Jin; Rahimi, Mohammad Reza; Gandomi, Amir Hossein; Lim, Gong-Cheol; Choi, Jun-Seong

2013-05-01

214

Wear-accelerated corrosion of Ti-6Al-4V and nitrogen-ion-implanted Ti-6Al-4V: mechanisms and influence of fixed-stress magnitude.  

PubMed

Wear-accelerated corrosion rates at constant anodic potentials were evaluated for unimplanted and nitrogen-ion-implanted surgical Ti-6Al-4V while wearing against ultrahigh-molecular-weight polyethylene at stress levels up to 6.90 MPa (1000 psi). The ion implantation processing was found to reduce the wear corrosion rates in both saline and serum solutions at all applied stress levels. During wear testing, all of the ion-implanted surfaces remained visually unchanged from the polished condition. However, many of the unimplanted surfaces developed damage zones characterized by wear tracks and black wear debris. A surface-damage mechanism is proposed and discussed which involves disruption of the Ti-6Al-4V protective oxide film, subsequent entrapment of oxide particles in the polyethylene, then self-perpetuating damage due to the abrasive action of the embedded particles. PMID:3558450

Buchanan, R A; Rigney, E D; Williams, J M

1987-03-01

215

Social Psychological and Neuroendocrine Stress Reactions in Highly Mechanised Work  

Microsoft Academic Search

Social psychological theory on relations between production technology and work satisfaction was combined with arousal theory based on psychophysiological stress research in a study of workers in a highly mechanised production industry. A group of workers whose tasks were characterised by rcpetitiveness, physical constraint, machine-regulation of work pace and high demands for continuous attention (high-risk group) was compared to a

G. JOHANSSON; G. ARONSSON; B. O. LINDSTROM

1978-01-01

216

Adolescents sleep in low-stress and high-stress (exam) times: A prospective quasi-experiment  

Microsoft Academic Search

This prospective quasi-experiment (N=175; mean age: 15.14 years) investigates changes in adolescents' sleep from low-stress (regular school week) to high-stress times (exam week) and examines the (moderating) role of chronic sleep reduction, baseline stress, and gender. Sleep was monitored over three consecutive weeks using actigraphy. Adolescents' sleep was more fragmented during the high-stress time than during the low-stress time, meaning

J. F. Dewald; A. M. Meijer; F. J. Oort; G. A. Kerkhof; S. M. Bgels

2012-01-01

217

Proteomics of rice grain under high temperature stress.  

PubMed

Recent proteomic analyses revealed dynamic changes of metabolisms during rice grain development. Interestingly, proteins involved in glycolysis, citric acid cycle, lipid metabolism, and proteolysis were accumulated at higher levels in mature grain than those of developing stages. High temperature (HT) stress in rice ripening period causes damaged (chalky) grains which have loosely packed round shape starch granules. The HT stress response on protein expression is complicated, and the molecular mechanism of the chalking of grain is obscure yet. Here, the current state on the proteomics research of rice grain grown under HT stress is briefly overviewed. PMID:23508632

Mitsui, Toshiaki; Shiraya, Takeshi; Kaneko, Kentaro; Wada, Kaede

2013-03-06

218

Proteomics of rice grain under high temperature stress  

PubMed Central

Recent proteomic analyses revealed dynamic changes of metabolisms during rice grain development. Interestingly, proteins involved in glycolysis, citric acid cycle, lipid metabolism, and proteolysis were accumulated at higher levels in mature grain than those of developing stages. High temperature (HT) stress in rice ripening period causes damaged (chalky) grains which have loosely packed round shape starch granules. The HT stress response on protein expression is complicated, and the molecular mechanism of the chalking of grain is obscure yet. Here, the current state on the proteomics research of rice grain grown under HT stress is briefly overviewed.

Mitsui, Toshiaki; Shiraya, Takeshi; Kaneko, Kentaro; Wada, Kaede

2013-01-01

219

Unusually High Stress Drops Associated with Shallow Moonquakes  

NASA Astrophysics Data System (ADS)

New estimates of stress drops and energy release associated with shallow moonquakes, believed to represent the only lunar seismic events of tectonic origin, have been made, taking into account (1) properties of source spectra, (2) radiation pattern of foci, (3) anelastic attenuation of seismic waves, (4) response of the seismometer, and (5) intense scattering of seismic signals. The results indicate that the three largest events show body wave magnitudes of mB > 5.5 and stress drops of ?? > 100 MPa. The values for stress drops are high compared with those generally associated with most terrestrial events, but they are compatible with results predicted from thermoelastic models of the moon. Presence of high stresses in the lunar crust may indicate that at the beginning of its history the moon was originally molten not only in the outer surface region, but throughout its whole volume.

Oberst, J.

1987-02-01

220

High flux isotope reactor redesigned beryllium reflector thermal stress calculations  

SciTech Connect

The Beryllium reflector of the High Flux Isotope Reactor is currently redesigned for upgrading the capability of the reactor. The original design criteria are adopted in the redesign analysis. Both nuclear heating and thermal stress calculations are revised. The results show that more margin of safety have been achieved and the updated design assures more precise design estimates for the reflector thermal stress conditions. 1 ref., 2 figs., 2 tabs.

Chang, S.J.

1996-06-01

221

Plastic deformation and fracture behaviour of Ti6Al4V alloy loaded with high strain rate under various temperatures  

Microsoft Academic Search

This study investigates the plastic deformation and fracture behaviour of titanium alloy (Ti6Al4V) under high strain rates and various temperature conditions. Mechanical tests are performed at constant strain rates ranging from 5102 to 3103 s?1 at temperatures ranging from room temperature to 1100C by means of the compressive split-Hopkinson bar technique. The material's dynamic stressstrain response, strain rate, temperature effects

Woei-Shyan Lee; Chi-Feng Lin

1998-01-01

222

Texture Evolution and Residual Stress Relaxation in a Cold-Rolled Al-Mg-Si-Cu Alloy Using Vibratory Stress Relief Technique  

NASA Astrophysics Data System (ADS)

Over the last half century, vibratory stress relief (VSR) has come to be recognized as a technique with several unique benefits, and it has found applications in various industries. However, the mechanisms involved remain unclear, and the textures corresponding to residual stress relaxation were rarely reported in the existing literature. The purpose of this study is to discuss the texture evolution and residual stress relaxation in a cold-rolled Al-Mg-Si-Cu alloy using VSR technique. All the residual stress measurements were performed using a standard X-ray diffraction (XRD) technique. Measurement of texture was performed on the specimen surface using conventional pole figure (PF) as well as orientation distribution functions (ODFs) methods. Results indicate that the VSR technique can be applied to weaken the ?-fiber and cause the residual stress of the rolled samples to gradually approach uniformity in XRD analysis. The best relaxation of the compressive residual stress reaches about 52.6 pct, but relaxation of the tensile residual stress is less than 10 pct. After the VSR process for 20 minutes, the texture intensities of PFs (200) and (220) as compared to those in nonvibration are nearly homogeneously distributed. Furthermore, the texture of (111) PF perpendicular to normal direction (ND), which is affected by vibratory force parallel to ND, almost disappears.

Wang, Jia-Siang; Hsieh, Chih-Chun; Lin, Chi-Ming; Kuo, Che-Wei; Wu, Weite

2013-02-01

223

The influence of Al2O3 particulate reinforcement on cyclic stress response and fracture behavior of 6061 aluminum alloy  

NASA Astrophysics Data System (ADS)

The cyclic stress response characteristics and cyclic fracture behavior of aluminum alloy 6061 discontinuously reinforced with particulates of Al2O3 are presented and discussed. The 6061/Al2O3 composite specimens and the unreinforced 6061 aluminum alloy were cyclically deformed using tension-compression loading under constant total strain amplitude control. Both the composite and the unreinforced alloy exhibited softening to failure from the onset of cyclic deformation. The degree of softening was observed to increase at the elevated test temperature for both the composite and the unreinforced counterpart. The intrisic micromechanisms controlling the stress response characteristics during fully-reversed cyclic straining are highlighted and rationale for the observed behavior is discussed. The cyclic fracture behavior of the composite is discussed in terms of the competing influences of intrinsic microstructural effects, deformation characteristics arising from a combination of mechanical and microstructural contributions, cyclic stress response, and test temperature.

Srivatsan, T. S.; Sriram, S.; Daniels, C.

1995-05-01

224

High voltage bushing having weathershed and surrounding stress relief collar  

DOEpatents

A high voltage electric bushing comprises a hollow elongated dielectric weathershed which encloses a high voltage conductor. A collar formed of high voltage dielectric material is positioned over the weathershed and is bonded thereto by an interface material which precludes moisture-like contaminants from entering between the bonded portions. The collar is substantially thicker than the adjacent weathershed which it surrounds, providing relief of the electric stresses which would otherwise appear on the outer surface of the weathershed. The collar may include a conductive ring or capacitive foil to further relieve electric stresses experienced by the bushing.

Cookson, Alan H. (Pittsburgh, PA)

1981-01-01

225

Magnetotransport properties of high equivalent Al composition AlGaN/GaN heterostructures using AlN/GaN superlattice as a barrier  

NASA Astrophysics Data System (ADS)

Magnetotransport properties of the two-dimensional electron gas (2DEG) in high equivalent Al composition AlGaN/GaN heterostructures using AlN/GaN superlattice as a barrier have been studied at low temperatures and high magnetic fields. Well resolved Shubnikov-de Haas oscillations were observed, indicating excellent quality of the quasi-AlGaN/GaN heterostructures. It is measured that the energy separation between the two subbands in the GaN triangular quantum well can be as large as 180.5 meV, depicting strong quantum confinement at the heterointerface. The strong quantum confinement results in a high 2DEG density of 2 1013 cm-2. The persistent photoconductivity investigation also indicates that the superlattice barrier layer has a low density of impurities/defects. It is believed that the AlN/GaN superlattice, instead of high Al composition alloy AlGaN layer, could greatly improve the device performance.

Liu, S. D.; Tang, N.; Shen, X. Q.; Duan, J. X.; Lu, F. C.; Yang, X. L.; Xu, F. J.; Wang, X. Q.; Ide, T.; Shimizu, M.; Ge, W. K.; Shen, B.

2013-07-01

226

On the effect of stress on nucleation and growth of precipitates in an Al-Cu-Mg-Ag alloy  

SciTech Connect

A study has been made of the effect of an externally applied tensile stress on {Omega} and {Theta}{prime} precipitate nucleation and growth in an Al-Cu-Mg-Ag alloy and a binary Al-Cu alloy which was used as a model system. Both solutionized and solutionized and aged conditions were studied. The mechanical properties have been measured and the microstructures have been characterized by transmission electron microscopy (TEM). The volume fraction and number density, as well as the precipitate size, have been experimentally determined. It was found that for as-solutionized samples aged under stress, precipitation occurs preferentially parallel to the stress axis. A threshold stress has to be exceeded before this effect can be observed. The critical stress for influencing the precipitate habit plane is between 120 and 140 MPa for {Omega} and between 16 and 19 MPa for {Theta}{prime} for the aging temperature of 160 C. The major effect of the applied stress is on the nucleation process. The results are discussed in terms of the role of the lattice misfit between the matrix and the precipitate nucleus.

Skrotzki, B. [Rhur-Univ., Bochum (Germany). Inst. fuer Werkstoffe; Shiflet, G.J.; Starke, E.A. Jr. [Univ. of Virginia, Charlottesville, VA (United States). Dept. of Materials Science and Engineering

1996-11-01

227

Modelling Of Residual Stresses Induced By High Speed Milling Process  

Microsoft Academic Search

Maintenance processes used in heavy industries often include high speed milling operations. The reliability of the post-process material state has to be studied. Numerical simulation appears to be a very interesting way to supply an efficient residual stresses (RS) distribution prediction. Because the adiabatic shear band and the serrated chip shaping are features of the austenitic stainless steel high speed

Olivier Desmaison; Katia Mocellin; Nicolas Jardin

2011-01-01

228

Microstructure and mechanical behavior of spray-deposited High-Li Al-Li alloys  

Microsoft Academic Search

High-Li alloys, with the composition Al-3.8Li-XCu-1.0Mg-0.4Ge-0.2Zr, were synthesized using a spray deposition technique (wt. pct, X=0?1.5). The microstructure of the spray-deposited Al-Li alloys consisted of equiaxed grains with an average grain size in\\u000a the range from 20 to 50 m. The grain-boundary phases were fine and discrete. The spray-deposited and thermomechanically processed materials were isothermally\\u000a heat treated at 150 C

L. del Castillo; H. M. Hu; E. J. Lavernia; Y. Wu

1999-01-01

229

High-temperature mechanical properties and deformation behavior of high Nb containing TiAl alloys fabricated by spark plasma sintering  

NASA Astrophysics Data System (ADS)

A high Nb containing TiAl alloy was prepared from the pre-alloyed powder of Ti-45Al-8.5Nb-0.2B-0.2W-0.02Y (at%) by spark plasma sintering (SPS). Its high-temperature mechanical properties and compressive deformation behavior were investigated in a temperature range of 700 to 1050C and a strain rate range of 0.002 to 0.2 s-1. The results show that the high-temperature mechanical properties of the high Nb containing TiAl alloy are sensitive to deformation temperature and strain rate, and the sensitivity to strain rate tends to rise with the deformation temperature increasing. The hot workability of the alloy is good at temperatures higher than 900C, while fracture occurs at lower temperatures. The flow curves of the samples compressed at or above 900C exhibit obvious flow softening after the peak stress. Under the deformation condition of 900-1050C and 0.002-0.2 s-1, the interrelations of peak flow stress, strain rate, and deformation temperature follow the Arrhenius' equation modified by a hyperbolic sine function with a stress exponent of 5.99 and an apparent activation energy of 441.2 kJmol-1.

Lu, Xin; Zhao, Li-hua; Zhu, Lang-ping; Zhang, Bin; Qu, Xuan-hui

2012-04-01

230

Advances in Swept High Frequency Eddy Current Residual Stress Characterization  

NASA Astrophysics Data System (ADS)

We report on recent progress of a swept high frequency eddy current (SHFEC) technique for nondestructive characterization of residual stresses in engine materials with specific applications to shot-peened superalloy components. The technique determines conductivity depth profiles by model-based inversion of SHFEC data, and converts them into residual stress profiles using a material-based model which generally includes the piezoresistivity (PR) and possibly other non-PR effects. Improvement in detection coil and upgrades to the measurement system have extended the effective frequency upper bound to 70 MHz. A modified piezoresistivity theory, including the effect of texture on stress-induced conductivity changes, was developed in light of the experimental evidences of shot-induced changes of texture in peened Inconel 718 samples. The theory was applied to convert the conductivity profile to a residual stress depth profile, which agrees with the data taken by the standard layer removal XRD method.

Shen, Y.; Frishman, A. M.; Lee, S. J.; Lo, C. C. H.; Nakagawa, N.

2008-02-01

231

Improved capacitive stress transducers for high-field superconducting magnets  

NASA Astrophysics Data System (ADS)

High-field (12-18 Tesla) superconducting magnets are required to enable an increase in the energy of future colliders. Such field strength requires the use of Nb3Sn superconductor, which has limited tolerance for compressive and shear strain. A strategy for stress management has been developed at Texas A&M University and is being implemented in TAMU3, a short-model 14 Tesla stress-managed Nb3Sn block dipole. The strategy includes the use of laminar capacitive stress transducers to monitor the stresses within the coil package. We have developed fabrication techniques and fixtures, which improve the reproducibility of the transducer response both at room temperature and during cryogenic operation. This is a report of the status of transducer development.

Benson, Christopher Pete; Holik, Eddie Frank, III; Jaisle, Andrew; McInturff, A.; McIntyre, P.

2012-06-01

232

High-pressure and high-temperature stability field of hydrous phase delta-AlOOH  

NASA Astrophysics Data System (ADS)

Stability field of hydrous phases is a key for understanding water concentration in the earth's mantle. ?-AlOOH is a high-pressure polymorph of diaspore (?-AlOOH) and boehmite (?-AlOOH). The space group of this phase is Pnn2 and it is similar to CaCl2-type SiO2 which is a high-pressure polymorph of stishovite; edge-sharing Al-O octahedra make single-chain along c-axis. Although it has a large stability field in pressure range from 18 GPa to 32 GPa and temperature of up to 1473 K, the high-pressure stability limits has not yet clarified. In this study, we investigated the stability field of ?-AlOOH up to 130 GPa. The high-pressure experiments were performed using a laser-heated diamond-anvil cell. Starting material was gibbsite (Al(OH)3) powder mixed with platinum black as a laser absorber. The sample was sandwiched by pure gibbsite layers and loaded into a rhenium gasket. Pressures were measured with ruby-fluorescence technique before and after heating. The sample was heated from both sides by a Nd:YAG laser operated in multimode. After experiment, stable phase in each condition was determined using the X-ray diffraction and Raman spectroscopy method. We also conducted in-situ X-ray diffraction experiments under high-pressure and temperature conditions together with the X-ray diffraction of the recovered samples both at BL10XU in SPring-8 and BL-13A in Photon Factory. In these runs, pressures were also calculated using the equation of state of platinum. The experimental conditions were in the pressures between 50-130 GPa and temperatures to 1800 K. X-ray analysis shows the sample recovered from the pressure and temperature range from 40 GPa and 1577 K to 130 GPa and 1800 K consists of ?-AlOOH. In the in-situ experiments, crystallization of ?-AlOOH was observed at 65 GPa and 1300 K and it was stable up to 1700 K. ?-AlOOH is stable in the large pressure range with a dehydration temperature around 1800K. It can be a water reservoir in subducting slabs in the deep lower mantle conditions beyond the dehydration conditions of the other hydrous phases such as dense hydrous magnesium silicates.

Sano, A.; Ohtani, E.; Kondo, T.; Hirao, N.; Sone, T.; Kikegawa, T.; Sata, N.; Ohishi, Y.

2005-12-01

233

An analysis of the flow stress of a two-phase alloy system, Ti-6Al-4V  

SciTech Connect

An analysis of the tensile deformation behavior of a two-phase body-centered cubic (bcc)-hexagonal close-packed (hcp) alloy, Ti-6Al-4V, has been made. This has shown that the temperature dependence of the flow stress, the logarithm of the effective stress, and the strain-rate sensitivities can be described by simple analytical equations if the thermally activated strain-rate equation contains the Yokobori activation enthalpy H = H{sup 0} ln ({sigma}*{sub 0}/{sigma}*), where H{sup 0} is a constant, {sigma}* the effective stress, and {sigma}*{sub 0} its 0 K value. The flow stress-temperature plateau region (500 to 600 K) also can be rationalized analytically in terms of oxygen dynamic strain aging in the alpha phase.

Reed-Hill, R.E.; Iswaran, C.V.; Kaufman, M.J. [Univ. of Florida, Gainesville, FL (United States). Dept. of Materials Science and Engineering

1996-12-01

234

Solid Solubility of Si in Al under High Pressure  

Microsoft Academic Search

By making use of a 15 mm cubic anvil apparatus, Al-Si alloys of Si-concentration up to 15 at% were studied at a pressure of 54 kbar. The liquidus, solidus and solvus of the Al-rich alloys were determined by means of the 4-probe electric resistance measurement. The solubility limit of Si in Al was extended beyond 15 at% at 54 kbar

Hisao Mii; Masafumi Senoo; Ikuya Fujishiro

1976-01-01

235

High-resistivity nanogranular Co-Al-O films for high-frequency applications  

NASA Astrophysics Data System (ADS)

This work presents a series of high-resistivity nanogranular Co-Al-O films with maximum resistivity of ~110 m? cm. The films were deposited using pulsed dc reactive sputtering of a Co72Al28 target in an oxygen/argon ambient. The samples were characterized by scanning electron microscopy (SEM), M-H loop measurements, and s-parameter measurements on microstrip transmission lines with Co-Al-O magnetic cores. The high-frequency magnetic permeability profile was extracted from the microstrip measurements. Reduction of deposition power resulted in resistivity enhancement, as well as reduction of coercivity and permeability. SEM images reveal an average grain size of ~80 nm for films with the highest resistivity.

Khalili Amiri, Pedram; Zhuang, Yan; Schellevis, Hugo; Rejaei, Behzad; Vroubel, Marina; Ma, Yue; Burghartz, Joachim N.

2007-05-01

236

High cycle fatigue behavior of implant Ti-6Al-4V in air and simulated body fluid.  

PubMed

Ti-6Al-4V implants that function as artificial joints are usually subjected to long-term cyclic loading. To study long-term fatigue behaviors of implant Ti-6Al-4V in vitro and in vivo conditions exceeding 107 cycles, constant stress amplitude fatigue experiments were carried out at ultrasonic frequency (20 kHz) with two different surface conditions (ground and polished) in ambient air and in a simulated body fluid. The initiation mechanisms of fatigue cracks were investigated with scanning electron microscopy. Improvement of fatigue strength is pronounced for polished specimens below 106 cycles in ambient air since fatigue cracks are initiated from surfaces of specimens. While the cycles exceed 106, surface conditions have no effect on fatigue behaviors because the defects located within the specimens become favorable sites for crack initiation. The endurance limit at 108 cycles of polished Ti-6Al-4V specimens decreases by 7% if it is cycled in simulated body fluid instead of ambient air. Fracture surfaces show that fatigue failure is initiated from surfaces in simulated body fluid. Surface improvement has a beneficial effect on fatigue behaviors of Ti-6Al-4V at high stress amplitudes. The fatigue properties of Ti-6Al-4V deteriorate and the mean endurance limits decrease significantly in simulated body fluid. PMID:24092135

Liu, Yong-Jie; Cui, Shi-Ming; He, Chao; Li, Jiu-Kai; Wang, Qing-Yuan

2013-01-01

237

High reliability interconnections for ULSI using Al-Si-Pd-Nb\\/Mo layered films  

Microsoft Academic Search

A new Al-Si-Pd-Nb alloy and a bilayered film using this alloy with Mo have been investigated for ULSI interconnections. Al-Si-0.3 wt.%-Pd-0.4 wt.%-Nb was found to have a five-times-better electromigration resistance than Al-Si-0.5% Cu. In addition, by layering this alloy with Mo, electromigration resistance was found to be ten times better than for Al-Si-Cu\\/TiW. Stress measurements detected the formation of PdO

J. Onuki; Y. Koubuchi; S. Fukada; M. Suwa; M. Koizumi; D. S. Gardner; H. Suzuki; E. Minowa

1990-01-01

238

Work at high altitude and oxidative stress: antioxidant nutrients.  

PubMed

A significant portion of the world's geography lies above 10,000 feet elevation, an arbitrary designation that separates moderate and high altitude. Although the number of indigenous people living at these elevations is relatively small, many people travel to high altitude for work or recreation, exposing themselves to chronic or intermittent hypoxia and the associated risk of acute mountain sickness (AMS) and less frequently, high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE). The symptoms of AMS (headache, nausea, anorexia, fatigue, lassitude) occur in those who travel too high, too fast. Some investigators have linked the development of these symptoms with the condition of altered blood-brain barrier permeability, possibly related to hypoxia induced free radical formation. The burden of oxidative stress increases during the time spent at altitude and may even persist for some time upon return to sea level. The physiological and medical consequences of increased oxidative stress engendered by altitude is unclear; indeed, hypoxia is believed to be the trigger for the cascade of signaling events that ultimately leads to adaptation to altitude. These signaling events include the generation of reactive oxygen species (ROS) that may elicit important adaptive responses. If produced in excess, however, these ROS may contribute to impaired muscle function and reduced capillary perfusion at altitude or may even play a role in precipitating more serious neurological and pulmonary crisis. Oxidative stress can be observed at altitude without strenuous physical exertion; however, environmental factors other than hypoxia, such as exercise, UV light exposure and cold exposure, can also contribute to the burden. Providing antioxidant nutrients via the diet or supplements to the diet can reduce oxidative stress secondary to altitude exposure. In summary, the significant unanswered question concerning altitude exposure and antioxidant supplementation is when does oxidative stress become potentially damaging enough to merit antioxidant therapy and conversely, what degree of oxidative stress is necessary to foster the adaptive response of altitude exposure? PMID:12324188

Askew, E W

2002-11-15

239

Anthropic selection of a Solar System with a high 26Al\\/27Al ratio: Implications and a possible mechanism  

Microsoft Academic Search

Since our technological civilisation depends on our planet's properties, anthropic selection can explain the close match between the high 26Al\\/27Al ratios in the earliest Solar System solids, which are difficult to produce in models of star-formation, and the limiting value required to cause (the widely observed) thermal processing of planetesimals. We suggest that volatile loss on heating of planetesimals favours

J. D. Gilmour; C. A. Middleton

2009-01-01

240

Anthropic selection of a Solar System with a high 26Al\\/ 27Al ratio: Implications and a possible mechanism  

Microsoft Academic Search

Since our technological civilisation depends on our planet's properties, anthropic selection can explain the close match between the high 26Al\\/27Al ratios in the earliest Solar System solids, which are difficult to produce in models of star-formation, and the limiting value required to cause (the widely observed) thermal processing of planetesimals. We suggest that volatile loss on heating of planetesimals favours

J. D. Gilmour; C. A. Middleton

2009-01-01

241

State of the art in high accuracy high detail DTMs derived from ALS  

Microsoft Academic Search

High-resolution Digital Terrain Models (DTMs) representing the bare Earth are a fundamental input for various applications in geomorphology. Airborne laser scanning (ALS) is established as a standard tool for deriving DTMs over large areas with unprecedented accuracy. Due to advances in sensor technology and in processing algorithms in the recent years the obtainable accuracy is still increasing. Accuracy is understood

N. Pfeifer; C. Briese; G. Mandlburger; B. Hfle; C. Ressl

2009-01-01

242

Research on High-Frequency Vibratory Stress Relief for Small Assembly  

Microsoft Academic Search

To relieve the residual stress in small assembly, a method called high-frequency vibratory stress relief was researched. Microscopic origin of residual stress was analyzed according to the theory of crystal dislocation, which shows that the appeared unstable dislocations and localized energy concentrating are the main reason to produce residual stress. And then the mechanism of high frequency vibratory stress relief

Wen He; Xiao-Yin Cheng; Run-Jie Shen

2006-01-01

243

Internal Stress Plasticity-Creep due to Dynamic Hydrogen Gradients in Ti-6Al-4V  

SciTech Connect

Internal-stress plasticity is a Newtonian creep mechanism which operates at low applied stress levels, when there is a concurrent internal stress. Common sources of internal stress are thermal-expansion or phase-transformation mismatch; in this work we explore the possibility of chemically-induced internal stresses. We report tensile creep experiments on the BCC {beta}-phase of Ti-6A1-4V, in which dynamic gradients of hydrogen concentration were introduced through cycling of the test atmosphere (between Ar/H{sub 2} mixture and pure Ar) under low applied stresses. Under these conditions, we observe Newtonian deformation at rates much higher than for constant-composition conditions, as expected for internal stress plasticity. Also, we present an analytical model which considers chemical, elastic, and creep strains during chemical cycling under stress, and find good agreement with the experimental results.

Schuh, C; Dunand, D C

2001-09-10

244

Influence of residual stress on bonding strength and fracture of plasma-sprayed hydroxyapatite coatings on Ti6Al4V substrate  

Microsoft Academic Search

Six hydroxyapatite coatings (HACs) were plasma sprayed on Ti6Al4V substrates by varying the substrate temperatures and the cooling conditions. This study is aimed not only to measure the residual stress of HACs under various conditions, but also to assess the influence of residual stress in HACs on their bonding strength. The residual stress and bonding strength were measured by XRD

Y. C Yang; Edward Chang

2001-01-01

245

Influence of residual stress on stress concentration factor for high strength steel welded joints  

Microsoft Academic Search

In this study, a set of plate-to-plate T and Y joints specimens made from high strength steel plates with yield stress equal to 690MPa is investigated. The joints are fabricated by SMAW welding procedure. Two groups of specimens with different welding procedures are included: one group is composed by the joints with welding completed at ambient temperature and the other

Jin Jiang; Mingshan Zhao

246

The High Secure Psychiatric Hospitals Nursing Staff Stress Survey 3: Identifying stress resistance resources in the stress process of physical assault  

Microsoft Academic Search

The present paper forms part of the High Secure Psychiatric Hospitals Nursing Staff Stress Survey and explores the causal role of generalized and specific stress resistance resources (SRRs) in the stress process following physical assault. Confidential self-report questionnaires were administered to all nurses working in English and Scottish High Secure Psychiatric Hospitals. A total of 636 nurses responded to questionnaires

Ulrich Reininghaus; Tom Craig; Kevin Gournay; Patrick Hopkinson; Jerome Carson

2007-01-01

247

Proteomic analysis of a high aluminum tolerant yeast Rhodotorula taiwanensis RS1 in response to aluminum stress.  

PubMed

Rhodotorula taiwanensis RS1 is a high-aluminum (Al)-tolerant yeast that can survive in Al concentrations up to 200mM. The mechanisms for the high Al tolerance of R. taiwanensis RS1 are not well understood. To investigate the molecular mechanisms underlying Al tolerance and toxicity in R. taiwanensis RS1, Al toxicity-induced changes in the total soluble protein profile were analyzed using two-dimensional gel electrophoresis (2-DE) coupled with mass spectrometry. A total of 33 differentially expressed proteins responding to Al stress were identified from approximately 850 reproducibly detected proteins. Among them, the abundance of 29 proteins decreased and 4 increased. In the presence of 100mM Al, the abundance of proteins involved in DNA transcription, protein translation, DNA defense, Golgi functions and glucose metabolism was decreased. By contrast, Al treatment led to increased abundance of malate dehydrogenase, which correlated with increased malate dehydrogenase activity and the accumulation of intracellular citrate, suggesting that Al-induced intracellular citrate could play an important role in detoxification of Al in R. taiwanensis RS1. PMID:23831152

Wang, Chao; Wang, Chang Yi; Zhao, Xue Qiang; Chen, Rong Fu; Lan, Ping; Shen, Ren Fang

2013-07-02

248

The effects of proton irradiation on the reliability of InAlN/GaN high electron mobility transistors  

SciTech Connect

We have investigated the effect of proton irradiation on reliability of InAlN/GaN high electron mobility transistors (HEMTs). Devices were subjected to 5-15 MeV proton irradiations with a fixed dose of 5 1015 cm-2, or to a different doses of 2 1011, 5 1013 or 2 1015 cm-2 of protons at a fixed energy of 5 MeV. During off-state electrical stressing, the typical critical voltage for un-irradiated devices was 45 to 55 V. By sharp contrast, no critical voltage was detected for proton irradiated HEMTs up to 100 V, which was instrument-limited. After electrical stressing, no degradation was observed for the drain or gate current-voltage characteristics of the proton-irradiated HEMTs. However, the drain current decreased ~12%, and the reverse bias gate leakage current increased more than two orders of magnitude for un-irradiated HEMTs as a result of electrical stressing.

Liu, L. [University of Florida, Gainesville; Lo, C. F. [University of Florida; Xi, Y. Y. [University of Florida, Gainesville; Wang, Y.l. [University of Florida; Kim, H.-Y. [Korea University; Kim, J. [Korea University; Pearton, S. J. [University of Florida; Laboutin, O. [Kopin Corporation, Taunton, MA; Cao, Yu [Kopin Corporation, Taunton, MA; Johnson, Wayne J. [Kopin Corporation, Taunton, MA; Kravchenko, Ivan I [ORNL; Ren, F. [University of Florida

2012-01-01

249

Frequency Comparison of Two High-Accuracy Al+ Optical Clocks  

NASA Astrophysics Data System (ADS)

We have constructed an optical clock with a fractional frequency inaccuracy of 8.610-18, based on quantum logic spectroscopy of an Al+ ion. A simultaneously trapped Mg+ ion serves to sympathetically laser cool the Al+ ion and detect its quantum state. The frequency of the S01?P03 clock transition is compared to that of a previously constructed Al+ optical clock with a statistical measurement uncertainty of 7.010-18. The two clocks exhibit a relative stability of 2.810-15?-1/2, and a fractional frequency difference of -1.810-17, consistent with the accuracy limit of the older clock.

Chou, C. W.; Hume, D. B.; Koelemeij, J. C. J.; Wineland, D. J.; Rosenband, T.

2010-02-01

250

High temperature oxidation of CrTiAlN hard coatings prepared by unbalanced magnetron sputtering  

Microsoft Academic Search

The present research aims to synthesize a multi-component CrTiAlN hard coating for the modification of high-temperature performance, as compared to the traditional TiN and TiAlN coatings. In this work, the quaternary CrTiAlN coatings were deposited on AISI M42 steel substrates by reactive unbalanced magnetron sputtering technique from Cr, Ti and Al elemental targets in Ar+N2 mixture atmosphere, and their high-temperature

Z. F. Zhou; P. L. Tam; P. W. Shum; K. Y. Li

2009-01-01

251

Al 2O 3 coatings deposited by filtered vacuum arc characterization of high temperature properties  

Microsoft Academic Search

Thin Al2O3 coatings can provide oxidation protection on metallic high temperature components. For this purpose Ni-base alloys for gas turbine applications are plasma spray coated with MeCrAlY alloy. At high temperatures this alloy forms a native Al2O3 scale for oxidation protection. In order to increase the efficiency of this oxidation protection a thin artificial Al2O3 layer can be deposited on

H. Bolt; F. Koch; J. L. Rodet; D. Karpov; S. Menzel

1999-01-01

252

Protective role of antioxidant enzymes under high temperature stress  

Microsoft Academic Search

An experiment was conducted to study the effect of high temperature stress on the antioxidant enzyme activity in five wheat genotypes viz., PBW 343, PBW 175, HDR-77, HD 2815 and HD 2865. There was significant increase in the activity of superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT) in the late and very late planting and at all stages

Moaed Almeselmani; P. S. Deshmukh; R. K. Sairam; S. R. Kushwaha; T. P. Singh

2006-01-01

253

Preparation and Pore Structure Stability at High Temperature of Porous Fe-Al Intermetallics  

NASA Astrophysics Data System (ADS)

Porous Fe-Al intermetallics with different nominal compositions (from Fe-8 wt.% Al to Fe-50 wt.% Al) were fabricated by Fe and Al elemental powders through reaction synthesis. The effects of the Al content on the pore structure properties, and the comparison of pore structure stabilities at high-temperatures among the porous Fe-Al intermetallics and porous Ti, Ni, 316L stainless steel samples, were systematically studied. Results showed that the open porosity, maximum pore size, and permeability vary with the Al content. Porous Fe-(25-30 wt.%) Al intermetallics show good shape controllability and excellent pore structure stability at 1073 K in air, which suggests that these porous Fe-Al intermetallics could be used for filtration at high temperatures.

Shen, P. Z.; Gao, H. Y.; Song, M.; He, Y. H.

2013-09-01

254

Texture analysis of L1[sub 2] Al[sub 66]Mn[sub 9]Ti[sub 25] intermetallic compound deformed at high temperatures  

Microsoft Academic Search

The authors investigated the deformation characteristics and microstructure change of L1[sub 2] Al[sub 66]Mn[sub 9]Ti[sub 25] by high temperature uniaxial compression tests. Three regimes appeared in the dynamics restoration process, depending on the flow stress level. When the flow stress is higher or lower, dynamic recovery is the dominant dynamic restoration process, while dynamic recrystallization is predominant at the intermediate

T. Suzuki; T. Takabayashi; H. Fukutomi; M. Dahms

1994-01-01

255

Growth of Highly (0002) Oriented InN Films on AlInN/AlN Bilayer  

NASA Astrophysics Data System (ADS)

InN film with an AlInN/AlN bilayer buffer was deposited on Si(111) substrate by radio frequency (RF) magnetron sputtering. X-ray diffraction and Raman spectroscopy measurements reveal that the InN film is of hexagonal wurtzite crystal structure with highly (0002) preferred orientation. An Al0.24In0.76N interface layer of about 50 nm was confirmed by transmission electron microscopy (TEM) and further analyzed by X-ray photoelectron spectroscopy (XPS). The quality of this film is remarkably better than InN films grown directly on Si substrate or with only an AlN buffer, due to the effective accommodation of mismatch between the film and substrate. Our results will be very useful in the fabrication of applicable nitride microelectronic materials.

Dong, C. J.; Xu, M.; Lu, W.; Huang, Q. Z.

2013-04-01

256

Modified Cu-Mn-Al High Damping Alloys.  

National Technical Information Service (NTIS)

Zirconium and erbium modified Cu-Mn-Al was spray formed in an effort to increase homogeneity and damping capacity and decrease impurity levels. Although the microstructure revealed that the optimum spray forming parameters have not yet been achieved, the ...

C. R Wong R. S. Venkatachalam

1994-01-01

257

Investigation on monotonic and cyclic stressstrain characteristics of Ti2Al2.5Zr alloy  

Microsoft Academic Search

The monotonic and cyclic deforming regularity of Ti2Al2.5Zr alloy rod, tube and profiled tube (PT) specimen was determined at room temperature (RT). The effects of tension speed, V, cycle number, N, strain ratio, R, strain amplitude, ?a and specimen shape on tensile and cyclic deforming behavior and characteristics were analyzed. The stressstrain relation equations under monotonic and cyclic loading, and

Yu Zhentao; Zhou Lian; Deng Ju; Gu Haicheng

2000-01-01

258

Stress dependence of non-chemical free energy contributions in CuAlNi shape memory alloy  

Microsoft Academic Search

A Cu24.0at.% Al2.2at.% Ni0.5at.% B shape memory alloy was investigated experimentally under uniaxial tensile stress (?) up to 10MPa. Transformation temperatures and transformation strains as a function of ? were evaluated from the simultaneously measured temperatureelongation and temperatureresistance curves. Using appropriate analysis [Philos. Mag. B 82 (2002) 105; Scripta Mater. 43 (2000) 691; J. Phys. IV 11 (2001) Pr8], it

L. Darczi; Z. Palnki; S. Szab; D. L. Beke

2004-01-01

259

Internal friction in [gamma]-TiAl at high temperatures  

SciTech Connect

The internal friction in TiAl polycrystals of technical purity was studied in the temperature range of 300--1500 K using an inverted torsion pendulum. Extruded single-phase [gamma]-TiAl with an aluminium content of 54.1 at.% shows a large, frequency-dependent relaxation maximum near 1300 K during cooling from temperatures above 1400 K, which is neither observed during heating from ambient temperature nor in two-phase [alpha][sub 2]/[gamma]-TiAl alloys with a lower Al content. This relaxation maximum is tentatively ascribed to the motion of grain boundaries or dislocations, which are pinned by precipitates in [gamma]-TiAl. The precipitates dissolve at temperatures above 1350 K and form again below 1200 K. No relaxation is observed in polycrystalline TiAl with a carbon content in the range from 0.009 to 0.22 at.% at temperatures below 900 K. This behavior may be an indication of hardening by finely dispersed precipitates, as observed in TEM and SEM micrographs.

Brossmann, U.; Hirscher, M.; Kronmueller, H. (Max-Planck-Inst. fuer Metallforschung, Stuttgart (Germany))

1999-06-22

260

Comparison of the developed thermal stresses in Al 2O 3SG, ZrO 212%Si+Al and ZrO 2SG coating systems subjected to thermal loading  

Microsoft Academic Search

In this investigation, thermal and structure finite element analysis has been employed to analyse the thermal stresses developed in Al2O3SG, ZrO212%Si+A1 and ZrO2SG.coatings subjected to thermal loading. Systems with 0.4 mm coating thickness and 4 mm substrate material thickness were modelled. Zirconiaspherical cast iron (SG) coatings with NiAl, NiCrAlY and NiCoCrAlY interlayers were also modelled. Nominal and shear stresses at

U Kocab?cak; A Mimaroglu; O Sar?kaya; O. H Mete

1999-01-01

261

Nanotwins and stacking faults in high-strength epitaxial Ag/Al multilayer films  

NASA Astrophysics Data System (ADS)

Epitaxial Ag/Al multilayer films have high hardness (up to 5.5 GPa) in comparison to monolithic Ag and Al films (2 and 1 GPa). High-density nanotwins and stacking faults appear in both Ag and Al layers, and stacking fault density in Al increases sharply with decreasing individual layer thickness, h. Hardness increases monotonically with decreasing h, with no softening. In comparison, epitaxial Cu/Ni multilayers reach similar peak hardness when h ~ 5 nm, but soften at smaller h. High strength in Ag/Al films is primarily a result of layer interfaces, nanotwins, and stacking faults, which are strong barriers to dislocation transmission.

Bufford, D.; Bi, Z.; Jia, Q. X.; Wang, H.; Zhang, X.

2012-11-01

262

Resilience in highly stressed urban children: concepts and findings.  

PubMed Central

The Rochester Child Resilience Project is a coordinated set of studies of the correlates and antecedents of outcomes relating to resilience among profoundly stressed urban children. The studies have been conducted over the course of the past decade. Based on child test data, parent, teacher, and self ratings of child adjustment, and in-depth individual interviews with parents and children, a cohesive picture has developed of child and family milieu variables that consistently differentiate children with resilient versus stress-affected outcomes within this highly stressed sample. Resilient children are characterized by an easy temperament and higher IQ; sound parent/child relationships; a parent's sense of efficacy; the parent's own wellness, especially mental health; and the child's perceived competence, realistic control, empathy, and social problem-solving.

Cowen, E. L.; Wyman, P. A.; Work, W. C.

1996-01-01

263

Thermal Fatigue Life of Glidcop Al-15 High-Heat-Load Components  

NASA Astrophysics Data System (ADS)

Shanghai Synchrotron Radiation Facility (SSRF) is a third-generation of synchrotron radiation light source and is presently under construction as a large scale national scientific project in China. Depending on the outstanding thermal and mechanical performance, Glidcop Al-15, a dispersion strengthened copper alloy, is chosen to serve for the high-heat-load components at beam line front end in SSRF. Present study is to investigate the thermal fatigue lives of critical SSRF components. A nonlinear finite element method (FEM) is used to simulate the nonlinear three dimensional stress-strain fields of the critical component-Mask2 at SSRF beam line. The method consists of transient temperature analyses followed by elastic-plastic stress analyses. Then, a critical plane approach is used to predict the thermal fatigue life of mask2. The critical plane approach is appropriate for estimating service life of critical SSRF components since the results are in good consistent with the experimental ones taken at the Advanced Photon Source (APS).

Jin, J. F.; Xiao, W. L.; Chen, H. B.

2010-05-01

264

Critical current of a rapid-quenched Nb3Al conductor under transverse compressive and axial tensile stress  

NASA Astrophysics Data System (ADS)

The electromechanical behavior of a Nb3Al wire manufactured according to the RHQT process (rapid-heating, quenching and transformation) has been investigated at magnetic fields between 15 and 19 T at 4.2 K. Of particular interest was the critical current, Ic, as a function of transverse pressure up to 300 MPa and as a function of axial tensile stress. The studied wires are pieces of a 870 m long copper stabilized Nb3Al wire with a rectangular cross section of 1.81 mm 0.80 mm. It was observed that the critical current at 300 MPa transverse pressure, applied to the narrow side, is reduced to 93%, 90% and 88% of its stress free value at 15 T, 17 T and 19 T, respectively. After unloading from 300 MPa Ic recovers to 94% and 97% at 19 T and 15 T, respectively. A field dependence of the effect is visible above 200 MPa. For completeness, the critical current was also measured under axial tensile strain. The maximum of Ic is at 0.15% applied strain and irreversibility has been observed above 0.26%. Finally a stress versus strain measurement at 4.2 K has been carried out allowing the conversion from axial strain to stress.

Seeber, B.; Ferreira, A.; Mondonico, G.; Buta, F.; Senatore, C.; Flkiger, R.; Takeuchi, T.

2011-03-01

265

Faceted growth of primary Al2Cu crystals during directional solidification in high magnetic field  

NASA Astrophysics Data System (ADS)

The high magnetic field is widely used to modify the crystal morphology. In this work, the effect of the magnetic field on growing behavior of faceted crystals in the Al-40 wt. %Cu alloy was investigated using directional solidification technique. It was found that the faceted growth of primary Al2Cu phase was degraded and the primary spacing was reduced upon applying the magnetic field. Additionally, the length of the mushy zone first decreased and then increased with increase of the magnetic field intensity. The quantitative analysis reveals that the shear stress induced by the fluid motion is insufficient to break the atom bonds at the solid-liquid interface. However, both of the thermoelectric magnetic convection (TEMC) and the thermoelectric magnetic force (TEMF) cause dendrites to fracture and reduce the primary spacing. The two effects also weaken the faceting growth. Moreover, the instability of the solid-liquid interface is generated by the TEMF, which further leads to degrade the faceted growth. The length of mushy zone was changed by the TEMC and reached the minimum in the magnetic field of 0.5 T, which is in good agreement with the predicted value (0.83 T).

Li, Chuanjun; Ren, Zhongming; Shen, Yu; Wang, Qiuliang; Dai, Yinming; Wang, Hui

2013-10-01

266

Residual stress distribution in an Al{sub 2}O{sub 3}-Ni joint bonded with a composite layer  

SciTech Connect

Neutron diffraction was used to study the residual stress distribution in an axisymmetric Al{sub 2}O{sub 3}-Ni joint bonded with a 40 vol% Al{sub 2}O{sub 3}-60 vol% Ni composite layer. A series of measurements was taken along the axis of symmetry through the Al{sub 2}O{sub 3} and composite layers. It is shown that after taking into account the finite neutron diffraction sampling volume, both the trends and peak values of the experimental strain distribution were in excellent agreement with calculations of a simple finite element model, where the rule-of-mixtures approach was used to describe the constitutive behavior of the composite interlayer. In particular, the predicted steep strain gradient near the interface was confirmed by the experimental data.

Wang, X.L.; Watkins, T.R. [Oak Ridge National Lab., TN (United States); Rabin, B.H.; Williamson, R.L.; Bruck, H.A. [Idaho National Engineering Lab., Idaho Falls, ID (United States)

1996-07-01

267

Stress and social support in high-risk pregnancy.  

PubMed

Relationships of stress, social support, and risk in pregnancy were tested in low-income women receiving outpatient antepartal care. Nineteen high-risk and 20 low-risk women completed the State Anxiety Inventory and Brown's Support Behavior Inventory. Urinary catecholamine levels from a single morning urine sample, determined using High Performance Liquid Chromatography, were used as the indicator of physiological stress. There was a significant difference between the groups in epinephrine level, but not in norepinephrine level, anxiety, or social support scores. In the high-risk group, norepinephrine level and partner support were negatively correlated; there were no other significant correlations. In the low-risk group, epinephrine level was positively correlated with norepinephrine level and age; anxiety was negatively correlated with partner support and age. PMID:2798954

Kemp, V H; Hatmaker, D D

1989-10-01

268

High pressure and high temperature stabilization of cubic AlN in Ti0.60Al0.40N  

NASA Astrophysics Data System (ADS)

In the present work, the decomposition of unstable arc evaporated Ti0.6Al0.4N at elevated temperatures and quasihydrostatic pressures has been studied both experimentally and by first-principles calculations. High pressure and high temperature (HPHT) treatment of the samples was realized using the multi anvil press and diamond anvil cell techniques. The products of the HPHT treatment of Ti0.6Al0.4N were investigated using x-ray diffractometry and transmission electron microscopy. Complimentary calculations show that both hydrostatic pressure and high temperature stabilize the cubic phase of AlN, which is one of the decomposition products of Ti0.6Al0.4N. This is in agreement with the experimental results which in addition suggest that the presence of Ti in the system serves to increase the stability region of the cubic c-AlN phase. The results are industrially important as they show that Ti0.6Al0.4N coatings on cutting inserts do not deteriorate faster under pressure due to the cubic AlN to hexagonal AlN transformation.

Norrby, N.; Lind, H.; Parakhonskiy, G.; Johansson, M. P.; Tasndi, F.; Dubrovinsky, L. S.; Dubrovinskaia, N.; Abrikosov, I. A.; Odn, M.

2013-02-01

269

The influence of water on the Peierls stress of olivine at high pressures  

NASA Astrophysics Data System (ADS)

To investigate the influence of water on the low-temperature plasticity of olivine under lithospheric conditions, we carried out a series of creep experiments on polycrystalline olivine at high pressures (~6 GPa), relatively low temperatures (873 ? T ? 1173 K), and hydrous conditions using a deformation-DIA. Samples were fabricated from fine powdered San Carlos olivine under hydrous conditions. In the experiments, a sample column composed of a sample and alumina pistons was assembled with a talc sleeve and graphite resistance heater into a 6.2-mm edge length cubic pressure medium. Experiments were carried out at the National Synchrotron Light Source at Brookhaven National Laboratory. In a run, differential stress and sample displacement were monitored in-situ using synchrotron x-ray diffraction and radiography, respectively. The low-temperature plasticity of olivine under hydrous conditions is constrained by our data with a Peierls stress of 4.2 0.3 GPa. This value is much lower than those reported the Peierls stress for olivine under anhydrous conditions (~ 6 - 15 GPa, Evans and Goetze, 1979; Raterron et al., 2004; Mei at al., 2010), indicating a significant influence of water on the low-temperature plasticity of olivine. The low-temperature flow behavior of olivine under hydrous conditions quantified in this study provides a necessary constraint for modeling the dynamic activities occurring within lithospheric mantle especially for those regions with the presence of water such as beneath a mid-ocean ridge and along a subducting slab.

Mei, S.; Suzuki, A. M.; Xu, L.; Kohlstedt, D. L.; Dixon, N. A.; Durham, W. B.

2012-04-01

270

Polarization effects on gate leakage in InAlN/AlN/GaN high-electron-mobility transistors  

NASA Astrophysics Data System (ADS)

Lattice-matched InAlN/AlN/GaN high electron mobility transistors offer high performance with attractive electronic and thermal properties. For high-voltage applications, gate leakage currents under reverse bias voltages remain a serious challenge. This current flow is dominated by field enhanced thermal emission from trap states or direct tunneling. We experimentally measure reverse-bias gate leakage currents in InAlN/AlN/GaN transistors at various temperatures and find that the conventional trap-assisted Frenkel-Poole model fails to explain the experimental data. Unlike the non-polar semiconductors Si, Ge, large polarization-induced electric fields exist in III-nitride heterojunctions. When the large polarization fields are accounted for, a modified Frenkel-Poole model is found to accurately explain the measured data at low reverse bias voltages. At high reverse bias voltages, we identify that the direct Fowler-Nordheim tunneling mechanism dominates. The accurate identification of the gate leakage current flow mechanism in these structures leads to the extraction of several useful physical parameters, highlights the importance of polarization fields, and leads to suggestions for improved behavior.

Ganguly, Satyaki; Konar, Aniruddha; Hu, Zongyang; Xing, Huili; Jena, Debdeep

2012-12-01

271

Study on Mold Slag with High Al2O3 Content for High Aluminum Steel  

NASA Astrophysics Data System (ADS)

The slag-steel equilibrium reaction between the newly developed mold slag ND-MSL and 20Mn23AlV steel has been studied at high temperatures in the laboratory. The crystal morphology, microanalysis, and phase analysis of the original and final ND-MSL slags were studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Results show that, in the final ND-MSL slag, the constitution of SiO2 decreased by 0.7 wt pct and Al2O3 increased by 6.46 wt pct, while the melting temperature, viscosity, and crystallization rate increased by 62 K, 0.66 dPa s, and 15 pct, respectively. NaAlSi3O8 and CaAl2Si2O8 were found to be precipitated in the final ND-MSL slag. Both the original and final ND-MSL slags have a small amount of LiF crystal and good glass form. The ND-MSL slag has little change in the composition and properties compared with the two currently used mold slags.

Wang, Qiang; Sun, Min; Qiu, Shengtao; Tian, Zhiling; Zhu, Guoling; Wang, Longmei; Zhao, Pei

2013-08-01

272

Differences in Al tolerance between Plantago algarbiensis and P. almogravensis reflect their ability to respond to oxidative stress.  

PubMed

We evaluated the impact of low pH and aluminum (Al) on the leaves and roots of Plantago almogravensis Franco and Plantago algarbiensis Samp., focusing on energy partitioning in photosystem II, H?O? levels, lipid peroxidation, electrolyte leakage (EL), protein oxidation, total soluble protein content and antioxidant enzyme activities. In both species, Al triggered more changes in oxidative metabolism than low pH alone, particularly in the roots. We found that Al increased the levels of H?O? in P. algarbiensis roots, but reduced the levels of H?O? in P. almogravensis leaves and roots. Neither low pH nor Al affected the spatial heterogeneity of chlorophyll fluorescence, the maximum photochemical efficiency of PSII (Fv/Fm), the actual quantum efficiency of PSII (?PSII) or the quantum yields of regulated (?NPQ) and nonregulated (?NO) energy dissipation, and there was no significant change in total soluble protein content and EL. In P. algarbiensis, Al increased the carbonyl content and the activities of superoxide dismutase (SOD) and catalase (CAT) in the roots, and also CAT, ascorbate peroxidase and guaiacol peroxidase activities in the leaves. In P. almogravensis, Al reduced the level of malondialdehyde in the roots as well as SOD activity in the leaves and roots. We found that P. almogravensis plantlets could manage the oxidative stress caused by low pH and Al, whereas the P. algarbiensis antioxidant system was unable to suppress Al toxicity completely, leading to the accumulation of H?O? and consequential protein oxidation in the roots. PMID:23563731

Martins, Neusa; Osrio, Maria Leonor; Gonalves, Sandra; Osrio, Jlio; Romano, Anabela

2013-04-08

273

Delineating the genetic heterogeneity of ALS using targeted high-throughput sequencing  

PubMed Central

Background Over 100 genes have been implicated in the aetiology of amyotrophic lateral sclerosis (ALS). A detailed understanding of their independent and cumulative contributions to disease burden may help guide various clinical and research efforts. Methods Using targeted high-throughput sequencing, we characterised the variation of 10 Mendelian and 23 low penetrance/tentative ALS genes within a population-based cohort of 444 Irish ALS cases (50 fALS, 394 sALS) and 311 age-matched and geographically matched controls. Results Known or potential high-penetrance ALS variants were identified within 17.1% of patients (38% of fALS, 14.5% of sALS). 12.8% carried variants of Mendelian disease genes (C9orf72 8.78%; SETX 2.48%; ALS2 1.58%; FUS 0.45%; TARDBP 0.45%; OPTN 0.23%; VCP 0.23%. ANG, SOD1, VAPB 0%), 4.7% carried variants of low penetrance/tentative ALS genes and 9.7% (30% of fALS, 7.1% of sALS) carried previously described ALS variants (C9orf72 8.78%; FUS 0.45%; TARDBP 0.45%). 1.6% of patients carried multiple known/potential disease variants, including all identified carriers of an established ALS variant (p<0.01); TARDBP:c.859G>A(p.[G287S]) (n=2/2 sALS). Comparison of our results with those from studies of other European populations revealed significant differences in the spectrum of disease variation (p=1.710?4). Conclusions Up to 17% of Irish ALS cases may carry high-penetrance variants within the investigated genes. However, the precise nature of genetic susceptibility differs significantly from that reported within other European populations. Certain variants may not cause disease in isolation and concomitant analysis of disease genes may prove highly important.

Kenna, Kevin P; McLaughlin, Russell L; Byrne, Susan; Elamin, Marwa; Heverin, Mark; Kenny, Elaine M; Cormican, Paul; Morris, Derek W; Donaghy, Colette G; Bradley, Daniel G; Hardiman, Orla

2013-01-01

274

High temperature oxidation behavior of multicomponent TiAlSiN coatings  

Microsoft Academic Search

Recently, multicomponent TiAlSiN coatings have been developed in order to possess high hardness and good thermal stability at a temperature exceeding 800C. In this study, a series of TiAlSiN coatings were synthesized with different ratios of Al0.89Si0.11\\/(Ti+Al0.89Si0.11) cathode current by using a cathodic arc evaporation system with lateral rotating arc sources. The high temperature oxidation behavior of TiAlSiN coatings with

Yin-Yu Chang; Sheng-Min Yang

2010-01-01

275

Single-quantum well InGaN green light emitting diode degradation under high electrical stress  

Microsoft Academic Search

We performed a degradation study of high-brightness Nichia single-quantum well AlGaN\\/InGaN\\/GaN green light-emitting diodes (LEDs). The devices were subjected to high current electrical stress with current pulse amplitudes between 1 and 7 A and voltages between 10 and 70 V with a pulse length of 100 ns and a 1 kHz repetition rate. The study showed that when the current

Daniel L. Barton; Marek Osinski; Piotr Perlin; Petr G. Eliseev; Jinhyun Lee

1999-01-01

276

Characterization of the reliability and uniformity of an anodization-free fabrication process for high-quality Nb/AlAlOx/Nb Josephson junctions  

NASA Astrophysics Data System (ADS)

We have developed a reliable and reproducible fabrication process for high-quality Nb/AlAlOx/Nb Josephson junctions that completely avoids anodization techniques, that are typically used to define the junction area, to electrically insulate the base electrode as well as the sidewalls of the counter-electrode and to protect the tunnel barrier. Hence, this process is well suited for the fabrication of electrically floating junction-based devices such as non-hysteretic rf-SQUIDs. Josephson junctions of various sizes have been produced and characterized at 4.2 K. We found that our junctions have a high quality, which is confirmed by measured gap voltages Vg and Ic Rn products up to 2.9 and 1.8 mV and on-wafer average values of the resistance ratio Rsg/Rn above 30 in most cases. Here, Rsg and Rn denote the subgap and the normal state resistance of a Josephson junction. Although the uniformity of the properties of the Josephson junctions across a wafer is high, we observe some systematic variations of the critical current density and the gap voltage over an entire wafer. These variations are most likely to be attributed to residual stress in the Nb films as well as the surface roughness of the Nb base electrode.

Kempf, S.; Ferring, A.; Fleischmann, A.; Gastaldo, L.; Enss, C.

2013-06-01

277

Stress corrosion failure of high-pressure gas pipeline  

Microsoft Academic Search

Incidents of failure due to corrosion\\/stress corrosion cracking of high-pressure gas pipelines in Pakistan have been observed to occur after about 1520 years of service. The present paper constitutes the failure analysis of an 18-inch diameter electric resistance-welded gas pipeline. The failure was characterized, on the basis of all the available evidence and the metallurgical examination carried out on the

F. Hasan; J. Iqbal; F. Ahmed

2007-01-01

278

Stress corrosion cracking of a superplastic and nonsuperplastic Zn-22.3Al alloy in 3% NaCl solution  

SciTech Connect

Through appropriate heat treatments, a Zn-22.3wt%Al (Zn-22.3Al) alloy can be prepared in both superplastic and nonsuperplastic specimens. It has been found that the superplastic Zn-22.3Al alloy possesses a very fine microduplex structure, while the nonsuperplastic alloy has a lamellar duplex structure with locally coarsened second phases. The very different microstructures of both specimens result in different corrosion and stress corrosion cracking (SCC) behaviors in 3% NaCl solution. In addition, the fractographs of both the superplastic and nonsuperplastic Zn-22.3Al specimens after SCC tests under various anodic applied potentials have been compared. Through the observations, a mechanism for the SCC in this case was proposed to show that the cracks proceeded with successive processes of oxide film rupture and Zn-Al matrix tearing. Such a mechanism is more evident for the fractography of nonsuperplastic specimens, on which a series of parallel strips inserted with dimple-bands can be obviously found.

Yeh, M.S. [Chung-Hua Univ., Hsinchu (Taiwan, Province of China). Dept. of Mechanical Engineering; Chang, J.C.; Chuang, T.H. [National Taiwan Univ., Taipei (Taiwan, Province of China). Inst. of Materials Science and Engineering

1999-04-01

279

Stress  

MedlinePLUS

... free. Enroll today. Home > Living with Diabetes > Complications Stress Listen Stress results when something causes your body ... so glucose piles up in the blood. How Stress Affects Diabetes Many sources of stress are long- ...

280

High-temperature deformation behavior of an Al-8.4Fe-3.6Ce dispersion-strengthened material  

SciTech Connect

The high-temperature deformation behavior of a dispersion-strengthened Al-8.4Fe-3.6Ce material studied by Yaney and Nix has been reanalyzed using concepts used in the analysis of the creep behavior of Al-Fe-V-Si materials. The Al-8.4Fe-3.6Ce material presents a high volume fraction of submicron dispersoids. The stress exponent and the activation energy values are anomalously high-temperature dependent, as it is usually found in most reinforced materials. Although the creep behavior of this material has been described by the deformation of dispersoids, however, direct evidence of the deformation of the second-phase precipitates was not obtained. In this work, a new approach is further developed. This approach is based on the constant substructure slip creep equation modified by the presence of an interaction between dislocations and dispersoids. This approach is able to satisfactorily predict the creep behavior of the Al-8.4Fe-3.6Ce material.

Carreno, F.; Ruano, O.A. [Centro Nacional de Investigaciones Metalurgicas, Madrid (Spain). Dept. of Physical Metallurgy

1999-02-01

281

High-quality Al{sub x}Ga{sub 1{minus}x}N using low temperature-interlayer and its application to UV detector[Ultraviolet  

SciTech Connect

Low-temperature (LT-) AlN interlayer reduces tensile stress during growth of Al{sub x}Ga{sub 1{minus}x}N, while simultaneously acts as the dislocation filter, especially for dislocations of which Burger's vector contains [0001] components. UV photodetectors using thus-grown high quality Al{sub x}Ga{sub 1{minus}x}N layers were fabricated. The dark current below 50 fA at 10 V bias for 10 {micro}m strip allowing a photocurrent to dark current ratio greater than one even at 40 nW/cm{sup 2} have been achieved.

Iwaya, M.; Terao, S.; Hayashi, N.; Kashima, T.; Detchprohm, T.; Amano, H.; Akasaki, I.; Hirano, A.; Pernot, C.

2000-07-01

282

Material flow stress and failure in multiscale machining titanium alloy Ti6Al4V  

Microsoft Academic Search

Titanium Ti-6Al-4V alloy is a typical difficult-to-machine material due to its unique physical and mechanical properties.\\u000a The material properties of Ti-6Al-4V play an important role in process design and optimization. However, the dynamic mechanical\\u000a behavior is poorly understood and accurate predictive models have yet to be developed. This work focuses on the dynamic mechanical\\u000a behavior of machining Ti-6Al-4V beyond the

J. Sun; Y. B. Guo

2009-01-01

283

Residual stresses in alumina scales grown on different types of FeCrAl alloys: effect of specimen geometry and cooling rate  

Microsoft Academic Search

Residual stress measurements in alumina scales grown on FeCrAl alloys were conducted using the ruby fluorescence technique and the results compared with common theoretical considerations. The oxidation experiments were carried out at 1200C using different FeCrAl-based materials, different substrate thickness values and varying cooling rates. In case of a conventional wrought alloy the cooling rate significantly influences the residual stress

H. Echsler; E. Alija Martinez; L. Singheiser; W. J. Quadakkers

2004-01-01

284

An Inducer of VGF Protects Cells against ER Stress-Induced Cell Death and Prolongs Survival in the Mutant SOD1 Animal Models of Familial ALS  

Microsoft Academic Search

Amyotrophic lateral sclerosis (ALS) is the most frequent adult-onset motor neuron disease, and recent evidence has suggested that endoplasmic reticulum (ER) stress signaling is involved in the pathogenesis of ALS. Here we identified a small molecule, SUN N8075, which has a marked protective effect on ER stress-induced cell death, in an in vitro cell-based screening, and its protective mechanism was

Masamitsu Shimazawa; Hirotaka Tanaka; Yasushi Ito; Nobutaka Morimoto; Kazuhiro Tsuruma; Michinori Kadokura; Shigeki Tamura; Teruyoshi Inoue; Mitsunori Yamada; Hitoshi Takahashi; Hitoshi Warita; Masashi Aoki; Hideaki Hara; Rafael Linden

2010-01-01

285

Electrorheological fluid with an extraordinarily high yield stress  

NASA Astrophysics Data System (ADS)

Surface modified complex strontium titanate microparticles are synthesized by means of a modified sol-gel technique. A suspension composed of these particles immersed in a silicone oil exhibits excellent electrorheological properties attractive to industry and technology applications: a yield stress as high as 27 kPa in an applied electric field of 3 kV/mm, a low leakage current, wide dynamic ranges in temperature and shear rate, and a long-term stability against sedimentation. In addition to the high dielectric constant of strontium titanate, surfactant and water-free character of the particles may be responsible for the dramatic improvement of the electrorheological properties of the suspension.

Zhang, Yuling; Lu, Kunquan; Rao, Guanghui; Tian, Yu; Zhang, Shaohua; Liang, Jingkui

2002-02-01

286

An analysis of thermal residual stresses in Ti-6-4 alloy reinforced with SiC and Al[sub 2]O[sub 3] fibers. [Ti-6Al-4V  

SciTech Connect

Thermal residual stresses in Ti-6Al-4V alloy reinforced with silicon carbide (SiC) and sapphire alumina (Al[sub 2]O[sub 3]) fibers are estimated based on an elastic-viscoplastic micromechanics analysis. Effects of fiber volume fraction and different manufacturing procedures are considered and comparisons made with published experimental results for the SiC fiber composite. Stress components in the Ti-6-4/Al[sub 2]O[sub 3] are generally less than half the corresponding values in the Ti-6-4/SiC composite.

Durodola, J.F. (Univ. of Oxford (United Kingdom). Oxford Centre for Advanced Materials and Composites); Derby, B. (Univ. of Oxford (United Kingdom). Dept. of Materials)

1994-05-01

287

High temperature oxidation resistance of multicomponent CrTiAlSiN coatings  

Microsoft Academic Search

Nanosrystalline CrAlSiN and CrTiAlSiN coatings were deposited by using a cathodic-arc deposition system with lateral rotating arc cathodes. Titanium, chromium and Al89Si11 cathodes were used for the deposition of CrAlSiN and CrTiAlSiN coatings. For the high temperature oxidation test, the coated samples were annealed at 900C in air for 2h. The oxidation characteristics of the deposited coatings were also studied

Yin-Yu Chang; Chia-Yuan Hsiao

2009-01-01

288

Effect of Al on High-Temperature Oxidation of CrW Alloys  

SciTech Connect

Abstract The effect of Al on the high temperature oxidation behavior of Cr10 wt.%W alloy was investigated using a cyclical oxidation test at 1,000 C in dry air. First, Al was added into the CrW alloy as an alloying element up to 8 weight percent. Although alloying with Al reduced the spalling, it did not eliminate it. Secondly, Al was applied to the surface using an aluminizing process. Forming an AlCr layer on the CrW alloy reduced oxidation rate significantly and eliminated spalling completely.

. N. Do?an

2008-02-01

289

Extrinsic and intrinsic causes of the electrical degradation of AlGaN/GaN high electron mobility transistors  

NASA Astrophysics Data System (ADS)

Electrical stress experiments under different bias configurations for AlGaN/GaN high electron mobility transistors were performed and analyzed. The electric field applied was found to be the extrinsic cause for the device instability, while the traps were recognized as the main intrinsic factor. The effect of the traps on the device degradation was identified by recovery experiments and pulsed I-V measurements. The total degradation of the devices consists of two parts: recoverable degradation and unrecoverable degradation. The electric field induced traps combined with the inherent ones in the device bulk are mainly responsible for the recoverable degradation.

Yulong, Fang; Shaobo, Dun; Bo, Liu; Jiayun, Yin; Shujun, Cai; Zhihong, Feng

2012-05-01

290

Analysis of the FeZn interface of galvanized high Allow Si TRIP steels  

Microsoft Academic Search

TRIP-assisted steels are ideal for lightweight automotive applications due to their high strength and ductility. The selective oxidation of the alloying elements Mn, Al and Si during annealing prior to galvanizing can cause poor reactive wetting during galvanizing, resulting in bare spot defects. Despite the selective oxidation of alloying elements two high Allow Si TRIP steels were successfully galvanized. It

E. M. Bellhouse; J. R. McDermid

2008-01-01

291

Eddy current measurement of residual stresses induced by shot peening in titanium Ti-6Al-4V  

SciTech Connect

An experimental investigation of the feasibility of using eddy current technology to nondestructively determine the residual stresses induced by shot peening in Ti-6Al-4V plate was undertaken. Because of the extremely small magnitude of the shot peening-induced conductivity changes, strict noise control was vital and was achieved by mechanical and thermal isolation of the apparatus. This was accomplished by modifying the instrument to improve temperature isolation of several key internal components and also by physically and electronically isolating the experimental apparatus. Results indicate that residual stress can be clearly determined for material shot peened to a depth of 0.3 mm (0.012 in.) or more with an experimental variation of less than 3 ppm.

Schoenig, F.C. Jr.; Soules, J.A.; Chang, H.; DiCillo, J.J. (Cleveland State Univ., OH (United States). Advanced Manufacturing Center)

1995-01-01

292

Anisotropy of tensile stresses and cracking in nonbasal plane Al{sub x}Ga{sub 1-x}N/GaN heterostructures  

SciTech Connect

Al{sub x}Ga{sub 1-x}N films grown on nonpolar m (1100) and (1122) semipolar orientations of freestanding GaN substrates were investigated over a range of stress states (x<=0.17). Cracking on the (0001) plane was observed beyond a critical thickness in the (1100) oriented films, while no cracking was observed for (1122) films. Theoretical analysis of tensile stresses in Al{sub x}Ga{sub 1-x}N for the relevant planes revealed that anisotropy of in-plane biaxial stress for the nonpolar (1100) planes results in the highest normal stresses on the c-planes, consistent with experimental observations. Shear stresses are significant in the semipolar case, suggesting that misfit dislocation formation provides an alternative mechanism for stress relief.

Young, Erin C.; Gallinat, Chad S.; Hirai, Asako; Speck, James S. [Department of Materials, University of California, Santa Barbara, California 93106 (United States); Romanov, Alexey E. [Department of Materials, University of California, Santa Barbara, California 93106 (United States); Ioffe Physical Technical Institute RAS, St. Petersburg 194021 (Russian Federation); Beltz, Glenn E. [Department of Mechanical Engineering, University of California, Santa Barbara, California 93106 (United States)

2010-01-25

293

High-pressure transitions in MgAl2O4 and a new high-pressure phase of Mg2Al2O5  

NASA Astrophysics Data System (ADS)

Phase transitions in MgAl2O4 were examined at 21-27 GPa and 1400-2500 C using a multianvil apparatus. A mixture of MgO and Al2O3 corundum that are high-pressure dissociation products of MgAl2O4 spinel combines into calcium-ferrite type MgAl2O4 at 26-27 GPa and 1400-2000 C. At temperature above 2000 C at pressure below 25.5 GPa, a mixture of Al2O3 corundum and a new phase with Mg2Al2O5 composition is stable. The transition boundary between the two fields has a strongly negative pressure-temperature slope. Structure analysis and Rietveld refinement on the basis of the powder X-ray diffraction profile of the Mg2Al2O5 phase indicated that the phase represented a new structure type with orthorhombic symmetry (Pbam), and the lattice parameters were determined as a=9.3710(6) , b=12.1952(6) , c=2.7916(2) , V=319.03(3) 3, Z=4. The structure consists of edge-sharing and corner-sharing (Mg, Al)O6 octahedra, and contains chains of edge-sharing octahedra running along the c-axis. A part of Mg atoms are accommodated in six-coordinated trigonal prism sites in tunnels surrounded by the chains of edge-sharing (Mg, Al)O6 octahedra. The structure is related with that of ludwigite (Mg, Fe2+)2(Fe3+, Al)(BO3)O2. The molar volume of the Mg2Al2O5 phase is smaller by 0.18% than sum of molar volumes of 2MgO and Al2O3 corundum. High-pressure dissociation to the mixture of corundum-type phase and the phase with ludwigite-related structure has been found only in MgAl2O4 among various A2+B3+2O4 compounds.

Enomoto, A.; Kojitani, H.; Akaogi, M.; Miura, H.; Yusa, H.

2009-02-01

294

Synthesis and stress relaxation of ZnO/Al-doped ZnO core-shell nanowires.  

PubMed

Doping nanostructures is an effective method to tune their electrical and photoelectric properties. Taking ZnO nanowires (NWs) as a model system, we demonstrate that atomic layer deposition (ALD) can be adopted for the realization of a doping process by the homo-epitaxial growth of a doped shell on the NW core. The Al-doped ZnO NWs have a layered superlattice structure with dopants mainly occupying the interstitial positions. After annealing, Al(3+) ions diffuse into the ZnO matrix and occupy substitutional locations, which is desirable for dopant activation. The stress accumulated during epitaxial growth is relaxed by the nucleation of dislocations, dislocation dipoles and anti-phase boundaries. We note that the proposed method can be easily adopted for doping different types of nanostructures, and fabricating superlattices and multiple quantum wells on NWs in a controllable way. PMID:23443575

Wang, Hong-Bo; Ma, Fei; Li, Qian-Qian; Dong, Ce-Zhou; Ma, Da-Yan; Wang, Hong-Tao; Xu, Ke-Wei

2013-04-01

295

Efficient stress relief in GaN heteroepitaxy on Si(1 1 1) using low-temperature AlN interlayers  

Microsoft Academic Search

Low-temperature (LT) AlN interlayers can be applied to reduce the tensile stress and cracks in thick GaN layers on Si. Here, we present an X-ray diffractometry study revealing the influence of metalorganic chemical vapor phase deposition parameters on stress relaxation by these interlayers. The degree of stress relaxation is observed to strongly depend on interlayer deposition temperature. At low temperatures,

A. Reiher; J. Blsing; A. Dadgar; A. Diez; A. Krost

2003-01-01

296

Itacolumite like High Damping Ceramics in the System Al2O3-TiO2-MgO  

SciTech Connect

Ceramics is rigid and brittle originally. If the weakness could be overcome, the application will be widely expanded. Itacolumite known as high flexibility rock is the group of sand stone which consist of quartz and slight amount of muscovite. The microstructure of itacolumite has a lot of narrow gaps between the grains, the gap was thought to be formed by the dissolution of minerals in between quartz grains into the groundwater. This narrow space enables a little displacement of the particles, and the rock can bend with stress like plastic deformation. These characters of itacolumite showed the new ceramic functions such as stress relaxation properties and high damping capacity (internal friction Q-1=0.03). The authors tried to develop high damping ceramics by the mimic of itacolumite, and found the Al2O3-TiO2-MgO ceramics. The ceramics had stress relaxation properties and high damping capacity (Q-1=0.01) since microcracks were formed during sintering by the discontinuous grain growth and the anisotropic thermal expansion in the cooling process.

Shimazu, T. [Graduate School of Environmental Studies Tohoku University, Sendai, Miyagi, 980-8579 (Japan); General Research Institute of Technology, INAX Corp., Minatomachi, Tokoname, Aichi, 479-8588 (Japan); Miura, M.; Isu, N. [General Research Institute of Technology, INAX Corp., Minatomachi, Tokoname, Aichi, 479-8588 (Japan); Ogawa, T. [Acoh Ceramic Corporation, Oroshicho, Toki, Gifu, 509-5202 (Japan); Ichikawa, A. [Sanwa Yuka Kogyo Corporation, Ichiriyamacho, Kariya, Aichi, 448-0002 (Japan); Ishida, E. H. [Graduate School of Environmental Studies Tohoku University, Sendai, Miyagi, 980-8579 (Japan)

2006-05-15

297

Compressive stresses and stabilisation in Cu-Al-Ni single crystals  

NASA Astrophysics Data System (ADS)

Cu-AI-Ni single crystals which present ?{-}?' (quenched samples) or ?{-}? (aged at 570K samples) thermally induced martensitic transformations, were submitted to compressive stresses at different temperatures. The test temperatures were chosen in order to have martensite-martensite stress induced transformations. The characteristics of the martensitic transformation and structural changes before and after the compression tests have been studied by means of calorimetry (DSC) and TEM. The obtained results show that when applying compressive stresses in both ensembles of samples, a non-twinned ?' martensite appears. In the quenched samples it is formed through the beta phase already present at room temperature. In the aged samples the non twinned ?' phase is stress induced from the ?' thermally formed (internally twinned). The amount of non twinned ?' phase increases with the applied deformation, for low strain values it coexists with the ?' or ?' (twinned) phases and is the only present phase for higher applied strain values. In all the cases a notable martensite stabilisation is observed in the first thermal induced transformation after the mechanical test only when the stress-strain loops are not closed, that means when a permanent strain remains in the material after unloading. The degree of mechanical stabilisation is more important as higher is the applied deformation and as much amount of ?' phase mechanically formed (non twinned) is still present in the material and it is slightly dependent on the test temperature if lower than Af The stress induced stabilisation mechanism is related to the presence of this non twinned martensite and its difficult retransformation to the parent phase.

Picornell, C.; Pons, J.; Cesari, E.

2003-10-01

298

High-dose implantations of Al into Si(111) and Si(100)  

SciTech Connect

High dose implants of Al (0.5 {times} 10{sup 18} to 2.0 {times} 10{sup 18}/cm{sup 2}) at 200 keV into silicon substrates at 375C were performed in an attempt to form a pure, monocrystalline buried layer of Al in silicon upon post-implant annealing. Nuclear reaction analysis (NRA) and Auger electron spectroscopy (AES) were used to determine the Al concentration and morphology as a function of depth. Results show a peak Al concentration of 83 at.% at a depth of {approx}350 run for the highest dose, and the morphology of the Al is of an interconnected network of 100 at.% Al. Failure to form a continuous elemental layer is explained by the as-implanted morphology resulting thermally induced precipitate coarsening rate at 375C. Formation of large, stable, individual Al precipitates was thermodynamically favored for the implant conditions and effectively precluded coalescence into a continuous layer.

Daley, R.S.; Musket, R.G.

1992-12-14

299

High-dose implantations of Al into Si(111) and Si(100)  

SciTech Connect

High dose implants of Al (0.5 [times] 10[sup 18] to 2.0 [times] 10[sup 18]/cm[sup 2]) at 200 keV into silicon substrates at 375C were performed in an attempt to form a pure, monocrystalline buried layer of Al in silicon upon post-implant annealing. Nuclear reaction analysis (NRA) and Auger electron spectroscopy (AES) were used to determine the Al concentration and morphology as a function of depth. Results show a peak Al concentration of 83 at.% at a depth of [approx]350 run for the highest dose, and the morphology of the Al is of an interconnected network of 100 at.% Al. Failure to form a continuous elemental layer is explained by the as-implanted morphology resulting thermally induced precipitate coarsening rate at 375C. Formation of large, stable, individual Al precipitates was thermodynamically favored for the implant conditions and effectively precluded coalescence into a continuous layer.

Daley, R.S.; Musket, R.G.

1992-12-14

300

Invasive Knotweeds are Highly Tolerant to Salt Stress  

NASA Astrophysics Data System (ADS)

Japanese knotweed s.l. are some of the most invasive plants in the world. Some genotypes are known to be tolerant to the saline concentrations found in salt marshes. Here we focus on tolerance to higher concentrations in order to assess whether the species are able to colonize and establish in highly stressful environments, or whether salt is an efficient management tool. In a first experiment, adult plants of Fallopia japonica, Fallopia bohemica and Fallopia sachalinensis were grown under salt stress conditions by watering with saline concentrations of 6, 30, 120, or 300 g L-1 for three weeks to assess the response of the plants to a spill of salt. At the two highest concentrations, their leaves withered and fell. There were no effects on the aboveground parts at the lowest concentrations. Belowground dry weight and number of buds were reduced from 30 and 120 g L-1 of salt, respectively. In a second experiment, a single spraying of 120 g L-1 of salt was applied to individuals of F. bohemica and their stems were clipped to assess the response to a potential control method. 60 % of the plants regenerated. Regeneration was delayed by the salt treatment and shoot growth slowed down. This study establishes the tolerance of three Fallopia taxa to strong salt stress, with no obvious differences between taxa. Their salt tolerance could be an advantage in their ability to colonize polluted environments and to survive to spills of salt.

Rouifed, Soraya; Byczek, Coline; Laffray, Daniel; Piola, Florence

2012-12-01

301

Invasive knotweeds are highly tolerant to salt stress.  

PubMed

Japanese knotweed s.l. are some of the most invasive plants in the world. Some genotypes are known to be tolerant to the saline concentrations found in salt marshes. Here we focus on tolerance to higher concentrations in order to assess whether the species are able to colonize and establish in highly stressful environments, or whether salt is an efficient management tool. In a first experiment, adult plants of Fallopia japonica, Fallopia bohemica and Fallopia sachalinensis were grown under salt stress conditions by watering with saline concentrations of 6, 30, 120, or 300 g L(-1) for three weeks to assess the response of the plants to a spill of salt. At the two highest concentrations, their leaves withered and fell. There were no effects on the aboveground parts at the lowest concentrations. Belowground dry weight and number of buds were reduced from 30 and 120 g L(-1) of salt, respectively. In a second experiment, a single spraying of 120 g L(-1) of salt was applied to individuals of F. bohemica and their stems were clipped to assess the response to a potential control method. 60 % of the plants regenerated. Regeneration was delayed by the salt treatment and shoot growth slowed down. This study establishes the tolerance of three Fallopia taxa to strong salt stress, with no obvious differences between taxa. Their salt tolerance could be an advantage in their ability to colonize polluted environments and to survive to spills of salt. PMID:22961615

Rouifed, Soraya; Byczek, Coline; Laffray, Daniel; Piola, Florence

2012-09-09

302

High-Mobility Group Box 1, Oxidative Stress, and Disease  

PubMed Central

Abstract Oxidative stress and associated reactive oxygen species can modify lipids, proteins, carbohydrates, and nucleic acids, and induce the mitochondrial permeability transition, providing a signal leading to the induction of autophagy, apoptosis, and necrosis. High-mobility group box 1 (HMGB1) protein, a chromatin-binding nuclear protein and damage-associated molecular pattern molecule, is integral to oxidative stress and downstream apoptosis or survival. Accumulation of HMGB1 at sites of oxidative DNA damage can lead to repair of the DNA. As a redox-sensitive protein, HMGB1 contains three cysteines (Cys23, 45, and 106). In the setting of oxidative stress, it can form a Cys23-Cys45 disulfide bond; a role for oxidative homo- or heterodimerization through the Cys106 has been suggested for some of its biologic activities. HMGB1 causes activation of nicotinamide adenine dinucleotide phosphate oxidase and increased reactive oxygen species production in neutrophils. Reduced and oxidized HMGB1 have different roles in extracellular signaling and regulation of immune responses, mediated by signaling through the receptor for advanced glycation end products and/or Toll-like receptors. Antioxidants such as ethyl pyruvate, quercetin, green tea, N-acetylcysteine, and curcumin are protective in the setting of experimental infection/sepsis and injury including ischemia-reperfusion, partly through attenuating HMGB1 release and systemic accumulation. Antioxid. Redox Signal. 14, 13151335.

Kang, Rui; Zeh, Herbert J.

2011-01-01

303

Effect of internal stresses and microstructure of sputtered TiN films on solid-phase reactions with Al-Si-Cu alloy films  

Microsoft Academic Search

Solid-phase reactions at the interface between Al-Si-Cu and reactively sputtered TiN thin films have been investigated by cross-sectional transmission electron microscopy, Auger electron spectroscopy, and x-ray diffraction. In the case in which the internal stress in the TiN thin film is extremely compressive at 209 MPa, a very thin amorphous Al-Ti-Si ternary compound layer (a-Al-Ti-Si) containing microcrystallites, about 4 nm

T. Yamauchi; T. Yamaoka; K. Yashiro; S. Sobue

1995-01-01

304

Effect of Zn Content on the Microstructure and Properties of Super-High Strength Al-Zn-Mg-Cu Alloys  

NASA Astrophysics Data System (ADS)

The microstructure and properties of three different Al-Zn-Mg-Cu alloys with high Zn content (9 wt pct, 10 wt pct, and 11 wt pct, marked as 9Zn, 10Zn, and 11Zn, respectively) were investigated. The strength of alloys increases as the Zn content increases from 9 wt pct to 10 wt pct, while it does not increase any more as the Zn content increases continuously from 10 wt pct to 11 wt pct. The stress-corrosion cracking (SCC) resistance decreases as the Zn content increases from 9 wt pct to 10 wt pct, while it changes unobviously as the Zn content increases continuously from 10 wt pct to 11 wt pct. The elongation and fracture toughness of alloys decrease as the Zn content increases in these Al-Zn-Mg-Cu alloys. The Zn content has little effect on the precipitation reaction of Al-Zn-Mg-Cu alloys that contain the mixture of GP zones, and ?' are the main Matrix Precipitates (MPt) in the peak-aging state, and the mixture of ?' and ? are the main MPt in the over-aging state. The amount of MPt and coarse T (AlZnMgCu) phases are shown to increase with the increasing Zn content in Al-Zn-Mg-Cu alloys. The coarse T phases hardly dissolve into the matrix and are the source for the crack initiation, which may be the responsibility for the negative effect on the properties of high Zn content Al-Zn-Mg-Cu alloys.

Chen, Ziyong; Mo, Yuanke; Nie, Zuoren

2013-04-01

305

Flow stresses in metal laminates and pure metals during high temperature extrusion  

Microsoft Academic Search

The flow stresses developed during elevated temperature extrusion in laminated metal composites are analyzed. The laminates consist either of ultrahigh carbon steels (UHCSs) or NiAl jacketed in a mild steel can. Flow stresses in the individual components of the laminate were determined by utilizing an isostrain model and by establishing the true coefficient of friction during extrusion. The average coefficient

D. R. Lesuer; C. K. Syn; J. D. Whittenberger; O. D. Sherby

2002-01-01

306

Community settings as buffers of life stress? Highly supportive churches, mutual help groups, and senior centers  

Microsoft Academic Search

Examined the stress-buffering potential of community settings in three studies. The first study focused on economic stress among 162 members of three churches, the second on bereavement stress among 80 members of eight mutual help groups for bereaved parents, and the third on bereavement stress among 85 members of six senior centers. In each study, high and low support settings

Kenneth I. Maton

1989-01-01

307

The Effect of Prenatal Stress on Birth Weight: Evidence from the al-Aqsa Intifada  

Microsoft Academic Search

No previous study has attempted to estimate the effect of intrauterine exposure to armed conflict, a potential source of stress, on pregnancy outcomes. Drawing on data from the 2004 Palestinian Demographic and Health Survey, we examine the relationship between fatalities caused by Israeli security forces (a measure of conflict intensity) and birth weight. Our estimates suggest that first-trimester fatalities are

Hani Mansour; Daniel I. Rees

2011-01-01

308

TEM investigation of age-hardenable Al 2519 alloy subjected to stress corrosion cracking tests  

Microsoft Academic Search

The influence of changes in chemical composition and pre-aging deformation on the resistance to stress corrosion cracking in the age-hardenable aluminum alloy 2519 was investigated by transmission electron microscopy. The improvement of this resistance may be accomplished by keeping the Cu concentration on the lower side of the allowed limit for the 2519 alloy. Also, plastic deformation prior to aging,

Stanis?aw Dymek; Marek Dollar

2003-01-01

309

Yield Stress of Periclase at High Pressure and Low Temperature  

NASA Astrophysics Data System (ADS)

Magnesiowustite (Mg,Fe)O is a significant constituent of the Earth lower mantle. In a follow-up investigation of the rheological properties of MgO periclase as an analog for magnesiowustite, one powder specimen of MgO (micrometric grain size) has been investigated at pressures up to 10 GPa and temperatures ranging from 25\\deg C to 300\\deg C. The experiment was performed in a multi-anvil (SAM85, DIA-type) high-pressure apparatus, with boron epoxy as pressure medium and a BN capsule enclosing the specimen. Temperature was measured with a W3%Re-W25%Re thermocouple situated next to the sample, while the cell pressure (NaCl Decker's scale) and the stress in the sample (diffraction peak broadening, a review in Weidner, 1998) were monitored by using in-situ synchrotron X-ray diffraction at the superconductor wiggler beam line of the NSLS facility (Brookhaven, NY). The run product was investigated by Transmission Electron Microscopy (MET) using a Jeol 200 CX microscope. From the X-ray diffraction data, we infer that periclase exhibits at room temperature a transition from elastic to plastic deformation at differential stresses higher than 3 GPa. A yield stress value of just over 4 GPa was measured under these conditions. Slight sample relaxation over time was also observed during heating at 300\\deg C. Although the specimen average grain size was larger than typically 150 nm during the run, the run-product exhibits a very small average grain size (about 40 nm measured by X-ray diffraction), which suggests that nano-cracking occurred in the highly stressed material during decompression. Investigation of the run product by TEM confirms the X-ray diffraction data. Most crystals exhibit, indeed, nanometric sub-domains and numerous defects. Among these defects, the expected <110>\\{1/line{1} 0\\} slip systems have been identified and seems to dominate the deformation at high pressure and low temperature, although cleavage along the \\{001\\} planes may also have occurred at low pressure during decompression. Weidner (1998) Rheological studies at high pressure, in "Ultrahigh-pressure mineralogy: Physics and chemistry of the Earth's deep interior", R. J. Hemley Ed., Reviews in Mineralogy, vol.37, Mineralogical Society of America, Washington D.C., pp.493-524.

Schmidt, N.; Chen, J.; Raterron, P.

2001-12-01

310

Functions of two genes in aluminium (Al) stress resistance: repression of oxidative damage by the AtBCB gene and promotion of efflux of Al ions by the NtGDI1gene.  

PubMed

The functions of two genes whose expression provides tolerance to aluminium (Al) stress were investigated using plants and Saccharomyces cerevisiae (yeast): the Arabidopsis thaliana blue copper binding gene (AtBCB) and Nicotiana tabacum guanosine diphosphate (GDP) dissociation inhibitor gene (NtGDI1). To determine the localization of these proteins, each gene was fused to the green fluorescent protein (GFP) gene and introduced into onion epidermal cells. AtBCB was localized to cell membrane region and NtGDI1 to cytoplasm. Transgenic lines over-expressing the AtBCB gene showed constitutive lignin production in whole roots. By contrast, wild-type Arabidopsis (Ler) produced a negligible level of lignin and enhanced lignin production in the root-tip region by Al stress. Compared with Ler, the AtBCB-expressing lines showed a lower deposition of malon dialdehyde after Al stress. Microscopic observation of the Al-treated roots indicated that the deposition of lipid peroxides was clearly low in the area where lignin accumulated. It was proposed that lipid peroxidation caused by Al stress was diminished by the formation of lignin. Expression of the NtGDI1 gene in yeast complemented the temperature-sensitive phenotype of a sec19 mutant at 37 degrees C. This gene also complemented an Al-sensitive phenotype shown by the sec19 mutant at the permissive temperature of 32 degrees C. These results suggested that the yeast Sec19 vesicle transport system has a function in providing basal Al resistance in yeast by the export of Al ions. It was also proposed that over-expression of the NtGDI1 protein activates an Al efflux system that protects Arabidopsis against Al toxicity. PMID:16143720

Ezaki, Bunichi; Sasaki, Kiyokuni; Matsumoto, Hideaki; Nakashima, Susumu

2005-09-05

311

High temperature properties of CrAlN, CrAlSiN and AlCrSiN coatings Structure and oxidation  

Microsoft Academic Search

CrAlN, CrAlSiN and AlCrSiN coatings were deposited by cathodic arc deposition technique from composite targets. Three targets were used: (i) Cr\\/Al ratio close to 1, (ii) Cr\\/Al ratio close to 1 with Si addition, and (iii) Cr\\/Al ratio close to 1\\/2 and Si addition. Nitrogen flow was kept constant during the depositions. The Cr\\/Al ratio of the films, measured by

Tomas Polcar; Albano Cavaleiro

2011-01-01

312

High resolution electron microscopy of the early decomposition stage of Al-Li alloys  

Microsoft Academic Search

The early decomposition stages of Al-7.8at.%Li, Al-10.4at%Li and Al-11.8at%Li alloys were studied by high resolution electron microscopy. In all the above alloys, it was confirmed that in the as-quenched stage small ordered domains of Ll structure were present surrounded by the disordered matrix. From this microstructure, it was concluded that the alloy was already decomposed as in the as-quenched stage.

G. Schmitz; K. Hono; P. Haasen

1994-01-01

313

Corrosion Properties of Lightweight and High-strength 2195 Al-Li Alloy  

Microsoft Academic Search

The intergranular corrosion and exfoliation corrosion of 2195 Al-Li alloy treated by multi-step heating-rate controlled aging (MSRC) are studied. The corrosion features of 2195 Al-Li alloys which are respectively treated by high-temperature nucleation MSRC (H-M) and low-temperature nucleation MSRC (L-M) are contrasted. And the corrosion mechanism of 2195 Al-Li alloy is also discussed from the viewpoint of microstructure (types, distribution,

Yue XU; Xiaojing WANG; Zhaotong YAN; Jiaxue LI

2011-01-01

314

High-Temperature Sulfidation of Fe3Al Thermal Spray Coatings at 600?C  

Microsoft Academic Search

Sulfidation behavior of FeAl thermal spray coatings was studied in Ar-3.5% H-0.1° hydrogen sulfide (HS) at 600 C for 500 h. Coatings were processed from the same lot of gas atomized FeAl powder using a high-velocity oxygen fuel (HVOF) process and an air plasma spray (APS) process. In general, the FeAl-type composition displayed excellent resistance to sulfidation corrosion at 600

K. R. Luer; A. R. Marder; J. N. DuPont

2000-01-01

315

Loss of ALS2 function is insufficient to trigger motor neuron degeneration in knock-out mice but predisposes neurons to oxidative stress.  

PubMed

Amyotrophic lateral sclerosis (ALS), the most common motor neuron disease, is caused by a selective loss of motor neurons in the CNS. Mutations in the ALS2 gene have been linked to one form of autosomal recessive juvenile onset ALS (ALS2). To investigate the pathogenic mechanisms of ALS2, we generated ALS2 knock-out (ALS2(-/-)) mice. Although ALS2(-/-) mice lacked obvious developmental abnormalities, they exhibited age-dependent deficits in motor coordination and motor learning. Moreover, ALS2(-/-) mice showed a higher anxiety response in the open-field and elevated plus-maze tasks. Although they failed to recapitulate clinical or neuropathological phenotypes consistent with motor neuron disease by 20 months of age, ALS2(-/-) mice or primary cultured neurons derived from these mice were more susceptible to oxidative stress compared with wild-type controls. These observations suggest that loss of ALS2 function is insufficient to cause major motor deficits or motor neuron degeneration in a mouse model but predisposes neurons to oxidative stress. PMID:16107644

Cai, Huaibin; Lin, Xian; Xie, Chengsong; Laird, Fiona M; Lai, Chen; Wen, Hongjin; Chiang, Hsueh-Cheng; Shim, Hoon; Farah, Mohamed H; Hoke, Ahmet; Price, Donald L; Wong, Philip C

2005-08-17

316

High level compressive residual stresses produced in aluminum alloys by laser shock processing  

NASA Astrophysics Data System (ADS)

Laser shock processing (LSP) has been proposed as a competitive alternative technology to classical treatments for improving fatigue and wear resistance of metals. We present a configuration and results for metal surface treatments in underwater laser irradiation at 1064 nm. A convergent lens is used to deliver 1.2 J/cm 2 in a 8 ns laser FWHM pulse produced by 10 Hz Q-switched Nd:YAG, two laser spot diameters were used: 0.8 and 1.5 mm. Results using pulse densities of 2500 pulses/cm 2 in 6061-T6 aluminum samples and 5000 pulses/cm 2 in 2024 aluminum samples are presented. High level of compressive residual stresses are produced -1600 MPa for 6061-T6 Al alloy, and -1400 MPa for 2024 Al alloy. It has been shown that surface residual stress level is higher than that achieved by conventional shot peening and with greater depths. This method can be applied to surface treatment of final metal products.

Gomez-Rosas, G.; Rubio-Gonzalez, C.; Ocaa, J. L.; Molpeceres, C.; Porro, J. A.; Chi-Moreno, W.; Morales, M.

2005-11-01

317

High strain rate deformation of Ti-48Al-2Cr-2Nb in the duplex morphology  

SciTech Connect

The compressive deformation behavior of Ti-48Al-2Nb-2Cr in the duplex microstructural morphology has been studied at strain rates of 0.001/s and 2000/s over the temperature range from -196 to 1100{degrees}C. The material was cast, homogenized, extruded and heat treated to obtain the duplex microstructure. The yield stress is strain rate sensitive at 25{degrees}C and increases with temperature at a strain rate of 2000/s from 500 to 1100{degrees}C. TEM investigations reveal that deformation occurs in {gamma}-TiAl by means of [111]<112> twinning, 1/2<110> slip, and <101> superdislocations under all conditions depending on the orientation of the grain with respect to the deformation axis. Optical metallography reveals that twinning increases with increasing strain rate. TEM results revealing the dislocation substructure are used to explain the yield stress anomaly.

Maloy, S.A.; Gray, G.T. III

1995-03-01

318

Aluminum Silicon Carbide (AlSiC) Thermal Management Packaging For High Density Packaging Applications  

Microsoft Academic Search

High-density microelectronics require packaging materials and systems that provide superior thermal management and highly functional interconnection schemes for component performance and reliability. Aluminum Silicon Carbide (AlSiC) metal matrix composite (MMC) packages have a unique set of material properties that are ideally suited to thermal management performance, and a functionality that supports high density interconnection microelectronic packaging applications. Furthermore, the AlSiC

Mark A. Occhionero; Robert A. Hay; Richard W. Adams; Kevin P. Fennessy

319

High temperature deformation behavior of ? + ?-type biomedical titanium alloy Ti6Al7Nb  

Microsoft Academic Search

Isothermal hot compression tests were carried out in the temperature range 750900C and strain rate range 0.00110s?1 for implant biomedical Ti6Al7Nb alloy to obtain the hot deformation behavior. Hot tensile tests were conducted to examine the hot ductility. The stressstrain curves in hot compression tests behave the characteristics of flow softening. According to the kinetic rate equation, the apparent activation

W. F. Cui; Z. Jin; A. H. Guo; L. Zhou

2009-01-01

320

Workability of Ti6Al4V alloy at high temperatures and strain rates  

Microsoft Academic Search

Hot workability of Ti6Al4V has been investigated by means of hot compression tests carried out in the 880950 C temperature range and 150 s?1 strain rate range. The effect of microstructural characteristics of the deformed specimens have been studied and correlated with the test temperature, total strain and strain rate. A constitutive equation for the flow stress has been defined

S. Bruschi; S. Poggio; F. Quadrini; M. E. Tata

2004-01-01

321

Stress distribution in a transversely loaded cross-shaped single fiber SCS-6/Ti-6Al-4V composite  

SciTech Connect

In most structural applications utilizing fiber reinforced metal matrix composites (MMCs), the mechanical response normal to the fiber direction has to be considered. The transverse response is very sensitive to the interface bond strength, which has commonly been determined by testing straight-sided 90{degree} specimens and interpreting debond initiation from the knee in the stress-strain curve as well as from a sudden drop in the Poisson`s ratio. In an attempt to modify the debond initiation site to an internal location free of uncharacteristic states of stress, a cross-shaped specimen has been developed. Experiments conducted by Gundel et al. indicated that this geometry was successful in obtaining the appropriate crack initiation site. In the present study, finite element analysis (FEA) was done on the cross-shaped specimen to obtain the stress distribution in the composite under transverse loading, in an effort to corroborate the success of this geometry in determining the true transverse response of the composite.

Warrier, S.G.; Gundel, D.B. [Systran Corp., Dayton, OH (United States); Majumdar, B.S. [UES Inc., Dayton, OH (United States); Miracle, D.B. [Wright Lab., Wright-Patterson AFB, OH (United States). Materials Directorate

1996-01-15

322

Stress-induced tuning of ultrasonic additive manufacturing Al-NiTi composites  

NASA Astrophysics Data System (ADS)

This paper addresses the development of active metal-matrix composites manufactured by Ultrasonic Additive Manufacturing (UAM), an emerging manufacturing process that allows the embedding of materials into seemingly solid metal components. In the UAM process, successive layers of metal tapes are ultrasonically bonded together at low temperatures to form a metal-matrix. Being a low-temperature process, UAM offers unprecedented opportunities to create metal components with embedded thermally-sensitive materials, such as shape memory alloys. In this study UAM is used to create composites with aluminum matrices and embedded NiTi ribbons. These composites exhibit tunability of both the coefficient of thermal expansion and natural frequencies. These effects are due to the phase-dependent modulus and transformation stresses developed by the prestrained NiTi phase. Since the embedded NiTi ribbons are constrained by the matrix, thermally-induced transformation from detwinned martensite to austenite will be accompanied by the generation of transformation stresses. The effect of transformation stress and changing phase of NiTi on thermally-induced strain is observed and modeled by combining strain matching algorithms with thermodynamic-based constitutive models. The composite model accurately describes effects due to changing NiTi modulus and strain recovery due to initial stress-induced martensitic volume fractions including a 200 ?? contraction with increasing temperature. The observed dynamic behaviors include up to a 16.6% increase in natural frequency at 100C as compared to room temperature tests. No substantial increase in damping ratio was observed relative to solid aluminum.

Hahnlen, Ryan; Dapino, Marcelo J.

2012-03-01

323

Anomalous temperature dependence of flow stress in a Fe{sub 3}Al alloy  

SciTech Connect

Iron aluminides have attracted much interest since 1930s when the excellent corrosion resistance was noted in alloys with the composition of more than about 18 at.% Al. These alloys have relatively low material cost, due to the reduced usage of strategic elements like Cr, Mo and Ni, and a lower density than stainless steels. Their tensile strength is also comparable to those of ferritic and austenitic steels. These advantages have led the iron aluminide alloys being considered for many applications in industries needing sulfidation and oxidation resistance (1). However, the poor ductility at ambient temperatures and an abrupt drop in strength above 600 C have limited these alloys for structural applications. In the past years, extensive efforts have been devoted to understanding and improving the metallurgical properties of iron aluminides with the aim of producing more strong, ductile, and corrosion-resistant materials for structural applications. These studies have resulted in significant contributions to the understanding of the fabrication and mechanical properties of iron aluminides. Deformation behavior in iron aluminides is now known to depend on composition, temperature, and the presence or absence of ordered structures. Recent studies have demonstrated that improved engineering ductility of 10--15% can be achieved in wrought Fe{sub 3}Al-based iron aluminide alloys, through the control of composition and microstructure. The effect of strain rate on the deformation behavior of Fe{sub 3}Al alloys, especially on the anomalous temperature dependence of strength is of interest recently and more systematic investigation is now necessitated. Load relaxation test has been generally regarded as a very effective technique to measure the strain rate sensitivity over a wider range of strain rates with very little microstructural changes and has been applied to the plasticity of various rate-sensitive materials. In the present study, the iron aluminide alloys with 27.6 at.% Al having the various single-phase field, i.e. the disordered solid solution ({alpha}), an Fe{sub 3}Al with an imperfectly ordered B2 structure, and an ordered Fe{sub 3}Al with the D0{sub 3} structure were first prepared. A series of load relaxation tests was then carried out at the various temperatures ranging from 300 to 800 C to investigate the effect of the tensile strain rate on the anomalous flow behavior.

Song, J.H.; Ha, T.K.; Chang, Y.W.

2000-01-01

324

Improved drought and salt stress tolerance in transgenic tobacco overexpressing a novel A20/AN1 zinc-finger "AlSAP" gene isolated from the halophyte grass Aeluropus littoralis.  

PubMed

We describe here the isolation of a novel gene, designated AlSAP, from A. littoralis in a first step to exploit the potential of this halophyte grass as a genetic resource to improve salt and drought tolerance in plants and, particularly, in cereals. The Aeluropus genome contains a single AlSAP gene which has an intron at its 5'UTR. Sequence homology analysis showed that the AlSAP protein is characterized by the presence of two conserved zinc-finger domains A20 and AN1. AlSAP is induced not only by various abiotic stresses such as salt, osmotic, heat and cold but, also by abscisic acid (ABA) and salicylic acid (SA). Tobacco plants expressing the AlSAP gene under the control of the duplicated CaMV35S promoter exhibited an enhanced tolerance to abiotic stresses such as salinity (350 mM NaCl), drought (soil Relative Water Content (RWC) = 25%), heat (55 degrees C for 2.5 h) and freezing (-20 degrees C for 3 h). Moreover, under high salt and drought conditions, the transgenic plants were able to complete their life cycle and to produce viable seeds while the wild-type plants died at the vegetative stage. Measurements of the leaf RWC and of the root and leaf endogenous Na(+) and K(+) levels in AlSAP transgenic lines compared to wild-type tobacco, showed an evident lower water loss rate and a higher Na(+) accumulation in senescent-basal leaves, respectively. Finally, we found that the steady state levels of transcripts of eight stress-related genes were higher in AlSAP transgenic lines than in wild-type tobacco. Taken together, these results show that AlSAP is a potentially useful candidate gene for engineering drought and salt tolerance in cultivated plants. PMID:19838809

Ben Saad, Rania; Zouari, Nabil; Ben Ramdhan, Walid; Azaza, Jalel; Meynard, Donaldo; Guiderdoni, Emmanuel; Hassairi, Afif

2009-10-17

325

In-situ studies of the TGO growth stresses and the martensitic transformation in the B2 phase in commercial Pt-modified NiAl and NiCoCrAlY bond coat alloys.  

SciTech Connect

Oxide growth stresses were measured in situ at 1100 C on commercial Pt-modified NiAl and NiCoCrAlY bond coat alloys using synchrotron X-rays. Measurements were taken on samples that had no preoxidation, as well as on samples that had experienced 24 one-hour thermal exposures at 1150 C, a condition known to induce rumpling in the Pt-modified NiAl alloy, but not in the NiCoCrAlY alloy. The NiCoCrAlY alloy showed continuous stress relaxation under all conditions, whereas the Pt-modified NiAl alloys would typically stabilize at a fixed (often non-zero) stress suggesting a higher creep strength in the 'Thermally Grown Oxide' on the latter alloy, though the precise behavior was dependent on initial surface preparation. The formation of martensite in the Pt-modified NiAl alloys was also observed upon cooling and occurred at temperatures below 200 C for all of the samples observed. Based on existing models, this M{sub s} temperature is too low to account for the rumpling observed in these alloys.

Hovis, D.; Hu, L.; Reddy, A.; Heuer, A. H.; Paulikas, A. P.; Veal, B. W. (Materials Science Division); (Case Western Reserve Univ.)

2007-12-01

326

High strength porous Ti 6Al 4V foams synthesized by solid state powder processing  

NASA Astrophysics Data System (ADS)

We demonstrate a powder metallurgy synthesis route for porous Ti-6Al-4V structures by consolidation of Ti-6Al-4V alloy powders and describe the influence of the processing conditions. Ti-6Al-4V foams with 50 vol% porosity having high strength were fabricated by low temperature solid state deformation at temperatures below 873 K. The open cellular structure consists of continuously connected Ti-6Al-4V struts and homogeneously distributed pores with nominal diameters between 10 and 50 m and 150-500 m length.

Lee, Min Ha; Buem Kim, Ki; Han, Jun Hee; Eckert, Jrgen; Sordelet, Daniel J.

2008-05-01

327

High-reliability interconnections for ULSI using Al-Si-Pd-Nd\\/Mo layered films  

Microsoft Academic Search

An Al-Si-Pd-Nb alloy and a bilayered interconnection using this alloy with molybdenum have been investigated for ULSI interconnections. The electromigration lifetime of Al-Si-0.3 wt.% Pd-0.4 wt.% Nb was 5 times better as compared to Al-Si-0.5 wt.% Cu. In addition, layering this alloy with low-resistivity molybdenum improved the electromigration resistance considerably as compared to Al-Si-Cu layered with a high-resistivity metal, i.e.,

Jin Onuki; Yasushi Koubuchi; Motoo Suwa; Masahiro Koizumi; Donald S. Gardner; H. Suzuki; E. Minowa

1992-01-01

328

Computation of the fracture stress in notched NiAl-polycrystals  

Microsoft Academic Search

Computer simulations were performed in order to investigate the influence of the geometry and the microstructure of macroscopic specimens on the brittle-to-ductile transition of NiAl. A model is proposed which permits the bridging of the gap between the length scales of mesoscopic and macroscopic modeling. The strength of the macroscopic specimen is described by conventional J2 flow theory with a

M Groe Gehling; H Vehoff

2002-01-01

329

Improving the Quality of GaN on Si(111) Substrate with a Medium-Temperature/High-Temperature Bilayer AlN Buffer  

NASA Astrophysics Data System (ADS)

A medium-temperature/high-temperature (MT/HT) bilayer AlN buffer was introduced for GaN grown on Si(111) by metal organic chemical vapor deposition. The properties of the GaN films with a MT/HT bilayer AlN buffer and those with a single-layer HT-AlN buffer were compared and the influence of the growth temperature of the MT-AlN layer was investigated. With a MT-AlN layer grown in the temperature range from 800 to 1000 C, the crystalline qualities of the subsequent HT-AlN layer and the GaN film were improved. According to the X-ray diffraction results and the transmission electron microscopy images, the dislocation density in GaN film was reduced with a MT/HT bilayer AlN buffer as compared to those with a single-layer HT-AlN buffer. Moreover, photoluminescence and Raman spectra exhibit enhanced optical properties and less tensile stresses of the GaN film. Better surface morphology of GaN was also obtained with a MT/HT bilayer AlN buffer.

Xiang, Peng; Liu, Minggang; Yang, Yibin; Chen, Weijie; He, Zhiyuan; Leung, Ka Kuen; Surya, Charles; Han, Xiaobiao; Wu, Zhisheng; Liu, Yang; Zhang, Baijun

2013-08-01

330

High-Efficiency DC-DC Converter With High Voltage Gain and Reduced Switch Stress  

Microsoft Academic Search

In this paper, a high-efficiency dc-dc converter with high voltage gain and reduced switch stress is proposed. Generally speaking, the utilization of a coupled inductor is useful for raising the step-up ratio of the conventional boost converter. However, the switch surge voltage may be caused by the leakage inductor so that it will result in the requirement of high-voltage-rated devices.

Rong-Jong Wai; Chung-You Lin; Rou-Yong Duan; Yung-Ruei Chang

2007-01-01

331

STRESS  

NSDL National Science Digital Library

During this activity, students will use the available resources to learn more about stress, the effects of stress and how to handle stress. This activity focuses on the Utah fifth grade health core Standard 1: The students will learn ways to improve mental health and manage stress. During this project, students are given two different scenarios and ...

Hancey, Ms.

2010-04-27

332

High-pressure elasticity of perovskite and post-perovskite (Mg,Fe,Al)(Al,Si)O3  

NASA Astrophysics Data System (ADS)

We determine the effect of chemistry on the elasticity and seismic wave velocities of perovskite and post-perovskite using first-principles calculations. The elastic constants tensor in perovskite is more isotropic than in post-perovskite. The pure shear elastic constants are comparable between perovskite and post-perovskite; for post-perovskite, MgSiO3 has the largest values, and both Al2O3 and FeSiO3 show elastic instability at low pressures. The shear modulus of post-perovskite is larger than of perovskite at high pressures in all three cases. The difference in bulk modulus between the perovskite and post-perovskite structures, for MgSiO3 and FeSiO3 is on the order of about 15-20 GPa. The post-perovskite phase of Al2O3 shows the smallest bulk modulus at high pressures. The Vp values for FeSiO3 and Al2O3 post-perovskite are respectively about 2.0 and 1.6 km/s below the values for MgSiO3 post-perovskite. V_s shows similar trends for all the three compositions: at low pressures post-perovskite is softer than perovskite and has lower V_s values, while at higher pressure post-perovskite has larger values than perovskite. At 120 GPa MgSiO3 post-perovskite has V_s higher than FeSiO3 post-perovskite by about 1.7 km/s and higher than Al2O3 by about 0.9 km/s. For a pyrolitic mantle the effect of chemistry is relatively small, decreases on the order of up to 2% for Vp and up to 1.5% for V_s. Due to the perovskite to post-perovskite transition in Fe- and Al- bearing MgSiO3, Vp increases by 0.7% (about 0.1 km/s) and Vs by 2.5% (about 0.2 km/s) at 120 GPa.

Caracas, R.; Cohen, R. E.

2005-12-01

333

High threshold for induction of the stress response in motor neurons is associated with failure to activate HSF1.  

PubMed

Heat shock protein 70 (Hsp70) protects cultured motor neurons from the toxic effects of mutations in Cu/Zn-superoxide dismutase (SOD-1), which is responsible for a familial form of the disease, amyotrophic lateral sclerosis (ALS). Here, the endogenous heat shock response of motor neurons was investigated to determine whether a high threshold for activating this protective mechanism contributes to their vulnerability to stresses associated with ALS. When heat shocked, cultured motor neurons failed to express Hsp70 or transactivate a green fluorescent protein reporter gene driven by the Hsp70 promoter, although Hsp70 was induced in glial cells. No increase in Hsp70 occurred in motor neurons after exposure to excitotoxic glutamate or expression of mutant SOD-1 with a glycine--> alanine substitution at residue 93 (G93A), nor was Hsp70 increased in spinal cords of G93A SOD-1 transgenic mice or sporadic or familial ALS patients. In contrast, strong Hsp70 induction occurred in motor neurons with expression of a constitutively active form of heat shock transcription factor (HSF)-1 or when proteasome activity was sufficiently inhibited to induce accumulation of an alternative transcription factor HSF2. These results indicate that the high threshold for induction of the stress response in motor neurons stems from an impaired ability to activate the main heat shock-stress sensor, HSF1. PMID:12843283

Batulan, Zarah; Shinder, Gayle A; Minotti, Sandra; He, Bei Ping; Doroudchi, Mohammad M; Nalbantoglu, Josephine; Strong, Michael J; Durham, Heather D

2003-07-01

334

Blood Pressure and Heart Rate Responses to Anticipated High-stress Dental Treatment  

Microsoft Academic Search

Twenty-four healthy adults participated in a study to determine the effects of anticipated high-stress dental treatment on blood pressure and heart rate. Blood pressure, heart rate, and state anxiety were assessed prior to four consecutive dental appointments. Appointments 1, 2, and 4 were of relatively low stress and appointment 3 was of relatively high stress. Blood pressure was unaffected while

Frank M. Beck; Jol M. Weaver

1981-01-01

335

EFFECT OF STRESS ON CORTISOL AND TESTOSTERONE IN LOW AND HIGH LIBIDO RAMS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Our objective was to determine effect of restraint stress on cortisol (C) and testosterone (T) in low versus high libido rams. Restraint stress or minimal stress was imposed on low (n = 14) and high libido (n = 16) rams in a 2 x 2 factorial. Rams were randomly assigned to restraint or control within...

336

The Voices of High School Counselors: Lived Experience of Job Stress  

ERIC Educational Resources Information Center

|There is a paucity of literature addressing high school counselors' experiences of job stress. Our qualitative phenomenological study adds to the professions' knowledge of job stress as experienced by counselors in large suburban high schools. Our study illustrates the job stress phenomenon in the counselors' own voices, identifies situations

Falls, Leigh; Nichter, Mary

2007-01-01

337

Orthostatic Tolerance During al-Adrenergic Receptor Blockade at High Altitude.  

National Technical Information Service (NTIS)

In the first two weeks of high altitude (HA) exposure, blood pressure typically rises due, in part, to a large increase in sympathetic stimulation. We hypothesized that blocking al-adrenergic receptors would impair circulatory compensation to an orthostat...

C. S. Fulco S. R. Muza P. B. Rock D. O. Matthews K. W. Kambis

1999-01-01

338

Heat Pipe Embedded AlSiC Plates for High Conductivity: Low CTE Heat Spreaders.  

National Technical Information Service (NTIS)

Heat pipe embedded aluminum silicon carbide (AlSiC) plates are innovative heat spreaders that provide high thermal conductivity and low coefficient of thermal expansion (CTE). Since heat pipes are two phase devices, they demonstrate effective thermal cond...

J. Weyant M. Johnson M. Occhionero S. Garner

2010-01-01

339

High Rate Deposition of High Quality ZnO:Al by Filtered Cathodic Arc  

SciTech Connect

High quality ZnO:Al (AZO) thin films were prepared on glass substrates by direct current filtered cathodic arc deposition. Substrate temperature was varied from room temperature to 425oC, and samples were grown with and without the assistance of low power oxygen plasma (75W). For each growth condition, at least 3 samples were grown to give a statistical look at the effect of the growth environment on the film properties and to explore the reproducibility of the technique. Growth rate was in the 100-400 nm/min range but was apparently random and could not be easily traced to the growth conditions explored. For optimized growth conditions, 300-600 nm AZO films had resistivities of 3-6 x 10-4 ?Omega cm, carrier concentrations in the range of 2-4 x 1020 cm3, Hall mobility as high as 55 cm2/Vs, and optical transmittance greater than 90percent. These films are also highly oriented with the c-axis perpendicular to the substrate and a surface roughness of 2-4 nm.

Mendelsberg, Rueben J.; Lim, S.H.N.; Milliron, D.J.; Anders, Andre

2010-11-18

340

Stress-cracking resistance of high-density polyethylene geomembranes  

SciTech Connect

A new index test method, the notched constant tensile load (NCTL) test, for evaluating high-density polyethylene (HDPE) geomembranes regarding stress-cracking resistance is presented in this paper. Eighteen commercially virgin geomembranes and 7-field-exhumed geomembranes were evaluated using the new test. Results show a wide variation in the onset of the transition time. For the 18 virgin geomembranes, the transition times range from 10 hours to 5,000 hours. In addition, all 7 field-exhumed geomembranes, were failure actually occurred, show transition times less than 100 hours. An evaluation of the test results leads to a tentative recommendation that the transition time for an acceptable HDPE geomembrane should be 100 hours or longer. A comparison between the results of NCTL test and the currently used ASTM D 1693 bent-strip test was conducted. It indicates that the bent-strip test cannot adequately evaluate stress cracking resistance, and that the NCTL test is a more critical test in the assessment of such behavior.

Hsuan, Y.G.; Koerner, R.M.; Lord, A.E. Jr. (Drexel Univ., Philadelphia, PA (United States). Geosynthetic Research Inst.)

1993-11-01

341

High-Cycle Fatigue Behavior of Microarc Oxidation Coatings Deposited on a 6061-T6 Al Alloy  

NASA Astrophysics Data System (ADS)

The objective of this article is to evaluate the influence of microarc oxidation (MAO) coatings on the high-cycle rotating bending fatigue behavior of the 6061-T6 aluminum alloy. Toward this purpose, the influence of the MAO coating process parameter (current density) and coating thickness on the fatigue life of the 6061-T6 Al alloy has been evaluated in the present study. In addition, the influence of the coating roughness on the fatigue life of the MAO-coated 6061-T6 Al-alloy sample has also been investigated. The results indicate that the high-cycle fatigue life of the 6061-T6 Al alloy is substantially degraded due to the presence of MAO coatings, especially at lower alternating stress values and for thicker coatings. Surface roughness, altered by polishing, does not have any effect on fatigue life. An examination of coated samples interrupted at various fractions of fatigue life leads to the conclusion that the crack propagates from the coating surface to the coating-substrate interface very rapidly and thus fatigue life is largely controlled by the propagation of the crack into the substrate.

Wasekar, Nitin P.; Ravi, N.; Suresh Babu, P.; Rama Krishna, L.; Sundararajan, G.

2010-01-01

342

DC and high-frequency performance of AlGaN\\/GaN Heterojunction Bipolar Transistors  

Microsoft Academic Search

The DC and high frequency performance of AlGaN\\/GaN Heterojunction Bipolar Transistors (HBTs) is analyzed using an enhanced drift-diffusion model and GaN\\/AlGaN material parameters, which were previously verified by modeling experimental device characteristics. The emitterbase diode turn-on voltage is as high as 2.7 V while the collector and base ideality factors are 1.16 and 1.46 respectively. A DC current gain of

Egor Alekseev; Dimitris Pavlidis

2000-01-01

343

High-temperature oxidation and hot corrosion of Cr 2AlC  

Microsoft Academic Search

High-temperature oxidation and hot corrosion behaviors of Cr2AlC were investigated at 8001300C in air. Thermogravimetricdifferential scanning calorimetric test revealed that the starting oxidation temperature for Cr2AlC is about 800C, which is 400C higher than other ternary transition metal aluminum carbides. Thermogravimetric analyses demonstrated that Cr2AlC displayed excellent high-temperature oxidation resistance with parabolic rate constants of 1.0810?12 and 2.9610?9kg2m?4s?1 at 800

Z. J. Lin; M. S. Li; J. Y. Wang; Y. C. Zhou

2007-01-01

344

Fabrication of High TCR TaAl-N Thin Film by Reactive Sputtering Method  

NASA Astrophysics Data System (ADS)

The electric characteristics of TaAl-N thin film were investigated. The resistivity of the TaAl-N thin films, having been prepared by DC reactive sputtering of Ta and Al (8:2 area ratio) target in a gas mixture of argon and nitrogen, showed pressure-ratio dependence of nitrogen (PN2/Ptotal). The condition of high PN2/Ptotal was effective for fabricating the films, having a high TCR (the temperature coefficient of the resistivity). As a result, in the condition of PN2/Ptotal=75%, the TCR values were (-)35000 ppm/C (at 100C) and (-)25000 ppm/C (at 200C, resistivity).

Okano, Yukiko; Tajiri, Shuichi; Aozono, Takashi; Okamoto, Akio; Ogawa, Soichi; Mima, Hiroshi

345

AlSiC, and AlSiC Hybrid Composites for Flip Chips, Optoelectronics, Power, and High Brightness LED Thermal Management Solutions  

Microsoft Academic Search

Aluminum silicon carbide (AlSiC) metal matrix composites (MMC) are providing thermal management solutions for numerous electronics applications today for improved reliability including flip chip lids, optoelectronics packaging, power devices and high brightness LED applications. AlSiC has a high thermal conductivity (200 W\\/mK) and thermal expansion coefficient (TCE) values that are compatible with materials that are used in electronic assemblies. AlSiC

Mark A. Occhionero; Richard W. Adams

2005-01-01

346

Residual Stresses in Ta, Mo, Al and Pd Thin Films Deposited by E-Beam Evaporation Process on Si and Si/SiO2 Substrates  

SciTech Connect

Residual stresses are commonly generated during the deposition process of thin films and can influence the reliability of the deposited systems e.g. due to fatigue, aging effects or debonding. Therefore, an evaluation of such stresses in thin films is of crucial importance for metallization of microelectronic devices and MEMS. Residual stresses can be determined experimentally by substrate curvature or X-ray diffraction measurements. The modeling of residual stresses generally deals with the calculation of the thermal ones alone. In the present work, a model is proposed, where intrinsic stresses are calculated explicitly based on the Tsui-Clyne model. The aim of this model, called self-consistent model, is to predict residual stresses in thin films independent on measurements. The simulated values are compared with experimental results for the following systems: Ta/Si, Mo/Si, Al/SiO2/Si and Pd/SiO2/Si.

Guisbiers, G.; Overschelde, O. van; Wautelet, M. [Physics of Condensed Matter, University of Mons-Hainaut, 23 Avenue Maistriau 7000 Mons (Belgium); Strehle, S. [Leibniz Institute for Solid State and Materials Research Dresden, P.O. Box 27 01 16, 01171 Dresden (Germany)

2006-02-07

347

Unidirectional crystallization and high-temperature oxidation of in situ Ti 3(Al,Si)Ti 5(Si,Al) 3 composite  

Microsoft Academic Search

The paper is devoted to preparation and high-temperature oxidation of in situ Ti3(Al,Si)Ti5(Si,Al)3 composite. The composite with nominal chemical composition of Ti19at.%Al11at.%Si was unidirectionally solidified using the optical floating zone technique. Two solidification rates were applied ?5 and 18.8mm\\/h. The composite comprises Ti5(Si,Al)3 particles dispersed in Ti3(Al,Si) matrix. Structural examination of unidirectionally crystallized samples shows that only crystallization rate of

D. Vojt?ch; M. Novk; P. Novk; P. Lej?ek; J. Kope?ek

2008-01-01

348

Epitaxial growth of high quality ZnO:Al film on silicon with a thin gamma-Al2O3 buffer layer  

Microsoft Academic Search

ZnO:Al thin films were grown epitaxially on epi-gamma-Al2O3\\/Si (111) substrates by rf sputtering and pulsed laser deposition. The gamma-Al2O3 buffer layer was deposited on Si (111) at a low substrate temperature of 500 C using the metalorganic chemical vapor deposition method. Reflection high energy electron diffraction and x-ray diffraction measurements indicated a near alignment of the ZnO:Al epilayer on gamma-Al2O3\\/Si

Manoj Kumar; R. M. Mehra; A. Wakahara; M. Ishida; A. Yoshida

2003-01-01

349

Optical floating zone growth of high-quality Cu2MnAl single crystals  

NASA Astrophysics Data System (ADS)

We report the growth of large single-crystals of Cu2MnAl, a ferromagnetic Heusler compound suitable for polarizing neutron monochromators, by means of optical floating zone under ultra-high vacuum compatible conditions. Unlike Bridgman or Czochralsky grown Cu2MnAl, our floating zone grown single-crystals show highly reproducible magnetic properties and an excellent crystal quality with a narrow and homogeneous mosaic spread as examined by neutron diffraction. An investigation of the polarizing properties in neutron scattering suggests a high polarization efficiency, limited by the relatively small sample dimensions studied. Our study identifies optical floating zone under ultra-high vacuum compatible conditions as a highly reproducible method to grow high-quality single-crystals of Cu2MnAl.

Neubauer, A.; Jonietz, F.; Meven, M.; Georgii, R.; Brandl, G.; Behr, G.; Bni, P.; Pfleiderer, C.

2012-10-01

350

High temperature deformation behaviour of high carbon cast AIM and ESR Fe 3Al alloys  

Microsoft Academic Search

The Fe3Al alloys with the following compositions, Fe16.2Al0.54C and Fe15.5Al1.1C were melted under flux cover by air induction melting (ATM). Conventional casting defects like shrinkage pipes and microporosity were observed in AIM ingots. Electroslag remelting (ESR) of AIM ingots has resulted in clean, sound ingots free from casting defects. Isothermal, constant strain rate compressive tests were carried out on a

R. G. Baligidad; Abhijit Datta

2001-01-01

351

Observation of high viscous stress of oriented polyolefin under uniaxial tensile  

NASA Astrophysics Data System (ADS)

In this work, by means of stress relaxation experiments, the viscous stress at various strains during tensile deformation of oriented polyolefin samples, including high density polyethylene (HDPE), linear low density polyethylene (LLDPE) and isotactic polypropylene (iPP), has been determined. The viscous stress in the oriented samples takes up to 50 -70% of the total stress, which is unusually high, compared with their isotropic counterparts. More over, the enhanced modulus of oriented polyolefin was found not mainly caused by the existence of shish-kebab structure, but mainly come from the contribution of viscous stress. The result is new and provides deep understanding of the origin of high modulus for oriented polymers.

Fu, Qiang; Na, Bing; Zou, Hao; Wang, Ke; Zhang, Qin; Han, Charles C.

2006-03-01

352

ALS-LAUS syndrome in a patient with high level of antiphospholipid antibodies: a case report.  

PubMed

When evaluating a patient with amyotrophic lateral sclerosis (ALS), a number of other motor neuron disorders and related motor syndromes should be considered. Herein, we describe a 55-year-old Persian man with typical presentation of ALS in whom based on further finding of elevated level of antiphospholipid antibodies, final diagnosis of ALS with laboratory abnormalities of uncertain significance (ALS-LAUS) was made. With respect to persistent increased titre of antiphospholipid antibodies, he was treated with plasma exchange and prednisolone. After 3 months of treatment, the symptoms improved and antiphospholipid antibody titres decreased. To the best of our knowledge, this is the first case of ALS-LAUS accompanied by high titre of antiphospholipid antibodies with response to plasma exchange and corticosteroids. PMID:19235108

Saadatnia, Mohammad; Fatehi, Farzad; Basiri, Keivan; Sariaslani, Payam

353

Heat Pipe Embedded AlSiC Plates for High Conductivity - Low CTE Heat Spreaders  

SciTech Connect

Heat pipe embedded aluminum silicon carbide (AlSiC) plates are innovative heat spreaders that provide high thermal conductivity and low coefficient of thermal expansion (CTE). Since heat pipes are two phase devices, they demonstrate effective thermal conductivities ranging between 50,000 and 200,000 W/m-K, depending on the heat pipe length. Installing heat pipes into an AlSiC plate dramatically increases the plates effective thermal conductivity. AlSiC plates alone have a thermal conductivity of roughly 200 W/m-K and a CTE ranging from 7-12 ppm/ deg C, similar to that of silicon. An equivalent sized heat pipe embedded AlSiC plate has effective thermal conductivity ranging from 400 to 500 W/m-K and retains the CTE of AlSiC.

Johnson, Matthew (DOE/NNSA Kansas City Plant (United States)); Weyant, J.; Garner, S. (Advanced Cooling Technologies, Inc. (Lancaster, PA (United States)); Occhionero, M. (CPS Technologies Corporation, Norton, MA (United States))

2010-01-07

354

The structural and optical properties of high-Al-content AlInGaN epilayers grown by RF-MBE  

NASA Astrophysics Data System (ADS)

AlInGaN Quaternary Alloys were successfully grown on sapphire substrate by radio-frequency plasma-excited molecular beam epitaxy (RF-MBE). Different Al content AlInGaN quaternary alloys were acquired by changing the Al cell's temperature. The streaky RHEED pattern observed during AlInGaN growth showed the layer-by-layer growth mode. Rutherford back-scattering spectrometry (RBS), X-Ray diffraction (XRD) and Cathodoluminescence (CL) were used to characterize the structural and optical properties of the AlInGaN alloys. The experimental results show that the AlInGaN with appropriate Al cell's temperature, could acquire Al/In ratio near 4.7, then could acquire better crystal and optical quality. The samllest X-ray and CL full-width at half-maximum (FWHM) of the AlInGaN are 5arcmin and 25nm, respectivly. There are some cracks and V-defects occur in high-Al/In-ratio AlInGaN alloys. In the CL image, the cracks and V-defect regions are the emission-enhanced regions. The emission enhancement of the cracked and V-defect regions may be related to the In-segregation.

Wang, Baozhu; An, Tao; Wen, Huanming; Wu, Ruihong; An, Shengbiao; Zhang, Xiuqing; Wang, Xiaoliang

2008-11-01

355

Formation of V-grooves on the (Al,Ga)N surface as means of tensile stress relaxation  

NASA Astrophysics Data System (ADS)

In this paper we present a study of the relaxation mechanism of the top Al0.30Ga0.70N layer grown on GaN, as used in High Electron Mobility Transistor (HEMT) structures. We show that the initial mechanism for relaxation of strain is by means of formation of V-grooves on the surface of the Al0.30Ga0.70N. It is also demonstrated that a thin Si3N4 layer, grown in-situ, immediately after the AlxGa1-xN can freeze-in the surface structure. Using tapping mode Atomic Force Microscopy (AFM) it can be observed that immediately after termination of the growth of the thin Al0.30Ga0.70N layer, the steps on the surface show round shape and spiral-like features. After about 1 min of annealing time under NH3 flow the surface structures become straighter. Upon prolonged annealing a V-groove pattern is observed. These V-grooves run along the <-1-120> directions.Although some other facets can be observed, from cross-sectional Transmission Electron Microscopy (TEM) images we can infer that the side walls of the grooves are {1-101} planes and that the grooves do not penetrate till the Al0.30Ga0.70N/GaN interface. Therefore, we come to the conclusion that the initial relaxation of a thin Al0.30Ga0.70N layer does not occur via a dislocation glide mechanism leading to the formation of an array of misfit dislocations at the Al0.30Gas.70N/GaN interface. Instead, we propose that the mechanism is by surface instability leading to V-groove formation.

Cheng, Kai; Leys, M.; Degroote, S.; Bender, H.; Favia, P.; Borghs, G.; Germain, M.

2012-08-01

356

Stress-corrosion cracking of Ti8Al-lMo-lV in aqueous environments: 2. Plastic zones, crack morphology, and fractography  

Microsoft Academic Search

Optical and electron metallographic studies of stress-corrosion cracks in Ti-8Al-lMo-lV have verified that the principal crack\\u000a extension mechanism is cleavage of the? grains. There are two distinct crack morphologies which correspond to the two regimes of subcritical crack velocity. At low\\u000a stress intensities(a ? K\\u000a I) the microscopic crack front consists of small cleavage facets approximately 1 to 4? grain

J. D. Boyd

1973-01-01

357

Aluminum hard mask technique for the fabrication of high quality submicron Nb/Al-AlOx/Nb Josephson junctions  

NASA Astrophysics Data System (ADS)

We have developed a combined photolithography and electron-beam lithography fabrication process for sub-m to m-size Nb/Al-AlOx/Nb Josephson junctions. In order to define the junction size and protect its top electrode during anodic oxidation, we developed and used the new concept of an aluminum hard mask. Josephson junctions of sizes down to 0.5 m2 have been fabricated and thoroughly characterized. We found that they have a very high quality, which is witnessed by the IV curves with quality parameters Vm > 50 mV and Vgap = 2.8 mV at 4.2 K, as well as IcRN products of 1.75-1.93 mV obtained at lower temperatures. In order to test the usability of our fabrication process for superconducting quantum bits, we have also designed, fabricated and experimentally investigated phase qubits made of these junctions. We found a relaxation time of T1 = 26 ns and a dephasing time of T2 = 21 ns.

Kaiser, Ch; Meckbach, J. M.; Ilin, K. S.; Lisenfeld, J.; Schfer, R.; Ustinov, A. V.; Siegel, M.

2011-03-01

358

Low-temperature plasma-assisted growth of optically transparent, highly oriented nanocrystalline AlN  

NASA Astrophysics Data System (ADS)

Optically transparent, highly oriented nanocrystalline AlN(002) films have been synthesized using a hybrid plasma enhanced chemical vapor deposition and plasma-assisted radio frequency (rf) magnetron sputtering process in reactive Ar+N2 and Ar+N2+H2 gas mixtures at a low Si(111)/glass substrate temperature of 350 C. The process conditions, such as the sputtering pressure, rf power, substrate temperature, and N2 concentration were optimized to achieve the desired structural, compositional, and optical characteristics. X-ray diffractometry reveals the formation of highly c-oriented AlN films at a sputtering pressure of 0.8 Pa. Field emission scanning electron microscopy suggests the uniform distribution of AlN grains over large surface areas and also the existence of highly oriented in the (002) direction columnar structures of a typical length ~100-500 nm with an aspect ratio of ~7-15. X-ray photoelectron and energy dispersive x-ray spectroscopy suggest that films deposited at a rf power of 400 W feature a chemically pure and near stoichiometric AlN. The bonding states of the AlN films have been confirmed by Raman and Fourier transform infrared spectroscopy showing strong E2 (high) and E1 transverse optical phonon modes. Hydrogenated AlN films feature an excellent optical transmittance of ~80% in the visible region of the spectrum, promising for advanced optical applications.

Mirpuri, C.; Xu, S.; Long, J. D.; Ostrikov, K.

2007-01-01

359

Light polarization characteristics of m-plane AlGa{sub 1-x}N films suffering from in-plane anisotropic tensile stresses  

Microsoft Academic Search

Polarization characteristics of the near-band-edge optical transitions in m-plane AlGa{sub 1-x}N epilayers suffering from anisotropic stresses were quantified. The epilayers were grown by both ammonia-source molecular beam epitaxy and metalorganic vapor phase epitaxy methods on an m-plane freestanding GaN substrate. The light polarization direction altered from E perpendicular c to E || c at the AlN molar fraction, x, between

K. Hazu; T. Hoshi; M. Kagaya; T. Onuma; S. F. Chichibu

2010-01-01

360

Thermal treatment and utilization of Al-rich waste in high calcium fly ash geopolymeric materials  

NASA Astrophysics Data System (ADS)

The Al-rich waste with aluminium and hydrocarbon as the major contaminant is generated at the wastewater treatment unit of a polymer processing plant. In this research, the heat treatment of this Al-rich waste and its use to adjust the silica/alumina ratio of the high calcium fly ash geopolymer were studied. To recycle the raw Al-rich waste, the waste was dried at 110C and calcined at 400 to 1000C. Mineralogical analyses were conducted using X-ray diffraction (XRD) to study the phase change. The increase in calcination temperature to 600, 800, and 1000C resulted in the phase transformation. The more active alumina phase of active ?-Al2O3 was obtained with the increase in calcination temperature. The calcined Al-rich waste was then used as an additive to the fly ash geopolymer by mixing with high calcium fly ash, water glass, 10 M sodium hydroxide (NaOH), and sand. Test results indicated that the calcined Al-rich waste could be used as an aluminium source to adjust the silica/alumina ratio and the strength of geopolymeric materials. The fly ash geopolymer mortar with 2.5wt% of the Al-rich waste calcined at 1000C possessed the 7-d compressive strength of 34.2 MPa.

Chindaprasirt, Prinya; Rattanasak, Ubolluk; Vongvoradit, Pimdao; Jenjirapanya, Supichart

2012-09-01

361

Pt-Al2O3 nanocoatings for high temperature concentrated solar thermal power applications  

NASA Astrophysics Data System (ADS)

Nano-phased structures based on metal-dielectric composites, also called cermets (ceramic-metal), are considered among the most effective spectral selective solar absorbers. For high temperature applications (stable up to 650 C) noble metal nanoparticles and refractory oxide host matrices are ideal as per their high temperature chemical inertness and stability: Pt/Al2O3 cermet nano-composites are a representative family. This contribution reports on the optical properties of Pt/Al2O3 cermet nano-composites deposited in a multilayered tandem structure. The radio-frequency sputtering optimized Pt/Al2O3 solar absorbers consist of stainless steel substrate/ Mo coating layer/ Pt-Al2O3/ protective Al2O3 layer and stainless steel substrate/ Mo coating layer /Pt-Al2O3 for different composition and thickness of the Pt-Al2O3 cermet coatings. The microstructure, morphology, theoretical modeling and optical properties of the coatings were analyzed by the x-ray diffraction, atomic force, microscopy, effective medium approximation and UV-vis specular and diffuse reflectance.

Nuru, Zebib. Y.; Arendse, C. J.; Nemutudi, R.; Nemraoui, O.; Maaza, M.

2012-05-01

362

Two unusual cataclysmic variables at high Galactic latitude - CP Eridani and AL Comae  

NASA Astrophysics Data System (ADS)

We present time-series photometry of two faint, interacting binary stars at high Galactic latitude: CP Eridani and AL Comae Berenices. We also present spectroscopy of CP Eri. CP Eri has a long-lived photometric periodicity near 28 min. Its spectrum has lines of helium that are sometimes in emission and some times in absorption; there are no lines of hydrogen in the spectrum. We identify CP Eri as a binary star consisting of a pair of white dwarfs undergoing mass transfer. AL Com has an unstable, high-amplitude photometric modulation with a period between 87 and 90 min. The previously identified photometric period at 41 min is also unstable. Some of the properties of AL Com are similar to the dwarf nova WZ Sge and others are similar to the intermediate polar EX Hya, but overall AL Com is unlike any other well-studied cataclysmic variable.

Abbott, Timothy M. C.; Robinson, Edward L.; Hill, Gary J.; Haswell, Carole A.

1992-11-01

363

Highly (111)-oriented Ge thin films on insulators formed by Al-induced crystallization  

NASA Astrophysics Data System (ADS)

(111)-oriented Ge thin films on insulators are essential for advanced electronics and photovoltaic applications. We investigate Al-induced crystallization of amorphous-Ge films (50-nm thickness) on insulators focusing on the annealing temperature and the diffusion controlling process between Ge and Al. The (111)-orientation fraction of the grown Ge layer reaches as high as 99% by combining the low-temperature annealing (325 C) and the native-oxidized Al (AlOx) diffusion-control layer. Moreover, the transmission electron microscopy reveals the absence of defects on the Ge surface. This (111)-oriented Ge on insulators promises to be the high-quality epitaxial template for various functional materials to achieve next-generation devices.

Toko, K.; Kurosawa, M.; Saitoh, N.; Yoshizawa, N.; Usami, N.; Miyao, M.; Suemasu, T.

2012-08-01

364

Botulinum toxin detection using AlGaN/GaN high electron mobility transistors  

NASA Astrophysics Data System (ADS)

Antibody-functionalized, Au-gated AlGaN/GaN high electron mobility transistors (HEMTs) were used to detect botulinum toxin. The antibody was anchored to the gate area through immobilized thioglycolic acid. The AlGaN/GaN HEMT drain-source current showed a rapid response of less than 5 s when the target toxin in a buffer was added to the antibody-immobilized surface. We could detect a range of concentrations from 1 to 10 ng/ml. These results clearly demonstrate the promise of field-deployable electronic biological sensors based on AlGaN/GaN HEMTs for botulinum toxin detection.

Wang, Yu-Lin; Chu, B. H.; Chen, K. H.; Chang, C. Y.; Lele, T. P.; Tseng, Y.; Pearton, S. J.; Ramage, J.; Hooten, D.; Dabiran, A.; Chow, P. P.; Ren, F.

2008-12-01

365

Raman study on dislocation in high Al content AlxGa1-xN  

NASA Astrophysics Data System (ADS)

The high Al content AlGaN epilayers have been obtained by metalorganic chemical vapor deposition (MOCVD), and the optical property has been investigated by photoluminescence (PL) spectroscopy. Longitudinal-optic (LO) phonon mode has been studied by Raman scattering. Further analysis shows that the edge dislocation is an important factor influencing optical quality of AlGaN epilayers, and it also shows that the correlation between the A1 (LO) polar modes and the edge dislocation is intensive, which may be expected to become a characterization method of the related crystal defects.

Pan, X.; Wang, X. L.; Xiao, H. L.; Wang, C. M.; Feng, C.; Jiang, L. J.; Yin, H.; Chen, H.

2012-04-01

366

High temperature deformation in 2036 Al and 0.2 wt % Zr-2036 A1  

SciTech Connect

The microstructure and high-temperature deformation of 2036 Al and a 0.2 wt % Zr modified 2036 Al were characterized. A particle-simulated- nucleation process was applied to refine grain structure in both alloys. Thermomechanically processed materials were tested from 450 to 500 C and strain rates from 2{times}10{sup {minus}1} to 2{times}10{sup {minus}4}s{sup {minus}1}. Strain rate sensitivity exponent, activation energy, and total elongation were measured, and the deformation mechanism was proposed. Effect of Zr on microstructure and deformation of 2036 Al at elevated temperatures was discussed.

Huang, J.S.; Schwartz, A.J.; Nieh, T.G.

1995-11-01

367

Static and kinetic friction of granite at high normal stress  

USGS Publications Warehouse

Frictional sliding on ground surfaces of granite, angle of sliding planes 30?? and 45??, was investigated as a function of confining pressure. Over the normal stress range of 2-12 kb, the static frictional shear stress ??s follows the relationship ??s = 0??5 + 0?? ??n and the kinetic frictional shear stress ??k was calculated to be ??k = 0??25 + 0??47 ??n. ?? 1970.

Byerlee, J. D.

1970-01-01

368

High trait anxiety in healthy subjects is associated with low neuroendocrine activity during psychosocial stress  

Microsoft Academic Search

Altered stress responsiveness has been repeatedly related to mood and anxiety disorders. In a traditional view, a reduction of the stress response has been thought favorable. The goal of the present study was to verify the hypothesis that high anxiety is accompanied by enhanced hormone release during stress. Healthy subjects at the upper (anxious, n=15) and lower (non-anxious, n=12) limits

Daniela Jezova; Aikaterini Makatsori; Roman Duncko; Fedor Moncek; Martin Jakubek

2004-01-01

369

Characterization of residual stresses in heat treated Ti-6Al-4V forgings by machining induced distortion  

NASA Astrophysics Data System (ADS)

To provide a solid base for improved material exploitation in dimensioning calculations it is necessary to determine the stress state in the part prior to service loading. In order to achieve higher material strength at elevated temperatures, the surface temperature gradient with respect to time has to be sufficiently high during heat treatment. This results in non-negligable residual stresses that can reduce the allowable load level upon which yielding occurs. For titanium alloys there are two common heat treatments, namely solution treatment and mill annealing. The latter one is the method of choice within the presented project. Mill annealing is utilized in order to significantly reduce the residual stresses in the parts without loosing much of the improved strength at elevated temperatures. Quantification of residual stresses is done by solving an inverse problem. From the measurement of distortion, induced by dividing the investigated part, the residual stress state can be calculated via analytical modeling or correlation with finite element models. To assure a minimum perturbation of the residual stress state during specimen production, dividing of the part is accomplished by electric discharge machining. The parts of interest are v-shaped prisms with a length of approximatly 450 mm and a thickness in the cross sectional area from about 20 mm to 45 mm. Figure 1(a) shows the forged part and 1(b) the dimensions of the cross section in millimeters as well as the material properties considered in the finite element model. The heat exchange between the part and the environment is modelled as heat transfer by convection superimposed with heat radiation. Since the parts are exposed to air during forging and heat treatment, the surface develops a strongly adhesive oxide layer, the so called alpha-case. After forging the parts are cooled in air and heat treated at a temperature of 720 C for a duration of 120 min. Subsequent air cooling and removing the alpha-case by shot peening and chemical treatment in a mixture of nitric and hydroflouric acid finishes the processing. The residual stress state in the parts is quantified through correlation of results obtained by finite element simulations and high precision deflection experiments. Experimental measuring errors are minimized by using the capability of the wire cutting machine to measure locations on the specimens with respect to the fixed machine coordinate system. A sophisticated design of cutting operations allows an analysis of the part without removing the fixture and hence makes it possible to achieve a very high accuracy of the displacement measurements of about 4 m. The quality of the obtained results also depends on the finite element models describing the mechanics of the experimental investigations as precise as possible. Since numerical modeling of shot peening and chemical milling is rather complicated, the whole processing route of the shapes is simplified assuming that the individual contribution of all process steps to the residual stress state can be described by virtual heat transfer coefficients. The overall virtual heat transfer coefficient for the whole processing route is calculated from the linear superposition of the individual heat transfer coeffcients for each processing step. Detailed analysis of the obtained overall virtual heat transfer coefficients in comparison with experimentally obtained ones shows, that other processing steps besides the heat treatment considerably influence the residual stress state. In order to make the conducted simulation scheme applicable in practise, advanced finite element modeling techniques are developed. The experimentally derived deflection curves are correlated to the finite element results via a least square fit.

Regener, B.; Krempaszky, C.; Werner, E.

2010-06-01

370

Porous reaction-sintered AlN tapes for high-performance microelectronics application  

Microsoft Academic Search

(Received 6 February 2001; accepted 8 November 2001) A novel approach was undertaken in producing porous AlN microelectronics tapes with high thermal conductivity and low dielectric constant. This method involved polymer microspherical powders used as a sacrificial mold to introduce controlled porosity into the green tapes during pyrolysis. The Al2O3-rich porous green tapes were then reaction sintered at 1680 C

F. Y. C. Boey; A. I. Y. Tok; W. J. Clegg

2002-01-01

371

Feasibility Study of Nb3Al Rutherford Cable for High Field Accelerator Magnet Application  

Microsoft Academic Search

Feasibility study of Cu stabilized Nb3Al strand and Rutherford cable for the application to high field accelerator magnets are being done at Fermilab in collaboration with NIMS. The Nb3Al strand, which was developed and manufactured at NIMS in Japan, has a non-copper Jc of about 844 A\\/mm2 at 15 Tesla at 4.2 K, a copper content of 50%, and filament

R. Yamada; A. Kikuchi; G. Ambrosio; N. Andreev; E. Barzi; C. Cooper; S. Feher; V. V. Kashikin; M. Lamm; I. Novitski; T. Takeuchi; M. Tartaglia; D. Turrioni; A. P. Verweij; M. Wake; G. Willering; A. V. Zlobin

2007-01-01

372

The sulfidation and oxidation behavior of sputter-deposited AlTa alloys at high temperatures  

Microsoft Academic Search

As a part of a systematic study to elucidate oxidation and sulfidation resistance of Al-refractory metal alloys at high temperatures, the behavior of sputter-deposited Al-(3380) at.%Ta alloys has been examined at temperatures ranging from 1073 K to 1273 K in He-S2 atmosphere and in Ar-O2 atmosphere. The sulfidation kinetics of these alloys follow a parabolic rate law in an early

H. Mitsui; H. Habazaki; K. Hashimoto; S. Mrowec

1997-01-01

373

Rapidly solidified Al-Fe-Mo-Si alloys for high temperatures applications  

Microsoft Academic Search

Iron solubility in aluminium can be extended through the rapid solidification route, allowing the precipitation of a high volume fraction of intermetallic phases. In the ternary Al-Fe-Si system, the observed metastable hardening phase Al13Fe3Si is sensitive to ripening. Thermal stability can be improved by modification of the surface energy of the precipitate, i.e. by lattice parameter variation, through addition of

M. C. S. DE MACEDO; G. MICHOT

1993-01-01

374

A Highly Stable Al-Si Contact to Mo-Silicided Shallow Junctions  

NASA Astrophysics Data System (ADS)

Highly stable (up to 550C) contacts have been realized in an Al-2%Si contact to n+-p and p+-n shallow junctions (Xj0.16 ?m) covered by a 0.1 ?m thick uniform MoSi2 layer, which was formed by the ion implantation through metal ITM technique. Low contact resistance was maintained, at submicron (0.5 ?m square) Al-Si/MoSi2 contacts, after 550C sintering for 30 minutes.

Nagasawa, Eiji; Okabayashi, Hidekazu; Iida, Yasuo

1987-03-01

375

Heat pipe embedded AlSiC plates for high conductivity - low CTE heat spreaders  

Microsoft Academic Search

Heat pipe embedded aluminum silicon carbide (AlSiC) plates are innovative heat spreaders that provide high thermal conductivity and low coefficient of thermal expansion (CTE). Since heat pipes are two phase devices, they demonstrate effective thermal conductivities ranging between 10,000 and 200,000 W\\/m-K, depending on the heat pipe length. Installing heat pipes into an AlSiC plate dramatically increases the plate's effective

J. Weyant; S. Garner; M. Johnson; M. Occhionero

2010-01-01

376

High-temperature tensile properties of Mg\\/Al 2O 3 nanocomposite  

Microsoft Academic Search

Mg\\/1.1Al2O3 nanocomposite was synthesized using solidification process called disintegrated melt deposition technique followed by hot extrusion. Microstructural characterization showed that reasonably uniform distribution of reinforcement leads to significant grain refinement of commercially pure magnesium matrix and effectively restricted the grain growth during high-temperature tensile test. Physical properties characterization revealed that addition of nano-Al2O3 particulates as reinforcement improves the dimensional stability

S. F. Hassan; M. J. Tan; M. Gupta

2008-01-01

377

High-temperature slow crack growth of silicon carbide determined by constant-stress-rate and constant-stress testing  

Microsoft Academic Search

High-temperature slow-crack-growth behaviour of hot-pressed silicon carbide was determined using both constant-stress-rate (dynamic fatigue) and constant-stress (static fatigue) testing in flexure at 1300 C in air. Slow crack growth was found to be a governing mechanism associated with failure of the material. Four estimation methods such as the individual data, the Weibull median, the arithmetic mean and the median deviation

SUNG R. CHOI; J. A. SALEM; N. N Nemeth

1998-01-01

378

Evolution of stress failure resulting from high-temperature stress-corrosion cracking in a hot isostatically pressed silicon nitride  

Microsoft Academic Search

Stress-corrosion cracking in a commercially available, hot isostatically pressed (HIPed), yttria-fluxed, silicon nitride was the prevalent mode of failure in specimens creep-ruptured at 1,370 C. High-temperature diffusional processes associated with oxygen were responsible for the creation of an advancing stress-corrosion front that had formed at the specimen surface and advanced radially inward. The volume of material in the wake of

Andrew A. Wereszczak; Mattison K. Ferber; Timothy P. Kirkland; Karren L. More; Michael R. Foley; Russell L. Yeckley

1995-01-01

379

High temperature stability, interface bonding, and mechanical behavior in (beta)-NiAl and Ni3Al matrix composites with reinforcements modified by ion beam enhanced deposition  

NASA Astrophysics Data System (ADS)

Diffusion-bonded NiAl-Al2O3 and Ni3Al-Al2O3 couples were thermally fatigued at 900 C for 1500 and 3500 cycles. The fiber-matrix interface weakened after 3500 cycles for the Saphikon fibers, while the Altex, PRD-166, and FP fibers showed little, if any, degradation. Diffusion bonding of fibers to Nb matrix is being studied. Coating the fibers slightly increases the tensile strength and has a rule-of-mixtures effect on elastic modulus. Push-out tests on Sumitomo and FP fibers in Ni aluminide matrices were repeated. Al2O3 was evaporated directly from pure oxide rod onto acoustically levitated Si carbide particles, using a down-firing, rod-fed electron beam hearth; superior coatings were subsequently produced using concurrent irradiation with 200-eV argon ion-assist beam. The assist beam produced adherent films with reduced tensile stresses. In diffusion bonding in B-doped Ni3Al matrices subjected to compressive bonding at 40 MPa at 1100 C for 1 hr, the diffusion barriers failed to prevent catastrophic particle-matrix reaction, probably because of inadequate film quality. AlN coatings are currently being experimented with, produced by both reactive evaporation and by N(+)-ion enhanced deposition. A 3-kW rod-fed electron-beam-heated evaporation source has been brought into operation.

Grummon, D. S.

1993-01-01

380

Stress-corrosion cracking of Ti8Al-lMo-lV in aqueous environments: 1. The kinetics of subcritical crack propagation  

Microsoft Academic Search

Precracked specimens of Ti-8Al-lMo-lV were tested in salt-water, and the subcritical crack velocity was measured as a function\\u000a of applied stress-intensity. The minimum applied stress intensity which produces subcritical cracking,K\\u000a Iscc, varies inversely with the average chloride-ion concentration of the environment, butK\\u000a Iscc does not vary significantly with temperature. Plots of subcritical crack velocity,a, against applied stress intensity,K\\u000a I, reveal

J. D. Boyd

1973-01-01

381

High reflectance-low stress Mo-Si multilayer reflective coatings  

Microsoft Academic Search

A high reflectance-low stress Mo-Si multilayer reflective coating particularly useful for the extreme ultraviolet (EUV) wavelength region. While the multilayer reflective coating has particular application for EUV lithography, it has numerous other applications where high reflectance and low stress multilayer coatings are utilized. Multilayer coatings having high near-normal incidence reflectance (R.gtoreq.65%) and low residual stress (.ltoreq.100 MPa) have been produced

Claude Montcalm; Paul B. Mirkarimi

2000-01-01

382

Process for fabricating high reflectance-low stress Mo--Si multilayer reflective coatings  

Microsoft Academic Search

A high reflectance-low stress Mo--Si multilayer reflective coating particularly useful for the extreme ultraviolet (EUV) wavelength region. While the multilayer reflective coating has particular application for EUV lithography, it has numerous other applications where high reflectance and low stress multilayer coatings are utilized. Multilayer coatings having high near-normal incidence reflectance (R.gtoreq.65%) and low residual stress (.ltoreq.100 MPa) have been produced

Claude Montcalm; Paul B. Mirkarimi

2001-01-01

383

Influence of Rare-Earth Additions on Properties of Titanium Alloys. Plane-Strain Fracture Toughness, Creep, and High-Temperature Deformation of Ti-6Al-4V with Erbium and Yttrium Additions.  

National Technical Information Service (NTIS)

The influence of additions of 0.05 wt% Y and 0.1 wt% Er on the room-temperature tensile properties, plane-strain and plane-stress fracture toughness, creep, and high-temperature high-strain-rate deformation characteristics of Ti-6Al-4V was studied. 75kg i...

S. M. L. Sastry R. J. Lederich P. S. Pao J. E. O'Neal

1979-01-01

384

X-ray high-pressure study of Ti2AlN and Ti2AlC  

NASA Astrophysics Data System (ADS)

The lattice parameters of Ti2AlN and Ti2AlC powders were measured as a function of pressure up to ?50 GPa, using a synchrotron radiation source and a diamond anvil cell. No phase transformations were observed. As for most related layered carbides and nitrides, such as Ti4AlN3 and Ti3SiC2, the compressibilities of Ti2AlN and Ti2AlC along the c-axes are larger than those along the a-axes. The bulk modulus of Ti2AlC at 1862 GPa, is ?10% higher than that of Ti2AlN at 1693 GPa.

Manoun, Bouchaib; Zhang, F. X.; Saxena, S. K.; El-Raghy, T.; Barsoum, M. W.

2006-09-01

385

Single Discharge Machining Insulating Al2O3 Ceramic with High Instantaneous Pulse Energy in Kerosene  

Microsoft Academic Search

A technique of machining insulating Al2O3 ceramic with a thin copper sheet assisting electrode and high instantaneous pulse energy is developed. The process uses the high peak voltage and large capacitor with high instantaneous pulse energy, and there is no current-limiting resistor in the discharge circuit, so the discharge energy and discharge explosive force are high, and the process is

Renjie Ji; Yonghong Liu; Yanzhen Zhang; Fei Wang; Baoping Cai; Xingsheng Fu

2011-01-01

386

Single Discharge Machining Insulating Al2O3 Ceramic with High Instantaneous Pulse Energy in Kerosene  

Microsoft Academic Search

A technique of machining insulating Al2O3 ceramic with a thin copper sheet assisting electrode and high instantaneous pulse energy is developed. The process uses the high peak voltage and large capacitor with high instantaneous pulse energy, and there is no current-limiting resistor in the discharge circuit, so the discharge energy and discharge explosive force are high, and the process is

Renjie Ji; Yonghong Liu; Yanzhen Zhang; Fei Wang; Baoping Cai; Xingsheng Fu

2012-01-01

387

High power GaAlAs\\/GaAs HBTs for microwave applications  

Microsoft Academic Search

This paper reports the attainment of high microwave output, up to 0.4 W cw at 10 GHz, with GaAlAs\\/ GaAs heterojunction bipolar transistors. In addition to high power, the HBTs displayed excellent power-added efficiency (4896) and power gain (7 dB). A key factor in obtaining these high powers and efficiencies is the ability to support high collector-emitter voltages without breakdown.

N. H. Sheng; M. F. Chang; P. M. Asbeck; K. C. Wang; G. J. Sullivan; D. L. Miller; J. A. Higgins; E. Sovero; H. Basit

1987-01-01

388

Improvement of the high temperature oxidation resistance of Ti50Al via ion-implantation  

Microsoft Academic Search

The TiAl intermetallic compound is very promising for high temperature applications, because of its good high temperature strength and its low density. At temperatures exceeding 800C, the low oxidation resistance is a limiting factor. It is known, that Cl doping reduces the oxidation strongly even in very low concentrations of about 500 ppm (`microalloy'). In the present investigation ion beam

U. Hornauer; E. Richter; E. Wieser; W. Mller; G. Schumacher; C. Lang; M. Schtze

1999-01-01

389

High brightness AlGaInP light-emitting diodes  

Microsoft Academic Search

This paper reviews the recent progress of AlGaInP high brightness light-emitting diodes. After the discussion of some basic material properties and the general problem of light extraction we will discuss several approaches of high efficiency devices

Klaus Streubel; Norbert Linder; Ralph Wirth; Arndt Jaeger

2002-01-01

390

The Effects of High Uniaxial Compressive Stress on Glass.  

National Technical Information Service (NTIS)

Necked Pyrex rods were used to obtain the values of uniaxial compression stress on glass. Stresses up to 547,000 psi were measured and some unusual phenomena were noted: instead of splintering, the glass failed by giving a coherent mass and at the same ti...

J. O. Outwater D. J. Gerry

1966-01-01

391

Cavity Optomechanics with High-Stress Silicon Nitride Films  

NASA Astrophysics Data System (ADS)

There has been a barrage of interest in recent years to marry the fields of nanomechanics and quantum optics. Mechanical systems provide sensitive and scalable architectures for sensing applications ranging from atomic force microscopy to gravity wave interferometry. Optical resonators driven by low noise lasers provide a quiet and well-understood means to read-out and manipulate mechanical motion, by way of the radiation pressure force. Taken to an extreme, a device consisting of a high-Q nanomechanical oscillator coupled to a high-finesse optical cavity may enable ground-state preparation of the mechanical element, thus paving the way for a new class of quantum technology based on chip-scale phononic devices coupled to optical photons. By way of mutual coupling to the optical field, this architecture may enable coupling of single phonons to real or artificial atoms, an enticing prospect because of the vast "quantum optics toolbox" already developed for cavity quantum electrodynamics. The first step towards these goals --- ground-state cooling of the mechanical element in a "cavity optomechanical" system --- has very recently been realized in a cryogenic setup. The work presented in this thesis describes an effort to extend this capability to a room temperature apparatus, so that the usual panoply of table-top optical/atomic physics tools can be brought to bear. This requires a mechanical oscillator with exceptionally low dissipation, as well as careful attention to extraneous sources of noise in both the optical and mechanical componentry. Our particular system is based on a high- Q, high-stress silicon nitride membrane coupled to a high-finesse Fabry-Perot cavity. The purpose of this thesis is to record in detail the procedure for characterizing/modeling the physical properties of the membrane resonator, the optical cavity, and their mutual interaction, as well as extraneous sources of noise related to multimode thermal motion of the oscillator, thermal motion of the cavity apparatus, optical absorption, and laser phase fluctuations. Our principle experimental result is the radiation pressure-based cooling of a high order, ? 4.8 MHz drum mode of the membrane from room temperature to ? 100 mK (? 500 phonons). Secondary results include an investigation of the Q-factor of membrane oscillators with various geometries, some of which exhibit state-of-the-art Qxfrequency products of 3 x 1013 Hz, and a novel technique to suppress extraneous radiation pressure noise using electro-optic feedback.

Wilson, Dalziel Joseph

392

A New High-Pressure Phase With Mg2Al2O5 Composition  

NASA Astrophysics Data System (ADS)

As MgAl2O4 is one of major components of both spinel phase and calcium ferrite phase in the Earth"fs mantle, many researchers have studied its high-pressure phase relations. However, the high- pressure high-temperature phase relation has been unclear at temperature higher than 2000 C. By performing high-pressure experiments, we found that MgAl2O4 spinel decomposes to Mg2Al2O5 and Al2O3 at 20-25 GPa and temperature higher than 2000 C. This is the first report of a compound with the composition of Mg2Al2O5. The powder X-ray diffraction pattern can not be explained by crystal structures of already known high-pressure phases like brownmillerite-type Ca2Al2O5. In this study, we tried to construct a crystal structure model of the new Mg2Al2O5 phase. The obtained structure model was used for structure refinement by the Rietveld analysis. The Mg2Al2O5 phase for a powder XRD measurement was synthesized using a Kawai-type multi-anvil high-pressure apparatus at Gakushuin University. The starting material of a mixture of MgO:Al2O3 = 2:1 (in molar ratio) was hold at 23 GPa and 2500 C for 10 min. After quenching, the sample was recoverd to ambient pressure. The sintered polycrystalline sample was crushed by a die and ground into powder. The powder X-ray diffraction profile was measured using Rigaku RINT2500V (Cr K?, 45 kV, 250 mA) with the step size of 0.02. The Rietveld analysis was made using RIETAN-2000 program. The XRD profile showed that symmetry of the Mg2Al2O5 phase is orthorhombic. The extinction rules of the powder XRD peaks suggested the space group of Pba2 or Pbam. Since it was found that the XRD pattern is close to that of (Mg, Fe2+)2(Fe3+, Al)(BO3)O2 ludwigite, a structure model of the Mg2Al2O5 phase was constructed based on it. It should be noted that planner three coordinated sites in ludwigite in which boron places were moved by 0.5 in atomic coordinate along c-axis, because interatomic distances between cation and oxygen in the planner three coordinated sites are too short for Mg2+ and Al3+. In this structure model, (Mg, Al)O6 octahedra connected by edge-sharing and corner-sharing form triangular tunnels along c-axis. Cation sites occupied by only Mg are placed in the tunnels. The sites have a coordination environment of trigonal prism- type MgO6. By the Rietveld analysis, lattice parameters were determined as a = 9.3710(6) , b = 12.1952(6) , c = 2.7916(2) . The calculated density of 3.801(1) g/cm3 is consistent with the high-pressure phase relations. R factor by adopting the space group of Pbam is smaller than that by Pba2. Therefore, it is suggested that the space group of the Mg2Al2O5 phase is Pbam

Kojitani, H.; Enomoto, A.; Tsukamoto, S.; Akaogi, M.; Miura, H.

2008-12-01

393

The Chinese High School Student's Stress in the School and Academic Achievement  

ERIC Educational Resources Information Center

|In a sample of 466 Chinese high school students, we examined the relationships between Chinese high school students' stress in the school and their academic achievements. Regression mixture modelling identified two different classes of the effects of Chinese high school students' stress on their academic achievements. One class contained 87% of

Liu, Yangyang; Lu, Zuhong

2011-01-01

394

Microstructure and high frequency properties of nanogranular CoAlO thin films  

NASA Astrophysics Data System (ADS)

Nanogranular CoAlO thin films were fabricated by rf magnetron sputtering using Co target partially covered by Al2O3 chips in argon atmosphere. The films consist of Co nanograins with a mean diameter of 5-30 nm surrounded by an amorphous Al-O phase. It was found that Co grains of face-centered-cubic and hexagonal-close-packed structures coexist in the films with relatively low (Al,O) content, whereas Co grains of face-centered-cubic structure are preferentially formed in the films with higher (Al,O) content. Due to the microstructure changes with increasing (Al,O) content in the films, coercivity and magnetization decrease but the anisotropy field increases. The high frequency properties of the CoAlO films were experimentally characterized, and the effects of magnetization, anisotropy field, and damping factor on the permeability spectrum are also analyzed using the Landau-Lifshitz-Gilbert equation. The ferromagnetic resonance frequency was found to increase from 2.1 to 2.8 GHz with the microstructure change in the films.

Liu, Yan; Tan, C. Y.; Liu, Z. W.; Ong, C. K.

2007-01-01

395

High resolution electron microscopy study of the (Sigma)11 (113)/(110) symmetric tilt grain boundary in pure Al and Al-1.5 wt% Cu.  

National Technical Information Service (NTIS)

Identical bicrystals of pure Al and Al-1.5 wt.% Cu were prepared by diffusion bonding in ultra-high vacuum. The boundary chosen was the (Sigma)11 (113)/(1(bar 1)0) symmetric tilt grain boundary. Characterization of the atomic structure of and segregation ...

G. H. Campbell W. E. King W. L. Wien S. M. Foiles

1996-01-01

396

Phase Composition and Superplastic Behavior of a Wrought AlCoCrCuFeNi High-Entropy Alloy  

NASA Astrophysics Data System (ADS)

A cast AlCoCrCuFeNi high-entropy alloy was multiaxially forged at 950C to produce a fine homogeneous mixture of grains/particles of four different phases with the average size of ~2.1 ?m. The forged alloy exhibited unusual superplastic behavior accompanied by a pronounced softening stage, followed by a steady-state flow stage, during tensile deformation at temperatures of 800C-1000C and at strain rates of 10-4-10-1 s-1. Despite the softening stage, no noticeable strain localization was observed and a total elongation of up to 1240% was obtained. A detailed analysis of the phase composition and microstructure of the alloy before and after superplastic deformation was conducted, the strain rate and temperature dependences of the flow stress were determined at different stages of the superplastic deformation, and the relationships between the microstructure and properties were identified and discussed.

Shaysultanov, D. G.; Stepanov, N. D.; Kuznetsov, A. V.; Salishchev, G. A.; Senkov, O. N.

2013-09-01

397

High-temperature phase equilibria in the Al-rich corner of the Al-Ti-C system  

SciTech Connect

A thermodynamic analysis of the Al-rich corner in the ternary Al-Ti-C diagram, providing phase relations and regions of phase stability, is presented. An invariant four-phase equilibrium between Al, Al{sub 4}C{sub 3}, Al{sub 3}Ti, and TiC{sub x} takes place at 0.53 at. pct Ti, 7.10{sup {minus}6} at. pct C, and TiC{sub 0.883} at 966 K. The carbon content of the TiC{sub x} phase, which extends from x = 0.48 to 0.98, exerts a significant effect on phase relationships in this ternary system. In particular, it is shown that stoichiometric TiC is not stable in the presence of liquid Al. For example, at 1,300 K, a two-phase equilibrium between Al{sub L} and TiC{sub x} exists only in the 0.91 < x < 0.82 range. Thus, the interaction of Al{sub L} with stoichiometric TiC leads to the formation of the Al{sub 4}C{sub 3} aluminum carbide phase, whereas for x < 0.82, only the intermetallic compound Al{sub 3}Ti can form at this temperature. The results of this analysis were confirmed by X-ray diffraction (XRD) measurements of relevant composites.

Frage, N.; Frumin, N.; Levin, L.; Polak, M.; Dariel, M.P. [Ben-Gurion Univ. of the Negev, Beer-Sheva (Israel). Dept. of Materials Engineering

1998-04-01

398

Highly textured growth of AlN films on sapphire by magnetron sputtering for high temperature surface acoustic wave applications  

SciTech Connect

Piezoelectric aluminum nitride films were deposited onto 3 in. [0001] sapphire substrates by reactive magnetron sputtering to explore the possibility of making highly (002)-textured AlN films to be used in surface acoustic wave (SAW) devices for high temperature applications. The synthesized films, typically 1 {mu}m thick, exhibited a columnar microstructure and a high c-axis texture. The relationship between the microstructures and process conditions was examined by x-ray diffraction (XRD), transmission electron microscopy, and atomic force microscopy analyses. The authors found that highly (002)-textured AlN films with a full width at half maximum of the rocking curve of less than 0.3 deg. can be achieved under high nitrogen concentration and moderate growth temperature, i.e., 250 deg. C. The phi-scan XRD reveals the high in-plane texture of deposited AlN films. The SAW devices, based on the optimized AlN films on sapphire substrate, were characterized before and after an air annealing process at 800 deg. C for 90 min. The frequency response, recorded after the annealing process, confirmed that the thin films were still strong in a high temperature environment and that they had retained their piezoelectric properties.

Aubert, T.; Assouar, M. B.; Legrani, O.; Elmazria, O.; Tiusan, C.; Robert, S. [Institut Jean Lamour, UMR 7198, Nancy University-CNRS, BP 70239, Bd des Aiguillettes, 54506 Vandoeuvre Cedex (France)

2011-03-15

399

Stress  

NSDL National Science Digital Library

This project collects resources for studying mental health and stress issues with middle schoolers. Teens and stress Science NetLinks: The Laughing Brain 2: A Good Laugh Dealing with anger Stress-o-meter Look at each of the above sites. Choose one and read the content. Write a one-paragraph summary. Play interactive games and take quizzes. Keep a log of what you do. Tell which site you liked best and why. Watch the following video for positive things teens do to reduce the stress ...

Deaton, Mrs.

2011-06-10

400

High Temperature Hall sensors using AlGaN/GaN HEMT Structures  

NASA Astrophysics Data System (ADS)

Hall effect sensors are the most widely used magnetic sensors, and are commonly fabricated using narrow band-gap semiconductors such as InSb and GaAs. However, the operation of InSb and GaAs-based Hall sensors is unstable at elevated temperatures. Here, we exploited the fact that gallium nitride- (GaN) based wide band-gap (3.4eV) semiconductors have high breakdown electric field strength and are robust at elevated temperatures and tested the high temperature electrical characteristics of AlGaN/GaN heterostructure micro-Hall effect sensors with a two-dimensional electron gas (2DEG). The AlGaN/GaN heterostructures had an electron mobility of 1360 cm2/Vs and a 2DEG density of 1.0 1013 cm-2. The supply-current-related sensitivity (SCRS) was 77VA-1T-1 at room temperature. Notably, the temperature coefficient of the Hall voltage was +0.05 %/C near room temperature, and SCRS was 67 VA-1T-1 at 400C. The results for AlGaN/GaN were compared with those for AlGaAs/GaAs and AlInSb/InAsSb/AlInSb QW Hall effect sensors.

Koide, S.; Takahashi, H.; Abderrahmane, A.; Shibasaki, I.; Sandhu, A.

2012-03-01

401

Mechanical alloying and high pressure processing of a TiAl-V intermetallic alloy.  

PubMed

An alloy with a chemical composition of Ti-45Al-5V (at.%) was synthesized by mechanical alloying in a Szegvari-type attritor from elemental powders of high purity. Before compaction, the powders were characterized by X-ray diffraction and scanning as well as transmission electron microscopy. The compaction of powders was carried out by hot isostatic pressing and hot isostatic extrusion. The resulting material was subjected to microstructural and mechanical characterization. The microstructure investigated by transmission and scanning electron microscopy supplemented by X-ray diffraction revealed that the bulk material was composed of a mixture of TiAl- and Ti(3)Al-based phases, however, the typical lamellar microstructure for such alloys was not observed. The materials exhibited exceptionally high yield strength together with satisfactory ductility and fracture toughness. The high strength was unequivocally due to grain refinement and the presence of oxide dispersoid. PMID:20500422

Dymek, S; Wrbel, M; Witczak, Z; Blicharski, M

2010-03-01

402

Cold expansion of holes and resulting fatigue life enhancement and residual stresses in Al 2024 T3 alloy An experimental study  

Microsoft Academic Search

This paper presents the experimental results of fatigue life enhancement and the residual stresses around the cold expanded holes in Al 2024, a widely used aerospace alloy. Two techniques for cold expansion of holes, namely split-sleeve with taper pin technique and split-sleeve with ball technique were considered for comparison, as the former involves surface contact and the latter has line

H. D. Gopalakrishna; H. N. Narasimha Murthy; M. Krishna; M. S. Vinod; A. V. Suresh

2010-01-01

403

Incorporating Small Fatigue Crack Growth in Probabilistic Life Prediction: Effect of Stress Ratio in Ti-6Al-2Sn-4Zr-6-Mo (Preprint).  

National Technical Information Service (NTIS)

The effect of stress ratio on the statistical aspects of small fatigue crack growth behavior was studied in a duplex microstructure of Ti-6Al- 2Sn-4Zr-6Mo (Ti-6-2-4-6) at 260 degrees C with particular emphasis on incorporating small-crack data into probab...

J. M. Larsen R. John S. K. Jha

2012-01-01

404

Preliminary study of the characteristics of a high Mg containing Al-Mg-Si alloy  

NASA Astrophysics Data System (ADS)

An Al-20Mg-4Si high Mg containing alloy has been produced and its characteristics investigated. The as-cast alloy revealed primary Mg2Si particles evenly distributed throughout an ?-Al matrix with a ?-Al3Mg2 fully divorced eutectic phase observed in interdendritic regions. The Mg2Si particles displayed octahedral, truncated octahedral, and hopper morphologies. Additions of Sb, Ti and Zr had a refining influence reducing the size of the Mg2Si from 52 4 ?m to 25 0.1 ?m, 35 1 ?m and 34 1 ?m respectively. HPDC tensile test samples could be produced with a 0.6 wt.% Mn addition which prevented die soldering. Solution heating for 1 hr was found to dissolve the majority of the Al3Mg2 eutectic phase with no evidence of any effect on the primary Mg2Si. Preliminary results indicate that the heat treatment has a beneficial effect on the elongation and the UTS.

Yan, F.; McKay, B. J.; Fan, Z.; Chen, M. F.

2012-01-01

405

Defects in AlN: High-frequency EPR and ENDOR studies  

NASA Astrophysics Data System (ADS)

Compensation by deep-level defects and self-compensation of shallow donors in AlN are discussed in the light of results of a high-frequency pulse electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) study. It was suggested on the basis of the large mostly isotropic hyperfine interaction with A(27Al)=406 MHz that one of the deep-level defect is isolated interstitial Al2+ atom. Two types of effective-mass-like shallow donors with a delocalised wave function were shown to exist in unintentionally doped AlN. The experiments demonstrate how the transformation from a shallow donor to a deep (DX) centre takes place and how the deep DX centre can be reconverted into a shallow donor forming a spin triplet and singlet states with an exchange interaction of about 24 cm-1 and with a lowest triplet state.

Orlinskii, Sergei B.; Baranov, Pavel G.; Bundakova, Anna P.; Bickermann, Matthias; Schmidt, Jan

2009-12-01

406

Al{sub 2}O{sub 3}-Ni composites with high strength and fracture toughness  

SciTech Connect

Al{sub 2}O{sub 3}-Ni composites were prepared by the reactive hot pressing of Al and NiO. The composites had a two-phase, interpenetrating microstructure and contained {approximately}35 vol% Ni. They exhibited an impressively high combination of strength and toughness at room temperature; the four-point bending strength was in excess of 600 MPa with a fracture toughness of more than 12 MPa{sm_bullet}m{sup 1/2}. Examination of fracture surfaces showed that Ni ligaments underwent ductile deformation during fracture. SEM analysis revealed knife-edged Ni ligaments with a limited amount of debonding around their periphery (i.e., at the Ni-Al{sub 2}O{sub 3} interface), indicating a strong Ni-Al{sub 2}O{sub 3} bond.

Fahrenholtz, W.G.; Ellerby, D.T.; Loehman, R.E.

2000-05-01

407

Laser remelting of Ti6AL4V using high power diode laser  

NASA Astrophysics Data System (ADS)

Titanium alloys present excellent mechanical and corrosion properties, being widely employed in different industries such as medical, aerospace, automotive, petrochemical, nuclear and power generation, etc. Ti6Al4V is the ?-? alloy most employed in industry. The modification of its properties can be achieved with convectional heat treatments and/or with laser processing. Laser remelting (LR) is a technology applied to Ti6Al4V by other authors with excimer and Nd-Yag laser with pure argon shielding gas to prevent risk of oxidation. In the present contribution, laser remelting has been applied for the first time to Ti6Al4V with a high power diode laser (with pure argon as shielding gas). Results showed that remelted samples (with medium energy densities) have higher microhardness and better corrosion resistance than Ti6Al4V base metal.

Amaya-Vzquez, M. R.; Snchez-Amaya, J. M.; Boukha, Z.; El Amrani, K.; Botana, F. J.

2012-04-01

408

Surface modification of Al-12.6Si alloy by high current pulsed electron beam  

NASA Astrophysics Data System (ADS)

The paper investigates the microstructure and property modifications of Al-12.6Si alloy induced by high current pulsed electron beam (HCPEB) treatment. The scanning electron microscope (SEM) results show a fine and equiaxed grain structure of several micrometers is obtained on the top surface of the melted layer. Underneath the top surface, a remelted layer with about 10 ?m thickness is obtained and a supersaturated solid solution of Al is formed in the remelted layer. XRD analysis shows that the relative strength of diffraction peaks of Al (1 1 1) and Si (1 1 1) crystal planes is increased after HCPEB treatment. As a result, relative wear resistance of HCPEB-treated sample is significantly improved by a factor of 2.5 due to fine grain strengthening and solid solution strengthening. Therefore, the HCPEB treatment has a good application future in treating Al-Si alloys.

Hao, Y.; Gao, B.; Tu, G. F.; Cao, H.; Hao, S. Z.; Dong, C.

2012-01-01

409

A High-Density Genome-Wide Association Screen of Sporadic ALS in US Veterans  

PubMed Central

Following reports of an increased incidence of amyotrophic lateral sclerosis (ALS) in U.S. veterans, we have conducted a high-density genome-wide association study (GWAS) of ALS outcome and survival time in a sample of U.S. veterans. We tested ?1.3 million single nucleotide polymorphisms (SNPs) for association with ALS outcome in 442 incident Caucasian veteran cases diagnosed with definite or probable ALS and 348 Caucasian veteran controls. To increase power, we also included genotypes from 5909 publicly-available non-veteran controls in the analysis. In the survival analysis, we tested for association between SNPs and post-diagnosis survival time in 639 Caucasian veteran cases with definite or probable ALS. After this discovery phase, we performed follow-up genotyping of 299 SNPs in an independent replication sample of Caucasian veterans and non-veterans (ALS outcome: 183 cases and 961 controls; survival: 118 cases). Although no SNPs reached genome-wide significance in the discovery phase for either phenotype, three SNPs were statistically significant in the replication analysis of ALS outcome: rs6080539 (177 kb from PCSK2), rs7000234 (4 kb from ZNF704), and rs3113494 (13 kb from LOC100506746). Two SNPs located in genes that were implicated by previous GWA studies of ALS were marginally significant in the pooled analysis of discovery and replication samples: rs17174381 in DPP6 (p?=?4.410?4) and rs6985069 near ELP3 (p?=?4.810?4). Our results underscore the difficulty of identifying and convincingly replicating genetic associations with a rare and genetically heterogeneous disorder such as ALS, and suggest that common SNPs are unlikely to account for a substantial proportion of patients affected by this devastating disorder.

Kwee, Lydia Coulter; Liu, Yutao; Haynes, Carol; Gibson, Jason R.; Stone, Annjanette; Schichman, Steven A.; Kamel, Freya; Nelson, Lorene M.; Topol, Barbara; Van Den Eeden, Stephen K.; Tanner, Caroline M.; Cudkowicz, Merit E.; Grasso, Daniela L.; Lawson, Robert; Muralidhar, Sumitra; Oddone, Eugene Z.

2012-01-01

410

The mechanisms of immune suppression by high-pressure stress in mice.  

PubMed

The effects of high-pressure stress on the induction of anti-sheep red blood cells (SRBC) and of plaque-forming cells (PFC), and on thymus weight, were studied in BALB/c mice in-vivo and in-vitro. The efficacy of high-pressure stress in suppressing PFC and thymic involution was maximum when the stress was applied 1 h day(-1) for 2 days before immunization with SRBC. Both effects were blocked by administration of indomethacin, atropine, naloxone or phentolamine before the first application of stress, whereas hexamethonium and propranolol had no such effect. Hexamethonium, naloxone and propranolol administered before the second application of high-pressure stress blocked both effects. Prostaglandin and acetylcholine given 24 h before application of high-pressure stress caused a marked reduction in PFC count, but not in thymus weight. The reduced PFC count caused by acetylcholine was blocked by pretreatment with indomethacin. When adrenaline was injected 24 h after application of high-pressure stress a marked reduction in PFC was observed, but without thymic involution. When adrenaline was injected 24 h after prostaglandin injection the PFC count was also markedly reduced, but not thymus weight. The decrease in PFC caused by two exposures to stress or one exposure to stress plus injection of adrenaline was blocked by diethylcarbamazine before the second exposure to stress or the injection of adrenaline. In addition, normal spleen cells, were induced as suppressor cells when incubated with the serum of stressed mice, but not when supplemented with anti-leukotriene C4, D4 antibody. These data suggest that mice fall into a pre-stress condition via the release of prostaglandin after the first stress, and then immunosuppression is induced in these prestressed mice via the release of leukotriene C4, D4, caused by the activation of the autonomic nervous system by the second exposure to stress. PMID:10678494

Fujiwara, R; Shibata, H; Komori, T; Yokoyama, M M; Okazaki, Y; Ohmori, M

1999-12-01

411

Highly stressed: stressful and traumatic experiences among individuals with HIV\\/AIDS in the Deep South  

Microsoft Academic Search

A history of traumatic and\\/or stressful experiences is prevalent among HIV-infected individuals and has been consistently associated with poorer health outcomes. However, little is known about incident stressful experiences and the factors that predict these experiences among HIV-infected individuals. Data from a longitudinal study of 611 HIV-infected individuals in the Southeastern USA were used to examine the frequency and types

Susan Reif; Michael Mugavero; James Raper; Nathan Thielman; Jane Leserman; Kathryn Whetten; Brian Wells Pence

2011-01-01

412

High quality AlN and GaN grown on Si(111) by gas source molecular beam epitaxy with ammonia  

SciTech Connect

The authors describe the growth of high quality AlN and GaN on Si(111) by gas source molecular beam epitaxy (GSMBE) with ammonia (NH{sub 3}). The initial nucleation (at 1130--1190K) of an AlN monolayer with full substrate coverage resulted in a very rapid transition to two-dimensional (2D) growth mode of AlN. The rapid transition to the 2D growth mode of AlN is essential for the subsequent growth of high quality GaN, and complete elimination of cracking in thick (>2 {micro}m) GaN layers. The authors show, using Raman scattering (RS) and photoluminescence (PL) measurements, that the tensile stress in the GaN is due to thermal expansion mismatch, is below the ultimate strength of breaking of GaN, and produces a sizable shift in the bandgap. They show that the GSMBE AlN and GaN layers grown on Si can be used as a substrate for subsequent deposition of thick AlN and GaN layers by hydride vapor phase epitaxy (HVPE).

Nikishin, S.A.; Faleev, N.N.; Antipov, V.G. [and others

2000-07-01

413

High breakdown voltage AlGaN/GaN MIS-HFET with low leakage current  

NASA Astrophysics Data System (ADS)

A high-breakdown voltage AlGaN/GaN MIS-HFET with extreme low leakage current was fabricated for power electronics applications. The fabricated device realized the high breakdown voltage of 550 V with the field plate structure and achieved dramatic reduction of the leakage current to 20 nA/mm due to the MIS gate structure. The leakage current of the MIS-HFET is three orders of magnitude lower than that of the AlGaN/GaN HFET without MIS structure.

Kuraguchi, Masahiko; Takada, Yoshiharu; Saito, Wataru; Omura, Ichiro; Tsuda, Kunio

2005-05-01

414

Constitutive equation for Ti6Al4V at high temperatures measured using the SHPB technique  

Microsoft Academic Search

A high temperature split Hopkinson pressure bar (SHPB) test system is used to investigate the effects of temperature as well as those of strain and strain-rate. Effects of temperature for the titanium alloy (Ti6Al4V) are investigated by developing a high temperature SHPB test system. In this work, high temperatures greater than 1000C are attained in the SHPB test specimens by

Songwon Seo; Oakkey Min; Hyunmo Yang

2005-01-01

415

High breakdown voltage AlGaN-GaN HEMTs achieved by multiple field plates  

Microsoft Academic Search

High-voltage Al0.22Ga0.78N-GaN high-electron mobility transistors have been fabricated using multiple field plates over dielectric passivation layers. The device breakdown voltage was found to increase with the addition of the field plates. With two field plates, the device showed a breakdown voltage as high as 900 V. This technique is easy to apply, based on the standard planar transistor fabrication, and

Huili Xing; Y. Dora; A. Chini; S. Heikman; S. Keller; U. K. Mishra

2004-01-01

416

High growth rate MOVPE of Al(Ga)N in planetary reactor  

NASA Astrophysics Data System (ADS)

Possibility of AlN growth by MOVPE in a planetary reactor with high growth rate was investigated. Growth was performed on (0001) Al2O3 substrates at the reactor pressure of 100 mbar. It was shown that deposition rate is close to diffusion limit at low NH3 flows and reduces abruptly above a certain threshold value of NH3 due to gas-phase parasitic reactions. At constant V/III ratio of 1.5-2, AlN growth rate dependence on TMAl flow was linear and a maximum growth rate of 8.6 ?m/h was achieved. Process modeling allowed predicting and explaining the trends related to the onset of parasitic chemistry for various V/III ratios and other growth conditions. Surface morphology planarization was achieved by either (1) NH3 flow rate reduction or (2) TMGa injection after the layer with thickness of 75-300 nm was grown. The second approach looks more fruitful resulting in atomically flat Al(Ga)N layers with a 2 ?m/h growth rate. For the conditions (high temperature, low NH3 and high H2 concentration) used Ga acts mostly as surfactant (Ga content in Al(Ga)N is about 3-5%).

Lundin, W. V.; Nikolaev, A. E.; Yagovkina, M. A.; Brunkov, P. N.; Rozhavskaya, M. M.; Ber, B. Ya.; Kazantsev, D. Yu.; Tsatsulnikov, A. F.; Lobanova, A. V.; Talalaev, R. A.

2012-08-01

417

High-temperature ultra-high cycle fatigue damage of notched single crystal superalloys at high mean stresses  

Microsoft Academic Search

Blade nickel superalloy CMSX-4 widely used in the aero industry and its potential low cost alternative, superalloy CM186LC intended for use in the industrial gas turbines, were subjected to ultra-high-cycle fatigue at high mean stresses to model the effect of vibrations superimposed on sustained load. Circumferentially notched cylindrical specimens of single crystals with the axis orientation of [001] were tested

P. Luk; L. Kunz; M. Svoboda

2005-01-01

418

Indium-silicon co-doping of high-aluminum-content AlGaN for solar blind photodetectors  

Microsoft Academic Search

We report on an indium-silicon co-doping approach for high-Al-content AlGaN layers. Using this approach, very smooth crack-free n-type AlGaN films as thick as 0.5 mum with Al mole fraction up to 40% were grown over sapphire substrates. The maximum electron concentration in the layers, as determined by Hall measurements, was as high as 81017 cm-3 and the Hall mobility was

V. Adivarahan; G. Simin; G. Tamulaitis; R. Srinivasan; J. Yang; M. Asif Khan; M. S. Shur; R. Gaska

2001-01-01

419

Rhombohedral AlPt films formed by self-propagating, high temperature synthesis.  

SciTech Connect

High-purity AlPt thin films prepared by self-propagating, high temperature combustion synthesis show evidence for a new rhombohedral phase. Sputter deposited Al/Pt multilayers of various designs are reacted at different rates in air and in vacuum, and each form a new trigonal/hexagonal aluminide phase with unit cell parameters a = 15.571(8) {angstrom}, c = 5.304(1) {angstrom}, space group R-3 (148), and Z, the number of formula units within a unit cell, = 39. The lattice is isostructural to that of the AlPd R-3 lattice as reported by Matkovic and Schubert (Matkovic, 1977). Reacted films have a random in-plane crystallographic texture, a modest out-of-plane (001) texture, and equiaxed grains with dimensions on the order of film thickness.

Adams, David Price; Rodriguez, Mark Andrew; Kotula, Paul Gabriel

2005-11-01

420

Amorphous and nanocrystalline phase formation in highly-driven Al-based binary alloys  

SciTech Connect

Remarkable advances have been made since rapid solidification was first introduced to the field of materials science and technology. New types of materials such as amorphous alloys and nanostructure materials have been developed as a result of rapid solidification techniques. While these advances are, in many respects, ground breaking, much remains to be discerned concerning the fundamental relationships that exist between a liquid and a rapidly solidified solid. The scope of the current dissertation involves an extensive set of experimental, analytical, and computational studies designed to increase the overall understanding of morphological selection, phase competition, and structural hierarchy that occurs under far-from equilibrium conditions. High pressure gas atomization and Cu-block melt-spinning are the two different rapid solidification techniques applied in this study. The research is mainly focused on Al-Si and Al-Sm alloy systems. Silicon and samarium produce different, yet favorable, systems for exploration when alloyed with aluminum under far-from equilibrium conditions. One of the main differences comes from the positions of their respective T{sub 0} curves, which makes Al-Si a good candidate for solubility extension while the plunging T{sub 0} line in Al-Sm promotes glass formation. The rapidly solidified gas-atomized Al-Si powders within a composition range of 15 to 50 wt% Si are examined using scanning and transmission electron microscopy. The non-equilibrium partitioning and morphological selection observed by examining powders at different size classes are described via a microstructure map. The interface velocities and the amount of undercooling present in the powders are estimated from measured eutectic spacings based on Jackson-Hunt (JH) and Trivedi-Magnin-Kurz (TMK) models, which permit a direct comparison of theoretical predictions. For an average particle size of 10 {micro}m with a Peclet number of {approx}0.2, JH and TMK deviate from each other. This deviation indicates an adiabatic type solidification path where heat of fusion is reabsorbed. It is interesting that this particle size range is also consistent with the appearance of a microcellular growth. While no glass formation is observed within this system, the smallest size powders appear to consist of a mixture of nanocrystalline Si and Al. Al-Sm alloys have been investigated within a composition range of 34 to 42 wt% Sm. Gas atomized powders of Al-Sm are investigated to explore the morphological and structural hierarchy that correlates with different degrees of departure from full equilibrium conditions. The resultant powders show a variety of structural selection with respect to amount of undercooling, with an amorphous structure appearing at the highest cooling rates. Because of the chaotic nature of gas atomization, Cu-block melt-spinning is used to produce a homogeneous amorphous structure. The as-quenched structure within Al-34 to 42 wt% Sm consists of nanocrystalline fcc-Al (on the order of 5 nm) embedded in an amorphous matrix. The nucleation density of fcc-Al after initial crystallization is on the order of 10{sup 22}-10{sup 23} m{sup -3}, which is 10{sup 5}-10{sup 6} orders of magnitude higher than what classical nucleation theory predicts. Detailed analysis of liquid and as-quenched structures using high energy synchrotron X-ray diffraction, high energy transmission electron microscopy, and atom probe tomography techniques revealed an Al-Sm network similar in appearance to a medium range order (MRO) structure. A model whereby these MRO clusters promote the observed high nucleation density of fcc-Al nanocrystals is proposed. The devitrification path was identified using high temperature, in-situ, high energy synchrotron X-ray diffraction techniques and the crystallization kinetics were described using an analytical Johnson-Mehl-Avrami (JMA) approach.

Kalay, Yunus Eren

2008-10-15

421

Comparative study of etching high crystalline quality AlN and GaN  

NASA Astrophysics Data System (ADS)

High-quality AlN and GaN bulk crystals were etched in a KOH aqueous solution or a KOH/H2O2 mixture. As etched surfaces were characterized by scanning electron microscope (SEM), atomic force microscope (AFM), and X-ray photoelectron spectroscopy (XPS). It was found that the N-polar surfaces had approximately 900 and 20 times higher etch rate than the III-polar surface for AlN and GaN, respectively. AlN had a higher total etch rate than GaN at the same condition. Hexagonal hillocks were observed on N-polar face with {10-1-1} boundary planes for both AlN and GaN, while metal polar surfaces remained smooth. Formation of aluminum oxide/hydroxide AlOx(OH)y was confirmed by XPS on as etched N polar AlN surface; the addition of H2O2 resulted in a higher total surface oxygen concentration. The smoothening effect by adding H2O2 oxidizer was explained by the formation and dissolution of aluminum oxide/hydroxide.

Guo, W.; Xie, J.; Akouala, C.; Mita, S.; Rice, A.; Tweedie, J.; Bryan, I.; Collazo, R.; Sitar, Z.

2013-03-01

422

High temperature oxidation of Ni{sub 50}(Al,Be){sub 50}  

SciTech Connect

Effect of Be on high-temperature oxidation of NiAl was investigated. From 1 to 10% Be was substituted for Al on a 1 to 1 atomic basis. Oxidation experiments were conducted in pure oxygen. Exposure temperatures ranged from 800 to 1200 C for 16 hours. In addition to thermogravimetry, postexposure analysis involved SEM of intact scales, XRD, XPS, and Rutherford backscattering spectroscopy. At every temperature tested, the Be modified NiAl containing 1, 2, or 5 at.% Be exhibited lower weight gain and comparable or slower oxidation rates than the pure binary material. The surfaces of the Be modified specimens showed minimal topography, with no evidence of the usual transient alumina phases grown on binary NiAl in this temperature range. XRD and surface analysis showed the presence of layers of Al{sub 2}O{sub 3} and ternary oxide phases, primarily BeO*Al{sub 2}O{sub 3}. The growth of this complex scale apparently prevents growth of the transient alumina phases.

Hanrahan, R.J. Jr.; Butt, D.P.; Thoma, D.J.; Taylor, T.N.; Maggiore, C.J.

1996-12-31

423

Characteristics of inclusions in high-Al steel during electroslag remelting process  

NASA Astrophysics Data System (ADS)

The characteristics of inclusions in high-Al steel refined by electroslag remelting (ESR) were investigated by image analysis, scanning electron microscopy (SEM), and energy-dispersive spectrometry (EDS). The results show that the size of almost all the inclusions observed in ESR ingots is less than 5 ?m. Inclusions smaller than 3 ?m take nearly 75% of the total inclusions observed in each ingot. Inclusions observed in ESR ingots are pure AlN as dominating precipitates and some fine spherical Al2O3 inclusions with a size of 1 ?m or less. It is also found that protective gas operation and slag deoxidation treatment during ESR process have significant effects on the number of inclusions smaller than 2 ?m but little effects on that of inclusions larger than 2 ?m. Thermodynamic calculations show that AlN inclusions are unable to precipitate in the liquid metal pool under the present experimental conditions, while the precipitation of AlN inclusions could take place at the solidifying front due to the microsegregation of Al and N in liquid steel during solidification.

Shi, Cheng-bin; Chen, Xi-chun; Guo, Han-jie

2012-04-01

424

High-efficiency solar cells based on Cu(InAl)Se2 thin films  

NASA Astrophysics Data System (ADS)

A Cu(InAl)Se2 solar cell with 16.9% efficiency is demonstrated using a Cu(InAl)Se2 thin film deposited by four-source elemental evaporation and a device structure of glass/Mo/Cu(InAl)Se2/CdS/ZnO/indium tin oxide/(Ni/Algrid)/MgF2. A key to high efficiency is improved adhesion between the Cu(InAl)Se2 and the Mo back contact layer, provided by a 5-nm-thick Ga interlayer, which enabled the Cu(InAl)Se2 to be deposited at a 530 degC substrate temperature. Film and device properties are compared to Cu(InGa)Se2 with the same band gap of 1.16 eV. The solar cells have similar behavior, with performance limited by recombination through trap states in the space charge region in the Cu(InAl)Se2 or Cu(InGa)Se2 layer.

Marsillac, S.; Paulson, P. D.; Haimbodi, M. W.; Birkmire, R. W.; Shafarman, W. N.

2002-08-01

425

Efficacy of Abbreviated Progressive Muscle Relaxation in a High-Stress College Sample  

Microsoft Academic Search

This study's purpose was to examine the efficacy of abbreviated progressive muscle relaxation (APMR) to enhance physiological and psychological functioning among high-stress college students. Participants (N = 128) were undergraduates, 19 years old on average, predominantly female and White, with high Perceived Stress Scale scores. After random assignment, for 20 min, 66 experimental group participants underwent APMR lying down and

Christyn L. Dolbier; Taylor E. Rush

2012-01-01

426

ALS-Associated Ataxin 2 PolyQ Expansions Enhance Stress-Induced Caspase 3 Activation and Increase TDP-43 Pathological Modifications  

PubMed Central

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease caused by the loss of motor neurons. The degenerating motor neurons of ALS patients are characterized by the accumulation of cytoplasmic inclusions containing phosphorylated and truncated forms of the RNA-binding protein TDP-43. Ataxin 2 intermediate-length polyglutamine (polyQ) expansions were recently identified as a risk factor for ALS; however, the mechanism by which they contribute to disease is unknown. Here, we show that intermediate-length ataxin 2 polyQ expansions enhance stress-induced TDP-43 C-terminal cleavage and phosphorylation in human cells. We also connect intermediate-length ataxin 2 polyQ expansions to the stress-dependent activation of multiple caspases, including caspase 3. Caspase activation is upstream of TDP-43 cleavage and phosphorylation since caspase inhibitors block these pathological modifications. Analysis of the accumulation of activated caspase 3 in motor neurons revealed a striking association with ALS cases harboring ataxin 2 polyQ expansions. These findings indicate that activated caspase 3 defines a new pathological feature of ALS with intermediate-length ataxin 2 polyQ expansions. These results provide mechanistic insight into how ataxin 2 intermediate-length polyQ expansions could contribute to ALSby enhancing stress-induced TDP-43 pathological modifications via caspase activation. Because longer ataxin 2 polyQ expansions are associated with a different disease, spinocerebellar ataxia 2, these findings help explain how different polyQ expansions in the same protein can have distinct cellular consequences, ultimately resulting in different clinical features. Finally, since caspase inhibitors are effective at reducing TDP-43 pathological modifications, this pathway could be pursued as a therapeutic target in ALS.

Hart, Michael P.; Gitler, Aaron D.

2012-01-01

427

AlGaN Ultraviolet A and Ultraviolet C Photodetectors with Very High Specific Detectivity D*  

NASA Astrophysics Data System (ADS)

The development of AlGaN pin photodetectors sensitive in the UV range with different narrow band active regions is reported in this paper. Structures were grown by metalorganic vapor phase epitaxy on (0001) sapphire substrates using three-dimensional GaN as well as high temperature AlN nucleation. Very high specific detectivities of 1 1014 cm Hz0.5 W-1 can be achieved based on optimized growth conditions of undoped and doped AlGaN layers with an Al-content ranging from 0% up to 100%. The crack-free AlGaN layers have edge dislocation densities in the range of 5 109 cm-2. Based on the two different nucleation types, pin layer structures were grown and fabricated to UV-A (320 to 365 nm) and UV-C (< 280 nm) photodetectors. The electro-optical performance of these photodetectors measured on-wafer will be presented in this paper, supplemented by the data of a single photodetector chip mounted in a TO 18 package.

Albrecht, Bjrn; Kopta, Susanne; John, Oliver; Kirste, Lutz; Driad, Rachid; Khler, Klaus; Walther, Martin; Ambacher, Oliver

2013-08-01

428

Uniaxial-stress dependence of the phonon behavior in the premartensitic phase of Ni62.5Al37.5  

NASA Astrophysics Data System (ADS)

Results of neutron-scattering experiments on a single crystal of Ni62.5Al37.5 as a function of uniaxial stress and temperature are reported. Emphasis is placed on the behavior of the low-energy part of the [??0]-TA2 phonon branch and its associated central peak. The dip in the phonon-dispersion curve is stress dependent and shifts from ?=0.14 for zero stress to ?=0.18 for an applied stress of 85 MPa at room temperature. As the temperature decreases the satellite shifts further, the phonon energy decreases considerably, and the linewidths become broad. These results are interpreted in terms of Clapp's localized soft-mode theory of nucleation in martensite.

Shapiro, S. M.; Svensson, E. C.; Vettier, C.; Hennion, B.

1993-11-01

429

Deformation pattern and strain hardening in a highly textured 8090 AlLi alloy sheet  

Microsoft Academic Search

Structure-deformation pattern analysis was made on a highly textured 8090 AlLi alloy sheet deformed in tension. It is shown that the sharp ?-fiber type crystallographic texture induces a strong orientation variation in the mechanical properties and in the deformation structure. The soft orientation is 55 in respect to the rolling direction (RD), while the hard orientation is parallel to the

E Romhanji; D Mitlin; V Radmilovic

2000-01-01

430

Derivation of Apollo 14 High-Al Basalts at Discrete Times: Rb-Sr Isotopic Constraints  

NASA Astrophysics Data System (ADS)

Four eruption episodes were identified for A-14 high-Al basalts. Rb-Sr isotopic data and ITE ratios show that their parental melt compositions of are correlated through mixing of evolved components with a relatively primitive magma ocean cumulate.

Hui, H.; Neal, C. R.; Shih, C.-Y.; Nyquist, L. E.

2012-03-01

431

Trace Element Signatures in the Apollo 14 High-Al Basalts: What Do They Represent?  

NASA Astrophysics Data System (ADS)

Analyses of olivine, plagioclase, and phosphate in the A14 high-Al basalts indicate that compatible and incompatible elements exhibit variability consistent with differences observed in the bulk samples. It is concluded that this variability is not the result of random sampling.

Hagerty, J. J.; Shearer, C. K.; Papike, J. J.

2002-03-01

432

Hot-Wall MOCVD for Highly Efficient and Uniform Growth of AlN  

Microsoft Academic Search

We demonstrated successful growth of AlN at a temperature of 1200 C in a set of hot-wall MOCVD systems with the possibility of straightforward scaling up the process on larger wafer areas to meet the demand of device technologies. We outlined several aspects of the carefully optimized design and process parameters with relevance to achievement of a high overall growth

A. Kakanakova-Georgieva; R. R. Ciechonski; U. Forsberg; A. Lundskog; E. Janze?n

2009-01-01

433

Effect of carbon content on high temperature tensile properties of Fe 3Al based intermetallic alloys  

Microsoft Academic Search

Ordered intermetallic alloys based on the iron aluminide FeAl are being considered for high temperature structural applications. Though these alloys exhibit poor room temperature ductility and low fracture toughness, significant improvement in these respects can be achieved by alloying addition and process control. Most of the reported literature is on compositions with very low (<0.01 wt.%) carbon contents because carbon

P. K. Rao; N. B. Ballal; A. Radhakrishna; V. R. Rao

1997-01-01

434

Families OverComing under Stress (FOCUS) for Early Childhood: Building Resilience for Young Children in High Stress Families  

ERIC Educational Resources Information Center

|Parental distress and trauma affects the entire family, including the youngest children. Families OverComing Under Stress (FOCUS) is a targeted prevention program for high-risk families that aims to enhance family cohesion, support the parent-child relationship, and build emotional regulation, communication, and problem-solving skills across the

Mogil, Catherine; Paley, Blair; Doud, Tricia; Havens, Linda; Moore-Tyson, Jessica; Beardslee, William R.; Lester, Patricia

2010-01-01

435

Feasibility study of Nb3Al Rutherford cable for high field accelerator magnet application  

SciTech Connect

Feasibility study of Cu stabilized Nb{sub 3}Al strand and Rutherford cable for the application to high field accelerator magnets are being done at Fermilab in collaboration with NIMS. The Nb{sub 3}Al strand, which was developed and manufactured at NIMS in Japan, has a non-copper Jc of about 844 A/mm{sup 2} at 15 Tesla at 4.2 K, a copper content of 50%, and filament size of about 50 microns. Rutherford cables with 27 Nb{sub 3}Al strands of 1.03 mm diameter were fabricated and tested. Quench tests on a short cable were done to study its stability with only its self field, utilizing a high current transformer. A pair of 2 meter long Nb{sub 3}Al cables was tested extensively at CERN at 4.3 and 1.9 K up to 11 Tesla including its self field with a high transport current of 20.2 kA. In the low field test we observed instability near splices and in the central region. This is related to the flux-jump like behavior, because of excessive amount of Nb in the Nb{sub 3}Al strand. There is possibility that the Nb in Nb{sub 3}Al can cause instability below 2 Tesla field regions. We need further investigation on this problem. Above 8 Tesla, we observed quenches near the critical surface at fast ramp rate from 1000 to 3000 A/sec, with quench velocity over 100 m/sec. A small racetrack magnet was made using a 14 m of Rutherford cable and successfully tested up to 21.8 kA, corresponding to 8.7 T.

Yamada, R.; /Fermilab; Kikuchi, A.; /Tsukuba Magnet Lab.; Ambrosio, G.; Andreev, N.; Barzi, E.; Cooper, C.; Feher, S.; Kashikhin, V.V.; Lamm, M.; Novitski, I.; /Fermilab; Takeuchi, T.; /Tsukuba Magnet Lab.; Tartaglia, M.; Turrioni, D.; /Fermilab; Verweij, A.P.; /CERN; Wake, M.; Willering, G; /Tsukuba Magnet Lab.; Zlobin, A.V.; /Fermilab

2006-08-01

436

Stress response of Barkhausen noise in high carbon steel cables and ropes  

NASA Astrophysics Data System (ADS)

Stress response of three magnetic parameters related to Barkhausen noise (BN) for three types of steel concrete reinforcement cables, in as-delivered and heat treated conditions, and three steel ropes, in the as-delivered state, is investigated. In all materials, rms value of BN and peak voltage of noise burst steadily decrease as a function of tensile stress up to a level of 1000 MPa, whereas peak position of noise burst is simultaneously delayed on the time axis, indicating an increase in coercive force. Stress response of rms and peak voltage of noise is strong in all reinforcement cables but weaker in ropes. Stress dependence of magnetic parameters is caused by the stress gradient effect at high stresses and at low stresses, either by <110> wire texture or by a decrease in mobility of Bloch walls oriented along the cementite lamellae or rows and, simultaneously, along the cables or ropes.

Rautioaho, R.; Kivimaa, J.; Moilanen, M.

1994-01-01

437

WC-Co and Cr3C2-NiCr Coatings in Low- and High-Stress Abrasive Conditions  

NASA Astrophysics Data System (ADS)

The article deals with the evaluation of abrasive wear resistance and adhesive strength of thermally sprayed coatings. The main attention was paid to differences between low- and high-stress abrasive conditions of the measuring. Conclusions include the evaluation of specific properties of the WC-Co and the Cr3C2-NiCr High Velocity Oxygen Fuel coatings and the evaluation of the changes in the behavior of the abrasive media. Mainly, the relationship between the low- and high-stress abrasion conditions and the wear mechanism in the tested materials was described. For the wear test, the abrasive media of Al2O3 and SiO2 sands were chosen. During wear tests, the volume loss of the tested materials and the surface roughness of the wear tracks were measured. The wear tracks on the tested materials and abrasive sands' morphologies were observed using Scanning Electron Microscopy. It was found that high-stress abrasive conditions change the coatings' behavior very significantly, particularly that of the Cr3C2-NiCr coating. Adhesive-cohesive properties of the coatings and relationships among individual structure particles were evaluated using tensile testing. It was found that the weak bond strength among the individual splats, structure particles, and phases plays a role in the poor wear resistance of the coatings.

Kaparov, Michaela; Zahlka, Frantiek; Houdkov, rka

2011-03-01

438

High-performance AlGaN/GaN High-electron-mobility transistors employing H2O annealing  

NASA Astrophysics Data System (ADS)

We have proposed and fabricated high performance AlGaN/GaN high-electron-mobility transistors (HEMTs), of which the breakdown voltage is considerably high and the leakage current is efficiently suppressed employing H2O annealing. We also investigated the effects of H2O annealing on the formation of GaOx film on the surface of AlGaN/GaN HEMT as well as reverse blocking characteristics including the breakdown voltage and the leakage current. We compared the reverse blocking characteristics of the AlGaN/GaN HEMTs fabricated by the proposed H2O annealing treatment with those of the HEMT by widely used O2 annealing method. Also, we investigated the reverse blocking characteristics of HEMT fabricated without any annealing treatment. We used the smaller molecular size, higher permeation probability, and the lower activation energy of H2O than O2. The breakdown voltage of AlGaN/GaN HEMT with the LGD of 20?m employing H2O and O2 annealing was 1674 and 1512V, respectively. The drain leakage current of these devices using H2O and O2 annealing was 13.1 and 60.1nA/mm under VDS of 100V and VGS of ?10V, respectively. A conventional device without any annealing process exhibited the breakdown voltage of 598V and the leakage current of 666.0?A/mm. In order to investigate the amounts of deep traps in the interface of AlGaN/GaN HEMT, we measured the pulsed IV. A low drain current of the device under pulsed bias indicated that the GaOx, which was formed by H2O annealing, induced the deeper level and longer emission time of traps compared to the shallow ones. These may be related to the surface leakage current in the AlGaN/GaN HEMTs.

Ahn, Woojin; Seok, Ogyun; Song, Seung Min; Han, Min-Koo; Ha, Min-Woo

2013-09-01

439

FTIR and Raman Studies of the Vibration Modes in High Purity AlN Films Grown on Silicon  

NASA Astrophysics Data System (ADS)

High purity, aluminum nitride films were grown on (111) oriented silicon substrates by gas source MBE methods. Films thicknesses ranged from 0.1 to 1.0 microns. The optical properties in the infrared regime were studied using Fourier-transform infrared (FTIR) spectroscopy. The vibrational spectrum was also studied using Raman scattering. FTIR absorption reveals one feature near 665 cm-1, assigned as the A_1(TO) phonon. FTIR reflectance shows two bands, the 665 cm-1 and the 884 cm-1. The latter is the A_1(LO) phonon. FTIR spectra were modeled using a damped Lorentz oscillator approach. Raman measurement reveal the A_1(LO) phonon and the E2 phonon at 665 cm-1. These measurements confirm that the AlN is oriented along the wurtzite (0001) growth axis. The E2 band is found to shift due to stress on the AlN due to the silicon substrate. Supported by NSF Grant DMR 9705498 and the J. F. Maddox Foundation.

Vanbuskirk, Jonathan W.; Prokofyeva, T.; Seon, M.; Nikishin, S. A.; Temkin, H.; Holtz, M.; Zollner, S.

1999-10-01

440

Functions of two genes in aluminium (Al) stress resistance: repression of oxidative damage by the AtBCB gene and promotion of efflux of Al ions by the NtGDI1gene  

Microsoft Academic Search

The functions of two genes whose expression provides tolerance to aluminium (Al) stress were investigated using plants and Saccharomyces cerevisiae (yeast): the Arabidopsis thaliana blue copper binding gene (AtBCB) and Nicotiana tabacum guanosine diphos- phate (GDP) dissociation inhibitor gene (NtGDI1). To determine the localization of these proteins, each gene was fused to the green fluorescent protein (GFP) gene and introduced

Bunichi Ezaki; Kiyokuni Sasaki; Hideaki Matsumoto; Susumu Nakashima

2005-01-01