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Sample records for high al stress

  1. Creep Strain and Strain Rate Response of 2219 Al Alloy at High Stress Levels

    NASA Technical Reports Server (NTRS)

    Taminger, Karen M. B.; Wagner, John A.; Lisagor, W. Barry

    1998-01-01

    As a result of high localized plastic deformation experienced during proof testing in an International Space Station connecting module, a study was undertaken to determine the deformation response of a 2219-T851 roll forging. After prestraining 2219-T851 Al specimens to simulate strains observed during the proof testing, creep tests were conducted in the temperature range from ambient temperature to 107 C (225 F) at stress levels approaching the ultimate tensile strength of 2219-T851 Al. Strain-time histories and strain rate responses were examined. The strain rate response was extremely high initially, but decayed rapidly, spanning as much as five orders of magnitude during primary creep. Select specimens were subjected to incremental step loading and exhibited initial creep rates of similar magnitude for each load step. Although the creep rates decreased quickly at all loads, the creep rates dropped faster and reached lower strain rate levels for lower applied loads. The initial creep rate and creep rate decay associated with primary creep were similar for specimens with and without prestrain; however, prestraining (strain hardening) the specimens, as in the aforementioned proof test, resulted in significantly longer creep life.

  2. High-Temperature Flow Stress and Recrystallization Characteristics of Al-Bearing Microalloyed TWIP Steels

    NASA Astrophysics Data System (ADS)

    Somani, Mahesh Chandra; Porter, David A.; Hamada, Atef S.; Karjalainen, L. Pentti

    2015-11-01

    In this study, the effects of microalloying (Nb,V) and aluminum on the constitutive flow behavior and static recrystallization (SRX) characteristics of microalloyed TWIP steels (Fe-20Mn-0.6C-Al-(Nb,V)) have been investigated under hot deformation conditions. Compression tests in a Gleeble simulator, including the double-hit technique, enabled the acquisition of flow stress and recrystallization data. These were analyzed to determine the powers of strain and strain rate as well as the activation energies of deformation and recrystallization ( Q def and Q rex). Aluminum increased the flow stress and activation energy of deformation and delayed the onset of dynamic recrystallization of microalloyed TWIP steels. While microalloying with V up to 0.3 pct seems to have little or no effect on the SRX kinetics, microalloying with 0.026 pct Nb significantly slowed down the SRX rate, similarly as in the case of low C-Mn steels. Addition of high aluminum (4.9 pct) marginally retarded the SRX kinetics in comparison with the steels with low aluminum (1.5 pct), with or without microalloying with V.

  3. Orientation dependence of high temperature creep strength and internal stress in Ni{sub 3}Al alloy single crystals

    SciTech Connect

    Miura, Seiji; Peng, Z.L.; Mishima, Yoshinao

    1997-12-31

    High temperature creep behavior of a nickel-rich Ni{sub 3}(Al,Ta) with the L1{sub 2} structure is investigated in order to clarify the influence of crystallographic orientation with respect to the stress axis. The single crystals with four different orientations are deformed in compressive creep at temperatures ranging from 1,123 to 1,273 K under a constant load, initial shear stress being 35 to 120 MPa for (111)[{bar 1}01] slip system. The results show a distinct orientation dependence of creep strength, although shape of creep curves, stress exponent and the activation energy seem to be independent of the orientation. It is shown, however, the internal stress, being measured by strain transient dip tests, is found to be orientation dependent and the creep behavior is independent on orientation if it is interpreted using the effective stress instead of the applied shear stress.

  4. Correlating stress generation and sheet resistance in InAlN/GaN nanoribbon high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Jones, Eric J.; Azize, Mohamed; Smith, Matthew J.; Palacios, Tomás; Gradečak, Silvija

    2012-09-01

    We report the nanoscale characterization of the mechanical stress in InAlN/GaN nanoribbon-structured high electron mobility transistors (HEMTs) through the combined use of convergent beam electron diffraction (CBED) and elastic mechanical modeling. The splitting of higher order Laue zone lines in CBED patterns obtained along the [540] zone axis indicates the existence of a large strain gradient in the c-direction in both the planar and nanoribbon samples. Finite element models were used to confirm these observations and show that a passivating layer of Al2O3 can induce a tensile stress in the active HEMT layer whose magnitude is dependent on the oxide layer thickness, thus, providing important ramifications for device design and fabrication.

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

    SciTech Connect

    Byeon, J; Liu, j; Hopkins, m; Fischer, W; Park, K; Brady, Michael P; Radovic, Miladin; Sohn, Yong Ho

    2007-01-01

    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.

  6. Recovery in dc and rf performance of off-state step-stressed AlGaN/GaN high electron mobility transistors with thermal annealing

    SciTech Connect

    Kim, Byung-Jae; Hwang, Ya-Hsi; Ahn, Shihyun; Zhu, Weidi; Dong, Chen; Lu, Liu; Ren, Fan; Holzworth, M. R.; Jones, Kevin S.; Pearton, Stephen J.; Smith, David J.; Kim, Jihyun; Zhang, Ming-Lan

    2015-04-13

    The recovery effects of thermal annealing on dc and rf performance of off-state step-stressed AlGaN/GaN high electron mobility transistors were investigated. After stress, reverse gate leakage current and sub-threshold swing increased and drain current on-off ratio decreased. However, these degradations were completely recovered after thermal annealing at 450 °C for 10 mins for devices stressed either once or twice. The trap densities, which were estimated by temperature-dependent drain-current sub-threshold swing measurements, increased after off-state step-stress and were reduced after subsequent thermal annealing. In addition, the small signal rf characteristics of stressed devices were completely recovered after thermal annealing.

  7. Protective effects of andrographolide derivative AL-1 on high glucose-induced oxidative stress in RIN-m cells.

    PubMed

    Yan, Hui; Li, Yongmei; Yang, Yali; Zhang, Zaijun; Zhang, Gaoxiao; Sun, Yewei; Yu, Pei; Wang, Yuqiang; Xu, Lipeng

    2016-01-01

    AL-1 is a novel andrographolide derivative synthesized by conjugating andrographolide and alpha lipoic acid. AL-1 has been found to increase insulin secretion, decrease blood glucose level and protect β-cell mass and function in alloxan-induced diabetic mouse model. However, the protective mechanism of AL-1 on high glucose-induced pancreatic β-cell injury is still not clear. In the present study, we found that AL-1 reduced reactive oxygen species (ROS) and nitric oxide (NO) generation induced by high glucose in RIN-m cells, and which elevated the activities of superoxide dismutase (SOD) and catalase (CAT). In addition, AL-1 increased the expression of NF-E2-related factor 2 (Nrf2), thioredoxin-1 (Trx-1) and heme oxygenase-1 (HO- 1) proteins in RIN-m cells. These results suggest that AL-1 prevented RIN-m cells from high glucose-induced oxidative damage via upregulation of Nrf2 signaling pathway. PMID:26391852

  8. Technical note; Stress corrosion cracking behavior of two high-strength Al-xCu-Li-Ag-Mg-Zr alloys

    SciTech Connect

    Moshier, W.C.; Tack, W.T. . Astronautics Group); Shaw, B.A. ); Phull, B. )

    1992-04-01

    Lithium is a potent addition to Al alloys for increasing their specific strength and stiffness, which makes Li-containing Al alloys attractive materials for typical aerospace applications in which reduced weight and increased strength and stiffness can improve system performance. Weldalite 049 (AA X2094) (Al-(4.0-6.3) Cu-1.3 Li-0.4 Ag-0.4 Mg-0.14 Zr) was recently developed as an ultra-high strength, weldable alloy designed for use in launch vehicle structures. Standard SCC testing contains the inherent difficulty of test duration and unclear interpretation of results. Use of slow strain rate tests (SSRTs) on aluminum alloys has met with mixed results, and the purpose of this paper is to evaluate the feasibility of using SSRT to evaluate the SCC susceptibility of two Weldalite 049 variants.

  9. High mobility AlGaN/GaN heterostructures grown on Si substrates using a large lattice-mismatch induced stress control technology

    SciTech Connect

    Cheng, Jianpeng; Yang, Xuelin Sang, Ling; Guo, Lei; Hu, Anqi; Xu, Fujun; Tang, Ning; Wang, Xinqiang; Shen, Bo

    2015-04-06

    A large lattice-mismatch induced stress control technology with a low Al content AlGaN layer has been used to grow high quality GaN layers on 4-in. Si substrates. The use of this technology allows for high mobility AlGaN/GaN heterostructures with electron mobility of 2040 cm{sup 2}/(V·s) at sheet charge density of 8.4 × 10{sup 12 }cm{sup −2}. Strain relaxation and dislocation evolution mechanisms have been investigated. It is demonstrated that the large lattice mismatch between the low Al content AlGaN layer and AlN buffer layer could effectively promote the edge dislocation inclination with relatively large bend angles and therefore significantly reduce the dislocation density in the GaN epilayer. Our results show a great potential for fabrication of low-cost and high performance GaN-on-Si power devices.

  10. Impacts of SiN passivation on the degradation modes of AlGaN/GaN high electron mobility transistors under reverse-bias stress

    SciTech Connect

    Chen, Wei-Wei; Ma, Xiao-Hua E-mail: yhao@xidian.edu.cn; Hou, Bin; Zhu, Jie-Jie; Chen, Yong-He; Zheng, Xue-Feng; Zhang, Jin-Cheng; Hao, Yue E-mail: yhao@xidian.edu.cn

    2014-10-27

    Impacts of SiN passivation on the degradation modes of AlGaN/GaN high electron mobility transistors are investigated. The gate leakage current decreases significantly upon removing the SiN layer and no clear critical voltage for the sudden degradation of the gate leakage current can be observed in the reverse-bias step-stress experiments. Gate-lag measurements reveal the decrease of the fast-state surface traps and the increase of slow-state traps after the passivation layer removal. It is postulated that consistent surface charging relieves the electric field peak on the gate edge, thus the inverse piezoelectric effect is shielded.

  11. Effect of OFF-state stress induced electric field on trapping in AlGaN/GaN high electron mobility transistors on Si (111)

    SciTech Connect

    Anand, M. J. E-mail: eging@ntu.edu.sg; Ng, G. I. E-mail: eging@ntu.edu.sg; Syamal, B.; Zhou, X.; Arulkumaran, S.; Manoj Kumar, C. M.; Ranjan, K.; Vicknesh, S.; Foo, S. C.

    2015-02-23

    The influence of electric field (EF) on the dynamic ON-resistance (dyn-R{sub DS[ON]}) and threshold-voltage shift (ΔV{sub th}) of AlGaN/GaN high electron mobility transistors on Si has been investigated using pulsed current-voltage (I{sub DS}-V{sub DS}) and drain current (I{sub D}) transients. Different EF was realized with devices of different gate-drain spacing (L{sub gd}) under the same OFF-state stress. Under high-EF (L{sub gd} = 2 μm), the devices exhibited higher dyn-R{sub DS[ON]} degradation but a small ΔV{sub th} (∼120 mV). However, at low-EF (L{sub gd} = 5 μm), smaller dyn-R{sub DS[ON]} degradation but a larger ΔV{sub th} (∼380 mV) was observed. Our analysis shows that under OFF-state stress, the gate electrons are injected and trapped in the AlGaN barrier by tunnelling-assisted Poole-Frenkel conduction mechanism. Under high-EF, trapping spreads towards the gate-drain access region of the AlGaN barrier causing dyn-R{sub DS[ON]} degradation, whereas under low-EF, trapping is mostly confined under the gate causing ΔV{sub th}. A trap with activation energy 0.33 eV was identified in the AlGaN barrier by I{sub D}-transient measurements. The influence of EF on trapping was also verified by Silvaco TCAD simulations.

  12. Progressive failure site generation in AlGaN/GaN high electron mobility transistors under OFF-state stress: Weibull statistics and temperature dependence

    SciTech Connect

    Sun, Huarui Bajo, Miguel Montes; Uren, Michael J.; Kuball, Martin

    2015-01-26

    Gate leakage degradation of AlGaN/GaN high electron mobility transistors under OFF-state stress is investigated using a combination of electrical, optical, and surface morphology characterizations. The generation of leakage “hot spots” at the edge of the gate is found to be strongly temperature accelerated. The time for the formation of each failure site follows a Weibull distribution with a shape parameter in the range of 0.7–0.9 from room temperature up to 120 °C. The average leakage per failure site is only weakly temperature dependent. The stress-induced structural degradation at the leakage sites exhibits a temperature dependence in the surface morphology, which is consistent with a surface defect generation process involving temperature-associated changes in the breakdown sites.

  13. Investigation of abrupt degradation of drain current caused by under-gate crack in AlGaN/GaN high electron mobility transistors during high temperature operation stress

    SciTech Connect

    Zeng, Chang; Liao, XueYang; Li, RuGuan; Wang, YuanSheng; Chen, Yiqiang Su, Wei; Liu, Yuan; Wang, Li Wei; Lai, Ping; Huang, Yun; En, YunFei

    2015-09-28

    In this paper, we investigate the degradation mode and mechanism of AlGaN/GaN based high electron mobility transistors (HEMTs) during high temperature operation (HTO) stress. It demonstrates that there was abrupt degradation mode of drain current during HTO stress. The abrupt degradation is ascribed to the formation of crack under the gate which was the result of the brittle fracture of epilayer based on failure analysis. The origin of the mechanical damage under the gate is further investigated and discussed based on top-down scanning electron microscope, cross section transmission electron microscope and energy dispersive x-ray spectroscopy analysis, and stress simulation. Based on the coupled analysis of the failure physical feature and stress simulation considering the coefficient of thermal expansion (CTE) mismatch in different materials in gate metals/semiconductor system, the mechanical damage under the gate is related to mechanical stress induced by CTE mismatch in Au/Ti/Mo/GaN system and stress concentration caused by the localized structural damage at the drain side of the gate edge. These results indicate that mechanical stress induced by CTE mismatch of materials inside the device plays great important role on the reliability of AlGaN/GaN HEMTs during HTO stress.

  14. Investigation of abrupt degradation of drain current caused by under-gate crack in AlGaN/GaN high electron mobility transistors during high temperature operation stress

    NASA Astrophysics Data System (ADS)

    Zeng, Chang; Liao, XueYang; Li, RuGuan; Wang, YuanSheng; Chen, Yiqiang; Su, Wei; Liu, Yuan; Wang, Li Wei; Lai, Ping; Huang, Yun; En, YunFei

    2015-09-01

    In this paper, we investigate the degradation mode and mechanism of AlGaN/GaN based high electron mobility transistors (HEMTs) during high temperature operation (HTO) stress. It demonstrates that there was abrupt degradation mode of drain current during HTO stress. The abrupt degradation is ascribed to the formation of crack under the gate which was the result of the brittle fracture of epilayer based on failure analysis. The origin of the mechanical damage under the gate is further investigated and discussed based on top-down scanning electron microscope, cross section transmission electron microscope and energy dispersive x-ray spectroscopy analysis, and stress simulation. Based on the coupled analysis of the failure physical feature and stress simulation considering the coefficient of thermal expansion (CTE) mismatch in different materials in gate metals/semiconductor system, the mechanical damage under the gate is related to mechanical stress induced by CTE mismatch in Au/Ti/Mo/GaN system and stress concentration caused by the localized structural damage at the drain side of the gate edge. These results indicate that mechanical stress induced by CTE mismatch of materials inside the device plays great important role on the reliability of AlGaN/GaN HEMTs during HTO stress.

  15. Stress evolution during ultrasonic Al ribbon bonding

    NASA Astrophysics Data System (ADS)

    Ando, Masaya; Takashima, Kazumasa; Maeda, Masakatsu; Takahashi, Yasuo

    2014-08-01

    The present study reveals the stress distribution in the substrate during ultrasonic bonding. The deformations of the Si substrate, Al ribbon, and Al pad were numerically analyzed using a finite element method. Experimental observation of the interface using a highspeed video camera was also conducted to determine the actual interfacial slip amplitude. This amplitude becomes smaller than that of tool-tip with bonding time. It was suggested from the numerical simulations that frictional adhesion enhanced the friction force, resulting in an increase in the equivalent stress in the ribbon and pad. As a result, very large stresses occur in the substrate during ultrasonic bonding. These stresses evolve with the progress of ultrasonic bonding, i.e., frictional adhesion.

  16. ALS and Oxidative Stress: The Neurovascular Scenario

    PubMed Central

    Thakur, Keshav; Gupta, Pawan Kumar

    2013-01-01

    Oxidative stress and angiogenic factors have been placed as the prime focus of scientific investigations after an establishment of link between vascular endothelial growth factor promoter (VEGF), hypoxia, and amyotrophic lateral sclerosis (ALS) pathogenesis. Deletion of the hypoxia-response element in the vascular endothelial growth factor promoter and mutant superoxide dismutase 1 (SOD1) which are characterised by atrophy and muscle weakness resulted in phenotype resembling human ALS in mice. This results in lower motor neurodegeneration thus establishing an important link between motor neuron degeneration, vasculature, and angiogenic molecules. In this review, we have presented human, animal, and in vitro studies which suggest that molecules like VEGF have a therapeutic, diagnostic, and prognostic potential in ALS. Involvement of vascular growth factors and hypoxia response elements also highlights the converging role of oxidative stress and neurovascular network for understanding and treatment of various neurodegenerative disorders like ALS. PMID:24367722

  17. Stress-anneal-induced magnetic anisotropy in highly textured Fe-Ga and Fe-Al magnetostrictive strips for bending-mode vibrational energy harvesters

    NASA Astrophysics Data System (ADS)

    Park, Jung Jin; Na, Suok-Min; Raghunath, Ganesh; Flatau, Alison B.

    2016-05-01

    Magnetostrictive Fe-Ga and Fe-Al alloys are promising materials for use in bending-mode vibrational energy harvesters. For this study, 50.8 mm × 5.0 mm × 0.5 mm strips of Fe-Ga and Fe-Al were cut from 0.50-mm thick rolled sheet. An atmospheric anneal was used to develop a Goss texture through an abnormal grain growth process. The anneal lead to large (011) grains that covered over 90% of sample surface area. The resulting highly-textured Fe-Ga and Fe-Al strips exhibited saturation magnetostriction values (λsat = λ∥ - λ⊥) of ˜280 ppm and ˜130 ppm, respectively. To maximize 90° rotation of magnetic moments during bending of the strips, we employed compressive stress annealing (SA). Samples were heated to 500°C, and a 100-150 MPa compressive stress was applied while at 500°C for 30 minutes and while being cooled. The effectiveness of the SA on magnetic moment rotation was inferred by comparing post-SA magnetostriction with the maximum possible yield of rotated magnetic moments, which is achieved when λ∥ = λsat and λ⊥ = 0. The uniformity of the SA along the sample length and the impact of the SA on sensing/energy harvesting performance were then assessed by comparing pre- and post-SA bending-stress-induced changes in magnetization at five different locations along the samples. The SA process with a 150 MPa compressive load improved Fe-Ga actuation along the sample length from 170 to 225 ppm (from ˜60% to within ˜80% of λsat). The corresponding sensing/energy harvesting performance improved by as much as a factor of eight in the best sample, however the improvement was not at all uniform along the sample length. The SA process with a 100 MPa compressive load improved Fe-Al actuation along the sample length from 60 to 73 ppm (from ˜46% to ˜56% of λsat, indicating only a marginally effective SA and suggesting the need for modification of the SA protocol. In spite of this, the SA was effective at improving the sensing/energy harvesting

  18. Tensile and Microindentation Stress-Strain Curves of Al-6061

    DOE Data Explorer

    Weaver, Jordan S [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Center for Integrated Nanotechnologies (CINT); Khosravani, Ali [Georgia Inst. of Technology, Atlanta, GA (United States); Castillo, Andrew [Georgia Inst. of Technology, Atlanta, GA (United States); Kalidind, Surya R [Georgia Inst. of Technology, Atlanta, GA (United States)

    2016-07-13

    Recent spherical microindentation stress-strain protocols were developed and validated on Al-6061 (DOI: 10.1186/s40192-016-0054-3). The scaling factor between the uniaxial yield strength and the indentation yield strength was determined to be about 1.9. The microindentation stress-strain protocols were then applied to a microstructurally graded sample in an effort to extract high throughput process-property relationships. The tensile and microindentation force-displacement and stress-strain data are presented in this data set.

  19. Local stress-induced effects on AlGaAs/AlOx oxidation front shape

    SciTech Connect

    Chouchane, F.; Almuneau, G. Arnoult, A.; Lacoste, G.; Fontaine, C.; Cherkashin, N.

    2014-07-28

    The lateral oxidation of thick AlGaAs layers (>500 nm) is studied. An uncommon shape of the oxide tip is evidenced and attributed to the embedded stress distribution, inherent to the oxidation reaction. Experimental and numerical studies of the internal strain in oxidized Al{sub x}Ga{sub 1−x}As/GaAs structures were carried out by dark-field electron holography and finite element methods. A mapping of the strain distribution around the AlGaAs/oxide interface demonstrates the main role of internal stress on the shaping of the oxide front. These results demonstrate the high relevance of strain in oxide-confined III-V devices, in particular, with over-500-nm thick AlOx confinement layers.

  20. Yield stress anomaly in B2 FeAl

    SciTech Connect

    Yoshimi, K.; Hanada, S.; Yoo, M.H.

    1996-12-31

    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.

  1. Local stress-induced effects on AlGaAs/AlOx oxidation front shape

    NASA Astrophysics Data System (ADS)

    Chouchane, F.; Almuneau, G.; Cherkashin, N.; Arnoult, A.; Lacoste, G.; Fontaine, C.

    2014-07-01

    The lateral oxidation of thick AlGaAs layers (>500 nm) is studied. An uncommon shape of the oxide tip is evidenced and attributed to the embedded stress distribution, inherent to the oxidation reaction. Experimental and numerical studies of the internal strain in oxidized AlxGa1-xAs/GaAs structures were carried out by dark-field electron holography and finite element methods. A mapping of the strain distribution around the AlGaAs/oxide interface demonstrates the main role of internal stress on the shaping of the oxide front. These results demonstrate the high relevance of strain in oxide-confined III-V devices, in particular, with over-500-nm thick AlOx confinement layers.

  2. Surface Residual Stresses in Ti-6Al-4V Friction Stir Welds: Pre- and Post-Thermal Stress Relief

    NASA Astrophysics Data System (ADS)

    Edwards, P.; Ramulu, M.

    2015-09-01

    The purpose of this study was to determine the residual stresses present in titanium friction stir welds and if a post-weld thermal stress relief cycle would be effective in minimizing those weld-induced residual stresses. Surface residual stresses in titanium 6Al-4V alloy friction stir welds were measured in butt joint thicknesses ranging from 3 to 12 mm. The residual stress states were also evaluated after the welds were subjected to a post-weld thermal stress relief cycle of 760 °C for 45 min. High (300-400 MPa) tensile residual stresses were observed in the longitudinal direction prior to stress relief and compressive residual stresses were measured in the transverse direction. After stress relief, the residual stresses were decreased by an order of magnitude to negligible levels.

  3. On the effect of deep-rolling and laser-peening on the stress-controlled low- and high-cycle fatigue behavior of Ti-6Al-4V at elevated temperatures up to 550?C

    SciTech Connect

    Ritchie, IAltenberger, RKNalla, YSano LWagner, RO

    2012-04-01

    The effect of surface treatment on the stress/life fatigue behavior of a titanium Ti-6Al-4V turbine fan blade alloy is investigated in the regime of 102 to 106 cycles to failure under fully reversed stress-controlled isothermal push-pull loading between 25? and 550?C at a frequency of 5 Hz. Specifically, the fatigue behavior was examined in specimens in the deep-rolled and laser-shock peened surface conditions, and compared to results on samples in the untreated (machined and stress annealed) condition. Although the fatigue resistance of the Ti-6Al-4V alloy declined with increasing test temperature regardless of surface condition, deep-rolling and laser-shock peening surface treatments were found to extend the fatigue lives by factors of more than 30 and 5-10, respectively, in the high-cycle and low-cycle fatigue regimes at temperatures as high as 550?C. At these temperatures, compressive residual stresses are essentially relaxed; however, it is the presence of near-surface work hardened layers, with a nanocystalline structure in the case of deep-rolling and dense dislocation tangles in the case of laser-shock peening, which remain fairly stable even after cycling at 450?-550?C, that provide the basis for the beneficial role of mechanical surface treatments on the fatigue strength of Ti-6Al-4V at elevated temperatures.

  4. Residual stress in AlN films grown on sapphire substrates by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Rong, Xin; Wang, Xinqiang; Chen, Guang; Pan, Jianhai; Wang, Ping; Liu, Huapeng; Xu, Fujun; Tan, Pingheng; Shen, Bo

    2016-05-01

    Residual stress in AlN films grown by molecular beam epitaxy (MBE) has been studied by Raman scattering spectroscopy. A strain-free Raman frequency and a biaxial stress coefficient for E2(high) mode are experimentally determined to be 657.8 ± 0.3 cm-1 and 2.4 ± 0.2 cm-1 / GPa, respectively. By using these parameters, the residual stress of a series of AlN layers grown under different buffer layer conditions has been investigated. The residual compressive stress is found to be obviously decreased by increasing the Al/N beam flux ratio of the buffer layer, indicating the generation of tensile stress due to stronger coalescence of AlN grains, as also confirmed by the in-situ reflection high energy electron diffraction (RHEED) monitoring observation. The stronger coalescence does lead to improved quality of AlN films as expected.

  5. Stress corrosion of high strength aluminum alloys.

    NASA Technical Reports Server (NTRS)

    Cocks, F. H.; Brummer, S. B.

    1972-01-01

    An investigation has been carried out to examine the relationship of the observed chemical and mechanical properties of Al-Cu and Al-Zn-Mg alloys to the stress corrosion mechanisms which dominate in each case. Two high purity alloys and analogous commercial alloys were selected. Fundamental differences between the behavior of Al-Cu and of Al-Zn-Mg alloys were observed. These differences in the corrosion behavior of the two types of alloys are augmented by substantial differences in their mechanical behavior. The relative cleavage energy of the grain boundaries is of particular importance.

  6. Residual stresses in continuous graphite fiber Al metal matrix composites

    NASA Technical Reports Server (NTRS)

    Park, Hun Sub; Zong, Gui Sheng; Marcus, Harris L.

    1988-01-01

    The residual stresses in graphite fiber reinforced aluminum (Gr/Al) composites with various thermal histories are measured using X-ray diffraction (XRD) methods. The XRD stress analysis is based on the determination of lattice strains by precise measurements of the interplanar spacings in different directions of the sample. The sample is a plate consisting of two-ply P 100 Gr/Al 6061 precursor wires and Al 6061 overlayers. Prior to XRD measurement, the 6061 overlayers are electrochemically removed. In order to calibrate the relationship between stress magnitude and lattice spacing shift, samples of Al 6061 are loaded at varying stress levels in a three-point bend fixture, while the stresses are simultaneously determined by XRD and surface-attached strain gages. The stresses determined by XRD closely match those determined by the strain gages. Using these calibrations, the longitudinal residual stresses of P 100 Gr/Al 6061 composites are measured for various heat treatments, and the results are presented.

  7. Effect of stress on the Al composition evolution in AlGaN grown using metal organic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    He, Chenguang; Qin, Zhixin; Xu, Fujun; Zhang, Lisheng; Wang, Jiaming; Hou, Mengjun; Zhang, Shan; Wang, Xinqiang; Ge, Weikun; Shen, Bo

    2016-05-01

    Two series of AlGaN samples with different stresses were designed to investigate the effect of stress on the Al composition. X-ray diffraction reciprocal space mapping (XRD RSM) demonstrated that the AlGaN epilayers with different stresses have large Al composition differences despite the same growth conditions. The largest Al composition difference reached up to 21.3%, which was also confirmed using secondary ion mass spectroscopy (SIMS). This result is attributed to a large stress discrepancy in the AlGaN epilayers. Finally, the dependences of the solid-phase Al composition on the gas-phase Al composition under different stresses were systematically analyzed.

  8. Clinical Perspective of Oxidative Stress in Sporadic ALS

    PubMed Central

    D’Amico, Emanuele; Factor-Litvak, Pam; Santella, Regina M.; Mitsumoto, Hiroshi

    2013-01-01

    Sporadic amyotrophic lateral sclerosis (sALS) is one of the most devastating neurological diseases; most patients die within 3 to 4 years after symptom onset. Oxidative stress is a disturbance in the pro-oxidative/anti-oxidative balance favoring the pro-oxidative state. Autopsy and laboratory studies in ALS indicate that oxidative stress plays a major role in motor neuron degeneration and astrocyte dysfunction. Oxidative stress biomarkers in cerebrospinal fluid, plasma, and urine, are elevated, suggesting that abnormal oxidative stress is generated outside of the central nervous system. Our review indicates that agricultural chemicals, heavy metals, military service, professional sports, excessive physical exertion, chronic head trauma, and certain foods might be modestly associated with ALS risk, with a stronger association between risk and smoking. At the cellular level, these factors are all involved in generating oxidative stress. Experimental studies indicate that a combination of insults that induce modest oxidative stress can exert additive deleterious effects on motor neurons, suggesting multiple exposures in real-world environments are important. As the disease progresses, nutritional deficiency, cachexia, psychological stress, and impending respiratory failure may further increase oxidative stress. Moreover, accumulating evidence suggests that ALS is possibly a systemic disease. Laboratory, pathologic, and epidemiologic evidence clearly support the hypothesis that oxidative stress is central in the pathogenic process, particularly in genetically susceptive individuals. If we are to improve ALS treatment, well-designed biochemical and genetic epidemiological studies, combined with a multidisciplinary research approach, are needed and will provide knowledge crucial to our understanding of ALS etiology, pathophysiology, and prognosis. PMID:23797033

  9. Electron velocity of 6 × 10{sup 7 }cm/s at 300 K in stress engineered InAlN/GaN nano-channel high-electron-mobility transistors

    SciTech Connect

    Arulkumaran, S. Manoj Kumar, C. M.; Ranjan, K.; Teo, K. L.; Ng, G. I.; Shoron, O. F.; Rajan, S.; Bin Dolmanan, S.; Tripathy, S.

    2015-02-02

    A stress engineered three dimensional (3D) Triple T-gate (TT-gate) on lattice matched In{sub 0.17}Al{sub 0.83}N/GaN nano-channel (NC) Fin-High-Electron-Mobility Transistor (Fin-HEMT) with significantly enhanced device performance was achieved that is promising for high-speed device applications. The Fin-HEMT with 200-nm effective fin-width (W{sub eff}) exhibited a very high I{sub Dmax} of 3940 mA/mm and a highest g{sub m} of 1417 mS/mm. This dramatic increase of I{sub D} and g{sub m} in the 3D TT-gate In{sub 0.17}Al{sub 0.83}N/GaN NC Fin-HEMT translated to an extracted highest electron velocity (v{sub e}) of 6.0 × 10{sup 7 }cm/s, which is ∼1.89× higher than that of the conventional In{sub 0.17}Al{sub 0.83}N/GaN HEMT (3.17 × 10{sup 7 }cm/s). The v{sub e} in the conventional III-nitride transistors are typically limited by highly efficient optical-phonon emission. However, the unusually high v{sub e} at 300 K in the 3D TT-gate In{sub 0.17}Al{sub 0.83}N/GaN NC Fin-HEMT is attributed to the increase of in-plane tensile stress component by SiN passivation in the formed NC which is also verified by micro-photoluminescence (0.47 ± 0.02 GPa) and micro-Raman spectroscopy (0.39 ± 0.12 GPa) measurements. The ability to reach the v{sub e} = 6 × 10{sup 7 }cm/s at 300 K by a stress engineered 3D TT-gate lattice-matched In{sub 0.17}Al{sub 0.83}N/GaN NC Fin-HEMTs shows they are promising for next-generation ultra-scaled high-speed device applications.

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

    SciTech Connect

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

    2005-04-20

    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.

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

    NASA Astrophysics Data System (ADS)

    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

    Compared to Ti-rich γ-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 γ-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 γ-TiAl, whereas the former can be rationalized by the instability of the microstructure containing metastable phases.

  12. Sleep in High Stress Occupations

    NASA Technical Reports Server (NTRS)

    Flynn-Evans, Erin

    2014-01-01

    High stress occupations are associated with sleep restriction, circadian misalignment and demanding workload. This presentation will provide an overview of sleep duration, circadian misalignment and fatigue countermeasures and performance outcomes during spaceflight and commercial aviation.

  13. High Temperature Mechanical Characterization and Analysis of Al2O3 /Al2O3 Composition

    NASA Technical Reports Server (NTRS)

    Gyekenyesi, John Z.; Jaskowiak, Martha H.

    1999-01-01

    Sixteen ply unidirectional zirconia coated single crystal Al2O3 fiber reinforced polycrystalline Al2O3 was tested in uniaxial tension at temperatures to 1400 C in air. Fiber volume fractions ranged from 26 to 31%. The matrix has primarily open porosity of approximately 40%. Theories for predicting the Young's modulus, first matrix cracking stress, and ultimate strength were applied and evaluated for suitability in predicting the mechanical behavior of Al2O3/Al2O3 composites. The composite exhibited pseudo tough behavior (increased area under the stress/strain curve relative to monolithic alumina) from 22 to 1400 C. The rule-of-mixtures provides a good estimate of the Young's modulus of the composite using the constituent properties from room temperature to approximately 1200 C for short term static tensile tests in air. The ACK theory provides the best approximation of the first matrix cracking stress while accounting for residual stresses at room temperature. Difficulties in determining the fiber/matrix interfacial shear stress at high temperatures prevented the accurate prediction of the first matrix cracking stress above room temperature. The theory of Cao and Thouless, based on Weibull statistics, gave the best prediction for the composite ultimate tensile strength.

  14. Thermal- and electromigration-induced stresses in passivated Al- and AlSiCu-interconnects

    SciTech Connect

    Beckers, D.; Schroeder, H.; Schilling, W.; Eppler, I.

    1997-05-01

    Mechanical stresses in microelectronic devices are of special interest because of degradation effects in microelectronic circuits such as stress induced voiding or electromigration. Al and al-alloys are commonly used as interconnect materials in integrated electronic devices. Stress induced voiding and degradation of metal lines by electromigration are closely related to the stresses in the lines. The authors have studied the strain and stress evolution during thermal cycling, isothermal relaxation and due to electromigration in passivated Al and AlSi(1%)Cu(0.5%) lines by X-Ray diffraction with variation of experimental parameters such as the aspect ratio and the electrical current density. Furthermore the extent of voiding and plastic shear deformation has been determined from the experimental metal strains with the help of finite element calculations. Main results are: (1) During thermal cycling the voiding is less than 2 {center_dot} 10{sup {minus}3}. The extent of plastic shear deformation increases with increasing line width and with decreasing flowstress. (2) During isothermal relaxation void growth occurs but no significant change in the plastic shear deformation. (3) An electric current in the lines causes no measurable additional change of the volume averaged stresses up to line failure.

  15. Effect of stress on creep of lamellar near {gamma}-TiAl

    SciTech Connect

    Beddoes, J.; Triantafillou, J.; Zhao, L.

    1997-12-31

    The creep behavior of a binary Ti-48%Al intermetallic is presented as a function of stress for two fully lamellar microstructures. The two lamellar conditions differ in terms of the lamellar interface spacing and grain boundary morphology. Air cooling (AC) from the single phase {alpha} region causes planar grain boundaries and lamellar spacing of 90 to 130 nm, while furnace cooling (FC) causes interlocked lamellae along grain boundaries and 350 to 550 nm lamellar spacing. Monotonic and stress increment creep tests at 760 C indicate that the AC condition exhibits a lower minimum creep strain rate at stresses between 105 MPa and 290 MPa. The stress exponent increases from {approx}1 at low stress to {approx}10 at high stress. Consecutive stress reduction creep tests indicate that the internal stress required for dislocation glide is higher for the AC condition. The results suggest that at low stress the creep rate is controlled by recovery mechanisms, while at high stress the creep rate is predominantly controlled by dislocation glide. It is postulated that at high stresses the lower creep rate of the AC condition, compared to the FC condition, results from the reduced lamellar interface spacing, which increases the internal stress required for dislocation glide.

  16. Profilin 1 Associates with Stress Granules and ALS-Linked Mutations Alter Stress Granule Dynamics

    PubMed Central

    Figley, Matthew D.; Bieri, Gregor; Kolaitis, Regina-Maria; Taylor, J. Paul

    2014-01-01

    Mutations in the PFN1 gene encoding profilin 1 are a rare cause of familial amyotrophic lateral sclerosis (ALS). Profilin 1 is a well studied actin-binding protein but how PFN1 mutations cause ALS is unknown. The budding yeast, Saccharomyces cerevisiae, has one PFN1 ortholog. We expressed the ALS-linked profilin 1 mutant proteins in yeast, demonstrating a loss of protein stability and failure to restore growth to profilin mutant cells, without exhibiting gain-of-function toxicity. This model provides for simple and rapid screening of novel ALS-linked PFN1 variants. To gain insight into potential novel roles for profilin 1, we performed an unbiased, genome-wide synthetic lethal screen with yeast cells lacking profilin (pfy1Δ). Unexpectedly, deletion of several stress granule and processing body genes, including pbp1Δ, were found to be synthetic lethal with pfy1Δ. Mutations in ATXN2, the human ortholog of PBP1, are a known ALS genetic risk factor and ataxin 2 is a stress granule component in mammalian cells. Given this genetic interaction and recent evidence linking stress granule dynamics to ALS pathogenesis, we hypothesized that profilin 1 might also associate with stress granules. Here we report that profilin 1 and related protein profilin 2 are novel stress granule-associated proteins in mouse primary cortical neurons and in human cell lines and that ALS-linked mutations in profilin 1 alter stress granule dynamics, providing further evidence for the potential role of stress granules in ALS pathogenesis. PMID:24920614

  17. Commentary: Beyond Stressful Life Events and Depression?--Reflections on Bogdan et al. (2014)

    ERIC Educational Resources Information Center

    Belsky, Jay

    2014-01-01

    In light of continuing disagreement, even at the meta-analytic level, as to whether the gene- × -environment (G×E) interaction involving 5-HTTLPR and stressful life events (SLEs) predicts depression, Bogdan and associates (this issue, Bogdan et al., 2014) sought to extend research on what has become a highly controversial general (GxE) and…

  18. Alloys based on NiAl for high temperature applications

    NASA Technical Reports Server (NTRS)

    Vedula, K. M.; Pathare, V.; Aslanidis, I.; Titran, R. H.

    1984-01-01

    The NiAl alloys for potential high temperature applications were studied. Alloys were prepared by powder metallurgy techniques. Flow stress values at slow strain rates and high temperatures were measured. Some ternary alloying additions (Hf, Ta and Nb) were identified. The mechanism of strengthening in alloys containing these additions appears to be a form of particle dislocation interaction. The effects of grain size and stoichiometry in binary alloys are also presented.

  19. Grain Flow at High Stresses

    NASA Astrophysics Data System (ADS)

    McSaveney, M. J.

    2015-12-01

    The transport mechanism of rapid long-runout rock avalanches was a hotly debated topic when I came on the scene in 1967. So how come it is still debated today? My explanation is that it is the expected outcome of peer review, poor comprehension, and technological advances outpacing intellectual advances. Why think about the problem when we can model it! So let us think about the problem. Shreve thought that rock avalanches fell upon and trapped a layer of air. What physics was he thinking about? It is how feathers and tissue papers fall. When my rock avalanches fly, they fly like unlubricated bricks using the physics of projectiles and ballistics. But the main transport mechanism is not flight. The dominant impression from watching a rock avalanche in motion is of fluid flow, as Heim described it in 1882. A rock avalanche is a very large grain flow. Bagnold studied dispersive grain flows, but why should one assume that rock avalanches are dispersive grain flows as many do. The more common grain flow type is a dense grain flow and rock avalanches are dense grain flows in which the weight can and does generate very high stresses at grain contacts. Brittle rock deforms elastically up to its compressive strength, whereupon it breaks, releasing elastic strain as transient elastic strain (seismic energy to a seismologist, acoustic energy to a physicist). Melosh and others have shown that acoustic energy can fluidize a grain mass. There is no exotic physics behind grain flow at high stress. When grains break, the released elastic strain has to go somewhere, and it goes somewhere principally by transmission though grain contacts. Depending on the state of stress at the grain contact, the contact will pass the stress or will slip at conventional values of Coulomb friction. Enough thinking! A physical model of the entire process is too big for any laboratory. So whose numerical model will do it?

  20. RBM45 homo-oligomerization mediates association with ALS-linked proteins and stress granules

    PubMed Central

    Li, Yang; Collins, Mahlon; Geiser, Rachel; Bakkar, Nadine; Riascos, David; Bowser, Robert

    2015-01-01

    The aggregation of RNA-binding proteins is a pathological hallmark of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). RBM45 is an RNA-binding protein that forms cytoplasmic inclusions in neurons and glia in ALS and FTLD. To explore the role of RBM45 in ALS and FTLD, we examined the contribution of the protein’s domains to its function, subcellular localization, and interaction with itself and ALS-linked proteins. We find that RBM45 forms homo-oligomers and physically associates with the ALS-linked proteins TDP-43 and FUS in the nucleus. Nuclear localization of RBM45 is mediated by a bipartite nuclear-localization sequence (NLS) located at the C-terminus. RBM45 mutants that lack a functional NLS accumulate in the cytoplasm and form TDP-43 positive stress granules. Moreover, we identify a novel structural element, termed the homo-oligomer assembly (HOA) domain, that is highly conserved across species and promote homo-oligomerization of RBM45. RBM45 mutants that fail to form homo-oligomers exhibit significantly reduced association with ALS-linked proteins and inclusion into stress granules. These results show that RMB45 may function as a homo-oligomer and that its oligomerization contributes to ALS/FTLD RNA-binding protein aggregation. PMID:26391765

  1. High strain-rate plastic flow in Fe and Al

    NASA Astrophysics Data System (ADS)

    Smith, Raymond; Eggert, Jon; Rudd, Robert; Bolme, Cynthia; Collins, Gilbert

    2011-06-01

    Understanding the nature and time-dependence of material deformation at high strain rates is an important goal in condensed matter physics. Under dynamic loading, the rate of plastic strain is determined by the flow of dislocations through the crystal lattice and is a complex function of time, distance, sample purity, temperature, internal stresses, microstructure and strain rate. Under shock compression time-dependent plasticity is typically inferred by fitting elastic precursor stresses as a function of propagation distance with a phenomenologically based dislocation kinetics model. We employ a laser-driven ramp wave loading technique to compress 6-70 micron thick samples of bcc-Fe and fcc-Al over a strain rate range of 1e6-1e8 1/s. Our data show that for fixed sample thickness, stresses associated the onset of plasticity are highly dependent on the strain rate of compression and do not readily fit into the elastic stress - distance evolution descriptive of instantaneous shock loading. We find that the elastic stress at the onset of plasticity is well correlated with the strain rate at the onset of plastic flow for both shock- and ramp-wave experiments. Our data, combined with data from other dynamic compression platforms, reveal a sharp increase in the peak elastic stress at high strain rates, consistent with a transition in dislocation flow dominated by phonon drag. smith248@llnl.gov

  2. Thermal Stability of Residual Stresses in Ti-6Al-4V components

    NASA Astrophysics Data System (ADS)

    Stanojevic, A.; Angerer, P.; Oberwinkler, B.

    2016-03-01

    The need for light weight design while maintaining a high safety is essential for many components, especially in the aircraft industry. Therefore, it's important to consider every aspect to reduce weight, improve fatigue life and maintain safety of crucial components. Residual stresses are a major factor which can positively influence components and fulfil all three requirements. However, due to the inconstancy of the behaviour of residual stresses during the life time of a component, residual stresses are often neglected. If the behaviour of residual stresses could be described reliably over the entire life time of a component, residual stresses could be taken into account and components could be optimized even further. Mechanical and thermal loads are the main reason for relaxation of residual stresses. This work covers the thermal stability of residual stresses in Ti-6Al-4V components. Therefore, exposure tests at raised temperatures were performed on specimens with different surface conditions. Residual stresses were measured by x-ray diffraction before and after testing. Creep tests were also carried out to describe the creep behaviour and thereby the ability for residual stress relaxation. A correlation between the creep rate and amount of relaxed stress was found. The creep behaviour of the material was described by using a combination of the Norton Power law and the Arrhenius equation. The Zener-Wert-Avrami model was used to describe the residual stress relaxation. With these models a satisfying correlation between measured and calculated data was found. Hence, the relaxation of residual stresses due to thermal load was described reliably.

  3. Joule-Heating-Induced Damage in Cu-Al Wedge Bonds Under Current Stressing

    NASA Astrophysics Data System (ADS)

    Yang, Tsung-Han; Lin, Yu-Min; Ouyang, Fan-Yi

    2014-01-01

    Copper wires are increasingly used to replace gold wires in wire-bonding technology owing to their better electrical properties and lower cost. However, not many studies have been conducted on electromigration-induced failure of Cu wedge bonds on Al metallization. In this study, we investigated the failure mechanism of Cu-Al wedge bonds under high current stressing from 4 × 104 A/cm2 to 1 × 105 A/cm2 at ambient temperature of 175°C. The resistance evolution of samples during current stressing and the microstructure of the joint interface between the Cu wire and Al-Si bond pad were examined. The results showed that abnormal crack formation accompanying significant intermetallic compound growth was observed at the second joint of the samples, regardless of the direction of electric current for both current densities of 4 × 104 A/cm2 and 8 × 104 A/cm2. We propose that this abnormal crack formation at the second joint is mainly due to the higher temperature induced by the greater Joule heating at the second joint for the same current stressing, because of its smaller bonded area compared with the first joint. The corresponding fluxes induced by the electric current and chemical potential difference between Cu and Al were calculated and compared to explain the failure mechanism. For current density of 1 × 105 A/cm2, the Cu wire melted within 0.5 h owing to serious Joule heating.

  4. High Density Sliding at Ta/Al and Al/Al Interfaces

    SciTech Connect

    Hammerberg, J. E.; Germann, T. C.; Ravelo, R.

    2006-07-28

    We present 3D-nonequilibrium molecular dynamics results for the velocity dependence of the frictional force at smooth sliding interfaces for Ta and Al single crystals. For Ta/Al we consider Al(100)/Ta(100) and Al(111)/Ta(110) interfaces sliding along [001] and [11(bar sign)0]fcc /[001]bcc respectively. These are compared with Al(111)/Al(100) interfaces at the same loads, corresponding to a pressure of 15 GPa. Both interfacial pairs show similar behavior in the velocity dependence of the frictional force: a low velocity regime with an increasing frictional force followed by a strain induced transformation regime at velocities above approximately 1/10 the transverse sound speed, followed by a fluidized interface at high velocities. For both interfacial pairs, the high velocity dependence of the frictional force exhibits power law behavior, Ft {proportional_to} v-{beta} with {beta}=3/4. We discuss the structural changes that influence dissipation in each of these regimes.

  5. Ratcheting fatigue behaviour of Al-7075 T6 alloy: Influence of stress parameters

    NASA Astrophysics Data System (ADS)

    Amarnath, Lala; Bhattacharjee, Antara; Dutta, K.

    2016-02-01

    The use of aluminium and aluminium based alloys are increasing rapidly on account of its high formability, good thermal and electrical conductivity, high strength and lightness. Aluminium alloys are extensively used in aerospace, automobile, marine and space research industries and are also put into structural applications where chances of fatigue damage cannot be ruled out. In the current work, it is intended to study the ratcheting fatigue behavior of 7075-T6 aluminium alloy at room temperature. This Al alloy is potentially used in aviation, marine and automotive components as well as in bicycle parts, rock mounting equipment and parts of ammunition where there is every chance of failure of the parts due to deformation caused by ratcheting. Ratcheting is the process of accruement of plastic stain produced when a component is subjected to asymmetric cyclic loading under the influence of low cycle fatigue. To accomplish the requirements of the projected research, stress-controlled cyclic loading experiments were done using a ±250 kN servo-hydraulic universal testing machine (Instron: 8800R). The effect of stress parameters such as mean stress and stress amplitude were investigated on the ratcheting behavior of the selected aluminium alloy. It was observed that, ratcheting strain increased with increase in the value of stress amplitude at any constant mean stress while a saturation in strain accumulation attained in the investigated material after around 10-20 cycles, under all test conditions. The analyses of hysteresis loop generated during cyclic loading indicate that the material exhibits cyclic hardening in the initial fifty cycles which gets softened in further loading up to about 70-80 cycles and finally attains a steady state. The increase in the ratcheting strain value with stress parameters happens owing to increased deformation domain during cycling. The cyclic hardening accompanied by softening is correlated with characteristic precipitation features of

  6. Growth and stress-induced transformation of zinc blende AlN layers in Al-AlN-TiN multilayers

    SciTech Connect

    Li, Nan; Yadav, Satyesh K.; Wang, Jian; Liu, Xiang -Yang; Misra, Amit

    2015-12-18

    We report that AlN nanolayers in sputter deposited {111}Al/AlN/TiN multilayers exhibit the metastable zinc-blende-structure (z-AlN). Based on density function theory calculations, the growth of the z-AlN is ascribed to the kinetically and energetically favored nitridation of the deposited aluminium layer. In situ nanoindentation of the as-deposited {111}Al/AlN/TiN multilayers in a high-resolution transmission electron microscope revealed the z-AlN to wurzite AlN phase transformation through collective glide of Shockley partial dislocations on every two {111} planes of the z-AlN.

  7. Growth and Stress-induced Transformation of Zinc blende AlN Layers in Al-AlN-TiN Multilayers

    PubMed Central

    Li, Nan; Yadav, Satyesh K.; Wang, Jian; Liu, Xiang-Yang; Misra, Amit

    2015-01-01

    AlN nanolayers in sputter deposited {111}Al/AlN/TiN multilayers exhibit the metastable zinc-blende-structure (z-AlN). Based on density function theory calculations, the growth of the z-AlN is ascribed to the kinetically and energetically favored nitridation of the deposited aluminium layer. In situ nanoindentation of the as-deposited {111}Al/AlN/TiN multilayers in a high-resolution transmission electron microscope revealed the z-AlN to wurzite AlN phase transformation through collective glide of Shockley partial dislocations on every two {111} planes of the z-AlN. PMID:26681109

  8. Growth and Stress-induced Transformation of Zinc blende AlN Layers in Al-AlN-TiN Multilayers.

    PubMed

    Li, Nan; Yadav, Satyesh K; Wang, Jian; Liu, Xiang-Yang; Misra, Amit

    2015-01-01

    AlN nanolayers in sputter deposited {111}Al/AlN/TiN multilayers exhibit the metastable zinc-blende-structure (z-AlN). Based on density function theory calculations, the growth of the z-AlN is ascribed to the kinetically and energetically favored nitridation of the deposited aluminium layer. In situ nanoindentation of the as-deposited {111}Al/AlN/TiN multilayers in a high-resolution transmission electron microscope revealed the z-AlN to wurzite AlN phase transformation through collective glide of Shockley partial dislocations on every two {111} planes of the z-AlN. PMID:26681109

  9. High temperature aqueous stress corrosion testing device

    DOEpatents

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

    1975-12-01

    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.

  10. STRESS ANNEALING INDUCED DIFFUSE SCATTERING FROM Ni3(Al,Si) PRECIPITATES

    SciTech Connect

    Barabash, Rozaliya; Ice, Gene E; Karapetrova, Evgenia; Zschack, P.

    2012-01-01

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

  11. Cu-Al-Ni-SMA-Based High-Damping Composites

    NASA Astrophysics Data System (ADS)

    López, Gabriel A.; Barrado, Mariano; San Juan, Jose; Nó, María Luisa

    2009-08-01

    Recently, absorption of vibration energy by mechanical damping has attracted much attention in several fields such as vibration reduction in aircraft and automotive industries, nanoscale vibration isolations in high-precision electronics, building protection in civil engineering, etc. Typically, the most used high-damping materials are based on polymers due to their viscoelastic behavior. However, polymeric materials usually show a low elastic modulus and are not stable at relatively low temperatures (≈323 K). Therefore, alternative materials for damping applications are needed. In particular, shape memory alloys (SMAs), which intrinsically present high-damping capacity thanks to the dissipative hysteretic movement of interfaces under external stresses, are very good candidates for high-damping applications. A completely new approach was applied to produce high-damping composites with relatively high stiffness. Cu-Al-Ni shape memory alloy powders were embedded with metallic matrices of pure In, a In-10wt.%Sn alloy and In-Sn eutectic alloy. The production methodology is described. The composite microstructures and damping properties were characterized. A good particle distribution of the Cu-Al-Ni particles in the matrices was observed. The composites exhibit very high damping capacities in relatively wide temperature ranges. The methodology introduced provides versatility to control the temperature of maximum damping by adjusting the shape memory alloy composition.

  12. Growth of high quality and uniformity AlGaN/GaN heterostructures on Si substrates using a single AlGaN layer with low Al composition.

    PubMed

    Cheng, Jianpeng; Yang, Xuelin; Sang, Ling; Guo, Lei; Zhang, Jie; Wang, Jiaming; He, Chenguang; Zhang, Lisheng; Wang, Maojun; Xu, Fujun; Tang, Ning; Qin, Zhixin; Wang, Xinqiang; Shen, Bo

    2016-01-01

    By employing a single AlGaN layer with low Al composition, high quality and uniformity AlGaN/GaN heterostructures have been successfully grown on Si substrates by metal-organic chemical vapor deposition (MOCVD). The heterostructures exhibit a high electron mobility of 2150 cm(2)/Vs with an electron density of 9.3 × 10(12) cm(-2). The sheet resistance is 313 ± 4 Ω/◻ with ±1.3% variation. The high uniformity is attributed to the reduced wafer bow resulting from the balance of the compressive stress induced and consumed during the growth, and the thermal tensile stress induced during the cooling down process. By a combination of theoretical calculations and in situ wafer curvature measurements, we find that the compressive stress consumed by the dislocation relaxation (~1.2 GPa) is comparable to the value of the thermal tensile stress (~1.4 GPa) and we should pay more attention to it during growth of GaN on Si substrates. Our results demonstrate a promising approach to simplifying the growth processes of GaN-on-Si to reduce the wafer bow and lower the cost while maintaining high material quality. PMID:26960730

  13. Growth of high quality and uniformity AlGaN/GaN heterostructures on Si substrates using a single AlGaN layer with low Al composition

    NASA Astrophysics Data System (ADS)

    Cheng, Jianpeng; Yang, Xuelin; Sang, Ling; Guo, Lei; Zhang, Jie; Wang, Jiaming; He, Chenguang; Zhang, Lisheng; Wang, Maojun; Xu, Fujun; Tang, Ning; Qin, Zhixin; Wang, Xinqiang; Shen, Bo

    2016-03-01

    By employing a single AlGaN layer with low Al composition, high quality and uniformity AlGaN/GaN heterostructures have been successfully grown on Si substrates by metal-organic chemical vapor deposition (MOCVD). The heterostructures exhibit a high electron mobility of 2150 cm2/Vs with an electron density of 9.3 × 1012 cm‑2. The sheet resistance is 313 ± 4 Ω/◻ with ±1.3% variation. The high uniformity is attributed to the reduced wafer bow resulting from the balance of the compressive stress induced and consumed during the growth, and the thermal tensile stress induced during the cooling down process. By a combination of theoretical calculations and in situ wafer curvature measurements, we find that the compressive stress consumed by the dislocation relaxation (~1.2 GPa) is comparable to the value of the thermal tensile stress (~1.4 GPa) and we should pay more attention to it during growth of GaN on Si substrates. Our results demonstrate a promising approach to simplifying the growth processes of GaN-on-Si to reduce the wafer bow and lower the cost while maintaining high material quality.

  14. Growth of high quality and uniformity AlGaN/GaN heterostructures on Si substrates using a single AlGaN layer with low Al composition

    PubMed Central

    Cheng, Jianpeng; Yang, Xuelin; Sang, Ling; Guo, Lei; Zhang, Jie; Wang, Jiaming; He, Chenguang; Zhang, Lisheng; Wang, Maojun; Xu, Fujun; Tang, Ning; Qin, Zhixin; Wang, Xinqiang; Shen, Bo

    2016-01-01

    By employing a single AlGaN layer with low Al composition, high quality and uniformity AlGaN/GaN heterostructures have been successfully grown on Si substrates by metal-organic chemical vapor deposition (MOCVD). The heterostructures exhibit a high electron mobility of 2150 cm2/Vs with an electron density of 9.3 × 1012 cm−2. The sheet resistance is 313 ± 4 Ω/◻ with ±1.3% variation. The high uniformity is attributed to the reduced wafer bow resulting from the balance of the compressive stress induced and consumed during the growth, and the thermal tensile stress induced during the cooling down process. By a combination of theoretical calculations and in situ wafer curvature measurements, we find that the compressive stress consumed by the dislocation relaxation (~1.2 GPa) is comparable to the value of the thermal tensile stress (~1.4 GPa) and we should pay more attention to it during growth of GaN on Si substrates. Our results demonstrate a promising approach to simplifying the growth processes of GaN-on-Si to reduce the wafer bow and lower the cost while maintaining high material quality. PMID:26960730

  15. Stress corrosion cracking of Ti-8Al-1 Mo-1V in molten salts

    NASA Technical Reports Server (NTRS)

    Smyrl, W. H.; Blackburn, M. J.

    1975-01-01

    The stress corrosion cracking (SCC) behavior of Ti-8Al-1 Mo-1V has been studied in several molten salt environments. Extensive data are reported for the alloy in highly pure LiCl-KCl. The influence of the metallurgical heat treatment and texture, and the mechanical microstructure show similarities with aqueous solutions at lower temperature. The fracture path and cracking modes are also similar to that found in other environments. The influence of H2O and H(-) in molten LiCl-KCl lead to the conclusion that hydrogen does not play a major role in crack extension in this environment.

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

    SciTech Connect

    Singh, DRP; Deng, X.; Chawla, N.; Bai, J.; Hubbard, Camden R; Tang, G; Shen, Y-L

    2010-01-01

    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.

  17. Residual Stress Characterization of Al/SiC Nanoscale Multilayers using X-ray

    SciTech Connect

    D Singh X Deng; N Chawla; J Bai; C Hubbard; G Tang; Y Shen

    2011-12-31

    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.

  18. Does a threshold stress for creep exist in HfC-dispersed NiAl?

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.; Ray, Ranjan; Jha, Sunil C.

    1991-01-01

    Recently it was proposed (Jha et al., 1989; Whittenberger et al., 1990) on the basis of constant velocity testing at 1300 K that dispersion strengthened NiAl composites containing about 4 wt pct HfC possess threshold stresses for creep. Further, 1300 K compression testing has been conducted on NiAl+4HfC, and diametrically opposite behavior has been found: for constant load creep tests a normal power law behavior was observed. However, additional constant velocity testing still indicates that the flow stress is essentially independent of strain rate below 10 exp -6/s. Examination of NiAl+4.3HfC specimens deformed under constant velocity conditions revealed that the original hot extruded small grain structure could be converted to large, elongated grains during testing. Such a transformation appears to be responsible for the apparent threshold stress behavior in HfC dispersed NiAl.

  19. Oxidative stress and mitochondrial damage: importance in non-SOD1 ALS

    PubMed Central

    Carrì, Maria Teresa; Valle, Cristiana; Bozzo, Francesca; Cozzolino, Mauro

    2015-01-01

    It is well known that mitochondrial damage (MD) is both the major contributor to oxidative stress (OS) (the condition arising from unbalance between production and removal of reactive oxygen species) and one of the major consequences of OS, because of the high dependance of mitochondrial function on redox-sensitive targets such as intact membranes. Conditions in which neuronal cells are not able to cope with MD and OS seem to lead or contribute to several neurodegenerative diseases including Amyotrophic Lateral Sclerosis (ALS), at least in the most studied superoxide dismutase 1 (SOD1)-linked genetic variant. As summarized in this review, new evidence indicates that MD and OS play a role also in non-SOD1 ALS and thus they may represent a target for therapy despite previous failures in clinical trials. PMID:25741238

  20. Softening Kinetics in High Al and High Al-Nb-Microalloyed Steels

    NASA Astrophysics Data System (ADS)

    Pereda, B.; Aretxabaleta, Z.; López, B.

    2015-03-01

    Double-hit torsion tests were performed in order to study the effect of high Al levels (up to 2 wt.%) and Nb microalloying (up to 0.07 wt.%) on the static softening kinetics of 0.2%C-2%Mn steels. The addition of 1%Al leads to a delay in the softening kinetics due to solute-drag effect, equivalent to that exerted by 0.027%Nb. For the 2%Al steels, at temperatures below 1000 °C, γ → α phase transformation occurs after deformation, resulting in a larger retardation of the softening kinetics. At temperatures higher than 1000 °C, Nb in solid solution also contributes to the retardation of the static softening kinetics, and at lower temperatures NbC strain-induced precipitation leads to incomplete softening for the 1%Al steel, and to a complex interaction between softening, phase transformation, and NbC strain-induced precipitation for the 2%Al-Nb steels. The effect of Al on the static softening kinetics was quantified and introduced in a model developed in previous works for the prediction of the austenite microstructural evolution. In order to validate the results of the model, multipass torsion tests were carried out at conditions representative of hot strip and plate rolling mills. Model predictions show reasonable agreement with the results obtained at different deformation conditions.

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

    SciTech Connect

    Barbour, J.C.; Follstaedt, D.M.; Knapp, J.A.; Myers, S.M.; Marshall, D.A.; Lad, R.J.

    1995-12-31

    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.

  2. Utilizing various test methods to study the stress corrosion behavior of Al-Li-Cu alloys

    NASA Technical Reports Server (NTRS)

    Pizzo, P. P.; Galvin, R. P.; Nelson, H. G.

    1984-01-01

    Recently, much attention has been given to aluminum-lithium alloys because of rather substantial specific-strength and specific-stiffness advantages offered over commercial 2000and 7000-series aluminum alloys. An obstacle to Al-Li alloy development has been inherent limited ductility. In order to obtain a more refined microstructure, powder metallurgy (P/M) has been employed in alloy development programs. As stress corrosion (SC) of high-strength aluminum alloys has been a major problem in the aircraft industry, the possibility of an employment of Al-Li alloys has been considered, taking into account a use of Al-Li-Cu alloys. Attention is given to a research program concerned with the evaluation of the relative SC resistance of two P/M processed Al-Li-Cu alloys. The behavior of the alloys, with and without an addition of magnesium, was studied with the aid of three test methods. The susceptibility to SC was found to depend on the microstructure of the alloys.

  3. Intrinsic stress evolution during amorphous oxide film growth on Al surfaces

    SciTech Connect

    Flötotto, D. Wang, Z. M.; Jeurgens, L. P. H.; Mittemeijer, E. J.

    2014-03-03

    The intrinsic stress evolution during formation of ultrathin amorphous oxide films on Al(111) and Al(100) surfaces by thermal oxidation at room temperature was investigated in real-time by in-situ substrate curvature measurements and detailed atomic-scale microstructural analyses. During thickening of the oxide a considerable amount of growth stresses is generated in, remarkably even amorphous, ultrathin Al{sub 2}O{sub 3} films. The surface orientation-dependent stress evolutions during O adsorption on the bare Al surfaces and during subsequent oxide-film growth can be interpreted as a result of (i) adsorption-induced surface stress changes and (ii) competing processes of free volume generation and structural relaxation, respectively.

  4. High-cycle fatigue characterization of titanium 5Al-2.5Sn alloy

    NASA Technical Reports Server (NTRS)

    Mahfuz, H.; Xin, Yu T.; Jeelani, S.

    1993-01-01

    High-cycle fatigue behavior of titanium 5Al 2.5Sn alloy at room temperature has been studied. S-N curve characterization is performed at different stress ratios ranging from 0 to 0.9 on a subsized fatigue specimen. Both two-stress and three-stress level tests are conducted at different stress ratios to study the cumulative fatigue damage. Life prediction techniques of linear damage rule, double linear damage rule and damage curve approaches are applied, and results are compared with the experimental data. The agreement between prediction and experiment is found to be excellent.

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

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

    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.

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

    SciTech Connect

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

    2004-09-20

    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.

  7. Bending fatigue tests on SiC-Al tapes under alternating stress at room temperature

    NASA Technical Reports Server (NTRS)

    Herzog, J. A.

    1981-01-01

    The development of a testing method for fatigue tests on SiC-Al tapes containing a small amount of SiC filaments under alternating stress is reported. The fatigue strength curves resulting for this composite are discussed. They permit an estimate of its behavior under continuous stress and in combination with various other matrices, especially metal matrices.

  8. The Influence of Al-Anon on Stress of Wives of Alcoholics.

    ERIC Educational Resources Information Center

    McGregor, Phyllis W.

    This study assessed Alcoholics Anonymous (Al-Anon) participation as a factor in stress of wives of alcoholics. Additional data focused on attitude and behavior variables. Two groups of 20 subjects each were enlisted from Al-Anon, personal contacts, treatment centers, and referrals in three urban areas in the southeastern United States. Group A…

  9. Modelling Of Residual Stresses Induced By High Speed Milling Process

    NASA Astrophysics Data System (ADS)

    Desmaison, Olivier; Mocellin, Katia; Jardin, Nicolas

    2011-05-01

    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® software, is based on data taken from Outeiro & 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&D to those given by numerical simulations is achieved.

  10. Modelling Of Residual Stresses Induced By High Speed Milling Process

    SciTech Connect

    Desmaison, Olivier; Mocellin, Katia; Jardin, Nicolas

    2011-05-04

    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.

  11. Micromechanical stresses in SiC-reinforced Al2O3 composites

    NASA Technical Reports Server (NTRS)

    Li, Zhuang; Bradt, Richard C.

    1989-01-01

    Applying an Eshelby (1957) approach, the internal micromechanical stresses within an SiC-inclusion-reinforced (platelet to whisker geometries) polycrystalline alumina matrix composite were calculated. The results are compared to the experimental residual stress measurements of a SiC-whisker-reinforced Al2O3 by Predecki, et al. (in press) and found to be in excellent agreement. The calculations are then extended to SiC-reinforced composites with polycrystalline mullite, silicon nitride, and cordierite matrices. It is concluded that the internal stresses are significantly influenced by the inclusion geometry as well as the thermoelastic differences between the inclusion and the matrix and also the volume fraction.

  12. High temperature deformation of NiAl and CoAl

    NASA Technical Reports Server (NTRS)

    Nix, W. D.

    1982-01-01

    The high temperature mechanical properties of the aluminides are reviewed with respect to their potential as high temperature structural materials. It is shown that NiAl and CoAl are substantially stronger than the pure metals Ni and Co at high temperatures and approach the strength of some superalloys, particularly when those superalloys are tested in "weak" directions. The factors that limit and control the high temperature strengths of NiAl and CoAl are examined to provide a basis for the development of intermetallic alloys of this type.

  13. Compensation effect of bacterium containing biofertilizer on the growth of Cucumis sativus L. under Al-stress conditions.

    PubMed

    Tóth, Brigitta; Lévai, L; Kovács, B; Varga, Mária Borbélyné; Veres, Szilvia

    2013-03-01

    Biofertilizers are used to improve soil fertility and plant production in sustainable agriculture. However, their applicability depends on several environmental parameters. The aim of our study was to evaluate the effect of free-living bacteria containing fertilizer on the growth of cucumber (Cucumis sativus L. cvs. Delicates) under aluminium (Al) stress. Different responses to Al stress of cucumber growth parameters were examined in terms of root elongation and physiological traits, such as Spad index (relative chlorophyll value), biomass accumulation of root and shoot, Al uptake and selected element contents (Fe, Mn, Zn, Mg) of leaves and root. The applied bacteria containing biofertilizer contains Azotobacter chroococcum and Bacillus megaterium. The dry weights of cucumber shoots and roots decreased in line with the increasing Al concentration. Due to different Al treatments (10-3 M, 10-4 M) higher Al concentration was observed in the leaves, while the amounts of other elements (Fe, Mn, Zn, Mg) decreased. This high Al content of the leaves decreased below the control value when biofertilizer was applied. In the case of the roots the additional biofertilizer treatments compensated the effect of Al. The relative chlorophyll content was reduced during Al-stress in older plants and the biofertilizer moderated this effect. The root/shoot ratio was decreased in all the Al-treatments in comparison to the control. The living bacteria containing fertilizer also had a modifying effect. The root/shoot ratio increased at the 10-4 M Al2(SO4)2 + biofertilizer and 10-4 M Al(NO3)3 + biofertilizer treatments compared to the control and Al-treatments. According to our results the biofertilizer is an alternative nutrient supply for replacing chemical fertilizers because it enhances dry matter production. Biofertilizer usage is also offered under Al polluted environmental conditions. Although, the nutrient solution is a clean system where we can examine the main processes without

  14. High electron mobility AlGaN/AlN/GaN HEMT structure with a nano-scale AlN interlayer

    NASA Astrophysics Data System (ADS)

    Huang, Shih-Chun; Chen, Wen-Ray; Hsu, Yu-Ting; Lin, Jia-Ching; Chang, Kuo-Jen; Lin, Wen-Jen

    2012-10-01

    Epitaxies of AlGaN/AlN/GaN high electron mobility transistor (HEMT) structures with different thickness of nano-scale AlN interlayers have been realized by metalorganic chemical vapor deposition (MOCVD) technology. After epitaxy, high resolution X-ray diffraction (HRXRD), temperature-dependent Hall Effect and atomic force microscopy (AFM) measurements were used to characterize the properties of these samples. First, it was found that the Al composition of AlGaN layer increases from 21.6 to 34.2% with increasing the thickness of AlN interlayer from 0 to 5 nm under the same AlGaN growth conditions. This result may due to the influences of compressive stress and Al incorporation induced by the AlN interlayer. Then, we also found that the room-temperature (RT) electron mobility stays higher than 1500 cm2/Vs in the samples within AlN interlayer thickness range of 1.5 nm, on the other hand, the low-temperature (80K) electron mobility drops dramatically from 8180 to 5720 cm2/Vs in the samples with AlN interlayer thickness increasing from 1 to 1.5 nm. Furthermore, it was found that the two-dimensional electron gas (2DEG) density increases from 1.15×1013 to 1.58×1013 cm-2 beyond the AlN interlayer thickness of 1 nm. It was also found that the temperature independent 2DEG densities are observed in the samples with AlN interlayer thickness of 0.5 and 1 nm. The degenerated characteristics of the samples with AlN thickness thicker than 1.5 nm show the degraded crystalline quality which matched the observation of surface defects and small cracks formations from their AFM images. Finally, the 2DEG mobilities of the proposed structures can be achieved as high as 1705 and 8180 cm2/Vs at RT and 80K, respectively.

  15. The Alfin-like homeodomain finger protein AL5 suppresses multiple negative factors to confer abiotic stress tolerance in Arabidopsis.

    PubMed

    Wei, Wei; Zhang, Yu-Qin; Tao, Jian-Jun; Chen, Hao-Wei; Li, Qing-Tian; Zhang, Wan-Ke; Ma, Biao; Lin, Qing; Zhang, Jin-Song; Chen, Shou-Yi

    2015-03-01

    Plant homeodomain (PHD) finger proteins affect processes of growth and development by changing transcription and reading epigenetic histone modifications, but their functions in abiotic stress responses remain largely unclear. Here we characterized seven Arabidopsis thaliana Alfin1-like PHD finger proteins (ALs) in terms of the responses to abiotic stresses. ALs localized to the nucleus and repressed transcription. Except AL6, all the ALs bound to G-rich elements. Mutations of the amino acids at positions 34 and 35 in AL6 caused loss of ability to bind to G-rich elements. Expression of the AL genes responded differentially to osmotic stress, salt, cold and abscisic acid treatments. AL5-over-expressing plants showed higher tolerance to salt, drought and freezing stress than Col-0. Consistently, al5 mutants showed reduced stress tolerance. We used ChIP-Seq assays to identify eight direct targets of AL5, and found that AL5 binds to the promoter regions of these genes. Knockout mutants of five of these target genes exhibited varying tolerances to stresses. These results indicate that AL5 inhibits multiple signaling pathways to confer stress tolerance. Our study sheds light on mechanisms of AL5-mediated signaling in abiotic stress responses, and provides tools for improvement of stress tolerance in crop plants. PMID:25619813

  16. High performance AlGaN/GaN HEMTs with AlN/SiNx passivation

    NASA Astrophysics Data System (ADS)

    Xin, Tan; Yuanjie, Lü; Guodong, Gu; Li, Wang; Shaobo, Dun; Xubo, Song; Hongyu, Guo; Jiayun, Yin; Shujun, Cai; Zhihong, Feng

    2015-07-01

    AlGaN/GaN high electron-mobility transistors (HEMTs) with 5 nm AlN passivation by plasma enhanced atomic layer deposition (PEALD) were fabricated, covered by 50 nm SiNx which was grown by plasma enhanced chemical vapor deposition (PECVD). With PEALD AlN passivation, current collapse was suppressed more effectively and the devices show better subthreshold characteristics. Moreover, the insertion of AlN increased the RF transconductance, which lead to a higher cut-off frequency. Temperature dependence of DC characteristics demonstrated that the degradations of drain current and maximum transconductance at elevated temperatures for the AlN/SiNx passivated devices were much smaller compared with the devices with SiNx passivation, indicating that PEALD AlN passivation can improve the high temperature operation of the AlGaN/GaN HEMTs. Project supported by the National Natural Science Foundation of China (No. 60890192).

  17. Numerical Simulation of Residual Stress in an Al-Cu Alloy Block During Quenching and Aging

    NASA Astrophysics Data System (ADS)

    Dong, Ya-Bo; Shao, Wen-Zhu; Lu, Liang-Xing; Jiang, Jian-Tang; Zhen, Liang

    2015-12-01

    In this study, residual stresses after different quenching and aging processes of Al-Cu forged blocks were investigated by numerical simulation method and experimental measurements. An iterative zone-based heat transfer calculation was coupled with the hyperbolic sine-type constitutive model to simulate the residual stress during quenching process. The simulation results were compared with experiment data using both x-ray diffraction and crack compliance methods. The simulation results were in good agreement with the experimental measurements with around 9-13% deviation at the largest. Residual stress reduction can be achieved by decreasing the cooling rate during quenching. Quenching in water with different temperatures of 60, 80, and 100 °C resulted in the maximum compressive residual stress reduction of approximately 28.2, 75.7, and 88.9%, respectively, in Al-Cu alloy samples. When quenched in 10, 20, and 30% PAG solution, the reduction of maximum compressive residual stress in Al-Cu alloy samples was approximately 35.1, 47.8, and 53.2%, respectively. In addition, in order to study the amount of residual stress relief after aging treatments, aging treatments at 140 and 170 °C for different times were also studied. Aging treatment used to obtain the peak-aged (T6) and overaged (T7) condition produces only about 22.5 to 34.7% reduction in residual stresses.

  18. Modeling of the dislocation dynamics in Ni{sub 3}Al and the flow stress anomaly

    SciTech Connect

    Devincre, B.; Veyssiere, P.; Kubin, L.; Saada, G.

    1997-12-31

    Ni{sub 3}Al single crystals are known to exhibit a flow stress anomaly between 200 and 800 K. The purpose of this work is to examine such an anomaly by means of a simulation of the dislocation dynamics at a mesoscopic scale. The simulation basic rules are: (i) the dislocation glide in {l_brace}111{r_brace} octahedral planes, (ii) the conditions at which screw lines are locked and unlocked by the formation of Kear-Wilsdorf locks, (iii) the mobility of jogs in the {l_brace}100{r_brace} cube plane. The results suggest that two different temperature regimes occur in the domain of the anomaly. At low temperatures, the plastic flow is governed by kink bow-out, itself a function of the kink length. At high temperatures, the plastic flow is governed by the unlocking of the weakest Kear-Wilsdorf locks in the microstructure. These outcomes of the simulation are discussed in relation with the existing theoretical models of the flow stress anomaly.

  19. Effect of laser spot size on the residual stress field of pure Al treated by laser shock processing: Simulations

    NASA Astrophysics Data System (ADS)

    Dai, F. Z.; Lu, J. Z.; Zhang, Y. K.; Wen, D. P.; Ren, X. D.; Zhou, J. Z.

    2014-10-01

    Laser shock processing (LSP) is a unique surface treatment technique. It induces high-depth compressive residual stresses for improved fatigue or stress corrosion cracking resistance. FEM simulation is an effective method to predict material behavior by LSP. A 2D quarter-infinite model was used to simulate the material behaviors of commercially pure Al by LSP. Different peak pressure with different laser spot diameter was applied to surface of pure Al. Each simulation included two steps: (i) explicit dynamics analysis for the analysis of the LSP; (ii) static equilibrium analysis for springback deformation analysis. The following conclusions could be made: (1) Plastically affected depth increased with the increase of laser spot diameter. There was an ultimate value about plastically affected depth when the laser spot diameter increased to some value, and the ultimate value was consistent with Ballard' model. When the laser spot diameter was small, there still existed tensile residual stresses on the surface layer of material although the peak pressure was below 2.5 HEL. When the diameter laser spot diameter was big enough, the tensile residual stresses on the surface layer of material were converted into compressive residual stresses although the peak pressure was higher than 2.5 HEL.

  20. Residual stress distribution in FeAl weld overlay on steel

    SciTech Connect

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

    1994-12-31

    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.

  1. NiAl-Base Composite Containing High Volume Fraction of AIN Particulate for Advanced Engines

    NASA Technical Reports Server (NTRS)

    Hebsur, Mohan G.; Whittenberger, J. D.; Lowell, C. E.; Garg, A.

    1995-01-01

    Cryomilling of prealloyed NiAl containing 53 at. % AJ was carried out to achieve high nitrogen levels. The consolidation of cryomilled powder by extrusion or hot pressing/ hot isostatic pressing resulted in a fully dense NiAl-base composite containing 30 vol. % of inhomogeneously distributed, nanosized AIN particulate. The NiAl-30AIN composite exhibited the highest compression yield strengths at all temperatures between 300 and 1300 K as compared with other compositions of NiAl-AIN composite. The NiAl-30AIN specimens tested under compressive creep loading between 1300 and 1500 K also exhibited the highest creep resistance with very little surface oxidation indicating also their superior elevated temperature oxidation resistance. In the high stress exponent regime, the strength is proportional to the square root of the AIN content and in the low stress exponent regime, the influence of AIN content on strength appears to be less dramatic. The specific creep strength of this material at 1300 K is superior to a first generation Ni-base single crystal superalloy. The improvements in elevated temperature creep strength and oxidation resistance have been achieved without sacrificing the room temperature fracture toughness of the NiAl-base material. Based on its attractive combination of properties, the NiAl-30AIN composite is a potential candidate for advanced engine applications,

  2. AlN/IDT/AlN/Sapphire SAW Heterostructure for High-Temperature Applications.

    PubMed

    Legrani, Ouarda; Aubert, Thierry; Elmazria, Omar; Bartasyte, Ausrine; Nicolay, Pascal; Talbi, Abdelkrim; Boulet, Pascal; Ghanbaja, Jaafar; Mangin, Denis

    2016-06-01

    Recent studies have evidenced that Pt/AlN/Sapphire surface acoustic wave (SAW) devices are promising for high-temperature high-frequency applications. However, they cannot be used above 700°C in air atmosphere as the Pt interdigital transducers (IDTs) agglomerate and the AlN layer oxidizes in such conditions. In this paper, we explore the possibility to use an AlN protective overlayer to concurrently hinder these phenomena. To do so, AlN/IDT/AlN/Sapphire heterostructures undergo successive annealing steps from 800°C to 1000°C in air atmosphere. The impact of each step on the morphology, microstructure, and phase composition of AlN and Pt films is evaluated using optical microscopy, scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD), and secondary ion mass spectroscopy (SIMS). Finally, acoustical performance at room temperature of both protected and unprotected SAW devices are compared, as well as the effects of annealing on these performance. These investigations show that the use of an overlayer is one possible solution to strongly hinder the Pt IDTs agglomeration up to 1000°C. Moreover, AlN/IDT/AlN/Sapphire SAW heterostructures show promising performances in terms of stability up to 800°C. At higher temperatures, the oxidation of AlN is more intense and makes it inappropriate to be used as a protective layer. PMID:27076407

  3. Residual Stress in Brazing of Submicron Al2O3 to WC-Co

    NASA Astrophysics Data System (ADS)

    Grunder, T.; Piquerez, A.; Bach, M.; Mille, P.

    2016-07-01

    This study evaluated the residual stresses induced by brazing and grinding submicron Al2O3, using different methods. Energy dispersive x-ray spectrometry analysis (EDX) of 72Ag-Cu filler and filler/WC-Co interface showed evidence of atomic diffusion and possible formation of titanium oxide layers between the joint and the bonding materials. An analytical model supported by the finite element method (FEM) based on strain determination due to the difference in variation of thermal expansion was used to assess the stress distribution at the coupling interface and in bulk materials. The model took into account the evolution of the Young's modulus and of the thermal expansion with temperature. The model could be used to follow strain and stress evolutions of the bonded materials during the cooling cycle. The maximum stress rose above -300 MPa at the center of the 100 × 100 × 3 mm ceramic plates. The residual stresses on the external surface of ceramic were investigated by x-ray diffraction (XRD) and indentation fracture method (IFM). After brazing and grinding the plate, the principal stresses were 128.1 and 94.9 MPa, and the shear stress was -20.1 MPa. Microscopic examination revealed grain pull-out promoted by the global residual stresses induced by the brazing and grinding processes. The surface stresses evaluated by the different methods were reasonably correlated.

  4. Residual Stress in Brazing of Submicron Al2O3 to WC-Co

    NASA Astrophysics Data System (ADS)

    Grunder, T.; Piquerez, A.; Bach, M.; Mille, P.

    2016-06-01

    This study evaluated the residual stresses induced by brazing and grinding submicron Al2O3, using different methods. Energy dispersive x-ray spectrometry analysis (EDX) of 72Ag-Cu filler and filler/WC-Co interface showed evidence of atomic diffusion and possible formation of titanium oxide layers between the joint and the bonding materials. An analytical model supported by the finite element method (FEM) based on strain determination due to the difference in variation of thermal expansion was used to assess the stress distribution at the coupling interface and in bulk materials. The model took into account the evolution of the Young's modulus and of the thermal expansion with temperature. The model could be used to follow strain and stress evolutions of the bonded materials during the cooling cycle. The maximum stress rose above -300 MPa at the center of the 100 × 100 × 3 mm ceramic plates. The residual stresses on the external surface of ceramic were investigated by x-ray diffraction (XRD) and indentation fracture method (IFM). After brazing and grinding the plate, the principal stresses were 128.1 and 94.9 MPa, and the shear stress was -20.1 MPa. Microscopic examination revealed grain pull-out promoted by the global residual stresses induced by the brazing and grinding processes. The surface stresses evaluated by the different methods were reasonably correlated.

  5. Mechanical Properties of High Strength Al-Mg Alloy Sheet

    NASA Astrophysics Data System (ADS)

    Choi, Bong-Jae; Hong, Kyung-Eui; Kim, Young-Jig

    The aim of this research is to develop the high strength Al alloy sheet for the automotive body. For the fabrication Al-Mg alloy sheet, the composition of alloying elements was designed by the properties database and CALPHAD (Calculation Phase Diagram) approach which can predict the phases during solidification using thermodynamic database. Al-Mg alloys were designed using CALPHAD approach according to the high content of Mg with minor alloying elements. After phase predictions by CALPHAD, designed Al-Mg alloys were manufactured. Addition of Mg in Al melts were protected by dry air/Sulphur hexafluoride (SF6) mixture gas which can control the severe Mg ignition and oxidation. After rolling procedure of manufactured Al-Mg alloys, mechanical properties were examined with the variation of the heat treatment conditions.

  6. Roof support performance in high stress conditions

    SciTech Connect

    Mucho, T.P.; Mark, C.; Zelanko, J.C.; Compton, C.S.

    1995-11-01

    To document the performance of mine roof and roof support systems the US Bureau of Mines (USBM) has been installing instrumentation at selected sites in US coal mines. Much of this support and roof instrumentation has been installed in high stress conditions to maximize differences in performance. Summarized in this paper are the results of four such site investigations. The roof geology at the four sites is quite different and is quantified using the USBM`s Coal Mine Roof Rating (CMRR). The studies included detailed measurements of roof movement using multi-point extensometers, as well as measurements and monitoring of bolt loading. The investigations include developmental loading and abutment loading from longwall and room-and-pillar mining operations. Some of the issues examined are the effect of the horizontal stress field, the effect of installed tension (torque-tension versus resin bolts), the effect of reduced annulus bolt holes, and the differences between similar bolts supplied by different manufacturers.

  7. Deposition of ultrathin AlN films for high frequency electroacoustic devices

    SciTech Connect

    Felmetsger, Valery V.; Laptev, Pavel N.; Graham, Roger J.

    2011-03-15

    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.

  8. Neutron diffraction measurement of residual stresses in Al-clad U-10Mo fuel plates

    NASA Astrophysics Data System (ADS)

    Brown, D. W.; Okuniewski, M. A.; Clausen, B.; Moore, G. A.; Sisneros, T. A.

    2016-06-01

    Neutron diffraction was used to determine residual stress in monolithic two Al-clad U 10 weight percent Mo mini-fuel plates and a full sized fuel plate. One mini-plate was cooled following hot isostatic pressing at a rate of 6.75 °C/min, the second at 0.675 °C/min. A non-traditional method of calibrating the neutron diffractometer at each measurement point was necessitated by the thin nature of the sample. The in-plane stresses in the U-10Mo foils are relatively large, -250 MPa in the U-10Mo foil of the fast cooled mini-plate,-150 MPa in the slow cooled mini-plate and -275 MPa in the full-sized plate. Likewise, the in-plane stresses in the Al-cladding of the fast-cooled mini-plate and full-sized plate were determined to reach ∼50 MPa, while in the slow-cooled sample the stresses in the Al cladding were on the level of the measurement uncertainty. The in-plane stresses in the Zr diffusion barrier were estimated to be as large as -300 MPa.

  9. A critical evaluation of the stress-corrosion cracking mechanism in high-strength aluminum alloys

    NASA Astrophysics Data System (ADS)

    Lee, Seong-Min; Pyun, Su-Il; Chun, Young-Gab

    1991-10-01

    Attempts have been made to elucidate the mechanism of stress-corrosion cracking (SCC) in high-strength Al-Zn-Mg and Al-Li-Zr alloys exposed to aqueous environments by considering the temperature dependence of SCC susceptibility based upon the anodic dissolution and hydrogen embrittlement models. A quantitative correlation which involves the change of threshold stress intensity, K ISCC, with temperature on the basis of anodic dissolution has been developed with the aid of linear elastic fracture mechanics. From the derived correlation, it is concluded that the threshold stress intensity decreases as the test temperature increases. This suggestion is inconsistent with that predicted on the basis of hydrogen embrittlement. It is experimentally observed from the Al-Zn-Mg and Al-Li-Zr alloys that the threshold stress intensity, K,ISCC, decreases and the crack propagation rate, da/dt, over the stress intensity increases with increasing test temperature. From considering the change in SCC susceptibility with temperature, it is suggested that a gradual transition in the mechanism for the stress-corrosion crack propagation occurs from anodic dissolution in stage I, where the crack propagation rate increases sharply with stress intensity, to hydrogen embrittlement in stage II, where the crack propagation rate is independent of stress intensity.

  10. Nuclear localization sequence of FUS and induction of stress granules by ALS mutants

    PubMed Central

    Gal, Jozsef; Zhang, Jiayu; Kwinter, David M.; Zhai, Jianjun; Jia, Hongge; Jia, Jianhang; Zhu, Haining

    2010-01-01

    Mutations in FUS have been reported to cause a subset of familial amyotrophic lateral sclerosis (ALS) cases. Wild-type FUS is mostly localized in the nuclei of neurons, but the ALS mutants are partly mislocalized in the cytoplasm and can form inclusions. Little is known about the regulation of FUS subcellular localization or how the ALS mutations alter FUS function. Here we demonstrate that the C-terminal 32 amino acid residues of FUS constitute an effective nuclear localization sequence (NLS) as it targeted beta-galactosidase (LacZ, 116 kDa) to the nucleus. Deletion of or the ALS point mutations within the NLS caused cytoplasmic mislocalization of FUS. Moreover, we identified the poly-A binding protein (PABP1), a stress granule marker, as an interacting partner of FUS. PABP1 formed large cytoplasmic foci that co-localized with the mutant FUS inclusions. No such foci, which resemble stress granules, were observed in the presence of wild-type FUS. In addition, processing bodies, which are functionally related to stress granules, were adjacent to but not co-localized with the mutant FUS inclusions. Our results suggest that the ALS mutations in the C-terminal NLS of FUS can impair FUS nuclear localization and induce cytoplasmic mislocalization, inclusion formation, and potential perturbation of RNA metabolism. PMID:20674093

  11. Novel high-strength ternary Zr-Al-Sn alloys with martensite structure for nuclear applications

    NASA Astrophysics Data System (ADS)

    Nie, Li; Zhan, Yongzhong; Hu, Tong; Chen, Xiaoxian; Wang, Chenghui

    2013-11-01

    High strength is essential for the practical application of Zr alloys as structural materials. In this work, Zr-5Al-xSn (x = 2, 3, 4, 5 and 6) alloys have been designed and fabricated through arc melting in order to effectively improve the strength while retaining good ductility. Phase analysis results show that all the samples consist of single phase α-Zr. The variation trend of lattice constants as a function of Sn content has been analyzed. The microstructural analysis indicates that the Zr-5Al-xSn alloys mainly contain martensite structure. Mechanical tests show that these Zr-5Al-xSn alloys exhibit high compressive strength (1250-1450 MPa), high yield stress (800-1000 MPa), and favorable plastic strain of 18-23%. The fracture mode has been experimentally analyzed. Finally, both Zr-5Al-3Sn and Zr-5Al-5Sn are subjected to heat treatments for further study on the roles of Sn element and controlled heat treatment on the microstructure and mechanical properties of Zr alloys. Sn is found to promote the formation of ZrAl in the Zr-5Al-xSn alloys. Moreover, the martensite laths are observed to evolve into larger strip grains and fine equiaxed grains after heat treatment at 900 °C for 2 h. These factors strengthen the Zr-5Al-xSn alloys.

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

    SciTech Connect

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

    2004-03-23

    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.

  13. Time-dependent stress concentration and microcrack nucleation in TiAl

    SciTech Connect

    Yoo, M.H.

    1995-07-01

    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.

  14. ALS Multicenter Cohort Study of Oxidative Stress (ALS COSMOS): The study methodology, recruitment, and baseline demographic and disease characteristics

    PubMed Central

    Mitsumoto, Hiroshi; Factor-Litvak, Pam; Andrews, Howard; Goetz, Raymond R.; Andrews, Leslie; Rabkin, Judith G.; McElhiney, Martin; Nieves, Jeri; Santella, Regina M.; Murphy, Jennifer; Hupf, Jonathan; Singleton, Jess; Merle, David; Kilty, Mary; Heitzman, Daragh; Bedlack, Richard S.; Miller, Robert G; Katz, Jonathan S.; Forshew, Dallas; Barohn, Richard J.; Sorenson, Eric J.; Oskarsson, Bjorn; Filho, J Americo M. Fernandes; Kasarskis, Edward J.; Lomen-Hoerth, Catherine; Mozaffar, Tahseen; Rollins, Yvonne D.; Nations, Sharon P.; Swenson, Andrea J.; Shefner, Jeremy M.; Andrews, Jinsy A.; Koczon-Jaremko, Boguslawa A.

    2015-01-01

    Objective In a multicenter study of newly diagnosed ALS patients without a reported family history of ALS, we are prospectively investigating whether markers of oxidative stress (OS) are associated with disease progression. Methods An extensive structured telephone interview ascertained environmental, lifestyle, dietary and psychological risk factors associated with OS. Detailed assessments were performed at baseline and at 3 to 6 month intervals during the ensuing 30 months. Our biorepository includes DNA, plasma, urine, and skin. Results 355 patients were recruited. Subjects were enrolled over a 36 month-period at 16 sites. To meet the target number of subjects, the recruitment period was prolonged and additional sites were included. Demographic and disease characteristics were similar between 477 eligible/non-enrolled and enrolled patients, with the only difference being type of health insurance among enrolled patients. Sites were divided into 3 groups by the number of enrolled subjects. Comparing these 3 groups, the Columbia site had fewer “definite ALS” diagnoses. Conclusion This is the first prospective, interdisciplinary, in-depth, multicenter epidemiological investigation of OS related to ALS progression and was accomplished by an aggressive recruitment process. The baseline demographic and disease features of the study sample are now fully characterized. PMID:24564738

  15. High noise suppression using magnetically isotropic (CoFe-AlN)/(AlN) multilayer films

    NASA Astrophysics Data System (ADS)

    Kijima, Hanae; Ohnuma, Shigehiro; Masumoto, Hiroshi; Shimada, Yutaka; Endo, Yasushi; Yamaguchi, Masahiro

    2015-05-01

    Magnetically isotropic (CoFe-AlN)n/(AlN)n+1 multilayer films, in which the number of CoFe-AlN magnetic layers n ranged from 1 to 27, were prepared by radio frequency sputtering to achieve noise suppression at gigahertz frequencies. The soft CoFe-AlN magnetic layers consisted of nanometer-sized CoFe ferromagnetic grains embedded in an insulating AlN amorphous matrix, while the insulating AlN layers comprised AlN columnar crystals. All films showed a similar frequency dependence of permeability and ferromagnetic resonance of 1.7 GHz. Noise suppression was evaluated using a microstrip line as a noise source by determining the in-line conductive loss and the near-field intensity picked up by magnetic field detective probes. High noise suppression effects were observed in every direction in the film plane. Maximum noise suppression values amounted to 60% for the in-line conductive loss and -20 dB for the magnetic near-field intensity at around 1.7 GHz in the 27-layer film. These high-frequency noise suppression levels may be attributed to eddy current losses and ferromagnetic resonance.

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

    PubMed Central

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

    2013-01-01

    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 protein–protein 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. PMID:23474818

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

    PubMed

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

    2013-07-01

    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 protein-protein 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. PMID:23474818

  18. The rate dependence of the saturation flow stress of Cu and 1100 Al

    SciTech Connect

    Preston, D.L.; Tonks, D.L.; Wallace, D.C.

    1991-01-01

    The strain-rate dependence of the saturation flow stress of OFHC Cu and 1100 Al from 10{sup {minus}3}s{sup {minus}1} to nearly to 10{sup 12}s{sup {minus}1} is examined. The flow stress above 10{sup 9}s{sup {minus}1} is estimated using Wallace's theory of overdriven shocks in metals. A transition to the power-law behavior {Psi} {approximately} {tau}{sub s}{sup 5} occurs at a strain rate of order 10{sup 5}s{sup {minus}1}. 10 refs., 2 figs.

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

    SciTech Connect

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

    2000-01-01

    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.

  20. Reduction of exciton mass by uniaxial stress in GaAs/AlGaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Loginov, D. K.; Grigoryev, P. S.; Efimov, Yu. P.; Eliseev, S. A.; Lovtcius, V. A.; Petrov, V. V.; Ubyivovk, E. V.; Ignatiev, I. V.

    2016-08-01

    It is experimentally shown that the pressure applied along the twofold symmetry axis of a heterostructure with a wide GaAs/AlGaAs quantum well leads to considerable modification of the polariton reflectance spectra. This effect is treated as the stress-induced decrease of the heavy-hole exciton mass. Theoretical modeling of the effect supports this assumption. The 5\\%-decrease of the exciton mass is obtained at pressure P=0.23 GPa.

  1. Tensile properties of cast and mechanically alloyed FeAl with high boron content

    SciTech Connect

    Kim, M.H.; Kwun, S.I.

    1996-08-01

    The FeAl with B2 structure has been considered as a potential structural material for use at elevated temperatures and severe environment. Two major problems with this polycrystalline aluminide are its brittleness through cleavage or grain boundary failure at ambient temperature and rapid strength drop at high temperatures above 750K. In order to expand the use of iron aluminide, these two problems must be overcome. Making a grain size small might be one of the effective ways as the stress distribution is more homogeneous throughout the material. Another method to increase the ductility of iron rich FeAl seems to add small amount of boron. Webb reported that the optimum B content for ambient temperature ductility enhancement was approximately 12 wppm in FeAl(40at%Al). With these points in mind, the authors have tried to modify room and high temperature mechanical properties of FeAl by mechanical alloying. The mechanical alloying is a unique process in that it is an entirely solid state process, permitting fine distribution of insoluble phases and fine grain size material. This paper compares the mechanical properties of the cast and the mechanically alloyed FeAl with B as much as 0.3wt%. The highest B content added in iron rich FeAl was reported to be 0.2wt% up to now.

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

    NASA Astrophysics Data System (ADS)

    Chesnut, Gary N.; Velisavljevic, Nenad; Sanchez, Lilliana

    2007-12-01

    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.

  3. Sputter deposition of stress-controlled piezoelectric AlN and AlScN films for ultrasonic and energy harvesting applications.

    PubMed

    Barth, Stephan; Bartzsch, Hagen; Gloess, Daniel; Frach, Peter; Herzog, Thomas; Walter, Susan; Heuer, Henning

    2014-08-01

    This paper reports on the deposition and characterization of piezoelectric AlN and AlXSc1-XN layers. Characterization methods include XRD, SEM, active thermo probe, pulse echo, and piezometer measurements. A special focus is on the characterization of AlN regarding the mechanical stress in the films. The stress in the films changed between -2.2 GPa (compressive) and 0.2 GPa (tensile) and showed a significant dependence on film thickness. The cause of this behavior is presumed to be the different mean grain sizes at different film thicknesses, with bigger mean grain sizes at higher thicknesses. Other influences on film stress such as the sputter pressure or the pulse mode are presented. The deposition of gradient layers using those influences allowed the adjustment of film stress while retaining the piezoelectric properties. PMID:25073140

  4. Local crystallography and stress voiding in Al-Si-Cu versus copper interconnects

    NASA Astrophysics Data System (ADS)

    Keller, R. R.; Kalnas, C. E.; Phelps, J. M.

    1999-07-01

    We compare the local crystallographic orientations associated with stress voids in Al-1Si-0.5Cu (wt %) with those in pure copper interconnects. Orientations were sorted by whether grains were immediately adjacent to voids. Grains adjacent to voids in Al-Si-Cu showed a <111> fiber texture that was slightly stronger than those in intact regions. This is in contrast to copper, which showed weaker local <111> texture around voids. We postulate the difference to be due to the relative effectiveness of the diffusion paths available in the lines. For Al-Si-Cu, the presence of defects associated with precipitates may allow more rapid diffusion than grain boundaries. Voiding in copper, which is free from such defects, depends more on grain boundary structure.

  5. Mechanism of stress-driven composition evolution during hetero-epitaxy in a ternary AlGaN system

    PubMed Central

    He, Chenguang; Qin, Zhixin; Xu, Fujun; Zhang, Lisheng; Wang, Jiaming; Hou, Mengjun; Zhang, Shan; Wang, Xinqiang; Ge, Weikun; Shen, Bo

    2016-01-01

    Two AlGaN samples with different strain were designed to investigate mechanism of stress-driven composition evolution. It is discovered that AlGaN grown on AlN or (AlN/GaN superlattices (SLs))/GaN both consist of two distinct regions with different compositions: transition region and uniform region, which is attributed to the compositional pulling effect. The formation of the transition region is due to the partial stress release caused by the generation of misfit dislocations near the hetero-interface. And the Al composition in the uniform region depends on the magnitude of residual strain. The difference in relaxation degree is 80.5% for the AlGaN epilayers grown on different underlayers, leading to a large Al composition difference of 22%. The evolutionary process of Al composition along [0001] direction was investigated in detail. PMID:27112969

  6. Mechanism of stress-driven composition evolution during hetero-epitaxy in a ternary AlGaN system.

    PubMed

    He, Chenguang; Qin, Zhixin; Xu, Fujun; Zhang, Lisheng; Wang, Jiaming; Hou, Mengjun; Zhang, Shan; Wang, Xinqiang; Ge, Weikun; Shen, Bo

    2016-01-01

    Two AlGaN samples with different strain were designed to investigate mechanism of stress-driven composition evolution. It is discovered that AlGaN grown on AlN or (AlN/GaN superlattices (SLs))/GaN both consist of two distinct regions with different compositions: transition region and uniform region, which is attributed to the compositional pulling effect. The formation of the transition region is due to the partial stress release caused by the generation of misfit dislocations near the hetero-interface. And the Al composition in the uniform region depends on the magnitude of residual strain. The difference in relaxation degree is 80.5% for the AlGaN epilayers grown on different underlayers, leading to a large Al composition difference of 22%. The evolutionary process of Al composition along [0001] direction was investigated in detail. PMID:27112969

  7. Mechanism of stress-driven composition evolution during hetero-epitaxy in a ternary AlGaN system

    NASA Astrophysics Data System (ADS)

    He, Chenguang; Qin, Zhixin; Xu, Fujun; Zhang, Lisheng; Wang, Jiaming; Hou, Mengjun; Zhang, Shan; Wang, Xinqiang; Ge, Weikun; Shen, Bo

    2016-04-01

    Two AlGaN samples with different strain were designed to investigate mechanism of stress-driven composition evolution. It is discovered that AlGaN grown on AlN or (AlN/GaN superlattices (SLs))/GaN both consist of two distinct regions with different compositions: transition region and uniform region, which is attributed to the compositional pulling effect. The formation of the transition region is due to the partial stress release caused by the generation of misfit dislocations near the hetero-interface. And the Al composition in the uniform region depends on the magnitude of residual strain. The difference in relaxation degree is 80.5% for the AlGaN epilayers grown on different underlayers, leading to a large Al composition difference of 22%. The evolutionary process of Al composition along [0001] direction was investigated in detail.

  8. Stress response by the strain-rate change in binary, stoichiometric Ni{sub 3}Al single crystal

    SciTech Connect

    Demura, M.; Hirano, T.

    1997-12-31

    The strain-rate dependence of flow stress in single crystals of binary, stoichiometric Ni{sub 3}Al was studied in the temperature region of the yield stress anomaly. Below 400 K, the steady-state flow stress was found to be independent of strain rate, though it changed temporarily when the strain rate was changed. The strain-rate insensitivity can be explained by assuming that the flow stress is controlled by the multiplication/immobilization of mobile dislocations.

  9. Highly strained AlAs-type interfaces in InAs/AlSb heterostructures

    NASA Astrophysics Data System (ADS)

    Vallet, M.; Claveau, Y.; Warot-Fonrose, B.; Gatel, C.; Nicolai, J.; Combe, N.; Magen, C.; Teissier, R.; Baranov, A. N.; Ponchet, A.

    2016-05-01

    Spontaneously formed Al-As type interfaces of the InAs/AlSb system grown by molecular beam epitaxy for quantum cascade lasers were investigated by atomic resolution scanning transmission electron microscopy. Experimental strain profiles were compared to those coming from a model structure. High negative out-of-plane strains with the same order of magnitude as perfect Al-As interfaces were observed. The effects of the geometrical phase analysis used for strain determination were evidenced and discussed in the case of abrupt and huge variations of both atomic composition and bond length as observed in these interfaces. Intensity profiles performed on the same images confirmed that changes of chemical composition are the source of high strain fields at interfaces. The results show that spontaneously assembled interfaces are not perfect but extend over 2 or 3 monolayers.

  10. ALS-associated peripherin spliced transcripts form distinct protein inclusions that are neuroprotective against oxidative stress.

    PubMed

    McLean, Jesse R; Smith, Gaynor A; Rocha, Emily M; Osborn, Teresia M; Dib, Samar; Hayes, Melissa A; Beagan, Jonathan A; Brown, Tana B; Lawson, Tristan F S; Hallett, Penelope J; Robertson, Janice; Isacson, Ole

    2014-11-01

    Intracellular proteinaceous inclusions are well-documented hallmarks of the fatal motor neuron disorder amyotrophic lateral sclerosis (ALS). The pathological significance of these inclusions remains unknown. Peripherin, a type III intermediate filament protein, is upregulated in ALS and identified as a component within different types of ALS inclusions. The formation of these inclusions may be associated with abnormal peripherin splicing, whereby an increase in mRNA retaining introns 3 and 4 (Per-3,4) leads to the generation of an aggregation-prone isoform, Per-28. During the course of evaluating peripherin filament assembly in SW-13 cells, we identified that expression of both Per-3,4 and Per-28 transcripts formed inclusions with categorically distinct morphology: Per-3,4 was associated with cytoplasmic condensed/bundled filaments, small inclusions (<10μM), or large inclusions (≥10μM); while Per-28 was associated with punctate inclusions in the nucleus and/or cytoplasm. We found temporal and spatial changes in inclusion morphology between 12 and 48h post-transfected cells, which were accompanied by unique immunofluorescent and biochemical changes of other ALS-relevant proteins, including TDP-43 and ubiquitin. Despite mild cytotoxicity associated with peripherin transfection, Per-3,4 and Per-28 expression increased cell viability during H2O2-mediated oxidative stress in BE(2)-M17 neuroblastoma cells. Taken together, this study shows that ALS-associated peripherin isoforms form dynamic cytoplasmic and intranuclear inclusions, effect changes in local endogenous protein expression, and afford cytoprotection against oxidative stress. These findings may have important relevance to understanding the pathophysiological role of inclusions in ALS. PMID:24907400

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

    SciTech Connect

    Yasuda, H.Y.; Behgozin, A.; Umakoshi, Y.

    1998-12-18

    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.

  12. Influence of Pre-Heated Al 6061 Substrate Temperature on the Residual Stresses of Multipass Al Coatings Deposited by Cold Spray

    NASA Astrophysics Data System (ADS)

    Rech, Silvano; Trentin, Andrea; Vezzù, Simone; Legoux, Jean-Gabriel; Irissou, Eric; Guagliano, Mario

    2011-01-01

    In this work, the influence of the substrate temperature on the deposition efficiency, on the coating properties and residual stress was investigated. Pure Al coatings were deposited on Al 6061 alloy substrates using a CGT Kinetics 3000 cold spray system. The substrate temperature was in a range between 20 (room temperature) and 375 °C and was kept nearly constant during a given deposition while all the other deposition parameters were unchanged. The deposited coatings were quenched in water (within 1 min from the deposition) and then characterized. The residual stress was determined by Almen gage method, Modified Layer Removal Method, and XRD in order to identify both the mean coating stress and the stress profile through the coating thickness from the surface to the coating-substrate interface. The residual stress results obtained by these three methods were compared and discussed. The coating morphology and porosity were investigated using optical and scanning electron microscopy.

  13. High-performance Ni3Al synthesized from composite powders

    NASA Astrophysics Data System (ADS)

    Chiou, Wen-Chih; Hu, Chen-Ti

    1994-05-01

    Specimens of Ni3Al + B of high density (>99.3 Pct RD) and relatively large dimension have been synthesized from composite powders through processes of replacing plating and electroless Ni-B plating on Al powder, sintering, and thermal-mechanical treatment. The uniformly coated Ni layer over fine Al or Ni core particles constituting these coating/core composite powders has advantages such as better resistance to oxidation relative to pure Al powder, a greater green density as a compacted powder than prealloyed powder, the possibility of atomically added B to the material by careful choice of a suitable plating solution, and avoidance of the expensive powder metallurgy (PM) equipment such as a hot isostatic press (HIP), hot press (HP), etc. The final Ni3Al + B product is made from Ni-B-Al and Ni-B-Ni mixed composite powders by means of traditional PM processes such as compacting, sintering, rolling, and annealing, and therefore, the dimensions of the product are not constrained by the capacity of an HIP or HP. The properties of Ni3Al composite powder metallurgy (CPM) specimens tested at room temperature have been obtained, and comparison with previous reports is conducted. A tensile elongation of about 16 Pct at room temperature was attained.

  14. Ni-Al2O3 and Ni-Al composite high-aspect-ratio microstructures

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Sorrell, Melford; Kelly, Kevin W.; Ma, Evan

    1998-09-01

    High-aspect-ratio microstructures (HARMs) have a variety of potential applications in heat transfer, fluid mechanics, catalysts and other microelectromechanical systems (MEMS). The aim of this work is to demonstrate the feasibility to fabricate high performance particulate metal-matrix composite and intermetallic micromechanical structures using the LIGA process. Well-defined functionally graded Ni-Al2O3 and Ni-Al high-aspect-ratio microposts were electroformed into lithographically patterned PMMA holes from a nickel sulfamate bath containing submicron alumina and a diluted Watts bath containing microsized aluminum particles, respectively. SEM image analysis showed that the volume fraction of the alumina reached up to around 30% in the Ni-Al2O3 deposit. The Vickers microhardness of these composites is in the range of 418 through 545, which is higher than those of nickel microstructures from a similar particle-free bath and other Ni-based electrodeposits. In the work on Ni-Al electroplating, a newly developed diluted Watts bath was used to codeposit micron-sized aluminum particles. The intermetallic compound Ni3Al was formed by the reaction of nickel matrices and aluminum particles through subsequent annealing at 630 degrees Celsius. WDS and XRD analyses confirmed that the annealed coating is a two-phase (Ni-Ni3Al) composite. The maximum aluminum volume fraction reached 19% at a cathode current density of 12 mA cm-2, and the Vickers microhardness of the as-deposited coatings is in the range 392 - 515 depending on the amount of aluminum incorporated.

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

    NASA Astrophysics Data System (ADS)

    Yao, Junqi; He, Yedong; Wang, Deren

    2013-03-01

    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 1000°C 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.

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

    SciTech Connect

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

    1995-09-28

    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.

  17. ZERODUR® glass ceramics for high stress applications

    NASA Astrophysics Data System (ADS)

    Hartmann, Peter; Nattermann, Kurt; Döhring, Thorsten; Jedamzik, Ralf; Kuhr, Markus; Thomas, Peter; Kling, Guenther; Lucarelli, Stefano

    2009-08-01

    Recently SCHOTT has shown in a series of investigations the suitability of the zero expansion glass ceramic material ZERODUR® for applications like mirrors and support structures of complicated design used at high mechanical loads. Examples are vibrations during rocket launches, bonded elements to support single mirrors or mirrors of a large array, or controlled deformations for optical image correction, i.e. adaptive mirrors. Additional measurements have been performed on the behavior of ZERODUR® with respect to the etching process, which is capable of increasing strength significantly. It has been determined, which minimum layer thickness has to be removed in order to achieve the strength increase reliably. New data for the strength of the material variant ZERODUR K20® prepared with a diamond grain tool D151 are available and compared with the data of ZERODUR® specimens prepared in the same way. Data for the stress corrosion coefficient n of ZERODUR® for dry and normal humid environment have been measured already in the 1980s. It has been remeasured with the alternative double cleavage drilled compression (DCDC) method.

  18. Effect of sputtering pressure on crystalline quality and residual stress of AlN films deposited at 823 K on nitrided sapphire substrates by pulsed DC reactive sputtering

    NASA Astrophysics Data System (ADS)

    Ohtsuka, Makoto; Takeuchi, Hiroto; Fukuyama, Hiroyuki

    2016-05-01

    Aluminum nitride (AlN) is a promising material for use in applications such as deep-ultraviolet light-emitting diodes (UV-LEDs) and surface acoustic wave (SAW) devices. In the present study, the effect of sputtering pressure on the surface morphology, crystalline quality, and residual stress of AlN films deposited at 823 K on nitrided a-plane sapphire substrates, which have high-crystalline-quality c-plane AlN thin layers, by pulsed DC reactive sputtering was investigated. The c-axis-oriented AlN films were homoepitaxially grown on nitrided sapphire substrates at sputtering pressures of 0.4–1.5 Pa. Surface damage of the AlN sputtered films increased with increasing sputtering pressure because of arcing (abnormal electrical discharge) during sputtering. The sputtering pressure affected the crystalline quality and residual stress of AlN sputtered films because of a change in the number and energy of Ar+ ions and Al sputtered atoms. The crystalline quality of AlN films was improved by deposition with lower sputtering pressure.

  19. Oxide growth stress measurements and relaxation mechanisms for alumina scales grown on FeCrAlY: Oxide growth stress measurements and relaxation mechanisms

    SciTech Connect

    Tortorelli, P. F.; Specht, E. D.; More, K. L.; Hou, P. Y.

    2012-08-08

    Early-stage tensile stress evolution in α-Al2O3 scales during oxidation of FeCrAlY at 1000, 1050, 1100, and 1200 °C was monitored in situ by use of synchrotron radiation. Tensile stress development as a function of oxidation temperature indicated a dynamic interplay between stress generation and relaxation. An analysis of the time dependence of the data indicated that the observed relaxation of the initial tensile stress in the oxide scales at 1100 and 1200°C is dominated by creep in the α-Al2O3. A thin layer of a (Fe,Cr,Al) oxide was observed at the oxide-gas interface, consistent with a mechanism whereby the conversion of (Fe,Cr,Al)2O3 to α-Al2O3 produces an initial tensile stress in the alumina scale.

  20. Coping with the Stress of High Stakes Testing

    ERIC Educational Resources Information Center

    Kruger, Louis J.; Wandle, Caroline; Struzziero, Joan

    2007-01-01

    High stakes testing puts considerable pressure on schools, teachers, and students to achieve at high levels. Therefore, how schools and individuals cope with this major source of stress may have important implications for the success of high stakes testing. This article reviews relevant theory and research on stress as they relate to public…

  1. ALS Patient Stem Cells for Unveiling Disease Signatures of Motoneuron Susceptibility: Perspectives on the Deadly Mitochondria, ER Stress and Calcium Triad

    PubMed Central

    Kaus, Anjoscha; Sareen, Dhruv

    2015-01-01

    Amyotrophic lateral sclerosis (ALS) is a largely sporadic progressive neurodegenerative disease affecting upper and lower motoneurons (MNs) whose specific etiology is incompletely understood. Mutations in superoxide dismutase-1 (SOD1), TAR DNA-binding protein 43 (TARDBP/TDP-43) and C9orf72, have been identified in subsets of familial and sporadic patients. Key associated molecular and neuropathological features include ubiquitinated TDP-43 inclusions, stress granules, aggregated dipeptide proteins from mutant C9orf72 transcripts, altered mitochondrial ultrastructure, dysregulated calcium homeostasis, oxidative and endoplasmic reticulum (ER) stress, and an unfolded protein response (UPR). Such impairments have been documented in ALS animal models; however, whether these mechanisms are initiating factors or later consequential events leading to MN vulnerability in ALS patients is debatable. Human induced pluripotent stem cells (iPSCs) are a valuable tool that could resolve this “chicken or egg” causality dilemma. Relevant systems for probing pathophysiologically affected cells from large numbers of ALS patients and discovering phenotypic disease signatures of early MN susceptibility are described. Performing unbiased ‘OMICS and high-throughput screening in relevant neural cells from a cohort of ALS patient iPSCs, and rescuing mitochondrial and ER stress impairments, can identify targeted therapeutics for increasing MN longevity in ALS. PMID:26635528

  2. Ab initio local energy and local stress: application to tilt and twist grain boundaries in Cu and Al.

    PubMed

    Wang, Hao; Kohyama, Masanori; Tanaka, Shingo; Shiihara, Yoshinori

    2013-07-31

    The energy-density and stress-density schemes (Shiihara et al 2010 Phys. Rev. B 81 075441) within the projector augmented wave (PAW) method based on the generalized gradient approximation (GGA) have been applied to tilt and twist grain boundaries (GBs) and single vacancies in Cu and Al. Local energy and local stress at GBs and defects are obtained by integrating the energy and stress densities in each local region by the Bader integration using a recent algorithm (Yu et al 2011 J. Chem. Phys. 134 064111) as well as by the layer-by-layer integration so as to settle the gauge-dependent problem in the kinetic terms. Results are compared with those by the fuzzy-Voronoi integration and by the embedded atom method (EAM). The features of local energy and local stress at GBs and vacancies depend on the bonding nature of each material. Valence electrons in Al mainly located in the interatomic regions show remarkable response to structural disorder as significant valence charge redistribution or bond reconstruction, often leading to long-range variations of charges, energies and stresses, quite differently from d electrons in Cu mainly located near nuclei. All these features can be well represented by our local energy and local stress. The EAM potential for Al does not reproduce correct local energy or local stress, while the EAM potential for Cu provides satisfactory results. PMID:23835349

  3. Spherical nanoindentation stress-strain curves of commercially pure titanium and Ti-6Al-4V

    DOE Data Explorer

    Weaver, Jordan S. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Priddy, Matthew W. [Georgia Inst. of Technology, Atlanta, GA (United States); McDowell, David L. [Georgia Inst. of Technology, Atlanta, GA (United States); Kalidindi, Surya R. [Georgia Inst. of Technology, Atlanta, GA (United States)

    2016-07-27

    Spherical nanoindentation combined with electron back-scattered diffraction was employed to characterize the grain-scale elastic and plastic anisotropy of single crystal alpha-Ti for commercially pure (CP-Ti) and alloyed (Ti-64) titanium. In addition, alpha-beta Ti (single colony) grains were characterized. The data set includes the nanoindentation force, displacement, and contact stiffness, the nanoindentation stress-strain analysis, and the alpha-Ti crystal orientations. Details of the samples and experimental protocols can be found in Weaver et al. (2016) Acta Materialia doi:10.1016/j.actamat.2016.06.053.

  4. Thermal residual stresses and their toughening effect in Al{sub 2}O{sub 3} platelet reinforced glass

    SciTech Connect

    Todd, R.I.; Sinclair, R.; Yallee, R.B.; Young, R.J.; Boccaccini, A.R.

    1999-09-08

    Fluorescence spectroscopy has been used to measure the thermal residual stresses in Al{sub 2}O{sub 3}-platelet/borosilicate glass composites. Tensile residual stresses were found in the platelets, implying the presence of compressive residual stresses in the glass matrix. Measurements of stresses in the bulk of the composite could be obtained using fluorescence from platelets below the specimen surface. The measured stresses lay between the predictions of models for spherical particles and thin platelets, but were closer to the former for the range of platelet contents investigated (5--30 vol.%). Estimates of the increase in toughness associated with the compressive residual stresses in the matrix suggest that this mechanism makes a significant contribution to the toughening effect of the Al{sub 2}O{sub 3} platelets.

  5. τ-MnAl with high coercivity and saturation magnetization

    SciTech Connect

    Wei, J. Z.; Song, Z. G.; Yang, Y. B.; Liu, S. Q.; Du, H. L.; Han, J. Z.; Zhou, D.; Wang, C. S.; Yang, Y. C.; Franz, A.; Többens, D.; Yang, J. B.

    2014-12-15

    In this paper, high purity τ-Mn{sub 54}Al{sub 46} and Mn{sub 54−x}Al{sub 46}C{sub x}alloys were successfully prepared using conventional arc-melting, melt-spinning, and heat treatment process. The magnetic and the structural properties were examined using x-ray diffraction (XRD), powder neutron diffraction and magnetic measurements. A room temperature saturation magnetization of 650.5 kAm{sup -1}, coercivity of 0.5 T, and a maximum energy product of (BH){sub max} = 24.7 kJm{sup -3} were achieved for the pure Mn{sub 54}Al{sub 46} powders without carbon doping. The carbon substituted Mn{sub 54−x}Al{sub 46}C{sub x}, however, reveals a lower Curie temperature but similar saturation magnetization as compared to the carbon-free sample. The electronic structure of MnAl shows that the Mn atom possesses a magnetic moment of 2.454 μ{sub B} which results from strong hybridization between Mn-Al and Mn-Mn. We also investigated the volume and c/a ratio dependence of the magnetic moments of Mn and Al. The results indicate that an increase in the intra-atomic exchange splitting due to the cell volume expansion, leads to a large magnetic moment for the Mn atom. The Mn magnetic moment can reach a value of 2.9 μ{sub B} at a volume expansion rate of ΔV/V ≈ 20%.

  6. Interfacial coherency stress distribution in TiN/AlN bilayer and multilayer films studied by FEM analysis

    PubMed Central

    Chawla, Vipin; Holec, David; Mayrhofer, Paul H.

    2012-01-01

    The development of interfacial coherency stresses in TiN/AlN bilayer and multilayer films was investigated by finite element method (ABAQUS) using the four-node bilinear quadrilateral axisymmetric element CAX4R. The TiN and AlN layers are always in compression and tension at the interface, respectively, as may be expected from the fact TiN has larger lattice parameter than AlN. Both, the bi-layer and the multilayer stacks bend due to the coherency stresses. For the TiN/AlN bilayer system, the curvature of the bending is largest for the TiN/AlN thickness ratios ∼0.5 and ∼2 (at which one of the two layers is fully in compression or tension), while it is smaller for the layers with the same thickness (at which both layers posses regions with compressive as well as tensile stresses). This stress distribution over the bi-layer thickness is shown to be strongly influenced by the presence and the properties of a substrate. Furthermore, the coherency stress profile and specimen curvature of a TiN/AlN multilayer system was studied as a function of the top-most layer thickness. The curvature is maximum for equal number of TiN and AlN layers, and decreases with increasing the number of TiN/AlN periods. Within the growth of an additional TiN/AlN bilayer, the curvature first decreases to zero for a vertically symmetrical geometry over the layers when the TiN layer growth is finished (e.g. for (n + 1) layers of TiN and n layers of AlN). At this stage, the coherency stresses in TiN and AlN are same in each layer type (independent on the layer position). The growth of the second half of the TiN/AlN bi-layer (i.e. the AlN) to finish the period, again bends the specimen, and generates a non-uniform stress distribution. This suggests that the top layer as well as the overall specimen geometry plays a critical role on the actual coherency stress profile.

  7. Relation between surface slip topography and stress corrosion cracking in Ti-8 wt % Al

    NASA Technical Reports Server (NTRS)

    Boyd, J. D.; Hoagland, R. G.

    1974-01-01

    The deformation behavior of Ti-8 wt % Al has been investigated in an inert environment (air), and an aggressive environment (salt water). Details of surface slip geometry were examined by high resolution surface replicas at various stages of deformation in both environments. Specimens aged to contain a fine dispersion of Ti3Al precipitates failed by subcritical crack growth in salt water, whereas specimens in the single phase condition showed no effects of environment on the yield or fracture characteristics. The Ti3Al precipitates produce little change in strength level or slip character compared to the single phase alloy, and there is no evidence of any effects of environment on the character of surface slip. Rather, the presence of trenches along slip bands on the surface of aged specimens suggest that the specific effect of the Ti3Al precipitates is to render the surface slip steps chemically active relative to the surrounding matrix by slip induced dissolution of the particles.

  8. Thermal stress in high temperature cylindrical fasteners

    NASA Technical Reports Server (NTRS)

    Blosser, Max L.

    1988-01-01

    Uninsulated structures fabricated from carbon or silicon-based materials, which are allowed to become hot during flight, are attractive for the design of some components of hypersonic vehicles. They have the potential to reduce weight and increase vehicle efficiency. Because of manufacturing contraints, these structures will consist of parts which must be fastened together. The thermal expansion mismatch between conventional metal fasteners and carbon or silicon-based structural materials may make it difficult to design a structural joint which is tight over the operational temperature range without exceeding allowable stress limits. In this study, algebraic, closed-form solutions for calculating the thermal stresses resulting from radial thermal expansion mismatch around a cylindrical fastener are developed. These solutions permit a designer to quickly evaluate many combinations of materials for the fastener and the structure. Using the algebraic equations developed, material properties and joint geometry were varied to determine their effect on thermal stresses. Finite element analyses were used to verify that the closed-form solutions derived give the correct thermal stress distribution around a cylindrical fastener and to investigate the effect of some of the simplifying assumptions made in developing the closed-form solutions for thermal stresses.

  9. [Clinical trials of ultra-high-dose methylcobalamin in ALS].

    PubMed

    Izumi, Yuishin; Kaji, Ryuji

    2007-10-01

    Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder affecting both upper and lower motor neurons. Weakness may begin in the legs, hands, proximal arms, or pharynx. The course is relentless and progressive without remissions, relapses, or even stable plateaus. There is no effective drug therapy for ALS, although riluzole has been shown to prolong life in sufferers, without tracheostomy. A vitamin B12 analog, methylcobalamin, has a protective effect on cultured cortical neurons against glutamate-induced cytotoxicity. We have shown the ultra-high-dose methylcobalamin (25 mg/day i.m.) slows down the progressive reduction of the CMAP (compound muscle action potential) amplitudes in ALS in the short term (4 weeks). The latencies of SSR (sympathetic skin response) were shorter after treatment (50 mg/day i.v., 2 weeks). In the long-term effect of methylcobalamin (50 mg/day i.m., twice a week), the survival time (or the period to become respirator-bound) was significantly longer in the treated group than in the untreated. Larger-scale randomized double blind trial was started in Japan in order to evaluate the long-term efficacy and the safety of ultra-high-dose methylcobalamin for sporadic or familial cases of ALS. PMID:17969354

  10. Nanotopography and Surface Stress Analysis of Ti6Al4V Bioimplant: An Alternative Design for Stability

    NASA Astrophysics Data System (ADS)

    Patel, Sweetu; Solitro, Giovanni Francesco; Sukotjo, Cortino; Takoudis, Christos; Mathew, Mathew T.; Amirouche, Farid; Shokuhfar, Tolou

    2015-11-01

    The mechanical stability of biomedical Ti6Al4V rods with vertically aligned nanotubes structure formed on their surface has yet to be fully tested during insertion into the bone. The surface of rods impacted during insertion into a bone makes shear contact with bone, generating an interfacial stress. This stress plays an important role in osseointegration and may contribute to loosening between the bone and the implant during surgery. In the current study, the mechanical stability of various Ti6Al4V surfaces, including machined (M), rough (R), machined-anodized (MA), and rough-anodized (RA) surfaces, were tested and fully analyzed during insertion and pullout test into a simulant bone with densities 15 and 20 pounds per cubic foot (pcf). Our initial results from the field emission scanning electron microscopy images taken before and after insertion reveal that titania nanotubes remained stable and maintained their structural integrity during the insertion and pullout Instron test. Furthermore, from the interfacial stress calculation during the insertion, it was observed that compared with nonanodized rods, a higher force was required to insert the anodized rods. The interfacial stress generated during the insertion of anodized rods was 1.03 ± 0.11 MPa for MA and 1.10 ± 0.36 MPa for RA, which is significantly higher ( p < 0.05) than nonanodized rods with 0.36 ± 0.07 MPa for M and 0.36 ± 0.08 MPa for R in simulant bone with density of 15 pcf. Similar behavior was also observed in 20 pcf simulant bone. Energy dissipated during anodized rod insertion (i.e., MA = 1.3 ± 0.04 Nm and RA = 1.23 ± 0.24 Nm) was not significantly different than nonanodized rod insertion (i.e., M = 0.9 ± 0.05 Nm and R = 1.04 ± 0.04 Nm) into 15 pcf simulant bone. The high stress during insertion of anodized rods suggests that the nanotubes on the surface can cause gripping and high friction on the radial side, resisting the counter motion of the bone. The latter may play a beneficial

  11. Strength of VGCF/Al Composites for High Thermal Conductivity

    NASA Astrophysics Data System (ADS)

    Fukuchi, Kohei; Sasaki, Katsuhiko; Imanishi, Terumitsu; Katagiri, Kazuaki; Kakitsuji, Atsushi; Shimizu, Akiyuki

    In this paper, the evaluation of the strength of the VGCF/Aluminum composites which have high thermal conductivity is reported. VGCF (Vapor Growth Carbon Fiber) is a kind of the Carbon nanotube (CNT) which has very high thermal conductivity as well as CNT. The composites are made by spark plasma sintering. The stress-strain curves of the composites are obtained by the tensile tests and show that the composites have brittle behavior. The brittleness of the composites increases with increase in the volume fraction of VGCF. A numerical simulation based on the micromechanics is conducted to estimate nonlinear behavior in the elastic deformation and plastic deformation of the stress-strain relations of the composites. The theories of Eshelby, Mori-Tanaka, Weibull, and Ramberg-Osgood are employed for the numerical simulation. The simulations give some information of the microstructural change in the composite related to the volume fraction of VGCF.

  12. Low-stress and high-stress singing have contrasting effects on glucocorticoid response.

    PubMed

    Fancourt, Daisy; Aufegger, Lisa; Williamon, Aaron

    2015-01-01

    Performing music in public is widely recognized as a potentially stress-inducing activity. However, despite the interest in music performance as an acute psychosocial stressor, there has been relatively little research on the effects of public performance on the endocrine system. This study examined the impact of singing in a low-stress performance situation and a high-stress live concert on levels of glucocorticoids (cortisol and cortisone) in 15 professional singers. The results showed a significant decrease in both cortisol and cortisone across the low-stress condition, suggesting that singing in itself is a stress-reducing (and possibly health-promoting) activity, but significant increases across the high-stress condition. This is the first study to demonstrate that singing affects cortisol as well as cortisone responses and that these responses are modulated by the conditions of performance. PMID:26388794

  13. Low-stress and high-stress singing have contrasting effects on glucocorticoid response

    PubMed Central

    Fancourt, Daisy; Aufegger, Lisa; Williamon, Aaron

    2015-01-01

    Performing music in public is widely recognized as a potentially stress-inducing activity. However, despite the interest in music performance as an acute psychosocial stressor, there has been relatively little research on the effects of public performance on the endocrine system. This study examined the impact of singing in a low-stress performance situation and a high-stress live concert on levels of glucocorticoids (cortisol and cortisone) in 15 professional singers. The results showed a significant decrease in both cortisol and cortisone across the low-stress condition, suggesting that singing in itself is a stress-reducing (and possibly health-promoting) activity, but significant increases across the high-stress condition. This is the first study to demonstrate that singing affects cortisol as well as cortisone responses and that these responses are modulated by the conditions of performance. PMID:26388794

  14. Degradation mechanism of enhancement-mode AlGaN/GaN HEMTs using fluorine ion implantation under the on-state gate overdrive stress

    NASA Astrophysics Data System (ADS)

    Sun, Wei-Wei; Zheng, Xue-Feng; Fan, Shuang; Wang, Chong; Du, Ming; Zhang, Kai; Chen, Wei-Wei; Cao, Yan-Rong; Mao, Wei; Ma, Xiao-Hua; Zhang, Jin-Cheng; Hao, Yue

    2015-01-01

    The degradation mechanism of enhancement-mode AlGaN/GaN high electron mobility transistors (HEMTs) fabricated by fluorine plasma ion implantation technology is one major concern of HEMT’s reliability. It is observed that the threshold voltage shows a significant negative shift during the typical long-term on-state gate overdrive stress. The degradation does not originate from the presence of as-grown traps in the AlGaN barrier layer or the generated traps during fluorine ion implantation process. By comparing the relationships between the shift of threshold voltage and the cumulative injected electrons under different stress conditions, a good agreement is observed. It provides direct experimental evidence to support the impact ionization physical model, in which the degradation of E-mode HEMTs under gate overdrive stress can be explained by the ionization of fluorine ions in the AlGaN barrier layer by electrons injected from 2DEG channel. Furthermore, our results show that there are few new traps generated in the AlGaN barrier layer during the gate overdrive stress, and the ionized fluorine ions cannot recapture the electrons. Project supported by the National Natural Science Foundation of China (Grant Nos. 61334002, 61106106, and 61474091), the Opening Project of Science and Techology on Reliability Physics and Application Technology of Electronic Component Laboratory (Grant No. ZHD201206), the New Experiment Development Funds for Xidian University, China (Grant No. SY1213), and the Scientific Research Foundation for the Returned Overseas Chinese Scholars.

  15. NiAl-base composite containing high volume fraction of AlN for advanced engines

    NASA Technical Reports Server (NTRS)

    Hebsur, Mohan (Inventor); Whittenbeger, John D. (Inventor); Lowell, Carl F. (Inventor)

    1994-01-01

    A particulate reinforced NiAl-AlN composite alloy has a NiAl matrix and greater than about 13 volume percent fine particles of AlN within the matrix. The particles preferably have a diameter from about 15 nanometers to about 50 nanometers. The particulate reinforced NiAl-AlN composite alloy may be prepared by cryomilling prealloyed NiAl in liquid nitrogen using grinding media having a diameter of from about 2 to 6 mm at an impeller speed of from about 450 RPM to about 800 RPM. The cryomilling may be done for a duration of from about 4 hours to about 20 hours to obtain a cryomilled powder. The cryomilled powder may be consolidated to form the particulate reinforced NiAl-AlN composite alloy. The particulate reinforced alloy can further include a toughening alloy. The toughening alloy may include NiCrAlY, FeCrAlY, and FeAl.

  16. High activity of the stress promoter contributes to susceptibility to stress in the tree shrew.

    PubMed

    Fang, Hui; Sun, Yun-Jun; Lv, Yan-Hong; Ni, Rong-Jun; Shu, Yu-Mian; Feng, Xiu-Yu; Wang, Yu; Shan, Qing-Hong; Zu, Ya-Nan; Zhou, Jiang-Ning

    2016-01-01

    Stress is increasingly present in everyday life in our fast-paced society and involved in the pathogenesis of many psychiatric diseases. Corticotrophin-releasing-hormone (CRH) plays a pivotal role in regulating the stress responses. The tree shrews are highly vulnerable to stress which makes them the promising animal models for studying stress responses. However, the mechanisms underlying their high stress-susceptibility remained unknown. Here we confirmed that cortisol was the dominate corticosteroid in tree shrew and was significantly increased after acute stress. Our study showed that the function of tree shrew CRH - hypothalamic-pituitary-adrenal (HPA) axis was nearly identical to human that contributed little to their hyper-responsiveness to stress. Using CRH transcriptional regulation analysis we discovered a peculiar active glucocorticoid receptor response element (aGRE) site within the tree shrew CRH promoter, which continued to recruit co-activators including SRC-1 (steroid receptor co-activator-1) to promote CRH transcription under basal or forskolin/dexamethasone treatment conditions. Basal CRH mRNA increased when the aGRE was knocked into the CRH promoter in human HeLa cells using CAS9/CRISPR. The aGRE functioned critically to form the "Stress promoter" that contributed to the higher CRH expression and susceptibility to stress. These findings implicated novel molecular bases of the stress-related diseases in specific populations. PMID:27125313

  17. High activity of the stress promoter contributes to susceptibility to stress in the tree shrew

    PubMed Central

    Fang, Hui; Sun, Yun-Jun; Lv, Yan-Hong; Ni, Rong-Jun; Shu, Yu-Mian; Feng, Xiu-Yu; Wang, Yu; Shan, Qing-Hong; Zu, Ya-Nan; Zhou, Jiang-Ning

    2016-01-01

    Stress is increasingly present in everyday life in our fast-paced society and involved in the pathogenesis of many psychiatric diseases. Corticotrophin-releasing-hormone (CRH) plays a pivotal role in regulating the stress responses. The tree shrews are highly vulnerable to stress which makes them the promising animal models for studying stress responses. However, the mechanisms underlying their high stress-susceptibility remained unknown. Here we confirmed that cortisol was the dominate corticosteroid in tree shrew and was significantly increased after acute stress. Our study showed that the function of tree shrew CRH - hypothalamic-pituitary-adrenal (HPA) axis was nearly identical to human that contributed little to their hyper-responsiveness to stress. Using CRH transcriptional regulation analysis we discovered a peculiar active glucocorticoid receptor response element (aGRE) site within the tree shrew CRH promoter, which continued to recruit co-activators including SRC-1 (steroid receptor co-activator-1) to promote CRH transcription under basal or forskolin/dexamethasone treatment conditions. Basal CRH mRNA increased when the aGRE was knocked into the CRH promoter in human HeLa cells using CAS9/CRISPR. The aGRE functioned critically to form the “Stress promoter” that contributed to the higher CRH expression and susceptibility to stress. These findings implicated novel molecular bases of the stress-related diseases in specific populations. PMID:27125313

  18. High temperature, oxidation resistant noble metal-Al alloy thermocouple

    NASA Technical Reports Server (NTRS)

    Smialek, James L. (Inventor); Gedwill, Michael G. (Inventor)

    1994-01-01

    A thermocouple is disclosed. The thermocouple is comprised of an electropositive leg formed of a noble metal-Al alloy and an electronegative leg electrically joined to form a thermocouple junction. The thermocouple provides for accurate and reproducible measurement of high temperatures (600 - 1300 C) in inert, oxidizing or reducing environments, gases, or vacuum. Furthermore, the thermocouple circumvents the need for expensive, strategic precious metals such as rhodium as a constituent component. Selective oxidation of rhodium is also thereby precluded.

  19. Energy dissipation of highly charged ions on Al oxide films.

    PubMed

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

    2010-03-01

    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 Xe(q +) 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. PMID:21389384

  20. Energy dissipation of highly charged ions on Al oxide films

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

    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.

  1. ALS-like skin changes in mice on a chronic low-Ca/Mg high-Al diet.

    PubMed

    Kihira, Tameko; Yoshida, Sohei; Kondo, Tomoyoshi; Yase, Yoshiro; Ono, Seiitsu

    2004-04-15

    Epidemiologic studies of endemic foci of amyotrophic lateral sclerosis (ALS) have shown low concentrations of Ca/Mg and high concentrations of Al/Mn in the drinking water and garden soil, which may play a causative role in the pathogenesis of endemic ALS. We studied the effects of chronic exposure to a low-Ca/Mg high-Al maltol diet on the skin of experimental animals. In ALS patients, atrophy of the epidermis, edematous changes with separated collagen fibrils and an accumulation of amorphous materials between collagen bundles were regarded as pathognomonic skin changes of ALS. Mice chronically fed a low-Ca/Mg high-Al maltol diet showed neuronal degeneration and loss in the spinal cords and cerebral cortices, as well as skin changes including atrophy, separation of collagen fibrils and accumulation of amorphous materials, similar to the skin changes characteristic of ALS. This is the first report of skin changes in animal models similar to those of ALS. We speculate that environmental factors such as chronic low-Ca/Mg high-Al condition play some causative role in the pathogenesis of Kii-ALS. PMID:15050431

  2. Characterization of Al2O3-HfO2-Al2O3 sandwiched MIM capacitor under DC and AC stresses

    NASA Astrophysics Data System (ADS)

    Kwak, Ho-Young; Kwon, Hyuk-Min; Jung, Yi-Jung; Kwon, Sung-Kyu; Jang, Jae-Hyung; Choi, Woon-Il; Ha, Man-Lyun; Lee, Ju-Il; Lee, Song-Jae; Lee, Hi-Deok

    2013-01-01

    In this paper, electrical properties and reliability of high capacitance density Metal-Insulator-Metal (MIM) capacitor with sandwiched hafnium-based dielectric is analyzed using three kinds of voltage stress; constant voltage stress (CVS), unipolar voltage and bipolar voltage stresses. The fabricated MIM capacitor shows not only high capacitance density but also low leakage current density of about ˜10 nA/cm2 at room temperature and 1 V. The relative variation of capacitance (ΔC/C0) increases and the variation of voltage linearity (α/α0) gradually decreases with stress-time due to the charge trapping effect in the high-k dielectric. The relative variations of capacitance and voltage linearity show the greater change by the bipolar voltage stress than CVS and unipolar voltage stresses.

  3. Fracture in stress engineered, high density, thin film interconnects

    NASA Astrophysics Data System (ADS)

    Modi, Mitul Bharat

    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

  4. TEM and HRTEM study of influence of thermal cycles with stress on dynamic recrystallization in Ti46Al8Nb1B during creep.

    PubMed

    Xu, Ningan; Jiang, Hui; Wu, Xingfang

    2008-12-01

    Short-term tension creep and thermal cycles under compressive stress were performed on Ti46Al8Nb1B in order to explore the dynamic recrystallization (DRX) grains formed during the creep and the impact of thermal cycles under stress to the DRX. After 1600 times' thermal cycles from 300 degrees C to 800 degrees C under 300 MPa compressive stress, high density of ledges and thick ledges are found in the interfaces. Two kinds of moiré fringes, instead of 9R structure, can be found in the thick ledges. Ti46Al8Nb1B sample and another sample which was treated by thermal cycles with stress were crept under 300 MPa compressive stress at 800 degrees C. DRX grains are found in the interfaces in those samples. Those grains, formed at the ledges, have an orientation relationship of [101](gamma)//[011](gammaR), (1 1 1)(gamma)//(1 11 )(gammaR) with the matrix of gamma phases. Thermal cycles with stress could lead to more DRX grains during creep. PMID:18635364

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

    SciTech Connect

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

    2009-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

    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.

  7. Alleviating Stress in Parents of High-Risk Preterm Infants.

    ERIC Educational Resources Information Center

    Lowenthal, Barbara

    1989-01-01

    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)

  8. Evolution of Grain Boundary Precipitates in Al 7075 Upon Aging and Correlation with Stress Corrosion Cracking Behavior

    NASA Astrophysics Data System (ADS)

    Goswami, Ramasis; Lynch, Stanley; Holroyd, N. J. Henry; Knight, Steven P.; Holtz, Ronald L.

    2013-03-01

    Transmission electron microscopy (TEM) was employed to investigate the microchemistry and microstructure of grain boundary precipitates in Al 7075 aged at room temperature for several hours, at 393 K (120 °C) for 12 hours (under aged), at peak aged (T651) and over aged (T73) conditions. High resolution TEM analysis of precipitates at grain boundaries and fine probe energy dispersive spectrometry showed that the grain boundary precipitates at peak and over aged conditions are hexagonal η phase with stoichiometry Mg(Cu x Zn1- x )2. Considerable increase in Cu content in the grain boundary η in the over aged condition compared to the peak aged condition was observed. The average Cu content in the over aged condition was found to be 20 at. pct. The higher Cu content of the precipitate is associated with a lower stress corrosion cracking plateau velocity.

  9. Corrosion Fatigue of High-Strength Titanium Alloys Under Different Stress Gradients

    NASA Astrophysics Data System (ADS)

    Baragetti, Sergio; Villa, Francesco

    2015-05-01

    Ti-6Al-4V is the most widely used high strength-to-mass ratio titanium alloy for advanced engineering components. Its adoption in the aerospace, maritime, automotive, and biomedical sectors is encouraged when highly stressed components with severe fatigue loading are designed. The extents of its applications expose the alloy to several aggressive environments, which can compromise its brilliant mechanical characteristics, leading to potentially catastrophic failures. Ti-6Al-4V stress-corrosion cracking and corrosion-fatigue sensitivity has been known since the material testing for pressurized tanks for Apollo missions, although detailed investigations on the effects of harsh environment in terms of maximum stress reduction have been not carried out until recent times. In the current work, recent experimental results from the authors' research group are presented, quantifying the effects of aggressive environments on Ti-6Al-4V under fatigue loading in terms of maximum stress reduction. R = 0.1 axial fatigue results in laboratory air, 3.5 wt.% NaCl solution, and CH3OH methanol solution at different concentrations are obtained for mild notched specimens ( K t = 1.18) at 2e5 cycles. R = 0.1 tests are also conducted in laboratory air, inert environment, 3.5 wt.% NaCl solution for smooth, mild and sharp notched specimens, with K t ranging from 1 to 18.65, highlighting the environmental effects for the different load conditions induced by the specimen geometry.

  10. Microstructure quantification and correlation with flow stress of ultrafine grained commercially pure Al fabricated by equal channel angular pressing (ECAP)

    SciTech Connect

    Reihanian, M.; Ebrahimi, R.; Moshksar, M.M.; Terada, D.; Tsuji, N.

    2008-09-15

    Commercial purity Al was severely deformed by equal channel angular pressing (ECAP) up to eight passes using route B{sub C}. The deformation microstructure was characterized quantitatively by electron-backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The microstructural homogeneity was investigated by EBSD at various locations from center to surface of the samples on a longitudinal section parallel to the pressing direction. Structural parameters including mean boundary spacing, boundary misorientation angle and fraction of high angle grain boundaries were measured and characterized through the section of the ECAP samples. EBSD scans revealed a homogeneous ultrafine grained microstructure after 8 passes. The analysis showed that the fraction of high angle grain boundaries was more than 70% at most locations of the sample section. Also, an average boundary spacing of 380 nm was obtained by the linear intercept method. TEM analysis was used for more detailed characterization of the microstructure, such as low angle boundaries with misorientation angles smaller than 2 deg. Using the structural parameters-flow stress relationship, the flow stress was estimated based on the EBSD and TEM/Kikuchi-line analyses and compared with measured values.

  11. Effect of Nano-Al2O3 on the Toxicity and Oxidative Stress of Copper towards Scenedesmus obliquus

    PubMed Central

    Li, Xiaomin; Zhou, Suyang; Fan, Wenhong

    2016-01-01

    Nano-Al2O3 has been widely used in various industries; unfortunately, it can be released into the aquatic environment. Although nano-Al2O3 is believed to be of low toxicity, it can interact with other pollutants in water, such as heavy metals. However, the interactions between nano-Al2O3 and heavy metals as well as the effect of nano-Al2O3 on the toxicity of the metals have been rarely investigated. The current study investigated copper toxicity in the presence of nano-Al2O3 towards Scenedesmus obliquus. Superoxide dismutase activity and concentration of glutathione and malondialdehyde in cells were determined in order to quantify oxidative stress in this study. Results showed that the presence of nano-Al2O3 reduced the toxicity of Cu towards S. obliquus. The existence of nano-Al2O3 decreased the growth inhibition of S. obliquus. The accumulation of copper and the level of oxidative stress in algae were reduced in the presence of nano-Al2O3. Furthermore, lower copper accumulation was the main factor that mitigated copper toxicity with the addition of nano-Al2O3. The decreased copper uptake could be attributed to the adsorption of copper onto nanoparticles and the subsequent decrease of available copper in water. PMID:27294942

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

    PubMed

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

    2011-11-01

    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

  13. Effect of Laser Shock Peening on surface properties and residual stress of Al6061-T6

    NASA Astrophysics Data System (ADS)

    Salimianrizi, A.; Foroozmehr, E.; Badrossamay, M.; Farrokhpour, H.

    2016-02-01

    The purpose of this study is to investigate the effects of Laser Shock Peening (LSP) on Al 6061-T6. The confined LSP regime using Nd: YAG laser with 1200 mJ of energy per pulse and 8 ns of pulse width were applied. The treated specimens were evaluated by means of surface integrity with optical microscopy, scanning electron microscope, microhardness, surface roughness and induced residual stress using an X-ray diffraction method. Results showed that by the use of LSP, compressive residual stress could effectively be induced on the surface of treated material. It was also revealed that the hardened depth of the material, up to a maximum depth of 1875 μm, could be achieved due to work hardening and grain refinement. In addition, surface roughness measurements showed that the LSP could deteriorate surface quality depending on the LSP parameters. The influences of beam overlap rates, number of laser shots and scanning pattern on microhardness as well as surface roughness are discussed.

  14. The stress-corrosion behavior of Al-Li-Cu alloys: A comparison of test methods

    NASA Technical Reports Server (NTRS)

    Rizzo, P. P.; Galvin, R. P.; Nelson, H. G.

    1982-01-01

    Two powder metallurgy processed (Al-Li-Cu) alloys with and without Mg addition were studied in aqueous 3.5% NaCl solution during the alternate immersion testing of tuning fork specimens, slow crack growth tests using fracture mechanics specimens, and the slow strain rate testing of straining electrode specimens. Scanning electron microscopy and optical metallography were used to demonstrate the character of the interaction between the Al-Li-Cu alloys and the selected environment. Both alloys are susceptible to SC in an aqueous 3.5% NaCl solution under the right electrochemical and microstructural conditions. Each test method yields important information on the character of the SC behavior. Under all conditions investigated, second phase particles strung out in rows along the extrusion direction in the alloys were rapidly attacked, and played principal role in the SC process. With time, larger pits developed from these rows of smaller pits and under certain electrochemical conditions surface cracks initiated from the larger pits and contributed directly to the fracture process. Evidence to support slow crack growth was observed in both the slow strain rate tests and the sustained immersion tests of precracked fracture mechanics specimens. The possible role of H2 in the stress corrosion cracking process is suggested.

  15. Studies of deep level transient spectroscopy of DX centers in GaAlAs: Te under uniaxial stress

    SciTech Connect

    Li, Ming-Fu |; Yu, Y.P. |; Weber, E.R.; Haller, E.E. |; Hansen, W.L.; Bauser, E.

    1991-11-01

    DX centers in Al{sub 0.38}Ga{sub 0.62}As doped with Te have been studied by Deep Level Transient Spectroscopy (DLTS) as a function of uniaxial stress. No splitting nor broadening of the DLTS peaks were observed. However, the peak positions and heights depend on the stress and its directions. The results have been analyzed by comparison with existing models and hydrostatic pressure measurements.

  16. Calcium aluminate silicate Ca2Al2SiO7 single crystal applicable to piezoelectric sensors at high temperature

    NASA Astrophysics Data System (ADS)

    Takeda, Hiroaki; Hagiwara, Manabu; Noguchi, Hiroaki; Hoshina, Takuya; Takahashi, Tomoko; Kodama, Nobuhiro; Tsurumi, Takaaki

    2013-06-01

    Ca2Al2SiO7 (CAS) bulk single crystals were grown by the Czochralski method. Material constants of the crystal were determined over the driving temperature range of a typical combustion pressure sensor. The electrical resistivity at 800 °C was found to be of the order of 108 Ωcm. We constructed a measurement system for the direct piezoelectric effect at high temperature, and characterized the crystals in a simulated engine cylinder combustion environment. Output charge signal against applied stress was detected at 700 °C. These observations suggest that CAS crystals are superior candidate materials for high temperature for stress sensing.

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

    PubMed Central

    2010-01-01

    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 400°C 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 900°C. 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

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

    PubMed

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

    2010-01-01

    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 400°C 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 900°C. 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

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

    SciTech Connect

    Liu, L.; Xi, Y. Y.; Ren, F.; Pearton, S. J.; Laboutin, O.; Cao, Yu; Johnson, Wayne J.; Kravchenko, Ivan I

    2012-01-01

    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.

  20. Ultrafast Bulk Diffusion of AlHxin High-Entropy Dehydrogenation Intermediates of NaAlH4

    SciTech Connect

    Zhang, Feng; Wood, Brandon C; Wang, Yan; Wang, Cai-Zhuang; Ho, Kai-Ming; Chou, Mei-Yin

    2014-08-14

    Using first-principles molecular dynamics (FPMD) and total-energy calculations, we demonstrate low-barrier bulk diffusion of Al-bearing species in γ-NaAlH4, a recently proposed high-entropy polymorph of NaAlH4. For charged AlH4– and neutral AlH3 vacancies, the computed barriers for diffusion are <0.1 eV, and we directly observe the predicted diffusive pathways in FPMD simulations at picosecond time scales. In contrast, such diffusion in the α phase is inaccessible to FPMD, consistent with much higher barriers. The transport behavior of γ-NaAlH4, in addition to key dynamical and structural signatures, is consistent with experimental observations of high-mobility species, strongly supporting the idea that an intermediate transition from the α phase to a high-entropy polymorph facilitates the hydrogen-releasing decomposition of NaAlH4. Our results provide an answer to longstanding questions regarding the responsible agent for the experimentally observed efficient Al transport during dehydrogenation and suggest that mass transport and phase transformation kinetics are coupled. Implications for understanding the (de)hydrogenation of undoped and catalyzed NaAlH4 are discussed.

  1. Effect of Stress Ratio on the Fatigue Behavior of a Friction Stir Processed Cast Al-Si-Mg Alloy

    SciTech Connect

    Jana, Saumyadeep; Mishra, Rajiv S.; Baumann, John B.; Grant, Glenn J.

    2009-11-01

    The effect of friction stir processing (FSP) on the fatigue life of a cast Al-7Si-0.6Mg alloy at a stress ratio of R=0 was evaluated. Two types of specimen geometry were used for the FSPed condition, through-thickness processed and partial thickness processed. FSP enhanced the fatigue life by a factor of 15 for the through thickness processed samples at lower stress amplitudes. This is different from the FSP specimens tested at R=-1 and similar stress amplitudes where a 5 times improvement in fatigue life was observed. In light of these observations, various closure mechanisms were examined.

  2. NiAl alloys for high-temperature structural applications

    NASA Astrophysics Data System (ADS)

    Darolia, Ram

    1991-03-01

    If their properties can be improved, nickel aluminide alloys offer significant payoffs in gas turbine engine applications. For these materials, excellent progress has been made toward understanding their mechanical behavior as well as improving their low-temperature ductility and high-temperature strength. For example, recent work shows that room-temperature ductility can be improved dramatically by microalloying with iron, gallium or molybdenum. The next challenge is to develop an alloy which has the required balance of ductility, toughness and strength. Development of design and test methodologies for components made out of low-ductility, anisotropic materials will also be required. While significant challenges remain, the continuing developments suggest that the prognosis for using NiAl alloys as high-temperature structural materials is good.

  3. High-temperature mechanical behavior of B2 type IrAl doped with Ni

    SciTech Connect

    Chiba, A.; Ono, T.; Li, X.G.; Takahashi, S.

    1997-12-31

    Constant-velocity and constant-load compression tests have been conducted to examine the mechanical behavior of polycrystalline IrAl and Ir{sub 1{minus}x}Ni{sub x}Al at ambient and elevated temperatures. Although IrAl exhibits brittle fracture before or immediately after yielding below 1,073 K, steady-state deformation takes place at temperatures higher than 1,273 K. Ductility of Ir{sub 1{minus}x}Ni{sub x}Al is improved with increasing x. On the contrary, strength decreases with increasing x. IrAl exhibits the 0.2% flow stress of 1,200MPa at 1,073 K and 350 MPa at 1,473 K, about an order of magnitude higher than NiAl. Secondary creep of IrAl and Ir{sub 0.2}Ni{sub 0.8}Al (i.e., modified NiAl) exhibits class II and class I behavior respectively. Creep strength of binary IrAl and modified NiAl with Ir is about a magnitude of 4 higher than that of single-phase and multi-phase NiAl at a given applied stress.

  4. Alterations in stress granule dynamics driven by TDP-43 and FUS: a link to pathological inclusions in ALS?

    PubMed Central

    Aulas, Anaïs; Vande Velde, Christine

    2015-01-01

    Stress granules (SGs) are RNA-containing cytoplasmic foci formed in response to stress exposure. Since their discovery in 1999, over 120 proteins have been described to be localized to these structures (in 154 publications). Most of these components are RNA binding proteins (RBPs) or are involved in RNA metabolism and translation. SGs have been linked to several pathologies including inflammatory diseases, cancer, viral infection, and neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). In ALS and FTD, the majority of cases have no known etiology and exposure to external stress is frequently proposed as a contributor to either disease initiation or the rate of disease progression. Of note, both ALS and FTD are characterized by pathological inclusions, where some well-known SG markers localize with the ALS related proteins TDP-43 and FUS. We propose that TDP-43 and FUS serve as an interface between genetic susceptibility and environmental stress exposure in disease pathogenesis. Here, we will discuss the role of TDP-43 and FUS in SG dynamics and how disease-linked mutations affect this process. PMID:26557057

  5. Cryogenic Treatment of Al-Li Alloys for Improved Weldability, Repairability, and Reduction of Residual Stresses

    NASA Technical Reports Server (NTRS)

    Malone, Tina W.; Graham, Benny F.; Gentz, Steven J. (Technical Monitor)

    2001-01-01

    Service performance has shown that cryogenic treatment of some metals provides improved strength, fatigue life, and wear resistance to the processed material. Effects such as these were initially discovered by NASA engineers while evaluating spacecraft that had returned from the cold vacuum of space. Factors such as high cost, poor repairability, and poor machinability are currently prohibitive for wide range use of some aerospace aluminum alloys. Application of a cryogenic treatment process to these alloys is expected provide improvements in weldability and weld properties coupled with a reduction in repairs resulting in a significant reduction in the cost to manufacture and life cycle cost of aerospace hardware. The primary purpose of this effort was to evaluate the effects of deep cryogenic treatment of some aluminum alloy plate products, welds, and weld repairs, and optimize a process for the treatment of these materials. The optimized process is being evaluated for improvements in properties of plate and welds, improvements in weldability and repairability of treated materials, and as an alternative technique for the reduction of residual stresses in repaired welds. This paper will present the results of testing and evaluation conducted in this effort. These results will include assessments of changes in strength, toughness, stress corrosion susceptability, weldability, repairability, and reduction in residual stresses of repaired welds.

  6. Au-Free GaN High-Electron-Mobility Transistor with Ti/Al/W Ohmic and WN X Schottky Metal Structures for High-Power Applications

    NASA Astrophysics Data System (ADS)

    Hsieh, Ting-En; Lin, Yueh-Chin; Chu, Chung-Ming; Chuang, Yu-Lin; Huang, Yu-Xiang; Shi, Wang-Cheng; Dee, Chang-Fu; Majlis, Burhanuddin Yeop; Lee, Wei-I.; Chang, Edward Yi

    2016-04-01

    In this study, an Au-free AlGaN/GaN high-electron-mobility transistor (HEMT) with Ti/Al/W ohmic and WNx Schottky metal structures is fabricated and characterized. The device exhibits smooth surface morphology after metallization and shows excellent direct-current (DC) characteristics. The device also demonstrates better performance than the conventional HEMTs under high voltage stress. Furthermore, the Au-free AlGaN/GaN HEMT shows stable device performance after annealing at 400°C. Thus, the Ti/Al/W ohmic and WN X Schottky metals can be applied in the manufacturing of GaN HEMT to replace the Au based contacts to reduce the manufacturing costs of the GaN HEMT devices with comparable device performance.

  7. Au-Free GaN High-Electron-Mobility Transistor with Ti/Al/W Ohmic and WN X Schottky Metal Structures for High-Power Applications

    NASA Astrophysics Data System (ADS)

    Hsieh, Ting-En; Lin, Yueh-Chin; Chu, Chung-Ming; Chuang, Yu-Lin; Huang, Yu-Xiang; Shi, Wang-Cheng; Dee, Chang-Fu; Majlis, Burhanuddin Yeop; Lee, Wei-I.; Chang, Edward Yi

    2016-07-01

    In this study, an Au-free AlGaN/GaN high-electron-mobility transistor (HEMT) with Ti/Al/W ohmic and WN x Schottky metal structures is fabricated and characterized. The device exhibits smooth surface morphology after metallization and shows excellent direct-current (DC) characteristics. The device also demonstrates better performance than the conventional HEMTs under high voltage stress. Furthermore, the Au-free AlGaN/GaN HEMT shows stable device performance after annealing at 400°C. Thus, the Ti/Al/W ohmic and WN X Schottky metals can be applied in the manufacturing of GaN HEMT to replace the Au based contacts to reduce the manufacturing costs of the GaN HEMT devices with comparable device performance.

  8. High Temperature Mechanical Behavior of Ti-45Al-8Nb and Its Cavity Evolution in Deformation

    NASA Astrophysics Data System (ADS)

    Du, Zhihao; Zhang, Kaifeng; Jiang, Shaosong; Zhu, Ruican; Li, Shuguang

    2015-10-01

    The tensile property of a high Nb containing TiAl-based alloy (Ti-45Al-8Nb) was investigated in the temperature range of 900-1050 °C and strain rate range of 1 × 10-3 to 2.5 × 10-2 s-1. The results revealed that the yield stress decreased with increasing temperature and decreasing strain rate, while the tensile elongation increased with an increase in temperature and a decrease in strain rate. Hence, The minimum yield stress of 119.2 MPa and the maximum elongation of 237% were obtained at the temperature of 1050 °C and strain rate of 1 × 10-3 s-1. Based on the experimental data, the activation energy of the alloy was calculated to be 360 kJ/mol. Moreover, the microstructure and the fracture morphology of the specimens were observed, and the results revealed that the distribution of cavities was related to deformation parameters and the fracture mode was typically dimple-type.

  9. An AlN/Al0.85Ga0.15N high electron mobility transistor

    NASA Astrophysics Data System (ADS)

    Baca, Albert G.; Armstrong, Andrew M.; Allerman, Andrew A.; Douglas, Erica A.; Sanchez, Carlos A.; King, Michael P.; Coltrin, Michael E.; Fortune, Torben R.; Kaplar, Robert J.

    2016-07-01

    An AlN barrier high electron mobility transistor (HEMT) based on the AlN/Al0.85Ga0.15N heterostructure was grown, fabricated, and electrically characterized, thereby extending the range of Al composition and bandgap for AlGaN channel HEMTs. An etch and regrowth procedure was implemented for source and drain contact formation. A breakdown voltage of 810 V was achieved without a gate insulator or field plate. Excellent gate leakage characteristics enabled a high Ion/Ioff current ratio greater than 107 and an excellent subthreshold slope of 75 mV/decade. A large Schottky barrier height of 1.74 eV contributed to these results. The room temperature voltage-dependent 3-terminal off-state drain current was adequately modeled with Frenkel-Poole emission.

  10. The Effect of Ballistic Impacts on the High Cycle Fatigue Properties of Ti-48Al-2Nb-2Cr (at.%)

    NASA Technical Reports Server (NTRS)

    Draper, S. L.; Lerch, B. A.; Pereira, J. M.; Nathal, M. V.; Austin, C. M.; Erdman, O.

    2000-01-01

    The ability of gamma - TiAl to withstand potential foreign and/or domestic object damage is a technical risk to the implementation of gamma - TiAl in low pressure turbine (LPT) blade applications. The overall purpose of the present study was to determine the influence of ballistic impact damage on the high cycle fatigue strength of gamma - TiAl simulated LPT blades. Impact and specimen variables included ballistic impact energy, projectile hardness, impact temperature, impact location, and leading edge thickness. The level of damage induced by the ballistic impacting was studied and quantified on both the impact (front) and backside of the specimens. Multiple linear regression was used to model the cracking and fatigue response as a function of the impact variables. Of the impact variables studied, impact energy had the largest influence on the response of gamma - TiAl to ballistic impacting. Backside crack length was the best predictor of remnant fatigue strength for low energy impacts (<0.74J) whereas Hertzian crack length (impact side damage) was the best predictor for higher energy impacts. The impacted gamma - TiAl samples displayed a classical mean stress dependence on the fatigue strength. For the fatigue design stresses of a 6th stage LPT blade in a GE90 engine, a Ti-48Al-2Nb-2Cr LPT blade would survive an impact of normal service conditions.

  11. High voltage bushing having weathershed and surrounding stress relief collar

    DOEpatents

    Cookson, Alan H.

    1981-01-01

    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.

  12. Uncertainties in obtaining high reliability from stress-strength models

    NASA Technical Reports Server (NTRS)

    Neal, Donald M.; Matthews, William T.; Vangel, Mark G.

    1992-01-01

    There has been a recent interest in determining high statistical reliability in risk assessment of aircraft components. The potential consequences are identified of incorrectly assuming a particular statistical distribution for stress or strength data used in obtaining the high reliability values. The computation of the reliability is defined as the probability of the strength being greater than the stress over the range of stress values. This method is often referred to as the stress-strength model. A sensitivity analysis was performed involving a comparison of reliability results in order to evaluate the effects of assuming specific statistical distributions. Both known population distributions, and those that differed slightly from the known, were considered. Results showed substantial differences in reliability estimates even for almost nondetectable differences in the assumed distributions. These differences represent a potential problem in using the stress-strength model for high reliability computations, since in practice it is impossible to ever know the exact (population) distribution. An alternative reliability computation procedure is examined involving determination of a lower bound on the reliability values using extreme value distributions. This procedure reduces the possibility of obtaining nonconservative reliability estimates. Results indicated the method can provide conservative bounds when computing high reliability. An alternative reliability computation procedure is examined involving determination of a lower bound on the reliability values using extreme value distributions. This procedure reduces the possibility of obtaining nonconservative reliability estimates. Results indicated the method can provide conservative bounds when computing high reliability.

  13. Stress Concentration and Fracture at Inter-variant Boundaries in an Al-Li Alloy

    NASA Technical Reports Server (NTRS)

    Crooks, Roy; Tayon, Wes; Domack, Marcia; Wagner, John; Beaudoin, Armand

    2009-01-01

    Delamination fracture has limited the use of lightweight Al-Li alloys. Studies of secondary, delamination cracks in alloy 2090, L-T fracture toughness samples showed grain boundary failure between variants of the brass texture component. Although the adjacent texture variants, designated B(sub s1) and B(sub s2), behave similarly during rolling, their plastic responses to mechanical tests can be quite different. EBSD data from through-thickness scans were used to generate Taylor factor maps. When a combined boundary normal and shear tensor was used in the calculation, the delaminating grains showed the greatest Taylor Factor differences of any grain pairs. Kernel Average Misorientation (KAM) maps also showed damage accumulation on one side of the interface. Both of these are consistent with poor slip accommodation from a crystallographically softer grain to a harder one. Transmission electron microscopy was used to confirm the EBSD observations and to show the role of slip bands in the development of large, interfacial stress concentrations. A viewgraph presentation accompanies the provided abstract.

  14. The Effect of Laves Phase (Fe,Al)2Zr on the High-Temperature Strength of Carbon-Alloyed Fe3Al Aluminide

    NASA Astrophysics Data System (ADS)

    Kratochvíl, Petr; Vodičková, Věra; Král, Robert; Švec, Martin

    2016-03-01

    The effects of carbon on the phase structure and on the yield stress σ 0.2 in the temperature range from 873 K to 1073 K (600 °C to 800 °C) of the Fe3Al type aluminides alloyed by Zr are analyzed. Four alloys with Zr and C in ranging from 1.0 to 5.0 at. pct of additives were used. The appearing of either Laves phase (Fe,Al)2Zr and/or carbides depend on the difference in concentrations, c Zr - c C. This parameter ( c Zr - c C) has been selected instead of the concentration ratio c Zr/ c C used in previous works since it exhibits a significantly better correlation with the Laves phase concentration which influences the high-temperature yield stress, σ 0.2, of the tested alloys. The presence of Laves phase or eutectic (matrix—Laves phase), respectively, enhances the value of the yield stress σ 0.2. The amount of Laves phase is decreased by the presence of C due to the affinity of carbon to Zr.

  15. Degradation and annealing effects caused by oxygen in AlGaN/GaN high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Jiang, R.; Shen, X.; Chen, J.; Duan, G. X.; Zhang, E. X.; Fleetwood, D. M.; Schrimpf, R. D.; Kaun, S. W.; Kyle, E. C. H.; Speck, J. S.; Pantelides, S. T.

    2016-07-01

    Hot-carrier degradation and room-temperature annealing effects are investigated in unpassivated ammonia-rich AlGaN/GaN high electron mobility transistors. Devices exhibit a fast recovery when annealed after hot carrier stress with all pins grounded. The recovered peak transconductance can exceed the original value, an effect that is not observed in control passivated samples. Density functional theory calculations suggest that dehydrogenation of pre-existing ON-H defects in AlGaN plays a significant role in the observed hot carrier degradation, and the resulting bare ON can naturally account for the "super-recovery" in the peak transconductance.

  16. The stress relaxation of cement clinkers under high temperature

    NASA Astrophysics Data System (ADS)

    Wang, Xiufang; Bao, Yiwang; Liu, Xiaogen; Qiu, Yan

    2015-12-01

    The energy consumption of crushing is directly affected by the mechanical properties of cement materials. This research provides a theoretical proof for the mechanism of the stress relaxation of cement clinkers under high temperature. Compression stress relaxation under various high temperatures is discussed using a specially developed load cell, which can measure stress and displacement under high temperatures inside an autoclave. The cell shows that stress relaxation dramatically increases and that the remaining stress rapidly decreases with an increase in temperature. Mechanical experiments are conducted under various temperatures during the cooling process to study the changes in the grinding resistance of the cement clinker with temperature. The effects of high temperature on the load-displacement curve, compressive strength, and elastic modulus of cement clinkers are systematically studied. Results show that the hardening phenomenon of the clinker becomes apparent with a decrease in temperature and that post-peak behaviors manifest characteristics of the transformation from plasticity to brittleness. The elastic modulus and compressive strength of cement clinkers increase with a decrease in temperature. The elastic modulus increases greatly when the temperature is lower than 1000 °C. The compressive strength of clinkers increases by 73.4% when the temperature drops from 1100 to 800 °C.

  17. Improved capacitive stress transducers for high-field superconducting magnets

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

    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.

  18. Anodizing of High Electrically Stressed Components

    SciTech Connect

    Flores, P.; Henderson, D. J.; Good, D. E.; Hogge, K.; Mitton, C. V.; Molina, I.; Naffziger, C.; Codova, S. R.; Ormond, E. U.

    2013-06-01

    Anodizing creates an aluminum oxide coating that penetrates into the surface as well as builds above the surface of aluminum creating a very hard ceramic-type coating with good dielectric properties. Over time and use, the electrical carrying components (or spools in this case) experience electrical breakdown, yielding undesirable x-ray dosages or failure. The spool is located in the high vacuum region of a rod pinch diode section of an x-ray producing machine. Machine operators have recorded decreases in x-ray dosages over numerous shots using the reusable spool component, and re-anodizing the interior surface of the spool does not provide the expected improvement. A machine operation subject matter expert coated the anodized surface with diffusion pump oil to eliminate electrical breakdown as a temporary fix. It is known that an anodized surface is very porous, and it is because of this porosity that the surface may trap air that becomes a catalyst for electrical breakdown. In this paper we present a solution of mitigating electrical breakdown by oiling. We will also present results of surface anodizing improvements achieved by surface finish preparation and surface sealing. We conclude that oiling the anodized surface and using anodized hot dip sealing processes will have similar results.

  19. Thermal oxidation of medical Ti6Al4V blasted with ceramic particles: Effects on the microstructure, residual stresses and mechanical properties.

    PubMed

    Lieblich, M; Barriuso, S; Multigner, M; González-Doncel, G; González-Carrasco, J L

    2016-02-01

    Roughening of Ti6Al4V by blasting with alumina or zirconia particles improves the mechanical fixation of implants by increasing the surface area available for bone/implant apposition. Additional thermal oxidation treatments of the blasted alloy have already shown to be a complementary low-cost solution to enhancing the in vitro biocompatibility and corrosion resistance of the alloy. In this work, the effects of oxidation treatment on a grit blasted Ti6Al4V biomedical alloy have been analysed in order to understand the net effect of the combined treatments on the alloy fatigue properties. Synchrotron radiation diffraction experiments have been performed to measure residual stresses before and after the treatments and microstructural and hardness changes have been determined. Although blasting of Ti6Al4V with small spherical zirconia particles increases the alloy fatigue resistance with respect to unblasted specimens, fatigue strength after oxidation decreases below the unblasted value, irrespective of the type of particle used for blasting. Moreover, at 700°C the as-blasted compressive residual stresses (700MPa) are not only fully relaxed but even moderate tensile residual stresses, of about 120MPa, are found beneath the blasted surfaces. Contrary to expectations, a moderate increase in hardness occurs towards the blasted surface after oxidation treatments. This can be attributed to the fact that grit blasting modifies the crystallographic texture of the Ti6Al4V shifting it to a random texture, which affects the hardness values as shown by additional experiments on cold rolled samples. The results indicate that the oxidation treatment performed to improve biocompatibility and corrosion resistance of grit blasted Ti6Al4V should be carried out with caution since the alloy fatigue strength can be critically diminished below the value required for high load-bearing components. PMID:26458115

  20. Oxidation and microstructure evolution of Al-Si coated Ni3Al based single crystal superalloy with high Mo content

    NASA Astrophysics Data System (ADS)

    Tu, Xiaolu; Peng, Hui; Zheng, Lei; Qi, Wenyan; He, Jian; Guo, Hongbo; Gong, Shengkai

    2015-01-01

    A Si modified aluminide (Al-Si) coating was prepared on a Ni3Al based single crystal superalloy with high Mo content by high-activity pack cementation. Cyclic oxidation test at 1150 °C was carried out and the microstructure evolution of the coating was investigated. The results show that the oxidation resistance of the substrate was greatly increased by applying an Al-Si coating. During oxidation, outward diffusion of Mo was effectively blocked due to its high affinity with Si. Besides, a layered structure was formed as a result of the elements inter-diffusion. An obvious degradation of the Al-Si coating was observed after 100 h oxidation. Possible mechanisms related to the oxidation and elements inter-diffusion behaviours were also discussed.

  1. High internal quantum efficiency in AlGaN multiple quantum wells grown on bulk AlN substrates

    SciTech Connect

    Bryan, Zachary Bryan, Isaac; Sitar, Zlatko; Collazo, Ramón; Xie, Jinqiao; Mita, Seiji

    2015-04-06

    The internal quantum efficiency (IQE) of Al{sub 0.55}Ga{sub 0.45}N/AlN and Al{sub 0.55}Ga{sub 0.45}N/Al{sub 0.85}Ga{sub 0.15}N UVC MQW structures was analyzed. The use of bulk AlN substrates enabled us to undoubtedly distinguish the effect of growth conditions, such as V/III ratio, on the optical quality of AlGaN based MQWs from the influence of dislocations. At a high V/III ratio, a record high IQE of ∼80% at a carrier density of 10{sup 18 }cm{sup −3} was achieved at ∼258 nm. The high IQE was correlated with the decrease of the non-radiative coefficient A and a reduction of midgap defect luminescence, all suggesting that, in addition to dislocations, point defects are another major factor that strongly influences optical quality of AlGaN MQW structures.

  2. Dependence of thermal residual stress on temperature in a SiC particle-reinforced 6061Al alloy

    NASA Astrophysics Data System (ADS)

    Li, H.; Wang, D. Z.; Li, J. B.; Wang, Z. G.; Chen, C. R.

    1998-07-01

    The thermal stresses (TS) in the matrix of a SiC p /6061Al composite during thermal cycling were measured by X-ray diffraction. Also, the TS during thermal cycling and residual stress distribution (RSD) at room temperature in the two phases of composite were calculated by finite element modeling (FEM). The measured and calculated results indicated that the closed stress-temperature loop was formed during thermal cycling. The stress state in the matrix changed from tension to compression during heating and from compression to tension during cooling. Plastic deformation took place in the matrix of the composite during thermal cycling. The general change trend of TS with temperature during thermal cycling was in agreement between the experiment and calculation.

  3. Stress evolution during growth of GaN (0001)/Al2O3(0001) by reactive dc magnetron sputter epitaxy

    NASA Astrophysics Data System (ADS)

    Junaid, M.; Sandström, P.; Palisaitis, J.; Darakchieva, V.; Hsiao, C.-L.; Persson, P. O. Å.; Hultman, L.; Birch, J.

    2014-04-01

    We study the real time stress evolution, by in situ curvature measurements, during magnetron sputter epitaxy of GaN (0 0 0 1) epilayers at different growth temperatures, directly on Al2O3(0 0 0 1) substrates. The epilayers are grown by sputtering from a liquid Ga target in a mixed N2/Ar discharge. For 600 °C, a tensile biaxial stress evolution is observed, while for 700 °C and 800 °C, compressive stress evolutions are observed. Structural characterization by cross-sectional transmission electron microscopy, and atomic force microscopy, revealed that films grew at 700 °C and 800 °C in a layer-by-layer mode while a growth temperature of 600 °C led to an island growth mode. High resolution x-ray diffraction data showed that edge and screw threading dislocation densities decreased with increasing growth temperature, with a total density of 5.5 × 1010 cm-2 at 800 °C. The observed stress evolution and growth modes are explained by a high surface mobility during magnetron sputter epitaxy at 700-800 °C. Other possible reasons for the different stress evolutions are also discussed.

  4. Observation of current polarity effect in stressing as-formed sub-micron Al-Si-Cu/TiW/TiSi 2 contacts

    NASA Astrophysics Data System (ADS)

    Chen, Li-Zen; Hsu, Klaus Y.-J.

    1999-06-01

    Formation of good silicide contacts becomes more important but difficult as the contact size continues shrinking toward the deep sub-micron regime. At the same time, higher current density, which may easily appear in small regions, could pose strong impact to the long-term reliability of sub-micron contacts. In this work, high current density stress experiments were conducted on the Al-Si-Cu/TiW/TiSi 2 contacts with the size ranging from 0.5×0.5 μm 2 down to 0.25×0.25 μm 2. The self-aligned silicide contacts were formed by using collimated sputtering, E-beam lithography, RTA, and RIE techniques. The silicide contacts were sintered at 400°C for 30 min. Cross-bridge Kelvin resistor structures were formed for electrical stressing and contact resistance measurement. One-way and two-way stressings were performed at high current density (˜10 7 A/cm 2) and the contact resistance was measured periodically at low current density during the stressing to monitor the evolution. It was found that the initial resistance of as-formed contacts was higher than expected. This is probably due to the difficulty of forming good interfaces in the small contact region by sputtering and that the sintering temperature may not be high enough to smear out the imperfection. The stressing was found to anneal the contacts. With electrons flowing from metal layer into the contact window, the contact resistance was reduced more efficiently than with reverse current of the same density. Stressed first by reverse current then by normal current, the resistance showed a two-step reduction with a significant transition at the switch of current polarity. For prolonged stressing, the contacts were gradually degraded and the reverse current induced more severe damage. These observations indicate strong electromigration effect at the small contacts.

  5. Temperature dependency and reliability of through substrate via InAlN/GaN high electron mobility transistors as determined using low frequency noise measurement

    NASA Astrophysics Data System (ADS)

    Chiu, Hsien-Chin; Peng, Li-Yi; Wang, Hou-Yu; Wang, Hsiang-Chun; Kao, Hsuan-Ling; Chien, Feng-Tso; Lin, Jia-Ching; Chang, Kuo-Jen; Cheng, Yi-Cheng

    2016-05-01

    The reliability of a InAlN/GaN/Si high electron mobility transistor device was studied using low frequency noise measurements under various stress conditions. By applying the through substrate via (TSV) technology beneath the active region of the device, buffer/transition layer trapping caused by the GaN/Si lattice mismatch was suppressed. In addition, a backside SiO2/Al heat sink material improved thermal stability and eliminated the vertical leakage current of the proposed device. Applying the TSV technology improved the subthreshold swing slope from 260 to 230 mV/dec, owing to the stronger channel modulation ability and reduced leakage current of the device. The latticed-matched InAlN/GaN heterostructure had a stable performance after high current operation stress. The suppression of buffer/transition layer traps of the TSV device is a dominant factor in device reliability after long-term high-electric-field stress.

  6. Effect of multiaxial stresses on the high-temperature behavior and rupture of advanced alloys

    NASA Astrophysics Data System (ADS)

    Johnson, Nancy Louise

    1998-05-01

    The evolution and effect of multiaxial stress states on the high temperature deformation and rupture behavior of materials with non-uniform microstructures has been investigated. Through a detailed description of the role that multiaxial stresses play on damage evolution and rupture, the abundant existing data for uniaxial rupture can be used to more successfully design for the life of high temperature components. Three dimensional finite element calculations of primary creep deformation were performed for particulate reinforced metal matrix composites under a variety of multiaxial loading conditions. A quasi-steady state stress distribution develops during primary creep for each of the conditions considered. The results indicate that higher stresses exist in regions above and below the particles and accommodate the development of creep damage. The nature of the stress state within these regions is not significantly altered by the presence of the particles. The strain fields show a distribution similar to the stress fields. Despite significantly large regions of enhanced stress, the overall creep strain rates for all models are decreased by the presence of the particles. The applied effective stress does not have a unique relationship with overall effective strain rate for particulate reinforced composites under different applied stress states. The failure of sections of turbine rotor disks formed from the superalloy V-57 which operate under highly multiaxial stresses has been investigated. Optical microscopy of a turbine rotor disk removed from service after 30,000 hrs showed an intergranular crack that initiated at the root of a fir-tree turbine rotor blade attachment. Transmission electron microscopy studies showed heavy grain boundary oxidation that could account for the cracking and failure of the rotor disks. Heat treatments of a TiAl alloy have been established for producing a microstructure suitable for high temperature multiaxial rupture testing. The

  7. Work at high altitude and oxidative stress: antioxidant nutrients.

    PubMed

    Askew, E W

    2002-11-15

    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

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

    SciTech Connect

    Schuh, C; Dunand, D C

    2001-09-10

    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.

  9. Computer simulation of stress-oriented nucleation and growth of {theta}{prime} precipitates in Al-Cu alloys

    SciTech Connect

    Li, D.Y.; Chen, L.Q.

    1998-05-01

    Many structural transformations result in several orientation variants whose volume fractions and distributions can be controlled by applied stresses during nucleation, growth or coarsening. Depending on the type of stress and the coupling between the applied stress and the lattice misfit strain, the precipitate variants may be aligned parallel or perpendicular to the stress axis. This paper reports their studies on the effect of applied stresses on nucleation and growth of coherent {theta}{prime} precipitates in Al-Cu alloys using computer simulations based on a diffuse-interface phase-field kinetic model. In this model, the orientational differences among precipitate variants are distinguished by non-conserved structural field variables, whereas the compositional difference between the precipitate and matrix is described by a conserved field variable. The temporal evolution of the spatially dependent field variables is determined by numerically solving the time-dependent Ginzburg-Landau (TDGL) equations for the structural variables and the Cahn-Hilliard diffusion equation for composition. Random noises were introduced in both the composition and the structural order parameter fields to simulate the nucleation of {theta}{prime} precipitates. It is demonstrated that although an applied stress affects the microstructural development of a two-phase alloy during both the nucleation and growth stages, it is most effective to apply stresses during the initial nucleation stage for producing anisotropic precipitate alignment.

  10. High shear stress induces atherosclerotic vulnerable plaque formation through angiogenesis

    PubMed Central

    Wang, Yi; Qiu, Juhui; Luo, Shisui; Xie, Xiang; Zheng, Yiming; Zhang, Kang; Ye, Zhiyi; Liu, Wanqian; Gregersen, Hans; Wang, Guixue

    2016-01-01

    Rupture of atherosclerotic plaques causing thrombosis is the main cause of acute coronary syndrome and ischemic strokes. Inhibition of thrombosis is one of the important tasks developing biomedical materials such as intravascular stents and vascular grafts. Shear stress (SS) influences the formation and development of atherosclerosis. The current review focuses on the vulnerable plaques observed in the high shear stress (HSS) regions, which localizes at the proximal region of the plaque intruding into the lumen. The vascular outward remodelling occurs in the HSS region for vascular compensation and that angiogenesis is a critical factor for HSS which induces atherosclerotic vulnerable plaque formation. These results greatly challenge the established belief that low shear stress is important for expansive remodelling, which provides a new perspective for preventing the transition of stable plaques to high-risk atherosclerotic lesions. PMID:27482467

  11. High shear stress induces atherosclerotic vulnerable plaque formation through angiogenesis.

    PubMed

    Wang, Yi; Qiu, Juhui; Luo, Shisui; Xie, Xiang; Zheng, Yiming; Zhang, Kang; Ye, Zhiyi; Liu, Wanqian; Gregersen, Hans; Wang, Guixue

    2016-12-01

    Rupture of atherosclerotic plaques causing thrombosis is the main cause of acute coronary syndrome and ischemic strokes. Inhibition of thrombosis is one of the important tasks developing biomedical materials such as intravascular stents and vascular grafts. Shear stress (SS) influences the formation and development of atherosclerosis. The current review focuses on the vulnerable plaques observed in the high shear stress (HSS) regions, which localizes at the proximal region of the plaque intruding into the lumen. The vascular outward remodelling occurs in the HSS region for vascular compensation and that angiogenesis is a critical factor for HSS which induces atherosclerotic vulnerable plaque formation. These results greatly challenge the established belief that low shear stress is important for expansive remodelling, which provides a new perspective for preventing the transition of stable plaques to high-risk atherosclerotic lesions. PMID:27482467

  12. Nanoindentation Creep Behavior of an Al0.3CoCrFeNi High-Entropy Alloy

    NASA Astrophysics Data System (ADS)

    Zhang, Lijun; Yu, Pengfei; Cheng, Hu; Zhang, Huan; Diao, Haoyan; Shi, Yunzhu; Chen, Bilin; Chen, Peiyong; Feng, Rui; Bai, Jie; Jing, Qin; Ma, Mingzhen; Liaw, P. K.; Li, Gong; Liu, Riping

    2016-03-01

    Nanoindentation creep behavior was studied on a coarse-grained Al0.3CoCrFeNi high-entropy alloy with a single face-centered cubic structure. The effects of the indentation size and loading rate on creep behavior were investigated. The experimental results show that the hardness, creep depth, creep strain rate, and stress exponent are all dependent on the holding load and loading rate. The creep behavior shows a remarkable indentation size effect at different maximum indentation loads. The dominant creep mechanism is dislocation creep at high indentation loads and self-diffusion at low indentation loads. An obvious loading rate sensitivity of creep behavior is found under different loading rates for the alloy. A high loading rate can lead to a high strain gradient, and numerous dislocations emerge and entangle together. Then during the holding time, a large creep deformation characteristic with a high stress exponent will happen.

  13. Al-Li alloy AA2198's very high cycle fatigue crack initiation mechanism and its fatigue thermal effect

    NASA Astrophysics Data System (ADS)

    Xu, Luopeng; Cao, Xiaojian; Chen, Yu; Wang, Qingyuan

    2015-10-01

    AA2198 alloy is one of the third generation Al-Li alloys which have low density, high elastic modulus, high specific strength and specific stiffness. Compared With the previous two generation Al-Li alloys, the third generation alloys have much improved in alloys strength, corrosion resistance and weldable characteristic. For these advantages, the third generation Al-Li alloys are used as aircraft structures, such as C919 aviation airplane manufactured by China and Russia next generation aviation airplane--MS-21. As we know, the aircraft structures are usually subjected to more than 108 cycles fatigue life during 20-30 years of service, however, there is few reported paper about the third generation Al-Li alloys' very high cycle fatigue(VHCF) which is more than 108 cycles fatigue. The VHCF experiment of AA2198 have been carried out. The two different initiation mechanisms of fatigue fracture have been found in VHCF. The cracks can initiate from the interior of the testing material with lower stress amplitude and more than 108 cycles fatigue life, or from the surface or subsurface of material which is the dominant reason of fatigue failures. During the experiment, the infrared technology is used to monitor the VHCF thermal effect. With the increase of the stress, the temperature of sample is also rising up, increasing about 15 °C for every 10Mpa. The theoretical thermal analysis is also carried out.

  14. Analysis of current instabilities of thin AlN/GaN/AlN double heterostructure high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Zervos, Ch; Adikimenakis, A.; Bairamis, A.; Kostopoulos, A.; Kayambaki, M.; Tsagaraki, K.; Konstantinidis, G.; Georgakilas, A.

    2016-06-01

    The current instabilities of high electron mobility transistors (HEMTs), based on thin double AlN/GaN/AlN heterostructures (∼0.5 μm total thickness), directly grown on sapphire substrates, have been analyzed and compared for different AlN top barrier thicknesses. The structures were capped by 1 nm GaN and non-passivated 1 μm gate-length devices were processed. Pulsed I–V measurements resulted in a maximum cold pulsed saturation current of 1.4 A mm‑1 at a gate-source voltage of +3 V for 3.7 nm AlN thickness. The measured gate and drain lag for 500 ns pulse-width varied between 6%–12% and 10%–18%, respectively. Furthermore, a small increase in the threshold voltage was observed for all the devices, possibly due to the trapping of electrons under the gate contact. The off-state breakdown voltage of V br = 70 V, for gate-drain spacing of 2 μm, was approximately double the value measured for a single AlN/GaN HEMT structure grown on a thick GaN buffer layer. The results suggest that the double AlN/GaN/AlN heterostructures may offer intrinsic advantages for the breakdown and current stability characteristics of high current HEMTs.

  15. Effects of high-temperature AIN buffer on the microstructure of AlGaN/GaN HEMTs

    SciTech Connect

    Coerekci, S.; Oeztuerk, M. K.; Yu, Hongbo; Cakmak, M.; Oezcelik, S.; Oezbay, E.

    2013-06-15

    Effects on AlGaN/GaN high-electron-mobility transistor structure of a high-temperature AlN buffer on sapphire substrate have been studied by high-resolution x-ray diffraction and atomic force microscopy techniques. The buffer improves the microstructural quality of GaN epilayer and reduces approximately one order of magnitude the edge-type threading dislocation density. As expected, the buffer also leads an atomically flat surface with a low root-mean-square of 0.25 nm and a step termination density in the range of 10{sup 8} cm{sup -2}. Due to the high-temperature buffer layer, no change on the strain character of the GaN and AlGaN epitaxial layers has been observed. Both epilayers exhibit compressive strain in parallel to the growth direction and tensile strain in perpendicular to the growth direction. However, an high-temperature AlN buffer layer on sapphire substrate in the HEMT structure reduces the tensile stress in the AlGaN layer.

  16. Creep and rupture of an ODS alloy with high stress rupture ductility. [Oxide Dispersion Strengthened

    NASA Technical Reports Server (NTRS)

    Mcalarney, M. E.; Arsons, R. M.; Howson, T. E.; Tien, J. K.; Baranow, S.

    1982-01-01

    The creep and stress rupture properties of an oxide (Y2O3) dispersion strengthened nickel-base alloy, which also is strengthened by gamma-prime precipitates, was studied at 760 and 1093 C. At both temperatures, the alloy YDNiCrAl exhibits unusually high stress rupture ductility as measured by both elongation and reduction in area. Failure was transgranular, and different modes of failure were observed including crystallographic fracture at intermediate temperatures and tearing or necking almost to a chisel point at higher temperatures. While the rupture ductility was high, the creep strength of the alloy was low relative to conventional gamma prime strengthened superalloys in the intermediate temperature range and to ODS alloys in the higher temperature range. These findings are discussed with respect to the alloy composition; the strengthening oxide phases, which are inhomogeneously dispersed; the grain morphology, which is coarse and elongated and exhibits many included grains; and the second phase inclusion particles occurring at grain boundaries and in the matrix. The creep properties, in particular the high stress dependencies and high creep activation energies measured, are discussed with respect to the resisting stress model of creep in particle strengthened alloys.

  17. Dynamic and failure properties of high damping rubber bearing under high axial stress

    SciTech Connect

    Ishizuka, Hidetake; Murota, Nobuo; Fukumori, Takeshi

    1995-12-01

    Seismic isolation bearings have been used under axial stresses less than 100(kgf/cm{sup 2}) for many years. If higher axial loads can be applied, however, a larger period shift will be achieved and the size of the isolation devices may be reduced resulting in a cost reduction of the bearing. This paper describes experimental studies of dynamic and failure properties of high damping rubber bearings (HDR) under high axial stress of over 120(kgf/cm{sup 2}) compared with the conventional stress of 65(kgf/cm{sup 2}). The results show that HDR continues to have stable performance under high axial stress with high shear strain. It indicates that high axial stress over 100(kgf/cm{sup 2}) is within the capability of the BDR isolation bearing.

  18. Integrating AlGaN/GaN high electron mobility transistor with Si: A comparative study of integration schemes

    NASA Astrophysics Data System (ADS)

    Mohan, Nagaboopathy; Singh, Manikant; Soman, Rohith; Raghavan, Srinivasan

    2015-10-01

    AlGaN/GaN high electron mobility transistor stacks deposited on a single growth platform are used to compare the most common transition, AlN to GaN, schemes used for integrating GaN with Si. The efficiency of these transitions based on linearly graded, step graded, interlayer, and superlattice schemes on dislocation density reduction, stress management, surface roughness, and eventually mobility of the 2D-gas are evaluated. In a 500 nm GaN probe layer deposited, all of these transitions result in total transmission electron microscopy measured dislocations densities of 1 to 3 × 109/cm2 and <1 nm surface roughness. The 2-D electron gas channels formed at an AlGaN-1 nm AlN/GaN interface deposited on this GaN probe layer all have mobilities of 1600-1900 cm2/V s at a carrier concentration of 0.7-0.9 × 1013/cm2. Compressive stress and changes in composition in GaN rich regions of the AlN-GaN transition are the most effective at reducing dislocation density. Amongst all the transitions studied the step graded transition is the one that helps to implement this feature of GaN integration in the simplest and most consistent manner.

  19. Integrating AlGaN/GaN high electron mobility transistor with Si: A comparative study of integration schemes

    SciTech Connect

    Mohan, Nagaboopathy; Raghavan, Srinivasan; Manikant,; Soman, Rohith

    2015-10-07

    AlGaN/GaN high electron mobility transistor stacks deposited on a single growth platform are used to compare the most common transition, AlN to GaN, schemes used for integrating GaN with Si. The efficiency of these transitions based on linearly graded, step graded, interlayer, and superlattice schemes on dislocation density reduction, stress management, surface roughness, and eventually mobility of the 2D-gas are evaluated. In a 500 nm GaN probe layer deposited, all of these transitions result in total transmission electron microscopy measured dislocations densities of 1 to 3 × 10{sup 9}/cm{sup 2} and <1 nm surface roughness. The 2-D electron gas channels formed at an AlGaN-1 nm AlN/GaN interface deposited on this GaN probe layer all have mobilities of 1600–1900 cm{sup 2}/V s at a carrier concentration of 0.7–0.9 × 10{sup 13}/cm{sup 2}. Compressive stress and changes in composition in GaN rich regions of the AlN-GaN transition are the most effective at reducing dislocation density. Amongst all the transitions studied the step graded transition is the one that helps to implement this feature of GaN integration in the simplest and most consistent manner.

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

    PubMed

    Liu, Yong-jie; Cui, Shi-ming; He, Chao; Li, Jiu-kai; Wang, Qing-yuan

    2014-01-01

    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:24211906

  1. Influence of Surface Passivation on AlN Barrier Stress and Scattering Mechanism in Ultra-thin AlN/GaN Heterostructure Field-Effect Transistors.

    PubMed

    Lv, Y J; Song, X B; Wang, Y G; Fang, Y L; Feng, Z H

    2016-12-01

    Ultra-thin AlN/GaN heterostructure field-effect transistors (HFETs) with, and without, SiN passivation were fabricated by the same growth and device processes. Based on the measured DC characteristics, including the capacitance-voltage (C-V) and output current-voltage (I-V) curves, the variation of electron mobility with gate bias was found to be quite different for devices with, and without, SiN passivation. Although the AlN barrier layer is ultra thin (c. 3 nm), it was proved that SiN passivation induces no additional tensile stress and has no significant influence on the piezoelectric polarization of the AlN layer using Hall and Raman measurements. The SiN passivation was found to affect the surface properties, thereby increasing the electron density of the two-dimensional electron gas (2DEG) under the access region. The higher electron density in the access region after SiN passivation enhanced the electrostatic screening for the non-uniform distributed polarization charges, meaning that the polarization Coulomb field scattering has a weaker effect on the electron drift mobility in AlN/GaN-based devices. PMID:27553382

  2. High breakdown voltage in AlGaN/GaN HEMTs using AlGaN/GaN/AlGaN quantum-well electron-blocking layers

    PubMed Central

    2014-01-01

    In this paper, we numerically study an enhancement of breakdown voltage in AlGaN/GaN high-electron-mobility transistors (HEMTs) by using the AlGaN/GaN/AlGaN quantum-well (QW) electron-blocking layer (EBL) structure. This concept is based on the superior confinement of two-dimensional electron gases (2-DEGs) provided by the QW EBL, resulting in a significant improvement of breakdown voltage and a remarkable suppression of spilling electrons. The electron mobility of 2-DEG is hence enhanced as well. The dependence of thickness and composition of QW EBL on the device breakdown is also evaluated and discussed. PMID:25206318

  3. The influence of growth conditions on the surface morphology and development of mechanical stresses in Al(Ga)N layers during metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Lundin, W. V.; Zavarin, E. E.; Brunkov, P. N.; Yagovkina, M. A.; Troshkov, S. I.; Sakharov, A. V.; Nikolaev, A. E.; Tsatsulnikov, A. F.

    2016-04-01

    We have studied the influence of technological parameters on the surface morphology and development of mechanical stresses in Al(Ga)N layers during their growth by metalorganic vapor phase epitaxy (MOVPE) on sapphire substrates. Minimization of tensile stresses under conditions of a retained atomically smooth surface can be achieved by using a combination of factors including (i) nitridation of substrate in ammonia flow, (ii) formation of two-layer AlN-Al(Ga)N structures by introducing a small amount (several percent) of Ga after growth of a thin AlN layer, and (iii) reduction of ammonia flow during growth of an Al(Ga)N layer.

  4. Effect of Al2O3 on the Crystallization of Mold Flux for Casting High Al Steel

    NASA Astrophysics Data System (ADS)

    Zhou, Lejun; Wang, Wanlin; Zhou, Kechao

    2015-06-01

    In order to lower the weight of automotive bodies for better fuel-efficiency and occupant safety, the demand for high Al-containing advanced high strength steel, such as transformation-induced plasticity and twinning-induced plasticity steel, is increasing. However, high aluminum content in steels would tend to significantly affect the properties of mold flux during the continuous casting process. In this paper, a kinetic study of the effect of Al2O3 content on the crystallization behavior of mold flux was conducted by using the single hot thermocouple technique and the Johnson-Mehl-Avrami model combined with the Arrhenius Equation. The results suggested that Al2O3 behaves as an amphoteric oxide in the crystallization process of mold flux. The precipitated phases of mold flux change from cuspidine (Ca4Si2O7F2) into nepheline (NaAlSiO4) and CaF2, and then into gehlenite (Ca2Al2SiO7) with the increase of Al2O3 content. The kinetics study of the isothermal crystallization process indicated that the effective crystallization rate ( k) and Avrami exponent ( n) also first increased and then decreased with the increase of Al2O3 content. The values for the crystallization activation energy of mold flux with different Al2O3 contents were E R0.8A7 = 150.76 ± 17.89 kJ/mol, E R0.8A20 = 136.43 ± 6.48 kJ/mol, E R0.8A30 = 108.63 ± 12.25 kJ/mol and E R0.8A40 = 116.15 ± 8.17 kJ/mol.

  5. High-Temperature CO2 Sorption on Hydrotalcite Having a High Mg/Al Molar Ratio.

    PubMed

    Kim, Suji; Jeon, Sang Goo; Lee, Ki Bong

    2016-03-01

    Hydrotalcites having a Mg/Al molar ratio between 3 and 30 have been synthesized as promising high-temperature CO2 sorbents. The existence of NaNO3 in the hydrotalcite structure, which originates from excess magnesium nitrate in the precursor, markedly increases CO2 sorption uptake by hydrotalcite up to the record high value of 9.27 mol kg(-1) at 240 °C and 1 atm CO2. PMID:26927529

  6. Increased oxidative stress following acute and chronic high altitude exposure.

    PubMed

    Jefferson, J Ashley; Simoni, Jan; Escudero, Elizabeth; Hurtado, Maria-Elena; Swenson, Erik R; Wesson, Donald E; Schreiner, George F; Schoene, Robert B; Johnson, Richard J; Hurtado, Abdias

    2004-01-01

    The generation of reactive oxygen species is typically associated with hyperoxia and ischemia reperfusion. Recent evidence has suggested that increased oxidative stress may occur with hypoxia. We hypothesized that oxidative stress would be increased in subjects exposed to high altitude hypoxia. We studied 28 control subjects living in Lima, Peru (sea level), at baseline and following 48 h exposure to high altitude (4300 m). To assess the effects of chronic altitude exposure, we studied 25 adult males resident in Cerro de Pasco, Peru (altitude 4300 m). We also studied 27 subjects living in Cerro de Pasco who develop excessive erythrocytosis (hematocrit > 65%) and chronic mountain sickness. Acute high altitude exposure led to increased urinary F(2)-isoprostane, 8-iso PGF(2 alpha) (1.31 +/- 0.8 microg/g creatinine versus 2.15 +/- 1.1, p = 0.001) and plasma total glutathione (1.29 +/- 0.10 micromol versus 1.37 +/- 0.09, p = 0.002), with a trend to increased plasma thiobarbituric acid reactive substance (TBARS) (59.7 +/- 36 pmol/mg protein versus 63.8 +/- 27, p = NS). High altitude residents had significantly elevated levels of urinary 8-iso PGF(2 alpha) (1.3 +/- 0.8 microg/g creatinine versus 4.1 +/- 3.4, p = 0.007), plasma TBARS (59.7 +/- 36 pmol/mg protein versus 85 +/- 28, p = 0.008), and plasma total glutathione (1.29 +/- 0.10 micromol versus 1.55 +/- 0.19, p < 0.0001) compared to sea level. High altitude residents with excessive erythrocytosis had higher levels of oxidative stress compared to high altitude residents with normal hematological adaptation. In conclusion, oxidative stress is increased following both acute exposure to high altitude without exercise and with chronic residence at high altitude. PMID:15072717

  7. Resilience in highly stressed urban children: concepts and findings.

    PubMed Central

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

    1996-01-01

    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. PMID:8982521

  8. Fatigue crack closure behavior at high stress ratios

    NASA Technical Reports Server (NTRS)

    Turner, C. Christopher; Carman, C. Davis; Hillberry, Ben M.

    1988-01-01

    Fatigue crack delay behavior at high stress ratio caused by single peak overloads was investigated in two thicknesses of 7475-T731 aluminum alloy. Closure measurements indicated no closure occurred before or throughout the overload plastic zones following the overload. This was further substantiated by comparing the specimen compliance following the overload with the compliance of a low R ratio test when the crack was fully open. Scanning electron microscope studies revealed that crack tunneling and possibly reinitiation of the crack occurred, most likely a result of crack-tip blunting. The number of delay cycles was greater for the thinner mixed mode stress state specimen than for the thicker plane strain stress state specimen, which is similar to low R ratio test results and may be due to a larger plastic zone for the mixed mode cased.

  9. Shear Load Transfer in High and Low Stress Tendons

    PubMed Central

    Kondratko-Mittnacht, Jaclyn; Duenwald-Kuehl, Sarah; Lakes, Roderic; Vanderby, Ray

    2016-01-01

    Background Tendon is an integral part of joint movement and stability, as it functions to transmit load from muscle to bone. It has an anisotropic, fibrous hierarchical structure that is generally loaded in the direction of its fibers/fascicles. Internal load distributions are altered when joint motion rotates an insertion site or when local damage disrupts fibers/fascicles, potentially causing inter-fiber (or inter-fascicular) shear. Tendons with different microstructure (helical versus linear) may redistribute loads differently. Method of Approach This study explored how shear redistributes axial loads in rat tail tendon (low stress tendons with linear microstructure) and porcine flexor tendon (high stress with helical microstructure) by creating lacerations on opposite sides of the tendon, ranging from about 20-60% of the tendon width, to create various magnitudes of shear. Differences in fascicular orientation were quantified using polarized light microscopy. Results and Conclusions Unexpectedly, both tendon types maintained about 20% of pre-laceration stress values after overlapping cuts of 60% of tendon width (no intact fibers end to end) suggesting that shear stress transfer can contribute more to overall tendon strength and stiffness than previously reported. All structural parameters for both tendon types decreased linearly with increasing laceration depth. The tail tendon had a more rapid decline in post-laceration elastic stress and modulus parameters as well as a more linear and less tightly packed fascicular structure, suggesting that positional tendons may be less well suited to redistribute loads via a shear mechanism. PMID:25700261

  10. Chronic mild stress facilitates melanoma tumor growth in mouse lines selected for high and low stress-induced analgesia.

    PubMed

    Ragan, Agnieszka R; Lesniak, Anna; Bochynska-Czyz, Marta; Kosson, Anna; Szymanska, Hanna; Pysniak, Kazimiera; Gajewska, Marta; Lipkowski, Andrzej W; Sacharczuk, Mariusz

    2013-09-01

    Both chronic stress conditions and hyperergic reaction to environmental stress are known to enhance cancer susceptibility. We described two mouse lines that displayed high (HA) and low (LA) swim stress-induced analgesia (SSIA) to investigate the relationship between inherited differences in sensitivity to stress and proneness to an increased growth rate of subcutaneously inoculated melanoma. These lines display several genetic and physiological differences, among which distinct sensitivity to mutagens and susceptibility to cancer are especially noticeable. High analgesic mice display high proneness both to stress and a rapid local spread of B16F0 melanoma. However, stress-resistant LA mice do not develop melanoma tumors after inoculation, or if so, tumors regress spontaneously. We found that the chronic mild stress (CMS) procedure leads to enhanced interlinear differences in melanoma susceptibility. Tumors developed faster in stress conditions in both lines. However, LA mice still displayed a tendency for spontaneous regression, and 50% of LA mice did not develop a tumor, even under stressed conditions. Moreover, we showed that chronic stress, but not tumor progression, induces depressive behavior, which may be an important clue in cancer therapy. Our results clearly indicate how the interaction between genetic susceptibility to stress and environmental stress determine the risk and progression of melanoma. To our knowledge, HA/LA mouse lines are the first animal models of distinct melanoma progression mediated by inherited differences in stress reactivity. PMID:23688070

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

    SciTech Connect

    Liu, L.; Lo, C. F.; Xi, Y. Y.; Wang, Y.l.; Kim, H.-Y.; Kim, J.; Pearton, S. J.; Laboutin, O.; Cao, Yu; Johnson, Wayne J.; Kravchenko, Ivan I; Ren, F.

    2012-01-01

    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.

  12. Multicharacterization approach for studying InAl(Ga)N/Al(Ga)N/GaN heterostructures for high electron mobility transistors

    SciTech Connect

    Naresh-Kumar, G. Trager-Cowan, C.; Vilalta-Clemente, A.; Morales, M.; Ruterana, P.; Pandey, S.; Cavallini, A.; Cavalcoli, D.; Skuridina, D.; Vogt, P.; Kneissl, M.; Behmenburg, H.; Giesen, C.; Heuken, M.; Gamarra, P.; Di Forte-Poisson, M. A.; Patriarche, G.; Vickridge, I.

    2014-12-15

    We report on our multi–pronged approach to understand the structural and electrical properties of an InAl(Ga)N(33nm barrier)/Al(Ga)N(1nm interlayer)/GaN(3μm)/ AlN(100nm)/Al{sub 2}O{sub 3} high electron mobility transistor (HEMT) heterostructure grown by metal organic vapor phase epitaxy (MOVPE). In particular we reveal and discuss the role of unintentional Ga incorporation in the barrier and also in the interlayer. The observation of unintentional Ga incorporation by using energy dispersive X–ray spectroscopy analysis in a scanning transmission electron microscope is supported with results obtained for samples with a range of AlN interlayer thicknesses grown under both the showerhead as well as the horizontal type MOVPE reactors. Poisson–Schrödinger simulations show that for high Ga incorporation in the Al(Ga)N interlayer, an additional triangular well with very small depth may be exhibited in parallel to the main 2–DEG channel. The presence of this additional channel may cause parasitic conduction and severe issues in device characteristics and processing. Producing a HEMT structure with InAlGaN as the barrier and AlGaN as the interlayer with appropriate alloy composition may be a possible route to optimization, as it might be difficult to avoid Ga incorporation while continuously depositing the layers using the MOVPE growth method. Our present work shows the necessity of a multicharacterization approach to correlate structural and electrical properties to understand device structures and their performance.

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

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

    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.

  14. Stress controlled pulsed direct current co-sputtered Al{sub 1−x}Sc{sub x}N as piezoelectric phase for micromechanical sensor applications

    SciTech Connect

    Fichtner, Simon; Reimer, Tim; Chemnitz, Steffen; Wagner, Bernhard; Lofink, Fabian

    2015-11-01

    Scandium alloyed aluminum nitride (Al{sub 1−x}Sc{sub x}N) thin films were fabricated by reactive pulsed direct current co-sputtering of separate scandium and aluminum targets with x ≤ 0.37. A significant improvement of the clamped transversal piezoelectric response to strain e{sub 31,f} from −1.28 C/m{sup 2} to −3.01 C/m{sup 2} was recorded, while dielectric constant and loss angle remain low. Further, the built-in stress level of Al{sub 1−x}Sc{sub x}N was found to be tuneable by varying pressure, Ar/N{sub 2} ratio, and Sc content. The thus resulting enhancement of the expectable signal to noise ratio by a factor of 2.1 and the ability to control built-in stress make the integration of Al{sub 1−x}Sc{sub x}N as the piezoelectric phase of micro-electro-mechanical system sensor applications highly attractive.

  15. High-cycle fatigue behavior of Ti-5Al-2.5Sn ELI alloy forging at low temperatures

    SciTech Connect

    Ono, Yoshinori; Yuri, Tetsumi; Ogata, Toshio; Demura, Masahiko; Matsuoka, Saburo; Sunakawa, Hideo

    2014-01-27

    High-cycle fatigue properties of Ti-5Al-2.5Sn Extra Low Interstitial (ELI) alloy forging were investigated at low temperatures. The high-cycle fatigue strength at low temperatures of this alloy was relatively low compared with that at ambient temperature. The crystallographic orientation of a facet formed at a fatigue crack initiation site was determined by electron backscatter diffraction (EBSD) method in scanning electron microscope (SEM) to understand the fatigue crack initiation mechanism and discuss on the low fatigue strength at low temperature. Furthermore, in terms of the practical use of this alloy, the effect of the stress ratio (or mean stress) on the high-cycle fatigue properties was evaluated using the modified Goodman diagram.

  16. High-cycle fatigue behavior of Ti-5Al-2.5Sn ELI alloy forging at low temperatures

    NASA Astrophysics Data System (ADS)

    Ono, Yoshinori; Yuri, Tetsumi; Ogata, Toshio; Demura, Masahiko; Matsuoka, Saburo; Sunakawa, Hideo

    2014-01-01

    High-cycle fatigue properties of Ti-5Al-2.5Sn Extra Low Interstitial (ELI) alloy forging were investigated at low temperatures. The high-cycle fatigue strength at low temperatures of this alloy was relatively low compared with that at ambient temperature. The crystallographic orientation of a facet formed at a fatigue crack initiation site was determined by electron backscatter diffraction (EBSD) method in scanning electron microscope (SEM) to understand the fatigue crack initiation mechanism and discuss on the low fatigue strength at low temperature. Furthermore, in terms of the practical use of this alloy, the effect of the stress ratio (or mean stress) on the high-cycle fatigue properties was evaluated using the modified Goodman diagram.

  17. Oxidative Stress Levels in Aqueous Humor from High Myopic Patients

    PubMed Central

    Kim, Eun Bi; Kim, Ha Kyoung; Hyon, Joon Young; Wee, Won Ryang

    2016-01-01

    Purpose To compare oxidative stress status in the aqueous humor of highly myopic eyes and control eyes. Methods Aqueous humor samples were collected from 15 highly myopic eyes (high myopia group) and 23 cataractous eyes (control group) during cataract surgery. Central corneal thickness, corneal endothelial cell density, hexagonality of corneal endothelial cells, and cell area of corneal endothelial cells were measured using specular microscopy. Axial length was measured using ultrasound biometry. 8-Hydroxydeoxyguanosine (8-OHdG) and malondialdehyde levels were measured using enzyme-linked immunosorbent assay. Results 8-OHdG level was lower in the aqueous humor of myopic patients than in that of control group (p = 0.014) and was positively correlated with central corneal thickness and negatively correlated with axial length (r = 0.511, p = 0.02; r = -0.382, p < 0.001). There was no correlation between 8-OHdG level and corneal endothelial cell density, hexagonality, or cell area. Malondialdehyde level did not show any correlation with any parameters evaluated. Conclusions 8-OHdG might be a sensitive biomarker for evaluating oxidative stress status in the eye. Oxidative stress level was lower in the aqueous humor of highly myopic eyes compared to that in control eyes, which indicates lower metabolic activity in these eyes. PMID:27247516

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    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.

  19. Genetic dissection of Al tolerance QTLs in the maize genome by high density SNP scan

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Aluminum (Al) toxicity is an important limitation to food security in the tropical and subtropical regions. High Al saturation in acid soils limits root development and its ability to uptake water and nutrients. In this study, we present a genome scan for Al tolerance loci with over 50,000 GBS-based...

  20. Microstructure and mechanical behavior of spray-deposited high-Li Al-Li alloys

    SciTech Connect

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

    1999-05-01

    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 {approximately} 1.5). The microstructure of the spray-deposited Al-Li alloys consisted of equiaxed grains with an average grain size in the range from 20 to 50 {micro}m. The grain-boundary phases were fine and discrete. The spray-deposited and thermomechanically processed materials were isothermally heat treated at 150 C and 170 C to investigate the age-hardening kinetics. It was noted that the spray-deposited Al-3.8Li-XCu-1.0Mg-0.4Ge-0.2Zr alloys exhibited relatively sluggish aging behavior. The peak-aged condition was achieved at 170 C in the range from 20 to 90 hours. It was noted that Cu increases the hardness of alloys during aging. Moreover, the influence of Cu on age-hardening kinetics is marginal. The mechanical properties of the spray-deposited and extruded Al-Li alloys were studied in the underaged, peak-aged, and overaged conditions. For example, the peak-aged yield strength, tensile strength, and ductility of Al-3.8Li-1.0Cu-1.0Mg-0.4Ge-0.2Zr are 455 MPa, 601 MPa, and 3.1 pct, respectively. Moreover, an increase in the Cu content of the alloy led to improvements in strength, with only slight changes in ductility, for Cu contents up to 1.0 wt pct. Beyond this range, an increase in Cu content led to decreases in both strength and ductility.

  1. High-resolution chromatin dynamics during a yeast stress response.

    PubMed

    Weiner, Assaf; Hsieh, Tsung-Han S; Appleboim, Alon; Chen, Hsiuyi V; Rahat, Ayelet; Amit, Ido; Rando, Oliver J; Friedman, Nir

    2015-04-16

    Covalent histone modifications are highly conserved and play multiple roles in eukaryotic transcription regulation. Here, we mapped 26 histone modifications genome-wide in exponentially growing yeast and during a dramatic transcriptional reprogramming-the response to diamide stress. We extend prior studies showing that steady-state histone modification patterns reflect genomic processes, especially transcription, and display limited combinatorial complexity. Interestingly, during the stress response we document a modest increase in the combinatorial complexity of histone modification space, resulting from roughly 3% of all nucleosomes transiently populating rare histone modification states. Most of these rare histone states result from differences in the kinetics of histone modification that transiently uncouple highly correlated marks, with slow histone methylation changes often lagging behind the more rapid acetylation changes. Explicit analysis of modification dynamics uncovers ordered sequences of events in gene activation and repression. Together, our results provide a comprehensive view of chromatin dynamics during a massive transcriptional upheaval. PMID:25801168

  2. High-Resolution Chromatin Dynamics during a Yeast Stress Response

    PubMed Central

    Weiner, Assaf; Hsieh, Tsung-Han S.; Appleboim, Alon; Chen, Hsiuyi V.; Rahat, Ayelet; Amit, Ido; Rando, Oliver J.; Friedman, Nir

    2015-01-01

    Summary Covalent histone modifications are highly conserved and play multiple roles in eukaryotic transcription regulation. Here, we mapped 26 histone modifications genome-wide in exponentially growing yeast and during a dramatic transcriptional reprogramming—the response to diamide stress. We extend prior studies showing that steady-state histone modification patterns reflect genomic processes, especially transcription, and display limited combinatorial complexity. Interestingly, during the stress response we document a modest increase in the combinatorial complexity of histone modification space, resulting from roughly 3% of all nucleosomes transiently populating rare histone modification states. Most of these rare histone states result from differences in the kinetics of histone modification that transiently uncouple highly correlated marks, with slow histone methylation changes often lagging behind the more rapid acetylation changes. Explicit analysis of modification dynamics uncovers ordered sequences of events in gene activation and repression. Together, our results provide a comprehensive view of chromatin dynamics during a massive transcriptional upheaval. PMID:25801168

  3. Finite element stress analysis of polymers at high strains

    NASA Technical Reports Server (NTRS)

    Durand, M.; Jankovich, E.

    1973-01-01

    A numerical analysis is presented for the problem of a flat rectangular rubber membrane with a circular rigid inclusion undergoing high strains due to the action of an axial load. The neo-hookean constitutive equations are introduced into the general purpose TITUS program by means of equivalent hookean constants and initial strains. The convergence is achieved after a few iterations. The method is not limited to any specific program. The results are in good agreement with those of a company sponsored photoelastic stress analysis. The theoretical and experimental deformed shapes also agree very closely with one another. For high strains it is demonstrated that using the conventional HOOKE law the stress concentration factor obtained is unreliable in the case of rubberlike material.

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

    SciTech Connect

    Yeh, M.S.; Chang, J.C.; Chuang, T.H.

    1999-04-01

    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.

  5. Controlling the stress of growing GaN on 150-mm Si (111) in an AlN/GaN strained layer superlattice

    NASA Astrophysics Data System (ADS)

    Lin, Po-Jung; Huang, Shih-Yung; Wang, Wei-Kai; Chen, Che-Lin; Chung, Bu-Chin; Wuu, Dong-Sing

    2016-01-01

    For growing a thicker GaN epilayer on a Si substrate, generally, a larger wafer bowing with tensile stress caused by the mismatch of thermal expansion coefficients between GaN and Si easily generates a cracked surface during cool down. In this work, wafer bowing was investigated to control stress by changing the thickness of a GaN layer from 18.6 to 27.8 nm in a 80-paired AlN/GaN strained layer superlattice (SLS) grown on a 150-mm Si (111) substrate. The results indicated that wafer bowing was inversely proportional to the total thickness of epilayer and the thickness of the GaN layer in the AlN/GaN SLS, since higher compressive stress caused by a thicker GaN layer during SLS growth could compensate for the tensile stress generated during cool down. After returning to room temperature, the stress of the AlN/GaN SLS was still compressive and strained in the a-axis. This is due to an unintended AlGaN grading layer was formed in the AlN/GaN SLS. This AlGaN layer reduced the lattice mismatch between AlN and GaN and efficiently accumulated stress without causing relaxation.

  6. Novel high-pressure phases of AlP from first principles

    NASA Astrophysics Data System (ADS)

    Liu, Chao; Hu, Meng; Luo, Kun; Yu, Dongli; Zhao, Zhisheng; He, Julong

    2016-05-01

    By utilizing a crystal structure prediction software via particle swarm optimization, this study proposes three new high-pressure phases of aluminum phosphide (AlP) with high density and high hardness, in addition to previously proposed phases (wz-, zb-, rs-, NiAs-, β-Sn-, CsCl-, and Cmcm-AlP). These new phases are as follows: (1) an I 4 ¯ 3d symmetric structure (cI24-AlP) at 55.2 GPa, (2) an R 3 ¯ m symmetric structure (hR18-AlP) at 9.9 GPa, and (3) a C222 symmetric structure (oC12-AlP) at 20.6 GPa. Based on first-principle calculations, these phases have higher energetic advantage than CsCl- and β-Sn-AlP at ambient pressure. The independent elastic constants and phonon dispersion spectra are calculated to check the mechanical and dynamic stabilities of these phases. According to mechanical property studies, these new AlP phases have higher hardness than NiAs-AlP, and oC12-AlP has the highest hardness of 7.9 GPa. Electronic band structure calculations indicate that NiAs- and hR18-AlP have electrical conductivity. Additionally, wz-, zb-, and oC12-AlP possess semiconductive properties with indirect bandgaps, and cI24-AlP has a semiconductive property with a direct bandgap.

  7. Fatigue Life and Short Crack Behavior in Ti-6Al-4V Alloy; Interactions of Foreign Object Damage, Stress, and Temperature

    NASA Astrophysics Data System (ADS)

    Majidi, Behzad

    2008-04-01

    High-cycle fatigue (HCF) failures associated with foreign object damage (FOD) in turbine engines of military aircrafts have been of major concern for the aeronautic industry in recent years. The present work is focused on characterizing the effects of FOD on crack initiation and small crack growth of a Ti-6Al-4V alloy at ambient and also elevated temperatures. Results show that the preferred crack initiation site depends on applied stress and temperature as maximum fractions of cracks emanating from the simulated damage site, and naturally initiated cracks are observed at 25 °C under the maximum stress of 700 MPa and at 300 °C under the maximum stress of 300 MPa. The fatigue crack growth rate is influenced by increasing temperature, and the FCG rate at 300 °C is higher than that at room temperature under the same Δ K, whereas this effect for FOD-site initiated cracks is not so remarkable. This observation seems to be due to the effect of stress relaxation at 300 °C. Results also indicate that fatigue crack initiation life ( N i ) and fatigue life ( N f ) are expressed by three-parameter Weibull distribution function.

  8. High temperature oxidation resistant coatings for the directionally solidified Ni-Nb-Cr-Al eutectic superalloy

    NASA Technical Reports Server (NTRS)

    Strangman, T. E.; Ulion, N. E.; Felten, E. J.

    1977-01-01

    Protective coatings required for the Ni-Nb-Cr-Al directionally solidified eutectic superalloy were developed and evaluated on the basis of oxidation resistance, diffusional stability, thermal fatigue, and creep resistance. NiCrAlY+Pt and NiCrAlY physical vapor-deposition coating systems exhibited the best combination of properties. Burner-rig testing indicated that the useful life of a 127-micron-thick NiCrAlY+Pt coating exceeds 1000 h at 1366 K. Eutectic-alloy creep lives at 1311 K and a stress of 151.7 MN/sq m were greater for NiCrAlY+Pt-coated specimens than for uncoated specimens by a factor of two.

  9. Simulation of AlGaN/GaN high-electron-mobility transistor gauge factor based on two-dimensional electron gas density and electron mobility

    NASA Astrophysics Data System (ADS)

    Chu, Min; Koehler, Andrew D.; Gupta, Amit; Nishida, Toshikazu; Thompson, Scott E.

    2010-11-01

    The gauge factor of AlGaN/GaN high-electron-mobility transistor was determined theoretically, considering the effect of stress on the two-dimensional electron gas (2DEG) sheet carrier density and electron mobility. Differences in the spontaneous and piezoelectric polarization between the AlGaN and GaN layers, with and without external mechanical stress, were investigated to calculate the stress-altered 2DEG density. Strain was incorporated into a sp3d5-sp3 empirical tight-binding model to obtain the change in electron effective masses under biaxial and uniaxial stress. The simulated longitudinal gauge factor (-7.9±5.2) is consistent with experimental results (-2.4±0.5) obtained from measurements eliminating parasitic charge trapping effects through continuous subbandgap optical excitation.

  10. Adolescents' sleep in low-stress and high-stress (exam) times: a prospective quasi-experiment.

    PubMed

    Dewald, Julia F; Meijer, Anne Marie; Oort, Frans J; Kerkhof, Gerard A; Bögels, Susan M

    2014-01-01

    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 that individuals slept more restless during stressful times. However, sleep efficiency, total sleep time, and sleep onset latency remained stable throughout the three consecutive weeks. High chronic sleep reduction was related to later bedtimes, later sleep start times, later sleep end times, later getting up times, and more time spent in bed. Furthermore, low chronic sleep reduction and high baseline stress levels were related to more fragmented sleep during stressful times. This study shows that stressful times can have negative effects on adolescents' sleep fragmentation, especially for adolescents with low chronic sleep reduction or high baseline stress levels. PMID:24786857

  11. Characterization of the reliability and uniformity of an anodization-free fabrication process for high-quality Nb/Al-AlOx/Nb Josephson junctions

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

    We have developed a reliable and reproducible fabrication process for high-quality Nb/Al-AlOx/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.

  12. High stress actuation by dielectric elastomer with oil capsules

    NASA Astrophysics Data System (ADS)

    La, Thanh-Giang; Lau, Gih-Keong; Shiau, Li-Lynn; Tan, Adrian W. Y.

    2014-03-01

    Though capable of generating a large strain, dielectric elastomer actuators (DEAs) generate only a moderate actuation stress not more than 200kPa, which seriously limits its use as artificial muscles for robotic arm. Enhancement of dielectric strength (greater than 500MV/m) by dielectric oil immersion could possibly enable it a larger force generation. Previously, the immersion was done in an oil bath, which limits portability together with DEAs. In this study, we developed portable capsules to enclose oil over the DEA substrate (VHB 4905). The capsules is made of a thinner soft acrylic membrane and they seals dielectric liquid oil (Dow Corning Fluid 200 50cSt). The DEA substrate is a graphiteclad VHB membrane, which is pre-stretched with pure-shear boundary condition for axial actuation. When activated under isotonic condition, the oil-capsule DEA can sustain a very high dielectric field up to 903 MV/m and does not fail; whereas, the dry DEA breaks down at a lower electric field at 570 MV/m. Furthermore, the oil-capsule DEA can produces higher isometric stress change up to 1.05MPa, which is 70% more than the maximum produced by the dry DEA. This study confirmed that oil capping helps DEA achieve very high dielectric strength and generate more stress change for work.

  13. Misinformation can influence memory for recently experienced, highly stressful events.

    PubMed

    Morgan, C A; Southwick, Steven; Steffian, George; Hazlett, Gary A; Loftus, Elizabeth F

    2013-01-01

    A large body of research has demonstrated that exposure to misinformation can lead to distortions in human memory for genuinely experienced objects or people. The current study examined whether misinformation could affect memory for a recently experienced, personally relevant, highly stressful event. In the present study we assessed the impact of misinformation on memory in over 800 military personnel confined in the stressful, mock POW camp phase of Survival School training. Misinformation introduced after the negatively affected memory for the details of the event (such as the presence of glasses or weapons), and also affected the accuracy of identification of an aggressive interrogator. In some conditions more than half of the subjects exposed to a misleading photograph falsely identified a different individual as their interrogator after the interrogation was over. These findings demonstrate that memories for stressful events are highly vulnerable to modification by exposure to misinformation, even in individuals whose level of training and experience might be thought to render them relatively immune to such influences. PMID:23219699

  14. Modeling of high composition AlGaN channel high electron mobility transistors with large threshold voltage

    SciTech Connect

    Bajaj, Sanyam Hung, Ting-Hsiang; Akyol, Fatih; Nath, Digbijoy; Rajan, Siddharth

    2014-12-29

    We report on the potential of high electron mobility transistors (HEMTs) consisting of high composition AlGaN channel and barrier layers for power switching applications. Detailed two-dimensional (2D) simulations show that threshold voltages in excess of 3 V can be achieved through the use of AlGaN channel layers. We also calculate the 2D electron gas mobility in AlGaN channel HEMTs and evaluate their power figures of merit as a function of device operating temperature and Al mole fraction in the channel. Our models show that power switching transistors with AlGaN channels would have comparable on-resistance to GaN-channel based transistors for the same operation voltage. The modeling in this paper shows the potential of high composition AlGaN as a channel material for future high threshold enhancement mode transistors.

  15. The association of very high hair manganese accumulation and high oxidative stress in Mongolian people.

    PubMed

    Komatsu, Fumio; Kagawa, Yasuo; Ishiguro, Kiyomi; Kawabata, Terue; Purvee, Baatar; Otgon, Jugder; Chimedregzen, Ulziiburen

    2009-03-01

    Oxidative stress induces several diseases and early aging. Previously, we reported that Mongolians are exposed in high oxidative stress, which may cause their early aging. In this study, to know the reason of high oxidative stress, we measured hair metals. This investigation was performed in Murun city, in the northern area of this country, and 469 healthy subjects, ranging from 10 to 82 years of age, were randomly enrolled. Oxidative stress was evaluated by the levels of serum reactive oxygen metabolites (ROM), malondialdehyde-modified low-density lipoprotein (MDA-LDL) and urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG). Antioxidant capacity (AOC) was estimated by the levels of biological antioxidant potential (BAP) and superoxide dismutase (SOD) activity. Scalp hair metals were measured using an inductively coupled plasma mass spectrometry method. Murun subjects showed high ROM levels of 394+/-75 Carr U (n=342), compared with Japanese healthy subjects (n=356, 326+/-51 Carr U, p<0.001). MDA-LDL and 8-OHdG levels also showed high levels. While, BAP levels of Murun subjects were 2263+/-203 micromol/L (n=210), Japanese subjects (n=356, 2087+/-215 micromol/L, p<0.001). SOD activities were also high, suggesting that the high oxidative may accelerate the state of AOC. Murun subjects demonstrated high accumulation of several metals in the hairs. In particular, Mn accumulation exhibited from 2 fold to 40 fold increases of Japanese standard. These findings are indicative that the high Mn accumulation may contribute to the high oxidative stress. The mechanism of its high accumulation was not explained by food materials or drinking water. We should further investigate another influence such as sandy wind. In order to suppress the high oxidative stress, elimination of the high Mn accumulation should be urgently studied. PMID:20021397

  16. Time evolution of off-state degradation of AlGaN/GaN high electron mobility transistors

    SciTech Connect

    Bajo, M. Montes E-mail: Martin.Kuball@bristol.ac.uk; Sun, H.; Uren, M. J.; Kuball, M. E-mail: Martin.Kuball@bristol.ac.uk

    2014-06-02

    The evolution of AlGaN/GaN high electron mobility transistors under off-state stress conditions is studied by gate leakage current (I{sub g}) monitoring, electroluminescence (EL), and atomic force microscope (AFM) imaging at room temperature. It is found that the number of off-state failure sites as identified by EL increases over time during stress until it reaches a saturation value. I{sub g} increases accordingly during stress until this saturation number of failure sites is reached. AFM scanning of the device surface stripped of metal contacts and passivation reveals surface pits corresponding to the location of the EL spots. These pits have an elongated shape oriented towards the drain contact whose length is correlated with the distance to the adjacent pits and with the time since their appearance during the stress experiment. A model for the generation and evolution of the off-state stress-related failure sites is proposed consistent with the experimental results, bringing together surface migration of electrochemical species with trap-based leakage mechanisms and resulting in the formation of an exclusion zone around each failure site.

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

    SciTech Connect

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

    2000-07-01

    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.

  18. Cation disorder determined by MAS {sup 27}Al NMR in high dose neutron irradiated spinel

    SciTech Connect

    Cooper, E.A.; Sickafus, K.E.; Hughes, C.D.; Earl, W.L.; Hollenberg, G.W.; Garner, F.A.; Bradt, R.C.

    1995-12-31

    Spinel (MgAl{sub 2}O{sub 4}) single crystals which had been neutron irradiated to high doses (53-250 dpa) were examined using {sup 27}Al magic angle spinning (MAS) nuclear magnetic resonance (NMR). The sensitivity of this procedure to a specific cation (Al) residing in different crystallographic environments allowed one to determine the distribution of the Al between the two cation sites in the spinel structure. The samples were irradiated at two different temperatures (400 and 750{degrees}C) and various doses. These results indicate that the Al was nearly fully disordered over the two lattice sites after irradiation.

  19. Electrochemical investigation on the hydrogen permeation behavior of 7075-T6 Al alloy and its influence on stress corrosion cracking

    NASA Astrophysics Data System (ADS)

    Zheng, Chuan-bo; Yan, Bing-hao; Zhang, Ke; Yi, Guo

    2015-07-01

    The hydrogen permeation behavior and stress corrosion cracking (SCC) susceptibility of precharged 7075-T6 Al alloy were investigated in this paper. Devanthan-Stachurski (D-S) cell tests were used to measure the apparent hydrogen diffusivity and hydrogen permeation current density of specimens immersed in 3.5wt% NaCl solution. Electrochemical experiment results show that the SCC susceptibility is low during anodic polarization. Both corrosion pits and hydrogen-induced cracking are evident in scanning electron microscope images after the specimens have been charging for 24 h.

  20. High pressure studies of A2Mo3O12 negative thermal expansion materials (A2=Al2, Fe2, FeAl, AlGa)

    NASA Astrophysics Data System (ADS)

    Young, Lindsay; Gadient, Jennifer; Gao, Xiaodong; Lind, Cora

    2016-05-01

    High pressure powder X-ray diffraction studies of several A2Mo3O12 materials (A2=Al2, Fe2, FeAl, and AlGa) were conducted up to 6-7 GPa. All materials adopted a monoclinic structure under ambient conditions, and displayed similar phase transition behavior upon compression. The initial isotropic compressibility first became anisotropic, followed by a small but distinct drop in cell volume. These patterns could be described by a distorted variant of the ambient pressure polymorph. At higher pressures, a distinct high pressure phase formed. Indexing results confirmed that all materials adopted the same high pressure phase. All changes were reversible on decompression, although some hysteresis was observed. The similarity of the high pressure cells to previously reported Ga2Mo3O12 suggested that this material undergoes the same sequence of transitions as all materials investigated in this paper. It was found that the transition pressures for all phase changes increased with decreasing radius of the A-site cations.

  1. Transient characteristics of AlGaN/GaN high-electron-mobility transistor with bias-controllable field plate

    NASA Astrophysics Data System (ADS)

    Mase, Suguru; Egawa, Takashi; Wakejima, Akio

    2015-03-01

    The trapping and emission of carriers in the gate-to-drain region of an AlGaN/GaN high-electron-mobility transistor (HEMT) have been investigated using a bias-controllable field plate (CFP). Once an instantaneous positive CFP voltage is applied after bias stress in a transient drain current measurement, carrier trapping occurs, which can subsequently be observed as a drain current discontinuity. Numerical analysis of carrier trapping using the Shockley-Read-Hall process also provides a trapped carrier density of 5.1 × 1012 cm-2 and an energy level of 0.6 eV.

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

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

    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.

  3. A High shear stress segment along the San Andreas Fault: Inferences based on near-field stress direction and stress magnitude observations in the Carrizo Plain Area

    SciTech Connect

    Castillo, D. A.,; Younker, L.W.

    1997-01-30

    Nearly 200 new in-situ determinations of stress directions and stress magnitudes near the Carrizo plain segment of the San Andreas fault indicate a marked change in stress state occurring within 20 km of this principal transform plate boundary. A natural consequence of this stress transition is that if the observed near-field ``fault-oblique`` stress directions are representative of the fault stress state, the Mohr-Coulomb shear stresses resolved on San Andreas sub-parallel planes are substantially greater than previously inferred based on fault-normal compression. Although the directional stress data and near-hydrostatic pore pressures, which exist within 15 km of the fault, support a high shear stress environment near the fault, appealing to elevated pore pressures in the fault zone (Byerlee-Rice Model) merely enhances the likelihood of shear failure. These near-field stress observations raise important questions regarding what previous stress observations have actually been measuring. The ``fault-normal`` stress direction measured out to 70 km from the fault can be interpreted as representing a comparable depth average shear strength of the principal plate boundary. Stress measurements closer to the fault reflect a shallower depth-average representation of the fault zone shear strength. If this is true, only stress observations at fault distances comparable to the seismogenic depth will be representative of the fault zone shear strength. This is consistent with results from dislocation monitoring where there is pronounced shear stress accumulation out to 20 km of the fault as a result of aseismic slip within the lower crust loading the upper locked section. Beyond about 20 km, the shear stress resolved on San Andreas fault-parallel planes becomes negligible. 65 refs., 15 figs.

  4. Effect of high hip center on stress for dysplastic hip.

    PubMed

    Nie, Yong; Pei, Fuxing; Li, Zongming

    2014-07-01

    High hip center reconstruction has been advocated in treating deficient acetabulum. However, there is no consensus on the clinical outcome of this technique. In addition, it remains unclear to what extend this technique restores the normal hip biomechanics. The goal of this study was to investigate stress above the acetabular dome in response to a range of high hip center positioning for Crowe type I and II hip dysplasia. This study consisted of 2 main parts, radiologic and biomechanical. Pelvic radiographs of 18 patients were studied to determine the amount of displacement of the hip center in the superior direction compared with the normal side. Second, qualitative and quantitative changes in stress on cortical and trabecular bone in the region of the acetabular dome as a result of superior displacement of the hip center were analyzed with subject-specific finite element models. The results showed that the range of the hip center position in the superior direction for Crowe type I and II hip dysplasia was 0 to 15 mm above the contralateral femoral head center. When superior displacement of the hip center exceeded 5 mm above the anatomic hip center, cortical bone mass on the 2 thickest cross-sections above the acetabular dome decreased quickly and the stress value on posterolateral cortical bone was obviously lower than the normal level. This study showed that to restore the normal load above the acetabular dome, there is a limit of 5 mm above the anatomic hip center for high hip center acetabular reconstruction for Crowe type I and II hip dysplasia. PMID:24992059

  5. Evaluation of the interfacial shear strength and residual stress of TiAlN coating on ZIRLO™ fuel cladding using a modified shear-lag model approach

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Bhamji, I.; Withers, P. J.; Wolfe, D. E.; Motta, A. T.; Preuss, M.

    2015-11-01

    This paper investigates the residual stresses and interfacial shear strength of a TiAlN coating on Zr-Nb-Sn-Fe alloy (ZIRLO™) substrate designed to improve corrosion resistance of fuel cladding used in water-cooled nuclear reactors, both during normal and exceptional conditions, e.g. a loss of coolant event (LOCA). The distribution and maximum value of the interfacial shear strength has been estimated using a modified shear-lag model. The parameters critical to this analysis were determined experimentally. From these input parameters the interfacial shear strength between the TiAlN coating and ZIRLO™ substrate was inferred to be around 120 MPa. It is worth noting that the apparent strength of the coating is high (∼3.4 GPa). However, this is predominantly due to the large compressive residuals stress (3 GPa in compression), which must be overcome for the coating to fail in tension, which happens at a load just 150 MPa in excess of this.

  6. Internal stress and degradation in short-wavelength AlGaAs double-heterojunction devices

    NASA Technical Reports Server (NTRS)

    Ladany, I.; Furman, T. R.; Marinelli, D. P.

    1979-01-01

    Aging tests of incoherently operated zinc-doped double-heterojunction (DH) lasers designed for short-wavelength (0.71-0.72 micron) operation show that the introduction of buffer layers between the substrate and the DH structure leads to a drastic reduction in gradual degradation. This is attributed to a decrease in lattice mismatch stress.

  7. In situ Formed α-Al2O3 Nanocrystals Repaired the Preexisting Microcracks in Plasma-Sprayed Al2O3 Coating via Stress-Induced Phase Transformation

    NASA Astrophysics Data System (ADS)

    Yang, Kai; Feng, Jingwei; Rong, Jian; Liu, Chenguang; Tao, Shunyan; Ding, Chuanxian

    2016-02-01

    In the present study, the phase composition and generation mechanism of the nanocrystals located in the microcracks of plasma-sprayed Al2O3 coating were reevaluated. The Al2O3 coatings were investigated using transmission electron microscopy and x-ray diffraction. We supply the detailed explanations to support the new viewpoint that in situ formation of α-Al2O3 nanocrystals in the preexisting microcracks of the as-sprayed Al2O3 coating may be due to the stress-induced phase transformation. Owing to the partially coherent relationship, the phase interfaces between the α-Al2O3 nanocrystals with the preferred orientation and the γ-Al2O3 matrix may possess better bonding strength. The α-Al2O3 nanocrystals could repair the microcracks in the coating, which further strengthens grain boundaries. Grain boundary strengthening is beneficial to the coating fracture toughness enhancement.

  8. Comparison Between Nb3Al and Nb3Sn Strands and Cables for High Field Accelerator Magnets

    SciTech Connect

    Yamada, R.; Kikuchi, A.; Barzi, E.; Chlachidze, G.; Rusy, A.; Takeuchi, T.; Tartaglia, M.; Turrioni, D.; Velev, V.; Wake, M.; Zlobin, A.V.; /Fermilab

    2010-01-01

    The Nb{sub 3}Al small racetrack magnet, SR07, has been successfully built and tested to its short sample limit beyond 10 Tesla without any training. Thus the practical application of Nb{sub 3}Al strands for high field accelerator magnets is established. The characteristics of the representative F4 strand and cable, are compared with the typical Nb{sub 3}Sn strand and cable. It is represented by the OST high current RRP Nb{sub 3}Sn strand with 108/127 configuration. The effects of Rutherford cabling to both type strands are explained and the inherent problem of the Nb{sub 3}Sn strand is discussed. Also the test results of two representative small racetrack magnets are compared from the stand point of Ic values, and training. The maximum current density of the Nb{sub 3}Al strands is still smaller than that of the Nb{sub 3}Sn strands, but if we take into account of the stress-strain characteristics, Nb{sub 3}Al strands become somewhat favorable in some applications.

  9. LuAlO3: A high density, high speed scintillator for gamma detection

    NASA Astrophysics Data System (ADS)

    Moses, W. W.; Derenzo, S. E.; Fyodorov, A.; Korzhik, M.; Gektin, A.; Minkov, B.; Aslanov, V.

    1994-11-01

    We present measurements of the scintillation properties cerium doped lutetium aluminum perovskite, LuAlO3:Ce, new dense ((rho)=8.34 g/cm(sup 3)) inorganic scintillator. This material has a 511 keV interaction length and photoelectric fraction 1.1 cm and 32% respectively, which are well suited to gamma ray detection. In powdered form with 0.5% cerium concentration, the scintillation light output is estimated to be 9,600 photons/MeV of deposited energy, the emission spectrum is a single peak centered at 390 nm, and the fluorescence lifetime is described by the sum of 3 exponential terms, with 60% of the light being emitted with a 11 ns decay time, 26% with a 28 ns decay time, and 13% with a 835 ns decay time. Single crystals contaminated with =10% lutetium aluminum garnet (Lu3Al5Ol2) have significantly altered scintillation properties. The light output is 26,000 photons/MeV (3.2 times that of BGO), but the decay time increases significantly (1% of the light is emitted with a 10 ns decay time, 15% with a 245 ns decay time, and 85% with a 2010 ns decay time) and the emission spectrum is dominated by a peak centered at 315 nm with a secondary peak centered at 500 rum. The short decay lifetime, high density, and reasonable light output of LuAlO3:Ce (the perovskite phase) suggest that it is useful for applications where high counting rates, good stopping power, good energy resolution, and fast timing are important. However, it is necessary to grow single crystals that are uncontaminated by the garnet phase to realize these properties.

  10. LuAlO{sub 3}: A high density, high speed scintillator for gamma detection

    SciTech Connect

    Moses, W.W.; Derenzo, S.E.; Fyodorov, A.; Korzhik, M.; Gektin, A.; Minkov, B.; Aslanov, V.

    1994-11-01

    We present measurements of the scintillation properties cerium doped lutetium aluminum perovskite, LuAlO{sub 3}:C, new dense ({rho}=8.34 g/cm{sup 3}) inorganic scintillator. This material has a 511 keV interaction length and photoelectric fraction 1.1 cm and 32% respectively, which are well suited to gamma ray detection. In powdered form with 0.5% cerium concentration, the scintillation light output is estimated to be 9,600 photons/MeV of deposited energy, the emission spectrum is a single peak centered at 390 nm, and the fluorescence lifetime is described by the sum of 3 exponential terms, with 60% of the light being emitted with a 11 ns decay time, 26% with a 28 ns decay time, and 13% with a 835 ns decay time. Single crystals contaminated with =10% lutetium aluminum garnet (Lu{sub 3}Al{sub 5}O{sub l2}) have significantly altered scintillation properties. The light output is 26,000 photons/MeV (3.2 times that of BGO), but the decay time increases significantly (1% of the light is emitted with a 10 ns decay time, 15% with a 245 ns decay time, and 85% with a 2010 ns decay time) and the emission spectrum is dominated by a peak centered at 315 nm with a secondary peak centered at 500 rum. The short decay lifetime, high density, and reasonable light output of LuAlO{sub 3}:C (the perovskite phase) suggest that it is useful for applications where high counting rates, good stopping power, good energy resolution, and fast timing are important. However, it is necessary to grow single crystals that are uncontaminated by the garnet phase to realize these properties.

  11. High throughput exploration of process-property linkages in Al-6061 using instrumented spherical microindentation and microstructurally graded samples

    DOE PAGESBeta

    Weaver, Jordan S.; Khosravani, Ali; Castillo, Andrew; Kalidindi, Surya R.

    2016-06-14

    Recent spherical nanoindentation protocols have proven robust at capturing the local elastic-plastic response of polycrystalline metal samples at length scales much smaller than the grain size. In this work, we extend these protocols to length scales that include multiple grains to recover microindentation stress-strain curves. These new protocols are first established in this paper and then demonstrated for Al-6061 by comparing the measured indentation stress-strain curves with the corresponding measurements from uniaxial tension tests. More specifically, the scaling factors between the uniaxial yield strength and the indentation yield strength was determined to be about 1.9, which is significantly lower thanmore » the value of 2.8 used commonly in literature. Furthermore, the reasons for this difference are discussed. Second, the benefits of these new protocols in facilitating high throughput exploration of process-property relationships are demonstrated through a simple case study.« less

  12. ALS mutant FUS proteins are recruited into stress granules in induced pluripotent stem cell-derived motoneurons

    PubMed Central

    Lenzi, Jessica; De Santis, Riccardo; de Turris, Valeria; Morlando, Mariangela; Laneve, Pietro; Calvo, Andrea; Caliendo, Virginia; Chiò, Adriano; Rosa, Alessandro; Bozzoni, Irene

    2015-01-01

    ABSTRACT Patient-derived induced pluripotent stem cells (iPSCs) provide an opportunity to study human diseases mainly in those cases for which no suitable model systems are available. Here, we have taken advantage of in vitro iPSCs derived from patients affected by amyotrophic lateral sclerosis (ALS) and carrying mutations in the RNA-binding protein FUS to study the cellular behavior of the mutant proteins in the appropriate genetic background. Moreover, the ability to differentiate iPSCs into spinal cord neural cells provides an in vitro model mimicking the physiological conditions. iPSCs were derived from FUSR514S and FUSR521C patient fibroblasts, whereas in the case of the severe FUSP525L mutation, in which fibroblasts were not available, a heterozygous and a homozygous iPSC line were raised by TALEN-directed mutagenesis. We show that aberrant localization and recruitment of FUS into stress granules (SGs) is a prerogative of the FUS mutant proteins and occurs only upon induction of stress in both undifferentiated iPSCs and spinal cord neural cells. Moreover, we show that the incorporation into SGs is proportional to the amount of cytoplasmic FUS, strongly correlating with the cytoplasmic delocalization phenotype of the different mutants. Therefore, the available iPSCs represent a very powerful system for understanding the correlation between FUS mutations, the molecular mechanisms of SG formation and ALS ethiopathogenesis. PMID:26035390

  13. ALS mutant FUS proteins are recruited into stress granules in induced pluripotent stem cell-derived motoneurons.

    PubMed

    Lenzi, Jessica; De Santis, Riccardo; de Turris, Valeria; Morlando, Mariangela; Laneve, Pietro; Calvo, Andrea; Caliendo, Virginia; Chiò, Adriano; Rosa, Alessandro; Bozzoni, Irene

    2015-07-01

    Patient-derived induced pluripotent stem cells (iPSCs) provide an opportunity to study human diseases mainly in those cases for which no suitable model systems are available. Here, we have taken advantage of in vitro iPSCs derived from patients affected by amyotrophic lateral sclerosis (ALS) and carrying mutations in the RNA-binding protein FUS to study the cellular behavior of the mutant proteins in the appropriate genetic background. Moreover, the ability to differentiate iPSCs into spinal cord neural cells provides an in vitro model mimicking the physiological conditions. iPSCs were derived from FUS(R514S) and FUS(R521C) patient fibroblasts, whereas in the case of the severe FUS(P525L) mutation, in which fibroblasts were not available, a heterozygous and a homozygous iPSC line were raised by TALEN-directed mutagenesis. We show that aberrant localization and recruitment of FUS into stress granules (SGs) is a prerogative of the FUS mutant proteins and occurs only upon induction of stress in both undifferentiated iPSCs and spinal cord neural cells. Moreover, we show that the incorporation into SGs is proportional to the amount of cytoplasmic FUS, strongly correlating with the cytoplasmic delocalization phenotype of the different mutants. Therefore, the available iPSCs represent a very powerful system for understanding the correlation between FUS mutations, the molecular mechanisms of SG formation and ALS ethiopathogenesis. PMID:26035390

  14. High damping Al-Fe-Mo-Si/Zn-Al composites produced by rapidly solidified powder metallurgy process

    SciTech Connect

    Li, P.Y.; Dai, S.L.; Chai, S.C.; Li, Y.R.

    2000-05-10

    The metallic materials commonly used in aircraft and aerospace fields, such as aluminum and titanium alloys, steels, etc., show extremely low damping capacity (usually of the order of or less than 10{sup {minus}3}). Thus, some problems related to vibration may emerge and influence the reliability, safety and life of airplanes, satellites, etc. It has been reported that almost two thirds of errors for rockets and satellites are related to vibration and noise. One effective way to solve these vibration-related problems is to adopt high damping metallic materials. Conventional high damping alloys exhibit damping capacity above 10{sup {minus}2}, however, their densities are usually great than 5 x 10{sup 3} kg m{sup {minus}3}, or their strengths are less than 200 MPa (for alloys based on dislocation damping), making them impossible to be applied to aircraft and aerospace areas. Recently, some low-density high-damping metal/metal composites based on aluminum and high damping alloys have been developed in Beijing Institute of Aeronautical Materials (BIAM) by the rapidly solidified power metallurgy process. This paper aims to report the properties of the composites based on a high temperature Al-Fe-Mo-Si alloy and a high damping Zn-Al alloy, and compare them with that of 2618-T61 alloy produced by the ingot metallurgy process.

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

    SciTech Connect

    Shimazu, T.; Miura, M.; Isu, N.; Ogawa, T.; Ichikawa, A.; Ishida, E. H.

    2006-05-15

    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.

  16. Evaluation of high-strength Cu-Ni-Mn-Al bolting used in oil and gas service

    SciTech Connect

    Andersen, O.; Joosten, M.W.; Murali, J.; Milliams, D.E.

    1996-08-01

    High strength bolts, nuts, studs and screws manufactured from a precipitation hardening Cu-Ni-Mn-Al alloy have experienced several failures in recent years in oilfield installations with varying degrees of severity and consequence. Such failures have been broadly attributed to Stress Corrosion Cracking (SCC) and Liquid Metal Embrittlement (LME) phenomena. A detailed test program using the Slow Strain Rate Testing (SSRT) method has been conducted to identify the various parameters which could contribute to SCC. Results indicate that the Cu-Ni-Mn-Al alloy is susceptible to SCC in a variety of environments commonly found in oilfield equipment manufacturing and field installations such as amine-containing additives, sulfides and even natural seawater at elevated temperatures. SSRT testing indicated, however, that, in seawater environments, low service temperatures and cathodic protection did not adversely affect the alloy`s performance. Discussion of test program results and qualitative correlations with field failures are presented.

  17. Atomistic clustering-ordering and high-strain deformation of an Al0.1CrCoFeNi high-entropy alloy

    DOE PAGESBeta

    Sharma, Aayush; Singh, Prashant; Johnson, Duane D.; Liaw, Peter K.; Balasubramanian, Ganesh

    2016-08-08

    Here, computational investigations of structural, chemical, and deformation behavior in high-entropy alloys (HEAs), which possess notable mechanical strength, have been limited due to the absence of applicable force fields. To extend investigations, we propose a set of intermolecular potential parameters for a quinary Al-Cr-Co-Fe-Ni alloy, using the available ternary Embedded Atom Method and Lennard-Jones potential in classical molecular-dynamics simulations. The simulation results are validated by a comparison to first-principles Korringa-Kohn-Rostoker (KKR) - Coherent Potential Approximation (CPA) [KKR-CPA] calculations for the HEA structural properties (lattice constants and bulk moduli), relative stability, pair probabilities, and high-temperature short-range ordering. The simulation (MD)-derived propertiesmore » are in quantitative agreement with KKR-CPA calculations (first-principles) and experiments. We study AlxCrCoFeNi for Al ranging from 0 ≤ x ≤2 mole fractions, and find that the HEA shows large chemical clustering over a wide temperature range for x < 0.5. At various temperatures high-strain compression promotes atomistic rearrangements in Al0.1CrCoFeNi, resulting in a clustering-to-ordering transition that is absent for tensile loading. Large fluctuations under stress, and at higher temperatures, are attributed to the thermo-plastic instability in Al0.1CrCoFeNi.« less

  18. Atomistic clustering-ordering and high-strain deformation of an Al0.1CrCoFeNi high-entropy alloy

    PubMed Central

    Sharma, Aayush; Singh, Prashant; Johnson, Duane D.; Liaw, Peter K.; Balasubramanian, Ganesh

    2016-01-01

    Computational investigations of structural, chemical, and deformation behavior in high-entropy alloys (HEAs), which possess notable mechanical strength, have been limited due to the absence of applicable force fields. To extend investigations, we propose a set of intermolecular potential parameters for a quinary Al-Cr-Co-Fe-Ni alloy, using the available ternary Embedded Atom Method and Lennard-Jones potential in classical molecular-dynamics simulations. The simulation results are validated by a comparison to first-principles Korringa-Kohn-Rostoker (KKR) - Coherent Potential Approximation (CPA) [KKR-CPA] calculations for the HEA structural properties (lattice constants and bulk moduli), relative stability, pair probabilities, and high-temperature short-range ordering. The simulation (MD)-derived properties are in quantitative agreement with KKR-CPA calculations (first-principles) and experiments. We study AlxCrCoFeNi for Al ranging from 0 ≤ x ≤2 mole fractions, and find that the HEA shows large chemical clustering over a wide temperature range for x < 0.5. At various temperatures high-strain compression promotes atomistic rearrangements in Al0.1CrCoFeNi, resulting in a clustering-to-ordering transition that is absent for tensile loading. Large fluctuations under stress, and at higher temperatures, are attributed to the thermo-plastic instability in Al0.1CrCoFeNi. PMID:27498807

  19. Atomistic clustering-ordering and high-strain deformation of an Al0.1CrCoFeNi high-entropy alloy

    NASA Astrophysics Data System (ADS)

    Sharma, Aayush; Singh, Prashant; Johnson, Duane D.; Liaw, Peter K.; Balasubramanian, Ganesh

    2016-08-01

    Computational investigations of structural, chemical, and deformation behavior in high-entropy alloys (HEAs), which possess notable mechanical strength, have been limited due to the absence of applicable force fields. To extend investigations, we propose a set of intermolecular potential parameters for a quinary Al-Cr-Co-Fe-Ni alloy, using the available ternary Embedded Atom Method and Lennard-Jones potential in classical molecular-dynamics simulations. The simulation results are validated by a comparison to first-principles Korringa-Kohn-Rostoker (KKR) - Coherent Potential Approximation (CPA) [KKR-CPA] calculations for the HEA structural properties (lattice constants and bulk moduli), relative stability, pair probabilities, and high-temperature short-range ordering. The simulation (MD)-derived properties are in quantitative agreement with KKR-CPA calculations (first-principles) and experiments. We study AlxCrCoFeNi for Al ranging from 0 ≤ x ≤2 mole fractions, and find that the HEA shows large chemical clustering over a wide temperature range for x < 0.5. At various temperatures high-strain compression promotes atomistic rearrangements in Al0.1CrCoFeNi, resulting in a clustering-to-ordering transition that is absent for tensile loading. Large fluctuations under stress, and at higher temperatures, are attributed to the thermo-plastic instability in Al0.1CrCoFeNi.

  20. Atomistic clustering-ordering and high-strain deformation of an Al0.1CrCoFeNi high-entropy alloy.

    PubMed

    Sharma, Aayush; Singh, Prashant; Johnson, Duane D; Liaw, Peter K; Balasubramanian, Ganesh

    2016-01-01

    Computational investigations of structural, chemical, and deformation behavior in high-entropy alloys (HEAs), which possess notable mechanical strength, have been limited due to the absence of applicable force fields. To extend investigations, we propose a set of intermolecular potential parameters for a quinary Al-Cr-Co-Fe-Ni alloy, using the available ternary Embedded Atom Method and Lennard-Jones potential in classical molecular-dynamics simulations. The simulation results are validated by a comparison to first-principles Korringa-Kohn-Rostoker (KKR) - Coherent Potential Approximation (CPA) [KKR-CPA] calculations for the HEA structural properties (lattice constants and bulk moduli), relative stability, pair probabilities, and high-temperature short-range ordering. The simulation (MD)-derived properties are in quantitative agreement with KKR-CPA calculations (first-principles) and experiments. We study AlxCrCoFeNi for Al ranging from 0 ≤ x ≤2 mole fractions, and find that the HEA shows large chemical clustering over a wide temperature range for x < 0.5. At various temperatures high-strain compression promotes atomistic rearrangements in Al0.1CrCoFeNi, resulting in a clustering-to-ordering transition that is absent for tensile loading. Large fluctuations under stress, and at higher temperatures, are attributed to the thermo-plastic instability in Al0.1CrCoFeNi. PMID:27498807

  1. Expression Characterization of Stress Genes Under High and Low Temperature Stresses in the Pacific Oyster, Crassostrea gigas.

    PubMed

    Zhu, Qihui; Zhang, Linlin; Li, Li; Que, Huayong; Zhang, Guofan

    2016-04-01

    As a characteristic sessile inhabitant of the intertidal zone, the Pacific oyster Crassostrea gigas occupies one of the most physically stressful environments on earth. With high exposure to terrestrial conditions, oysters must tolerate broad fluctuations in temperature range. However, oysters' cellular and molecular responses to temperature stresses have not been fully characterized. Here, we analyzed oyster transcriptome data under high and low temperatures. We also identified over 30 key temperature stress-responsive candidate genes, which encoded stress proteins such as heat shock proteins and apoptosis-associated proteins. The expression characterization of these genes under short-term cold and hot environments (5 and 35 °C) and long-term cold environments (5 °C) was detected by quantitative real-time PCR. Most of these genes reached expression peaks during the recovery stage after 24 h of heat stress, and these genes were greatly induced around day 3 in long-term cold stress while responded little to short-term cold stress. In addition, in the second heat stress after 2 days of recovery, oysters showed milder expression in these genes and a lower mortality rate, which indicated the existence of plasticity in the oyster's response to heat stress. We confirmed that homeostatic flexibility and anti-apoptosis might be crucial centers of temperature stress responses in oysters. Furthermore, we analyzed stress gene families in 11 different species and found that the linage-specific expansion of stress genes might be implicated in adaptive evolution. These results indicated that both plasticity and evolution played an important role in the stress response adaptation of oysters. PMID:26746430

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

    NASA Astrophysics Data System (ADS)

    Chen, Ziyong; Mo, Yuanke; Nie, Zuoren

    2013-08-01

    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 η' are the main Matrix Precipitates (MPt) in the peak-aging state, and the mixture of η' and η 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.

  3. Development and High Temperature Property Evaluation of Ni-Co-Cr-Al Composite Electroforms

    NASA Astrophysics Data System (ADS)

    Srivastava, Meenu; Siju; Balaraju, J. N.; Ravisankar, B.

    2015-05-01

    Ni-Co-Cr-Al composite electroforms were developed with cobalt content of 10 and 40 wt.%. Cr and Al nano-particles were suspended in sulphamate electrolyte and co-deposited in the Ni-Co matrices. The surface morphology was investigated using field emission scanning electron microscope and the composition analyzed by energy-dispersive x-ray analysis. The oxidation resistance of the electroforms was studied from 600 to 1000 °C. The weight gain of Ni-10 wt.%Co-Cr-Al was less (better oxidation resistance) compared to Ni-Cr-Al and Ni-40 wt.%Co-Cr-Al. The x-ray diffraction studies revealed that the oxidation product formed on the surface of Ni-Cr-Al and Ni-10 wt.%Co-Cr-Al consisted of NiO and Al2O3, while Ni-40 wt.%Co-Cr-Al comprised oxides such as NiCo2O4, CrO3, CoO, NiO, and Al2O3. The hot corrosion behavior was investigated in 75%Na2SO4 + 25%NaCl environment at 800 °C. It was found that the hot corrosion resistance of the composite coating improved with increase in cobalt content. The probable composition suitable for high-temperature applications was found to be Ni-10 wt.%Co-Cr-Al.

  4. Anomalous temperature dependence of flow stress in a Fe{sub 3}Al alloy

    SciTech Connect

    Song, J.H.; Ha, T.K.; Chang, Y.W.

    2000-01-01

    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

  5. Deposition of highly textured AlN thin films by reactive high power impulse magnetron sputtering

    SciTech Connect

    Moreira, Milena A.; Törndahl, Tobias; Katardjiev, Ilia; Kubart, Tomas

    2015-03-15

    Aluminum nitride thin films were deposited by reactive high power impulse magnetron sputtering (HiPIMS) and pulsed direct-current on Si (100) and textured Mo substrates, where the same deposition conditions were used for both techniques. The films were characterized by x-ray diffraction and atomic force microscopy. The results show a pronounced improvement in the AlN crystalline texture for all films deposited by HiPIMS on Si. Already at room temperature, the HiPIMS films exhibited a strong preferred (002) orientation and at 400 °C, no contributions from other orientations were detected. Despite the low film thickness of only 200 nm, an ω-scan full width at half maximum value of 5.1° was achieved on Si. The results are attributed to the high ionization of sputtered material achieved in HiPIMS. On textured Mo, there was no significant difference between the deposition techniques.

  6. Structural stability of the icosahedral AlCuFe quasicrystal under high-pressure and high-temperature

    NASA Astrophysics Data System (ADS)

    Takagi, S.; Kyono, A.; Nakamoto, Y.; Hirao, N.

    2015-12-01

    We report high-pressure and high-temperature in-situ X-ray diffraction study of icosahedral (i)-AlCuFe quasicrystal "icosahedrite" which is the first known naturally occurring quasicrystal mineral discovered in the Khatyrka meteorite. The i-AlCuFe quasicrystal was synthesized in laboratory from a powder mixture with an atomic ratio of Al : Cu : Fe = 65 : 20 : 15. The high-temperature and high-pressure X-ray diffraction experiments were performed using the laser-heated diamond anvil cell system installed at BL10XU, SPring-8, Japan. The i-AlCuFe showed a characteristic X-ray diffraction pattern of quasicrystal. With only compression, the diffraction patterns of the i-AlCuFe were continued until 75 GPa. At a pressure of 87 GPa two small new peaks occurred and then kept up to the maximum pressure of 104 GPa in the study. The results indicate that the pressure-induced structural phase transition of the i-AlCuFe occurs above 87 GPa, and the structure of the i-AlCuFe remains unchanged at least up to 75 GPa. Under simultaneously high pressure and high temperature, on the other hand, the i-AlCuFe was readily transformed to crystalline phase. It can be characterized by an irreversible transformation process. The structure of the i-AlCuFe is therefore more affected by thermal metamorphism than by pressure metamorphism. The present high-pressure and high-temperature experiments clearly revealed the thermal and pressure stability of the i-AlCuFe quasicrystal which may help to explain the formation of the naturally occurring quasicrystal in the solar system.

  7. High lung volume increases stress failure in pulmonary capillaries

    NASA Technical Reports Server (NTRS)

    Fu, Z.; Costello, M. L.; Tsukimoto, K.; Prediletto, R.; Elliott, A. R.; Mathieu-Costello, O.; West, J. B.

    1992-01-01

    We previously showed that when pulmonary capillaries in anesthetized rabbits are exposed to a transmural pressure (Ptm) of approximately 40 mmHg, stress failure of the walls occurs with disruption of the capillary endothelium, alveolar epithelium, or sometimes all layers. The present study was designed to test whether stress failure occurred more frequently at high than at low lung volumes for the same Ptm. Lungs of anesthetized rabbits were inflated to a transpulmonary pressure of 20 cmH2O, perfused with autologous blood at 32.5 or 2.5 cmH2O Ptm, and fixed by intravascular perfusion. Samples were examined by both transmission and scanning electron microscopy. The results were compared with those of a previous study in which the lung was inflated to a transpulmonary pressure of 5 cmH2O. There was a large increase in the frequency of stress failure of the capillary walls at the higher lung volume. For example, at 32.5 cmH2O Ptm, the number of endothelial breaks per millimeter cell lining was 7.1 +/- 2.2 at the high lung volume compared with 0.7 +/- 0.4 at the low lung volume. The corresponding values for epithelium were 8.5 +/- 1.6 and 0.9 +/- 0.6. Both differences were significant (P less than 0.05). At 52.5 cmH2O Ptm, the results for endothelium were 20.7 +/- 7.6 (high volume) and 7.1 +/- 2.1 (low volume), and the corresponding results for epithelium were 32.8 +/- 11.9 and 11.4 +/- 3.7. At 32.5 cmH2O Ptm, the thickness of the blood-gas barrier was greater at the higher lung volume, consistent with the development of more interstitial edema. Ballooning of the epithelium caused by accumulation of edema fluid between the epithelial cell and its basement membrane was seen at 32.5 and 52.5 cmH2O Ptm. At high lung volume, the breaks tended to be narrower and fewer were oriented perpendicular to the axis of the pulmonary capillaries than at low lung volumes. Transmission and scanning electron microscopy measurements agreed well. Our findings provide a physiological

  8. Investigation of the biaxial stress of Al-doped ZnO thin films on a flexible substrate with RF magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Huang, Kuo-Ting; Chen, Hsi-Chao; Cheng, Po-Wei; Chang, Jhe-Ming

    2016-01-01

    Transparent conductive Al-doped ZnO (AZO) thin films were deposited onto poly(ethylene terephthalate) (PET) substrate, using the radio frequency (RF) magnetron sputtering method. The residual stress of flexible electronics was investigated by a double beam shadow moiré interferometer with phase shifting interferometry (PSI). Moreover, the biaxial stress of AZO thin films can be graphically represented by using Mohr’s circle of stress. The residual stress of AZO thin films becomes more compressive with the increase in sputtering power. The maximum residual stress is -1115.74 MPa, and the shearing stress is 490.57 MPa at a sputtering power of 200 W. The trends of residual stress were evidenced by the X-ray diffraction (XRD) patterns and optical properties of AZO thin films. According to the evaluation results of the refractive index and the extinction coefficient, the AZO thin films have better quality when the sputtering power less than 100 W.

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

    SciTech Connect

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

    1995-03-01

    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.

  10. All AlGaN epitaxial structure solar-blind avalanche photodiodes with high efficiency and high gain

    NASA Astrophysics Data System (ADS)

    Wu, Hualong; Wu, Weicong; Zhang, Hongxian; Chen, Yingda; Wu, Zhisheng; Wang, Gang; Jiang, Hao

    2016-05-01

    Solar-blind avalanche photodiodes were fabricated with an all AlGaN-based epitaxial structure on sapphire by metal–organic chemical vapor deposition. The devices demonstrate a maximum responsivity of 114.1 mA/W at 278 nm and zero bias, corresponding to an external quantum efficiency (EQE) of 52.7%. The EQE improves to 64.8% under a bias of ‑10 V. Avalanche gain higher than 2 × 104 was obtained at a bias of ‑140 V. The high performance is attributed to the all AlGaN-based p–i–n structure comprised of undoped and Si-doped n-type Al0.4Ga0.6N on a high quality AlN layer and highly conductive p-type AlGaN grown with In-surfactant-assisted Mg-delta doping.

  11. Morphology Control for Al2O3 Inclusion Without Ca Treatment in High-Aluminum Steel

    NASA Astrophysics Data System (ADS)

    He, Shengping; Chen, Gujun; Guo, Yintao; Shen, Boyi; Wang, Qian

    2015-04-01

    Nozzle blockage is a major problem during continuous casting of Al-containing steel. Herein, we analyzed the thermodynamic equilibrium behavior between aluminum and oxygen in steel at 1873 K (1600 °C) and demonstrated that, the dissolved [O] initially decreases with increasing the dissolved [Al] until approximately 0.1 wt pct [Al], and after that, the dissolved [O] increases with dissolved [Al]. Thus, for high-aluminum steel with 1.0 wt pct dissolved [Al], the precipitation of Al2O3 inclusion can be avoided during cooling from deoxidation temperature to the liquidus temperature, if the actual dissolved [O] can be kept from increasing when the dissolved [Al] further increases from 0.1 to 1.0 wt pct. Hence, a method of inclusion control for high-aluminum steel without traditional Ca treatment technology was proposed based on the thermodynamic analysis. Industrial tests confirmed that low-melting point Ca-aluminate inclusions were observed typically through a slag washing with SiO2-minimized high-basicity slag during tapping, accompanied by two-step Al-adding process for production of high-aluminum steel. Moreover, there was no nozzle clogging occurred for five heats of continuous casting.

  12. The effect of residual stress on the fatigue crack growth behavior of Al-Si-Mg cast alloys—Mechanisms and corrective mathematical models

    NASA Astrophysics Data System (ADS)

    Lados, Diana A.; Apelian, Diran

    2006-01-01

    The fatigue crack growth (FCG) behavior of various types of alloys is significantly affected by the presence of residual stress induced by manufacturing and post-manufacturing processes. There is a qualitative understanding of the effects of residual stress on fatigue behavior, but the effects are not comprehensively quantified or accounted for. The difficulty in quantifying these effects is largely due to the complexity of residual-stress measurements (especially considering that parts produced in similar conditions can have different residual-stress levels) and the lack of mathematical models able to convert experimental data with residual stress into residual-stress-free data. This article provides experimental, testing, and mathematical techniques to account for residual-stress effects on crack growth rate data, together with two methods for eliminating residual stresses in crack growth test specimens. Fracture-mechanics concepts are used to calculate, in simple and convenient ways, stress-intensity factors caused by residual stresses. The method is advantageous, considering that stress-intensity factors are determined before the actual test is conducted. Further on, residual-stress-intensity factors are used to predict the residual-stress distribution in compact tension (CT) specimens prior to testing. Five cast Al-Si-Mg alloys with three Si levels (in unmodified (UM) as well as Sr-modified (M) conditions) were analyzed both with and without residual stress. Fatigue cracks are grown under both constant stress ratio, R=0.1, and constant maximum stress-intensity factor, K max = const., conditions. The mechanisms involved in crack growth through residual-stress fields are presented.

  13. High spatial resolution Mg/Al maps of the western Crisium and Sulpicius Gallus regions

    NASA Technical Reports Server (NTRS)

    Schonfeld, E.

    1982-01-01

    High spatial resolution Mg/Al ratio maps of the western Crisium and Sulpicius Gallus regions of the moon are presented. The data is from the X-ray fluorescence experiment and the image enhancement technique in the Laplacian subtraction method using a special least-squares version of the Laplacian to reduce noise amplification. In the highlands region west of Mare Crisium several relatively small patches of smooth material have high local Mg/Al ratio similar to values found in mare sites, suggesting volcanism in the highlands. In the same highland region there were other smooth areas with no high Mg/Al local values and they are probably Cayley Formation material produced by impact mass wasting. The Sulpicius Gallus region has variable Mg/Al ratios. In this region there are several high Mg/Al ratio spots, two of which occur at the highland-mare interface. Another high Mg/Al ratio area corresponds to the Sulpicius Gallus Rima I region. The high Mg/Al ratio material in the Sulpicius Gallus region is probably pyroclastic.

  14. High cardiovascular mortality in postcommunist countries: participation of oxidative stress?

    PubMed

    Ginter, E

    1996-01-01

    Age-standardized death rates from cardiovascular diseases (0-64 years) of male populations in postcommunistic Central and Eastern Europe are now several times higher than those in Western Europe. This phenomenon is only partly explainable by the higher prevalence of "classical" cardiovascular risk factors (smoking, hypertension, hypercholesterolemia). Socio-economic background of the cardiovascular epidemic in the USA and Western Europe after 1950, and in the Soviet bloc in 1960-1990 was substantially different. It is suggested that the influence of further risk factors should be considered: oxidative stress caused by prolonged disorders in life style (alcoholism, smoking), high degree of environmental pollution and nutritional disbalances (chronic deficiency of antioxidants due to low consumption of fruits, vegetables and vegetable oils); psychosocial factors-chronic stress, tension, anger, hostility, frustration and apathy leading to a lowered interest in one's own health. The situation in postcommunist countries is unique and its analysis could provide important new information about the etiology of cardiovascular diseases and their prevention. PMID:8899449

  15. Interfacial Characterization of Dissimilar Joints Between Al/Mg/Al-Trilayered Clad Sheet to High-Strength Low-Alloy Steel

    NASA Astrophysics Data System (ADS)

    Macwan, A.; Jiang, X. Q.; Chen, D. L.

    2015-07-01

    Magnesium (Mg) alloys are increasingly used in the automotive and aerospace sectors to reduce vehicle weight. Al/Mg/Al tri-layered clad sheets are deemed as a promising alternative to improve the corrosion resistance and formability of Mg alloys. The structural application of Al/Mg/Al tri-layered clad sheets inevitably involves welding and joining in the multi-material vehicle body manufacturing. This study aimed to characterize the bonding interface microstructure of the Al/Mg/Al-clad sheet to high-strength low-alloy steel with and without Zn coating using ultrasonic spot welding at different levels of welding energy. It was observed that the presence of Zn coating improved the bonding at the interface due to the formation of Al-Zn eutectic structure via enhanced diffusion. At a higher level of welding energy, characteristic flow patterns of Zn into Al-clad layer were observed with an extensive penetration mainly along some high angle grain boundaries. The dissimilar joints without Zn coating made at a high welding energy of 800 J failed partially from the Al/Fe weld interface and partially from the Al/Mg clad interface, while the joints with Zn coating failed from the Al/Mg clad interface due to the presence of brittle Al12Mg17 phase.

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

    NASA Astrophysics Data System (ADS)

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

    1995-08-01

    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 thick, is found to form at the Al-Si-Cu/TiN interface by annealing at the temperature of 450 °C for 30 min. On the other hand, in the case of a minimally compressive stress of 21 MPa, it is in a marked contrast to form a polycrystalline TiAl3 layer (c-TiAl3) on the amorphous intermediate layer ununiformly. Behavior of the internal stress in the latter TiN film as a function of heating and cooling temperature shows nonlinear characteristics, indicating that a rearrangement of the TiN film actively occurs even at low temperatures below 300 °C. Monte Carlo simulations of internal microstructures based on a ballistic aggregation model suggest to us that a short migration length corresponding to the condition of low internal stress brings about numerous vacancies and disordered regions in the TiN films. It is considered that the rearrangement of the TiN films with a diffusion of Ti atoms governs the solid-phase reactions at the Al-Si-Cu/TiN interfaces and that the formation of the bilayer of c-TiAl3/a-Al-Ti-Si originates in phase separation of the resultant Al-Ti mixing layer.

  17. Stress Management Model for the Elementary/Middle/High School.

    ERIC Educational Resources Information Center

    Matthews, Doris B.

    The Matthews Stress Management formula is a stress management model for use in schools. This effective, practical, and inexpensive model entails the awareness of the physiology of stress, perception of tangible bases of motivation for children, appropriate and simplified techniques, applicability to other areas, and full recognition of the…

  18. Degradation of blue AlGaN/InGaN/GaN LEDs subjected to high current pulses

    SciTech Connect

    Barton, D.L.; Zeller, J.; Phillips, B.S.; Chiu, P.C.; Askar, S.; Lee, D.S.; Osinski, M.; Malloy, K.J.

    1994-12-31

    Short-wavelength, visible-light emitting optoelectronic devices are needed for a wide range of commercial applications, including high-density optical data storage, full-color displays, and underwater communications. In 1994, high-brightness blue LEDs based on gallium nitride and related compounds (InGaN/AlGaN) were introduced by Nichia Chemical Industries. The Nichia diodes are 100 times brighter than the previously available SiC blue LEDs. Group-III nitrides combine a wide, direct bandgap with refractory properties and high physical strength. So far, no studies of degradation of GaN based LEDs have been reported. The authors study, reported in this paper, focuses on the performance of GaN LEDs under high electrical stress conditions. Their observations indicate that, in spite of a high defect density, which normally would have been fatal to other III-V devices, defects in group-III nitrides are not mobile even under high electrical stress. Defect tubes, however, can offer a preferential path for contact metals to electromigrate towards the p-n junction, eventually resulting in a short. The proposed mechanism of GaN diode degradation raises concern for prospects of reliable lasers in the group-III nitrides grown on sapphire.

  19. High temperature degradation behavior of sputtered nanostructured Co-Al coatings on superalloy

    NASA Astrophysics Data System (ADS)

    Rahman, Atikur; Jayaganthan, R.; Chandra, Ramesh; Ambardar, R.

    2013-01-01

    Microstructure and cyclic high temperature oxidation behavior of nanostructured Co-Al coatings on Superni-718 substrate have been investigated. Cyclic high temperature oxidation tests were conducted on uncoated and coated samples at peak temperatures of 800 °C and 900 °C for up to 100 thermal cycles between the peak and room temperatures. The results showed that bare substrate has higher oxidation resistance at 800 °C as compared to 900 °C and coated sample has slightly higher oxidation resistance at 900 °C. The external scale of both coated sample exhibited good spallation resistance during cyclic oxidation testing at both temperatures. The improvement in oxide scale spallation resistance is believed to be related to the fine-grained structure of the coating. Nanostructured Co-Al coatings on Superni-718 substrate were deposited by DC/RF magnetron sputtering. FE-SEM/EDS and XRD were used to characterize the morphology and formation of different phases in the coatings, respectively. The Co-Al coating on superalloy substrate showed better performance of cyclic high temperature oxidation resistance due to its possession of β-CoAl phase as Al reservoir and the formation of Al2O3 and spinel phases such as CoCr2O4 and CoAl2O4 in the scale. The oxidation results confirmed an improved oxidation resistance of the Co-Al coating on superalloy as compared to bare substrate up to 100 cycles.

  20. Stress

    MedlinePlus

    ... sudden negative change, such as losing a job, divorce, or illness Traumatic stress, which happens when you ... stress, so you can avoid more serious health effects. NIH: National Institute of Mental Health

  1. Highly transparent and conductive ZnO:Al thin films prepared by vacuum arc plasma evaporation

    NASA Astrophysics Data System (ADS)

    Miyata, Toshihiro; Minamino, Youhei; Ida, Satoshi; Minami, Tadatsugu

    2004-07-01

    A vacuum arc plasma evaporation (VAPE) method using both oxide fragments and gas sources as the source materials is demonstrated to be very effective for the preparation of multicomponent oxide thin films. Highly transparent and conductive Al-doped ZnO (AZO) thin films were prepared by the VAPE method using a ZnO fragment target and a gas source Al dopant, aluminum acethylacetonate (Al(C5H7O2)3) contained in a stainless steel vessel. The Al content in the AZO films was altered by controlling the partial pressure (or flow rate) of the Al dopant gas. High deposition rates as well as uniform distributions of resistivity and thickness on the substrate surface were obtained on large area glass substrates. A low resistivity on the order of 10-4 Ω cm and an average transmittance above 80% in the visible range were obtained in AZO thin films deposited on glass substrates. .

  2. Relationships among Stress, Coping, and Mental Health in High-Achieving High School Students

    ERIC Educational Resources Information Center

    Suldo, Shannon M.; Shaunessy, Elizabeth; Hardesty, Robin

    2008-01-01

    This study investigates the relationships among stress, coping, and mental health in 139 students participating in an International Baccalaureate (IB) high school diploma program. Mental health was assessed using both positive indicators (life satisfaction, academic achievement, academic self-efficacy) and negative indicators (psychopathology) of…

  3. High Rate Deposition of High Quality ZnO:Al by Filtered Cathodic Arc

    SciTech Connect

    Mendelsberg, Rueben J.; Lim, S.H.N.; Milliron, D.J.; Anders, Andre

    2010-11-18

    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.

  4. Comparative study on the charge-trapping properties of TaAlO and ZrAlO high-k composites with designed band alignment

    SciTech Connect

    Lu, W.; Wei, C. Y.; Jiang, K.; Liu, J. Q.; Lu, J. X.; Han, P.; Li, A. D.; Xia, Y. D.; Xu, B.; Yin, J. Liu, Z. G.

    2015-08-15

    The charge-trapping memory (CTM) structures Pt/Al{sub 2}O{sub 3}/TaAlO/Al{sub 2}O{sub 3}/p-Si and Pt/Al{sub 2}O{sub 3}/ZrAlO/Al{sub 2}O{sub 3}/p-Si were fabricated by using rf-sputtering and atomic layer deposition techniques, in which the potentials at the bottom of the conduction band (PBCB) of high-k composites TaAlO and ZrAlO were specially designed. With a lower PBCB difference between TaAlO and p-Si than that between ZrAlO and p-Si, TaAlO CTM device shows a better charge-trapping performance. A density of trapped charges 2.88 × 10{sup 13}/cm{sup 2} at an applied voltage of ±7 V was obtained for TaAlO CTM device, and it could keep about 60% of initially trapped charges after 10 years. It was suggested that the PBCB difference between high-k composite and p-Si dominates their charge-trapping behaviors.

  5. Improved n-channel Ge gate stack performance using HfAlO high-k dielectric for various Al concentrations

    NASA Astrophysics Data System (ADS)

    Kothari, Shraddha; Joishi, Chandan; Ghosh, Sayantan; Biswas, Dipankar; Vaidya, Dhirendra; Ganguly, Swaroop; Lodha, Saurabh

    2016-07-01

    We demonstrate improved Ge n-channel gate stack performance versus HfO2 using HfAlO high-k dielectric for a wide (1.5–33%) range of Al% and post-high-k-deposition annealing (PDA) at 400 °C. Addition of Al to HfO2 is shown to mitigate degradation of the GeO2/Ge interface during PDA. HfAlO stacks with an equivalent oxide thickness (EOT) of 8 nm and large Al% exhibit improved transistor mobility (1.8 times higher) and midgap D it (2 times lower), whereas thin (1.9 nm) EOT HfAlO stacks show reduced gate leakage J g (by 10 times) and D it (by 1.5 times) and 1.6 times higher mobility for Al% as low as 1.5% at matched EOT.

  6. High quality semipolar (11{sup ¯}02) AlGaN/AlN quantum wells with remarkably enhanced optical transition probabilities

    SciTech Connect

    Ichikawa, S. Iwata, Y.; Funato, M.; Kawakami, Y.; Nagata, S.

    2014-06-23

    Adjusting the growth conditions from those for c-plane growth realizes high-quality semipolar (11{sup ¯}02) AlGaN/AlN quantum wells (QWs) with atomically smooth surfaces and abrupt interfaces on AlN substrates. Upon comparing the optical properties to those of c-plane QWs using time-integrated and time-resolved photoluminescence spectroscopy, the estimated internal electric field is much smaller in (11{sup ¯}02) AlGaN/AlN QWs than in c-plane QWs. Thus, (11{sup ¯}02) AlGaN/AlN QWs have narrower emission line widths and remarkably faster radiative recombination lifetimes, realizing highly efficient deep ultraviolet emissions.

  7. High-power AlInGaN light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Wierer, Jonathan J.; Bhat, Jerome C.; Chen, Chien-Hua; Christenson, G.; Cook, Lou W.; Craford, M. G.; Gardner, Nathan F.; Goetz, Werner K.; Kern, R. Scott; Khare, Reena; Kim, A.; Krames, Michael R.; Ludowise, Mike J.; Mann, Richard; Martin, Paul S.; Misra, Mira; O'Shea, J.; Shen, Yu-Chen; Steranka, Frank M.; Stockman, Steve A.; Subramanya, Sudhir G.; Rudaz, S. L.; Steigerwald, Dan A.; Yu, Jingxi

    2001-05-01

    High-power light-emitting diodes (LEDs) in both the AlInGaP (red to amber) and the AlGaInN (blue-green) material systems are now commercially available. These high-power LEDs enable applications wherein high flux is necessary, opening up new markets that previously required a large number of conventional LEDs. Data are presented on high-power AlGaInN LEDs utilizing flip-chip device structures. The high-power flip-chip LED is contained in a package that provides high current and temperature operation, high reliability, and optimized radiation patterns. These LEDs produce record powers of 350 mW (1A dc, 300 K) with low (<4V) forward voltages. The performance of these LEDs is demonstrated in terms of output power, efficiency, and electrical characteristics.

  8. The comparison of perceived stress in idiopathic thrombocytopenic purpura patients referred to Seyed Al-Shohada Hospital with healthy people in Isfahan, Iran, 2013

    PubMed Central

    Hemati, Zeinab; Kiani, Davood

    2015-01-01

    Background: Mental stress and daily crises comprise a part of physical and mental threats. Perceived stress is a physical and mental threat, as well. Perceived stress is a psychological process during which the individual considers his/ her physical and psychological welfare as being threatened. Since idiopathic thrombocytopenic purpura (ITP) is one of the chronic diseases being able to affect patients' perceived stress, this study was conducted to compare perceived stress in ITP patients and healthy people. Materials and Methods: This is a descriptive-comparative study with control and case groups. In this study, 64 ITP patients referring Seyed Al-Shohada Hospital and the same number of healthy individuals from the patients' neighborhood, as the control group, were selected randomly and compared. The Kohen Perceived Stress Standard Questionnaire was used to collect the data. The data were analyzed by SPSS and Student’s independent t-test, chi-square, and Mann-Whitney test. Results : 64.1%, 59.4% and 53.1% of participants in case group were older than 35 years old, female and had elementary education. 78.1% of case group had severe perceived stress. 70.3% of participants in control group experienced mild perceived stress. Mann-Whitney test showed significant difference between two groups in level of stress (p<0.001). Conclusion: In ITP patients, perceived stress was considerable. Planning interventional measures to determine stress-making agents and subside or at least control them is very essential. PMID:25922646

  9. [Approach to easing occupational stress for high-stress workers: applying the brief job stress questionnaire to workplace mental health promotion].

    PubMed

    Hase, Yoko; Hori, Hiroko; Nakayasu, Ikuyo; Matsushita, Yuko; Inagaki, Michiko; Unno, Aiko; Nishigaya, Eri; Nishijima, Chiharu; Enta, Kazuhiko; Sashihara, Shunsuke

    2008-07-01

    We investigated job stress among 442 employees from 19 divisions in a Japanese company using the Brief Job Stress Questionnaire. Job stress of the employees was estimated by the score for total health risk. Among the 19 divisions, two divisions showed over 120 points of mean total health risk score. Intervention with a stress-reduction program was carried out in these 2 divisions. First, to assess the job stress, health care staff interviewed all workers in the 2 divisions. Second, the results of the interviews were reported to the divisions' managers. Third, the managers applied the best remedy for job stress in their workplaces. In addition, occupational health staff conducted mental health education as well as individual interviews for the workers from the 2 divisions. At reevaluation one year later, both divisions showed a decreased general health risk (under 120 points). No sick leaves for depression occurred within the 2 divisions during the intervention. The results of the present study suggest that the intervention was effective in easing occupational stress for high-stress workers. The stress reduction program also seemed to have helped managers to change their recognition of occupational mental health and enabled close cooperation with occupational health staff, which may improve mental health in the workplace. PMID:18566525

  10. Fabrication of Al-Doped ZnO Film with High Conductivity Induced by Photocatalytic Activity

    NASA Astrophysics Data System (ADS)

    Hong, Jeongsoo; Katsumata, Ken-ichi; Matsushita, Nobuhiro

    2016-06-01

    We have fabricated Al-doped ZnO films by a spin-spray method, achieving high conductivity by Al-ion doping and photocatalytic activity of the ZnO. The surface morphology of the as-deposited films was varied by changing the Al concentration and addition of citrate ions. As-deposited Al-doped ZnO film without citrate ions showed rod array structure with increasing rod width as the Al concentration was increased. Meanwhile, Al-doped ZnO film deposited with addition of citrate ions changed to exhibit dense and continuous surface morphology with high transmittance of 85%. The lowest resistivity recorded for undoped and Al-doped ZnO film was 2.1 × 10-2 Ω cm and 5.9 × 10-3 Ω cm, after ultraviolet (UV) irradiation. The reason for the decreased resistivity is thought to be that Al-ion doping and the photocatalytic activity of ZnO contributed to improve the conductivity.

  11. Synthesis and in situ high pressure Raman spectroscopy study of AlN dendritic crystal

    SciTech Connect

    Li, Xuefei; Kong, Lingnan; Shen, Longhai; Yang, Jinghai; Gao, Ming; Hu, Tingjing; Wu, Xingtong; Li, Ming

    2013-09-01

    Graphical abstract: - Highlights: • The sample is the typical dendritic crystal structure. • The phase transition of AlN dendritic crystal is researched. • The Raman signal of rock salt AlN is observed under high pressure. • Grüneisen parameters and phase transition criterion are discussed. - Abstract: AlN dendritic crystal was synthesized by the direct current arc discharge apparatus. X-ray diffraction (XRD) patterns indicated that the sample is hexagonal AlN and preferentially grown along the a-axis direction. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) images reveal that the product mainly consists of micron AlN dendritic crystal. In situ high pressure Raman spectra of AlN dendritic crystal has been measured in the pressure ranged from ambient pressure to 32.97 GPa at room temperature by using diamond anvil cell. According to the Raman scattering results, the phase transition from the wurtzite to rock salt was found at about 20.73 GPa by the appearance of a new Raman signal. Above 20.73 GPa, a new Raman signal due to disorder-activated Raman scattering in the rock salt phase was observed. In addition, the pressure coefficients, phase transition criterion, and mode Grüneisen parameters of AlN dendritic crystal, which could be different from that of other AlN, are carefully discussed.

  12. Effects of AlN Coating Layer on High Temperature Characteristics of Langasite SAW Sensors.

    PubMed

    Shu, Lin; Peng, Bin; Cui, Yilin; Gong, Dongdong; Yang, Zhengbing; Liu, Xingzhao; Zhang, Wanli

    2016-01-01

    High temperature characteristics of langasite surface acoustic wave (SAW) devices coated with an AlN thin film have been investigated in this work. The AlN films were deposited on the prepared SAW devices by mid-frequency magnetron sputtering. The SAW devices coated with AlN films were measured from room temperature to 600 °C. The results show that the SAW devices can work up to 600 °C. The AlN coating layer can protect and improve the performance of the SAW devices at high temperature. The SAW velocity increases with increasing AlN coating layer thickness. The temperature coefficients of frequency (TCF) of the prepared SAW devices decrease with increasing thickness of AlN coating layers, while the electromechanical coupling coefficient (K²) of the SAW devices increases with increasing AlN film thickness. The K² of the SAW devices increases by about 20% from room temperature to 600 °C. The results suggest that AlN coating layer can not only protect the SAW devices from environmental contamination, but also improve the K² of the SAW devices. PMID:27608027

  13. Structure and high temperature oxidation of mechanical alloyed Fe-Al coating

    NASA Astrophysics Data System (ADS)

    Aryanto, Didik; Sudiro, Toto; Wismogroho, Agus S.

    2016-04-01

    The structure and high temperature oxidation resistance of Fe-Al coating on low carbon steel were investigated. The Fe-Al coating was deposited on the surface of low carbon steel using a mechanical alloying method. The coating was then annealed at 600°C for 2 hour in a vacuum of 5 Pa. The cyclic-oxidation tests of low carbon steel, Fe-Al coatings with and without annealing were performed at 600°C for up to 60h in air. The structure of oxidized samples was studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy X-ray spectroscopy (EDS). The results show that the Fe-Al coatings exhibit high oxidation resistance compared to the uncoated steel. After 60 h exposure, the uncoated steel formed mainly Fe3O4 and Fe2O3 layers with the total thickness of around 75.93 µm. Fe-Al coating without annealing formed a thin oxide layer, probably (Fe,Al)2O3. Meanwhile, for annealed sample, EDX analysis observed the formation of two Fe-Al layers with difference in elements concentration. The obtained results suggest that the deposition of Fe-Al coating on low carbon steel can improve the oxidation resistance of low carbon steel.

  14. Microstructure Characterization and Stress Corrosion Evaluation of Autogenous and Hybrid Friction Stir Welded Al-Cu-Li 2195 Alloy

    NASA Technical Reports Server (NTRS)

    Li, Zhixian; Arbegast, William J.; Meletis, Efstathios I.

    1997-01-01

    Friction stir welding process is being evaluated for application on the Al-Cu-Li 2195 Super-Light Weight External Tank of the Space Transportation System. In the present investigation Al-Cu-Li 2195 plates were joined by autogenous friction stir welding (FSW) and hybrid FSW (friction stir welding over existing variable polarity plasma arc weld). Optical microscopy and transmission electron microscopy (TEM) were utilized to characterize microstructures of the weldments processed by both welding methods. TEM observations of autogenous FSW coupons in the center section of the dynamically-recrystallized zone showed an equiaxed recrystallized microstructure with an average grain size of approx. 3.8 microns. No T(sub 1), precipitates were present in the above-mentioned zone. Instead, T(sub B) and alpha precipitates were found in this zone with a lower population. Alternate immersion, anodic polarization, constant load, and slow strain tests were carried out to evaluate the general corrosion and stress-corrosion properties of autogenous and hybrid FSW prepared coupons. The experimental results will be discussed.

  15. High power, high brightness Al-free active region tapered lasers at 915 nm

    NASA Astrophysics Data System (ADS)

    Hassiaoui, I.; Michel, N.; Lecomte, M.; Parillaud, O.; Calligaro, M.; Krakowski, M.

    2006-04-01

    To achieve high power and high brightness, we have developed tapered diode lasers based on an Al-free active region at 915 nm. The material structure was grown by MOCVD (Metallorganic Chemical Vapor Deposition). It shows very low internal losses of only 0.5 cm -1, a very low transparency current density of 86 A/cm2, an excellent internal quantum efficiency of 86%, and a high characteristic temperature T 0 of 171 K. Based on these good results, at first, we have realised index-guided tapered lasers (IG1) with a narrow output width and a narrow taper angle, which deliver 1 W CW, together with an M2 beam quality parameter of 2.9 at 1/e2, and a narrow divergence angle in the slow axis of 5.1° FWHM and 7.5° at 1/e2. We have also fabricated new index-guided tapered lasers with a Clarinet shape, which were recently proposed to achieve high brightness together with a very narrow divergence angle. The Clarinet lasers deliver 0.6W CW, together with an excellent M2 beam quality factor of 1.2 at 1/e2, and a very narrow divergence angle in the slow axis of only 2.5° FWHM, and 3.9° at 1/e2, which is stable with current. These very narrow divergences are very advantageous for the collective coupling of tapered bars into optical fibers. In this work we have also investigated the influence of taper length on the output power and beam quality.

  16. Stress-corrosion crack-growth study of titanium alloy Ti-6Al-4V exposed to freon PCA and nitrogen tetroxide MON-1

    NASA Technical Reports Server (NTRS)

    Bjorklund, R. A.

    1983-01-01

    An experimental fracture mechanics program was performed to determine the stress corrosion crack growth sensitivity of the propellant tank material, titanium alloy Ti-6Al-4V, for aerospace satellite applications involving long term exposure to Freon PCA and nitrogen tetroxide MON-1. Sustained load tests were made at a 49 C (120 F) constant temperature using thin gauge tensile test specimens containing semielliptical surface flaws. Test specimen types included parent metal, center of weld, and weld heat affected zone. It was concluded that Ti-6Al-4V alloy is not adversely affected in a stress environment when exposed to Freon PCA for 1000 hours followed by exposure to nitrogen tetroxide MON-1 for 2000 hours at stress levels up to 80% of the experimental critical plane strain stress intensity factor.

  17. Electrical and structural degradation of GaN high electron mobility transistors under high-power and high-temperature Direct Current stress

    SciTech Connect

    Wu, Y. Alamo, J. A. del; Chen, C.-Y.

    2015-01-14

    We have stressed AlGaN/GaN HEMTs (High Electron Mobility Transistors) under high-power and high-temperature DC conditions that resulted in various levels of device degradation. Following electrical stress, we conducted a well-established three-step wet etching process to remove passivation, gate and ohmic contacts so that the device surface can be examined by SEM and AFM. We have found prominent pits and trenches that have formed under the gate edge on the drain side of the device. The width and depth of the pits under the gate edge correlate with the degree of drain current degradation. In addition, we also found visible erosion under the full extent of the gate. The depth of the eroded region averaged along the gate width under the gate correlated with channel resistance degradation. Both electrical and structural analysis results indicate that device degradation under high-power DC conditions is of a similar nature as in better understood high-voltage OFF-state conditions. The recognition of a unified degradation mechanism provides impetus to the development of a degradation model with lifetime predictive capabilities for a broad range of operating conditions spanning from OFF-state to ON-state.

  18. Degradation mechanisms in high-power multi-mode InGaAs-AlGaAs strained quantum well lasers for high-reliability applications

    NASA Astrophysics Data System (ADS)

    Sin, Yongkun; Presser, Nathan; Brodie, Miles; Lingley, Zachary; Foran, Brendan; Moss, Steven C.

    2015-03-01

    Laser diode manufacturers perform accelerated multi-cell lifetests to estimate lifetimes of lasers using an empirical model. Since state-of-the-art laser diodes typically require a long period of latency before they degrade, significant amount of stress is applied to the lasers to generate failures in relatively short test durations. A drawback of this approach is the lack of mean-time-to-failure data under intermediate and low stress conditions, leading to uncertainty in model parameters (especially optical power and current exponent) and potential overestimation of lifetimes at usage conditions. This approach is a concern especially for satellite communication systems where high reliability is required of lasers for long-term duration in the space environment. A number of groups have studied reliability and degradation processes in GaAs-based lasers, but none of these studies have yielded a reliability model based on the physics of failure. The lack of such a model is also a concern for space applications where complete understanding of degradation mechanisms is necessary. Our present study addresses the aforementioned issues by performing long-term lifetests under low stress conditions followed by failure mode analysis (FMA) and physics of failure investigation. We performed low-stress lifetests on both MBE- and MOCVD-grown broad-area InGaAs- AlGaAs strained QW lasers under ACC (automatic current control) mode to study low-stress degradation mechanisms. Our lifetests have accumulated over 36,000 test hours and FMA is performed on failures using our angle polishing technique followed by EL. This technique allows us to identify failure types by observing dark line defects through a window introduced in backside metal contacts. We also investigated degradation mechanisms in MOCVD-grown broad-area InGaAs-AlGaAs strained QW lasers using various FMA techniques. Since it is a challenge to control defect densities during the growth of laser structures, we chose to

  19. InAlN high electron mobility transistor Ti/Al/Ni/Au Ohmic contact optimisation assisted by in-situ high temperature transmission electron microscopy

    SciTech Connect

    Smith, M. D.; Parbrook, P. J.; O'Mahony, D.; Conroy, M.; Schmidt, M.

    2015-09-14

    This paper correlates the micro-structural and electrical characteristics associated with annealing of metallic multi-layers typically used in the formation of Ohmic contacts to InAlN high electron mobility transistors. The multi-layers comprised Ti/Al/Ni/Au and were annealed via rapid thermal processing at temperatures up to 925 °C with electrical current-voltage analysis establishing the onset of Ohmic (linear IV) behaviour at 750–800 °C. In-situ temperature dependent transmission electron microscopy established that metallic diffusion and inter-mixing were initiated near a temperature of 500 °C. Around 800 °C, inter-diffusion of the metal and semiconductor (nitride) was observed, correlating with the onset of Ohmic electrical behaviour. The sheet resistance associated with the InAlN/AlN/GaN interface is highly sensitive to the anneal temperature, with the range depending on the Ti layer thickness. The relationship between contact resistivity and measurement temperature follow that predicted by thermionic field emission for contacts annealed below 850 °C, but deviated above this due to excessive metal-semiconductor inter-diffusion.

  20. High-photosensitivity AlGaN-based UV heterostructure-field-effect-transistor-type photosensors

    NASA Astrophysics Data System (ADS)

    Yoshikawa, Akira; Yamamoto, Yuma; Murase, Takuya; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu

    2016-05-01

    We report the development of high-performance AlGaN/AlN heterostructure-field-effect-transistor-type (HFET) photosensors with a p-type GaN optical gate and detection wavelengths that are restricted to 220–280 nm. These photosensors employ a two-dimensional electron gas induced at the hetero-interface between Al0.6Ga0.4N and Al0.5Ga0.5N as a highly conductive channel. In addition, a p-type GaN optical gate is employed to deplete a channel. Consequently, we obtained a high photosensitivity of over 4 × 103 A/W and an externally low dark current density of approximately 5 × 10‑10 A/mm at a source–drain voltage of 3 V. We also determined that the detection range of light wavelength in these HFET photosensors can be controlled by controlling the AlN molar fraction in the AlGaN channel layer. The results are very promising for the development of completely solar-blind high-performance photosensors with high photosensitivity.

  1. Nitrogen Plasma Ion Implantation of Al and Ti alloys in the High Voltage Glow Discharge Mode

    NASA Astrophysics Data System (ADS)

    Oliveira, R. M.; Ueda, M.; Rossi, J. O.; Reuther, H.; Lepienski, C. M.; Beloto, A. F.

    2006-11-01

    Enhanced surface properties can be attained for aluminum and its alloys (mechanical and tribological) and Ti6Al4V (mainly tribological) by Plasma Immersion Ion Implantation (PIII) technique. The main problem here, more severe for Al case, is the rapid oxygen contamination even in low O partial pressure. High energy nitrogen ions during PIII are demanded for this situation, in order to enable the ions to pass through the formed oxide layer. We have developed a PIII system that can operate at energies in excess of 50keV, using a Stacked Blumlein (SB) pulser which can nominally provide up to 100 kV pulses. Initially, we are using this system in the High Voltage Glow Discharge (HVGD) mode, to implant nitrogen ions into Al5052 alloy with energies in the range of 30 to 50keV, with 1.5μs duration pulses at a repetition rate of 100Hz. AES, pin-on-disc, nanoindentation measurements are under way but x-ray diffraction results already indicated abundant formation of AlN in the surface for Al5052 treated with this HVGD mode. Our major aim in this PIII experiment is to achieve this difficult to produce stable and highly reliable AlN rich surface layer with high hardness, high corrosion resistance and very low wear rate.

  2. Static and kinetic friction of granite at high normal stress

    USGS Publications Warehouse

    Byerlee, J.D.

    1970-01-01

    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.

  3. 76 FR 24541 - HighMark Capital Management, Inc., et al.,

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-05-02

    ... COMMISSION HighMark Capital Management, Inc., et al., Notice of Application April 26, 2011. AGENCY... 17(a) of the Act. Applicants: HighMark Capital Management, Inc. (``HCM'' or ``Adviser''),\\1\\ HighMark... existing or future registered management investment companies and their series that are advised...

  4. The effect of the built-in stress level of AlN layers on the properties of piezoelectric vibration energy harvesters

    NASA Astrophysics Data System (ADS)

    Karakaya, K.; Renaud, M.; Goedbloed, M.; van Schaijk, R.

    2008-10-01

    In this paper we investigated the effects of built-in stress on the dielectric and piezoelectric properties of sputtered AlN layers, meant to be implemented in micromachined piezoelectric vibration energy harvesters. Test structures including cantilevers, 4-point bending beams and metal-insulator-metal capacitors were manufactured with reactive sputtered AlN layers in a thickness range of 400-1200 nm. Various bias conditions during the deposition process allowed controlling the built-in stress level in the layers, from tensile to compressive. The clamped dielectric permittivity ɛ33S, the voltage response and the piezoelectric coefficient e31 of the deposited AlN layers were measured by performing capacitance, voltage-deflection and 4-point bending measurements, respectively. In addition, we obtained from electrical impedance analyses the generalized electromechanical coupling (GEMC) and the quality factors of the fabricated test cantilevers, which are the critical parameters directly connected to the performance of the device in terms of energy harvesting. It is found that the permittivity ɛ33S and the piezoelectric constant e31 were not significantly affected by the different stress levels for a given layer thickness. However, the GEMC and the quality factor were found to be decreasing for structures that have a larger residual stress. We concluded that large residual stress has to be avoided in order to optimize the output power of AlN-based vibration harvesters.

  5. Heat Pipe Embedded AlSiC Plates for High Conductivity - Low CTE Heat Spreaders

    SciTech Connect

    Johnson, Matthew ); Weyant, J.; Garner, S. ); Occhionero, M. )

    2010-01-07

    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 plate’s 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.

  6. Experimental study on a Nb3Al insert coil under high magnetic field

    NASA Astrophysics Data System (ADS)

    Zhu, Guang; Dai, Yinming; Cheng, Junsheng; Chang, Kun; Liu, Jianhua; Wang, Qiuliang; Pan, Xifeng; Li, Chao

    2016-06-01

    Nb3Al is one of the most promising superconductors to replace Nb3Sn in large scale, high field superconducting magnet. Since the complicated conductor manufacturing process, long and stable Nb3Al conductor is difficult to acquire in a commercial scale. Based on a 70 m length of Nb-Al precursor conductor, we designed and fabricated a Nb3Al coil. The coil winding, low temperature diffusion heat treatment and epoxy impregnation are described in detail. The finished Nb3Al coil is tested as an insert in a background magnet. The test is performed at the background field from 7 T to 15 T. The test results are analyzed and presented in this paper.

  7. Influence of Aging Treatments on Alterations of Microstructural Features and Stress Corrosion Cracking Behavior of an Al-Zn-Mg Alloy

    NASA Astrophysics Data System (ADS)

    Rout, Prasanta Kumar; Ghosh, M. M.; Ghosh, K. S.

    2015-07-01

    7xxx series Al-Zn-Mg-(Cu) alloys have higher strength in their peak-aged (T6) states compared with other age-hardenable aluminum alloys; however, the maximum strength peak-aged state is more susceptible to stress corrosion cracking (SCC) which leads to catastrophic failure. The over-aged (T7) temper with 10-15% lower strength has higher resistance to SCC requiring oversized structural aerospace component applications. The medium-strength AA7017 Al-Zn-Mg weldable alloy without Cu is also prone to SCC under certain environmental conditions. In the present investigation, the SCC behaviors of an AA7017 Al-Zn-Mg alloys of different tempers have been assessed. Specific aging schedules have been adapted to an AA7017 alloy to produce various tempers, e.g., under-, peak-(T6), over-(T7), and highly over-aged tempers. Artificial aging behavior of the AA7017 alloy has been characterized by hardness, electrical conductivity measurements, x-ray diffraction, differential scanning calorimetry, and electrochemical studies. Slow strain rate test technique was used to assess the SCC behaviors of the AA7017 alloys of under-, T6, T7, and highly over-aged tempers in 3.5 wt.% NaCl solution at free corrosion potential (FCP) and at applied anodic potential, as well. Results revealed that the AA7017 alloy tempers are not susceptible to SCC in 3.5 wt.% NaCl solution at FCP, but severely damaging to SCC at applied anodic potentials. Microstructural features, showing a non-recrystallized grain structure and the presence of discrete, widely spaced, not-interconnected η precipitates at the grain boundaries, are the contributive factors by virtue of which the alloy tempers at FCP did not exhibit SCC. However, the applied anodic potential resulted in rapid metal dissolution from the grain boundary region and led to SCC. The local anodic dissolution (LAD) is believed to be the associated SCC mechanism.

  8. Cast Aluminum Alloys for High Temperature Applications Using Nanoparticles Al2O3 and Al3-X Compounds (X = Ti, V, Zr)

    NASA Technical Reports Server (NTRS)

    Lee, Jonathan A.

    2009-01-01

    In this paper, the effect of nanoparticles Al2O3 and Al3-X compounds (X = Ti, V, Zr) on the improvement of mechanical properties of aluminum alloys for elevated temperature applications is presented. These nanoparticles were selected based on their low cost, chemical stability and low diffusions rates in aluminum at high temperatures. The strengthening mechanism at high temperature for aluminum alloy is based on the mechanical blocking of dislocation movements by these nanoparticles. For Al2O3 nanoparticles, the test samples were prepared from special Al2O3 preforms, which were produced using ceramic injection molding process and then pressure infiltrated by molten aluminum. In another method, Al2O3 nanoparticles can also be homogeneously mixed with fine aluminum powder and consolidated into test samples through hot pressing and sintering. With the Al3-X nanoparticles, the test samples are produced as precipitates from in-situ reactions with molten aluminum using conventional permanent mold or die casting techniques. It is found that cast aluminum alloy using nanoparticles Al3-X is the most cost effective method to produce high strength aluminum alloys for high temperature applications in comparison to nanoparticles Al2O3. Furthermore, significant mechanical properties retention in high temperature environment could be achieved with Al3-X nanoparticles, resulting in tensile strength of nearly 3 times higher than most 300- series conventional cast aluminum alloys tested at 600 F.

  9. Lattice stabilities, mechanical and thermodynamic properties of Al3Tm and Al3Lu intermetallics under high pressure from first-principles calculations

    NASA Astrophysics Data System (ADS)

    Xu-Dong, Zhang; Wei, Jiang

    2016-02-01

    The effects of high pressure on lattice stability, mechanical and thermodynamic properties of L12 structure Al3Tm and Al3Lu are studied by first-principles calculations within the VASP code. The phonon dispersion curves and density of phonon states are calculated by using the PHONONPY code. Our results agree well with the available experimental and theoretical values. The vibrational properties indicate that Al3Tm and Al3Lu keep their dynamical stabilities in L12 structure up to 100 GPa. The elastic properties and Debye temperatures for Al3Tm and Al3Lu increase with the increase of pressure. The mechanical anisotropic properties are discussed by using anisotropic indices AG, AU, AZ, and the three-dimensional (3D) curved surface of Young’s modulus. The calculated results show that Al3Tm and Al3Lu are both isotropic at 0 GPa and anisotropic under high pressure. In the present work, the sound velocities in different directions for Al3Tm and Al3Lu are also predicted under high pressure. We also calculate the thermodynamic properties and provide the relationships between thermal parameters and temperature/pressure. These results can provide theoretical support for further experimental work and industrial applications. Project supported by the Scientific Technology Plan of the Educational Department of Liaoning Province and Liaoning Innovative Research Team in University, China (Grant No. LT2014004) and the Program for the Young Teacher Cultivation Fund of Shenyang University of Technology, China (Grant No. 005612).

  10. Characterization of interface states in Al{sub 2}O{sub 3}/AlGaN/GaN structures for improved performance of high-electron-mobility transistors

    SciTech Connect

    Hori, Y.; Yatabe, Z.; Hashizume, T.

    2013-12-28

    We have investigated the relationship between improved electrical properties of Al{sub 2}O{sub 3}/AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) and electronic state densities at the Al{sub 2}O{sub 3}/AlGaN interface evaluated from the same structures as the MOS-HEMTs. To evaluate Al{sub 2}O{sub 3}/AlGaN interface state densities of the MOS-HEMTs, two types of capacitance-voltage (C-V) measurement techniques were employed: the photo-assisted C-V measurement for the near-midgap states and the frequency dependent C-V characteristics for the states near the conduction-band edge. To reduce the interface states, an N{sub 2}O-radical treatment was applied to the AlGaN surface just prior to the deposition of the Al{sub 2}O{sub 3} insulator. As compared to the sample without the treatment, the N{sub 2}O-radical treated Al{sub 2}O{sub 3}/AlGaN/GaN structure showed smaller frequency dispersion of the C-V curves in the positive gate bias range. The state densities at the Al{sub 2}O{sub 3}/AlGaN interface were estimated to be 1 × 10{sup 12} cm{sup −2} eV{sup −1} or less around the midgap and 8 × 10{sup 12} cm{sup −2} eV{sup −1} near the conduction-band edge. In addition, we observed higher maximum drain current at the positive gate bias and suppressed threshold voltage instability under the negative gate bias stress even at 150 °C. Results presented in this paper indicated that the N{sub 2}O-radical treatment is effective both in reducing the interface states and improving the electrical properties of the Al{sub 2}O{sub 3}/AlGaN/GaN MOS-HEMTs.

  11. Electroluminescence of hot electrons in AlGaN/GaN high-electron-mobility transistors under radio frequency operation

    SciTech Connect

    Brazzini, Tommaso Sun, Huarui; Uren, Michael J.; Kuball, Martin; Casbon, Michael A.; Lees, Jonathan; Tasker, Paul J.; Jung, Helmut; Blanck, Hervé

    2015-05-25

    Hot electrons in AlGaN/GaN high electron mobility transistors are studied during radio frequency (RF) and DC operation by means of electroluminescence (EL) microscopy and spectroscopy. The measured EL intensity is decreased under RF operation compared to DC at the same average current, indicating a lower hot electron density. This is explained by averaging the DC EL intensity over the measured load line used in RF measurements, giving reasonable agreement. In addition, the hot electron temperature is lower by up to 15% under RF compared to DC, again at least partially explainable by the weighted averaging along the specific load line. However, peak electron temperature under RF occurs at high V{sub DS} and low I{sub DS} where EL is insignificant suggesting that any wear-out differences between RF and DC stress of the devices will depend on the balance between hot-carrier and field driven degradation mechanisms.

  12. High-pressure polymorphism as a step towards high density structures of LiAlH{sub 4}

    SciTech Connect

    Huang, Xiaoli; Duan, Defang; Li, Xin; Li, Fangfei; Huang, Yanping; Wu, Gang; Liu, Yunxian; Zhou, Qiang; Liu, Bingbing; Cui, Tian

    2015-07-27

    Two high density structures β- and γ-LiAlH{sub 4} are detected in LiAlH{sub 4}, a promising hydrogen storage compound, upon compression in diamond anvil cells, investigated with synchrotron X-ray diffraction and first-principle calculations. The joint of the experimental and theoretical results has confirmed the sequence of the pressure-induced structural phase transitions from α-LiAlH{sub 4} (space group P2{sub 1}/c) to β-LiAlH{sub 4} (P2{sub 1}/c-6C symmetry), and then to γ-LiAlH{sub 4} (space group Pnc2), which are not reported in previous literatures. At the α to β transition point for LiAlH{sub 4}, the estimated difference in cell volume is about 20%, while the transformation from β to γ phase is with a volume drop smaller than 1%. The α to β phase transition is accompanied by the local structure change from a AlH{sub 4} tetrahedron into a AlH{sub 6} octahedron, which contributes to a large volume collapse.

  13. Characterization of Al2O3 in High-Strength Mo Alloy Sheets by High-Resolution Transmission Electron Microscopy.

    PubMed

    Zhou, Yucheng; Gao, Yimin; Wei, Shizhong; Hu, Yajie

    2016-02-01

    A novel type of alumina (Al2O3)-doped molybdenum (Mo) alloy sheet was prepared by a hydrothermal method and a subsequent powder metallurgy process. Then the characterization of α-Al2O3 was investigated using high-resolution transmission electron microscopy as the research focus. The tensile strength of the Al2O3-doped Mo sheet is 43-85% higher than that of the pure Mo sheet, a very obvious reinforcement effect. The sub-micron and nanometer-scale Al2O3 particles can increase the recrystallization temperature by hindering grain boundary migration and improve the tensile strength by effectively blocking the motion of the dislocations. The Al2O3 particles have a good bond with the Mo matrix and there exists an amorphous transition layer at the interface between Al2O3 particles and the Mo matrix in the as-rolled sheet. The sub-structure of α-Al2O3 is characterized by a number of nanograins in the $\\left[ {2\\bar{2}1} \\right]$ direction. Lastly, a new computer-based method for indexing diffraction patterns of the hexagonal system is introduced, with 16 types of diffraction patterns of α-Al2O3 indexed. PMID:26914997

  14. First-principles investigation on vibrational, anisotropic elastic and thermodynamic properties for L12 structure of Al3Er and Al3Yb under high pressure

    NASA Astrophysics Data System (ADS)

    Zhang, Xudong; Jiang, Wei

    2016-02-01

    To better clarify the physical properties for Al3RE precipitates, first-principles calculations are performed to investigate the vibrational, anisotropic elastic and thermodynamic properties of Al3Er and Al3Yb. The calculated results agree well with available experimental and theoretical ones. The vibrational properties indicate that Al3Er and Al3Yb will keep their dynamical stabilities with L12 structure up to 100 GPa. The elastic constants are satisfied with mechanical stability criteria up to the external pressure of 100 GPa. The mechanical anisotropy is predicted by anisotropic constants AG, AU, AZ and 3D curved surface of Young's modulus. The calculated results show that both Al3Er and Al3Yb are isotropic at zero pressure and obviously anisotropic under high pressure. Further, we systematically investigate the thermodynamic properties and provide the relationships between thermal parameters and pressure. Finally, the pressure-dependent behaviours of density of states, Mulliken charge and bond length are discussed.

  15. Characterization of residual stresses in heat treated Ti-6Al-4V forgings by machining induced distortion

    NASA Astrophysics Data System (ADS)

    Regener, B.; Krempaszky, C.; Werner, E.

    2010-06-01

    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

  16. Graphene-assisted growth of high-quality AlN by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Zeng, Qing; Chen, Zhaolong; Zhao, Yun; Wei, Tongbo; Chen, Xiang; Zhang, Yun; Yuan, Guodong; Li, Jinmin

    2016-08-01

    High-quality AlN films were directly grown on graphene/sapphire substrates by metalorganic chemical vapor deposition (MOCVD). The graphene layers were directly grown on sapphire by atmospheric-pressure chemical vapor deposition (APCVD), a low-cost catalyst-free method. We analyzed the influence of the graphene layer on the nucleation of AlN at the initial stage of growth and found that sparse AlN grains on graphene grew and formed a continuous film via lateral coalescence. Graphene-assisted AlN films are smooth and continuous, and the full width at half maximum (FWHM) values for (0002) and (10\\bar{1}2) reflections are 360 and 622.2 arcsec, which are lower than that of the film directly grown on sapphire. The high-resolution TEM images near the AlN/sapphire interface for graphene-assisted AlN films clearly show the presence of graphene, which kept its original morphology after the 1200 °C growth of AlN.

  17. Thermal treatment and utilization of Al-rich waste in high calcium fly ash geopolymeric materials

    NASA Astrophysics Data System (ADS)

    Chindaprasirt, Prinya; Rattanasak, Ubolluk; Vongvoradit, Pimdao; Jenjirapanya, Supichart

    2012-09-01

    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 110°C and calcined at 400 to 1000°C. Mineralogical analyses were conducted using X-ray diffraction (XRD) to study the phase change. The increase in calcination temperature to 600, 800, and 1000°C resulted in the phase transformation. The more active alumina phase of active γ-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 1000°C possessed the 7-d compressive strength of 34.2 MPa.

  18. High-Stakes Testing and Its Relationship to Stress Levels of Coastal Secondary Teachers

    ERIC Educational Resources Information Center

    McDaniel, Sheneatha Lashelle Alexander

    2012-01-01

    The purpose of this research was to examine the relationship between high-stakes tests and stress with secondary teachers. Furthermore, this study investigated whether veteran teachers experience more stress than novice teachers and whether or not self-efficacy, gender, accountability status, and years of experience influence teacher stress as it…

  19. Evaluation of Perfluoropolyether Lubricant Lifetime in the High Stress and High Stress-Cycle Regime for Mars Applications

    NASA Technical Reports Server (NTRS)

    Herman, Jason; Davis, Kiel

    2008-01-01

    The successful operation of long-life, highly loaded mechanisms used for planetary exploration or autonomous structures assembly will depend upon the ability to effectively lubricate rolling-element bearings. As new tools are developed (i.e., drill, abraders, robotic manipulators, etc.) that interact with their environment in a more direct manner, lubricants will be pushed past the bounds that current scientific literature has published. This paper details results from bearing lubrication lifetime testing performed in support of Honeybee Robotics development of the Mars Science Laboratory (MSL) Surface Removal Tool (SRT). This testing was done due to the lack of available data in research literature that is applicable to the lubrication regime the SRT bearings are being designed for. Based on the test results, the chosen bearing arrangement can be used for the SRT Grind Shaft bearings with the use of a Braycote Micronic 601EF grease-plate with a 10 vol% grease slurry fill (50/50 wt% Braycote Micronic 601EF and Brayco 815Z). This arrangement showed no signs of detrimental degradation over the course of the 3x life test. The purely grease-plated bearing ran at a consistently higher torque and showed signs of failure beginning at approximately 2.2 x 10(exp 7) revs (approximately 6.3 x 10(exp 7) stress-cycles) with a torque over-limit failure at approximately 4.5 x 10(exp 7) revs (approximately 1.3 x 10(exp 8) stress-cycles). Barring cold-start torque margin limitations, it is recommended that any long-life bearing application include some vol% grease-pack in addition to a standard grease-plate to reduce parasitic torque and increase bearing life. While these results are specific to a particular environment and loading condition, they demonstrate the extended capabilities of a commonly used flight lubricant outside of the range that is published in current research literature.

  20. Fabrication of Al2O3/glass/Cf Composite Substrate with High Thermal Conductivity

    NASA Astrophysics Data System (ADS)

    Wang, S. X.; Liu, G. S.; Ouyang, X. Q.; Wang, Y. D.; Zhang, D.

    2016-02-01

    In this paper, carbon fiber with high thermal conductivity was introduced into the alumina-based composites. To avoid oriented alignment of carbon fibers (Cf) and carbothermal reactions during the sintering process, the Al2O3/glass/Cf substrate was hot-pressed under a segmental-pressure procedure at 1123 K. Experimental results show that carbon fibers randomly distribute and form a bridging structure in the matrix. The three-dimensional network of Cf in Al2O3/glass/Cf substrate brings excellent heat conducting performance due to the heat conduction by electrons. The thermal conductivity of Al2O3/30%glass/30%Cf is as high as 28.98 W mK-1, which is 4.56 times larger than that of Al2O3/30%glass.

  1. Cavity Optomechanics with High-Stress Silicon Nitride Films

    NASA Astrophysics Data System (ADS)

    Wilson, Dalziel Joseph

    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

  2. Traps and defects in pre- and post-proton irradiated AlGaN-GaN high electron mobility transistors and AlGaN Schottky diodes

    NASA Astrophysics Data System (ADS)

    Sin, Yongkun; Foran, Brendan; Presser, Nathan; LaLumondiere, Stephen; Lotshaw, William; Moss, Steven C.

    2013-03-01

    High electron mobility transistors (HEMTs) based on AlGaN-GaN hetero-structures are promising for both commercial and military applications that require high voltage, high power, and high efficiency operation. Study of reliability and radiation effects of AlGaN-GaN HEMTs is necessary before solid state power amplifiers based on GaN HEMT technology are successfully deployed in satellite communication systems. Several AlGaN HEMT manufacturers have recently reported encouraging reliability data, but long-term reliability of these devices in the space environment still remains a major concern because a large number of traps and defects are present both in the bulk as well as at the surface leading to undesirable characteristics. This study is to investigate the effects of the AlGaN-GaN HEMTs and AlGaN Schottky diodes irradiated with protons.

  3. Pb nanowire formation on Al/lead zirconate titanate surfaces in high-pressure hydrogen

    SciTech Connect

    Alvine, Kyle J.; Shutthanandan, V.; Arey, Bruce W.; Wang, Chong M.; Bennett, Wendy D.; Pitman, Stan G.

    2012-07-12

    Thin films of Al on lead zirconate titanate (PZT) annealed in high-pressure hydrogen at 100C exhibit surface Pb nanowire growth. Wire diameter is approximately 80 nm and length can exceed 100 microns. Based on microstructural analysis using electron microscopy and ion scattering, a vapor-solid scheme with hydrogen as a carrier gas was proposed as a growth mechanism. We expect that these observations may lead to controlled Pb nanowires growth through pattering of the Al film.

  4. AlGaAs/GaAs photovoltaic converters for high power narrowband radiation

    SciTech Connect

    Khvostikov, Vladimir; Kalyuzhnyy, Nikolay; Mintairov, Sergey; Potapovich, Nataliia; Shvarts, Maxim; Sorokina, Svetlana; Andreev, Viacheslav; Luque, Antonio

    2014-09-26

    AlGaAs/GaAs-based laser power PV converters intended for operation with high-power (up to 100 W/cm{sup 2}) radiation were fabricated by LPE and MOCVD techniques. Monochromatic (λ = 809 nm) conversion efficiency up to 60% was measured at cells with back surface field and low (x = 0.2) Al concentration 'window'. Modules with a voltage of 4 V and the efficiency of 56% were designed and fabricated.

  5. Band gap bowing parameter in pseudomorphic Al{sub x}Ga{sub 1−x}N/GaN high electron mobility transistor structures

    SciTech Connect

    Goyal, Anshu; Kapoor, Ashok K.; Raman, R.; Dalal, Sandeep; Mohan, Premila; Muralidharan, R.

    2015-06-14

    A method for evaluation of aluminium composition in pseudomorphic Al{sub x}Ga{sub 1−x}N layer from the measured photoluminescence (PL) peak energy is presented here. The layers were grown by metalorganic chemical vapor deposition and characterized by high resolution X-ray diffraction (HRXRD), PL, cathodoluminescence, and atomic force microscopy. We estimated the value of biaxial stress in pseudomorphic Al{sub x}Ga{sub 1−x}N layers grown on sapphire and silicon carbide substrates using HRXRD scans. The effect of biaxial stress on the room temperature band edge luminescence in pseudomorphic Al{sub x}Ga{sub 1−x}N/GaN layers for various aluminium compositions in the range of 0.2 < x < 0.3 was determined. The value of pressure coefficient of band gap was also estimated. The stress corrected bowing parameter in Al{sub x}Ga{sub 1−x}N was determined as 0.50 ± 0.06 eV. Our values match well with the theoretically obtained value of bowing parameter from the density functional theory.

  6. 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)

    Grummon, D. S.

    1993-01-01

    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.

  7. Derivation of Apollo 14 High-Al Basalts at Discrete Times: Rb-Sr Isotopic Constraints

    NASA Technical Reports Server (NTRS)

    Hui. Hejiu; Neal, Clive, R.; Shih, Chi-Yu; Nyquist, Laurence E.

    2012-01-01

    Pristine Apollo 14 (A-14) high-Al basalts represent the oldest volcanic deposits returned from the Moon [1,2] and are relatively enriched in Al2O3 (>11 wt%) compared to other mare basalts (7-11 wt%). Literature Rb-Sr isotopic data suggest there are at least three different eruption episodes for the A-14 high-Al basalts spanning the age range approx.4.3 Ga to approx.3.95 Ga [1,3]. Therefore, the high-Al basalts may record lunar mantle evolution between the formation of lunar crust (approx.4.4 Ga) and the main basin-filling mare volcanism (<3.85 Ga) [4]. The high-Al basalts were originally classified into five compositional groups [5,6], and then regrouped into three with a possible fourth comprising 14072 based on the whole-rock incompatible trace element (ITE) ratios and Rb-Sr radiometric ages [7]. However, Rb-Sr ages of these basalts from different laboratories may not be consistent with each other because of the use of different 87Rb decay constants [8] and different isochron derivation methods over the last four decades. This study involved a literature search for Rb-Sr isotopic data previously reported for the high-Al basalts. With the re-calculated Rb-Sr radiometric ages, eruption episodes of A-14 high-Al basalts were determined, and their petrogenesis was investigated in light of the "new" Rb-Sr isotopic data and published trace element abundances of these basalts.

  8. Evolution of the Reynolds shear stresses in highly accelerated turbulent boundary layers

    NASA Astrophysics Data System (ADS)

    Araya, Guillermo; Castillo, Luciano; Hussain, Fazle

    2014-11-01

    Turbulent boundary layers subjected to severe acceleration or strong Favorable Pressure Gradients (FPG) are of great fundamental and technological importance; examples of the latter include nozzle design, underwater bodies and drag reduction applications. Scientifically, they pose great interest from the point of view of scaling laws, the complex interaction between the outer and inner regions, and relaminarization phenomena. Direct Numerical Simulations (DNS) of highly accelerated turbulent boundary layers are performed by means of the Dynamic Multi-scale Approach (DMA) recently developed by [Araya et al. JFM 670, 581 (2011)]. It is shown that the Reynolds shear stress monotonically decreases and exhibits a logarithmic layer in the meso-layer region during the laminarization process. In addition, the local maxima of streamwise velocity fluctuations in wall units remain almost constant in the very strong FPG region, which prevents the flow to become completely laminar. Furthermore, the re-distribution of Reynolds shear stresses due to sweeps and ejections in the FPG region is performed and a physical mechanism is proposed.

  9. Surface Thiolation of Al Microspheres to Deposite Thin and Compact Ag Shells for High Conductivity.

    PubMed

    Wang, Yilong; Wen, Jianghong; Zhao, Suling; Chen, Zhihong; Ren, Ke; Sun, Jie; Guan, Jianguo

    2015-12-15

    In this work, we have demonstrated a method for controllable thiolated functionalization coupled with electroless silver plating to achieve aluminum@silver (Al@Ag) core-shell composite particles with thin and compact layers. First, Al microspheres were functionalized by a well-known polymerizable silane coupling agent, i.e., 3-mercaptopropyltrimethoxysilane (MPTMS). Decreasing the ethanol-to-water volume ratio (F) in silane solution produces modification films with high content of thiol groups on Al microspheres, owing to the dehydration of silane molecules with hydroxyl groups on Al microspheres and self-polymerization of silane molecules. Then, ethanol was used as one of the solvents to play a major role in the uniform dispersion of silane coupling agent in the solution, resulting in uniformly distributing and covalently attaching thiol groups on Al microspheres. In electroless silver plating, thiol groups being densely grafted on the surface of Al microspheres favor the heterogeneous nucleation of Ag, since the thiol group can firmly bind with Ag(+) and enable the in situ reduction by the reducing reagent. In this manner, dense Ag nuclei tend to produce thin and compact silver shells on the Al microspheres surfaces. The as-obtained Al@Ag core-shell composite particles show a resistivity as low as (8.58 ± 0.07) × 10(-5) Ω·cm even when the Ag content is as low as 15.46 wt %. Therefore, the as-obtained Al@Ag core-shell composite particles have advantages of low weight, low silver content and high conductivity, which could make it a promising candidate for application in conductive and electromagnetic shielding composite materials. PMID:26574653

  10. Assessment of microalloying effects on the high temperature fatigue behavior of NiAl

    NASA Technical Reports Server (NTRS)

    Noebe, R. D.; Lerch, B. A.; Rao, K. B. S.

    1995-01-01

    Binary NiAl suffers from a lack of strength and poor creep properties at and above 1000 K. Poor creep resistance in turn affects low cycle fatigue (LCF) lives at low strain ranges due to the additional interactions of creep damage. One approach for improving these properties involved microalloying with either Zr or N. As an integral part of a much larger alloying program the low cycle fatigue behavior of Zr and N doped nickel aluminides produced by extrusion of prealloyed powders has been investigated. Strain controlled LCF tests were performed in air at 1000 K. The influence of these microalloying additions on the fatigue life and cyclic stress response of polycrystalline NiAl are discussed.

  11. Demonstration of InAlN/AlGaN high electron mobility transistors with an enhanced breakdown voltage by pulsed metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Xue, JunShuai; Zhang, JinCheng; Hao, Yue

    2016-01-01

    In this work, InAlN/AlGaN heterostructures employing wider bandgap AlGaN instead of conventional GaN channel were grown on sapphire substrate by pulsed metal organic chemical vapor deposition, where the nominal Al composition in InAlN barrier and AlGaN channel were chosen to be 83% and 5%, respectively, to achieve close lattice-matched condition. An electron mobility of 511 cm2/V s along with a sheet carrier density of 1.88 × 1013 cm-2 were revealed in the prepared heterostructures, both of which were lower compared with lattice-matched InAlN/GaN due to increased intrinsic alloy disorder scattering resulting from AlGaN channel and compressively piezoelectric polarization in barrier, respectively. While the high electron mobility transistor (HEMT) processed on these structures not only exhibited a sufficiently high drain output current density of 854 mA/mm but also demonstrated a significantly enhanced breakdown voltage of 87 V, which is twice higher than that of reported InAlN/GaN HEMT with the same device dimension, potential characteristics for high-voltage operation of GaN-based electronic devices.

  12. The Chinese High School Student's Stress in the School and Academic Achievement

    ERIC Educational Resources Information Center

    Liu, Yangyang; Lu, Zuhong

    2011-01-01

    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…

  13. Effect of high fluoride and high fat on serum lipid levels and oxidative stress in rabbits.

    PubMed

    Sun, Liyan; Gao, Yanhui; Zhang, Wei; Liu, Hui; Sun, Dianjun

    2014-11-01

    The purpose of this study was to explore the effects of high fluoride and high fat on triglyceride (TG), total cholesterol (TC), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), total antioxidant capacity (T-AOC), lipid peroxide (LPO) and malondialdehyde (MDA) in rabbits. A factorial experimental design was used, with two factors (fluoride and fat) and three levels. Seventy-two male rabbits were randomly assigned into nine groups according to initial weight and serum lipid levels. The rabbits were fed with basic feed, moderate fat feed or high fat feed and drank tap water, fluoridated water at levels of 50 and 100mgfluorion/L freely. Biological materials were collected after 5 months, and serum lipid, T-AOC, LPO, and MDA levels were then measured. Using these data, the separate and interactive effects of high fluoride and high fat were analyzed. High fluoride and high fat both increased serum levels of TC, HDL-C and LDL-C significantly (P<0.05), and there was also a synergistic effect between high fluoride and high fat (P<0.05). High fluoride and high fat had different effects on TG levels: high fat significantly increased TG levels (P<0.01) whereas high fluoride had nothing to do with TG levels (P>0.05). High fat significantly elevated LPO and MDA levels and lowered T-AOC levels in serum (P<0.05). Similarly, high fluoride significantly increased LPO and MDA levels in serum (P<0.05). However, there was no interactive effect between high fat and high fluoride on these indexes. In summary, high fluoride and high fat increased serum TC and LDL-C levels individually and synergistically, and this would cause and aggravate hypercholesterolemia in rabbits. At the same time, high fluoride and high fat both made the accumulation of product of oxidative stress in experimental animals. PMID:25461561

  14. High-Temperature Slow Crack Growth of Silicon Carbide Determined by Constant-Stress-Rate and Constant-Stress Testing

    NASA Technical Reports Server (NTRS)

    Choi, Sung H.; Salem, J. A.; Nemeth, N. N.

    1998-01-01

    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 methods were used to determine the slow crack growth parameters. The four estimation methods were in good agreement for the constant-stress-rate testing with a small variation in the slow-crack-growth parameter, n, ranging from 28 to 36. By contrast, the variation in n between the four estimation methods was significant in the constant-stress testing with a somewhat wide range of n= 16 to 32.

  15. Investigations on AlN/sapphire piezoelectric bilayer structure for high-temperature SAW applications.

    PubMed

    Aubert, Thierry; Elmazria, Omar; Assouar, Badreddine; Blampain, Eloi; Hamdan, Ahmad; Genève, Damien; Weber, Sylvain

    2012-05-01

    This paper explores the possibility of using AlN/sapphire piezoelectric bilayer structures for high-temperature SAW applications. To determine the temperature stability of AlN, homemade AlN/sapphire samples are annealed in air atmosphere for 2 to 20 h at temperatures from 700 to 1000°C. Ex situ X-ray diffraction measurements reveal that the microstructure of the thin film is not affected by temperatures below 1000°C. Ellipsometry and secondary ion mass spectroscopy investigations attest that AlN/sapphire is reliable up to 700°C. Beyond this temperature, both methods indicate ongoing surface oxidation of AlN. Additionally, Pt/Ta and Al interdigital transducers are patterned on the surface of the AlN film. The resulting SAW devices are characterized up to 500°C and 300°C, respectively, showing reliable frequency response and a large, quasi-constant temperature sensitivity, with a first-order temperature coefficient of frequency around -75 ppm/°C. Between room temperature and 300°C, both electromechanical coupling coefficient K(2) and propagation losses increase, so the evolution of delay lines' insertion losses with temperature strongly depends on the length of the propagation path. PMID:22622985

  16. Investigation of gate-diode degradation in normally-off p-GaN/AlGaN/GaN high-electron-mobility transistors

    SciTech Connect

    Ťapajna, M. Kuzmík, J.; Hilt, O.; Bahat-Treidel, E.; Würfl, J.

    2015-11-09

    Gate diode conduction mechanisms were analyzed in normally-off p-GaN/AlGaN/GaN high-electron mobility transistors grown on Si wafers before and after forward bias stresses. Electrical characterization of the gate diodes indicates forward current to be limited by channel electrons injected through the AlGaN/p-GaN triangular barrier promoted by traps. On the other hand, reverse current was found to be consistent with carrier generation-recombination processes in the AlGaN layer. Soft breakdown observed after ∼10{sup 5 }s during forward bias stress at gate voltage of 7 V was attributed to formation of conductive channel in p-GaN/AlGaN gate stack via trap generation and percolation mechanism, likely due to coexistence of high electric field and high forward current density. Possible enhancement of localized conductive channels originating from spatial inhomogeneities is proposed to be responsible for the degradation.

  17. Effects of High Mean Stress on High-cycle Fatigue Behavior of PWA 1480

    NASA Technical Reports Server (NTRS)

    Majumdar, S.; Antolovich, S. D.; Milligan, W. W.

    1985-01-01

    PWA 1480 is a potential candidate material for use in the high-pressure fuel turbine blade of the space shuttle main engine. As an engine material it will be subjected to high-cycle fatigue loading superimposed on a high mean stress due to combined centrifugal and thermal loadings. The present paper describes the results obtained in an ongoing program at the Argonne National Laboratory, sponsored by NASA Lewis, to determine the effects of a high mean stress on the high-cycle fatigue behavior of this material. Straight-gauge high-cycle fatigue specimens, 0.2 inch in diameter and with the specimen axis in the 001 direction, were supplied by NASA Lewis. The nominal room temperature yield and ultimate strength of the material were 146 and 154 ksi, respectively. Each specimen was polished with 1-micron diamond paste prior to testing. However, the surface of each specimen contained many pores, some of which were as large as 50 micron. In the initial tests, specimens were subjected to axial-strain-controlled cycles. However, very little cyclic plasticity was observed.

  18. High Sensitivity Stress Sensor Based on Hybrid Materials

    NASA Technical Reports Server (NTRS)

    Cao, Xian-An (Inventor)

    2014-01-01

    A sensing device is used to detect the spatial distributions of stresses applied by physical contact with the surface of the sensor or induced by pressure, temperature gradients, and surface absorption. The sensor comprises a hybrid active layer that includes luminophores doped in a polymeric or organic host, altogether embedded in a matrix. Under an electrical bias, the sensor simultaneously converts stresses into electrical and optical signals. Among many applications, the device may be used for tactile sensing and biometric imaging.

  19. Laser remelting of Ti6AL4V using high power diode laser

    NASA Astrophysics Data System (ADS)

    Amaya-Vázquez, M. R.; Sánchez-Amaya, J. M.; Boukha, Z.; El Amrani, K.; Botana, F. J.

    2012-04-01

    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 α-β 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.

  20. High elemental selectivity to Sn submonolayers embedded in Al using positron annihilation spectroscopy

    NASA Astrophysics Data System (ADS)

    Hugenschmidt, C.; Pikart, P.; Stadlbauer, M.; Schreckenbach, K.

    2008-03-01

    In the present work, we demonstrate that metal layers in the submonolayer range embedded in a matrix are revealed with unprecedented sensitivity by coincident Doppler-broadening spectroscopy of the positron annihilation using a monoenergetic positron beam. The measured electron momentum distribution specific for Sn is clearly observable in Al/Sn/Al -layered samples even at a Sn area density of as low as 7.3×10-2μg/cm2 below 200nm Al. An explanation for the high elemental selectivity for the thin Sn layers is set forward in terms of efficient positron trapping due to the changing positron affinity at the Al/Sn -interface and quantum-dot-like positron states in Sn nanoparticles.

  1. Investigation of Aluminate and Al2O3 Crystals and Melts at High Temperature Using XANES Spectroscopy

    SciTech Connect

    Neuville, Daniel R.; Roux, Jacques; Cormier, Laurent; Henderson, Grant S.; Ligny, Dominique de; Flank, Anne-Marie; Lagarde, Pierre

    2007-02-02

    Using X-ray absorption at the Al K-edge at high temperature, structural information was determined on Al2O3, CaAl2O4 (CA), Ca3Al2O6 (C3A) and CaAl2Si2O8 (anorthite) in the crystalline and liquid states (2380 K). Important changes are observed for Al2O3 where all oscillation in the XANES spectra disappear above the liquidus temperature. For the three other compositions some modifications of the XANES spectra can be attributed to changes in the Al coordination.

  2. Induction of engineered residual stresses fields and enhancement of fatigue life of high reliability metallic components by laser shock processing

    NASA Astrophysics Data System (ADS)

    Ocaña, J. L.; Porro, J. A.; Díaz, M.; Ruiz de Lara, L.; Correa, C.; Gil-Santos, A.; Peral, D.

    2013-02-01

    Laser shock processing (LSP) is being increasingly applied as an effective technology for the improvement of metallic materials mechanical and surface properties in different types of components as a means of enhancement of their corrosion and fatigue life behavior. As reported in previous contributions by the authors, a main effect resulting from the application of the LSP technique consists on the generation of relatively deep compression residual stresses field into metallic alloy pieces allowing an improved mechanical behaviour, explicitly the life improvement of the treated specimens against wear, crack growth and stress corrosion cracking. Additional results accomplished by the authors in the line of practical development of the LSP technique at an experimental level (aiming its integral assessment from an interrelated theoretical and experimental point of view) are presented in this paper. Concretely, follow-on experimental results on the residual stress profiles and associated surface properties modification successfully reached in typical materials (especially Al and Ti alloys characteristic of high reliability components in the aerospace, nuclear and biomedical sectors) under different LSP irradiation conditions are presented along with a practical correlated analysis on the protective character of the residual stress profiles obtained under different irradiation strategies. Additional remarks on the improved character of the LSP technique over the traditional "shot peening" technique in what concerns depth of induced compressive residual stresses fields are also made through the paper.

  3. Surface modification of Al-20Si alloy by high current pulsed electron beam

    NASA Astrophysics Data System (ADS)

    Hao, Y.; Gao, B.; Tu, G. F.; Li, S. W.; Hao, S. Z.; Dong, C.

    2011-02-01

    Hypereutectic Al-20Si (Si 20 wt.%, Al balance)alloy surface was treated with high current pulsed electron beam (HCPEB) under different pulse numbers. The results indicate that HCPEB irradiation induces the formation of metastable structures on the treated surface. The coarse primary Si particle melts, producing a "halo" microstructure with primary Si as the center on the melted surface. A supersaturated solid solution of Al is formed in the melted layer caused by Si atoms dissolving into the Al matrix. Cross-section structure analysis shows that a 4 μm remelted layer is formed underneath the top surface of the HCEPB-treated sample. Compared with the matrix, the Al and Si elements in the remelted layer are distributed uniformly. In addition, the grains of the Al-20Si alloy surface are refined after HCPEB treatment, as shown by TEM observation. Nano-silicon particles are dispersed on the surface of remelted layer. Polygonal subgrains, approximately 50-100 nm in size, are formed in the Al matrix. The hardness test results show that the microhardness of the α(Al) and eutectic structure is increased with increasing pulse number. The hardness of the "halo" microstructure presents a gradient change after 15 pulse treatment due to the diffusion of Si atoms. Furthermore, hardness tests of the cross-section at different depths show that the microhardness of the remelted layer is higher than that of the matrix. Therefore, HCPEB technology is a good surface modification method for enhancing the surface hardness of hypereutectic Al-20Si alloy.

  4. Microstructural stability of AlN diffusion barrier for nanocomposite Ni + CrAlYSiHfN coating on single crystal superalloy at high temperatures

    NASA Astrophysics Data System (ADS)

    Ren, Pan; Zhu, Shenglong; Wang, Fuhui

    2015-12-01

    An AlN interlayer was fabricated by filtered vacuum arc evaporation as a diffusion barrier (DB) between Ni + CrAlYSiHfN composite coating and K417G superalloy. Microstructure changes of the AlN DB were investigated after exposure at 1000 and 1100 °C. Amorphous structure was found in the as-deposited AlN DB, which went through crystallization when exposing at high temperature. The AlN DB suppressed interdiffusion between overlayer and substrate effectively after 200 h exposure at both 1000 °C and 1100 °C. A few substrate element precipitates were observed within the grain boundary of the AlN DB after exposure at 1100 °C for 200 h.

  5. The Role of PentaCoordinated Al3+ Ions in the High Temperature Phase Transformation of γ-Al2O3

    SciTech Connect

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

    2008-06-26

    In this work, the structural stability of gamma-alumina (γ-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 γ-Al2O3 undergoes a phase transition to θ-Al2O3 during calcination at 1000oC for 10hr. The formation of the θ-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 1000°C for 10 hrs, the ratio of the θ-Al2O3 phase to the total alumina in samples modified by either BaO or La2O3 is significantly reduced in comparison with γ-Al2O3. 27Al MAS NMR spectra revealed that the reduction in the extent of θ-Al2O3 formation was highly correlated with the reduction in the amount of penta-coordinated aluminum ions, measured after 500°C calcination, in both BaO- and La2O3-modified γ-Al2O3 samples. These results strongly suggest that the penta-coordinated aluminum ions, present exclusively on the surface of γ-Al2O3, play a critical role in the phase transformation of γ-Al2O3 to θ-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 (≤1000°C) calcination.

  6. Advantages of the AlGaN spacer in InAlN high-electron-mobility transistors grown using metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Yamada, Atsushi; Ishiguro, Tetsuro; Kotani, Junji; Tomabechi, Shuichi; Nakamura, Norikazu; Watanabe, Keiji

    2016-05-01

    We demonstrate the advantages of an AlGaN spacer layer in an InAlN high-electron-mobility transistor (HEMT). We investigated the effects of the growth parameters of the spacer layer on electron mobility in InAlN HEMTs grown by metalorganic vapor phase epitaxy, focusing on the surface roughness of the spacer layer and sharpness of the interface with the GaN channel layer. The electron mobility degraded, as evidenced by the formation of a graded AlGaN layer at the top of the GaN channel layer and the surface roughness of the AlN spacer layer. We believe that the short migration length of aluminum atoms is responsible for the observed degradation. An AlGaN spacer layer was employed to suppress the formation of the graded AlGaN layer and improve surface morphology. A high electron mobility of 1550 cm2 V‑1 s‑1 and a low sheet resistance of 211 Ω/sq were achieved for an InAlN HEMT with an AlGaN spacer layer.

  7. Constitutive Modeling of High-Temperature Flow Behavior of Al-0.62Mg-0.73Si Aluminum Alloy

    NASA Astrophysics Data System (ADS)

    Sun, Y.; Ye, W. H.; Hu, L. X.

    2016-04-01

    The high-temperature flow behavior of an aerospace structural material Al-0.62 Mg-0.73Si aluminum alloy was researched in this work. The isothermal compression tests were carried out in the temperature range of 683-783 K and strain rate range of 0.001-1 s-1. Based on the obtained true stress-true strain curves, the constitutive relationship of the alloy was revealed by establishing the Arrhenius-type constitutive model and a modified Johnson-Cook model. It was found that the flow characteristics were closely related to deformation temperature and strain rate. The activation energy of the studied material was calculated to be approximately 174 kJ mol-1. A comparative study has been conducted on the accuracy and reliability of the proposed models using statistics analysis method. It was proved by error analysis that the Arrhenius-type model had a better performance than the modified Johnson-Cook model.

  8. Structural analysis of highly porous γ-Al{sub 2}O{sub 3}

    SciTech Connect

    Samain, Louise; Jaworski, Aleksander; Edén, Mattias; Ladd, Danielle M.; Seo, Dong-Kyun; Javier Garcia-Garcia, F.; Häussermann, Ulrich

    2014-09-15

    Two highly porous γ-aluminas, a commercial catalyst obtained from the calcination of boehmite and a highly mesoporous product obtained from amorphous aluminum (oxy)hydroxide via a sol–gel-based process were investigated by {sup 27}Al nuclear magnetic resonance (NMR), transmission electron microscopy (TEM), and atomic pair distribution function (PDF) analysis of synchrotron powder diffraction data. NMR data showed for both materials a distribution of tetrahedrally and octahedrally coordinated Al at a 0.30:0.70 ratio, which is typical for γ-aluminas. TEM studies revealed that rod-shaped particles with about 5 nm in thickness are the building blocks of the porous structure in both materials. These particles often extend to a length of 50 nm in the commercial catalyst and are considerably shorter in the sol–gel-based material, which has a higher surface area. Refinement of PDFs revealed the presence of a ∼1 nm scale local structure and the validity of a tetragonal average structure for both materials. This tetragonal average structure contains a substantial fraction of non-spinel octahedral Al atoms. It is argued that the presence of local structure is a general feature of γ-alumina, independent of precursor and synthesis conditions. The concentration of “non-spinel” Al atoms seems to correlate with surface properties, and increases with increasing pore size/surface area. This should have implications to the catalytic properties of porous γ-alumina. - Graphical abstract: Boehmite-derived and sol–gel synthesized porous γ-Al{sub 2}O{sub 3} possess identical structural properties, featuring a nm scale local structure and a tetragonal average structure. - Highlights: • Porous γ-Al{sub 2}O{sub 3} generally possesses a nm-scale local structure. • The tetragonal average structure contains a substantial fraction of “non-spinel” Al atoms. • The concentration of “non-spinel” Al atoms correlates with surface properties.

  9. Microstructure, mechanical properties, and high-temperature oxidation resistance of boronized {gamma}-TiAl(Mn)

    SciTech Connect

    Kim, S.; Yoon, Y.; Kim, H.; Park, K.

    1997-12-31

    Titanium aluminide (TiAl) based intermetallic compounds are considered as potential materials for high-performance automobile and aircraft engine components and airframe applications because of their low density (3.8 g/cm{sup 3}), high melting temperature (1,480 C), and good elevated temperature strength retention. To improve the wear and high-temperature oxidation resistance of reactively sintered {gamma}-TiAl(Mn) intermetallic compounds, they were boronized in the temperature range of 900 to 1,100 C for 5 to 11 hours with powder mixtures of B{sub 4}C and Na{sub 2}B{sub 4}O{sub 7}. It was found that the coating layer consisted of three sublayers, i.e., outer, middle, and inner sublayers. The outer, middle, and inner sublayers were identified as a mixture of TiB{sub 2} and TiO{sub 2}, a mixture of Al{sub 2}O{sub 3} and TiO{sub 2}, and Ti-rich TiAl based compounds, respectively. The coating layer significantly improved the surface hardness and the wear and high-temperature oxidation resistances. The highest surface hardness (Hv {approx} 2,720) was obtained at 900 C for 11 hours. This surface hardness is much higher than that of TiAl(Mn) (Hv {approx} 400). In addition, the specimens boronized at both 1,000 and 1,050 C for 9 hours showed an excellent high-temperature oxidation resistance. It is believed that the boronizing on the TiAl(Mn) intermetallics is very effective to improve the wear and high-temperature oxidation resistances.

  10. Failure mechanism of coated biomaterials under high impact-sliding contact stresses

    NASA Astrophysics Data System (ADS)

    Chen, Ying

    This study uses a newly developed testing method--- inclined cyclic impact-sliding test to investigate the failure behaviors of different types of biomaterials, (SS316L, Ti6Al4V and CoCr) coated by different coatings (TiN, DLC and PEO), under extremely high dynamic contact stress conditions. This test method can simulate the combined impact and sliding/rolling loading conditions, which is very practical in many aspects of commercial usages. During the tests, fatigue cracking, chipping, peeling and material transferring were observed in damaged area. This research is mainly focused on the failure behaviors of load-bearing materials which cyclic impacting and sliding are always involved. This purpose was accomplished in the three stages: First, impact-sliding test was carried out on TiN coated unhardened M2. It was found that soft substrate can cause early failure of coating due to the considerable plastic deformation in the substrate. In this case, stronger substrate is required to support coating better when tested under high contact stresses. Second, PEO coated Ti-6Al-4V was tested under pure sliding and impact-sliding wear conditions. PEO coating was found not strong enough to afford the high contact pressure under cyclic impact-sliding wear test due to its porous surface structure. However, the wear performance of PEO coating was enhanced due to the sub-stoichiometric oxide. To sum up, for load-bearing biomedical implants involved in high impacting movement, PEO coating may not be a promising surface protection. Third, the dense, smooth PVD/CVD bio-inert coatings were reconsidered. DLC and TiN coatings, combined by different substrates together with different interface materials were tested under the cyclic impact-sliding test using a set of proper loading. The results show that to choose a proper combination of coating, interface and substrate based on their mechanical properties is of great importance under the test condition. Hard substrates provide support

  11. Al-21Ti-23Cr high-temperature protective coating on TiAl intermetallic compounds by RF magnetron sputtering

    SciTech Connect

    Park, J.Y.; Lee, H.N.; Wee, D.M.; Park, S.W.; Oh, M.H.

    1997-12-31

    Ti-48Al specimens were coated with Al-21Ti-23Cr film at 200 W, 0.8 Pa and 573 K by RF magnetron sputtering. The oxidation behavior of the coated specimens was investigated through isothermal and cyclic oxidation tests, and the tensile deformation properties of the coated specimens were also investigated before and after oxidation. The isothermal and cyclic oxidation curves showed that the Al-21Ti-23Cr film was very effective in decreasing the oxidation rate of Ti-48Al. This excellent oxidation resistance is attributable to the formation of a protective Al{sub 2}O{sub 3} layer on the surface of the Al-21Ti-23Cr film. It was found from the results of the tensile test that the protective Al{sub 2}O{sub 3} layer on the surface of the Al-21Ti-23Cr film enabled the Ti-48Al to maintain its tensile properties in an oxidizing environment.

  12. Normally-Off AlGaN/GaN High Electron Mobility Transistors with Thin and High Al Composition Barrier Layers

    NASA Astrophysics Data System (ADS)

    Zhang, Kai; Mi, Minhan; Chen, Yonghe; Cao, Mengyi; Wang, Chong; Ma, Xiaohua; Zhang, Jincheng; Hao, Yue

    2013-11-01

    A GaN-based enhancement-mode high electron mobility transistor (HEMT) with a 1.5 nm GaN/9 nm Al0.65Ga0.35N thin barrier was reported. Without any treatment on barrier layer under the gate, the as-grown HEMTs exhibited a threshold voltage of 0.3 V, a maximum drain current density of 441 mA/mm at VGS = 3 V and a peak extrinsic transconductance of 204 mS/mm at VGS = 1.1 V. At the same time, both a low Schottky leakage current and an insignificant surface defects induced current dispersion were observed. Moreover, drain induction barrier lower (DIBL) effect was determined to be merely 3.28 mV/V at 1 mA/mm for a gate length of 0.5 µm. Additionally, post-gate annealing experiment at step temperatures up to 450 °C was implemented, only causing a minor shift in threshold voltage. These results demonstrated the substantial potential of thin and high Al composition barrier layers for high-voltage and highly reliable enhancement mode operation.

  13. High-temperature powder synchrotron diffraction studies of synthetic cryolite Na 3AlF 6

    NASA Astrophysics Data System (ADS)

    Zhou, Qingdi; Kennedy, Brendan J.

    2004-03-01

    A high-resolution synchrotron diffraction study of the structures of a synthetic sample of cryolite Na 3AlF 6 from room temperature to 800°C is reported. At room temperature Na 3AlF 6 is monoclinic and the structure is described in space group P2 1/n. Heating the sample to 560°C results in only minor changes to the structure. A first-order transition from this monoclinic structure to a high-temperature cubic structure is observed near 567°C. The cubic Fm 3¯m structure is characterized by disorder of the fluoride atoms.

  14. Stress corrosion cracking of several high strength ferrous and nickel alloys

    NASA Technical Reports Server (NTRS)

    Nelson, E. E.

    1971-01-01

    The stress corrosion cracking resistance of several high strength ferrous and nickel base alloys has been determined in a sodium chloride solution. Results indicate that under these test conditions Multiphase MP35N, Unitemp L605, Inconel 718, Carpenter 20Cb and 20Cb-3 are highly resistant to stress corrosion cracking. AISI 410 and 431 stainless steels, 18 Ni maraging steel (250 grade) and AISI 4130 steel are susceptible to stress corrosion cracking under some conditions.

  15. Deletion of the BH3-only protein puma protects motoneurons from ER stress-induced apoptosis and delays motoneuron loss in ALS mice

    PubMed Central

    Kieran, Dairín; Woods, Ina; Villunger, Andreas; Strasser, Andreas; Prehn, Jochen H. M.

    2007-01-01

    BH3-only proteins couple diverse stress signals to the evolutionarily conserved mitochondrial apoptosis pathway. Previously, we reported that the activation of the BH3-only protein p53-up-regulated mediator of apoptosis (Puma) was necessary and sufficient for endoplasmic reticulum (ER) stress- and proteasome inhibition-induced apoptosis in neuroblastoma and other cancer cells. Defects in protein quality control have also been suggested to be a key event in ALS, a fatal neurodegenerative condition characterized by motoneuron degeneration. Using the SOD1G93A mouse model as well as human post mortem samples from ALS patients, we show evidence for increased ER stress and defects in protein degradation in motoneurons during disease progression. Before symptom onset, we detected a significant up-regulation of Puma in motoneurons of SOD1G93A mice. Genetic deletion of puma significantly improved motoneuron survival and delayed disease onset and motor dysfunction in SOD1G93A mice. However, it had no significant effect on lifespan, suggesting that other ER stress-related cell-death proteins or other factors, such as excitotoxicity, necrosis, or inflammatory injury, may contribute at later disease stages. Indeed, further experiments using cultured motoneurons revealed that genetic deletion of puma protected motoneurons against ER stress-induced apoptosis but showed no effect against excitotoxic injury. These findings demonstrate that a single BH3-only protein, the ER stress-associated protein Puma, plays an important role during the early stages of chronic neurodegeneration in vivo. PMID:18077368

  16. Degradation of (InAlGa)N-based UV-B light emitting diodes stressed by current and temperature

    SciTech Connect

    Glaab, Johannes Ploch, Christian; Kelz, Rico; Stölmacker, Christoph; Lapeyrade, Mickael; Ploch, Neysha Lobo; Rass, Jens; Kolbe, Tim; Einfeldt, Sven; Weyers, Markus; Mehnke, Frank; Kuhn, Christian; Wernicke, Tim; Kneissl, Michael

    2015-09-07

    The degradation of the electrical and optical properties of (InAlGa)N-based multiple quantum well light emitting diodes (LEDs) emitting near 308 nm under different stress conditions has been studied. LEDs with different emission areas were operated at room temperature and at constant current densities of 75 A/cm{sup 2}, 150 A/cm{sup 2}, and 225 A/cm{sup 2}. In addition, the heat sink temperature was varied between 15 °C and 80 °C. Two main modes for the reduction of the optical power were found, which dominate at different times of operation: (1) Within the first 100 h, a fast drop of the optical power is observed scaling exponentially with the temperature and having an activation energy of about 0.13 eV. The drop in optical power is accompanied by changes of the current-voltage (I-V) characteristic. (2) For operation times beyond 100 h, the optical power decreases slowly which can be reasonably described by a square root time dependence. Here, the degradation rate depends on the current density, rather than the current. Again, the rate of optical power reduction of the second mode depends exponentially on the temperature with an activation energy of about 0.21 eV. The drop in the optical power is accompanied by an increased reverse-bias leakage current.

  17. Degradation of (InAlGa)N-based UV-B light emitting diodes stressed by current and temperature

    NASA Astrophysics Data System (ADS)

    Glaab, Johannes; Ploch, Christian; Kelz, Rico; Stölmacker, Christoph; Lapeyrade, Mickael; Ploch, Neysha Lobo; Rass, Jens; Kolbe, Tim; Einfeldt, Sven; Mehnke, Frank; Kuhn, Christian; Wernicke, Tim; Weyers, Markus; Kneissl, Michael

    2015-09-01

    The degradation of the electrical and optical properties of (InAlGa)N-based multiple quantum well light emitting diodes (LEDs) emitting near 308 nm under different stress conditions has been studied. LEDs with different emission areas were operated at room temperature and at constant current densities of 75 A/cm2, 150 A/cm2, and 225 A/cm2. In addition, the heat sink temperature was varied between 15 °C and 80 °C. Two main modes for the reduction of the optical power were found, which dominate at different times of operation: (1) Within the first 100 h, a fast drop of the optical power is observed scaling exponentially with the temperature and having an activation energy of about 0.13 eV. The drop in optical power is accompanied by changes of the current-voltage (I-V) characteristic. (2) For operation times beyond 100 h, the optical power decreases slowly which can be reasonably described by a square root time dependence. Here, the degradation rate depends on the current density, rather than the current. Again, the rate of optical power reduction of the second mode depends exponentially on the temperature with an activation energy of about 0.21 eV. The drop in the optical power is accompanied by an increased reverse-bias leakage current.

  18. High density Al2O3/TaN-based metal insulator metal capacitors in application to radio frequency integrated circuits

    NASA Astrophysics Data System (ADS)

    Ding, Shi-Jin; Huang, Yu-Jian; Huang, Yue; Pan, Shao-Hui; Zhang, Wei; Wang, Li-Kang

    2007-09-01

    Metal-insulator-metal (MIM) capacitors with atomic-layer-deposited Al2O3 dielectric and reactively sputtered TaN electrodes in application to radio frequency integrated circuits have been characterized electrically. The capacitors exhibit a high density of about 6.05 fF/μm2, a small leakage current of 4.8×10-8 A/cm2 at 3V, a high breakdown electric field of 8.61MV/cm as well as acceptable voltage coefficients of capacitance (VCCs) of 795 ppm/V2 and 268ppm/V at 1 MHz. The observed properties should be attributed to high-quality Al2O3 film and chemically stable TaN electrodes. Further, a logarithmically linear relationship between quadratic VCC and frequency is observed due to the change of relaxation time with carrier mobility in the dielectric. The conduction mechanism in the high field ranges is dominated by the Poole-Frenkel emission, and the leakage current in the low field ranges is likely to be associated with trap-assisted tunnelling. Meanwhile, the Al2O3 dielectric presents charge trapping under low voltage stresses, and defect generation under high voltage stresses, and it has a hard-breakdown performance.

  19. Unraveling the Origin of Structural Disorder in High Temperature Transition Al2O3: Structure of θ-Al2O3

    SciTech Connect

    Kovarik, Libor; Bowden, Mark E.; Shi, Dachuan; Washton, Nancy M.; Anderson, Amity; Hu, Jian Z.; Lee, Jaekyoung; Szanyi, Janos; Kwak, Ja Hun; Peden, Charles HF

    2015-09-22

    The crystallography of transition Al2O3 has been extensively studied in the past due to the advantageous properties of the oxide in catalytic and a range of other technological applications. However, existing crystallographic models are insufficient to describe the structure of many important Al2O3 polymorphs due to their highly disordered nature. In this work, we investigate structure and disorder in high-temperature treated transition Al2O3, and provide a structural description for θ-Al2O3 by using a suite of complementary imaging, spectroscopy and quantum calculation techniques. Contrary to current understanding, our high-resolution imaging shows that θ-Al2O3 is a disordered composite phase of at least two different end members. By correlating imaging and spectroscopy results with DFT calculations, we propose a model that describes θ-Al2O3 as a disordered intergrowth of two crystallographic variants at the unit cell level. One variant is based on β-Ga2O3, and the other on a monoclinic phase that is closely-related to δ-Al2O3. The overall findings and interpretations afford new insight into the origin of poor crystallinity in transition Al2O3, and also provide new perspectives on structural complexity that can emerge from intergrowth of closely related structural polymorphs.

  20. Probing the electronic and vibrational structure of Au2Al2(-) and Au2Al2 using photoelectron spectroscopy and high resolution photoelectron imaging.

    PubMed

    Lopez, Gary V; Czekner, Joseph; Jian, Tian; Li, Wei-Li; Yang, Zheng; Wang, Lai-Sheng

    2014-12-14

    The electronic and vibrational structures of Au2Al2(-) and Au2Al2 have been investigated using photoelectron spectroscopy (PES), high-resolution photoelectron imaging, and theoretical calculations. Photoelectron spectra taken at high photon energies with a magnetic-bottle apparatus reveal numerous detachment transitions and a large energy gap for the neutral Au2Al2. Vibrationally resolved PE spectra are obtained using high-resolution photoelectron imaging for the ground state detachment transition of Au2Al2(-) at various photon energies (670.55-843.03 nm). An accurate electron affinity of 1.4438(8) eV is obtained for the Au2Al2 neutral cluster, as well as two vibrational frequencies at 57 ± 8 and 305 ± 13 cm(-1). Hot bands transitions yield two vibrational frequencies for Au2Al2(-) at 57 ± 10 and 144 ± 12 cm(-1). The obtained vibrational and electronic structure information is compared with density functional calculations, unequivocally confirming that both Au2Al2(-) and Au2Al2 possess C2v tetrahedral structures. PMID:25494751

  1. Probing the electronic and vibrational structure of Au2Al2- and Au2Al2 using photoelectron spectroscopy and high resolution photoelectron imaging

    NASA Astrophysics Data System (ADS)

    Lopez, Gary V.; Czekner, Joseph; Jian, Tian; Li, Wei-Li; Yang, Zheng; Wang, Lai-Sheng

    2014-12-01

    The electronic and vibrational structures of Au2Al2- and Au2Al2 have been investigated using photoelectron spectroscopy (PES), high-resolution photoelectron imaging, and theoretical calculations. Photoelectron spectra taken at high photon energies with a magnetic-bottle apparatus reveal numerous detachment transitions and a large energy gap for the neutral Au2Al2. Vibrationally resolved PE spectra are obtained using high-resolution photoelectron imaging for the ground state detachment transition of Au2Al2- at various photon energies (670.55-843.03 nm). An accurate electron affinity of 1.4438(8) eV is obtained for the Au2Al2 neutral cluster, as well as two vibrational frequencies at 57 ± 8 and 305 ± 13 cm-1. Hot bands transitions yield two vibrational frequencies for Au2Al2- at 57 ± 10 and 144 ± 12 cm-1. The obtained vibrational and electronic structure information is compared with density functional calculations, unequivocally confirming that both Au2Al2- and Au2Al2 possess C2v tetrahedral structures.

  2. Tuneable ultra high specific surface area Mg/Al-CO3 layered double hydroxides.

    PubMed

    Chen, Chunping; Wangriya, Aunchana; Buffet, Jean-Charles; O'Hare, Dermot

    2015-10-01

    We report the synthesis of tuneable ultra high specific surface area Aqueous Miscible Organic solvent-Layered Double Hydroxides (AMO-LDHs). We have investigated the effects of different solvent dispersion volumes, dispersion times and the number of re-dispersion cycles specific surface area of AMO-LDHs. In particular, the effects of acetone dispersion on two different morphology AMO-LDHs (Mg3Al-CO3 AMO-LDH flowers and Mg3Al-CO3 AMO-LDH plates) was investigated. It was found that the amount of acetone used in the dispersion step process can significantly affect the specific surface area of Mg3Al-CO3 AMO-LDH flowers while the dispersion time in acetone is critical factor to obtain high specific surface area Mg3Al-CO3 AMO-LDH plates. Optimisation of the acetone washing steps enables Mg3Al-CO3 AMO-LDH to have high specific surface area up to 365 m(2) g(-1) for LDH flowers and 263 m(2) g(-1) for LDH plates. In addition, spray drying was found to be an effective and practical drying method to increase the specific surface area by a factor of 1.75. Our findings now form the basis of an effective general strategy to obtain ultrahigh specific surface area LDHs. PMID:26308729

  3. Stress generation in Al-Si-Cu metallization resulting from thermal cycling between -196 °C and 250 °C

    NASA Astrophysics Data System (ADS)

    Baldwin, Frank; Holloway, Paul H.; Bordelon, Mark; Watkins, Thomas R.

    1996-06-01

    The effects of thermally cycling Al-Si-Cu VLSI metallization down to -196 °C have been studied in unpatterned and patterned films with and without surface passivation using wafer curvature and x-ray diffraction techniques. Both passivated and unpassivated unpatterned metallization showed development of compressive stresses in the thin film after cooling to -196 °C and warming to 22 °C. This was attributed to plastic deformation at -196 °C leading to a reversal of stress from tensile to compressive upon warming to room temperature. The relaxation of this compressive stress was characterized at room temperature immediately after warming from -196 °C and after cooling from anneals between 50 °C and 250 °C. The stress in patterned (1 to 2 μm line widths) thin films with passivation remained tensile, and this was attributed to a reduction in grain boundary area and inhibition of grain boundary diffusion. Therefore, the tensile stress was maintained even after thermal cycling several times between -196 °C and 22 °C. Higher stress levels were observed on smaller line widths, and lower tensile stresses were observed on metal lines that exhibited stress voids.

  4. Secondary Al-Si-Mg High-pressure Die Casting Alloys with Enhanced Ductility

    NASA Astrophysics Data System (ADS)

    Bösch, Dominik; Pogatscher, Stefan; Hummel, Marc; Fragner, Werner; Uggowitzer, Peter J.; Göken, Mathias; Höppel, Heinz Werner

    2015-03-01

    Al-Si-Mg-based secondary cast alloys are attractive candidates for thin-walled high-pressure die castings for applications in the transport industry. The present study investigates the effect of manganese additions at high cooling rates on microstructure, mechanical properties, and on the dominating fracture mechanisms of alloy AlSi10Mg with an elevated iron concentration. Systematic variations of the Mn content from 0.20 to 0.85 wt pct at a constant Fe content of 0.55 wt pct illustrate the key changes in type, phase fraction, and shape of the Fe-containing intermetallic phases, and the corresponding influence on the alloy's ductility. For high-pressure die casting (HPDC), an optimal range of the Mn content between 0.40 and 0.60 wt pct, equivalent to a Mn/Fe ratio of approximately 1, has been identified. At these Mn and Fe contents, the high cooling rates obtained in HPDC result in the formation of fine and homogeneously distributed α-Al15(Fe,Mn)3Si2 phase, and crack initiation is transferred from AlFeSi intermetallics to eutectic silicon. The study interprets the microstructure-property relationship in the light of thermodynamic calculations which reveal a significant increase in undercooling of the α-Al15(Fe,Mn)3Si2 phase with increased Mn content. It concludes that the interdependence of the well-defined Mn/Fe ratio and the high cooling rate in HPDC can generate superior ductility in secondary AlSi10Mg cast alloys.

  5. High-temperature sulfidation of Fe{sub 3}Al thermal spray coatings at 600 C

    SciTech Connect

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

    2000-02-01

    Sulfidation behavior of Fe{sub 3}Al thermal spray coatings was studied in Ar-3.5% H{sub 2}-0.1{degree} hydrogen sulfide (H{sub 2}S) at 600 C for 500 h. Coatings were processed from the same lot of gas atomized Fe{sub 3}Al powder using a high-velocity oxygen fuel (HVOF) process and an air plasma spray (APS) process. In general, the Fe{sub 3}Al-type composition displayed excellent resistance to sulfidation corrosion at 600 C, which correlated with the reported literature on wrought Fe{sub 3}Al alloys. However, the method of processing affected the corrosion response. Particle degradation and porosity were two important factors that affected corrosion resistance. HVOF processing did not degrade significantly the composition of the powder and produced coatings with low porosity, low oxide content, high sulfidation resistance, and high resistance to sulfur penetration. HVOF coatings produced from finer sized powders exhibited slightly more corrosion damage because a greater percentage of the consumable was degraded. In contrast, APS processing caused significant degradation to the consumable and created coatings with a significant quantity of alloy-depleted regions, high oxide content, and high porosity. As a result, sulfur attached alloy-depleted regions within the splats and permeated through the porous splat boundaries to the coating-substrate interface.

  6. Influence of high-temperature processing on the surface properties of bulk AlN substrates

    NASA Astrophysics Data System (ADS)

    Tojo, Shunsuke; Yamamoto, Reo; Tanaka, Ryohei; Thieu, Quang Tu; Togashi, Rie; Nagashima, Toru; Kinoshita, Toru; Dalmau, Rafael; Schlesser, Raoul; Murakami, Hisashi; Collazo, Ramón; Koukitu, Akinori; Monemar, Bo; Sitar, Zlatko; Kumagai, Yoshinao

    2016-07-01

    Deep-level luminescence at 3.3 eV related to the presence of Al vacancies (VAl) was observed in room temperature photoluminescence (RT-PL) spectra of homoepitaxial AlN layers grown at 1450 °C by hydride vapor-phase epitaxy (HVPE) and cooled to RT in a mixture of H2 and N2 with added NH3. However, this luminescence disappeared after removing the near surface layer of AlN by polishing. In addition, the deep-level luminescence was not observed when the post-growth cooling of AlN was conducted without NH3. Secondary ion mass spectrometry (SIMS) studies revealed that although the point defect density of the interior of the AlN layers remained low, the near surface layer cooled in the presence of NH3 was contaminated by Si impurities due to both suppression of the surface decomposition by the added NH3 and volatilization of Si by decomposition of the quartz reactor walls at high temperatures. The deep-level luminescence reappeared after the polished AlN wafers were heated in presence of NH3 at temperatures above 1400 °C. The surface contamination by Si is thought to generate VAl near the surface by lowering their formation energy due to the Fermi level effect, resulting in deep-level luminescence at 3.3 eV caused by the shallow donor (Si) to VAl transition.

  7. Improved wear resistance of Al-15Si alloy with a high current pulsed electron beam treatment

    NASA Astrophysics Data System (ADS)

    Hao, Y.; Gao, B.; Tu, G. F.; Li, S. W.; Dong, C.; Zhang, Z. G.

    2011-07-01

    A hypereutectic Al-15Si alloy (Si 15 wt.%, Al balance) was irradiated by high current pulsed electron beam (HCPEB). The HCPEB treatment causes ultra-rapid heating, melting and cooling at the top surface layer. As a result, the special "halo" microstructure centering on the primary Si phase is formed on the surface due to interdiffusion of Al and Si elements. The composition of the "halo" microstructure is distributed continuously from the center to the edge of the "halo". Compared to an untreated matrix, the remelted layer underneath the surface presents single contrast because of the compositional homogeneity after HCPEB treatment. The thickness of the remelted layer increases slightly from 4.4 μm (5 pulses) to 5.6 μm (25 pulses). HCPEB treatment broadens and shifts the diffraction peaks of Al and Si. The lattice parameters of Al decreases due to the formation of a supersaturated solid solution of Al in the melted layer. Through analysis of Raman spectra and transmission electron microscopy (TEM), the amorphous Si (a-Si) and nanocrystalline Si are formed in the near-surface region under multiple bombardments of HCPEB. The relative wear resistance of a 15-pulse sample is effectively improved by a factor of 9, which can be attributed to the formation of metastable structures.

  8. Characteristics of inclusions in high-Al steel during electroslag remelting process

    NASA Astrophysics Data System (ADS)

    Shi, Cheng-bin; Chen, Xi-chun; Guo, Han-jie

    2012-04-01

    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 μm. Inclusions smaller than 3 μm 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 μm 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 μm but little effects on that of inclusions larger than 2 μm. 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.

  9. Amorphous and nanocrystalline phase formation in highly-driven Al-based binary alloys

    SciTech Connect

    Kalay, Yunus Eren

    2009-01-01

    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 T0 curves, which makes Al-Si a good candidate for solubility extension while the plunging T0 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 ~0.2, JH and TMK deviate from

  10. Solution-processed Al-chelated gelatin for highly transparent non-volatile memory applications

    SciTech Connect

    Chang, Yu-Chi; Wang, Yeong-Her

    2015-03-23

    Using the biomaterial of Al-chelated gelatin (ACG) prepared by sol-gel method in the ITO/ACG/ITO structure, a highly transparent resistive random access memory (RRAM) was obtained. The transmittance of the fabricated device is approximately 83% at 550 nm while that of Al/gelatin/ITO is opaque. As to the ITO/gelatin/ITO RRAM, no resistive switching behavior can be seen. The ITO/ACG/ITO RRAM shows high ON/OFF current ratio (>10{sup 5}), low operation voltage, good uniformity, and retention characteristics at room temperature and 85 °C. The mechanism of the ACG-based memory devices is presented. The enhancement of these electrical properties can be attributed to the chelate effect of Al ions with gelatin. Results show that transparent ACG-based memory devices possess the potential for next-generation resistive memories and bio-electronic applications.

  11. Advances in processing of NiAl intermetallic alloys and composites for high temperature aerospace applications

    NASA Astrophysics Data System (ADS)

    Bochenek, Kamil; Basista, Michal

    2015-11-01

    Over the last few decades intermetallic compounds such as NiAl have been considered as potential high temperature structural materials for aerospace industry. A large number of investigations have been reported describing complex fabrication routes, introducing various reinforcing/alloying elements along with theoretical analyses. These research works were mainly focused on the overcoming of main disadvantage of nickel aluminides that still restricts their application range, i.e. brittleness at room temperature. In this paper we present an overview of research on NiAl processing and indicate methods that are promising in solving the low fracture toughness issue at room temperature. Other material properties relevant for high temperature applications are also addressed. The analysis is primarily done from the perspective of NiAl application in aero engines in temperature regimes from room up to the operating temperature (over 1150 °C) of turbine blades.

  12. Operating limits of AL-alloyed high-low junctions for BSF solar cells

    NASA Astrophysics Data System (ADS)

    del Alamo, J.; Eguren, J.; Luque, A.

    1981-05-01

    Experimental estimations of the effective surface recombination velocity of the high-low junction and of the base diffusion length are carried out for Al-alloyed n(plus)pp(plus) bifacial cells and the results are presented in form of histograms. These results agree with calculated values of the effective surface recombination velocity when the characteristics of the recrystallized Si layer and heavy doping effects are taken into account. It is concluded that thick Al layers and high alloying temperatures (over 800 C) are necessary to obtain low values of the velocity. This conclusion agrees with experimental results of other authors. Recommendations to avoid diffusion length degradation are given and the operating limits of the Al alloying technology are discussed.

  13. Rhombohedral AlPt films formed by self-propagating, high temperature synthesis.

    SciTech Connect

    Adams, David Price; Rodriguez, Mark Andrew; Kotula, Paul Gabriel

    2005-11-01

    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.

  14. Job Satisfaction, Stress and Coping Strategies among Moroccan High School Teachers.

    ERIC Educational Resources Information Center

    Benmansour, Naima

    1998-01-01

    Studied job stress, job satisfaction, and coping strategies through self-report measures from 153 Moroccan high school teachers. Results show that 45% of the teachers were satisfied with their jobs, but over half reported high levels of stress, negatively correlated with job satisfaction. Factor analysis of 16 coping strategies produced four…

  15. A Study Concerning Stress among High School Students in Selected Rural Schools.

    ERIC Educational Resources Information Center

    Peach, Larry

    This study identifies stressful events in the lives of high school students in a rural region of Tennessee. Questionnaires were completed by 240 high school students (144 female and 96 male). The questionnaires included 19 statements to which the participants were to respond concerning their belief about the stressfulness of the situation…

  16. Parenting Stress and Parent Support Among Mothers With High and Low Education

    PubMed Central

    2015-01-01

    Current theorizing and evidence suggest that parenting stress might be greater among parents from both low and high socioeconomic positions (SEP) compared with those from intermediate levels because of material hardship among parents of low SEP and employment demands among parents of high SEP. However, little is known about how this socioeconomic variation in stress relates to the support that parents receive. This study explored whether variation in maternal parenting stress in a population sample was associated with support deficits. To obtain a clearer understanding of support deficits among mothers of high and low education, we distinguished subgroups according to mothers’ migrant and single-parent status. Participants were 5,865 mothers from the Growing Up in Scotland Study, who were interviewed when their children were 10 months old. Parenting stress was greater among mothers with either high or low education than among mothers with intermediate education, although it was highest for those with low education. Support deficits accounted for around 50% of higher stress among high- and low-educated groups. Less frequent grandparent contact mediated parenting stress among both high- and low-educated mothers, particularly migrants. Aside from this common feature, different aspects of support were relevant for high- compared with low-educated mothers. For high-educated mothers, reliance on formal childcare and less frequent support from friends mediated higher stress. Among low-educated mothers, smaller grandparent and friend networks and barriers to professional parent support mediated higher stress. Implications of differing support deficits are discussed. PMID:26192130

  17. Parenting stress and parent support among mothers with high and low education.

    PubMed

    Parkes, Alison; Sweeting, Helen; Wight, Daniel

    2015-12-01

    Current theorizing and evidence suggest that parenting stress might be greater among parents from both low and high socioeconomic positions (SEP) compared with those from intermediate levels because of material hardship among parents of low SEP and employment demands among parents of high SEP. However, little is known about how this socioeconomic variation in stress relates to the support that parents receive. This study explored whether variation in maternal parenting stress in a population sample was associated with support deficits. To obtain a clearer understanding of support deficits among mothers of high and low education, we distinguished subgroups according to mothers' migrant and single-parent status. Participants were 5,865 mothers from the Growing Up in Scotland Study, who were interviewed when their children were 10 months old. Parenting stress was greater among mothers with either high or low education than among mothers with intermediate education, although it was highest for those with low education. Support deficits accounted for around 50% of higher stress among high- and low-educated groups. Less frequent grandparent contact mediated parenting stress among both high- and low-educated mothers, particularly migrants. Aside from this common feature, different aspects of support were relevant for high- compared with low-educated mothers. For high-educated mothers, reliance on formal childcare and less frequent support from friends mediated higher stress. Among low-educated mothers, smaller grandparent and friend networks and barriers to professional parent support mediated higher stress. Implications of differing support deficits are discussed. PMID:26192130

  18. Ky-2, a Histone Deacetylase Inhibitor, Enhances High-Salinity Stress Tolerance in Arabidopsis thaliana.

    PubMed

    Sako, Kaori; Kim, Jong-Myong; Matsui, Akihiro; Nakamura, Kotaro; Tanaka, Maho; Kobayashi, Makoto; Saito, Kazuki; Nishino, Norikazu; Kusano, Miyako; Taji, Teruaki; Yoshida, Minoru; Seki, Motoaki

    2016-04-01

    Adaptation to environmental stress requires genome-wide changes in gene expression. Histone modifications are involved in gene regulation, but the role of histone modifications under environmental stress is not well understood. To reveal the relationship between histone modification and environmental stress, we assessed the effects of inhibitors of histone modification enzymes during salinity stress. Treatment with Ky-2, a histone deacetylase inhibitor, enhanced high-salinity stress tolerance in Arabidopsis. We confirmed that Ky-2 possessed inhibition activity towards histone deacetylases by immunoblot analysis. To investigate how Ky-2 improved salt stress tolerance, we performed transcriptome and metabolome analysis. These data showed that the expression of salt-responsive genes and salt stress-related metabolites were increased by Ky-2 treatment under salinity stress. A mutant deficient inAtSOS1(Arabidopis thaliana SALT OVERLY SENSITIVE 1), which encodes an Na(+)/H(+)antiporter and was among the up-regulated genes, lost the salinity stress tolerance conferred by Ky-2. We confirmed that acetylation of histone H4 atAtSOS1was increased by Ky-2 treatment. Moreover, Ky-2 treatment decreased the intracellular Na(+)accumulation under salinity stress, suggesting that enhancement of SOS1-dependent Na(+)efflux contributes to increased high-salinity stress tolerance caused by Ky-2 treatment. PMID:26657894

  19. Ulnar Shaft Stress Fracture in a High School Softball Pitcher

    PubMed Central

    Bigosinski, Krystian; Palmer, Trish; Weber, Kathleen; Evola, Jennifer

    2010-01-01

    This article presents a case of a 17-year-old softball pitcher with insidious onset of right forearm pain. On presentation, the patient had tenderness on palpation of the midshaft of the ulna, pain with resisted pronation, and pain with fulcrum-type stressing of the forearm. A bone scan revealed increased uptake in the right ulna, and a subsequent magnetic resonance imaging revealed bone marrow edema and numerous small ulnar stress fractures. She was treated with bone stimulation and complete rest and is in the process of returning to pitching. PMID:23015929

  20. Stress corrosion in high-strength aluminum alloys

    NASA Technical Reports Server (NTRS)

    Dorward, R. C.; Hasse, K. R.

    1980-01-01

    Report describes results of stress-corrosion tests on aluminum alloys 7075, 7475, 7050, and 7049. Tests compare performance of original stress-corrosion-resistant (SCR) aluminum, 7075, with newer, higher-strength SCR alloys. Alloys 7050 and 7049 are found superior in short-transverse cross-corrosion resistance to older 7075 alloy; all alloys are subject to self-loading effect caused by wedging of corrosion products in cracks. Effect causes cracks to continue to grow, even at very-low externally applied loads.

  1. Acceleration of degradation by highly accelerated stress test and air-included highly accelerated stress test in crystalline silicon photovoltaic modules

    NASA Astrophysics Data System (ADS)

    Suzuki, Soh; Tanahashi, Tadanori; Doi, Takuya; Masuda, Atsushi

    2016-02-01

    We examined the effects of hyper-hygrothermal stresses with or without air on the degradation of crystalline silicon (c-Si) photovoltaic (PV) modules, to shorten the required duration of a conventional hygrothermal-stress test [i.e., the “damp heat (DH) stress test”, which is conducted at 85 °C/85% relative humidity for 1,000 h]. Interestingly, the encapsulant within a PV module becomes discolored under the air-included hygrothermal conditions achieved using DH stress test equipment and an air-included highly accelerated stress test (air-HAST) apparatus, but not under the air-excluded hygrothermal conditions realized using a highly accelerated stress test (HAST) machine. In contrast, the reduction in the output power of the PV module is accelerated irrespective of air inclusion in hyper-hygrothermal test atmosphere. From these findings, we conclude that the required duration of the DH stress test will at least be significantly shortened using air-HAST, but not HAST.

  2. Families OverComing under Stress (FOCUS) for Early Childhood: Building Resilience for Young Children in High Stress Families

    ERIC Educational Resources Information Center

    Mogil, Catherine; Paley, Blair; Doud, Tricia; Havens, Linda; Moore-Tyson, Jessica; Beardslee, William R.; Lester, Patricia

    2010-01-01

    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…

  3. Effect of Diffusion Control Layer on Reverse Al-Induced Layer Exchange Process for High-Quality Ge/Al/Glass Structure

    NASA Astrophysics Data System (ADS)

    Nakazawa, K.; Toko, K.; Suemasu, T.

    2015-05-01

    Fabricating large-grained polycrystalline Ge (poly-Ge) thin films on conducting-layer coated glass is a promising approach to lower the manufacturing cost of high-efficiency III-V tandem solar cells. We investigated the self-organizing formation of poly-Ge/Al/glass structures by using Al-induced layer exchange. The layer exchange between amorphous Ge and Al layers was completed at a low temperature of 350°C. Forming the interlayer between Ge and Al, i.e., limiting the diffusion of Ge to Al lowered the Ge nucleation rate and then enlarged the grain size of the resulting poly-Ge layer. The natively oxidized Al interlayer, formed by exposing a thin Al membrane (2-nm thickness) to air for 180 min, led to the poly-Ge with grains 46 μm in size. Moreover, the Ge layer was highly (111)-oriented. This Ge/Al/glass structure appears promising for use in the bottom cell of the III-V semiconductor based tandem solar cells, as well as in the epitaxial templates for aligned nanowires and other advanced materials.

  4. Thermal vacancy formation and positron-vacancy interaction in Ti3Al at high temperatures

    NASA Astrophysics Data System (ADS)

    Würschum, R.; Kümmerle, E. A.; Badura-Gergen, K.; Seeger, A.; Herzig, Ch.; Schaefer, H.-E.

    1996-07-01

    In order to study the formation of thermal vacancies in the Ti-Al alloy system, high-temperature positron lifetime measurements together with a modeling of defect formation in the framework of nearest-neighbor pair bonds were performed for α2Ti3Al and compared to recent results on γTiAl [U. Brossmann, R. Würschum, K. Badura, and H.-E. Schaefer, Phys. Rev. B 49, 6457 (1994)]. Substantial increases of the positron lifetime τ were observed for Ti65.6Al34.4 and Ti77.1Al22.9 in the temperature range T≳1200 K where thermal vacancy concentrations above the detection limit of positron annihilation are expected from the model calculations for the α2 phase. Within the high-temperature increase of the positron lifetime in the α2 and the β phase single-component positron lifetime spectra were observed. This behavior is in contrast to the two-component spectra observed conventionally at intermediate positron trapping rates and is attributed to a fast detrapping and retrapping of positrons at vacancies due to a low positron-vacancy binding energy. For this case, a vacancy formation enthalpy of HFV=(1.55±0.2) eV in α2Ti65.6Al34.4 and HFV=(1.8±0.2) eV in βTi77.1Al22.9 can be derived. These results are discussed in the context of recent 44Ti tracer diffusion studies.

  5. High temperature properties of equiatomic FeAl with ternary additions

    NASA Technical Reports Server (NTRS)

    Titran, R. H.; Vedula, K. M.; Anderson, G. G.

    1984-01-01

    The aluminide intermetallic compounds are considered potential structural materials for aerospace applications. The B2 binary aluminide FeAl has a melting point in excess of 1500 K, is of simple cubic structure, exits over a wide range of composition with solubility for third elements and is potentially self-protecting in extreme environments. The B2 FeAl compound has been alloyed with 1 to 5 at % ternary additions of Si, Ti, Zr, Hf, Cr, Ni, Co, Nb, Ta, Mo, W, and Re. The alloys were prepared by blending a third elemental powder with prealloyed binary FeAl powder. Consolidation was by hot extrusion at 1250 K. Annealing studies on the extruded rods showed that the third element addition can be classified into three categories based upon the amount of homogenization and the extent of solid solutioning. Constant strain rate compression tests were performed to determine the flow stress as a function of temperature and composition. The mechanical strength behavior was dependent upon the third element homogenization classification.

  6. High temperature properties of equiatomic FeAl with ternary additions

    NASA Technical Reports Server (NTRS)

    Titran, R. H.; Vedula, K. M.; Anderson, G. G.

    1985-01-01

    The aluminide intermetallic compounds are considered potential structural materials for aerospace applications. The B2 binary aluminide FeAl has a melting point in excess of 1500 K, is of simple cubic structure, exists over a wide range of composition with solubility for third elements and is potentially self-protecting in extreme environments. The B2 FeAl compound has been alloyed with 1 to 5 at. pct ternary additions of Si, Ti, Zr, Hf, Cr, Ni, Co, Nb, Ta, Mo, W, and Re. The alloys were prepared by blending a third elemental powder with pre-alloyed binary FeAl powder. Consolidation was by hot extrusion at 1250 K. Annealing studies on the extruded rods showed that the third element addition can be classified into three categories based upon the amount of homogenization and the extent of solid solutioning. Constant strain rate compression tests were performed to determine the flow stress as a function of temperature and composition. The mechanical strength behavior was dependent upon the third element homogenization classification.

  7. High-Temperature Thermometer Using Cr-Doped GdAlO3 Broadband Luminescence

    NASA Technical Reports Server (NTRS)

    Eldridge, Jeffrey; Chambers, Matthew

    2011-01-01

    A new concept has been developed for a high-temperature luminescence-based optical thermometer that both shows the desired temperature sensitivity in the upper temperature range of present state-of-the-art luminescence thermometers (above 1,300 C), while maintaining substantial stronger luminescence signal intensity that will allow these optical thermometers to operate in the presence of the high thermal background radiation typical of industrial applications. This objective is attained by using a Cr-doped GdAlO3 (Cr:GdAlO3) sensor with an orthorhombic perovskite structure, resulting in broadband luminescence that remains strong at high temperature due to the favorable electron energy level spacing of Cr:GdAlO3. The Cr:GdAlO3 temperature (and pressure) sensor can be incorporated into, or applied onto, a component s surface when a non-contact surface temperature measurement is desired, or alternatively, the temperature sensor can be attached to the end of a fiber-optic probe that can then be positioned at the location where the temperature measurement is desired. In the case of the fiber-optic probe, both the pulsed excitation and the luminescence emission travel through the fiber-optic light guide. In either case, a pulsed light source provides excitation of the luminescence, and the broadband luminescence emission is collected. Real-time temperature measurements are obtain ed using a least-squares fitting algorithm that determines the luminescence decay time, which has a known temperature dependence established by calibration. Due to the broad absorption and emission bands for Cr:GdAlO3, there is considerable flexibility in the choice of excitation wavelength and emission wavelength detection bands. The strategic choice of the GdAlO3 host is based on its high crystal field, phase stability, and distorted symmetry at the Cr3+ occupation sites. The use of the broadband emission for temperature sensing at high temperatures is a key feature of the invention and is

  8. Fabrication of Highly-Oleophobic and Superhydrophobic Surfaces on Microtextured al Substrates

    NASA Astrophysics Data System (ADS)

    Liu, Changsong; Zhou, Jigen; Zheng, Dongmei; Wan, Yong; Li, Zhiwen

    2011-06-01

    Theoretical calculations suggest that creating highly-oleophobic surfaces would require a surface energy lower than that of any known materials. In the present work, we demonstrate microtextured Al substrate surfaces with veins-like micro/nanostructures displaying apparent contact angles (CA) greater than 120°, even with nitromethane (surface tension γ1 = 37 mN/m). The Al substrate was microtextured by a chemical solution mixed by zinc nitrate hexahydrate, hexamethyltetramine and a little of hydrofluoric acid. A fluoroalkylsilane (FAS) agent was used to tune the surface wettability. The Al substrates were microtextured by veins-like micro/nanostructures and generating a solid-liquid-vapor composite interface. Combination with FAS modification, the Al surfaces resulted in an oleophobicity with CA for nitromethane was 126.3° (152.7° for diethylene glycol, γ1 = 45.2 mN/m). In addition, the Al surfaces demonstrated a low rolling-off angle with < 6° even for diethylene glycol. However, nitromethane droplet favored to pin on the sample surface even the sample stage is tilted to 90°. It is noted that this highly-oleophobic behavior is induced mainly by topography, which form a composite surface of air and solid with oil drop sitting partially on air. The results are expected to promote the study on self-cleaning applications, especially in the condition with oil contaminations.

  9. Improved Stress Corrosion Cracking Resistance and Strength of a Two-Step Aged Al-Zn-Mg-Cu Alloy Using Taguchi Method

    NASA Astrophysics Data System (ADS)

    Lin, Lianghua; Liu, Zhiyi; Ying, Puyou; Liu, Meng

    2015-12-01

    Multi-step heat treatment effectively enhances the stress corrosion cracking (SCC) resistance but usually degrades the mechanical properties of Al-Zn-Mg-Cu alloys. With the aim to enhance SCC resistance as well as strength of Al-Zn-Mg-Cu alloys, we have optimized the process parameters during two-step aging of Al-6.1Zn-2.8Mg-1.9Cu alloy by Taguchi's L9 orthogonal array. In this work, analysis of variance (ANOVA) was performed to find out the significant heat treatment parameters. The slow strain rate testing combined with scanning electron microscope and transmission electron microscope was employed to study the SCC behaviors of Al-Zn-Mg-Cu alloy. Results showed that the contour map produced by ANOVA offered a reliable reference for selection of optimum heat treatment parameters. By using this method, a desired combination of mechanical performances and SCC resistance was obtained.

  10. Hydrogen role in stress corrosion cracking process of iron aluminide Fe{sub 3}Al in NaCl solution

    SciTech Connect

    Chiu, H.; Qiao, L.; Mao, X.

    1995-09-01

    The stress corrosion cracking behavior of Fe3AI based intermetallic alloy in 3.5% NaCl solution was studied. The role of hydrogen in the cracking process was also defined. The susceptibility of the alloy to hydrogen embrittlement was first investigated by performing tensile tests in air environment and mineral oil. It was found that ductility increased with increasing strain rate when tested in air, but stayed at a high value when tested in mineral oil. This behavior indicates that the alloy is sensitive to hydrogen embrittlement in air. In 3.5% NaCl solution, the environmental effect was studied by slow strain rate tests that were done at electrochemical potentials ranging from {minus}1,000 mV to 0 mV vs SCE. When tested at anodic potentials, from {minus}500 mV to 0 mV vs SCE, ductility reduced from 8.7% to 3.9%. When tested in cathodic region, from {minus}500 mV to {minus}1,000 mV, the ductility was between 7.3% to 9.1%. Results of tests done on pre-immersed specimens and notched tensile specimens confirmed this material degradation to be caused by stress corrosion cracking (SCC). To identify the mechanism, an electrochemical permeation technique was employed. By measuring the diffusible hydrogen concentration, sensitivity to hydrogen embrittlement has been assessed at different potentials. Anodic dissolution is believed to be the controlling mechanism of the SCC as the alloy is less sensitive to hydrogen embrittlement at anodic potentials. Fracture surfaces were examined under the scanning electron microscope (SEM). Fracture mode was found to be mainly transgranular quasi-cleavage, except the ones tested at anodic potentials on which intergranular fracture area was found near the edge. This intergranular fracture, which increases with increasing anodic potential, is believed to be the stress corrosion cracking area. Pits which corroded intergranularly are the crack initiation sites.

  11. Fundamental studies of stress distributions and stress relaxation in oxide scales on high temperature alloys. [Final progress report

    SciTech Connect

    Shores, D.A.; Stout, J.H.; Gerberich, W.W.

    1993-06-01

    This report summarizes a three-year study of stresses arising in the oxide scale and underlying metal during high temperature oxidation and of scale cracking. In-situ XRD was developed to measure strains during oxidation over 1000{degrees}C on pure metals. Acoustic emission was used to observe scale fracture during isothermal oxidation and cooling, and statistical analysis was used to infer mechanical aspects of cracking. A microscratch technique was used to measure the fracture toughness of scale/metal interface. A theoretical model was evaluated for the development and relaxation of stresses in scale and metal substrate during oxidation.

  12. Teachers Stress in Public High Schools in Kuwait

    ERIC Educational Resources Information Center

    Tayeh, Raja

    2013-01-01

    The purpose of this study was to identify the factors that may influence stress levels of secondary teachers in Kuwait. This study was important for two reasons; first, no previous investigation on this topic among Kuwaiti secondary educators had taken place, and second, the findings of this study could serve to develop and implement secondary…

  13. Conducting High Cycle Fatigue Strength Step Tests on Gamma TiAl

    NASA Technical Reports Server (NTRS)

    Lerch, Brad; Draper, Sue; Pereira, J. Mike

    2002-01-01

    High cycle fatigue strength testing of gamma TiAl by the step test method is investigated. A design of experiments was implemented to determine if the coaxing effect occurred during testing. Since coaxing was not observed, step testing was deemed a suitable method to define the fatigue strength at 106 cycles.

  14. WC-Co and Cr3C2-NiCr Coatings in Low- and High-Stress Abrasive Conditions

    NASA Astrophysics Data System (ADS)

    Kašparová, Michaela; Zahálka, František; Houdková, Šárka

    2011-03-01

    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.

  15. Feasibility study of Nb3Al Rutherford cable for high field accelerator magnet application

    SciTech Connect

    Yamada, R.; Kikuchi, A.; Ambrosio, G.; Andreev, N.; Barzi, E.; Cooper, C.; Feher, S.; Kashikhin, V.V.; Lamm, M.; Novitski, I.; Takeuchi, T.; Tartaglia, M.; Turrioni, D.; Verweij, A.P.; Wake, M.; Willering, G; Zlobin, A.V.; /Fermilab

    2006-08-01

    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.

  16. Acute stress differentially affects spatial configuration learning in high and low cortisol-responding healthy adults

    PubMed Central

    Meyer, Thomas; Smeets, Tom; Giesbrecht, Timo; Quaedflieg, Conny W. E. M.; Merckelbach, Harald

    2013-01-01

    Background Stress and stress hormones modulate memory formation in various ways that are relevant to our understanding of stress-related psychopathology, such as posttraumatic stress disorder (PTSD). Particular relevance is attributed to efficient memory formation sustained by the hippocampus and parahippocampus. This process is thought to reduce the occurrence of intrusions and flashbacks following trauma, but may be negatively affected by acute stress. Moreover, recent evidence suggests that the efficiency of visuo-spatial processing and learning based on the hippocampal area is related to PTSD symptoms. Objective The current study investigated the effect of acute stress on spatial configuration learning using a spatial contextual cueing task (SCCT) known to heavily rely on structures in the parahippocampus. Method Acute stress was induced by subjecting participants (N = 34) to the Maastricht Acute Stress Test (MAST). Following a counterbalanced within-subject approach, the effects of stress and the ensuing hormonal (i.e., cortisol) activity on subsequent SCCT performance were compared to SCCT performance following a no-stress control condition. Results Acute stress did not impact SCCT learning overall, but opposing effects emerged for high versus low cortisol responders to the MAST. Learning scores following stress were reduced in low cortisol responders, while high cortisol-responding participants showed improved learning. Conclusions The effects of stress on spatial configuration learning were moderated by the magnitude of endogenous cortisol secretion. These findings suggest a possible mechanism by which cortisol responses serve an adaptive function during stress and trauma, and this may prove to be a promising route for future research in this area. PMID:23671762

  17. Self-stressing test structures used for high-frequency electromigration

    SciTech Connect

    Snyder, E.S.; Pierce, D.G.; Campbell, D.V.; Swanson, S.E.

    1994-02-01

    We demonstrate for the first time high frequency (500 mhz) electromigration at the wafer-level using on-chip, self-stressing test structures. Since the stress temperature, frequency, duty cycle and current are controlled by DC signals in these structures, we used conventional DC test equipment without any special modifications (such as high frequency cabling, high temperature probe cards, etc.). This structure significantly reduces the cost of performing realistic high frequency electromigration experiments.

  18. Achieving reversibility of ultra-high mechanical stress by hydrogen loading of thin films

    NASA Astrophysics Data System (ADS)

    Hamm, M.; Burlaka, V.; Wagner, S.; Pundt, A.

    2015-06-01

    Nano-materials are commonly stabilized by supports to maintain their desired shape and size. When these nano-materials take up interstitial atoms, this attachment to the support induces mechanical stresses. These stresses can be high when the support is rigid. High stress in the nano-material is typically released by delamination from the support or by the generation of defects, e.g., dislocations. As high mechanical stress can be beneficial for tuning the nano-materials properties, it is of general interest to deduce how real high mechanical stress can be gained. Here, we show that below a threshold nano-material size, dislocation formation can be completely suppressed and, when delamination is inhibited, even the ultrahigh stress values of the linear elastic limit can be reached. Specifically, for hydrogen solved in epitaxial niobium films on sapphire substrate supports a threshold film thickness of 6 nm was found and mechanical stress of up to (-10 ± 1) GPa was reached. This finding is of basic interest for hydrogen energy applications, as the hydride stability in metals itself is affected by mechanical stress. Thus, tuning of the mechanical stress-state in nano-materials may lead to improved storage properties of nano-sized materials.

  19. Achieving reversibility of ultra-high mechanical stress by hydrogen loading of thin films

    SciTech Connect

    Hamm, M.; Burlaka, V.; Wagner, S.; Pundt, A.

    2015-06-15

    Nano-materials are commonly stabilized by supports to maintain their desired shape and size. When these nano-materials take up interstitial atoms, this attachment to the support induces mechanical stresses. These stresses can be high when the support is rigid. High stress in the nano-material is typically released by delamination from the support or by the generation of defects, e.g., dislocations. As high mechanical stress can be beneficial for tuning the nano-materials properties, it is of general interest to deduce how real high mechanical stress can be gained. Here, we show that below a threshold nano-material size, dislocation formation can be completely suppressed and, when delamination is inhibited, even the ultrahigh stress values of the linear elastic limit can be reached. Specifically, for hydrogen solved in epitaxial niobium films on sapphire substrate supports a threshold film thickness of 6 nm was found and mechanical stress of up to (−10 ± 1) GPa was reached. This finding is of basic interest for hydrogen energy applications, as the hydride stability in metals itself is affected by mechanical stress. Thus, tuning of the mechanical stress-state in nano-materials may lead to improved storage properties of nano-sized materials.

  20. The impact of high and low stress on the health of Lebanese families.

    PubMed

    Farhood, Laila F

    2004-01-01

    During the Lebanese war (1975-1991) families were subjected to a substantial number of war and nonwar life events that were shown to have a negative impact on family adaptation. The study was undertaken to classify and predict family adaptation outcomes in high and low perceived stress groups for war and nonwar life events. The study took the form of an analysis of cross-sectional data of families in Beirut. The cluster sample consisted of 438 families chosen at random. Variables included perceived stress for war and nonwar events, and health and interactional indicators of the outcome family adaptation assessed in terms of physical and psychological health, depression, and interpersonal and marital relationships. Families were classified into high/low stress based on their score for war and non-war life events. Based on discriminant function analysis, a significant difference existed between the high- and low-stress groups (for war, nonwar, and a combination of the two) on all predictor variables. Interpersonal relationships, physical health, and depression were the best predictors of membership in the high/low war stress groups. In the perceived nonwar stress groups, depression, interpersonal relationships, marital relations, and physical and psychological health were the best predictors separating high/low stress groups. When the combination score of war and nonwar stress was used, interpersonal relationships, physical health, depression, and marital relations were the best predictors distinguishing among the groups. Findings indicated a high degree of consistency in the prediction and classification of the high/low stress groups and for all stress categories. Families in the low-stress groups had a more positive adaptation than those in the high-stress groups and could be classified on the basis of their stress score. Families in the high-stress groups had more complaints than their counterparts in the low-stress groups. This classification may help mental

  1. High frequency elastic losses in LaAlO3 and its importance for LaAlO3/SrTiO3 heterojunctions

    NASA Astrophysics Data System (ADS)

    Salje, Ekhard K. H.; Carpenter, Michael A.

    2011-08-01

    Cooling heterojunctions on LaAlO3 substrates or thick layers of LaAlO3 on SrTiO3 substrates below 820 K lead to a ferroelastic phase transition Pm3-m→ R3-c in LaAlO3, with extensive twinning and elastic softening. Twin boundaries add to structural disorder near the heterojunction and generate partially localized carriers. Resonant Ultrasound Spectroscopy data relating to the elastic instability in LaAlO3 show that elastic Cole-Cole circles and the background autocorrelation function follow Vogel-Fulcher behaviour, with a Vogel-Fulcher temperature of 230 K. An extremely low activation energy, 0.02 eV, would promote the formation of highly structured, "glassy" LaAlO3 near the junction.

  2. Process for preparing high-transition-temperature superconductors in the Nb-Al-Ge system

    DOEpatents

    Giorgi, A.L.; Szklarz, E.G.

    1973-01-30

    The patent describes a process for preparing superconducting materials in the Nb-Al-Ge system having transition temperatures in excess of 19K. The process comprises premixing powdered constituents, pressing them into a plug, heating the plug to 1,450-1,800C for 30 minutes to an hour under vacuum or an inert atmosphere, and annealing at moderate temperatures for reasonably long times (approximately 50 hours). High transition-temperature superconductors, including those in the Nb3(Al,Ge) system, prepared in accordance with this process exhibit little degradation in the superconducting transition temperature on being ground to -200 mesh powder. (GRA)

  3. Very High Efficiency Triple Junction Solar Cells Based On (AL)InGaP Compounds

    NASA Astrophysics Data System (ADS)

    Gori, Gabriele; Campesato, Roberta; Casale, Maria Cristina; Gabetta, Giuseppe

    2011-10-01

    In this paper we report the theoretical and experimental results related to the use of Aluminium Gallium Indium Phosphide (AlInGaP) as substitute of Gallium Indium Phosphide (InGaP) semiconductor, in the realization of high efficiency triple junction solar cells for space applications. The (Al)InGaP/GaAs/Ge solar cells have been modelled and manufactured on standard and thin Germanium wafers; the measurements under AM0 spectrum 25 °C, showed efficiencies above 30% both on standard and thin Ge wafers.

  4. B2 structure of high-entropy alloys with addition of Al

    SciTech Connect

    Li, C.; Zhao, M.; Li, J. C.; Jiang, Q.

    2008-12-01

    A series of AlCrCoNiFe based alloys with equal percentage of principal components (high-entropy alloys or HE alloys) is fabricated. The related crystalline structures of the alloys are measured and calculated. Results show that the formed bcc phase is a compound based B2 structure where there is partial ionic bonding between Al and other transition metals. Thus, the bcc structure of the alloys should be a B2 instead of an A2 due to the large difference in electronegativities among the components consisting of the HE alloys.

  5. First results from the high-brightness x-ray spectroscopy beamline at ALS

    SciTech Connect

    Perera, R.C.C.; Ng, W.; Jones, G.

    1997-04-01

    Beamline 9.3.1 at the Advanced Light Source (ALS) is a windowless beamline, covering the 1-6 keV photon-energy range, designed to achieve the goal of high brightness at the sample for use in the X-ray Atomic and Molecular Spectroscopy (XAMS) science, surface and interface science, biology and x-ray optical development programs at ALS. X-ray absorption and time of flight photo emission measurements in 2 - 5 keV photon energy in argon along with the flux, resolution, spot size and stability of the beamline will be discussed. Prospects for future XAMS measurements will also be presented.

  6. Solid state amorphization in the Al-Fe binary system during high energy milling

    SciTech Connect

    Urban, P. Montes, J. M.; Cintas, J.

    2013-12-16

    In the present study, mechanical alloying (MA) of Al75Fe25 elemental powders mixture was carried out in argon atmosphere, using a high energy attritor ball mill. The microstructure of the milled products at different stages of milling was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The results showed that the amorphous phase content increased by increasing the milling time, and after 50 hours the amorphization process became complete. Heating the samples resulted in the crystallization of the synthesized amorphous alloys and the appearance of the equilibrium intermetallic compounds Al{sub 5}Fe{sub 2}.

  7. Isentropic Compression Driven by High-Explosive Application to TI-6AL-4V

    NASA Astrophysics Data System (ADS)

    Voltz, C.; Sollier, A.; Maillet, J.-B.; Bouyer, V.

    2009-12-01

    We report on an isentropic compression experiment of Ti-6Al-4V alloy based on the use of the release of detonation products from a high-explosive to generate a ramp wave compression in a multisteps target. VISAR and DLI measurements of the rear free surface velocities of the different steps allow computing the sound velocity of the material during its compression, which is characteristic of the EOS of the material. The experimental device is described and the sound velocity measurements are analyzed. We obtain Ti-6Al-4V strength along the compression up to 15 GPa. The results are compared with two dimensional elastic-plastic simulations.

  8. High Temperature Aerogels in the Al2O3-SiO2 System

    NASA Technical Reports Server (NTRS)

    Hurwitz, Frances I.; Aranda, Denisse V.; Gallagher, Meghan E.

    2008-01-01

    Al2O3-SiO2 aerogels are of interest as constituents of thermal insulation systems for use at high temperatures. Al2O3 and mullite aerogels are expected to crystallize at higher temperatures than their SiO2 counterparts, hence avoiding the shrinkages that accompany the formation of lower temperature SiO2 phases and preserving pore structures into higher temperature regimes. The objective of this work is to determine the influence of processing parameters on shrinkage, gel structure (including surface area, pore size and distribution) and pyrolysis behavior.

  9. High-temperature neutron diffraction and first-principles study of temperature-dependent crystal structures and atomic vibrations in Ti3AlC2, Ti2AlC, and Ti5Al2C3

    NASA Astrophysics Data System (ADS)

    Lane, Nina J.; Vogel, Sven C.; Caspi, El'ad N.; Barsoum, Michel W.

    2013-05-01

    Herein we report on the thermal expansions and temperature-dependent crystal structures of select ternary carbide Mn +1AXn (MAX) phases in the Ti-Al-C phase diagram in the 100-1000 °C temperature range. A bulk sample containing 38(±1) wt. % Ti5Al2C3 ("523"), 32(±1) wt. % Ti2AlC ("211"), 18(±1) wt. % Ti3AlC2 ("312"), and 12(±1) wt. % (Ti0.5Al0.5)Al is studied by Rietveld analysis of high-temperature neutron diffraction data. We also report on the same for a single-phase sample of Ti3AlC2 for comparison. The thermal expansions of all the MAX phases studied are higher in the c direction than in the a direction. The bulk expansion coefficients—9.3(±0.1)×10-6 K-1 for Ti5Al2C3, 9.2(±0.1) ×10-6 K-1 for Ti2AlC, and 9.0(±0.1)×10-6 K-1 for Ti3AlC2—are comparable within one standard deviation of each other. In Ti5Al2C3, the dimensions of the Ti-C octahedra for the 211-like and 312-like regions are comparable to the Ti-C octahedra in Ti2AlC and Ti3AlC2, respectively. The isotropic mean-squared atomic displacement parameters are highest for the Al atoms in all three phases, and the values predicted from first-principles phonon calculations agree well with those measured.

  10. Faceted growth of primary Al{sub 2}Cu crystals during directional solidification in high magnetic field

    SciTech Connect

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

    2013-10-21

    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 Al{sub 2}Cu 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)

  11. Performance of AlGaN/GaN high electron mobility transistors at nanoscale gate lengths.

    PubMed

    Johnson, J W; Ren, F; Pearton, S J; Baca, A G; Han, J; Dabiran, A M; Chow, P P

    2002-01-01

    The DC and RF performance of AlGaN/GaN high electron mobility transistors with nanoscale gate lengths is presented. The layer structures were grown by either metal organic chemical vapor deposition or rf plasma-assisted molecular beam epitaxy. Excellent scaling properties were observed as a function of both gate length and width and confirm that these devices are well suited to both high speed switching and power microwave applications. PMID:12908259

  12. Preliminary Thermal Stress Analysis of a High-Pressure Cryogenic Storage Tank

    NASA Technical Reports Server (NTRS)

    Baker, J. Mark

    2003-01-01

    The thermal stresses on a cryogenic storage tank strongly affect the condition of the tank and its ability to withstand operational stresses. These thermal stresses also affect the growth of any surface damage that might occur in the tank walls. These stresses are particularly of concern during the initial cooldown period for a new tank placed into service, and during any subsequent thermal cycles. A preliminary thermal stress analysis of a high-pressure cryogenic storage tank was performed. Stresses during normal operation were determined, as well as the transient temperature distribution. An elastic analysis was used to determine the thermal stresses in the inner wall based on the temperature data. The results of this elastic analysis indicate that the inner wall of the storage tank will experience thermal stresses of approximately 145,000 psi (1000 MPa). This stress level is well above the room-temperature yield strength of 304L stainless steel, which is about 25,000 psi (170 MPa). For this preliminary analysis, several important factors have not yet been considered. These factors include increased strength of 304L stainless steel at cryogenic temperatures, plastic material behavior, and increased strength due to strain hardening. In order to more accurately determine the thermal stresses and their affect on the tank material, further investigation is required, particularly in the area of material properties and their relationship to stress.

  13. High hydrostatic pressure leads to free radicals accumulation in yeast cells triggering oxidative stress.

    PubMed

    Bravim, Fernanda; Mota, Mainã M; Fernandes, A Alberto R; Fernandes, Patricia M B

    2016-08-01

    Saccharomyces cerevisiae is a unicellular organism that during the fermentative process is exposed to a variable environment; hence, resistance to multiple stress conditions is a desirable trait. The stress caused by high hydrostatic pressure (HHP) in S. cerevisiae resembles the injuries generated by other industrial stresses. In this study, it was confirmed that gene expression pattern in response to HHP displays an oxidative stress response profile which is expanded upon hydrostatic pressure release. Actually, reactive oxygen species (ROS) concentration level increased in yeast cells exposed to HHP treatment and an incubation period at room pressure led to a decrease in intracellular ROS concentration. On the other hand, ethylic, thermic and osmotic stresses did not result in any ROS accumulation in yeast cells. Microarray analysis revealed an upregulation of genes related to methionine metabolism, appearing to be a specific cellular response to HHP, and not related to other stresses, such as heat and osmotic stresses. Next, we investigated whether enhanced oxidative stress tolerance leads to enhanced tolerance to HHP stress. Overexpression of STF2 is known to enhance tolerance to oxidative stress and we show that it also leads to enhanced tolerance to HHP stress. PMID:27388472

  14. A new type of Cu-Al-Ta shape memory alloy with high martensitic transformation temperature

    NASA Astrophysics Data System (ADS)

    Wang, C. P.; Su, Y.; Y Yang, S.; Shi, Z.; Liu, X. J.

    2014-02-01

    In this study, a new type of Cu-Al-Ta (Cu86Al12Ta2 wt%) shape memory alloy with high martensitic transformation temperature is explored. The microstructure, reversible martensitic transformation and shape memory properties are investigated by means of optical microscopy, back-scattered electron, electron probe microanalysis, x-ray diffraction, differential scanning calorimetry and tensile tests. It is proposed that Cu86Al12Ta2 alloy consists of a mixture of primarily {\\beta }_{1}^{\\prime} martensite and a little {\\gamma }_{1}^{\\prime} martensite and some different precipitates. The tiny thin-striped Ta2(Al,Cu)3 precipitate is predominant in the as-quenched condition, whereas the particle-shaped Cu(Al, Ta) precipitate is dominant after hot-rolling. Additionally, the dendritic-shaped γ1(Cu9Al4) phase begins to appear after hot-rolling, but it disappears when the sample is re-quenched. All studied samples have reversible martensitic transformation temperatures higher than 450 ° C. The results show that two-step martensitic transformation behavior is observed for Cu86Al12Ta2 alloy in all three different conditions due to the transformations between ({\\beta }_{1}^{\\prime}+{\\gamma }_{1}^{\\prime}) martensites and the austenite parent phase. The results further show that the recovery ratios are almost 100% when the pre-strains are ≤2.5%, then they gradually decrease with further increase of the pre-strains. The shape memory effects clearly increase as a result of increase of the pre-strains, up to a maximum value of 3.2%.

  15. An Electrochemical Framework to Explain Intergranular Stress Corrosion Cracking in an Al-5.4%Cu-0.5%Mg-0.5%Ag Alloy

    NASA Technical Reports Server (NTRS)

    Little, D. A.; Connolly, B. J.; Scully, J. R.

    2001-01-01

    A modified version of the Cu-depletion electrochemical framework was used to explain the metallurgical factor creating intergranular stress corrosion cracking susceptibility in an aged Al-Cu-Mg-Ag alloy, C416. This framework was also used to explain the increased resistance to intergranular stress corrosion cracking in the overaged temper. Susceptibility in the under aged and T8 condition is consistent with the grain boundary Cu-depletion mechanism. Improvements in resistance of the T8+ thermal exposure of 5000 h at 225 F (T8+) compared to the T8 condition can be explained by depletion of Cu from solid solution.

  16. Effect of geometrical stress concentrators on the current-induced suppression of the serrated deformation in an aluminum-magnesium AlMg5 alloy

    NASA Astrophysics Data System (ADS)

    Shibkov, A. A.; Zolotov, A. E.; Zheltov, M. A.; Denisov, A. A.; Gasanov, M. F.; Kochegarov, S. S.

    2016-05-01

    The effect of an electric current on the band formation and the serrated deformation of planar specimens made of an aluminum-magnesium AlMg5 alloy and weakened by holes is experimentally studied. It is found that the concentration of elastic stress fields and the self-localized unstable plastic deformation field near a hole decreases the critical strain of appearance of the first stress drop and hinders the currentinduced suppression of band formation and the serrated Portevin-Le Chatelier deformation. These results are shown not to be related to the concentration of Joule heat near a hole.

  17. High Novelty-Seeking Rats Are Resilient to Negative Physiological Effects of the Early Life Stress

    PubMed Central

    Clinton, Sarah M.; Watson, Stanley J.; Akil, Huda

    2014-01-01

    Exposure to early life stress dramatically impacts adult behavior, physiology, and neuroendocrine function. Using rats bred for novelty-seeking differences and known to display divergent anxiety, depression, and stress vulnerability, we examined the interaction between early life adversity and genetic predisposition for high- versus low-emotional reactivity. Thus, bred Low Novelty Responder (bLR) rats, which naturally exhibit high anxiety- and depression-like behavior, and bred High Novelty Responder (bHR) rats, which show low anxiety/depression together with elevated aggression, impulsivity, and addictive behavior, were subjected to daily 3 h maternal separation (MS) stress postnatal days 1–14. We hypothesized that MS stress would differentially impact adult bHR/bLR behavior, physiology (stress-induced defecation), and neuroendocrine reactivity. While MS stress did not impact bHR and bLR anxiety-like behavior in the open field test and elevated plus maze, it exacerbated bLRs’ already high physiological response to stressstress-induced defecation. In both tests, MS bLR adult offspring showed exaggerated stress-induced defecation compared to bLR controls while bHR offspring were unaffected. MS also selectively impacted bLRs’ (but not bHRs’) neuroendocrine stress reactivity, producing an exaggerated corticosterone acute stress response in MS bLR versus control bLR rats. These findings highlight how genetic predisposition shapes individuals’ response to early life stress. Future work will explore neural mechanisms underlying the distinct behavioral and neuroendocrine consequences of MS in bHR/bLR animals. PMID:24090131

  18. The role of fungal symbiosis in the adaptation of plants to high stress environments

    USGS Publications Warehouse

    Rodriguez, Russell J.; Redman, Regina S.; Henson, Joan M.

    2004-01-01

    All plants studied in natural ecosystemsare symbiotic with fungi that either resideentirely (endophytes) or partially(mycorrhizae) within plants. Thesesymbioses appear to adapt to biotic andabiotic stresses and may be responsible forthe survival of both plant hosts and fungalsymbionts in high stress habitats. Here wedescribe the role of symbiotic fungi inplant stress tolerance and present astrategy based on adaptive symbiosis topotentially mitigate the impacts of globalchange on plant communities.

  19. Prostate specific antigen detection using AlGaN /GaN high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Kang, B. S.; Wang, H. T.; Lele, T. P.; Tseng, Y.; Ren, F.; Pearton, S. J.; Johnson, J. W.; Rajagopal, P.; Roberts, J. C.; Piner, E. L.; Linthicum, K. J.

    2007-09-01

    Antibody-functionalized Au-gated AlGaN /GaN high electron mobility transistors (HEMTs) were used to detect prostate specific antigen (PSA). The PSA antibody was anchored to the gate area through the formation of carboxylate succinimdyl ester bonds with immobilized thioglycolic acid. The AlGaN /GaN HEMT drain-source current showed a rapid response of less than 5s when target PSA in a buffer at clinical concentrations was added to the antibody-immobilized surface. The authors could detect a wide range of concentrations from 10pg/mlto1μg/ml. The lowest detectable concentration was two orders of magnitude lower than the cutoff value of PSA measurements for clinical detection of prostate cancer. These results clearly demonstrate the promise of portable electronic biological sensors based on AlGaN /GaN HEMTs for PSA screening.

  20. Nanoscale investigation of AlGaN/GaN-on-Si high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Fontserè, A.; Pérez-Tomás, A.; Placidi, M.; Llobet, J.; Baron, N.; Chenot, S.; Cordier, Y.; Moreno, J. C.; Jennings, M. R.; Gammon, P. M.; Fisher, C. A.; Iglesias, V.; Porti, M.; Bayerl, A.; Lanza, M.; Nafría, M.

    2012-10-01

    AlGaN/GaN HEMTs are devices which are strongly influenced by surface properties such as donor states, roughness or any kind of inhomogeneity. The electron gas is only a few nanometers away from the surface and the transistor forward and reverse currents are considerably affected by any variation of surface property within the atomic scale. Consequently, we have used the technique known as conductive AFM (CAFM) to perform electrical characterization at the nanoscale. The AlGaN/GaN HEMT ohmic (drain and source) and Schottky (gate) contacts were investigated by the CAFM technique. The estimated area of these highly conductive pillars (each of them of approximately 20-50 nm radius) represents around 5% of the total contact area. Analogously, the reverse leakage of the gate Schottky contact at the nanoscale seems to correlate somehow with the topography of the narrow AlGaN barrier regions producing larger currents.

  1. A Review of Mold Flux Development for the Casting of High-Al Steels

    NASA Astrophysics Data System (ADS)

    Wang, Wanlin; Lu, Boxun; Xiao, Dan

    2016-02-01

    Mold flux plays key roles during the continuous casting process of molten steel, which accounts for the quality of final slabs. With the development of advanced high strength steels (AHSS), certain amounts of Al have been added into steels that would introduce severe slag/metal interaction problems during process of continuous casting. The reaction is between Al and SiO2 that is the major component in the mold flux system. Intensive efforts have been conducted to optimize the mold flux and a CaO-Al2O3-based mold flux system has been proposed, which shows the potential to be applied for the casting process of AHSS. The latest developments for this new mold flux system were summarized with the aim to offer technical guidance for the design of new generation mold flux system for the casting of AHSS.

  2. Nano features of Al/Au ultrasonic bond interface observed by high resolution transmission electron microscopy

    SciTech Connect

    Ji Hongjun; Li Mingyu Kim, Jong-Myung; Kim, Dae-Won; Wang Chunqing

    2008-10-15

    Nano-scale interfacial details of ultrasonic AlSi1 wire wedge bonding to a Au/Ni/Cu pad were investigated using high resolution transmission electron microscopy (HRTEM). The intermetallic phase Au{sub 8}Al{sub 3} formed locally due to diffusion and reaction activated by ultrasound at the Al/Au bond interface. Multilayer sub-interfaces roughly parallel to the wire/pad interface were observed among this phase, and interdiffusional features near the Au pad resembled interference patterns, alternately dark and bright bars. Solid-state diffusion theory cannot be used to explain why such a thick compound formed within milliseconds at room temperature. The major formation of metallurgical bonds was attributed to ultrasonic cyclic vibration.

  3. High Density Hydrogen Storage System Demonstration Using NaAlH4 Based Complex Compound Hydrides

    SciTech Connect

    Daniel A. Mosher; Xia Tang; Ronald J. Brown; Sarah Arsenault; Salvatore Saitta; Bruce L. Laube; Robert H. Dold; Donald L. Anton

    2007-07-27

    This final report describes the motivations, activities and results of the hydrogen storage independent project "High Density Hydrogen Storage System Demonstration Using NaAlH4 Based Complex Compound Hydrides" performed by the United Technologies Research Center under the Department of Energy Hydrogen Program, contract # DE-FC36-02AL67610. The objectives of the project were to identify and address the key systems technologies associated with applying complex hydride materials, particularly ones which differ from those for conventional metal hydride based storage. This involved the design, fabrication and testing of two prototype systems based on the hydrogen storage material NaAlH4. Safety testing, catalysis studies, heat exchanger optimization, reaction kinetics modeling, thermochemical finite element analysis, powder densification development and material neutralization were elements included in the effort.

  4. Sonochemical preparation of high surface area MgAl2O4 spinel.

    PubMed

    Troia, A; Pavese, M; Geobaldo, F

    2009-01-01

    High surface area MgAl(2)O(4) has been synthesised by a sonochemical method. Two kinds of precursors were used, alkoxides and nitrates/acetates and in both cases nanostructured MgAl(2)O(4) was obtained. The effect of the addition of a surfactant during the sonication, cetyl trimethyl ammonium bromide, was also investigated. In the case of alkoxides precursors the as-made product is a mixture of hydroxides of aluminium and magnesium, while with nitrates/acetates a gel is obtained after sonication, containing the metal hydroxides and ammonium nitrate. Heating at 500 degrees C transforms the as-made products into MgAl(2)O(4) spinel phase. The surface area is up to 267 m(2)/g after treatment at 500 degrees C and 138 m(2)/g at 800 degrees C. PMID:18658004

  5. Electronic and Mechanical Properties of Tetragonal Nb2Al Under High Pressure: First-Principles Calculations

    NASA Astrophysics Data System (ADS)

    Jiao, Zhen; Liu, Qi-Jun; Liu, Fu-Sheng; Wang, Wen-Peng; Wang, Yi-Gao; Li, Yong; Liu, Zheng-Tang

    2016-04-01

    We have investigated the structure, density of states, mechanical stability, elastic properties, and Debye temperature of tetragonal Nb2Al under high pressure using the generalized gradient approximation WC (GGA-WC) functional within density functional theory (DFT). Our obtained lattice constants were in good agreement with the reported experimental and theoretical data at zero pressure. The volume decreased with the increasing pressure. The effects of pressure on the electronic properties have been discussed. The elastic constants under pressure have been calculated, which all satisfied the stability criterion, meaning that tetragonal Nb2Al was mechanical stability from 0 to 100 GPa. Then, the mechanical properties including bulk modulus B, shear modulus G, Young's modulus E, G/B, and Poisson's ratio ν under pressure were determined using the Voigt-Reuss-Hill method. The G/B value suggested that tetragonal Nb2Al exhibited ductile behavior under pressure. Poisson's ratio indicated that the interatomic forces in tetragonal Nb2Al were mainly central forces. Finally, the transverse, longitudinal, and average sound velocities and Debye temperature of tetragonal Nb2Al under pressure have been estimated.

  6. High-precision mass measurements of 25Al and 30P at JYFLTRAP

    NASA Astrophysics Data System (ADS)

    Canete, L.; Kankainen, A.; Eronen, T.; Gorelov, D.; Hakala, J.; Jokinen, A.; Kolhinen, V. S.; Koponen, J.; Moore, I. D.; Reinikainen, J.; Rinta-Antila, S.

    2016-05-01

    The masses of the astrophysically relevant nuclei 25Al and 30P have been measured with a Penning trap for the first time. The mass-excess values for 25Al ( Δ = -8915.962(63) keV) and 30P ( Δ = -20200.854(64) keV) obtained with the JYFLTRAP double Penning trap mass spectrometer are in good agreement with the Atomic Mass Evaluation 2012 values but ≈ 5-10 times more precise. A high precision is required for calculating resonant proton-capture rates of astrophysically important reactions 25Al ( p, γ)26Si and 30P( p, γ)31S . In this work, Q_{(p,γ)} = 5513.99(13) keV and Q_{(p,γ)} = 6130.64(24) keV were obtained for 25Al and 30P , respectively. The effect of the more precise values on the resonant proton-capture rates has been studied. In addition to nuclear astrophysics, the measured QEC value of 25Al , 4276.805(45) keV, is relevant for studies of T = 1/2 mirror beta decays which have a potential to be used to test the Conserved Vector Current hypothesis.

  7. New Powder Metallurgical Approach to Achieve High Fatigue Strength in Ti-6Al-4V Alloy

    NASA Astrophysics Data System (ADS)

    Cao, Fei; Ravi Chandran, K. S.; Kumar, Pankaj; Sun, Pei; Zak Fang, Z.; Koopman, Mark

    2016-05-01

    Recently, manufacturing of titanium by sintering and dehydrogenation of hydride powders has generated a great deal of interest. An overarching concern regarding powder metallurgy (PM) titanium is that critical mechanical properties, especially the high-cycle fatigue strength, are lower than those of wrought titanium alloys. It is demonstrated here that PM Ti-6Al-4V alloy with mechanical properties comparable (in fatigue strength) and exceeding (in tensile properties) those of wrought Ti-6Al-4V can be produced from titanium hydride powder, through the hydrogen sintering and phase transformation process. Tensile and fatigue behavior, as well as fatigue fracture mechanisms, have been investigated under three processing conditions. It is shown that a reduction in the size of extreme-sized pores by changing the hydride particle size distribution can lead to improved fatigue strength. Further densification by pneumatic isostatic forging leads to a fatigue strength of ~550 MPa, comparable to the best of PM Ti-6Al-4V alloys prepared by other methods and approaching the fatigue strengths of wrought Ti-6Al-4V alloys. The microstructural factors that limit fatigue strength in PM titanium have been investigated, and pathways to achieve greater fatigue strengths in PM Ti-6Al-4V alloys have been identified.

  8. Characterization of high energy ion implantation into Ti-6Al-4V

    NASA Astrophysics Data System (ADS)

    Carroll, M. P.; Stephenson, K.; Findley, K. O.

    2009-06-01

    Ion implantation is a surface modification process that can improve the wear, fatigue, and corrosion resistance for several metals and alloys. Much of the research to date has focused on ion energies less than 1 MeV. With this in mind, Ti-6Al-4V was implanted with Al 2+, Au 3+, and N + ions at energies of 1.5 and 5 MeV and various doses to determine the effects on strengthening of a high energy beam. A post heat treatment on the specimens implanted with Al 2+ samples was conducted to precipitate Ti xAl type intermetallics near the surface. Novel techniques, such as nanoindentation, are available now to determine structure-mechanical property relationships in near-surface regions of the implanted samples. Thus, nanoindentation was performed on pre-implanted, as-implanted, and post heat treated samples to detect differences in elastic modulus and hardness at the sub-micron scale. In addition, sliding wear tests were performed to qualitatively determine the changes in wear performance. The effect of this processing was significant for samples implanted with Al 2+ ions at 1.5 MeV with a dose higher than 1 × 10 16 ions/cm 2 where precipitation hardening likely occurs and with N + ions.

  9. Shock compression response of highly reactive Ni + Al multilayered thin foils

    NASA Astrophysics Data System (ADS)

    Kelly, Sean C.; Thadhani, Naresh N.

    2016-03-01

    The shock-compression response of Ni + Al multilayered thin foils is investigated using laser-accelerated thin-foil plate-impact experiments over the pressure range of 2 to 11 GPa. The foils contain alternating Ni and Al layers (parallel but not flat) of nominally 50 nm bilayer spacing. The goal is to determine the equation of state and shock-induced reactivity of these highly reactive fully dense thin-foil materials. The laser-accelerated thin-foil impact set-up involved combined use of photon-doppler-velocimetry to monitor the acceleration and impact velocity of an aluminum flyer, and VISAR interferometry was used to monitor the back free-surface velocity of the impacted Ni + Al multilayered target. The shock-compression response of the Ni + Al target foils was determined using experimentally measured parameters and impedance matching approach, with error bars identified considering systematic and experimental errors. Meso-scale CTH shock simulations were performed using real imported microstructures of the cross-sections of the multilayered Ni + Al foils to compute the Hugoniot response (assuming no reaction) for correlation with their experimentally determined equation of state. It was observed that at particle velocities below ˜150 m/s, the experimentally determined equation of state trend matches the CTH-predicted inert response and is consistent with the observed unreacted state of the recovered Ni + Al target foils from this velocity regime. At higher particle velocities, the experimentally determined equation of state deviates from the CTH-predicted inert response. A complete and self-sustained reaction is also seen in targets recovered from experiments performed at these higher particle velocities. The deviation in the measured equation of state, to higher shock speeds and expanded volumes, combined with the observation of complete reaction in the recovered multilayered foils, confirmed via microstructure characterization, is indicative of the occurrence

  10. High-brightness beamline for x-ray spectroscopy at the ALS

    SciTech Connect

    Perera, R.C.C.; Jones, G.; Lindle, D.W.

    1997-04-01

    Beamline 9.3.1 at the Advanced Light Source (ALS) is a windowless beamline, covering the 1-6 keV photon-energy range, designed to achieve the goals of high energy resolution, high flux, and high brightness at the sample. When completed later this year, it will be the first ALS monochromatic hard x-ray beamline, and its brightness will be an order of magnitude higher than presently available in this energy range. In addition, it will provide flux and resolution comparable to any other beamline now in operation. To achieve these goals, two technical improvements, relative to existing x-ray beamlines, were incorporated. First, a somewhat novel optical design for x-rays, in which matched toroidal mirrors are positioned before and after the double-crystal monochromator, was adopted. This configuration allows for high resolution by passing a collimated beam through the monochromator, and for high brightness by focusing the ALS source on the sample with unit magnification. Second, a new {open_quotes}Cowan type{close_quotes} double-crystal monochromator based on the design used at NSLS beamline X-24A was developed. The measured mechanical precision of this new monochromator shows significant improvement over existing designs, without using positional feedback available with piezoelectric devices. Such precision is essential because of the high brightness of the radiation and the long distance (12 m) from the source (sample) to the collimating (focusing) mirror. This combination of features will provide a bright, high resolution, and stable x-ray beam for use in the x-ray spectroscopy program at the ALS.

  11. A high-temperature neutron diffraction study of Nb2AlC and TiNbAlC

    DOE PAGESBeta

    Bentzel, Grady W.; Lane, Nina J.; Vogel, Sven C.; An, Ke; Barsoum, Michel W.; Caspi, El'ad N.

    2014-12-16

    In this paper, we report on the crystal structures of Nb2AlC and TiNbAlC actual composition (Ti0.45,Nb0.55)2AlC compounds determined from Rietveld analysis of neutron diffraction patterns in the 300-1173 K temperature range. The average linear thermal expansion coefficients of a Nb2AlC sample in the a and c directions are, respectively, 7.9(5)x10-6 K-1 and 7.7(5)x10-6 K-1 on one neutron diffractometer and 7.3(3)x10-6 K-1 and 7.0(2)x10-6 K-1 on a second diffractometer. The respective values for the (Ti0.45,Nb0.55)2AlC composition - only tested on one diffractometer - are 8.5(3)x10-6 K-1 and 7.5(5)x10-6 K-1. These values are relatively low compared to other MAX phases. Like othermore » MAX phases, however, the atomic displacement parameters show that the Al atoms vibrate with higher amplitudes than the Ti and C atoms, and 1 more along the basal planes than normal to them. In addition, when the predictions of the atomic displacement parameters obtained from density functional theory are compared to the experimental results, good quantitative agreement is found for the Al atoms. In case of the Nb and C atoms, the agreement was more qualitative.« less

  12. Low Cost Al-Si Casting Alloy As In-Situ Composite for High Temperature Applications

    NASA Technical Reports Server (NTRS)

    Lee, Jonathan A.

    2000-01-01

    A new aluminum-silicon (Al-Si) alloy has been successfully developed at NASA- Marshall Space Flight Center (MSFC) that has significant improvement in tensile and fatigue strength at elevated temperatures (500 F-700 F). The alloy offers a number of benefits such as light weight, high hardness, low thermal expansion and high surface wear resistance. In hypereutectic form, this alloy is considered as an in-situ Al-Si composite with tensile strength of about 90% higher than the auto industry 390 alloy at 600 F. This composite is very economically produced by using either conventional permanent steel molds or die casting. The projected material cost is less than $0.90 per pound, and automotive components such as pistons can be cast for high production rate using conventional casting techniques with a low and fully accounted cost. Key Words: Metal matrix composites, In-situ composite, aluminum-silicon alloy, hypereutectic alloy, permanent mold casting, die casting.

  13. High power AlGaAs-GaAs visible diode lasers

    SciTech Connect

    Tihanyi, P.L.; Jain, F.C. . Dept. of Electrical Engineering); Robinson, M.J.; Dixon, J.E. ); Williams, J.E.; Meehan, K.; O'Neill, M.S.; Heath, L.S.; Beyea, D.M. . Microelectronics and Materials Center)

    1994-07-01

    A high-power room-temperature AlGaAs graded index separately confined heterostructure (GRINSCH) laser emitting in the visible spectral regime ([approx equal]715 nm) is reported for the first time. The device is gain-guided and consists of 12 stripes, each 5 [mu]m in width with a centerline separation of 9 [mu]m. This high-power visible laser has been successfully fabricated using a GaAlAs active layer. The epitaxial layer was grown with significantly lower levels of oxygen compared to those grown using standard metalorganic sources. Threshold currents of 310 mA at 10 C were routinely measured on uncoated devices. The uncoated device had a catastrophic optical damage limit of 540 mW and has a slope efficiency as high as 0.48. No degradation in device performance was observed during a 50-hour 150-mW burn-in.

  14. Overexpression of monoubiquitin improves photosynthesis in transgenic tobacco plants following high temperature stress.

    PubMed

    Tian, Fengxia; Gong, Jiangfeng; Zhang, Jin; Feng, Yanan; Wang, Guokun; Guo, Qifang; Wang, Wei

    2014-09-01

    The ubiquitin/26S proteasome system (Ub/26S) is implicated in abiotic stress responses in plants. In this paper, transgenic tobacco plants overexpressing Ta-Ub2 from wheat were used to study the functions of Ub in the improvement of photosynthesis under high temperature (45°C) stress. We observed higher levels of Ub conjugates in transgenic plants under high temperature stress conditions compared to wild type (WT) as a result of the constitutive overexpression of Ta-Ub2, suggesting increased protein degradation by the 26S proteasome system under high temperature stress. Overexpressing Ub increased the photosynthetic rate (Pn) of transgenic tobacco plants, consistent with the improved ATPase activity in the thylakoid membrane and enhanced efficiency of PSII photochemistry. The higher D1 protein levels following high temperature stress in transgenic plants than WT were also observed. These findings imply that Ub may be involved in tolerance of photosynthesis to high temperature stress in plants. Compared with WT, the transgenic plants showed lower protein carbonylation and malondialdehyde (MDA) levels, less reactive oxygen species (ROS) accumulation, but higher antioxidant enzyme activity under high temperature stress. These findings suggest that the improved antioxidant capacity of transgenic plants may be one of the most important mechanisms underlying Ub-regulated high temperature tolerance. PMID:25113454

  15. Stress and success: individual differences in the glucocorticoid stress response predict behavior and reproductive success under high predation risk.

    PubMed

    Vitousek, Maren N; Jenkins, Brittany R; Safran, Rebecca J

    2014-11-01

    A fundamental element of how vertebrates respond to stressors is by rapidly elevating circulating glucocorticoid hormones. Individual variation in the magnitude of the glucocorticoid stress response has been linked with reproductive success and survival. But while the adaptive value of this response is believed to stem in part from changes in the expression of hormone-mediated behaviors, it is not clear how the behavior of stronger and weaker glucocorticoid responders differs during reproduction, or during exposure to ecologically relevant stressors. Here we report that in a population of barn swallows (Hirundo rustica erythrogaster) experiencing high rates of nest predation, circulating levels of corticosterone (the primary avian glucocorticoid) during exposure to a standardized stressor predict aspects of subsequent behavior and fitness. Individuals that mounted a stronger corticosterone stress response during the early reproductive period did not differ in clutch size, but fledged fewer offspring. Parents with higher stress-induced corticosterone during the early reproductive period later provisioned their nestlings at lower rates. Additionally, in the presence of a model predator stress-induced corticosterone was positively associated with the latency to return to the nest, but only among birds that were observed to return. Model comparisons revealed that stress-induced hormones were better predictors of the behavioral and fitness effects of exposure to transient, ecologically relevant stressors than baseline corticosterone. These findings are consistent with functional links between individual variation in the hormonal and behavioral response to stressors. If such links occur, then selection on the heritable components of the corticosterone stress response could promote adaptation to novel environments or predation regimes. PMID:25461975

  16. ER Stress Mediates TiAl6V4 Particle-Induced Peri-Implant Osteolysis by Promoting RANKL Expression in Fibroblasts

    PubMed Central

    Wang, Zhenheng; Liu, Naicheng; Shi, Tongguo; Zhou, Gang; Wang, Zhenzhen; Gan, Jingjing; Guo, Ting; Qian, Hongbo; Bao, Nirong; Zhao, Jianning

    2015-01-01

    Wear particle-induced osteolysis is a major cause of aseptic loosening, which is one of the most common reasons for total hip arthroplasty (THA) failure. Previous studies have shown that the synovial fibroblasts present in the periprosthetic membrane are important targets of wear debris during osteolysis. However, the interaction mechanisms between the wear debris and fibroblasts remain largely unknown. In the present study, we investigated the effect of ER (endoplasmic reticulum) stress induced by TiAl6V4 particles (TiPs) in human synovial fibroblasts and calvarial resorption animal models. The expression of ER stress markers, including IRE1-α, GRP78/Bip and CHOP, were determined by western blot in fibroblasts that had been treated with TiPs for various times and concentration. To address whether ER stress was involved in the expression of RANKL, the effects of ER stress blockers (including 4-PBA and TUDCA) on the expression of RANKL in TiPs-treated fibroblasts were examined by real-time PCR, western blot and ELISA. Osteoclastogenesis was assessed by tartrate resistant acid phosphatase (TRAP) staining. Our study demonstrated that ER stress markers were markedly upregulated in TiPs-treated fibroblasts. Blocking ER stress significantly reduced the TiPs-induced expression of RANKL both in vitro and in vivo. Moreover, the inhibition of ER stress ameliorated wear particle-induced osteolysis in animal models. Taken together, these results suggested that the expression of RANKL induced by TiPs was mediated by ER stress in fibroblasts. Therefore, down regulating the ER stress of fibroblasts represents a potential therapeutic approach for wear particle-induced periprosthetic osteolysis. PMID:26366858

  17. ER Stress Mediates TiAl6V4 Particle-Induced Peri-Implant Osteolysis by Promoting RANKL Expression in Fibroblasts.

    PubMed

    Wang, Zhenheng; Liu, Naicheng; Shi, Tongguo; Zhou, Gang; Wang, Zhenzhen; Gan, Jingjing; Guo, Ting; Qian, Hongbo; Bao, Nirong; Zhao, Jianning

    2015-01-01

    Wear particle-induced osteolysis is a major cause of aseptic loosening, which is one of the most common reasons for total hip arthroplasty (THA) failure. Previous studies have shown that the synovial fibroblasts present in the periprosthetic membrane are important targets of wear debris during osteolysis. However, the interaction mechanisms between the wear debris and fibroblasts remain largely unknown. In the present study, we investigated the effect of ER (endoplasmic reticulum) stress induced by TiAl6V4 particles (TiPs) in human synovial fibroblasts and calvarial resorption animal models. The expression of ER stress markers, including IRE1-α, GRP78/Bip and CHOP, were determined by western blot in fibroblasts that had been treated with TiPs for various times and concentration. To address whether ER stress was involved in the expression of RANKL, the effects of ER stress blockers (including 4-PBA and TUDCA) on the expression of RANKL in TiPs-treated fibroblasts were examined by real-time PCR, western blot and ELISA. Osteoclastogenesis was assessed by tartrate resistant acid phosphatase (TRAP) staining. Our study demonstrated that ER stress markers were markedly upregulated in TiPs-treated fibroblasts. Blocking ER stress significantly reduced the TiPs-induced expression of RANKL both in vitro and in vivo. Moreover, the inhibition of ER stress ameliorated wear particle-induced osteolysis in animal models. Taken together, these results suggested that the expression of RANKL induced by TiPs was mediated by ER stress in fibroblasts. Therefore, down regulating the ER stress of fibroblasts represents a potential therapeutic approach for wear particle-induced periprosthetic osteolysis. PMID:26366858

  18. A numerical model to investigate the role of residual stresses on the mechanical behavior of Al/Al{sub 2}O{sub 3} particulate composites

    SciTech Connect

    Guagliano, M.

    1998-04-01

    Research is presented about the mechanical behavior of a 6061 aluminum alloy reinforced with alumina particles. In particular, the role of thermal-induced residual stresses on the mechanical behavior of this composite is analyzed. Experimental tests were carried out to evaluate the mechanical characteristics of this type of material under static and fatigue loading. Fractographies on broken specimens evidenced the failure mechanisms under different load conditions. Also carried out were measurements using the x-ray diffractometric (XRD) technique to determine the residual stresses due to the thermal treatment both in the matrix and in the particles. A microscale finite-element model (FEM) of this material was developed to investigate the actual stress state caused by the thermal treatment and an applied load. A comparison of the numerical results and the experimental observations helped to explain the fracture modes under static and cyclic loading and to determine the role of the residual stresses under both monotone and cyclic loads. These results suggest some treatment to improve fatigue strength of the material.

  19. Polysynthetic twinned TiAl single crystals for high-temperature applications.

    PubMed

    Chen, Guang; Peng, Yingbo; Zheng, Gong; Qi, Zhixiang; Wang, Minzhi; Yu, Huichen; Dong, Chengli; Liu, C T

    2016-08-01

    TiAl alloys are lightweight, show decent corrosion resistance and have good mechanical properties at elevated temperatures, making them appealing for high-temperature applications. However, polysynthetic twinned TiAl single crystals fabricated by crystal-seeding methods face substantial challenges, and their service temperatures cannot be raised further. Here we report that Ti-45Al-8Nb single crystals with controlled lamellar orientations can be fabricated by directional solidification without the use of complex seeding methods. Samples with 0° lamellar orientation exhibit an average room temperature tensile ductility of 6.9% and a yield strength of 708 MPa, with a failure strength of 978 MPa due to the formation of extensive nanotwins during plastic deformation. At 900 °C yield strength remains high at 637 MPa, with 8.1% ductility and superior creep resistance. Thus, this TiAl single-crystal alloy could provide expanded opportunities for higher-temperature applications, such as in aeronautics and aerospace. PMID:27322822

  20. High output power AlN vibration-driven energy harvesters

    NASA Astrophysics Data System (ADS)

    Cao, Z.; He, J.; Wang, Q.; Hara, M.; Oguchi, H.; Kuwano, H.

    2013-12-01

    This paper presents miniature AlN harvesters for harvesting low-frequency and two-dimensional vibration energy. A high fracture toughness and high yield strength stainless steel substrate was used to enhance output power and reduce resonate frequency of vibration energy harvesters. The thickness of 1.89 μm AlN films were deposited on 50 μm thick stainless steel (SUS) substrates for fabricating the harvesters. The Al/AlN/SUS multi-layer sheet was made into long and thin plate-like cantilevers with heavy proof masses attached at their free ends. The devices can collect vibration energy efficiently not only under perpendicular direction to the plate surface of cantilevers but also under the parallel direction. When vibration acceleration was 1.0 g, output power was 28.114 μW for perpendicular vibration and 51.735 μW for parallel vibration. When the acceleration of parallel vibration was 1.6 g, output power was 89.339 μW.

  1. AlN/GaN high electron mobility transistors on sapphire substrates for Ka band applications

    NASA Astrophysics Data System (ADS)

    Xubo, Song; Yuanjie, Lü; Guodong, Gu; Yuangang, Wang; Xin, Tan; Xingye, Zhou; Shaobo, Dun; Peng, Xu; Jiayun, Yin; Bihua, Wei; Zhihong, Feng; Shujun, Cai

    2016-04-01

    We report the DC and RF characteristics of AlN/GaN high electron mobility transistors (HEMTs) with the gate length of 100 nm on sapphire substrates. The device exhibits a maximum drain current density of 1.29 A/mm and a peak transconductance of 440 mS/mm. A current gain cutoff frequency and a maximum oscillation frequency of 119 GHz and 155 GHz have been obtained, respectively. Furthermore, the large signal load pull characteristics of the AlN/GaN HEMTs were measured at 29 GHz. An output power density of 429 mW/mm has been demonstrated at a drain bias of 10 V. To the authors' best knowledge, this is the earliest demonstration of power density at the Ka band for AlN/GaN HEMTs in the domestic, and also a high frequency of load-pull measurements for AlN/GaN HEMTs. Project supported by the National Natural Science Foundation of China (No. 61306113).

  2. Structural analysis of highly porous γ-Al2O3

    NASA Astrophysics Data System (ADS)

    Samain, Louise; Jaworski, Aleksander; Edén, Mattias; Ladd, Danielle M.; Seo, Dong-Kyun; Javier Garcia-Garcia, F.; Häussermann, Ulrich

    2014-09-01

    Two highly porous γ-aluminas, a commercial catalyst obtained from the calcination of boehmite and a highly mesoporous product obtained from amorphous aluminum (oxy)hydroxide via a sol-gel-based process were investigated by 27Al nuclear magnetic resonance (NMR), transmission electron microscopy (TEM), and atomic pair distribution function (PDF) analysis of synchrotron powder diffraction data. NMR data showed for both materials a distribution of tetrahedrally and octahedrally coordinated Al at a 0.30:0.70 ratio, which is typical for γ-aluminas. TEM studies revealed that rod-shaped particles with about 5 nm in thickness are the building blocks of the porous structure in both materials. These particles often extend to a length of 50 nm in the commercial catalyst and are considerably shorter in the sol-gel-based material, which has a higher surface area. Refinement of PDFs revealed the presence of a ~1 nm scale local structure and the validity of a tetragonal average structure for both materials. This tetragonal average structure contains a substantial fraction of non-spinel octahedral Al atoms. It is argued that the presence of local structure is a general feature of γ-alumina, independent of precursor and synthesis conditions. The concentration of “non-spinel” Al atoms seems to correlate with surface properties, and increases with increasing pore size/surface area. This should have implications to the catalytic properties of porous γ-alumina.

  3. Polysynthetic twinned TiAl single crystals for high-temperature applications

    NASA Astrophysics Data System (ADS)

    Chen, Guang; Peng, Yingbo; Zheng, Gong; Qi, Zhixiang; Wang, Minzhi; Yu, Huichen; Dong, Chengli; Liu, C. T.

    2016-08-01

    TiAl alloys are lightweight, show decent corrosion resistance and have good mechanical properties at elevated temperatures, making them appealing for high-temperature applications. However, polysynthetic twinned TiAl single crystals fabricated by crystal-seeding methods face substantial challenges, and their service temperatures cannot be raised further. Here we report that Ti-45Al-8Nb single crystals with controlled lamellar orientations can be fabricated by directional solidification without the use of complex seeding methods. Samples with 0° lamellar orientation exhibit an average room temperature tensile ductility of 6.9% and a yield strength of 708 MPa, with a failure strength of 978 MPa due to the formation of extensive nanotwins during plastic deformation. At 900 °C yield strength remains high at 637 MPa, with 8.1% ductility and superior creep resistance. Thus, this TiAl single-crystal alloy could provide expanded opportunities for higher-temperature applications, such as in aeronautics and aerospace.

  4. Optimal microelectromechanical systems (MEMS) device for achieving high pyroelectric response of AlN

    NASA Astrophysics Data System (ADS)

    Kebede, Bemnnet; Coutu, Ronald A.; Starman, LaVern

    2014-03-01

    This paper discusses research being conducted on aluminum nitride (AlN) as a pyroelectric material for use in detecting applications. AlN is being investigated because of its high pyroelectric coefficient, thermal stability, and high Curie temperature. In order to determine suitability of the pyroelectric properties of AlN for use as a detector, testing of several devices was conducted. These devices were fabricated using microelectromechanical systems (MEMS) fabrication processes; the devices were also designed to allow for voltage and current measurements. The deposited AlN films used were 150 nm - 300 nm in thickness. Thin-films were used to rapidly increase the temperature response after the thermal stimulus was applied to the pyroelectric material. This is important because the pyroelectric effect is directly proportional to the rate of temperature change. The design used was a face-electrode bridge that provides thermal isolation which minimizes heat loss to the substrate, thereby increasing operation frequency of the pyroelectric device. A thermal stimulus was applied to the pyroelectric material and the response was measured across the electrodes. A thermal imaging camera was used to monitor the changes in temperature. Throughout the testing process, the annealing temperatures, type of layers, and thicknesses were also varied. These changes resulted in improved MEMS designs, which were fabricated to obtain an optimal design configuration for achieving a high pyroelectric response. A pyroelectric voltage response of 38.9 mVp-p was measured without filtering, 12.45 mVp-p was measured in the infrared (IR) region using a Si filter, and 6.38 mVp-p was measured in the short wavelength IR region using a long pass filter. The results showed that AlN's pyroelectric properties can be used in detecting applications.

  5. Twin Roll Casting of Al-Mg Alloy with High Added Impurity Content

    NASA Astrophysics Data System (ADS)

    Kumar, S.; Hari Babu, N.; Scamans, G. M.; Fan, Z.; O'Reilly, K. A. Q.

    2014-06-01

    The microstructural evolution during twin roll casting (TRC) and downstream processing of AA5754 Al alloy with high added impurity content have been investigated. Strip casts with a high impurity content resulted in coarse α-Al grains and complex secondary phases. The grain size and centerline segregation reduced significantly on the addition of Al-Ti-B grain refiner (GR). Coarse-dendrite arm spacing (DAS) "floating" grains are observed in the impure alloy (IA) with higher volume in the GR strips. Two-dimensional (2D) metallographic analysis of the as-cast strip suggests that secondary phases (Fe-bearing intermetallics and Mg2Si) are discrete and located at the α-Al cell/grain boundaries, while three-dimensional (3D) analysis of extracted particles revealed that they were intact, well interconnected, and located in interdendritic regions. Homogenizing heat treatment of the cast strip breaks the interconnective networks and modifies the secondary phases to a more equiaxed morphology. During rolling, the equiaxed secondary phases align along the rolling direction. X-ray diffraction (XRD) analysis suggests that α-Al(FeMn)Si and Mg2Si are the predominant secondary phases that are formed during casting and remain throughout the downstream processing of the GR-IA. The high-impurity sheet processed from TRC resulted in superior strength and ductility over the sheet processed from small book mold ingot casting. The current study has shown that the TRC process can tolerate higher impurity levels and produce formable sheets from the recycled aluminum for structural applications.

  6. High-Temperature Sliding Wear Testing of Cathodic Arc Physical Vapor Deposition AlTiN- and AlTiON-Coated Hot Work Tool Steels

    NASA Astrophysics Data System (ADS)

    Birol, Yucel; Isler, Duygu; Urgen, Mustafa

    2011-11-01

    Thin hard coatings provide the much needed protection for steel thixoforming tools that must resist wear at high temperatures. The wear resistance of AlTiN- and AlTiON-coated hot work tool steel was investigated at 1023 K (750 °C), measured to be the cavity surface temperature shortly after the steel slurry was forced into the thixoforming die. The wear tests were repeated in exactly the same fashion with uncoated tool steel samples to identify the impact of AlTiN and AlTiON coatings on the high-temperature wear performance of X32CrMoV33 tool steel. The nature, the thickness, and the adherence of the oxide scales impact the tribological behavior. The poor adherence and limited ductility of ferrous oxides promote the failure of the oxide scale impairing the resistance to wear of the hot work tool steel at elevated temperatures. The substantial softening in the X32CrMoV33 hot work tool steel is also critical in the wear volume loss it suffers. AlTiN and AlTiON coatings, on the other hand, form a stable and protective oxide surface layer at high temperatures and therefore provide an enhanced resistance to oxidation. The latter is relatively more resistant to oxidation and is thus the better of the two coatings tested in the present work.

  7. Sulfide stress cracking characteristics of high strength steels from the viewpoint of fracture mechanics

    SciTech Connect

    Asahi, H.; Ueno, M.

    1994-12-31

    Sulfide stress cracking (SSC) evaluation of high strength OCTG (oil country tubular goods) from the view point of environmental factors has been studied to some extent, but little research has been conducted from the view point of fracture mechanics. In the present study, SSC resistance was evaluated using threshold stress and K{sub 1ssc}. The same ranking of SSC resistance is obtained from both methods. However, SSC resistant steels show higher K{sub 1ssc} than conventional steels even if their respective threshold stresses are the same. For steel products bearing cracks and dents, SSC evaluation using both the threshold stress and the K{sub 1ssc} is suggested.

  8. High resolution electron microscopy study of a high Cu variant of Weldalite (tm) 049 and a high strength Al-Cu-Ag-Mg-Zr alloy

    NASA Technical Reports Server (NTRS)

    Herring, R. A.; Gayle, Frank W.; Pickens, Joseph R.

    1991-01-01

    Weldalite (trademark) 049 is an Al-Cu-Li-Ag-Mg alloy that is strengthened in artificially aged tempers primarily by very thin plate-like precipitates lying on the set of (111) matrix planes. This precipitate might be expected to be the T(sub 1) phase, Al2CuLi, which has been observed in Al-Cu-Li alloys. However, in several ways this precipitate is similar to the omega phase which also appears as the set of (111) planes plates and is found in Al-Cu-Ag-Mg alloys. The study was undertaken to identify the set of (111) planes precipitate or precipitates in Weldalite (trademark) 049 in the T8 (stretched and artificially aged) temper, and to determine whether T(sub 1), omega, or some other phase is primarily responsible for the high strength (i.e., 700 MPa tensile strength) in this Al-Cu-Li-Ag-Mg alloy.

  9. High-Performance Laser Peening for Effective Mitigation of Stress Corrosion Cracking

    SciTech Connect

    Hackel, L; Hao-Lin, C; Wong, F; Hill, M

    2002-10-02

    Stress corrosion cracking (SCC) in the Yucca Mountain waste package closure welds is believed to be the greatest threat to long-term containment. Use of stress mitigation to eliminate tensile stresses resulting from welding can prevent SCC. A laser technology with sufficient average power to achieve high throughput has been developed and commercially deployed with high peak power and sufficiently high average power to be an effective laser peening system. An appropriately applied version of this process could be applied to eliminate SCC in the waste package closure welds.

  10. Synchronized Stress-strain Measurements in Dynamic Loading at High Pressure using D-DIA

    SciTech Connect

    L Li; D Weidner

    2011-12-31

    A new data collection protocol for forced oscillation experiments using a multianvil high pressure device is reported. We derive the stress of the sample at high pressure and temperature from synchrotron x-ray diffraction that is synchronized with sample strain measurements from x-ray radiographs. This method yields stress directly from the sample rather than a stress proxy. Furthermore, the diffraction pattern yields useful information concerning time evolution of structurally related phenomena. Here we illustrate some of these possibilities with high pressure experimental data.

  11. Mean stress effects on high-cycle fatigue of Alloy 718

    SciTech Connect

    Korth, G E

    1980-07-01

    This report covers an investigation of the effects of tensile mean stress on the high-cycle fatigue properties of Alloy 718. Three test temperatures (24, 427, and 649{degree}C) were employed, and there were tests in both strain and load control. Results were compared with three different models: linear Modified-Goodman, Peterson cubic, and stress-strain parameter. The linear Modified-Goodman model gave good correlation with actual test data for low and moderate mean stress values, but the stress-strain parameter showed excellent correlation over the entire range of possible mean stresses and therefore is recommended for predicting mean stress effects of Alloy 718. 13 refs., 12 figs.

  12. Time exposure studies on stress corrosion cracking of aluminum 2014-T6, 2219-T87, 2014-T651, 7075-T651, and titanium 6Al-4V

    NASA Technical Reports Server (NTRS)

    Terrell, J.

    1973-01-01

    The effect of a constant applied stress in crack initiation of aluminum 2014-T6, 2219-T87, 2014-T651, 7075-T651 and titanium 6Al-4V has been investigated. Aluminum c-ring specimens (1-inch diameter) and u-band titanium samples were exposed continuously to a 3.5% NaCl solution (pH 7) and organic fluids of ethyl, methyl, and iso-propyl alcohol (reagent purity), and demineralized distilled water. Corrosive action was observed to begin during the first and second day of constant exposure as evidenced by accumulation of hydrogen bubbles on the surface of stressed aluminum samples. However, titanium stressed specimens showed no reactions to its environment. Results of this investigation seems to suggest that aluminum 2014-T6, aluminum 7075-T651 and aluminum 2014-T651 are susceptible to stress corrosion cracking in chloride solution (NaCl), while aluminum 2219-T87 seem to resist stress corrosion cracking in sodium chloride at three levels of stress (25%, 50%, and 75% Y.S.). In organic fluids of methyl, ethyl, and iso-propyl alcohol, 2014-T6 and 7075-T651 did not fail by SCC; but 2014-T651 was susceptible to SCC in methly alcohol, but resistant in ethyl alcohol, iso-propyl alcohol and demineralized distilled water.

  13. Neutron diffraction analysis of residual strain/stress distribution in the vicinity of high strength welds

    NASA Astrophysics Data System (ADS)

    Mráz, L.; Karlsson, L.; Hamák, I.; Vrána, M.; Mikula, P.

    2010-06-01

    Residual stresses resulting from non homogeneous heat distribution during welding process belong to most significant factor influencing behavior of welded structures. These stresses are responsible for defect occurrence during welding and they are also responsible for crack initiation and propagation at the either static or dynamic load. The significant effect of weld metal chemical composition as well as the effect of fatigue load and local plastic deformation on residual stress distribution and fatigue life have been recognized for high strength steels welds. The changes in residual stress distribution have then positive effect on cold cracking behavior and also on fatigue properties of the welds [1-3]. Several experimental methods, both destructive and non-destructive, such as hole drilling method, X-ray diffraction, neutron diffraction and others, have been used to examine residual stress distribution in all three significant orientations in the vicinity of the welds. The present contribution summarizes the results of neutron diffraction measurements of residual stress distribution in the vicinity of single-pass high-strength-steel welds having different chemical composition as well as the influence of fatigue load and local plastic deformation. It has been observed that the chemical composition of the weld metal has a significant influence on the stress distribution around the weld. Similarly, by aplying both cyclic load or pre-stress load on the specimens, stress relaxation was observed even in the region of approximately 40 mm far from the weld toe.

  14. Boechera Species Exhibit Species-Specific Responses to Combined Heat and High Light Stress

    PubMed Central

    Gallas, Genna; Waters, Elizabeth R.

    2015-01-01

    As sessile organisms, plants must be able to complete their life cycle in place and therefore tolerance to abiotic stress has had a major role in shaping biogeographical patterns. However, much of what we know about plant tolerance to abiotic stresses is based on studies of just a few plant species, most notably the model species Arabidopsis thaliana. In this study we examine natural variation in the stress responses of five diverse Boechera (Brassicaceae) species. Boechera plants were exposed to basal and acquired combined heat and high light stress. Plant response to these stresses was evaluated based on chlorophyll fluorescence measurements, induction of leaf chlorosis, and gene expression. Many of the Boechera species were more tolerant to heat and high light stress than A. thaliana. Gene expression data indicates that two important marker genes for stress responses: APX2 (Ascorbate peroxidase 2) and HsfA2 (Heat shock transcription factor A2) have distinct species-specific expression patterns. The findings of species-specific responses and tolerance to stress indicate that stress pathways are evolutionarily labile even among closely related species. PMID:26030823

  15. Combat high or traumatic stress: violent offending is associated with appetitive aggression but not with symptoms of traumatic stress

    PubMed Central

    Köbach, Anke; Schaal, Susanne; Elbert, Thomas

    2015-01-01

    Former members of armed groups in eastern DR Congo had typically witnessed, experienced, and perpetrated extreme forms of violence. Enhanced trauma-related symptoms had been shown in prior research. But also lashing out in self-defense is a familiar response to threat defined as reactive aggression. Another potential response is appetitive aggression, in which the perpetration of excessive violence is perceived as pleasurable (combat high). What roles do these forms of aggressive behavior play in modern warfare and how are they related to posttraumatic stress symptoms? To answer the question, we sought to determine predictors for appetitive aggressive and trauma-related mental illness, and investigated the frequency of psychopathological symptoms for high- and low-intensity conflict demobilization settings. To this end, we interviewed 213 former members of (para)military groups in the eastern Democratic Republic of Congo in regard to their combat exposure, posttraumatic stress, appetitive aggression, depression, suicidality, and drug dependence. Random forest regression embedded in a conditional inference framework revealed that perpetrated violent acts are not necessarily stressful. In fact, the experience of violent acts that typically implicated salient cues of hunting (e.g., blood, suffering of the victim, etc.) had the strongest association with an appetite for aggression. Furthermore, the number of lifetime perpetrated violent acts was the most important predictor of appetitive aggression. However, the number of perpetrated violent acts did not significantly affect the posttraumatic stress. Greater intensity of conflict was associated with more severe posttraumatic stress symptoms and depression. Psychotherapeutic interventions that address appetitive aggression in addition to trauma-related mental illness, including drug dependence, therefore seem indispensible for a successful reintegration of those who fought in the current civil wars. PMID:25709586

  16. Abnormal positive bias stress instability of In-Ga-Zn-O thin-film transistors with low-temperature Al2O3 gate dielectric

    NASA Astrophysics Data System (ADS)

    Chang, Yu-Hong; Yu, Ming-Jiue; Lin, Ruei-Ping; Hsu, Chih-Pin; Hou, Tuo-Hung

    2016-01-01

    Low-temperature atomic layer deposition (ALD) was employed to deposit Al2O3 as a gate dielectric in amorphous In-Ga-Zn-O thin-film transistors fabricated at temperatures below 120 °C. The devices exhibited a negligible threshold voltage shift (ΔVT) during negative bias stress, but a more pronounced ΔVT under positive bias stress with a characteristic turnaround behavior from a positive ΔVT to a negative ΔVT. This abnormal positive bias instability is explained using a two-process model, including both electron trapping and hydrogen release and migration. Electron trapping induces the initial positive ΔVT, which can be fitted using the stretched exponential function. The breakage of residual AlO-H bonds in low-temperature ALD Al2O3 is triggered by the energetic channel electrons. The hydrogen atoms then diffuse toward the In-Ga-Zn-O channel and induce the negative ΔVT through electron doping with power-law time dependence. A rapid partial recovery of the negative ΔVT after stress is also observed during relaxation.

  17. Petrogenesis of the Northwest Africa 4898 high-Al mare basalt

    NASA Astrophysics Data System (ADS)

    Li, Shaolin; Hsu, Weibiao; Guan, Yunbin; Wang, Linyan; Wang, Ying

    2016-07-01

    Northwest Africa (NWA) 4898 is the only low-Ti, high-Al basaltic lunar meteorite yet recognized. It predominantly consists of pyroxene (53.8 vol%) and plagioclase (38.6 vol%). Pyroxene has a wide range of compositions (En12-62Fs25-62Wo11-36), which display a continuous trend from Mg-rich cores toward Ca-rich mantles and then to Fe-rich rims. Plagioclase has relatively restricted compositions (An87-96Or0-1Ab4-13), and was transformed to maskelynite. The REE zoning of all silicate minerals was not significantly modified by shock metamorphism and weathering. Relatively large (up to 1 mm) olivine phenocrysts have homogenous inner parts with Fo ~74 and sharply decrease to 64 within the thin out rims (~30 μm in width). Four types of inclusions with a variety of textures and modal mineralogy were identified in olivine phenocrysts. The contrasting morphologies of these inclusions and the chemical zoning of olivine phenocrysts suggest NWA 4898 underwent at least two stages of crystallization. The aluminous chromite in NWA 4898 reveals that its high alumina character was inherited from the parental magma, rather than by fractional crystallization. The mineral chemistry and major element compositions of NWA 4898 are different from those of 12038 and Luna 16 basalts, but resemble those of Apollo 14 high-Al basalts. However, the trace element compositions demonstrate that NWA 4898 and Apollo 14 high-Al basalts could not have been derived from the same mantle source. REE compositions of its parental magma indicate that NWA 4898 probably originated from a unique depleted mantle source that has not been sampled yet. Unlike Apollo 14 high-Al basalts, which assimilated KREEPy materials during their formation, NWA 4898 could have formed by closed-system fractional crystallization.

  18. Petrogenesis of the Northwest Africa 4898 high-Al mare basalt

    NASA Astrophysics Data System (ADS)

    Li, Shaolin; Hsu, Weibiao; Guan, Yunbin; Wang, Linyan; Wang, Ying

    2016-05-01

    Northwest Africa (NWA) 4898 is the only low-Ti, high-Al basaltic lunar meteorite yet recognized. It predominantly consists of pyroxene (53.8 vol%) and plagioclase (38.6 vol%). Pyroxene has a wide range of compositions (En12-62Fs25-62Wo11-36), which display a continuous trend from Mg-rich cores toward Ca-rich mantles and then to Fe-rich rims. Plagioclase has relatively restricted compositions (An87-96Or0-1Ab4-13), and was transformed to maskelynite. The REE zoning of all silicate minerals was not significantly modified by shock metamorphism and weathering. Relatively large (up to 1 mm) olivine phenocrysts have homogenous inner parts with Fo ~74 and sharply decrease to 64 within the thin out rims (~30 μm in width). Four types of inclusions with a variety of textures and modal mineralogy were identified in olivine phenocrysts. The contrasting morphologies of these inclusions and the chemical zoning of olivine phenocrysts suggest NWA 4898 underwent at least two stages of crystallization. The aluminous chromite in NWA 4898 reveals that its high alumina character was inherited from the parental magma, rather than by fractional crystallization. The mineral chemistry and major element compositions of NWA 4898 are different from those of 12038 and Luna 16 basalts, but resemble those of Apollo 14 high-Al basalts. However, the trace element compositions demonstrate that NWA 4898 and Apollo 14 high-Al basalts could not have been derived from the same mantle source. REE compositions of its parental magma indicate that NWA 4898 probably originated from a unique depleted mantle source that has not been sampled yet. Unlike Apollo 14 high-Al basalts, which assimilated KREEPy materials during their formation, NWA 4898 could have formed by closed-system fractional crystallization.

  19. Improved austenitic stainless steel for high temperature applications. [Improved stress-rupture properties

    DOEpatents

    Not Available

    This invention describes a composition for an austenitic stainless steel which has been found to exhibit improved high temperature stress rupture properties. The composition of this alloy is about (in wt. %): 12.5 to 14.5 Cr; 14.5 to 16.5 Ni; 1.5 to 2.5 Mo; 1.5 to 2.5 Mn; 0.1 to 0.4 Ti; 0.02 to 0.08 C; 0.5 to 1.0 Si; 0.01 maximum, N; 0.02 to 0.08 P; 0.002 to 0.008 B; 0.004-0.010 S; 0.02-0.05 Nb; .01-.05 V; 0.005-0.02 Ta; 0.02-0.05 Al; 0.01-0.04 Cu; 0.02-0.05 Co; .03 maximum, As; 0.01 maximum, 0; 0.01 maximum, Zr; and with the balance of the alloy being essentially iron. The carbon content of the alloy is adjusted such that wt. % Ti/(wt. % C+wt. % N) is between 4 and 6, and most preferably about 5. In addition the sum of the wt. % P + wt. % B + wt. % S is at least 0.03 wt. %. This alloy is believed to be particularly well suited for use as fast breeder reactor fuel element cladding.

  20. Investigation of trap states under Schottky contact in GaN/AlGaN/AlN/GaN high electron mobility transistors

    SciTech Connect

    Ma, Xiao-Hua E-mail: yhao@xidian.edu.cn; Chen, Wei-Wei; Hou, Bin; Zhu, Jie-Jie; Zhang, Kai; Zhang, Jin-Cheng; Zheng, Xue-Feng; Hao, Yue E-mail: yhao@xidian.edu.cn

    2014-03-03

    Forward gate-bias stress experiments are performed to investigate the variation of trap states under Schottky contact in GaN-based high electron mobility transistors. Traps with activation energy E{sub T} ranging from 0.22 eV to 0.31 eV are detected at the gate-semiconductor interface by dynamic conductance technique. Trap density decreases prominently after stressing, particularly for traps with E{sub T} > 0.24 eV. X-ray photoelectron spectroscopy measurements reveal a weaker Ga-O peak on the stressed semiconductor surface. It is postulated that oxygen is stripped by Ni to form NiO upon electrical stress, contributing to the decrease in O{sub N} donor sates under the gate contact.

  1. Impact ionization in N-polar AlGaN/GaN high electron mobility transistors

    SciTech Connect

    Killat, N. E-mail: Martin.Kuball@bristol.ac.uk; Uren, M. J.; Kuball, M. E-mail: Martin.Kuball@bristol.ac.uk; Keller, S.; Kolluri, S.; Mishra, U. K.

    2014-08-11

    The existence of impact ionization as one of the open questions for GaN device reliability was studied in N-polar AlGaN/GaN high electron mobility transistors. Electroluminescence (EL) imaging and spectroscopy from underneath the device gate contact revealed the presence of hot electrons in excess of the GaN bandgap energy even at moderate on-state bias conditions, enabling impact ionization with hole currents up to several hundreds of pA/mm. The detection of high energy luminescence from hot electrons demonstrates that EL analysis is a highly sensitive tool to study degradation mechanisms in GaN devices.

  2. AlN/3C-SiC composite plate enabling high-frequency and high-Q micromechanical resonators.

    PubMed

    Lin, Chih-Ming; Chen, Yung-Yu; Felmetsger, Valery V; Senesky, Debbie G; Pisano, Albert P

    2012-05-22

    An AlN/3C-SiC composite layer enables the third-order quasi-symmetric (QS(3)) Lamb wave mode with a high quality factor (Q) characteristic and an ultra-high phase velocity up to 32395 ms(-1). A Lamb wave resonator utilizing the QS(3) mode exhibits a low motional impedance of 91 Ω and a high Q of 5510 at a series resonance frequency (f(s)) of 2.92 GHz, resulting in the highest f(s)·Q product of 1.61 × 10(13) Hz among the suspended piezoelectric thin film resonators reported to date. PMID:22495881

  3. Enthalpies of formation of CaAl4O7 and CaAl12O19 (hibonite) by high temperature, alkali borate solution calorimetry

    NASA Technical Reports Server (NTRS)

    Geiger, C. A.; Kleppa, O. J.; Grossman, L.; Mysen, B. O.; Lattimer, J. M.

    1988-01-01

    Enthalpies of formation were determined for two calcium aluminate phases, CaAl4O7 and CaAl12O19, using high-temperature alkali borate solution calorimetry. The aluminates were synthesized by multiple-cycle heating and grinding stoichiometric mixtures of CaCO3 and Al2O3, and the products were characteized by X-ray diffraction and SEM microbeam analysis. The data on impurities (CaAl4O7 was found to be about 89.00 percent pure by weight and the CaAl12O19 samples about 91.48 percent pure) were used to correct the heat of solution values of the synthetic products. The enthalpies of formation, at 1063 K, from oxides, were found to be equal to -(25.6 + or - 4.7) kJ/g.f.w. for CaAl4O7 and -(33.0 + or - 9.7) kJ/g.f.w. for CaAl12O19; the respective standard enthalpies of formation from elements, at 298 K, were estimated to be -4007 + or - 5.2 kJ/g.f.w. and -10,722 + or - 12 kJ/g.f.w.

  4. Low-ohmic-contact-resistance V-based electrode for n-type AlGaN with high AlN molar fraction

    NASA Astrophysics Data System (ADS)

    Mori, Kazuki; Takeda, Kunihiro; Kusafuka, Toshiki; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu; Amano, Hiroshi

    2016-05-01

    We investigated a V-based electrode for the realization of low ohmic-contact resistivity in n-type AlGaN with a high AlN molar fraction characterized by the circular transmission line model. The contact resistivity of n-type Al0.62Ga0.38N prepared using the V/Al/Ni/Au electrode reached 1.13 × 10‑6 Ω cm2. Using this electrode, we also demonstrated the fabrication of UV light-emitting diodes (LEDs) with an emission wavelength of approximately 300 nm. An operating voltage of LED prepared using a V/Al/Ni/Au electrode was 1.6 V lower at 100 mA current injection than that prepared using a Ti/Al/Ti/Au electrode, with a specific contact resistance of approximately 2.36 × 10‑4 Ω cm2 for n-type Al0.62Ga0.38N.

  5. The psychological effects of Intifada Al Aqsa: acute stress disorder and distress in Palestinian-Israeli students.

    PubMed

    Musallam, Naiera; Ginzburg, Karni; Lev-Shalem, Liat; Solomon, Zahava

    2005-01-01

    The study assesses the effects of exposure to nationality-related and personal stressful events, threat appraisal and coping strategies on level of distress of Palestinian Israeli students. One hundred forty-eight Palestinian Israeli students filled out a battery of questionnaires that tapped their exposure to stressful life events, terrorism and political related violence, their primary and secondary appraisals, and coping strategies. Level of distress was evaluated by (1) acute stress disorder, and (2) psychiatric symptomatology. Results reveal relatively low exposure to terrorism-related traumatic events, yet considerable exposure (35.8%) to nationality-related stressful events during the last two years. Twenty-five percent of the students suffered from acute stress disorder, and their levels of psychiatric symptomatology exceeded norms for the general population. Primary appraisal processes and emotion-focused coping strategies made unique contribution to the respondents' level of (1) acute stress disorder and (2) psychiatric symptomatology. The implications of these findings are discussed. PMID:16342606

  6. Combined effects of weld-induced residual stresses and flaws on the fracture strength of Ti-5Al-2.5Sn

    NASA Technical Reports Server (NTRS)

    Hall, L. R.

    1973-01-01

    The combined effects of weld-induced residual stresses and flaws on fracture strength were experimentally evaluated by testing Ti-5Al-2.5Sn surface flawed specimens at -320F (-195C) in liquid nitrogen. Flaws were located in weld metal with crack planes either parallel to or perpendicular to gas tungsten arc weld centerlines, and in base metal with the crack plane perpendicular to the rolling direction. Tests were conducted using two different flaw sizes to effect fracture stresses at two different levels including one level either at or near, and one level well below the tensile yield strength. Three different residual stress levels were generated, measured, and tested. Results were evaluated using modified linear elastic fracture mechanics theory.

  7. Evaluation of Wheat Chromosome Translocation Lines for High Temperature Stress Tolerance at Grain Filling Stage

    PubMed Central

    Pradhan, Gautam Prasad; Prasad, P. V. Vara

    2015-01-01

    High temperature (HT, heat) stress is detrimental to wheat (Triticum aestivum L.) production. Wild relatives of bread wheat may offer sources of HT stress tolerance genes because they grow in stressed habitats. Wheat chromosome translocation lines, produced by introgressing small segments of chromosome from wild relatives to bread wheat, were evaluated for tolerance to HT stress during the grain filling stage. Sixteen translocation lines and four wheat cultivars were grown at optimum temperature (OT) of 22/14°C (day/night). Ten days after anthesis, half of the plants were exposed to HT stress of 34/26°C for 16 d, and other half remained at OT. Results showed that HT stress decreased grain yield by 43% compared with OT. Decrease in individual grain weight (by 44%) was the main reason for yield decline at HT. High temperature stress had adverse effects on leaf chlorophyll content and Fv/Fm; and a significant decrease in Fv/Fm was associated with a decline in individual grain weight. Based on the heat response (heat susceptibility indices, HSIs) of physiological and yield traits to each other and to yield HSI, TA5594, TA5617, and TA5088 were highly tolerant and TA5637 and TA5640 were highly susceptible to HT stress. Our results suggest that change in Fv/Fm is a highly useful trait in screening genotypes for HT stress tolerance. This study showed that there is genetic variability among wheat chromosome translocation lines for HT stress tolerance at the grain filling stage and we suggest further screening of a larger set of translocation lines. PMID:25719199

  8. High-brightness AlGaInP light-emitting diodes using surface texturing

    NASA Astrophysics Data System (ADS)

    Linder, Norbert; Kugler, Siegmar; Stauss, Peter; Streubel, Klaus P.; Wirth, Ralph; Zull, Heribert

    2001-05-01

    There is a large number of new applications in lighting and display technology where high-brightness AlGaInP-LEDs can provide cost-efficient solutions for the red to yellow color range. Osram Opto Semiconductors has developed a new generation of MOVPE-grown AlInGaP-LEDs to meet these demands. Our structures use optimized epitaxial layer design, improved contact geometry and a new type of surface texturing. Based on this technology we achieve luminous efficiencies of more than 30 lm/W and wallplug efficiencies exceeding 10% of LEDs on absorbing GaAs substrates. The epitaxial structure does not require the growth of extremely thick window layer and standard processes are used for the chip fabrication. This allows for high production yields and cost-efficient production.

  9. Magnetic anisotropy and high frequency permeability of multilayered nanocomposite FeAlO thin films

    SciTech Connect

    Ma, Y. G.; Liu, Y.; Tan, C. Y.; Liu, Z. W.; Ong, C. K.

    2006-09-01

    A cool-down step deposition process (multistep deposition with cool-down interval) was used to grow nanocomposite FeAlO thin films of various thicknesses up to 440 nm by magnetron sputtering at a substrate temperature of 15 deg. C. The effect of the number of cool-down steps on the soft magnetic properties and high frequency characteristics of the nanocomposite FeAlO films were investigated. The deposition process was proved very effective in improving the soft magnetic properties and high frequency characteristics of the films. The eight-layered samples, fabricated by eight cool-down step deposition process, of thicknesses of 220 and 440 nm had obvious in-plane uniaxial anisotropies while the single-layered films were nearly isotropic. The resulting real permeability value of the eight-layered films was larger than 300 for the 220 nm film and between 200 and 300 for the 440 nm film.

  10. Very high channel conductivity in low-defect AlN/GaN high electron mobility transistor structures

    SciTech Connect

    Dabiran, A. M.; Wowchak, A. M.; Osinsky, A.; Xie, J.; Hertog, B.; Cui, B.; Chow, P. P.; Look, D. C.

    2008-08-25

    Low defect AlN/GaN high electron mobility transistor (HEMT) structures, with very high values of electron mobility (>1800 cm{sup 2}/V s) and sheet charge density (>3x10{sup 13} cm{sup -2}), were grown by rf plasma-assisted molecular beam epitaxy (MBE) on sapphire and SiC, resulting in sheet resistivity values down to {approx}100 {omega}/{open_square} at room temperature. Fabricated 1.2 {mu}m gate devices showed excellent current-voltage characteristics, including a zero gate saturation current density of {approx}1.3 A/mm and a peak transconductance of {approx}260 mS/mm. Here, an all MBE growth of optimized AlN/GaN HEMT structures plus the results of thin-film characterizations and device measurements are presented.

  11. Post-CMOS compatible high-throughput fabrication of AlN-based piezoelectric microcantilevers

    NASA Astrophysics Data System (ADS)

    Pérez-Campos, A.; Iriarte, G. F.; Hernando-Garcia, J.; Calle, F.

    2015-02-01

    A post-complementary metal oxide semiconductor (CMOS) compatible microfabrication process of piezoelectric cantilevers has been developed. The fabrication process is suitable for standard silicon technology and provides low-cost and high-throughput manufacturing. This work reports design, fabrication and characterization of piezoelectric cantilevers based on aluminum nitride (AlN) thin films synthesized at room temperature. The proposed microcantilever system is a sandwich structure composed of chromium (Cr) electrodes and a sputtered AlN film. The key issue for cantilever fabrication is the growth at room temperature of the AlN layer by reactive sputtering, making possible the innovative compatibility of piezoelectric MEMS devices with CMOS circuits already processed. AlN and Cr have been etched by inductively coupled plasma (ICP) dry etching using a BCl3-Cl2-Ar plasma chemistry. As part of the novelty of the post-CMOS micromachining process presented here, a silicon Si (1 0 0) wafer has been used as substrate as well as the sacrificial layer used to release the microcantilevers. In order to achieve this, the Si surface underneath the structure has been wet etched using an HNA (hydrofluoric acid + nitric acid + acetic acid) based solution. X-ray diffraction (XRD) characterization indicated the high crystalline quality of the AlN film. An atomic force microscope (AFM) has been used to determine the Cr electrode surface roughness. The morphology of the fabricated devices has been studied by scanning electron microscope (SEM). The cantilevers have been piezoelectrically actuated and their out-of-plane vibration modes were detected by vibrometry.

  12. Deformation of polysynthetically twinned (PST) TiAl crystals at high strain rate and high temperature

    SciTech Connect

    Jin, Z.; Gray, G.T. III; Yamaguchi, Masaharu

    1997-12-31

    Deformation microstructures in a 435{degree} <{bar 3}21> oriented polysynthetically twinned (PST) TiAl crystal deformed in compression at 3000 s{sup {minus}1} and 800 C was studied. Deformation of this PST crystal is characterized as follows: (1) Deformation of domains [III] and [IV] is dominated by 1/6[11{bar 2}](111) parallel twinning (twinning parallel to lamellar interfaces). Ordinary dislocations observed in these domains are found to be a complementary deformation mode. (2) Deformation of domains [II], [V] and [VI] is controlled by ordinary dislocation slip. Complementary deformation modes in these domains are ordinary dislocation slip, superdislocation slip and cross-twinning. (3) Domain [I] is not deformed after the specimen deforms up to {approximately}7% strain.

  13. Effects of high temperature stress at different development stages on soybean isoflavone and tocopherol concentrations.

    PubMed

    Chennupati, Pratyusha; Seguin, Philippe; Liu, Wucheng

    2011-12-28

    Soybean contains a range of compounds with putative health benefits including isoflavones and tocopherols. A study was conducted to determine the effects on these compounds of high temperature stress imposed at specific development stages [i.e., none, pre-emergence, vegetative, early reproductive (R1-4), late-reproductive (R5-8), or all stages]. Two cultivars (AC Proteina and OAC Champion) were grown in growth chambers set at contrasting temperatures [i.e., stress conditions of 33/25 °C (day/night temperature) and control conditions of 23/15 °C] in order to generate these treatments. Isoflavone and tocopherol concentrations in mature seeds were determined using high-performance liquid chromatography. In both cultivars isoflavone response was greatest when stress occurred during the R5-8 stages and during all development stages, these treatments reducing total isoflavone concentration by an average of 85% compared to the control. Stress imposed at other stages also affected isoflavone concentration although the response was smaller. For example, stress during the vegetative stages reduced total isoflavones by 33% in OAC Champion. Stress imposed pre-emergence had an opposite effect increasing daidzein concentration by 24% in AC Proteina. Tocopherol concentrations were affected the most when stress was imposed during all stages of development, followed by stress restricted to stages R5-8; response to stress during other stages was limited. The specific response of tocopherols differed, α-tocopherol being increased by high temperature by as much as 752%, the reverse being observed for δ-tocopherol and γ-tocopherol. The present study demonstrates that while isoflavone and tocopherol concentrations in soybeans are affected the most by stress occurring during seed formation, concentrations can also be affected by stress occurring at other stages including stages as early as pre-emergence. PMID:22098462

  14. Fabrication of Al{sub 2}O{sub 3}-20 vol.% Al nanocomposite powders using high energy milling and their sinterability

    SciTech Connect

    Zawrah, M.F.; Abdel-kader, H.; Elbaly, N.E.

    2012-03-15

    Highlights: Black-Right-Pointing-Pointer Al{sub 2}O{sub 3}/Al nanocomposite powders were prepared via high energy ball milling. After 20 h milling, the size of Al{sub 2}O{sub 3}-20 vol.% Al nanocomposite particles was in the range of 23-29 nm. A uniform distribution of nanosized Al reinforcement throughout the Al{sub 2}O{sub 3} matrix, coating the particles was successfully obtained. Black-Right-Pointing-Pointer There was no any sign of phase changes during the milling. A competition between the cold welding mechanism and the fracturing mechanism were found during milling and finally the above two mechanisms reached an equilibrium. Black-Right-Pointing-Pointer The highest value of relative density was obtained for the sintered bodies at 1500 Degree-Sign C. Black-Right-Pointing-Pointer The harness of the sintered composite was decreased while the fracture toughness was improved after addition Al into alumina. -- Abstract: In this study, alumina-based matrix nanocomposite powders reinforced with Al particles were fabricated and investigated. The sinterability of the prepared nanocomposite powder at different firing temperature was also conducted. Their mechanical properties in terms of hardness and toughness were tested. Alumina and aluminum powder mixtures were milled in a planetary ball mill for various times up to 30 h in order to produce Al{sub 2}O{sub 3}-20% Al nanocomposite. The phase composition, morphological and microstructural changes during mechanical milling of the nanocomposite particles were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM) techniques, respectively. The crystallite size and internal strain were evaluated by XRD patterns using Scherrer methods. A uniform distribution of the Al reinforcement in the Al{sub 2}O{sub 3} matrix was successfully obtained after milling the powders. The results revealed that there was no any sign of phase changes during the milling. The crystal

  15. New Al0.25Ga0.75N/GaN high electron mobility transistor with partial etched AlGaN layer

    NASA Astrophysics Data System (ADS)

    Yuan, Song; Duan, Baoxing; Yuan, Xiaoning; Cao, Zhen; Guo, Haijun; Yang, Yintang

    2016-05-01

    In this letter, a new Al0.25Ga0.75N/GaN high electron mobility transistor (HEMT) with the AlGaN layer is partial etched is reported for the first time. The two-dimensional electron gas (2DEG) density in the HEMTs is changed by partially etching the AlGaN layer. A new electric field peak is introduced along the interface between the AlGaN layer and the GaN buffer by the electric field modulation effect. The high electric field near the gate in the proposed Al0.25Ga0.75N/GaN HEMT is effectively decreased, which makes the surface electric field more uniform. Compared with the conventional structure, the breakdown voltage can be improved by 58% for the proposed Al0.25Ga0.75N/GaN HEMT and the current collapse can be reduced resulting from the more uniform surface electric field.

  16. Structure and energetics of high index Fe, Al, Cu and Ni surfaces using equivalent crystal theory

    NASA Technical Reports Server (NTRS)

    Rodriguez, Agustin M.; Bozzolo, Guillermo; Ferrante, John

    1993-01-01

    Equivalent crystal theory (ECT) is applied to the study of multilayer relaxations and surface energies of high-index faces of Fe, Al, Ni, and Cu. Changes in interplanar spacing as well as registry of planes close to the surface and the ensuing surface energies changes are discussed in reference to available experimental data and other theoretical calculations. Since ECT is a semiempirical method, the dependence of the results on the variation of the input used was investigated.

  17. High Frequency Properties of Ferrite/Fe-Si-Al Alloy Soft Magnetic Composites

    NASA Astrophysics Data System (ADS)

    Stergiou, Charalampos A.; Zaspalis, Vassilios

    The inclusion of Fe-Si-Al alloy particles in NiCuZn ferrite matrix was investigated with regard to the high frequency electromagnetic properties (complex permeability and permittivity). The resultant composites of relatively low density exhibit a shift of the permeability spectra to higher frequencies and an increase of dielectric polarization, which finally favour the electromagnetic wave attenuation at microwave frequencies. Thus, wider band return loss peaks are attained at frequencies above 6 GHz by thinner composite materials.

  18. Step buffer layer of Al0.25Ga0.75N/Al0.08Ga0.92N on P-InAlN gate normally-off high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Shrestha, Niraj M.; Li, Yiming; Chang, E. Y.

    2016-07-01

    Normally-off AlGaN/GaN high electron mobility transistors (HEMTs) are indispensable devices for power electronics as they can greatly simplify circuit designs in a cost-effective way. In this work, the electrical characteristics of p-type InAlN gate normally-off AlGaN/GaN HEMTs with a step buffer layer of Al0.25Ga0.75N/Al0.1Ga0.9N is studied numerically. Our device simulation shows that a p-InAlN gate with a step buffer layer allows the transistor to possess normally-off behavior with high drain current and high breakdown voltage simultaneously. The gate modulation by the p-InAlN gate and the induced holes appearing beneath the gate at the GaN/Al0.25Ga0.75N interface is because a hole appearing in the p-InAlN layer can effectively vary the threshold voltage positively. The estimated threshold voltage of the normally-off HEMTs explored is 2.5 V at a drain bias of 25 V, which is 220% higher than the conventional p-AlGaN normally-off AlGaN/GaN gate injection transistor (GIT). Concurrently, the maximum current density of the explored HEMT at a drain bias of 10 V slightly decreases by about 7% (from 240 to 223 mA mm‑1). At a drain bias of 15 V, the current density reached 263 mA mm‑1. The explored structure is promising owing to tunable positive threshold voltage and the maintenance of similar current density; notably, its breakdown voltage significantly increases by 36% (from 800 V, GIT, to 1086 V). The engineering findings of this study indicate that novel p-InAlN for both the gate and the step buffer layer can feature a high threshold voltage, large current density and high operating voltage for advanced AlGaN/GaN HEMT devices.

  19. Observations of Glide and Decomposition of a<101> Dislocations at High Temperatures in Ni-Al Single Crystals Deformed along the Hard Orientation

    NASA Technical Reports Server (NTRS)

    Srinivasan, R.; Daw, M. S.; Noebe, R. D.; Mills, M. J.

    2003-01-01

    Ni-44at.% Al and Ni-50at.% single crystals were tested in compression in the hard (001) orientations. The dislocation processes and deformation behavior were studied as a function of temperature, strain and strain rate. A slip transition in NiAl occurs from alpha(111) slip to non-alphaaaaaaaaaaa9111) slip at intermediate temperatures. In Ni-50at.% Al single crystal, only alpha(010) dislocations are observed above the slip transition temperature. In contrast, alpha(101)(101) glide has been observed to control deformation beyond the slip transition temperature in Ni-44at.%Al. alpha(101) dislocations are observed primarily along both (111) directions in the glide plane. High-resolution transmission electron microscopy observations show that the core of the alpha(101) dislocations along these directions is decomposed into two alpha(010) dislocations, separated by a distance of approximately 2nm. The temperature window of stability for these alpha(101) dislocations depends upon the strain rate. At a strain rate of 1.4 x 10(exp -4)/s, lpha(101) dislocations are observed between 800 and 1000K. Complete decomposition of a alpha(101) dislocations into alpha(010) dislocations occurs beyond 1000K, leading to alpha(010) climb as the deformation mode at higher temperature. At lower strain rates, decomposition of a alpha(101) dislocations has been observed to occur along the edge orientation at temperatures below 1000K. Embedded-atom method calculations and experimental results indicate that alpha(101) dislocation have a large Peieris stress at low temperature. Based on the present microstructural observations and a survey of the literature with respect to vacancy content and diffusion in NiAl, a model is proposed for alpha(101)(101) glide in Ni-44at.%Al, and for the observed yield strength versus temperature behavior of Ni-Al alloys at intermediate and high temperatures.

  20. Stress and Strain Distributions during Machining of Ti-6Al-4V at Ambient and Cryogenic Temperatures

    NASA Astrophysics Data System (ADS)

    Rahman, Md. Fahim

    Dry and liquid nitrogen pre-cooled Ti-6Al-4V samples were machined at a cutting speed of 43.2 m/min and at low (0.1 mm/rev) to high (0.4 mm/rev) feed rates for understanding the effects of temperature and strain rate on chip microstructures. During cryogenic machining, it was observed that between feed rates of 0.10 and 0.30 mm/rev, a 25% pressure reduction on tool occurred. Smaller number of chips and low tool/chip contact time and temperature were observed (compared to dry machining under ambient conditions). An in-situ set-up that consisted of a microscope and a lathe was constructed and helped to propose a novel serrated chip formation mechanism when microstructures (strain localization) and surface roughness were considered. Dimpled fracture surfaces observed in high-speed-machined chips were formed due to stable crack propagation that was also recorded during in-situ machining. An instability criterion was developed that showed easier strain localization within the 0.10-0.30mm/rev feed rate range.

  1. Understanding phase stability of Al-Co-Cr-Fe-Ni high entropy alloys

    DOE PAGESBeta

    Zhang, Chuan; Zhang, Fan; Diao, Haoyan; Gao, Michael C.; Tang, Zhi; Poplawsky, Jonathan D.; Liaw, Peter K.

    2016-07-19

    The concept of high entropy alloy (HEA) opens a vast unexplored composition range for alloy design. As a well-studied system, Al-Co-Cr-Fe-Ni has attracted tremendous amount of attention to develop new-generation low-density structural materials for automobile and aerospace applications. In spite of intensive investigations in the past few years, the phase stability within this HEA system is still poorly understood and needs to be clarified, which poses obstacles to the discovery of promising Al-Co-Cr-Fe-Ni HEAs. In the present work, the CALPHAD approach is employed to understand the phase stability and explore the phase transformation within the Al-Co-Cr-Fe-Ni system. As a result,more » the phase-stability mapping coupled with density contours is then constructed within the composition - temperature space, which provides useful guidelines for the design of low-density Al-Co-Cr-Fe-Ni HEAs with desirable properties.« less

  2. Preliminary study of the characteristics of a high Mg containing Al-Mg-Si alloy

    NASA Astrophysics Data System (ADS)

    Yan, F.; McKay, B. J.; Fan, Z.; Chen, M. F.

    2012-01-01

    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 α-Al matrix with a β-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 μm to 25 ± 0.1 μm, 35 ± 1 μm and 34 ± 1 μm 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.

  3. XRD and XAS structural study of CuAlO2 under high pressure.

    PubMed

    Pellicer-Porres, J; Segura, A; Ferrer-Roca, Ch; Polian, A; Munsch, P; Kim, D

    2013-03-20

    We present the results of x-ray diffraction and x-ray absorption spectroscopy experiments in CuAlO(2) under high pressure. We discuss the polarization dependence of the x-ray absorption near-edge structure at the Cu K-edge. XRD under high pressure evidences anisotropic compression, the a-axis being more compressible than the c-axis. EXAFS yields the copper-oxygen bond length, from which the only internal parameter of the delafossite structure is deduced. The combination of anisotropic compression and the internal parameter decrease results in a regularization of the AlO(6) octahedra. The anisotropic compression is related to the chemical trends observed in the lattice parameters when Al is substituted by other trivalent cations. Both experiments evidence the existence of an irreversible phase transition that clearly manifests at 35 ± 2 GPa. The structure of the high-pressure polymorph could not be determined, but it implies a change of the Cu environment, which remains anisotropic. Precursor effects are observed from the lowest pressures, which are possibly related to crystal breaking at a submicroscopic scale with partial reorientation of the crystallites. PMID:23423689

  4. Laminated metal composite formed from low flow stress layers and high flow stress layers using flow constraining elements and making same

    DOEpatents

    Syn, C.K.; Lesuer, D.R.

    1995-07-04

    A laminated metal composite of low flow stress layers and high flow stress layers is described which is formed using flow constraining elements, preferably in the shape of rings, individually placed around each of the low flow stress layers while pressure is applied to the stack to bond the layers of the composite together, to thereby restrain the flow of the low flow stress layers from the stack during the bonding. The laminated metal composite of the invention is made by the steps of forming a stack of alternate layers of low flow stress layers and high flow stress layers with each layer of low flow stress material surrounded by an individual flow constraining element, such as a ring, and then applying pressure to the top and bottom surfaces of the resulting stack to bond the dissimilar layers together, for example, by compression rolling the stack. In a preferred embodiment, the individual flow constraining elements surrounding the layers of low flow stress material are formed of a material which may either be the same material as the material comprising the high flow stress layers, or have similar flow stress characteristics to the material comprising the high flow stress layers. Additional sacrificial layers may be added to the top and bottom of the stack to avoid damage to the stack during the bonding step; and these additional layers may then be removed after the bonding step. 5 figs.

  5. Laminated metal composite formed from low flow stress layers and high flow stress layers using flow constraining elements and making same

    DOEpatents

    Syn, Chol K.; Lesuer, Donald R.

    1995-01-01

    A laminated metal composite of low flow stress layers and high flow stress layers is described which is formed using flow constraining elements, preferably in the shape of rings, individually placed around each of the low flow stress layers while pressure is applied to the stack to bond the layers of the composite together, to thereby restrain the flow of the low flow stress layers from the stack during the bonding. The laminated metal composite of the invention is made by the steps of forming a stack of alternate layers of low flow stress layers and high flow stress layers with each layer of low flow stress material surrounded by an individual flow constraining element, such as a ring, and then applying pressure to the top and bottom surfaces of the resulting stack to bond the dissimilar layers together, for example, by compression rolling the stack. In a preferred embodiment, the individual flow constraining elements surrounding the layers of low flow stress material are formed of a material which may either be the same material as the material comprising the high flow stress layers, or have similar flow stress characteristics to the material comprising the high flow stress layers. Additional sacrificial layers may be added to the top and bottom of the stack to avoid damage to the stack during the bonding step; and these additional layers may then be removed after the bonding step.

  6. High-temperature studies of multiple fluorinated traps within an Al2O3 gate dielectric for E-Mode AlGaN/GaN power MIS-HEMTs

    NASA Astrophysics Data System (ADS)

    Wang, Yun-Hsiang; Liang, Yung C.; Samudra, Ganesh S.; Chu, Po-Ju; Liao, Ya-Chu; Huang, Chih-Fang; Kuo, Wei-Hung; Lo, Guo-Qiang

    2016-02-01

    Normally-off AlGaN/GaN MIS-HEMT devices with multiple fluorinated ALD-Al2O3 layers as the gate dielectric have been reported to achieve a high threshold voltage for normally-off operations with satisfactory performance for both on and off states at room temperature. However, a large swing in gate threshold voltage is found when devices operate at elevated temperatures. Hence, further study of the gate dielectric on the distribution of fluorinated trap states in the energy band are required to assess the gate function at higher temperatures. Through the use of the charge analytical model and Poole-Frenkel trap emission theory, the gate voltage stressing measurement was carried out to accurately find the effective trap state distribution within the Al2O3 energy bandgap created by fluorinated treatments. For the samples fabricated and used in the investigation, we found that a higher population of fluorinated trap states located deeper than 1.1 eV corresponding to emission levels above 200 °C would allow more trapped charges to remain in the dielectric at high temperature for better threshold voltage retention. We also discovered that a higher fluorine treatment power on the gate dielectric could yield a higher trap state density at deeper levels, resulting in better temperature stability.

  7. Occupational Stress and Cardiovascular Risk Factors in High-Ranking Government Officials and Office Workers

    PubMed Central

    Mirmohammadi, Seyyed Jalil; Taheri, Mahmoud; Mehrparvar, Amir Houshang; Heydari, Mohammad; Saadati Kanafi, Ali; Mostaghaci, Mehrdad

    2014-01-01

    Background: Cardiovascular diseases are among the most important sources of mortality and morbidity, and have a high disease burden. There are some major well-known risk factors, which contribute to the development of these diseases. Occupational stress is caused due to imbalance between job demands and individual’s ability, and it has been implicated as an etiology for cardiovascular diseases. Objectives: This study was conducted to evaluate the cardiovascular risk factors and different dimensions of occupational stress in high-ranking government officials, comparing an age and sex-matched group of office workers with them. Patients and Methods: We invited 90 high-ranking officials who managed the main governmental offices in a city, and 90 age and sex-matched office workers. The subjects were required to fill the occupational role questionnaire (Osipow) which evaluated their personal and medical history as well as occupational stress. Then, we performed physical examination and laboratory tests to check for cardiovascular risk factors. Finally, the frequency of cardiovascular risk factors and occupational stress of two groups were compared. Results: High-ranking officials in our study had less work experience in their current jobs and smoked fewer pack-years of cigarette, but they had higher waist and hip circumference, higher triglyceride level, more stress from role overload and responsibility, and higher total stress score. Our group of office workers had more occupational stress because of role ambiguity and insufficiency, but their overall job stress was less than officials. Conclusions: The officials have higher scores in some dimensions of occupational stress and higher overall stress score. Some cardiovascular risk factors were also more frequent in managers. PMID:25389469

  8. Stress.

    PubMed

    Chambers, David W

    2008-01-01

    We all experience stress as a regular, and sometimes damaging and sometimes useful, part of our daily lives. In our normal ups and downs, we have our share of exhaustion, despondency, and outrage--matched with their corresponding positive moods. But burnout and workaholism are different. They are chronic, dysfunctional, self-reinforcing, life-shortening habits. Dentists, nurses, teachers, ministers, social workers, and entertainers are especially susceptible to burnout; not because they are hard-working professionals (they tend to be), but because they are caring perfectionists who share control for the success of what they do with others and perform under the scrutiny of their colleagues (they tend to). Workaholics are also trapped in self-sealing cycles, but the elements are ever-receding visions of control and using constant activity as a barrier against facing reality. This essay explores the symptoms, mechanisms, causes, and successful coping strategies for burnout and workaholism. It also takes a look at the general stress response on the physiological level and at some of the damage American society inflicts on itself. PMID:18846841

  9. High hemoglobin mixed disulfide content in hemolysates from stressed shark.

    PubMed

    Dafré, A L; Reischl, E

    1990-01-01

    1. Hemolysate from heavily stressed smooth hammerhead shark, Sphyrna zygaena, shows three electrophoretic components, SZ I, SZ II and SZ III, whose relative concentrations are 36.4 +/- 6.8, 36.4 +/- 5.0 and 20.8 +/- 5.7%, respectively. After reduction with DTE only SZ I remained. 2. SZ I reacted with glutathione disulfide reconstitute SZ II and SZ III. 3. Non-reduced, DTE-reduced, and denatured hemoglobin were found to have 2.0 +/- 0.4, 3.7 +/- 0.6, and 9.4 +/- 0.7-SH groups, respectively. 4. Erythrocyte non-protein--SH (NPSH), including glutathione present as mixed disulfide with SZ II and SZ III, is 1.7 NPSH/Hb. PMID:2361357

  10. Advantages of MgAlOx over gamma-Al2O3 as a support material for potassium-based high temperature lean NOx traps

    SciTech Connect

    Luo, Jinyong; Gao, Feng; Karim, Ayman M.; Xu, Pinghong; Browning, Nigel D.; Peden, Charles HF

    2015-08-07

    MgAlOx mixed oxides were employed as supports for potassium-based lean NOx traps (LNTs) targeted for high temperature applications. Effects of support compositions, K/Pt loadings, thermal aging and catalyst regeneration on NOx storage capacity were systematically investigated. The catalysts were characterized by XRD, NOx-TPD, TEM, STEM-HAADF and in-situ XAFS. The results indicate that MgAlOx mixed oxides have significant advantages over conventional gamma-Al2O3-supports for LNT catalysts, in terms of high temperature NOx trapping capacity and thermal stability. First, as a basic support, MgAlOx stabilizes stored nitrates (in the form of KNO3) to much higher temperatures than mildly acidic gamma-Al2O3. Second, MgAlOx minimizes Pt sintering during thermal aging, which is not possible for gamma-Al2O3 supports. Notably, combined XRD, in-situ XAFS and STEM-HAADF results indicate that Pt species in the thermally aged Pt/MgAlOx samples are finely dispersed in the oxide matrix as isolated atoms. This strong metal-support interaction stabilizes Pt and minimizes the extent of sintering. However, such strong interactions result in Pt oxidation via coordination with the support so that NO oxidation activity can be adversely affected after aging which, in turn, decreases NOx trapping ability for these catalysts. Interestingly, a high-temperature reduction treatment regenerates essentially full NOx trapping performance. In fact, regenerated Pt/K/MgAlOx catalyst exhibits much better NOx trapping performance than fresh Pt/K/Al2O3 LNTs over the entire temperature range investigated here. In addition to thermal aging, Pt/K loading effects were systemically studied over the fresh samples. The results indicate that NOx trapping is kinetically limited at low temperatures, while thermodynamically limited at high temperatures. A simple conceptual model was developed to explain the Pt and K loading effects on NOx storage. An optimized K loading, which allows balancing between the

  11. Mixed-mode fatigue-crack growth thresholds in Ti-6Al-4V at high frequency

    SciTech Connect

    Campbell, J.P.; Ritchie, R.O.

    1999-10-22

    Multiaxial loading conditions exist at fatigue-critical locations within turbine engine components, particularly in association with fretting fatigue in the blade dovetail/disk contact section. For fatigue-crack growth in such situations, the resultant crack-driving force is a combination of the influence of a mode I (tensile opening) stress-intensity range, {Delta}K{sub I}, as well as mode II (in-plane shear) and/or mode III (anti-plane shear) stress-intensity ranges, {Delta}K{sub II} and {Delta}K{sub III}, respectively. For the case of the high-cycle fatigue of turbine-engine alloys, it is critical to quantify such behavior, as the extremely high cyclic loading frequencies ({approximately}1--2 kHz) and correspondingly short times to failure may necessitate a design approached based on the fatigue-crack growth threshold. Moreover, knowledge of such thresholds is required for accurate prediction of fretting fatigue failures. Accordingly, this paper presents the mixed-mode fatigue crack growth thresholds for mode I + II loading (phase angles from 0{degree} to 82{degree}) in a Ti-6Al-4V blade alloy. These results indicate that when fatigue-crack growth in this alloy is characterized in terms of the crack-driving force {Delta}G, which incorporates both the applied tensile and shear loading, the mode 1 fatigue-crack growth threshold is a lower bound (worst case) with respect to mixed-mode (I + II) crack-growth behavior.

  12. Social structure, life stress and depressive symptoms in a high school-aged population.

    PubMed

    Gore, S; Aseltine, R H; Colton, M E

    1992-06-01

    Data from a randomly selected sample of 1,208 high school-aged adolescents were used to examine the means through which life stress is associated with depressive symptoms. Analyses focus on family structure, socioeconomic status, and gender as background risks which directly and indirectly influence symptoms, as well as vulnerability contexts that shape differential responsiveness to stressful experiences. Findings indicate (1) significant gender differences in aspects of stress exposure and in additive models of stress effects, but stresses and supports do not explain the significant gender difference in depressive symptoms; (2) girls in low education backgrounds have the highest levels of depressive symptoms; (3) there are no gender differences in vulnerability to stress; (4) children in single-parent families have higher symptom levels, effects explained by economic conditions and stress exposure--they are no more vulnerable than others to the depressing effects of these stresses; and (5) both boys and girls in low SES backgrounds are more vulnerable to a wide range of stresses and support deficits. PMID:1619266

  13. High power single mode 980 nm AlGaInAs/AlGaAs quantum well lasers with a very low threshold current

    NASA Astrophysics Data System (ADS)

    Zhen, Dong; Cuiluan, Wang; Hongqi, Jing; Suping, Liu; Xiaoyu, Ma

    2013-11-01

    To achieve low threshold current as well as high single mode output power, a graded index separate confinement heterostructure (GRIN-SCH) AlGaInAs/AlGaAs quantum well laser with an optimized ridge waveguide was fabricated. The threshold current was reduced to 8 mA. An output power of 76 mW was achieved at 100 mA current at room temperature, with a slope efficiency of 0.83 W/A and a horizon divergent angle of 6.3°. The maximum single mode output power of the device reached as high as 450 mW.

  14. Internal strains and stresses measured in cortical bone via high-energy X-ray diffraction.

    PubMed

    Almer, J D; Stock, S R

    2005-10-01

    High-energy synchrotron X-ray diffraction was used to study internal stresses in bone under in situ compressive loading. A transverse cross-section of a 12-14 year old beagle fibula was studied with 80.7 keV radiation, and the transmission geometry was used to quantify internal strains and corresponding stresses in the mineral phase, carbonated hydroxyapatite. The diffraction patterns agreed with tabulated patterns, and the distribution of diffracted intensity around 00.2/00.4 and 22.2 diffraction rings was consistent with the imperfect 00.1 fiber texture expected along the axis of a long bone. Residual compressive stress along the bone's longitudinal axis was observed in the specimen prior to testing: for 22.2 this stress equaled -95 MPa and for 00.2/00.4 was between -160 and -240 MPa. Diffraction patterns were collected for applied compressive stresses up to -110 MPa, and, up to about -100 MPa, internal stresses rose proportionally with applied stress but at a higher rate, corresponding to stress concentration in the mineral of 2.8 times the stress applied. The widths of the 00.2 and 00.4 diffraction peaks indicated that crystallite size perpendicular to the 00.1 planes increased from t=41 nm before stress was applied to t=44 nm at -118 MPa applied stress and that rms strain epsilon(rms) rose from 2200 muepsilon before loading to 4600 muepsilon at the maximum applied stress. Small angle X-ray scattering of the unloaded sample, recorded after deformation was complete, showed a collagen D-period of 66.4 nm (along the bone axis). PMID:16183302

  15. Evidence for a lower crustal origin of high-Al orthopyroxene megacrysts in Proterozoic anorthosites

    SciTech Connect

    Wiebe, R.A.

    1985-01-01

    Nodules and xenocrysts dominated by high-Al orthopyroxene (HAO) occur in strongly chilled Proterozoic basaltic dikes which cut the Nain anorthosite complex, Labrador. HAO (En 73-68, Al/sub 2/O/sub 3/ = 6.5-4.5) lacks exsolution; it occurs both as anhedral xenocrysts up to 10 cm in diameter and with euhedral plagioclase (An55) in ophitic nodules. Rarely, olivine occurs with HAO and Al-spinel with plagioclase. Scarce Fe-rich nodules contain: (1) opx + pig, (2) aug + pig, and (3) coarsely exsolved ulvospinel. Pyroxene pairs yield T's of 1250 to 1170/degree/C, whereas coexisting lamellae in exsolved ulvospinel yield T's between 1145 and 1120/degree/C, with fO/sub 2/ near the WM buffer. If all nodules came from a similar depth, the rare occurrence of olivine with plagioclase suggests a maximum pressure of about 11 kb. The high subsolidus T's of the nodules contrasts with the low T of the host anorthosites at the time of dike emplacement and hence indicates a deep source for the nodules. HAO is nearly identical in composition to the high-Al orthopyroxene megacrysts with exsolved plagioclase (HAOM) found in most Proterozoic anorthosites. Many nodules of plagioclase and HAO also have textures comparable to ophitic occurrences of HAOM in anorthosite. Rafting of cotectic nodules from the lower crust could explain occurrences of HAOM in shallow-level anorthosites. The nodules and xenocrysts are samples of lower crustal cumulates. Their compositions suggest that they were produced by magmas similar to those that were parental to the anorthosites. They lend support to models which derive anorthosites by fractional crystallization of basaltic magma.

  16. 26Al Production in the Early Solar Nebula by Neutral High-Energy Plasma Winds

    NASA Astrophysics Data System (ADS)

    Spergel, M. S.

    1995-09-01

    In the light of recent observations, I believe that the sources for the presence of ^26Al within the solar nebula must be reconsidered [2,3]. Recent low observational estimates of the probability of encounters between mass-losing evolved stars and molecular clouds [4] for the production of ^26Al and the observed low production [5] of 26 Al from AGB (Asymptotic Giant Branch stars) along with the predicted low abundance of cosmic ray induced local production [6] in the early solar nebula all support continued investigation for additional sources of the solar nebula ^26Al presence. It is suggested based on the presences of new cross section data [7], that an important source of this ^26Al presence might be from enhanced interactions from the collisions of the local "T. Tauri" like plasma winds with the atomic and molecular Early Solar Nebula (ESN). Interactions like ^26Mg (p,n) ^26Al in this "neutral" electrical setting may provide the needed selective production. The ESN provides an environment where plasma winds can lead to such nucleosynthesis. Stellar winds of 300-700 km/s (about 3x10^7 K) are seen to T. Tauri like stars, presumed precursor to solar like stars, and also within the Solar heliosphere [8.9]. These winds provide the source of Solar High Energy Particles which can interact with such in situ targets such as ^26Mg to produce the ^26Al. The presence of the atomic and molecular environments, will enhance [10] nucleosynthesis over that seen in scattering of protons off bare nuclei. Such enhancement has been recently observed in low energy scattering on electrically shield targets [7]. There it was also suggested that in stellar convective zones, electron clouds of the plasma shield may also shield bare target nuclei. Measured values of low energy proton scattered on atomic and molecular targets indicated [7] that fusion cross sections are enlarged and elastic cross sections are reduced, therefore simple extrapolation of accelerator data can lead to an

  17. Phase composition and elemental partitioning in glass-ceramics containing high-Na/Al high level waste

    NASA Astrophysics Data System (ADS)

    Stefanovsky, S. V.; Sorokaletova, A. N.; Nikonov, B. S.

    2012-05-01

    Mixtures of surrogates of high level waste with high sodium and aluminum contents and sodium-lithium borosilicate frit were melted in alumina crucibles in a resistive furnace followed by quenching of one portion of the melt and annealing of the residual material in a turned-off furnace. The annealed materials with waste loading of up to 45 wt.% contained minor spinel type phase and trace of nepheline (Na,K)AlSiO4. In the annealed materials contained waste oxides in amount of 50 wt.% and more nepheline and spinel were found to be major and minor phases, respectively. At high waste loadings two extra phases: Cs-aluminosilicate (CsAlSiO4) and mixed Na/Cs-aluminosilicate were found in amount of 3-5 vol.% each. The latter phase contains of up to ˜5.7 wt.% SO3 or 0.13 formula units S (Na0.75K0.05Cs0.29Ca0.02Sr0.02Al0.99Fe0.03Si0.76S0.13O4). Sulfur incorporation as S6+ or SO42- ions into crystal lattice may be facilitated in the presence of large-size Cs+ cations. Simplified suggested formula of this phase may be represented as Na0.8Cs0.3AlSi0.8S0.1O3.95. It was also synthesized by sintering of mixture of chemicals at 1300 °C and found to be instable at temperatures higher than 1300 °C.

  18. Preparation of γ-AlON transparent ceramics by one-step method with high-activity Al2O3 powders

    NASA Astrophysics Data System (ADS)

    Sun, Wenzhou; Chen, Yuhong; Wu, Laner; Jiang, Yong

    2013-06-01

    In this paper, γ-AlON transparent ceramics are fabricated by one-step method—reactived hot-pressuring sintering technology by using as-prepared γ-Al2O3 powder as raw material. And the sintering process is also improved from two aspects: adjusting sintered technique parameters and improving the sintering agents. XRD, SEM, ICP-AES analysis results show that as-prepared γ-Al2O3 powders have advantages of super-fine, high-purity and high-activity so that can meet the requirements of starting material. By adding 1wt% Y2O3 as sintering agent, single-phase γ-AlON transparent ceramic can be fabricated under the optimum technological condition: hot-pressure sintering at 1950°C for 6h, under nitrogen atmosphere. The results from XRD and SEM indicate that the γ-AlON ceramic has high density and fine microstructures with relative density of 99.22%. The test result of IR spectrum show that the ceramic yield the best transmittance of 18.42% at 2.5μm and its transmitting wavelength range extend from 1.5 to 4.5μm.

  19. Atomic structure of luminescent centers in high-efficiency Ce-doped w-AlN single crystal.

    PubMed

    Ishikawa, Ryo; Lupini, Andrew R; Oba, Fumiyasu; Findlay, Scott D; Shibata, Naoya; Taniguchi, Takashi; Watanabe, Kenji; Hayashi, Hiroyuki; Sakai, Toshifumi; Tanaka, Isao; Ikuhara, Yuichi; Pennycook, Stephen J

    2014-01-01

    Rare-earth doped wurtzite-type aluminum nitride (w-AlN) has great potential for high-efficiency electroluminescent applications over a wide wavelength range. However, because of their large atomic size, it has been difficult to stably dope individual rare-earth atoms into the w-AlN host lattice. Here we use a reactive flux method under high pressure and high temperature to obtain cerium (Ce) doped w-AlN single crystals with pink-colored luminescence. In order to elucidate the atomic structure of the luminescent centers, we directly observe individual Ce dopants in w-AlN using annular dark-field scanning transmission electron microscopy. We find that Ce is incorporated as single, isolated atoms inside the w-AlN lattice occupying Al substitutional sites. This new synthesis method represents a new alternative strategy for doping size-mismatched functional atoms into wide band-gap materials. PMID:24445335

  20. Atomic Structure of Luminescent Centers in High-Efficiency Ce-doped w-AlN Single Crystal

    PubMed Central

    Ishikawa, Ryo; Lupini, Andrew R.; Oba, Fumiyasu; Findlay, Scott D.; Shibata, Naoya; Taniguchi, Takashi; Watanabe, Kenji; Hayashi, Hiroyuki; Sakai, Toshifumi; Tanaka, Isao; Ikuhara, Yuichi; Pennycook, Stephen J.

    2014-01-01

    Rare-earth doped wurtzite-type aluminum nitride (w-AlN) has great potential for high-efficiency electroluminescent applications over a wide wavelength range. However, because of their large atomic size, it has been difficult to stably dope individual rare-earth atoms into the w-AlN host lattice. Here we use a reactive flux method under high pressure and high temperature to obtain cerium (Ce) doped w-AlN single crystals with pink-colored luminescence. In order to elucidate the atomic structure of the luminescent centers, we directly observe individual Ce dopants in w-AlN using annular dark-field scanning transmission electron microscopy. We find that Ce is incorporated as single, isolated atoms inside the w-AlN lattice occupying Al substitutional sites. This new synthesis method represents a new alternative strategy for doping size-mismatched functional atoms into wide band-gap materials. PMID:24445335