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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. The impact of mechanical stress on the degradation of AlGaN/GaN high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Choi, Sukwon; Heller, Eric; Dorsey, Donald; Vetury, Ramakrishna; Graham, Samuel

    2013-10-01

    Coupled electro-thermo-mechanical simulation and Raman thermometry were utilized to analyze the evolution of mechanical stress in AlGaN/GaN high electron mobility transistors (HEMTs). This combined analysis was correlated with electrical step stress tests to determine the influence of mechanical stress on the degradation of actual devices under diverse bias conditions. It was found that the total stress as opposed to one dominant stress component correlated the best with the degradation of the HEMT devices. These results suggest that minimizing the total stress as opposed to the inverse piezoelectric stress in the device is necessary in order to avoid device degradation which can be accomplished through various growth methods.

  4. Analysis of the residual stress distribution in AlGaN/GaN high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Choi, Sukwon; Heller, Eric; Dorsey, Donald; Vetury, Ramakrishna; Graham, Samuel

    2013-03-01

    A comparative analysis of the residual stress distributions across the conductive channel of Ga-face AlGaN/GaN high electron mobility transistors (HEMTs) is presented. Stress was measured by means of micro-Raman spectroscopy and micro-photoluminescence (PL). Raman measurements probed the volume average of the stress through the GaN layer whereas the stress near the GaN surface (AlGaN/GaN heterointerface) was acquired via PL. By combining Raman, PL, and x-ray diffraction, a self-consistent method was developed to accurately determine the variation in magnitude of stress throughout the thickness of the GaN layer. Based on this framework, it is observed in AlGaN/GaN HEMTs that a depth variation in the GaN residual stress occurs near the gate and ohmic electrodes. At these regions, the stress near the AlGaN/GaN interface (or GaN surface) exhibits a tensile shift compared to the stress averaged through the entire thickness of GaN. Across the conductive channel (away from the metal pads), the bulk average stress and the stress near this interface remain nearly identical, showing little evidence of a vertical gradient. It is expected that the induced tensile strain at the drain side gate edge will have an impact on device reliability by contributing to the elastic energy built in the AlGaN barrier in addition to the inverse piezoelectric contribution at operating conditions, which may lead to formation of crystallographic defects.

  5. Effect of high voltage stress on the DC performance of the Al2O3/AlN GaN metal-insulator-semiconductor high-electron mobility transistor for power applications

    NASA Astrophysics Data System (ADS)

    Hsieh, Ting-En; Lin, Yueh-Chin; Liao, Jen-Ting; Lan, Wei-Cheng; Chin, Ping-Chieh; Chang, Edward Yi

    2015-10-01

    We demonstrate an Al2O3/AlN/AlGaN/GaN metal-insulator-semiconductor high-electron mobility transistor (MIS-HEMT) device with stable electrical properties under high-voltage stress, by using an Al2O3/AlN stack layer as the gate dielectric layer. Excellent quality AlN/Al2O3 GaN interface was obtained by using plasma-enhanced ALD (PE-ALD), resulting in a very low interface trap density (Dit) of ˜1.8 × 1011 eV-1 cm-2, obtained by using the conductance method. The device exhibits a small threshold voltage hysteresis of ˜200 mV and a lower gate-source leakage current. No obvious changes in the drain-source current and ON-resistance were observed for the device that was subject to the drain-source voltage stress of 100 V for 15 h.

  6. 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 ?-cell mass and function in alloxan-induced diabetic mouse model. However, the protective mechanism of AL-1 on high glucose-induced pancreatic ?-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

  7. Influence of stress on structural properties of AlGaN/GaN high electron mobility transistor layers grown on 150 mm diameter Si (111) substrate

    NASA Astrophysics Data System (ADS)

    Liu, H. F.; Dolmanan, S. B.; Zhang, L.; Chua, S. J.; Chi, D. Z.; Heuken, M.; Tripathy, S.

    2013-01-01

    Effects of stress imposed by individual nitride layers on structural properties of an AlGaN/GaN high-electron-mobility-transistor (HEMT) structure, which was grown on a 150 mm diameter Si (111) substrate by metal-organic chemical vapor deposition employing high-temperature step-graded AlxGa1-xN/AlN buffer layers, were studied using transmission electron microscopy, visible micro-Raman spectroscopy, and high-resolution x-ray diffraction. It is revealed that all the nitride layers are more or less tensile strained on the Si (111) substrate; however, strain relaxations occurred at all the heterointerfaces except for the AlGaN/(AlN/)GaN two-dimensional electron gas interface, which is desired for achieving high performance HEMT. The wafer curvature, an important parameter for large area epitaxy of GaN-on-Si, is modeled on the basis of stress distribution within individual layers of the multilayered AlGaN/GaN HEMT structure via the close-form expression developed by Olsen and Ettenberg [J. Appl. Phys. 48, 2543 (1977)]. The evolution of wafer curvature induced by substrate thinning and stress redistribution is predicted by this model, which is further qualitatively confirmed by experimental results.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

    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

    2015-04-01

    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.

  10. Coherency stresses in lamellar Ti-Al

    NASA Astrophysics Data System (ADS)

    Grinfeld, M. A.; Hazzledine, P. M.; Shoykhet, B.; Dimiduk, D. M.

    1998-03-01

    General formulas are given for the coherency strains and stresses in a multilayer far from the free surfaces. The multilayer is assumed to be a periodic stack of different elastically isotropic materials, but there may be any number of layers in the stack and they may each have any thickness and any elastic constants. The results are applied to lamellar Ti-Al alloys, in which there are shear misfits between different γ layers and both shear and biaxial misfits between the γ and α2 layers. In a fully coherent multilayer, the stresses would be large, in the GPa range, and in high strength, thin lamella alloys, the coherency stresses are a substantial fraction of a GPa. The shear stresses act principally on hard mode deformation systems, and the biaxial stresses place every α2 lamella in biaxial compression. This biaxial compression, which, for dislocation glide, is equivalent to a uniaxial tension normal to the lamella, is particularly large when the α2 volume fraction is small.

  11. 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.

  12. Mechanism of the self-changing parameters and characteristics in AlGaN/GaN high-electron mobility transistors after a step voltage stress

    NASA Astrophysics Data System (ADS)

    Lei, Shi; Shiwei, Feng; Kun, Liu; Yamin, Zhang

    2015-07-01

    The phenomenon of self-changing on the device parameters and characteristics after a step voltage stress was applied to the gate is studied in AlGaN/GaN high electron mobility transistors. The device was measured every 5 min after the stress was removed. The large-signal parasitic source (drain) resistance, transfer characteristics, threshold voltage, drain-source current, gate-source (drain) reverse current-voltage characteristics changed spontaneously after the removal of the stress. The time constant of the self-changing was about 25-27 min. The gate-source (drain) capacitance-voltage characteristics were constant during this process. Electrons were trapped by the surface states and traps in the AlGaN barrier layer when the device was under stress. The traps in the AlGaN barrier layer then released electrons in less than 10 s. The surface states released electrons continuously during the entire measurement stage, leading to the self-changing of mearsurement result. Project supported by the National Natural Science Foundation of China (Nos. 61376077, 61201046, 61204081), and the Beijing Natural Science Foundation (Nos. 4132022, 4122005).

  13. 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.

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

    NASA Astrophysics Data System (ADS)

    Anand, M. J.; Ng, G. I.; Arulkumaran, S.; Manoj Kumar, C. M.; Ranjan, K.; Vicknesh, S.; Foo, S. C.; Syamal, B.; Zhou, X.

    2015-02-01

    The influence of electric field (EF) on the dynamic ON-resistance (dyn-RDS[ON]) and threshold-voltage shift (?Vth) of AlGaN/GaN high electron mobility transistors on Si has been investigated using pulsed current-voltage (IDS-VDS) and drain current (ID) transients. Different EF was realized with devices of different gate-drain spacing (Lgd) under the same OFF-state stress. Under high-EF (Lgd = 2 ?m), the devices exhibited higher dyn-RDS[ON] degradation but a small ?Vth (120 mV). However, at low-EF (Lgd = 5 ?m), smaller dyn-RDS[ON] degradation but a larger ?Vth (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-RDS[ON] degradation, whereas under low-EF, trapping is mostly confined under the gate causing ?Vth. A trap with activation energy 0.33 eV was identified in the AlGaN barrier by ID-transient measurements. The influence of EF on trapping was also verified by Silvaco TCAD simulations.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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 performance by a factor of ˜2.5 in the best sample. As with the Fe-Ga strip, improvement in performance was quite varied along the strip length.

  2. Stress granules as crucibles of ALS pathogenesis

    PubMed Central

    King, Oliver D.

    2013-01-01

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

  3. Effect of sulfuric acid, oxygen, and hydrogen in high temperature water on stress corrosion cracking of sensitized AlSl 304 stainless steel

    SciTech Connect

    Ruther, W.E.; Ayrault, G.; Kassner, T.F.; Soppet, W.K.

    1984-10-01

    The influence of dissolved oxygen and hydrogen and dilute sulfuric acid in 289 C water on the stress corrosion cracking susceptibility of lightly and moderately sensitized AlSl 304 stainless steel was determined in constant extension rate tensile (CERT) tests. The CERT parameters and fracture surface morphologies correlated with the concentrations of dissolved oxygen and sulfate and the electrochemical potentials of platinum and AlSl 304 stainless steel electrodes in simulated boiling water reactor (BWR) environments. A high susceptibility to intergranular cracking was found for lightly sensitized steel at oxygen concentrations between 0.05 and 0.2 ppm under slightly acidic conditions (pH 6.0 at 25 C), which may, in part, account for the pervasive nature of intergranular cracking in BWR piping systems. Scanning-transmission electron microscopy analyses revealed significant differences between samples in the lightly and the moderately sensitized conditions with respect to the width, but not the depth, of the chromium-depleted region at the grain boundaries. The addition of 0.5 ppm hydrogen had only a slight mitigating effect in water containing oxygen and sulfuric acid at low concentrations; however, oxygen suppression to less than or equal to0.05 ppm in the reactor coolant water by means of hydrogen additions to the feedwater would be beneficial, provided impurities are also maintained at low levels.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

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

    SciTech Connect

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

    2004-12-01

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

  9. 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.

  10. 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.

  11. ER Dysfunction and Protein Folding Stress in ALS

    PubMed Central

    Matus, Soledad; Valenzuela, Vicente; Medinas, Danilo B.; Hetz, Claudio

    2013-01-01

    Amyotrophic lateral sclerosis (ALS) is the most frequent paralytic disease in adults. Most ALS cases are considered sporadic with no clear genetic component. The disruption of protein homeostasis due to chronic stress responses at the endoplasmic reticulum (ER) and the accumulation of abnormal protein inclusions are extensively described in ALS mouse models and patient-derived tissue. Recent studies using pharmacological and genetic manipulation of the unfolded protein response (UPR), an adaptive reaction against ER stress, have demonstrated a complex involvement of the pathway in experimental models of ALS. In addition, quantitative changes in ER stress-responsive chaperones in body fluids have been proposed as possible biomarkers to monitor the disease progression. Here we review most recent advances attributing a causal role of ER stress in ALS. PMID:24324498

  12. ER Dysfunction and Protein Folding Stress in ALS.

    PubMed

    Matus, Soledad; Valenzuela, Vicente; Medinas, Danilo B; Hetz, Claudio

    2013-01-01

    Amyotrophic lateral sclerosis (ALS) is the most frequent paralytic disease in adults. Most ALS cases are considered sporadic with no clear genetic component. The disruption of protein homeostasis due to chronic stress responses at the endoplasmic reticulum (ER) and the accumulation of abnormal protein inclusions are extensively described in ALS mouse models and patient-derived tissue. Recent studies using pharmacological and genetic manipulation of the unfolded protein response (UPR), an adaptive reaction against ER stress, have demonstrated a complex involvement of the pathway in experimental models of ALS. In addition, quantitative changes in ER stress-responsive chaperones in body fluids have been proposed as possible biomarkers to monitor the disease progression. Here we review most recent advances attributing a causal role of ER stress in ALS. PMID:24324498

  13. 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.

  14. 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

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

    NASA Astrophysics Data System (ADS)

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

    2012-09-01

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

  16. 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.

  17. 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.

  18. Stress relaxation and electromigration confined Al(Cu) line structures

    NASA Astrophysics Data System (ADS)

    Moske, M. A.; Ho, P. S.; Hu, C. K.; Small, M. B.

    1992-08-01

    The confinement of interconnect lines by a dielectric layer gives rise to a triaxial stress state in the line structure. Relaxation of the stress under operating conditions can lead to void formation in fine lines. The principal stress components and their relaxation behavior have been determined in Al(Cu) line structures passivated by a quartz dielectric layer on a Si substrate. This was carried out using a bending beam method to measure the thermal deformation of periodic line structures with parallel and perpendicular line configurations. By analyzing the mechanics of quartz confinement, we are able to deduce the magnitude and relaxation behavior of the three principal stress components. Results of the measurements are consistent with those determined using X-ray techniques, showing a substantial stress enhancement as a result of quartz confinement. The stress relaxation behavior is characterized by a two-stage process, first with fast followed by slow kinetics. The results are attributed to the relaxation mechanism and interaction at the metal-dielectric interface. Electromigration can also generate stress in a metal line with a finite length, which has been measured for Al(Cu) fine lines using a drift velocity technique. The stress induced by electromigration was found to be comparable to the thermal stress. The implications on void formation are discussed.

  19. 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.

  20. 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.

  1. 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

  2. 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…

  3. TRANSCRIPTIONAL ANALYSIS BETWEEN TWO WHEAT NEAR-ISOGENIC LINES CONTRASTING IN ALUMINUM (AL) TOLERANCE UNDER AL STRESS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    To understand the mechanisms of aluminum (Al) tolerance and identify genes responsible for Al tolerance in wheat (Triticum aestivum L.), suppression subtractive hybridization (SSH) libraries were constructed from Al-stressed roots for two wheat near- isogenic lines (NILs), Chisholm-T (Al-tolerant) a...

  4. Alloys based on NiAl for high temperature applications

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

    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.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2005-07-01

    We present 3D-NEMD results for the velocity dependence of the frictional force at smooth and roughened interfaces for Ta and Al single crystals. For Ta/Al we consider Ta (100)/Al (100) and Ta (110)/Al (111) interfaces sliding along [001] and [11&-circ;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, v^-β, with β = 3/4. We discuss the structural changes that influence dissipation in these regimes.

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

    NASA Astrophysics Data System (ADS)

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

    2006-07-01

    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¯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 ∝ v-β with β=3/4. We discuss the structural changes that influence dissipation in each of these regimes.

  8. 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

  9. 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.

  10. 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 the investigated Al 7075 alloy.

  11. Stress and texture evolution of Ni/Al multi-film by laser interference irradiation

    SciTech Connect

    Daniel, Claus; Lasagni, Andres Fabian; M�cklich, Frank

    2004-01-01

    Ni/Al multi-layered thin film systems are important to protect the mechanical and chemical impact on the bulk component. The mechanical properties of these compounds can be further improved by combining different stress and texture situations. Such optimized surface composites have been achieved by laser interference irradiation. In this study, the thin film system Ni/Al was produced by physical vapor deposition and irradiated by the interference pattern of two coherent laser beams. A thermal simulation of the irradiation with a focus on the temperature and phase transition evolution was investigated. The stress and texture distribution before and after interference irradiation were thoroughly investigated by high resolution X-ray diffraction.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    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.

  13. 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

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. Dysregulated miRNA biogenesis downstream of cellular stress and ALS-causing mutations: a new mechanism for ALS.

    PubMed

    Emde, Anna; Eitan, Chen; Liou, Lee-Loung; Libby, Ryan T; Rivkin, Natali; Magen, Iddo; Reichenstein, Irit; Oppenheim, Hagar; Eilam, Raya; Silvestroni, Aurelio; Alajajian, Betty; Ben-Dov, Iddo Z; Aebischer, Julianne; Savidor, Alon; Levin, Yishai; Sons, Robert; Hammond, Scott M; Ravits, John M; Möller, Thomas; Hornstein, Eran

    2015-11-01

    Interest in RNA dysfunction in amyotrophic lateral sclerosis (ALS) recently aroused upon discovering causative mutations in RNA-binding protein genes. Here, we show that extensive down-regulation of miRNA levels is a common molecular denominator for multiple forms of human ALS. We further demonstrate that pathogenic ALS-causing mutations are sufficient to inhibit miRNA biogenesis at the Dicing step. Abnormalities of the stress response are involved in the pathogenesis of neurodegeneration, including ALS. Accordingly, we describe a novel mechanism for modulating microRNA biogenesis under stress, involving stress granule formation and re-organization of DICER and AGO2 protein interactions with their partners. In line with this observation, enhancing DICER activity by a small molecule, enoxacin, is beneficial for neuromuscular function in two independent ALS mouse models. Characterizing miRNA biogenesis downstream of the stress response ties seemingly disparate pathways in neurodegeneration and further suggests that DICER and miRNAs affect neuronal integrity and are possible therapeutic targets. PMID:26330466

  19. 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

  20. 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.

  1. 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

  2. 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

  3. 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.

  4. 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.

  5. Stress induced metallurgical effects in Ti/TiN/AlCu/TiN metal stacks

    NASA Astrophysics Data System (ADS)

    Koller, Klaus; Hommel, Martina; Hummelt, Stefan; Koerner, Heinrich

    2002-04-01

    Integrated circuits with aluminum metallization for products with high current densities need a metal stack with liner and antireflective coating (ARC) which can fulfill several requirements (e.g. low sheet resistance, high reliability, smooth surface, good adhesion, thermal stability, etc.). In this work different multilayer metal stacks are investigated and several phenomena which can be observed after thermal annealing of Ti/TiN/AlCu/TiN stacks are described and discussed. Metallurgical, electrical and mechanical properties of different layer combinations are investigated after thermal annealing and stress tests are done to compare the electromigration and life time behavior of each metal stack. For all investigated metal stacks it is shown that an interface reaction between Ti and aluminum will form TiAl3 phase. Even with very thick TiN layers on top of titanium or with only TiN liner the phase formation occurred. Explanations and models for the formation of different phenomena (hillocks, depressions and elevations), are discussed. The origin of each phenomena is stress related and assisted either by the liner material and/or the ARC layer. A qualitative model which explains the different observed layer reactions is discussed.

  6. 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.

  7. 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

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

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Insights into the proteomic response of soybean towards Al2O3, ZnO, and Ag nanoparticles stress.

    PubMed

    Hossain, Zahed; Mustafa, Ghazala; Sakata, Katsumi; Komatsu, Setsuko

    2016-03-01

    Understanding the complex mechanisms involved in plant response to nanoparticles is indispensable in assessing the impact of nano-pollutants on environment. The present study compares the phytotoxicity of three different metal-based nanoparticles (Al2O3, ZnO, and Ag) in soybean seedling at proteome level. Plant growth, rigidity of roots, and root cell viability were markedly affected by ZnO- and Ag-NPs stress; while, Al2O3-NPs challenged soybean maintained normal seedling growth like control. Moreover, severe oxidative burst was evident in ZnO-NPs and Ag-NPs treatments. Gel-free proteomic analysis of NPs stressed soybean roots revealed 104 commonly changed proteins primarily associated with secondary metabolism, cell organization, and hormone metabolism. Oxidation-reduction cascade related genes, such as GDSL motif lipase 5, SKU5 similar 4, galactose oxidase, and quinone reductase were up-regulated in Al2O3-NPs challenged roots and down-regulated in ZnO- and Ag-NPs treatments. In comparison to root, 16 common proteins were found to be significantly changed in leaves of NPs exposed soybean that were predominantly associated to photosystem and protein degradation. The proteomic findings suggest that high abundance of proteins involved in oxidation-reduction, stress signaling, hormonal pathways related to growth and development might be the principal key for optimum growth of soybean under Al2O3-NPs stress. PMID:26561753

  13. Optimization on hardness and internal stress of micro-electroformed NiCo/nano-Al2O3 composites with the constraint of low surface roughness

    NASA Astrophysics Data System (ADS)

    Hung, Shih-Yu

    2009-01-01

    In this paper, Ni-Co/nano-Al2O3 composite electroforming was used to make the metallic micro-mold for a microlens array. The microstructures require higher hardness to improve the wear resistance and lifetime. Nano-Al2O3 was applied to strengthen the Ni-Co matrix by a new micro-electroforming technique. The hardness and internal stress of Ni-Co/nano-Al2O3 composite deposit were investigated. The results showed that the hardness increased with the increasing Al2O3 content, but at the cost of deformation. Increasing the Al2O3 content in the composite was not always beneficial to the electroformed mold for microlens array fabrication. This work will concentrate on the relationship between important mechanical properties and electrolyte parameters of Ni-Co/nano-Al2O3 composite electroforming. Electrolyte parameters such as Al2O3 content, Al2O3 particle diameter, Co content, stress reducer and current density will be examined with respect to internal stress and hardness. In the present study, low stress and high hardness electroforming with the constraint of low surface roughness is carried out using SNAOA algorithm to reduce internal stress and increase service life of micro-mold during the forming process. The results show that the internal stress and the RMS roughness are only 0.54 MPa and 4.8 nm, respectively, for the optimal electrolyte parameters combination of SNAOA design.

  14. Effect of thermal residual stress on the mechanical properties of NiAl-based composites

    SciTech Connect

    Choo, H.; Bourke, M.; Nash, P.

    1999-07-01

    NiAl-based hybrid composites containing 5, 15 and 30 volume percent of Al{sub 2}O{sub 3} fibers in addition to AlN dispersion particles were fabricated via a powder metallurgy route. The strengthening mechanisms associated with the short Al{sub 2}O{sub 3} fiber in NiAl-(AlN){sub dispersion}-(Al{sub 2}O{sub 3}){sub fiber} composite were studied with an emphasis on the effect of thermal residual stress on the compressive strength at room temperature and 1,300K. At 300K, the yield strength of the composites was predicted using a linear superposition of the monolithic yield strength, direct fiber strengthening and tensile matrix residual stresses. The prediction shows good agreement with the measured data. The majority of the room temperature strengthening is attributable to the residual stress. At 1,300K, the strengthening was achieved only by the load sharing of the fibers and there is no direct influence from the process-induced thermal residual stresses since they were completely relaxed at this temperature.

  15. 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.

  16. 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

  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. Analysis of residual stresses in Al-Li repair welds and mitigation techniques

    SciTech Connect

    Dong, P.; Hong, J.K.; Rogers, P.

    1998-11-01

    In this paper, the recent results based on a comprehensive study on repair weld residual stresses are presented. Advanced finite element techniques were used to characterize the residual stress evolution in Al-Li alloy weldments, particularly under repair welding conditions. The present analysis procedures considered three-dimensional residual stress characteristics in the repair welds using a shell element model. Local residual stress details were analyzed by a generalized plane-strain model with prescribed translation and rotation conditions established from the global shell element model. Experimental residual stress measurements were conducted using X-ray diffraction methods. A good agreement between the finite element results and experimental measurements was obtained. Finally, a novel welding repair procedure (termed as a thermal stretching technique) was proposed to mitigate the weld residual stresses in repair.

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

  20. Stacking fault energy, yield stress anomaly, and twinnability of Ni3Al: A first principles study

    NASA Astrophysics Data System (ADS)

    Liu, Li-Li; Wu, Xiao-Zhi; Wang, Rui; Li, Wei-Guo; Liu, Qing

    2015-07-01

    Using first principles calculations combined with the quasiharmonic approach, we study the effects of temperature on the elastic constants, generalized stacking fault energies, and generalized planar fault energies of Ni3Al. The antiphase boundary energies, complex stacking fault energies, superlattice intrinsic stacking fault energies, and twinning energies decrease slightly with temperature. Temperature dependent anomalous yield stress of Ni3Al is predicted by the energy-based criterion based on elastic anisotropy and antiphase boundary energies. It is found that p increases with temperature and this can give a more accurate description of the anomalous yield stress in Ni3Al. Furthermore, the predicted twinnablity of Ni3Al is also decreasing with temperature. Project supported by the National Natural Science Foundation of China (Grant Nos. 11104361 and 11304403) and the Fundamental Research Funds for the Central Universities, China (Grant Nos. CQDXWL2014003 and CDJZR14328801).

  1. Minimization of Residual Stress in an Al-Cu Alloy Forged Plate by Different Heat Treatments

    NASA Astrophysics Data System (ADS)

    Dong, Ya-Bo; Shao, Wen-Zhu; Jiang, Jian-Tang; Zhang, Bao-You; Zhen, Liang

    2015-06-01

    In order to improve the balance of mechanical properties and residual stress, various quenching and aging treatments were applied to Al-Cu alloy forged plate. Residual stresses determined by the x-ray diffraction method and slitting method were compared. The surface residual stress measured by x-ray diffraction method was consistent with that measured by slitting method. The residual stress distribution of samples quenched in water with different temperatures (20, 60, 80, and 100 °C) was measured, and the results showed that the boiling water quenching results in a 91.4% reduction in residual stress magnitudes compared with cold water quenching (20 °C), but the tensile properties of samples quenched in boiling water were unacceptably low. Quenching in 80 °C water results in 75% reduction of residual stress, and the reduction of yield strength is 12.7%. The residual stress and yield strength level are considerable for the dimensional stability of aluminum alloy. Quenching samples into 30% polyalkylene glycol quenchants produced 52.2% reduction in the maximum compressive residual stress, and the reduction in yield strength is 19.7%. Moreover, the effects of uphill quenching and thermal-cold cycling on the residual stress were also investigated. Uphill quenching and thermal-cold cycling produced approximately 25-40% reduction in residual stress, while the effect on tensile properties is quite slight.

  2. 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.

  3. 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.

  4. High-temperature deformation of uniaxially aligned lamellar TiAl/Ti{sub 3}Al

    SciTech Connect

    Heinrich, H.; Abaecherli, V.; Wilkins, D.J.; Kostorz, G.

    1999-07-01

    Uniaxially aligned polysynthetically twinned two-phase TiAl/Ti{sub 3}Al material is produced by induction zone melting and deformed in uniaxial compression. Above 1,000 K the strain rate sensitivity is independent of the lamellar orientation and increases strongly with increasing deformation temperature. Results for the strain rate sensitivity parameters are somewhat lower than those obtained for {gamma}-TiAl single- and polycrystals. If the lamellae are oriented parallel or perpendicular to the deformation axis, the flow stress decreases with increasing strain. After plastic deformation the dislocation density in the lamellae is remarkably low indicating recovery processes. At the lamellar interfaces misfit dislocations and periodic arrangements of dislocations with Burgers vectors inclined to the lamellar boundaries are found. In contrast to deformation at lower temperatures, deformation twinning is rare.

  5. 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.

  6. 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

  7. High temperature dispersion strengthening of NiAl

    NASA Technical Reports Server (NTRS)

    Sherman, M.; Vedula, K.

    1986-01-01

    A potential high temperature strengthening mechanism for alloys based on the intermetallic compound NiAl was investigated. This study forms part of an overall program at NASA Lewis Research Center for exploring the potential of alloys based on NiAl for high temperature applications. An alloy containing 2.26 at% Nb and produced by hot extrusion of blended powders was examined in detail using optical and electron microscopy. Interdiffusion between the blended Nb and NiAl powders results in the formation of intermediate phases. A fine dispersion of precipitates of a hexagonal, ordered NiAlNb phases in a matrix of NiAl can be produced and this results in strengthening of the alloy by interfering with dislocation motion at high temperature. These precipitates are, however, found to coarsen during the high temperature (1300 K) deformation at slow strain rates and this may impose some limitatioins on the use of this strengthening mechanism.

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

    NASA Astrophysics Data System (ADS)

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

    2008-03-01

    The effect of β grain size on trigger stress for stress-induced martensitic transformation during tensile deformation in Ti-Al-Nb alloys was investigated. The trigger stress for stress-induced martensitic transformation (SIMT) in Ti-Al-Nb alloys exhibited a U-shaped behavior with variation in grain size. The variation of trigger stress with grain size was explained qualitatively, in terms of the contrasting change in the internal elastic energy stored in matrix due to formation of martensite (Δ E el ) and the irreversible work done in overcoming the internal frictional resistance to phase boundary movement (∂ E irr) with β grain size.

  9. 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.

  10. Tropical soils with high aluminum concentrations cause oxidative stress in two tomato genotypes.

    PubMed

    Nogueirol, Roberta Corra; Monteiro, Francisco Antonio; Grato, Priscila Lupino; Borgo, Luclia; Azevedo, Ricardo Antunes

    2015-03-01

    Tropical and subtropical soils are usually acidic and have high concentrations of aluminum (Al). Aluminum toxicity in plants is caused by the high affinity of the Al cation for cell walls, membranes, and metabolites. In this study, the response of the antioxidant-enzymatic system to Al was examined in two tomato genotypes: Solanum lycopersicum var. esculentum (Calabash Rouge) and Solanum lycopersicum var. cerasiforme (CNPH 0082) grown in tropical soils with varying levels of Al. Plant growth; activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPOX), and glutathione reductase (GR) enzymes; stress-indicating compounds (malondialdehyde (MDA) and hydrogen peroxide); and morphology (root length and surface area) were analyzed. Increased levels of Al in soils were correlated with reduced shoot and root biomass and with reduced root length and surface area. Calabash Rouge exhibited low Al concentrations and increased growth in soils with the highest levels of Al. Plants grown in soils with high availability of Al exhibited higher levels of stress indicators (MDA and hydrogen peroxide) and higher enzyme activity (CAT, APX, GPOX, and GR). Calabash Rouge absorbed less Al from soils than CNPH 0082, which suggests that the genotype may possess mechanisms for Al tolerance. PMID:25647795

  11. Evolution of residual stresses in micro-arc oxidation ceramic coatings on 6061 Al alloy

    NASA Astrophysics Data System (ADS)

    Shen, Dejiu; Cai, Jingrui; Guo, Changhong; Liu, Peiyu

    2013-11-01

    Most researches on micro-arc oxidation mainly focus on the application rather than discovering the evolution of residual stresses. However, residual stresses in the surface coatings of structural components have adverse effects on their properties, such as fatigue life, dimensional stability and corrosion resistance, etc. The micro-arc oxidation ceramic coatings are produced on the surfaces of 6061 aluminum alloy by a homemade asymmetric AC type of micro-arc oxidation equipment of 20 kW. A constant current density of 4.4±0.1 A/dm2 and a self-regulated composite electrolyte are used. The micro-arc oxidation treatment period ranges from 10 min to 40 min, and the thickness of the ceramic coatings is more than 20 μm. Residual stresses attributed to γ-Al2O3 constituent in the coatings at different micro-arc oxidation periods are analyzed by an X-ray diffractometer using the sin2 ψ method. The analysis results show that the residual stress in the ceramic coatings is compressive in nature, and it increases first and then decreases with micro-arc oxidation time increase. The maximum stress value is 1 667±20 MPa for period of 20 min. Through analyzing the coating thickness, surface morphology and phase composition, it is found that the residual stress in the ceramic coatings is linked closely with the coating growth, the phase composition and the micro cracks formed. It is also found that both the heat treatment and the ultrasonic action release remarkably the residual compressive stress. The heat treatment makes the residual compressive stress value decrease 1 378 MPa. The ultrasonic action even alters the nature of the residual stress, making the residual compressive stress change into a residual tensile stress.

  12. Stress investigation of the AlGaN/GaN micromachined circular diaphragms of a pressure sensor

    NASA Astrophysics Data System (ADS)

    Dzuba, J.; Vanko, G.; Drk, M.; Rger, I.; Vallo, M.; Kuti, V.; Hako, D.; Choleva, P.; Lalinsk, T.

    2015-01-01

    In this paper, selected mechanical properties of a circular AlGaN/GaN diaphragm with an integrated circular high electron mobility transistor (HEMT) intended for pressure sensing are investigated. Two independent methods were used to determine the residual stress in the proposed diaphragms. The resonant frequency method using laser Doppler vibrometry (LDV) for vibration measurement was chosen to measure the natural frequencies while the diaphragms were excited by acoustic impulse. It is shown that resonant frequency is strongly dependent on the built-in residual stress. The finite element analysis (FEM) in Ansys software was performed to determine the stress value from frequency spectra measured. The transition behavior of proposed diaphragms between the ideal circular membrane and plate is observed and discussed. Secondly, the bulging method and white light interferometry (WLI) are used to determine the stress-dependent deflection response of the AlGaN/GaN diaphragm under static pressure loading. Regarding the results obtained, the optimal design of the sensing electrodes is outlined.

  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. Magnetic properties and high frequency characteristics of FeCoAlON alloy films

    NASA Astrophysics Data System (ADS)

    Zheng, Kuohai; Yang, Shengsheng; Zheng, Fu; Luo, Feilong; Bai, Jianmin; Cao, Jiangwei; Wei, Fulin

    2015-06-01

    In this work, we report the magnetic properties, domain structures and high frequency properties of FeCoAlON alloy films prepared by reactive magnetron sputtering. With increasing N addition content, the films transfer from in-plane anisotropic properties to isotropic behavior. The obvious stripe domain structure is observed in the films with high N content, and the domain parameters depend on the thickness of the films. The XRD analysis indicates that the stripe domain may origin from the stress-induced perpendicular anisotropy by Al, O and N addition. Meanwhile, a double-peak resonance behavior is observed in the permeability spectra of the films with stripe domain structure.

  16. 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.

  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. Observation of morphology and stress distribution around dislocation in Ni3Al on the atomic scale

    NASA Astrophysics Data System (ADS)

    Ma, S. Y.; Ren, N. N.; Zhang, J. X.

    2015-06-01

    Dislocation is very important for the properties of materials. In this work, morphology and stress distribution around dislocation in Ni3Al are observed in atomic scale by the molecular dynamics. We obtained the dislocation morphology by the simulation and found that the atom distribution around the dislocation core is irregular. Layers of atoms on both the left and right sides of the dislocation core leans to the core, and about six layers of atoms are fractured due to the missing of the half plane of atoms. Along the [1 1 1] direction, there are about eight layers of atoms deviating from its equilibrium position. These results demonstrated that influenced area of dislocation is pipe-like. The stress distribution agrees with the results from the formula. Both normal stress and shear stress components exist in the edge dislocation stress field, normal stress mainly concentrating on two sides of the dislocation line, while the shear stress exist several angstrom away from the dislocation line.

  19. 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.

  20. Recovery of AlMg alloys: Flow stress and strain-hardening properties

    SciTech Connect

    Verdier, M.; Brechet, Y.; Guyot, P.

    1998-12-11

    The recovery of Al-2.5wt% Mg alloys cold-rolled to several strains between 0.1 and 3 has been studied essentially using tensile tests. The yield stress and strain-hardening properties are studied as a function of the initial prestrain, and of the temperature and the duration of annealing treatments. A theoretical model based on the dislocation structure is proposed. The kinetic evolution of the yield stress is related to the variation of the total dislocation density as a single structural parameter. The pseudo-logarithmic time decay is explained on the basis of a relaxation of the internal stresses by thermally activated dislocation motion. A strain-hardening model is proposed based on Kocks` constitutive law of plasticity, where the dislocation storage and dislocation annihilation parameters are adapted to a heterogeneous cell/subgrain dislocation structure. The adjustment of the model to the work-hardening behavior is in agreement with TEM observations.

  1. Crystallized Ohmic Contact Effect in AlGaN/GaN High Electron Mobility Transistor

    NASA Astrophysics Data System (ADS)

    Liao, Sheng Yu; Chang, Tsu; Hsu, Hsiao-Hsuan; Cheng, Chun-Hu; Chang, Liann-Be; Cheng, Chin-Pao; Teng, Tun-Chien

    2013-08-01

    In this study, we investigate the grain size effect of high electron mobility transistor devices with ohmic contact metals of stacked Ti/Al/Ni/Au and Ti/Al/Mo/Au. In addition to a comparison of electrical characteristics, the ohmic contacts were also examined by a scratch test for the observation of adhesion behavior. The experimental results demonstrate that the metal grain size is strongly dependent on metal adhesion, which may lead to bonding issues. Moreover, the grain-induced lateral stress lowers the drive current and increases the off-state current owing to the degraded gate swing and transconductance of transistor switching characteristics.

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

    PubMed Central

    Petri, Susanne; Krner, Sonja; Kiaei, Mahmoud

    2012-01-01

    Nrf2 (nuclear erythroid 2-related factor 2) is a basic region leucine-zipper transcription factor which binds to the antioxidant response element (ARE) and thereby regulates the expression of a large battery of genes involved in the cellular antioxidant and anti-inflammatory defence as well as mitochondrial protection. As oxidative stress, inflammation and mitochondrial dysfunctions have been identified as important pathomechanisms in amyotrophic lateral sclerosis (ALS), this signaling cascade has gained interest both with respect to ALS pathogenesis and therapy. Nrf2 and Keap1 expressions are reduced in motor neurons in postmortem ALS tissue. Nrf2-activating compounds have shown therapeutic efficacy in the ALS mouse model and other neurodegenerative disease models. Alterations in Nrf2 and Keap1 expression and dysregulation of the Nrf2/ARE signalling program could contribute to the chronic motor neuron degeneration in ALS and other neurodegenerative diseases. Therefore, Nrf2 emerges as a key neuroprotective molecule in neurodegenerative diseases. Our recent studies strongly support that the Nrf2/ARE signalling pathway is an important mediator of neuroprotection and therefore represents a promising target for development of novel therapies against ALS, Parkinson's disease (PD), Huntington's disease (HD), and Alzheimer's disease (AD). PMID:23050144

  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. High-temperature Oxidation Resistance of Al2O3-Au Laminated Composite Coating Prepared on TiAl-based Alloy

    NASA Astrophysics Data System (ADS)

    Ma, Xiaoxu; He, Yedong; Wang, Deren; Lin, Junpin; Gao, Wei

    2012-04-01

    Novel composite coatings consist of Al2O3 micro-layers alternating with Au nano-layers have been prepared on TiAl-based alloy by magnetron sputtering. The results of high-temperature cyclic oxidation test at 900 °C for 200 h revealed that the multi-sealed α-Al2O3 and Au layers effectively suppress the inward diffusion of oxygen to a low level. The formed oxide scales and composite coatings are compact and free of cracks. The thermal stress is decreased owing to the increase of thermal-expansion coefficient. And the surface scratch test exhibited that the brittle/ductile laminated structure can remarkably enhance the strength and toughness in combination with improved damage resistance of the Al2O3-Au laminated composite coatings. Consequently, the oxidation and spallation resistance of TiAl-based alloy have been improved significantly.

  8. Stress-diffusion interaction during oxidation at high temperature

    NASA Astrophysics Data System (ADS)

    Dong, Xuelin; Feng, Xue; Hwang, Keh-Chih

    2014-10-01

    Superalloy or other thermal protective materials are often oxidized seriously at high temperature. For most materials diffusion is the controlling step of oxidation. During oxidation, stress would be induced by growth strain and it can affect the diffusion process through chemical potential and diffusivity. Governing equation for diffusion is derived considering chemo-mechanical potential and diffusivity affected by stress. Oxidation kinetics is obtained to interpret the stress-diffusion coupling effects. The stress and its gradient influences on oxidation are also discussed.

  9. The cyclic stress-strain curve of discontinuously-reinforced Al- and Mg-based composites

    SciTech Connect

    Llorca, J. . Dept. of Materials Science)

    1994-03-15

    The analysis of the mechanical behavior of discontinuously-reinforced metal-matrix composites (MMC) has received considerable attention in recent years, owing to the potential of these materials in structural applications. Interest was initially focused on the strengthening, as well as on the new failure mechanisms, induced by the presence of ceramic reinforcements under monotonic loading conditions. Understandably, research on the constitutive response under fully-reversed cyclic loading conditions was left for a later stage, and to date this topic has been addressed in only a few studies, and the complete cyclic stress-strain curve only measured in. However, the cyclic stress-strain curve is a critical parameter in the design of structural components subjected to low-cycle fatigue, and it is also important to obtain better knowledge of the deformation and failure micromechanisms. In particular, the range of validity and of the limitations of the models developed to explain the monotonic behavior can be tested by checking the model predictions with experimental results obtained under different loading conditions, e.g. cyclic deformation. This research was aimed at measuring the cyclic stress-strain response of several Al-based composites and one Mg-based reinforced with either ceramic particulates (SiC, Al[sub 2]O[sub 3]) or whiskers (SiC), and subjected to different thermal treatments. The experimental results are discussed in the light of the emerging theories of cyclic deformation for MMC, and the areas where further research is needed are indicated.

  10. 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…

  11. Reliability Issues in AlGaN/GaN High Electron Mobility Transistors

    NASA Astrophysics Data System (ADS)

    Douglas, E. A.; Liu, L.; Lo, C. F.; Gila, B. P.; Ren, F.; Pearton, Stephen J.

    As AlGaN/GaN high electron mobility transistors gain commercial acceptance for use in high-power and high-frequency applications, it is becoming ever important to understand the degradation mechanisms that drive failure in the field. Because of the complex nature and multifaceted operation modes of these devices, reliability studies must go beyond the typical Arrhenius accelerated life tests. To do this, we investigated the electric field-driven degradation in devices with different gate metallization, device dimensions, and electric field mitigation techniques (such as source field plate) and the effect of device fabrication processes for both dc and RF stress conditions.

  12. Reliability studies of AlGaN/GaN high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Cheney, D. J.; Douglas, E. A.; Liu, L.; Lo, C. F.; Xi, Y. Y.; Gila, B. P.; Ren, F.; Horton, David; Law, M. E.; Smith, David J.; Pearton, S. J.

    2013-07-01

    AlGaN/GaN high electron mobility transistors are gaining commercial acceptance for use in high power and high frequency applications, but the degradation mechanisms that drive failure in the field are not completely understood. Since some of these mechanisms are current or field driven, reliability studies must go beyond the typical Arrhenius-accelerated life tests. In this paper, we summarize recent work on electric field or current driven degradation in devices with different gate metallization, device dimensions, electric field mitigation techniques (such as source field plates) and the effect of device fabrication processes for both dc and RF stress conditions.

  13. Stress corrosion cracking of sensitized AA5083 (Al-4.5Mg-1.0Mn)

    NASA Astrophysics Data System (ADS)

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

    2001-11-01

    The AA5083 (Al-4.4Mg-0.7Mn-0.15Cr) alloy is a nonheat-treatable aluminum alloy known for its excellent corrosion resistance. However, it can become susceptible to intergranular stress corrosion cracking (IGSCC) when exposed to temperatures ranging from 50 C to 200 C for sufficient lengths of time. This IGSCC is widely believed to be associated with dissolution of the electrochemically active ? phase, Al3Mg2, which is precipitated on grain boundaries. Recently, alternative mechanisms have been invoked related to hydrogen effects and/or free Mg segregation or depletion in the grainboundary regions. To establish a baseline for the sensitization effect, constant-extension-rate tests (CERTs) were conducted under open-circuit conditions and under potential control in 3.5 pct NaCl on samples isothermally treated at 150 C. To aid in interpreting the CERT results, grain-boundary precipitation and solute depletion were characterized by transmission electron microscopy (TEM). Additionally, the electrochemical behavior of the ? phase was characterized by anodic polarization of the intermetallic compound synthesized in bulk form. In CERTs under open-circuit conditions, the measured ductility depended strongly on sensitization time, reaching a minimum at 189 hours, followed by a slight increase at longer times. This trend correlated well with the fractional coverage of ? phase on grain boundaries, which increased up to 189 hours, where it existed with nearly continuous coverage. At longer times, this film coarsened and became discontinuous. Correspondingly, some resistance to IGSCC was recovered. In polarization experiments, bulk synthesized ? phase was found to be spontaneously passive from its corrosion potential (-1.40 VSCE) up to about -0.92 VSCE, where passivity was observed to break down. Sensitized AA5083 samples polarized below the ?-phase breakdown potential showed almost no evidence of IGSCC, indicating that a high ? dissolution rate is a requirement for IGSCC. Mg-depleted zones were observed along grain boundaries in sensitized alloys, but a clear role for solute depletion in IGSCC could not be defined on the basis of the results developed in this study.

  14. 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.

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

    SciTech Connect

    Blokhin, S.A.; Smirnov, A.N.; Sakharov, A.V.; Gladyshev, A.G.; Kryzhanovskaya, N.V.; Maleev, N.A.; Zhukov, A.E.; Semenova, E.S.; Bedarev, D.A.; Nikitina, E.V.; Kulagina, M.M.; Maksimov, M.V.; Ledentsov, N.N.; Ustinov, V.M.

    2005-07-15

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

  16. 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

  17. 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.

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

    SciTech Connect

    Warrier, S.G.; Majumdar, B.S.; Gundel, D.B.; Miracle, D.B.

    1997-08-01

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

  19. Oxidative stress affects FET proteins localization and alternative pre-mRNA processing in cellular models of ALS.

    PubMed

    Svetoni, Francesca; Caporossi, Daniela; Paronetto, Maria Paola

    2014-10-01

    FUS/TLS, EWS and TAF15 are members of the FET family of DNA and RNA binding proteins, involved in multiple steps of DNA and RNA processing and implicated in the regulation of gene expression and cell-signaling. All members of the FET family contribute to human pathologies, as they are involved in sarcoma translocations and neurodegenerative diseases. Mutations in FUS/TLS, in EWSR1 and in TAF15 genescause Amyotrophic Lateral Sclerosis (ALS), a fatal human neurodegenerative disease that affects primarily motor neurons and is characterized by the progressive loss of motor neurons and degradation of the neuromuscular junctions.ALS-associated FET mutations cause FET protein relocalization into cytoplasmic aggregates, thus impairing their normal function. Protein aggregation has been suggested as a co-opting factor during the disease pathogenesis. Cytoplasmic mislocalization of FET proteins contributes to the formation of cytoplasmic aggregates that may alter RNA processing and initiate motor neuron degeneration. Interestingly, oxidative stress, which is implicated in the pathogenesis of ALS, triggers the accumulation of mutant FUS in cytoplasmic stress granules where it binds and sequester wild-type FUS.In order to evaluate the role of FET proteins in ALS and their involvement in the response to oxidative stress, we have developed cellular models of ALS expressing ALS-related FET mutants in neuroblastoma cell lines. Upon treatment with sodium arsenite, cells were analysed by immunofluorescence to monitor the localization of wild-type and mutated FET proteins. Furthermore, we have characterized signal transduction pathways and cell survival upon oxidative stress in our cellular models of ALS. Interestingly, we found that EWS mutant proteins display a different localization from FUS mutants and neither wild-type nor mutated EWS protein translocate into stress granules upon oxidative stress treatment. Collectively, our data provide a new link between the oxidative stress response and RNA metabolism in ALS disease. PMID:26461404

  20. Texture and microstructure development in Al-2%Mg during high- temperature deformation

    SciTech Connect

    Chen, S.R.; Kocks, U.F.

    1990-12-01

    The high rate sensitivity of the flow stress that is exhibited by alloys under solute drag control, such as Al-Mg at high temperatures, influences texture development because more slip systems contribute to deformation. Al-2% Mg was tested in channel-die compression, i.e. idealized rolling, at 290{degree}C and 400{degree}C, at strain rates from 10{sup {minus}1}/s to 10{sup {minus}5}/s. The texture development in rolling predicted by polycrystal plasticity simulation indicates that the brass component increases while the copper component decreases when the rate sensitivity is raised. The experimental results are in good agreement with this prediction. In addition, cube component appears when microstructural change occurs due to dynamic recrystallization. This microstructural change leads to the shift from {l angle}011{r angle} to {l angle}001{r angle} fiber texture in free compression at high temperature. 18 refs., 13 figs.

  1. 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.

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

    SciTech Connect

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

    1991-05-01

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

  3. 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%.

  4. 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

  5. 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

  6. 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

  7. 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 role in preventing micromotion between the bone and implant and therefore reducing the chance of fretting/fatigue corrosion.

  8. High-temperature creep of Nb-Al-V alloys

    SciTech Connect

    Rong, T.S.; Aindow, M.

    1999-07-01

    Nb-15Al-20V alloys with about 45% by volume of an A15 phase in a B2 matrix have been subjected to creep deformation at temperatures between 1,000 C and 1,200 C and stresses from 80 MPa to 240 MPa in vacuum. The creep curves show a rapid transition from primary to steady-state creep with a well-defined activation energy. Microstructural observations show that the creep deformation occurs mainly in the B2 matrix and is controlled by dislocation mechanisms. Samples which had been cold-rolled and annealed to reduce the size of A15 precipitates and increase the yield strength were found to have lower creep resistance than those with unrefined microstructures. The significance of these observations for the creep mechanisms is discussed.

  9. Flow stress of rapidly solidified Al-5Cr-2Zr alloy as a function of processing variables

    SciTech Connect

    Brahmi, A.; Gerique, T.; Torralba, M.; Lieblich, M.

    1997-12-01

    In a previous work, Lieblich et al. determined that room temperature hardness and tensile strength of as-extruded Al-5Cr-2Zr (wt.%) alloys obtained by gas atomization increased with decreasing powder particle size and extrusion temperature, and depended only very little on extrusion ratio and ram speed. The aim of the present study was to determine the influence of powder particle diameter and extrusion temperature on the flow stress of Al-5Cr-2Zr at temperatures ranging from 373 to 773 K. The contribution to the flow stress of different strengthening mechanisms is evaluated and related to the processing parameters.

  10. Stress controlled pulsed direct current co-sputtered Al1-xScxN as piezoelectric phase for micromechanical sensor applications

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    Scandium alloyed aluminum nitride (Al1-xScxN) 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 e31,f from -1.28 C/m2 to -3.01 C/m2 was recorded, while dielectric constant and loss angle remain low. Further, the built-in stress level of Al1-xScxN was found to be tuneable by varying pressure, Ar/N2 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 Al1-xScxN as the piezoelectric phase of micro-electro-mechanical system sensor applications highly attractive.

  11. High velocity sliding at a compressed Al(111)/Al(100) interface

    NASA Astrophysics Data System (ADS)

    Hammerberg, J. E.; Ravelo, R.; Germann, T. C.; Holian, B. L.

    2007-03-01

    We discuss high velocity sliding at a compressed Al(111)/Al(100) interface sliding in the 110 direction at a pressure of 15 GPa. Three temperatures are considered, T=232, 464 and 696 K. System sizes are 1.4 10^6 atoms .We find that for velocities above a critical velocity, vc, the frictional force scales as (v/vc)^-β with β 3/4. We discuss the temperature and size dependence of vc. We find that below vc the frictional force is an increasing function of velocity with an initial linear dependence. Above vc there is a regime of interfacial instability characterized by a (100) transformation front moving into the (111) material. This is followed by a fluid regime for which a Couette flow profile develops at the interface, the thickness of which grows with increasing velocity.

  12. High mobility two-dimensional electron gases in nitride heterostructures with high Al composition AlGaN alloy barriers

    SciTech Connect

    Li Guowang; Cao Yu; Xing Huili Grace; Jena, Debdeep

    2010-11-29

    We report high-electron mobility nitride heterostructures with >70% Al composition AlGaN alloy barriers grown by molecular beam epitaxy. Direct growth of such AlGaN layers on GaN resulted in hexagonal trenches and a low mobility polarization-induced charge. By applying growth interruption at the heterojunction, the surface morphology improved dramatically and the room temperature two-dimensional electron gas (2DEG) mobility increased by an order of magnitude, exceeding 1300 cm{sup 2}/V s. The 2DEG density was tunable at 0.4-3.7x10{sup 13}/cm{sup 2} by varying the total barrier thickness (t). Surface barrier heights of the heterostructures were extracted and exhibited dependence on t.

  13. 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.

  14. 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.

  15. 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.

  16. 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

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

    NASA Astrophysics Data System (ADS)

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

    2012-07-01

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

  18. High strain rate deformation of NiAl

    SciTech Connect

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

    1994-07-01

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

  19. 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.

  20. 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.

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

    NASA Astrophysics Data System (ADS)

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

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

  2. 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.

  3. 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. Sustained aeration of joint fluid, as well as proper tolerancing of mating surfaces, along with a proper choice of material microstructure may be utilized to extend implant life. PMID:22098898

  4. 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.

  5. High-Risk Stress Fractures: Diagnosis and Management.

    PubMed

    McInnis, Kelly C; Ramey, Lindsay N

    2016-03-01

    Stress fractures are common overuse injuries in athletes. They occur during periods of increased training without adequate rest, disrupting normal bone reparative mechanisms. There are a host of intrinsic and extrinsic factors, including biochemical and biomechanical, that put athletes at risk. In most stress fractures, the diagnosis is primarily clinical, with imaging indicated at times, and management focused on symptom-free relative rest with advancement of activity as tolerated. Overall, stress fractures in athletes have an excellent prognosis for return to sport, with little risk of complication. There is a subset of injuries that have a greater risk of fracture progression, delayed healing, and nonunion and are generally more challenging to treat with nonoperative care. Specific locations of high-risk stress fracture include the femoral neck (tension side), patella, anterior tibia, medial malleolus, talus, tarsal navicular, proximal fifth metatarsal, and great toe sesamoids. These sites share a characteristic region of high tensile load and low blood flow. High-risk stress fractures require a more aggressive approach to evaluation, with imaging often necessary, to confirm early and accurate diagnosis and initiate immediate treatment. Treatment consists of nonweight-bearing immobilization, often with a prolonged period away from sport, and a more methodic and careful reintroduction to athletic activity. These stress fractures may require surgical intervention. A high index of suspicion is essential to avoid delayed diagnosis and optimize outcomes in this subset of stress fractures. PMID:26972260

  6. 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.

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

    SciTech Connect

    Lei Li; He Duanwei Zou Yongtao; Zhang Wei; Wang Zhao; Jiang Ming; Du Maolu

    2008-08-15

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

  8. AlN films deposited by dc magnetron sputtering and high power impulse magnetron sputtering for SAW applications

    NASA Astrophysics Data System (ADS)

    Ait Aissa, K.; Achour, A.; Elmazria, O.; Simon, Q.; Elhosni, M.; Boulet, P.; Robert, S.; Djouadi, M. A.

    2015-04-01

    In this work, aluminium nitride (AlN) films were deposited on silicon substrates buffered by an epitaxial AlN thin film for surface acoustic wave (SAW) applications. The films were deposited by dc magnetron sputtering (dcMS) and high power impulse magnetron sputtering (HiPIMS) deposition techniques. The structural properties of AlN films were investigated using x-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy and atomic force microscopy. In both cases of films deposited by dcMS and HiPIMS, the XRD results showed that the obtained films are oriented, with full width at half maximum rocking curves of around 1°. Raman spectroscopy revealed higher residual stress relaxation in the AlN epilayers grown by HiPIMS compared to AlN grown by dcMS, highlighted by a blue shift in the E2(high) Raman mode. The SAW measurements indicated an insertion loss of AlN-SAW devices of about 53 and 35 dB for the AlN films deposited by dcMS and HiPIMS respectively. The relation between the structural properties of AlN and the characteristics of AlN-SAW devices were correlated and discussed.

  9. High-resolution electron microscopy study of tunnelling junctions with AlN and AlON barriers

    SciTech Connect

    Shang, Ping; Petford-Long, Amanda K.; Nickel, Janice H.; Sharma, Manish; Anthony, Thomas C.

    2001-06-01

    Spin-dependent tunnel junctions with AlON and AlN barriers have been investigated using high-resolution electron microscopy. Plasma gas composition, nitridation time, and deposited Al thickness were studied independently. Plasma-nitrided Al produces thinner tunnel barriers than those obtained with an oxygen or oxygen+nitrogen plasma, for the same plasma exposure time. Experiments to study an increase in plasma nitridation time for a constant Al deposition thickness showed that overexposure to the plasma resulted in a thinner barrier{emdash}possibly due to the competing processes of nitride formation and slight etching of the barrier. The AlN barrier thickness increases monotonically with deposited Al thickness for a constant nitridation time. Electron energy loss spectroscopy compositional mapping has confirmed that nitrogen is present in the barrier layer. The roughness between the barrier layer and the two ferromagnetic layers has also been estimated. {copyright} 2001 American Institute of Physics.

  10. Electrostatic Discharge Effects on AlGaN/GaN High Electron Mobility Transistors on Sapphire Substrates

    NASA Astrophysics Data System (ADS)

    Lee, Seung-Chul; Her, Jin-Cherl; Han, Sang-Myeon; Seo, Kwang-Seok; Han, Min-Koo

    2004-04-01

    The effects of electrostatic discharge (ESD) on the variation of electrical characteristics of AlGaN/GaN high electron mobility transistors (HEMTs), such as on-current, leakage current of gate and transconductance (gm), have been investigated. The failure phenomena of HEMTs due to the ESD stress have also been studied. We have applied the ESD stress by transmission line pulsing (TLP) method, which is widely used in ESD stress experiments, and measured the electrical characteristics before and after applying ESD stress. The on-current after applying ESD stress was increased because the space between the drain and the gate was narrowed due to the migration of the metal caused by the high electric field and temperature under the ESD stress. The leakage current was decreased and gm was changed slightly. The failure points were located mainly in the middle and on each side of the gate. AlGaN/GaN HEMTs, in contrast with GaAs HEMTs, have been shown to easily fail due to the poor thermal characteristics of the sapphire substrate.

  11. High occupational stress and low career satisfaction of Korean surgeons.

    PubMed

    Kang, Sang Hee; Boo, Yoon Jung; Lee, Ji Sung; Han, Hyung Joon; Jung, Cheol Woong; Kim, Chong Suk

    2015-02-01

    Surgery is a demanding and stressful field in Korea. Occupational stress can adversely affect the quality of care, decrease job satisfaction, and potentially increase medical errors. The aim of this study was to investigate the occupational stress and career satisfaction of Korean surgeons. We have conducted an electronic survey of 621 Korean surgeons for the occupational stress. Sixty-five questions were used to assess practical and personal characteristics and occupational stress using the Korean occupational stress scale (KOSS). The mean KOSS score was 49.31, which was higher than the average of Korean occupational stress (45.86) or that of other specialized professions (46.03). Young age, female gender, long working hours, and frequent night duties were significantly related to the higher KOSS score. Having spouse, having hobby and regular exercise decreased the KOSS score. Multiple linear regression analysis showed that long working hours and regular exercise were the independent factors associated with the KOSS score. Less than 50% of surgeons answered that they would become a surgeon again. Most surgeons (82.5%) did not want to recommend their child follow their career. Korean Surgeons have high occupational stress and low level of career satisfaction. PMID:25653482

  12. Effects of Cd and Al stress on secondary metabolites, antioxidant and antibacterial activity of Hypoxis hemerocallidea Fisch. & C.A. Mey.

    PubMed

    Okem, Ambrose; Stirk, Wendy A; Street, Rene A; Southway, Colin; Finnie, Jeffrey F; Van Staden, Johannes

    2015-12-01

    This study investigated the effects of cadmium (Cd) and aluminium (Al) on the accumulation of phenolics, flavonoids and the bioactive compound hypoxoside in Hypoxis hemerocallidea. In addition, antioxidant scavenging and antibacterial activity were assessed to evaluate if Cd and Al stress affect the accumulation of bioactive compounds in H.hemerocallidea. Invitro grown plantlets of H.hemerocallidea were acclimatized for seven months in a greenhouse. Thereafter plants were exposed to various concentrations of Cd and Al both singularly and in combination in the form of Cd(NO3)2 (2, 5, 10mg Cd/L); Al3(NO3)3 (500, 1000, 1500mg Al/L) and combinations of Cd and Al (Cd 2:Al 500, Cd 5:Al 1000 and Cd 10:Al 1500mg/L) for a further six weeks. The highest amounts of Cd and Al translocated to the shoot were 34 and 1608mg/L respectively. Phytochemical screening showed significantly high amounts of total phenolics and flavonoids at the moderate Cd treatment (5mg/L) compared to the controls. Exposure to Cd and Al significantly decreased the accumulation of hypoxoside. There was a significant increase in diphenylpicrylhydrazyl (DPPH) antioxidant scavenging activity in most of the metal-treated plants compared to the positive control ascorbic acid. Extracts from Cd 2mg/L treatment exhibited moderate antibacterial activity against Staphylococcus aureus compared to the control. The results of the present study revealed that cultivating H.hemerocallidea on metal contaminated soils affects the accumulation of the bioactive compound, hypoxoside. PMID:26473664

  13. 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

  14. Transport characteristics of AlGaN/GaN/AlGaN double heterostructures with high electron mobility

    NASA Astrophysics Data System (ADS)

    Meng, Fanna; Zhang, Jincheng; Zhou, Hao; Ma, Juncai; Xue, Junshuai; Dang, Lisha; Zhang, Linxia; Lu, Ming; Ai, Shan; Li, Xiaogang; Hao, Yue

    2012-07-01

    The AlGaN/GaN/AlGaN double heterostructure (DH) with high electron mobility of 1862 cm2/Vs at room temperature and 478 cm2/Vs at 573 K high temperature was obtained by a combination of optimization schemes considering scattering mechanisms. First, a composite buffer layer structure, including GaN and AlGaN layer, was used to improve the crystal quality of the AlGaN/GaN/AlGaN DH. Second, interface roughness scattering was reduced by increasing the channel thickness, thus the two-dimensional electron gas mobility was further improved. Moreover, an ultrathin AlN interlayer was inserted between the GaN channel layer and the AlGaN buffer layer to decrease the alloy disorder scattering. The Hall effect measurements showed that the DH had better transport characteristics at high temperatures, and an electron mobility of 478 cm2/Vs was achieved at 573 K, which is twice larger than that of the conventional single heterostructure (˜200 cm2/Vs at 573 K). Therefore, AlGaN/GaN/AlGaN DH is more suitable for the applications in high temperature electronic devices.

  15. 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.

  16. High-resolution electron microscopy of dislocation cores in NiAl

    SciTech Connect

    Stoeckle, D.; Sigle, W.; Seeger, A.

    1999-07-01

    The atomic structure of dislocation cores in NiAl is studied by high-resolution transmission electron microscopy (HRTEM) and molecular dynamics (MD) calculations. Results are presented on dislocations with Burgers vectors b = a{lt}100{gt} and a{lt}111{gt}. A comparison of HRTEM image simulations indicates that the core of a 45{degree} a{lt}100{gt} dislocation consists of Al atoms. The Burgers vector distribution shows a width of 2.2b. This corresponds very closely to MD results and is consistent with the relatively low Peierls stress of this dislocation. By detailed image analysis the angular dependence of the shear stress components of the dislocation are made visible. MD results obtained from 45{degree} dislocations with opposite screw components suggest, that the helicity of the screw component might be discernible from high-resolution electron micrographs. A a{lt}111{gt} dislocation with {l{underscore}angle}110{r{underscore}angle} line direction is shown which exhibits a rather wide dissociation, probably into two a/2{lt}111{gt} partials.

  17. 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.

  18. Proteomics of rice grain under high temperature stress

    PubMed Central

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

    2013-01-01

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

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

    PubMed Central

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

    2012-01-01

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

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  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. 222-282 nm AlGaN and InAlGaN based deep-UV LEDs fabricated on high-quality AlN template

    NASA Astrophysics Data System (ADS)

    Hirayama, Hideki; Noguchi, Norimichi; Fujikawa, Sachie; Norimatsu, Jun; Kamata, Norihiko; Takano, Takayoshi; Tsubaki, Kenji

    2009-02-01

    We demonstrate 222-282 nm AlGaN and InAlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs) fabricated on low threading dislocation density (TDD) AlN template. Low TDD AlN templates were realized by using ammonia (NH3) pulse-flow multilayer (ML) growth technique. The edge- and screw-type dislocation densities of AlN layer were reduced to 7.5×108 and 3.8×107, respectively. We obtained significant increase of an AlGaN quantum well (QW) emission (by more than 50 times) by fabricating them on a low TDD ML-AlN template. We fabricated AlGaN multi (M)QW DUV-LEDs with emission range of 222-273 nm on ML-AlN templates. Single-peaked electroluminescence (EL) was obtained for AlGaN DUV-LEDs. We obtained the maximum output power of 1.1, 2.4 and 3.3 mW for the AlGaN LEDs with wavelengths of 241, 253 and 273 nm, respectively, under RT CW operation. The maximum output power of 227 and 222 nm AlGaN-QW were 0.15mW and 0.014mW, respectively, under RT pulsed operation. The maximum external quantum efficiency (EQE) of the 227 and 250 nm AlGaN LEDs were 0.2% and 0.43 %, respectively. We also fabricated 280 nm-band quaternary InAlGaN-MQW DUV-LEDs with p-type InAlGaN layers on low TDD ML-AlN templates. We obtained significant increase of photoluminescence (PL) intensity by introducing Si-doped InAlGaN buffer and barrier layers and undoped InAlGaN interlayer. We then demonstrated high internal quantum efficiency (IQE) of 284 nm InAlGaN-QW emission, which was confirmed by the fact that the ratio of the integrated intensity of the RT-PL against the 77K-PL was 86%. The maximum output power and EQE of the 282 nm InAlGaN LED were 10.6 mW and 1.2%, respectively, under RT CW operation.

  6. Effect of Volume Fraction of Primary α 2 on the Trigger Stress for Stress-Induced Martensitic Transformation in Two-Phase Ti-Al-Nb Alloys

    NASA Astrophysics Data System (ADS)

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

    2008-09-01

    Ti-Al-Nb alloys in the composition range studied in the present investigation were found to undergo stress-induced martensitic transformation (SIMT) in α 2 + β heat-treated (two-phase) condition under tensile loading. The effect of different volume fractions of primary α 2 on trigger stress for SIM transformation in these alloys was investigated. The trigger stress required for SIM transformation decreased initially when the volume fraction of primary α 2 was increased from 0 to 5 pct. However, subsequently, the trigger stress was found to increase with further increase in volume fraction of primary α 2 from 5 to 40 pct in all three alloys. An increase in the volume fraction of primary α 2 is achieved by changing the solution treatment temperatures, which also results in a change in the β composition and β grain size. The observed variation of trigger stress with the volume fraction of primary α 2 from 5 to 40 pct was then explained on the basis of the effect of composition and grain size of the β phase on trigger stress required for stress-induced transformation of β to martensite.

  7. 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.

  8. Nanocrystalline Ni-Al ferrites for high frequency applications

    NASA Astrophysics Data System (ADS)

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

    2013-02-01

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

  9. Identification of a high-risk anterior tibial stress fracture.

    PubMed

    Thelen, Mark D

    2010-12-01

    The patient was a deployed 34-year-old female soldier with a chief complaint of bilateral anterior shin pain for the past 8 weeks. Due to concern for a stress fracture, radiographic views of the bilateral tibia and fibula were completed, which revealed cortical thickening through the anterior midtibial regions bilaterally, consistent with stress reactive changes. Furthermore, a transverse lucency through the anterior cortex of the anterior right midtibial region was noted, which was consistent with a stress fracture. The patient was immediately placed in a short leg cast and was given strict non-weight-bearing instructions for gait. She was subsequently evacuated to her home duty station for consultation with an orthopaedic surgeon to determine if surgical intervention was warranted. This report illustrates the importance of identifying stress fractures considered to be high risk. PMID:21169720

  10. 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.

  11. Residual stress anisotropy in high pressure sodium lamp seals

    NASA Astrophysics Data System (ADS)

    Tóth, Zoltán; Koltai, Zoltán; Steinbach, Gábor; Juhász, András; Váradi, Károly

    2005-09-01

    Residual stresses in the seal material connecting the metallic feedthrough and the ceramic body of high pressure sodium lamps have been investigated. Anisotropy of the residual stresses were examined experimentally with Vickers indentation and were also modelled with the finite element modelling method. The two techniques resulted in good qualitative agreement. No microcrack formation or other microscale change happened during ageing, but relaxation of the stresses took place. Application of the technique based on counting the cracks initiated by Vickers indentation is described. The method is capable of showing relative changes in the stress level of samples after various ageing times. The method is also capable of testing systems with characteristic sizes of even less than 1 mm.

  12. 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.

  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. 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.

  15. 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.

  16. L. V. Al'tshuler, and High Energy Density Research

    NASA Astrophysics Data System (ADS)

    Gibson, Carl H.; Krikorian, Nerses H.; Keeler, R. Norris

    2012-03-01

    Knowledge of high energy densities critical to cosmology and astrophysics was achieved and exchanged among a very few scientists at a time when science was even more constrained by political considerations that it is today. Resources for the early studies necessarily involved atomic weaponry. A history of L. V. Al'tshuler and some others in his science is given in cosmological context. In the beginning of cosmology and the Universe, negative Fortov-Planck1 pressures c7h-1G-2 of 4.6 10115 Pa are overcome by inertial-vortex anti-gravity (dark energy) pressures to achieve a turbulent big bang and the first turbulent combustion with power 1066 watts at the Kolmogorov-Planck scale 10-35 meters. The big bang event ceased when negative- pressure gluon-viscous-forces extracted 10100 kg of mass-energy from the vacuum to produce the observed fossil vorticity turbulence Universe and its inflation with power 10145 watts.

  17. TorsinA rescues ER-associated stress and locomotive defects in C. elegans models of ALS.

    PubMed

    Thompson, Michelle L; Chen, Pan; Yan, Xiaohui; Kim, Hanna; Borom, Akeem R; Roberts, Nathan B; Caldwell, Kim A; Caldwell, Guy A

    2014-02-01

    Molecular mechanisms underlying neurodegenerative diseases converge at the interface of pathways impacting cellular stress, protein homeostasis and aging. Targeting the intrinsic capacities of neuroprotective proteins to restore neuronal function and/or attenuate degeneration represents a potential means toward therapeutic intervention. The product of the human DYT1 gene, torsinA, is a member of the functionally diverse AAA+ family of proteins and exhibits robust molecular-chaperone-like activity, both in vitro and in vivo. Although mutations in DYT1 are associated with a rare form of heritable generalized dystonia, the native function of torsinA seems to be cytoprotective in maintaining the cellular threshold to endoplasmic reticulum (ER) stress. Here we explore the potential for torsinA to serve as a buffer to attenuate the cellular consequences of misfolded-protein stress as it pertains to the neurodegenerative disease amyotrophic lateral sclerosis (ALS). The selective vulnerability of motor neurons to degeneration in ALS mouse models harboring mutations in superoxide dismutase (SOD1) has been found to correlate with regional-specific ER stress in brains. Using Caenorhabditis elegans as a system to model ER stress, we generated transgenic nematodes overexpressing either wild-type or mutant human SOD1 to evaluate their relative impact on ER stress induction in vivo. These studies revealed a mutant-SOD1-specific increase in ER stress that was further exacerbated by changes in temperature, all of which was robustly attenuated by co-expression of torsinA. Moreover, through complementary behavioral analysis, torsinA was able to restore normal neuronal function in mutant G85R SOD1 animals. Furthermore, torsinA targeted mutant SOD1 for degradation via the proteasome, representing mechanistic insight on the activity that torsinA has on aggregate-prone proteins. These results expand our understanding of proteostatic mechanisms influencing neuronal dysfunction in ALS, while simultaneously highlighting the potential for torsinA as a novel target for therapeutic development. PMID:24311730

  18. Al-rich precipitation in CoNiCrAlY bondcoat at high temperature

    NASA Astrophysics Data System (ADS)

    Koomparkping, T.; Damrongrat, S.; Niranatlumpong, P.

    2005-06-01

    A thermal barrier coating (TBC) is applied on a surface of a gas turbine blade to provide a thermal barrier and oxidation resistant properties for the components. The ability to resist oxidation of the coating arises from the self-healing, protective Al2O3 scale on top of the bondcoat, which is formed during service. However, if Al depletion occurs within the bondcoat, the protective scale will lose its self-healing ability, and hence, its oxidation-resistant property. This paper investigated the depletion of Al within the bondcoat by studying the microstructure of the bondcoat on a gas turbine blade after it has been in 4000 h service at 1200 °C. The results showed that Al depletion had occurred at different levels throughout the turbine blade. In the area where Al depletion had not yet occurred, precipitation of an Al-rich phase was detected. Most of the Al was contained within this phase, leaving only small amount of Al in the surrounding matrix. A well-defined boundary was observed between the depleted and non-depleted regions.

  19. 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.

  20. 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

    2015-12-01

    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.

  1. 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.

  2. 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.

  3. 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

  4. Machine Learning for High-Throughput Stress Phenotyping in Plants.

    PubMed

    Singh, Arti; Ganapathysubramanian, Baskar; Singh, Asheesh Kumar; Sarkar, Soumik

    2016-02-01

    Advances in automated and high-throughput imaging technologies have resulted in a deluge of high-resolution images and sensor data of plants. However, extracting patterns and features from this large corpus of data requires the use of machine learning (ML) tools to enable data assimilation and feature identification for stress phenotyping. Four stages of the decision cycle in plant stress phenotyping and plant breeding activities where different ML approaches can be deployed are (i) identification, (ii) classification, (iii) quantification, and (iv) prediction (ICQP). We provide here a comprehensive overview and user-friendly taxonomy of ML tools to enable the plant community to correctly and easily apply the appropriate ML tools and best-practice guidelines for various biotic and abiotic stress traits. PMID:26651918

  5. 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.

  6. 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.

  7. Characterization of AlInN/GaN structures on AlN templates for high-performance ultraviolet photodiodes

    NASA Astrophysics Data System (ADS)

    Sakai, Yusuke; Khai, Pum Chian; Ichikawa, Junki; Egawa, Takashi; Jimbo, Takashi

    2011-02-01

    The authors characterize AlInN/GaN structures on AlN templates for high-performance ultraviolet photodiodes. AlInN/GaN structures were grown with various growth parameters by metal organic chemical vapor deposition. In the case of nearly lattice-matched to GaN underlying layers, AlInN/GaN structures are found to have smooth interface. AlInN layers grown at the low pressure are confirmed to have high crystal quality from x-ray diffraction measurements and good surface morphology from atomic force microscope images. The noble AlInN-based photodiodes were fabricated. Their performances show the leakage current of 48 nA at a reverse voltage of 5 V and the cutoff wavelength around 260 nm. A cutoff-wavelength responsivity of 21.84 mA/W is obtained, corresponding to quantum efficiency of 10.6%. It may be possible to realize high-performance ultraviolet photodiodes by further optimizing AlInN/GaN structures.

  8. 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.

  9. 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.

  10. 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.

  11. Stresses and strains in high-pressure composite hoses

    SciTech Connect

    Nair, S.; Dollar, A.

    1997-08-01

    A simple mechanical model for a high-pressure hose made of ethylene-propylene rubber reinforced with two helical steel wires and a layer of fabric is analyzed. The model assumes perfect bonding between the different constituents and the torsional effect due to the right-handed helical wires is neglected. Both linear and nonlinear stress-strain relations are considered for the rubber which is assumed to be incompressible. Stresses and strains of the constituents are obtained for different internal pressures and geometrical parameters.

  12. 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.

  13. 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.

  14. 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

  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. 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.

  17. 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

  18. High-G stress and orientational stress: physiologic effects of aerial maneuvering.

    PubMed

    Gillingham, K K

    1988-11-01

    G stress can readily incapacitate pilots of modern fighter aircraft and result in mishaps due to G-induced loss of consciousness (GLC). The physiologic effects of high-G stress, including decreased head-level blood pressure due to hydrostatic pressure drop and decreased cardiac output due to inadequate venous return, result in the symptoms of visual loss and GLC. The body's primary natural defenses against the effects of G stress in flight, i.e., the neural tissue energy reserve and the cardiovascular baroceptor reflexes, determine the characteristic shape of the G-time tolerance curve, which is presented. Means of raising G tolerance fall into three categories: mechanical, physiological, and educational. Mechanical means include anti-G suits and valves, assisted positive-pressure breathing (APPB) systems, and special seats in which the seatback is reclined and/or the pilot's legs are elevated. Physiological means include frequent exposure to G stress, physical conditioning (weight training and moderate aerobic conditioning), selection of pilots for high natural tolerance, and performance of a vigorous and efficient anti-G straining maneuver. Educational means include briefings on methods of enhancing tolerance, and high-G training in a centrifuge to allow the pilot to perfect his anti-G straining maneuver. An improved anti-G valve, physical conditioning, high-G awareness briefings, and centrifuge training are now being applied in efforts to prevent GLC in current fighter aircraft. Future generations of even more maneuverable aircraft will probably necessitate the use of APPB, pilot selection, and high-G seats for protection of pilots from the effect of sustained high G forces. PMID:3060092

  19. 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

  20. Investigation of gate-diode degradation in normally-off p-GaN/AlGaN/GaN high-electron-mobility transistors

    NASA Astrophysics Data System (ADS)

    Tapajna, M.; Hilt, O.; Bahat-Treidel, E.; Würfl, J.; Kuzmík, J.

    2015-11-01

    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 ˜105 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.

  1. 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

  2. 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

  3. 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.

  4. High reflectivity ultraviolet distributed Bragg reflector based on AlGaN/AlGaN multilayer

    NASA Astrophysics Data System (ADS)

    Shimada, Ryoko; Xie, Jinqiao; Morkoç, Hadis

    2007-02-01

    AlGaN/AlGaN distributed Bragg reflectors (DBRs) designed for the ultraviolet spectral region have been attained. The crack-free structures were grown on c-plane sapphire by plasma assisted molecular beam epitaxy (MBE). To minimize the built-in strain in DBRs, a thin buffer layer was used directly on c-plane sapphire. A peak reflectivity of 95% at 381 nm with a 21 nm stop band width was obtained at room temperature (RT) using a 32.5 pairs Al 0.7Ga 0.3N/Al 0.15Ga 0.85N DBR. With a driving force for DBRs and emitting regions in wide band gap semiconductor microcavities, such as those based on GaN and ZnO, is the quest for cavity polariton which is the coupled mode between the exciton and photon modes. Moreover, the exploitation of cavity polaritons could be expected in the course of the development of extremely low-threshold optoelectronics devices.

  5. 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.

  6. The behavior of off-state stress-induced electrons trapped at the buffer layer in AlGaN/GaN heterostructure field effect transistors

    SciTech Connect

    Liao, W. C.; Chen, Y. L.; Chen, C. H.; Chyi, J. I.; Hsin, Y. M.

    2014-01-20

    A measurement methodology involving the synchronous switching of gate to source voltage and drain to source voltage (V{sub DS}) was proposed for determining the shift of threshold voltage after an AlGaN/GaN heterostructure transistor endures high V{sub DS} off-state stress. The measurement results indicated slow electron detrapping behavior. The trap level was determined as (E{sub C} – 0.6 eV). Simulation tool was used to analyze the measurement results. The simulation results were consistent with the experimental results; and a relationship between the buffer trap and threshold voltage shift over time was observed.

  7. Seasonal changes in stress indicators in high level football.

    PubMed

    Faude, O; Kellmann, M; Ammann, T; Schnittker, R; Meyer, T

    2011-04-01

    This study aimed at describing changes in stress and performance indicators throughout a competitive season in high level football. 15 players (19.5±3.0 years, 181±5 cm, 75.7±9.0 kg) competing under professional circumstances were tested at baseline and 3 times during the season 2008/09 (in-season 1, 2, 3). Testing consisted of the Recovery-Stress Questionnaire for Athletes (Total Stress and Recovery score), vertical jump tests (counter movement and drop jump (DJ)), and a maximal ramp-like running test. Average match exposure was higher during a 3-weeks period prior to in-season 3 compared to in-season 1 and 2 (1.5 vs. 1 h/week, p=0.05). Total Stress score was elevated at in-season 1 and 2 compared to baseline (p<0.01) with a further increase at in-season 3 (p<0.03; generalized eta squared (η(2)(g))=0.37). Total Recovery score was decreased at in-season 1 and 3 compared to baseline (p<0.05; η(2)(g)=0.21). Maximal running velocity (V(max)) and jumping heights were not significantly affected (η(2)(g)≤0.04). Changes in DJ height and V (max) between baseline and in-season 3 were correlated with the corresponding changes in Total Stress score (r=-0.55 and r=-0.61, p<0.03). Usual match exposure during a professional football season does not induce relevant changes in performance indicators. Accumulated stress and a lack of recovery towards the end of a season might be indicated by psychometric deteriorations. PMID:21271495

  8. Interfacial shear stress measurement using high spatial resolution multiphase PIV

    NASA Astrophysics Data System (ADS)

    Andr, Matthieu A.; Bardet, Philippe M.

    2015-06-01

    In multiphase flows, form drag and viscous shear stress transfer momentum between phases. For numerous environmental and man-made flows, it is of primary importance to predict this transfer at a liquid-gas interface. In its general expression, interfacial shear stress involves local velocity gradients as well as surface velocity, curvature, and surface tension gradients. It is therefore a challenging quantity to measure experimentally or compute numerically. In fact, no experimental work to date has been able to directly resolve all the terms contributing to the shear stress in the case of curved and moving surfaces. In an attempt to fully resolve the interface shear stress when surface tension gradients are negligible, high-resolution particle image velocimetry (PIV) data are acquired simultaneously on both sides of a water-air interface. The flow consists of a well-conditioned uniform and homogeneous water jet discharging in quiescent air, which exhibits two-dimensional surface waves as a result of a shear layer instability below the surface. PIV provides velocity fields in both phases, while planar laser-induced fluorescence is used to track the interface and obtain its curvature. To compute the interfacial shear stress from the data, several processing schemes are proposed and compared, using liquid and/or gas phase data. Vorticity at the surface, which relates to the shear stress through the dynamic boundary condition at the surface, is also computed and provides additional strategies for estimating the shear. The various schemes are in agreement within the experimental uncertainties, validating the methodology for experimentally resolving this demanding quantity.

  9. 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.

  10. Quaternary InAlGaN-based deep-UV LED with high-Al-content p-type AlGaN

    NASA Astrophysics Data System (ADS)

    Hirayama, Hideki; Aoyagi, Yoshinobu

    2004-07-01

    For the realization of 250-350 nm band deep ultraviolet (UV) emitters using group III-nitride materials, it is required to obtain high-efficiency UV emission and hole conductivity for wide-bandgap (In)AlGaN. For achieving high-efficiency deep UV emission, it is quite effective to use In segregation effect which has been already used for InGaN blue emitting devices. We have demonstrated high-efficiency UV emission by introducing several percent of In into AlGaN in the wavelength range of 300-360 nm at room temperature with an In segregation effect. The emission fluctuation in the submicron region due to In segregation was clearly observed for the quaternary InAlGaN epitaxial layers. An internal quantum efficiency as high as 15% was estimated from quaternary InAlGaN based single quantum well (SQW) at around 350 nm at room temperature. Such a high efficiency UV emission can be obtained even on high threading dislocation density buffers. Also, hole conductivity was obtained for high Al content (>53%) Mg-doped AlGaN by using alternative gas flow growth process in metal-organic vapor phase epitaxy (MOVPE). Using these techniques we fabricated 310 nm band deep UV light-emitting diodes (LEDs) with quaternary InxAlyGa1-x-yN active region. We achieved output power of 0.4 mW for a 308 nm LED and 0.8 mW for a 314 nm LED under room temperature pulsed operation.

  11. Residual stress stability in fiber textured stoichiometric AlN film grown using rf magnetron sputtering

    SciTech Connect

    Sah, R. E.; Kirste, L.; Baeumler, M.; Hiesinger, P.; Cimalla, V.; Lebedev, V.; Baumann, H.; Zschau, H.-E.

    2010-05-15

    The authors report on the stability of mechanical stress with aging and thermal cycling for columnar structured stoichiometric and homogeneous aluminum nitride thin films grown using radio frequency magnetron sputtering technique. The set of deposition parameters were optimized for the best possible orientation of crystallites in the c axis of compositionally stoichiometric films. The as-grown stress in the slightly nitrogen-rich film does not change when exposed to the atmosphere following deposition, while that in the nitrogen-deficient film, it changes due to oxidation. Additionally, the magnitude of as-grown stress has been found to depend on the substrate material in addition to the deposition parameters. The stress in the film grown on a Si(001) substrate was more tensile than in the film grown on a semi-insulating (si) GaAs(001) substrate for a given set of deposition parameters. Furthermore, the stress in the film grown on Si decreased with temperature, while that on si GaAs increased, indicating the thermally induced stress component to be the major component in the residual stress. Upon subsequent cooling the stress changes in both substrates followed the same path as of heating, thus exhibiting no hysteresis with thermal cycles between room temperature and 400 deg. C.

  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. 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

  14. 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

  15. 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.

  16. Distortion and Residual Stress in High-Pressure Die Castings: Simulation and Measurements

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    Two individual high-pressure die casting geometries were developed to study the influence of process parameters and alloy composition on the distortion behavior of aluminum alloy castings. These geometries, a stress lattice and a V-shaped lid, tend to form residual stress due to a difference in wall thickness and a deliberate massive gating system. Castings were produced from two alloys: AlSi12(Fe) and AlSi10MnMg. In the experimental castings, the influence of important process parameters such as die temperature, ejection time, and cooling regime was examined. The time evolution of process temperatures was measured using thermal imaging. Subsequent to casting, distortion was measured by means of a tactile measuring device at ambient temperatures. The measured results were compared against a numerical process and stress simulations of the casting, ejection, and cooling process using the commercial finite element method software ANSYS Workbench. The heat transfer coefficients were adapted to the temperature distributions of the die, and the castings were observed by thermal imaging. A survey of the results of the comparison between simulation and experiment is given for both alloys.

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

  19. Solid-fluid transitions at high sliding rates at Al/Al interfaces

    NASA Astrophysics Data System (ADS)

    Hammerberg, J. E.; Holian, B. L.; Ravelo, R.; Germann, T. C.

    2008-03-01

    Large scale NonEquilibrium Molecular Dynamics (NEMD) simulations (1.4 10^6 atoms) for single crystal Al have shown a transition as a function of sliding velocity from a defective solid phase to a fluid phase beyond a critical velocity, vc, which depends very nearly linearly with the homologous temperature T/Tm where Tm is the melting temperature and T is the sample temperature far from the interface. Above vc, a Couette flow pattern develops with a slope which is independent of velocity. We discuss the properties of this transition and the power law dependence of the frictional force with velocity observed in this regime.

  20. 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...

  1. 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.

  2. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  4. High-resolution axial MR imaging of tibial stress injuries

    PubMed Central

    2012-01-01

    Purpose To evaluate the relative involvement of tibial stress injuries using high-resolution axial MR imaging and the correlation with MR and radiographic images. Methods A total of 33 patients with exercise-induced tibial pain were evaluated. All patients underwent radiograph and high-resolution axial MR imaging. Radiographs were taken at initial presentation and 4 weeks later. High-resolution MR axial images were obtained using a microscopy surface coil with 60 × 60 mm field of view on a 1.5T MR unit. All images were evaluated for abnormal signals of the periosteum, cortex and bone marrow. Results Nineteen patients showed no periosteal reaction at initial and follow-up radiographs. MR imaging showed abnormal signals in the periosteal tissue and partially abnormal signals in the bone marrow. In 7 patients, periosteal reaction was not seen at initial radiograph, but was detected at follow-up radiograph. MR imaging showed abnormal signals in the periosteal tissue and entire bone marrow. Abnormal signals in the cortex were found in 6 patients. The remaining 7 showed periosteal reactions at initial radiograph. MR imaging showed abnormal signals in the periosteal tissue in 6 patients. Abnormal signals were seen in the partial and entire bone marrow in 4 and 3 patients, respectively. Conclusions Bone marrow abnormalities in high-resolution axial MR imaging were related to periosteal reactions at follow-up radiograph. Bone marrow abnormalities might predict later periosteal reactions, suggesting shin splints or stress fractures. High-resolution axial MR imaging is useful in early discrimination of tibial stress injuries. PMID:22574840

  5. High strength and high electrical conductivity of UFG Al-2%Fe alloy achieved by high-pressure torsion and aging

    NASA Astrophysics Data System (ADS)

    Cubero-Sesin, J. M.; Arita, M.; Watanabe, M.; Horita, Z.

    2014-08-01

    In this study, Al-2%Fe samples extracted from a cast ingot in the shape of rings were processed by High-Pressure Torsion (HPT) at room temperature. Suitable specimens were extracted for evaluation of mechanical properties and electrical resistivity. High tensile strength of ~600 MPa was attained by HPT due to grain refinement down to an average grain size of ~130 nm and by subsequent aging accompanied by nano-sized (~10 nm) AhFe precipitates. The resulting conductivity (IACS%) was recovered from ~40% in the steady state after HPT to well above 50% in the peak-aged condition, which is in the range of current Al electrical alloys.

  6. 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.

  7. 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.

  8. AlGaN/GaN high electron mobility transistor with Al2O3+BCB passivation

    NASA Astrophysics Data System (ADS)

    Zhang, Sheng; Wei, Ke; Yu, Le; Liu, Guo-Guo; Huang, Sen; Wang, Xin-Hua; Pang, Lei; Zheng, Ying-Kui; Li, Yan-Kui; Ma, Xiao-Hua; Sun, Bing; Liu, Xin-Yu

    2015-11-01

    In this paper, A12O3 ultrathin film used as the surface passivation layer for AlGaN/GaN high electron mobility transistor (HEMT) is deposited by thermal atomic layer deposition (ALD), thereby avoiding plasma-induced damage and erosion to the surface. A comparison is made between the surface passivation in this paper and the conventional plasma enhanced chemical vapor deposition (PECVD) SiN passivation. A remarkable reduction of the gate leakage current and a significant increase in small signal radio frequency (RF) performance are achieved after applying Al2O3+BCB passivation. For the Al2O3+BCB passivated device with a 0.7 μm gate, the value of fmax reaches up to 100 GHz, but it decreases to 40 GHz for SiN HEMT. The fmax/ft ratio (≥ 4) is also improved after Al2O3+BCB passivation. The capacitance-voltage (C-V) measurement demonstrates that Al2O3+BCB HEMT shows quite less density of trap states (on the order of magnitude of 1010 cm-2) than that obtained at commonly studied SiN HEMT.

  9. Invasive Knotweeds are Highly Tolerant to Salt Stress

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

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

    PubMed Central

    Kang, Rui; Zeh, Herbert J.

    2011-01-01

    Abstract Oxidative stress and associated reactive oxygen species can modify lipids, proteins, carbohydrates, and nucleic acids, and induce the mitochondrial permeability transition, providing a signal leading to the induction of autophagy, apoptosis, and necrosis. High-mobility group box 1 (HMGB1) protein, a chromatin-binding nuclear protein and damage-associated molecular pattern molecule, is integral to oxidative stress and downstream apoptosis or survival. Accumulation of HMGB1 at sites of oxidative DNA damage can lead to repair of the DNA. As a redox-sensitive protein, HMGB1 contains three cysteines (Cys23, 45, and 106). In the setting of oxidative stress, it can form a Cys23-Cys45 disulfide bond; a role for oxidative homo- or heterodimerization through the Cys106 has been suggested for some of its biologic activities. HMGB1 causes activation of nicotinamide adenine dinucleotide phosphate oxidase and increased reactive oxygen species production in neutrophils. Reduced and oxidized HMGB1 have different roles in extracellular signaling and regulation of immune responses, mediated by signaling through the receptor for advanced glycation end products and/or Toll-like receptors. Antioxidants such as ethyl pyruvate, quercetin, green tea, N-acetylcysteine, and curcumin are protective in the setting of experimental infection/sepsis and injury including ischemia-reperfusion, partly through attenuating HMGB1 release and systemic accumulation. Antioxid. Redox Signal. 14, 13151335. PMID:20969478

  11. 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.

  12. 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.

  13. 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.

  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. Yield Stress of Periclase at High Pressure and Low Temperature

    NASA Astrophysics Data System (ADS)

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

    2001-12-01

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

  16. Stress, coping, and work engagement within the -specific job context: comment on Kaiseler, et Al. (2014).

    PubMed

    Gracia, Esther

    2015-04-01

    This work discusses the use of tools that make use of context information. Comments are based on a previous study that looked into the relationship between stressors, coping, and work engagement (Kaiseler, Queirós, Passos & Sousa, 2014). A set of propositions are provided for research that will allow the design of contextualized stress interventions in specific job settings. PMID:25799121

  17. 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.

  18. 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.

  19. On the Influence of Alloy Composition on the Fracture Toughness of Two-Phase Ti-Al-Nb Alloys Undergoing Stress-Induced Martensitic Transformation

    NASA Astrophysics Data System (ADS)

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

    2009-07-01

    The effect of alloy composition on the fracture toughness of Ti-Al-Nb alloys, which undergo stress-induced martensitic transformation (SIMT), was investigated for a given volume fraction of primary α 2. Both Ti-18Al-8Nb and Ti-15Al-12Nb alloys exhibited lower fracture toughness values as compared to Ti-15Al-8Nb alloy, which indicated that higher Al or Nb was detrimental to fracture toughness in these alloys in the presence of primary α 2. The results were explained on the basis of the effect of composition on fracture toughness contributions due to SIMT as well as ductile fracture.

  20. 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.

  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. 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.

  3. High breakdown AlGaN/GaN MOSHEMT with thermal oxidized Ni/Ti as gate insulator

    NASA Astrophysics Data System (ADS)

    Dong, Zhihua; Wang, Jinyan; Wen, C. P.; Gong, Danian; Li, Ying; Yu, Min; Hao, Yilong; Xu, Fujun; Shen, Bo; Wang, Yangyuan

    2010-11-01

    Direct oxidation of composite Ni/Ti metal film structure for AlGaN/GaN MOSHEMT has been successfully demonstrated. In comparison with normal HEMT with Schottky-gate, transistors fabricated with this novel process exhibit three orders of magnitude reduction in gate leakage current, superior breakdown voltage ( V br = 471 V vs. 88 V for normal HEMT) and electrical stability (˜0.3% electric field stress induced drain current degradation versus ˜6% for normal HEMT after 25 V drain bias). The drastic improvement in device performance stability, renders the new process highly promising for GaN based, microwave power amplifier applications in communication and radar systems.

  4. Orientation effect on the stress response by strain-rate change at 400 K in Ni{sub 3}Al single crystals

    SciTech Connect

    Demura, M.; Hirano, T.

    1999-07-01

    Cyclic strain-rate change tests were performed by using binary, stoichiometric Ni{sub 3}Al single crystalline specimens with different tensile orientations at 400K. In all the specimens, the flow stress was independent of strain rate in steady state and exhibited a temporary change by the strain-rate change. The characteristics of the temporary stress change, the initial stress change and transient time, were independent of orientation. Based on the multiplication-immobilization model, the authors concluded that the immobilization mechanism, the Kear-Wilsdorf locking mechanism, is independent of orientation in binary, stoichiometric Ni{sub 3}Al.

  5. 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; Chi, 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

  6. 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

  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 mechanism for other studies showing increased capillary permeability at high states of lung inflation.

  8. Thermodynamic properties of highly undercooled liquid TiAl alloy

    NASA Astrophysics Data System (ADS)

    Wang, N.; Wei, B.

    2002-05-01

    The specific heat of an undercooled liquid TiAl alloy was measured by an electromagnetic levitation drop calorimeter and the related thermodynamic properties, difference in Gibbs free energy and change in entropy are calculated based on the experimental results and some well known models. Under the containerless processing condition, the liquid alloy was undercooled by up to 219 K (0.122TL). The change in enthalpy shows a linear relationship with the temperature and a nearly constant specific heat was determined even though this alloy was undercooled far below its liquidus temperature. The calculated results of the thermodynamic properties reveal that even though semiquantitative models fit with the experimental curve of the difference in Gibbs free energy well, they lead to different degrees of deviation in the entropy difference calculation.

  9. High Fluid Shear Stress and Spatial Shear Stress Gradients Affect Endothelial Proliferation, Survival, and Alignment

    PubMed Central

    Dolan, Jennifer M.; Meng, Hui; Singh, Sukhjinder; Paluch, Rocco; Kolega, John

    2016-01-01

    Cerebral aneurysms develop near bifurcation apices, where complex hemodynamics occur: Flow impinges on the apex, accelerates into branches, then slows again distally, creating high wall shear stress (WSS) and positive and negative spatial gradients in WSS (WSSG). Endothelial responses to these kinds of high WSS hemodynamic environments are not well characterized. We examined endothelial cells (ECs) under elevated WSS and positive and negative WSSG using a flow chamber with constant-height channels to create regions of uniform WSS and converging and diverging channels to create positive and negative WSSG, respectively. Cultured bovine aortic ECs were subjected to 3.5 and 28.4 Pa with and without WSSG for 24 and 36 h. High WSS inhibited EC alignment to flow, increased EC proliferation assessed by bromodeoxyuridine incorporation, and increased apoptosis determined by terminal deoxynu-cleotidyl transferase dUTP-mediated nick-end labeling. These responses to high WSS were either accentuated or ameliorated by WSSG: Positive WSSG (+980 Pa/m) inhibited alignment and stimulated proliferation and apoptosis, whereas negative WSSG (−1120 Pa/m) promoted alignment and suppressed proliferation and apoptosis. These results demonstrate that ECs discriminate between positive and negative WSSG under high WSS conditions. EC responses to positive WSSG may contribute to pathogenic remodeling that occurs at bifurcations preceding aneurysm formation. PMID:21312062

  10. Stress-induced tuning of ultrasonic additive manufacturing Al-NiTi composites

    NASA Astrophysics Data System (ADS)

    Hahnlen, Ryan; Dapino, Marcelo J.

    2012-04-01

    This paper addresses the development of active metal-matrix composites manufactured by Ultrasonic Additive Manufacturing (UAM), an emerging manufacturing process that allows the embedding of materials into seemingly solid metal components. In the UAM process, successive layers of metal tapes are ultrasonically bonded together at low temperatures to form a metal-matrix. Being a low-temperature process, UAM offers unprecedented opportunities to create metal components with embedded thermally-sensitive materials, such as shape memory alloys. In this study UAM is used to create composites with aluminum matrices and embedded NiTi ribbons. These composites exhibit tunability of both the coefficient of thermal expansion and natural frequencies. These effects are due to the phase-dependent modulus and transformation stresses developed by the prestrained NiTi phase. Since the embedded NiTi ribbons are constrained by the matrix, thermally-induced transformation from detwinned martensite to austenite will be accompanied by the generation of transformation stresses. The effect of transformation stress and changing phase of NiTi on thermally-induced strain is observed and modeled by combining strain matching algorithms with thermodynamic-based constitutive models. The composite model accurately describes effects due to changing NiTi modulus and strain recovery due to initial stress-induced martensitic volume fractions including a 200 μɛ contraction with increasing temperature. The observed dynamic behaviors include up to a 16.6% increase in natural frequency at 100°C as compared to room temperature tests. No substantial increase in damping ratio was observed relative to solid aluminum.

  11. 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.

  12. 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.

  13. 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 27.6 at.% Al having the various single-phase field, i.e. the disordered solid solution ({alpha}), an Fe{sub 3}Al with an imperfectly ordered B2 structure, and an ordered Fe{sub 3}Al with the D0{sub 3} structure were first prepared. A series of load relaxation tests was then carried out at the various temperatures ranging from 300 to 800 C to investigate the effect of the tensile strain rate on the anomalous flow behavior.

  14. Chronic High Pressure-Induced Arterial Oxidative Stress

    PubMed Central

    Ungvari, Zoltan; Csiszar, Anna; Kaminski, Pawel M.; Wolin, Michael S.; Koller, Akos

    2004-01-01

    Regardless of the underlying pathological mechanisms oxidative stress seems to be present in all forms of hypertension. Thus, we tested the hypothesis that chronic presence of high pressure itself elicits increased arterial O2.− production. Hypertension was induced in rats by abdominal aortic banding (Ab). Rats with Ab had elevated pressure in vessels proximal and normal pressure in vessels distal to the coarctation, yet both vascular beds were exposed to the same circulating factors. Compared to normotensive hind limb arteries (HLAs) hypertensive forelimb arteries (FLAs) exhibited 1) impaired dilations to acetylcholine and the nitric oxide donor S-nitroso-N-acetyl-d,l-penicillamine that were restored by administration of superoxide dismutase; 2) an increased production of O2.− (measured by lucigenin chemiluminescence and ethidium bromide fluorescence) that was inhibited or reduced by superoxide dismutase, the NAD(P)H oxidase inhibitors diphenyleneiodonium and apocynin, or the protein kinase C (PKC) inhibitors chelerythrine and staurosporine or by the angiotensin-converting enzyme (ACE) inhibitor captopril; and 3) increased ACE activity. In organ culture, exposure of isolated arteries of normotensive rats to high pressure (160 mmHg, for 24 hours) significantly increased O2.− production compared to that in arteries exposed to 80 mmHg. High pressure-induced O2.− generation was reduced by inhibitors of ACE and PKC. Incubation of cultured arteries with angiotensin II elicited significantly increased O2.− generation that was inhibited by chelerythrine. Thus, we propose that chronic presence of high pressure itself can elicit arterial oxidative stress, primarily by activating directly a PKC-dependent NAD(P)H oxidase pathway, but also, in part, via activation of the local renin-angiotensin system. PMID:15215177

  15. 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.

    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.

  16. 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.

  17. Stress distribution in a transversely loaded cross-shaped single fiber SCS-6/Ti-6Al-4V composite

    SciTech Connect

    Warrier, S.G.; Gundel, D.B.; Majumdar, B.S.; Miracle, D.B.

    1996-01-15

    In most structural applications utilizing fiber reinforced metal matrix composites (MMCs), the mechanical response normal to the fiber direction has to be considered. The transverse response is very sensitive to the interface bond strength, which has commonly been determined by testing straight-sided 90{degree} specimens and interpreting debond initiation from the knee in the stress-strain curve as well as from a sudden drop in the Poisson`s ratio. In an attempt to modify the debond initiation site to an internal location free of uncharacteristic states of stress, a cross-shaped specimen has been developed. Experiments conducted by Gundel et al. indicated that this geometry was successful in obtaining the appropriate crack initiation site. In the present study, finite element analysis (FEA) was done on the cross-shaped specimen to obtain the stress distribution in the composite under transverse loading, in an effort to corroborate the success of this geometry in determining the true transverse response of the composite.

  18. Regulation of residual stress in elastic solid component with high-energy acoustic field

    NASA Astrophysics Data System (ADS)

    Song, W. T.; Xu, C. G.; Pan, Q. X.; Yang, X. C.; Xu, L.; Guo, J.

    2013-01-01

    The ultrasonic regulation of internal residual stress in metal and nonmetal elastic solid component has been investigated. High-energy ultrasonic wave is applied to carbon steel and ordinary flat glass for residual stress control. An ultrasonic residual stress measurement device developed with the acoustoelastic theory is used to measure macro residual stress in time, to evaluate the residual stress regulation effectiveness. Based on the essence of residual stress, the interaction between acoustic wave and residual stress is analyzed, and dislocations theory is considered. When the ultrasonic energy supplied to the elastic solid is greater than the energy of dislocation, the internal residual stress will be released. Experiments result shows that as high energy acoustic field is applied, the local residual tensile stress in elastic solid specimen will shift gradually to beneficial compressive stress, thus the component's fatigue strength, corrosion resistance and service life will be greatly improved.

  19. Improved properties of high-Al-composition AlGaN/GaN high electron mobility transistor structures with thin GaN cap layers

    NASA Astrophysics Data System (ADS)

    Li, Haoran; Keller, Stacia; DenBaars, Steven P.; Mishra, Umesh K.

    2014-09-01

    GaN cap layers with thicknesses between 0.6 and 2.4 nm were shown to effectively suppress the degradation of the structural and electrical properties of AlGaN/GaN high electron mobility transistor (HEMT) structures with xAl ˜ 0.5 grown by metal-organic chemical vapor deposition (MOCVD). The formation of platelets and trench networks on free AlGaN surfaces was successfully mitigated by GaN cap layers as thin as 0.6 nm. Simultaneously, a rise in sheet charge density and mobility of the two-dimensional electron gas (2DEG) was observed, the magnitude of which depended on the AlGaN thickness. GaN was also shown to be a superior capping material compared to in-situ grown Si3N4.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. Investigation of trap states in high Al content AlGaN/GaN high electron mobility transistors by frequency dependent capacitance and conductance analysis

    SciTech Connect

    Zhu, Jie-Jie; Ma, Xiao-Hua Hou, Bin; Chen, Wei-Wei; Hao, Yue; School of Microelectronics, Xidian University, Xi'an 710071

    2014-03-15

    Trap states in Al{sub 0.55}Ga{sub 0.45}N/GaN Schottky-gate high-electron-mobility transistors (S-HEMTs) and Al{sub 2}O{sub 3}/Al{sub 0.55}Ga{sub 0.45}N/GaN metal-oxide-semiconductor HEMTs (MOS-HEMTs) were investigated with conductance method in this paper. Surface states with time constant of (0.09–0.12) μs were found in S-HEMTs, and electron tunneling rather than emission was deemed to be the dominant de-trapping mechanism due to the high electric field in high Al content barrier. The density of surface states evaluated in S-HEMTs was (1.02–4.67)×10{sup 13} eV{sup −1}·cm{sup −2}. Al{sub 2}O{sub 3} gate insulator slightly reduced the surface states, but introduced low density of new traps with time constant of (0.65–1.29) μs into MOS-HEMTs.

  6. 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.

  7. The Voices of High School Counselors: Lived Experience of Job Stress

    ERIC Educational Resources Information Center

    Falls, Leigh; Nichter, Mary

    2007-01-01

    There is a paucity of literature addressing high school counselors' experiences of job stress. Our qualitative phenomenological study adds to the professions' knowledge of job stress as experienced by counselors in large suburban high schools. Our study illustrates the job stress phenomenon in the counselors' own voices, identifies situations…

  8. Stress

    MedlinePlus

    ... seriously hurt or killed. Examples include a major accident, war, assault, or a natural disaster. This type of stress can cause post-traumatic stress disorder (PTSD). Different people may feel stress in different ways. Some people experience digestive symptoms. Others may have ...

  9. AlGaN-based deep-ultraviolet light-emitting diodes grown on High-quality AlN template using MOVPE

    NASA Astrophysics Data System (ADS)

    Yan, Jianchang; Wang, Junxi; Zhang, Yun; Cong, Peipei; Sun, Lili; Tian, Yingdong; Zhao, Chao; Li, Jinmin

    2015-03-01

    In this article, we report the growth of high-quality AlN film using metal-organic vapor phase epitaxy. Three layers of middle-temperature (MT) AlN were introduced during the high-temperature (HT) AlN growth. During the MT-AlN layer growth, aluminum and nitrogen sources were closed for 6 seconds after every 5-nm MT-AlN, while H2 carrier gas was always on. The threading dislocation density in an AlN epi-layer on a sapphire substrate was reduced by almost half. AlGaN-based deep-ultraviolet light-emitting diodes were further fabricated based on the AlN/sapphire template. At 20 mA driving current, the emitted peak wavelength is 284.5 nm and the light output power exceeds 3 mW.

  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. 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

  12. 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…

  13. 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.

  14. High-Temperature Oxidation Behavior of Al-Co-Cr-Ni-(Fe or Si) Multicomponent High-Entropy Alloys

    NASA Astrophysics Data System (ADS)

    Butler, T. M.; Alfano, J. P.; Martens, R. L.; Weaver, M. L.

    2015-01-01

    High-entropy alloys (HEAs) are a class of alloys that are being considered for a number of applications. In the present study, the microstructures and 1050°C oxidation behaviors of two HEAs, Al10Cr22.5Co22.5Ni22.5Fe22.5 (at.%) and Al20Cr25Co25Ni25Si5 have been investigated along with Al15Cr10Co35Ni35Si5, which is a high-temperature shape-memory alloy. Oxide formation occurred via selective oxidation in a manner that was consistent with the oxide formation model devised by Giggins and Pettit for model Ni-Cr-Al alloys. The lower Al content alloy formed an external Cr2O3 scale and an internal subscale consisting of Al2O3 and AlN precipitates. The higher Al content alloys exhibited smaller mass gains and formed external Al2O3 scales without any internal oxidation of the alloys.

  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. 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

  17. Al/C/MnO2 sandwich nanowalls with highly porous surface for electrochemical energy storage

    NASA Astrophysics Data System (ADS)

    He, Shuijian; Zhang, Ruizhong; Zhang, Chunmei; Liu, Minmin; Gao, Xiaohui; Ju, Jian; Li, Lei; Chen, Wei

    2015-12-01

    Hierarchical materials supported on metal substrates present promising applications in flexible energy storage and conversion devices. Compared to Au, Ag, Cu, Ni, Ti, W and their alloys, Al, the most abundant metal in the crust has been less used in supercapacitors due to its high activity which makes it unstable in acid and base electrolytes. In this paper, we explore a novel Al/C/MnO2 sandwich structured material for the first time for supercapacitor. Owing to the highly porous and open surface structure and the highly conductive Al/C double core current collector on nanoscale, the Al/C/MnO2 sandwich nanowall arrays supported on Al foil show excellent capacitance performance with a maximum area specific capacitance of 1008.3 mF cm-2 and a high energy density of 35.2 μWh cm-2 at 2 mA cm-2. Moreover, a supercapacitor device with 4 supercapacitors connected in series can power a LED lamp. The present study demonstrates a novel electrode architecture based on Al foil with remarkably high area specific capacitance and stability for promising supercapacitor applications. Our strategy provides a new approach to the fabrication of hierarchical electrode materials from Al metal (could also be extend to other metal substrates) for supercapacitors and other energy storage and conversion devices.

  18. 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.

  19. 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.

  20. High-resolution electron microscope observation of interface microstructure of a cast Al-Mg-Si-Bi-Pb(6262)/Al2O3p composite.

    PubMed

    Zhou, Z.; Fan, Z.; Peng, H. X.; Li, D. X.

    2001-02-01

    High-resolution electron microscopy was employed to characterize the interface structure of a cast Al-Mg-Si-Bi-Pb aluminium(6262)-based composite reinforced by alpha alumina particles with a trace of beta alumina in order to investigate the behaviour of alloying elements in cast composites. Except for a few primary Mg2Si particles, few reaction products were detected at the interface of Al/alpha-Al2O3 due to the unfavourable reaction kinetics during the squeeze-casting process. The Mg2Si particle has an orientation relationship with alpha-Al2O3 of [011]Mg2Si//[1210]alpha-Al2O3 (111)Mg2Si//(0006)alpha-Al2O3. A significant amount of MgAl2O4 was found on the surface of the beta-Al2O3 particles, which is in contrast to the small degree of reaction found on alpha-Al2O3 particles. MgAl2O4 and beta-Al2O3 particles have the following orientation relationship: [011]MgAl2O4//[1210]beta-Al2O3 (111) MgAl2O4//(0006)beta-Al2O3. The similar crystal structure of beta-Al2O3 to MgAl2O4 favours MgAl2O4 nucleation and growth on the surface of beta-Al2O3. Interfacial energy minimization dominates the atomic structure of the interface with the result that close packed planes and directions in the Al2O3 reinforcement and reaction products are parallel to the interfaces. Bi and Pb were found in the form of metallic nanometre particles between Al2O3 particles, or between the MgAl2O4 and Al2O3 particles, or in the open channels of beta-Al2O3 filled by the Al matrix. PMID:11207916

  1. 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.

  2. 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.

  3. 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.

  4. High-Cycle Fatigue Behavior of Microarc Oxidation Coatings Deposited on a 6061-T6 Al Alloy

    NASA Astrophysics Data System (ADS)

    Wasekar, Nitin P.; Ravi, N.; Suresh Babu, P.; Rama Krishna, L.; Sundararajan, G.

    2010-01-01

    The objective of this article is to evaluate the influence of microarc oxidation (MAO) coatings on the high-cycle rotating bending fatigue behavior of the 6061-T6 aluminum alloy. Toward this purpose, the influence of the MAO coating process parameter (current density) and coating thickness on the fatigue life of the 6061-T6 Al alloy has been evaluated in the present study. In addition, the influence of the coating roughness on the fatigue life of the MAO-coated 6061-T6 Al-alloy sample has also been investigated. The results indicate that the high-cycle fatigue life of the 6061-T6 Al alloy is substantially degraded due to the presence of MAO coatings, especially at lower alternating stress values and for thicker coatings. Surface roughness, altered by polishing, does not have any effect on fatigue life. An examination of coated samples interrupted at various fractions of fatigue life leads to the conclusion that the crack propagates from the coating surface to the coating-substrate interface very rapidly and thus fatigue life is largely controlled by the propagation of the crack into the substrate.

  5. Dependence of ohmic contact properties on AlGaN layer thickness for AlGaN/GaN high-electron-mobility transistors

    NASA Astrophysics Data System (ADS)

    Takei, Yusuke; Tsutsui, Kazuo; Saito, Wataru; Kakushima, Kuniyuki; Wakabayashi, Hitoshi; Iwai, Hiroshi

    2016-04-01

    The dependence of ohmic contact resistance on the AlGaN layer thickness was evaluated for AlGaN/GaN high-electron-mobility transistor (HEMT) structures. Mo/Al/Ti contacts were formed on AlGaN layers with various thicknesses. The observed resistance characteristics are discussed on the basis of a model in which the overall contact resistance is composed of a series of three resistance components. Different dependences on the AlGaN layer thickness was observed after annealing at low temperatures (800-850 °C) and at high temperatures (900-950 °C). It was determined that lowering the resistance at the metal/AlGaN interface and that of the AlGaN layer is important for obtaining low-resistance ohmic contacts.

  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. 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.

  8. 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.

  9. Reliability of self-aligned, ledge passivated 7.5 GHz GaAs/AlGaAs HBT power amplifiers under RF bias stress at elevated temperatures

    SciTech Connect

    Henderson, T.S.; Ikalainen, P.K.

    1995-12-31

    The authors report a two-temperature RF bias stress test on nominal 1.2 W 7.5 GHz GaAs/AlGaAs HBT unit cell amplifiers. MTTF`s of 2020 and 1340 hours were obtained at Tj = 218{degrees}C and 245{degrees}C, respectively, under nominal input bias. An activation energy of 0.42 eV is estimated, consistent with published results for similar devices under DC bias stress.

  10. 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 control defect densities by introducing extrinsic point defects to the laser via proton irradiation with different energies and fluences. These lasers were subsequently lifetested to study degradation processes in the lasers with different defect densities and also to study precursor signatures of failures - traps and non-radiative recombination centers (NRCs) in pre- and post-stressed lasers. Lastly, we employed focused ion beam (FIB), electron beam induced current (EBIC), and highresolution TEM (HR-TEM) techniques to further study dark line defects and dislocations in both post-aged and postproton irradiated lasers. We report on our long-term low-stress lifetest results and physics of failure investigation results.

  11. 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…

  12. 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.

  13. 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 shot peening and chemical treatment in a mixture of nitric and hydroflouric acid finishes the processing. The residual stress state in the parts is quantified through correlation of results obtained by finite element simulations and high precision deflection experiments. Experimental measuring errors are minimized by using the capability of the wire cutting machine to measure locations on the specimens with respect to the fixed machine coordinate system. A sophisticated design of cutting operations allows an analysis of the part without removing the fixture and hence makes it possible to achieve a very high accuracy of the displacement measurements of about 4 µm. The quality of the obtained results also depends on the finite element models describing the mechanics of the experimental investigations as precise as possible. Since numerical modeling of shot peening and chemical milling is rather complicated, the whole processing route of the shapes is simplified assuming that the individual contribution of all process steps to the residual stress state can be described by virtual heat transfer coefficients. The overall virtual heat transfer coefficient for the whole processing route is calculated from the linear superposition of the individual heat transfer coeffcients for each processing step. Detailed analysis of the obtained overall virtual heat transfer coefficients in comparison with experimentally obtained ones shows, that other processing steps besides the heat treatment considerably influence the residual stress state. In order to make the conducted simulation scheme applicable in practise, advanced finite element modeling techniques are developed. The experimentally derived deflection curves are correlated to the finite element results via a least square fit.

  14. 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 of the cavity apparatus, optical absorption, and laser phase fluctuations. Our principle experimental result is the radiation pressure-based cooling of a high order, ≃ 4.8 MHz drum mode of the membrane from room temperature to ≃ 100 mK (≃ 500 phonons). Secondary results include an investigation of the Q-factor of membrane oscillators with various geometries, some of which exhibit state-of-the-art Qxfrequency products of 3 x 1013 Hz, and a novel technique to suppress extraneous radiation pressure noise using electro-optic feedback.

  15. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    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.

  17. 76 FR 45303 - ING Asia Pacific High Dividend Equity Income Fund, et al.; Notice of Application

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-07-28

    ... COMMISSION ING Asia Pacific High Dividend Equity Income Fund, et al.; Notice of Application July 21, 2011... outstanding preferred stock that such investment companies may issue. Applicants: ING Asia Pacific High Dividend Equity Income Fund (``IAE''), ING Emerging Markets High Dividend Equity Fund (``IHD''); ING...

  18. 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.

  19. Protective SiAlON Coating with Embedded High Temperature Corrosion Sensor

    NASA Astrophysics Data System (ADS)

    Rivers, S. B.; Krassikoff, J. I.; Bernhardt, G.; Bocchino, C. J.; Lad, R. J.

    2007-03-01

    We have fabricated oxidation resistant and wear resistant SiAlON films by RF magnetron co-sputtering of Al and Si targets in Ar/O2/N2 mixtures. The SiAlON films are amorphous, extremely smooth, and have very low oxygen permeability making them extremely attractive as passivation layers on a variety of sensors and other microelectronic devices used in high-temperature oxidizing environments. To analyze the performance of these films as passivation coatings, we incorporated a corrosion sensor at the SiAlON-substrate interface to monitor oxygen penetration through the coating. This corrosion sensor is a serpentine metal pattern. The conductivity changes as a function of time are monitored giving an in situ quantitative measure of the oxidation rate of the metal sensor due to oxygen diffusion through the SiAlON film.

  20. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    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 VDS and low IDS 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.

  2. 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.

  3. 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.

  4. 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).

  5. 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.

  6. 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.

  7. 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

  8. 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

  9. 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…

  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. Low-temperature plasma-assisted growth of optically transparent, highly oriented nanocrystalline AlN

    SciTech Connect

    Mirpuri, C.; Xu, S.; Long, J. D.; Ostrikov, K.

    2007-01-15

    Optically transparent, highly oriented nanocrystalline AlN(002) films have been synthesized using a hybrid plasma enhanced chemical vapor deposition and plasma-assisted radio frequency (rf) magnetron sputtering process in reactive Ar+N{sub 2} and Ar+N{sub 2}+H{sub 2} gas mixtures at a low Si(111)/glass substrate temperature of 350 degree sign C. The process conditions, such as the sputtering pressure, rf power, substrate temperature, and N{sub 2} concentration were optimized to achieve the desired structural, compositional, and optical characteristics. X-ray diffractometry reveals the formation of highly c-oriented AlN films at a sputtering pressure of 0.8 Pa. Field emission scanning electron microscopy suggests the uniform distribution of AlN grains over large surface areas and also the existence of highly oriented in the (002) direction columnar structures of a typical length {approx}100-500 nm with an aspect ratio of {approx}7-15. X-ray photoelectron and energy dispersive x-ray spectroscopy suggest that films deposited at a rf power of 400 W feature a chemically pure and near stoichiometric AlN. The bonding states of the AlN films have been confirmed by Raman and Fourier transform infrared spectroscopy showing strong E2 (high) and E1 transverse optical phonon modes. Hydrogenated AlN films feature an excellent optical transmittance of {approx}80% in the visible region of the spectrum, promising for advanced optical applications.

  12. 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

  13. 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.

  14. 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.

    2015-12-01

    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.

  15. 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.

  16. Metallographic assessment of Al-12Si high-pressure die casting escalator steps.

    PubMed

    Vander Voort, George Frederic; Suárez-Peña, Beatriz; Asensio-Lozano, Juan

    2014-10-01

    A microstructural characterization study was performed on high-pressure die cast specimens extracted from escalator steps manufactured from an Al-12 wt.% Si alloy designed for structural applications. Black and white, color light optical imaging and scanning electron microscopy techniques were used to conduct the microstructural analysis. Most regions in the samples studied contained globular-rosette primary α-Al grains surrounded by an Al-Si eutectic aggregate, while primary dendritic α-Al grains were present in the surface layer. This dendritic microstructure was observed in the regions where the melt did not impinge directly on the die surface during cavity filling. Consequently, microstructures in the surface layer were nonuniform. Utilizing physical metallurgy principles, these results were analyzed in terms of the applied pressure and filling velocity during high-pressure die casting. The effects of these parameters on solidification at different locations of the casting are discussed. PMID:24999947

  17. [Stress reactions and stress fractures in the high performance athlete. Causes, diagnosis and therapy].

    PubMed

    Geyer, M; Sander-Beuermann, A; Wegner, U; Wirth, C J

    1993-02-01

    From 1987 until July 1991 70 athletes with stress reactions or stress fractures were treated in the orthopaedic department of the Hannover Medical School. The average age of the 42 male and 28 female athletes was 22.6 years. The number of athletes involved in track and field sports was 29 (41.4%), in gymnastics 9 (12.9%) and in soccer 5 (7.1%). The most common bone injured was the tibia in 29 (41.4%), followed by the tarsal navicular in 21 (30.0%), the midfoot in 17 (24.3%) and the fibula in 4 (5.7%) athletes. In three cases double stress fractures were found in adjacent locations; in one case a stress fracture of the opposite navicular occurred after the initial tarsal navicular stress fracture had healed, and in another case the tarsal navicular was found to be fractured again. Thirty-seven percent of the athletes claimed sudden increase in training intensity was the cause; 33% felt that the increased sprinting and jump activities were the reason for their complaints. In some athletes pain started after an ankle sprain. Standard diagnostic procedure consisted in X-rays in two planes and three-phase bone scanning. In tarsal navicular or tibial locations additional tomograms were performed. MRI and CT scans were reserved for unclear findings and to exclude the possibility of a tumorous or inflammatory process. A new grading system was introduced that covers all forms of stress reactions from periostitis to pseudarthrosis. Clinical symptoms, sport disabilities, radiological and bone scan findings were graded from A to D. Using a modified Wilson classification, all radiologically recognizable stress reactions could be classified.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:8451651

  18. 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.

  19. 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.

  20. Cryogenic Resistivities of NbTiAlVTaLax, CoCrFeNiCu and CoCrFeNiAl High Entropy Alloys

    NASA Astrophysics Data System (ADS)

    Yang, Xiao; Zhang, Yong

    2011-06-01

    In the paper, NbTiAlVTaLax (molar ratio, x=0, 0.1, 0.2) high entropy alloys were prepared by arc melting mixtures of the pure metal elements. The NbTiAlVTaLax alloys are composed mainly of BCC solid solution, and have a typical cast dendritic microstructure. The cryogenic resistivities of NbTiAlVTaLax, CoCrFeNiCu and CoCrFeNiAl high entropy alloys had been investigated. With the increase of La addition, the resistivities of NbTiAlVTaLax alloys increase. With the temperature increasing, the resistivity of CoCrFeNiCu alloy decreases, while that of CoCrFeNiAl alloy increases.

  1. 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.

  2. 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.

  3. AlGaAs/GaAs photovoltaic converters for high power narrowband radiation

    NASA Astrophysics Data System (ADS)

    Khvostikov, Vladimir; Kalyuzhnyy, Nikolay; Mintairov, Sergey; Potapovich, Nataliia; Shvarts, Maxim; Sorokina, Svetlana; Luque, Antonio; Andreev, Viacheslav

    2014-09-01

    AlGaAs/GaAs-based laser power PV converters intended for operation with high-power (up to 100 W/cm2) 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.

  4. 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.

  5. 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.

  6. Effect of Plasticity on Stress Heterogeneity at High Pressure

    NASA Astrophysics Data System (ADS)

    Weidner, D. J.; Li, L.

    2003-12-01

    It has become routine to measure the differential strain field in both diamond anvil and multi-anvil cells using synchrotron x-rays. In these experiments, the x-rays pass through the sample along a path perpendicular to the compressive axis of a cylindrical stress field. Then the diffracted x-rays sample the lattice spacings both parallel and perpendicular to the maximum stress. Detection can be by means of a 2-D system such as an imaging plate or a CCD detector with monochromatic x-rays, where the Debye rings are recorded as a function of the azimuthal angle, ŸO. Then the lattice spacings parallel to the maximum stress axis can be compared with those parallel to minimum stress axis. White x-rays provide the same results with multiple solid state detectors, used in conjunction with a conical slit. These measurements have been possible with the use of x-ray transparent gaskets, usually Be for the diamond cell, and x-ray transparent anvils, such as cubic boron nitride, for the multi-anvil system. Each diffraction line will give rise to a measure of the stress field in the sample, giving stress measures for distinct populations of grains, namely those whose orientations meet the necessary diffraction conditions. If the sample has been compressed and strained elastically, then the Reuss ­V Voight bounds become the defining relationship among the stress ­V strain fields of the different populations of grains that are sampled by x-ray diffraction lines. Singh indicates the relationship between the strain field and the average stress field using the parameter, alpha = 1 to indicate a ­\\x9DReuss­Ý solid (uniform stress) and alpha = 0 indicating a ­\\x9DVoight­Ý solid (uniform strain). A value between 0 and 1 indicates a mixed boundary condition solid. However, when the polycrystal is plastically deformed, several important changes occur. First, the x-ray diffraction is only sampling a portion of the total strain field. It does not reflect the plastic portion. Second, the stress in an individual grain is no longer controlled by the elastic properties, but rather by the plastic properties. The Schmidt factor, which represents the ratio of a stress on a dislocation to the stress on the grain, becomes the relevant measure of anisotropy and the stress fields in the different grain populations now evolve to maintain the necessary stress on the dislocations as to enable plastic deformation. The Taylor ­V Sachs bounds replace the Reuss ­V Voight bounds. In general, the stress field of the various populations of grains will change radically. Calculations, using a self-consistent polycrystalline model indicate that once plastic deformation has occurred in the sample, it will generally be no longer possible to use the Singh formalism to define the single-crystal elastic properties.

  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. 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.

  9. Equation of State of an AlCoCrCuFeNi High-Entropy Alloy

    NASA Astrophysics Data System (ADS)

    Li, Gong; Xiao, Daihong; Yu, Pengfei; Zhang, Lijun; Liaw, Peter K.; Li, Yanchun; Liu, Riping

    2015-08-01

    The pressure-volume (P-V) relationship of the AlCoCrCuFeNi high-entropy alloy (HEA) at room temperature has been studied using in situ high-pressure energy-dispersive x-ray diffraction with synchrotron radiation at high pressures. The equation of state of the AlCoCrCuFeNi HEA is determined by the calculation of the radial distribution function. The experimental results indicate that the HEA keeps a stable face-centered-cubic + body-centered-cubic structure in the experimental pressure range from 0 GPa to 24 GPa.

  10. 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

  11. Friction Stir Processing of a High Entropy Alloy Al0.1CoCrFeNi

    NASA Astrophysics Data System (ADS)

    Kumar, N.; Komarasamy, M.; Nelaturu, P.; Tang, Z.; Liaw, P. K.; Mishra, R. S.

    2015-05-01

    High entropy alloys are a new class of metallic materials with a potential for use in structural applications. However, most of the studies have focused on microhardness and compressive strength measurements for mechanical properties determination. This study presents the tensile deformation behavior of a single-phase, face-centered cubic Al0.1CoCrFeNi high entropy alloy (HEA). Friction stir processing was carried out to refine the grain size. Scanning electron microscopy and electron backscatter diffraction were carried out for microstructural examination. The grain size of the alloy was on the order of millimeters in the as-received condition. The average grain size after friction stir processing of the alloy was 14 ± 10 micrometers. The mechanical properties were determined through microhardness measurement and mini-tensile tests. The friction stir processed alloy showed a total elongation of ~75% for the mini-tensile sample used and yield strength of 315 MPa. It is an exceptional combination of strength and ductility. Friction stress was determined to be 174 MPa and the Hall-Petch coefficient was 371 MPa ( µm)1/2. Such a high value of Hall-Petch coefficient suggests that grain boundary strengthening can be a very effective strengthening mechanism for the HEA Al0.1CoCrFeNi.

  12. 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.

  13. 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.

  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. 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 to coating better and a ductile and adhesive interface layer can delay the cracked coating from peeled-off.

  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. Bimetallic Pd/Al particles for highly efficient hydrodechlorination of 2-chlorobiphenyl in acidic aqueous solution.

    PubMed

    Yang, Bo; Deng, Shubo; Yu, Gang; Zhang, Hong; Wu, Jinhua; Zhuo, Qiongfang

    2011-05-15

    Pd-based bimetallic materials have been widely studied for the effective hydrodechlorination (HDC) of aqueous chloroorganic compounds. However, the reaction functions of metal substrates and mechanism responsible for changes in reactivity have not been fully elucidated. Here, we synthesized Pd-based bimetals with Mg, Al, Mn, Zn, Fe, Sn, and Cu to explore the influence of metal substrates on HDC reactivity of 2-chlorobiphenyl (2-PCB). Bimetals exhibited disparate reactivity toward 2-PCB in acidic solution. Among these bimetals, Pd/Al particles presented the highest stability and relatively high reactivity to remove 2-PCB. The maintenance and regeneration of Al substrate are attributed to its particular corrosion properties which provide an efficient recycling between Al element and its oxide layer. The fresh and reacted Pd/Al samples were characterized by ICP-OES, SEM, XRD, and BET. The investigation of the pH effect on 2-PCB HDC further revealed the particular behaviour of Al surface. The effect of Pd loading amount on the HDC indicated that the optimal Pd content in terms of catalytic activity was related to the Pd dispersion degree. Finally, a mechanism for 2-PCB HDC on the Pd/Al surface was proposed. PMID:21377789

  18. Highly textured growth of AlN films on sapphire by magnetron sputtering for high temperature surface acoustic wave applications

    SciTech Connect

    Aubert, T.; Assouar, M. B.; Legrani, O.; Elmazria, O.; Tiusan, C.; Robert, S.

    2011-03-15

    Piezoelectric aluminum nitride films were deposited onto 3 in. [0001] sapphire substrates by reactive magnetron sputtering to explore the possibility of making highly (002)-textured AlN films to be used in surface acoustic wave (SAW) devices for high temperature applications. The synthesized films, typically 1 {mu}m thick, exhibited a columnar microstructure and a high c-axis texture. The relationship between the microstructures and process conditions was examined by x-ray diffraction (XRD), transmission electron microscopy, and atomic force microscopy analyses. The authors found that highly (002)-textured AlN films with a full width at half maximum of the rocking curve of less than 0.3 deg. can be achieved under high nitrogen concentration and moderate growth temperature, i.e., 250 deg. C. The phi-scan XRD reveals the high in-plane texture of deposited AlN films. The SAW devices, based on the optimized AlN films on sapphire substrate, were characterized before and after an air annealing process at 800 deg. C for 90 min. The frequency response, recorded after the annealing process, confirmed that the thin films were still strong in a high temperature environment and that they had retained their piezoelectric properties.

  19. 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.

  20. Trap states in AlGaN channel high-electron-mobility transistors

    SciTech Connect

    Zhao, ShengLei; Zhang, Kai; Ha, Wei; Chen, YongHe; Zhang, Peng; Zhang, JinCheng; Hao, Yue; Ma, XiaoHua; School of Advanced Materials and Nanotechnology, Xidian University, Xi'an 710071

    2013-11-18

    Frequency dependent capacitance and conductance measurements were performed to analyze the trap states in the AlGaN channel high-electron-mobility transistors (HEMTs). The trap state density in the AlGaN channel HEMTs decreases from 1.26 × 10{sup 13} cm{sup −2}eV{sup −1} at the energy of 0.33 eV to 4.35 × 10{sup 11} cm{sup −2}eV{sup −1} at 0.40 eV. Compared with GaN channel HEMTs, the trap states in the AlGaN channel HEMTs have deeper energy levels. The trap with deeper energy levels in the AlGaN channel HEMTs is another reason for the reduction of the reverse gate leakage current besides the higher Schottky barrier height.

  1. 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.

  2. Phase Composition and Superplastic Behavior of a Wrought AlCoCrCuFeNi High-Entropy Alloy

    NASA Astrophysics Data System (ADS)

    Shaysultanov, D. G.; Stepanov, N. D.; Kuznetsov, A. V.; Salishchev, G. A.; Senkov, O. N.

    2013-12-01

    A cast AlCoCrCuFeNi high-entropy alloy was multiaxially forged at 950°C to produce a fine homogeneous mixture of grains/particles of four different phases with the average size of ~2.1 μm. The forged alloy exhibited unusual superplastic behavior accompanied by a pronounced softening stage, followed by a steady-state flow stage, during tensile deformation at temperatures of 800°C-1000°C and at strain rates of 10-4-10-1 s-1. Despite the softening stage, no noticeable strain localization was observed and a total elongation of up to 1240% was obtained. A detailed analysis of the phase composition and microstructure of the alloy before and after superplastic deformation was conducted, the strain rate and temperature dependences of the flow stress were determined at different stages of the superplastic deformation, and the relationships between the microstructure and properties were identified and discussed.

  3. 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.

    2016-03-01

    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.

  4. 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.

  5. 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…

  6. 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

  7. 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

  8. 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…

  9. 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.

  10. Fibular stress fracture in a high school athlete.

    PubMed

    Greenberg, Elliot M; Gohn, Nicholas; Grady, Matthew

    2013-01-01

    The patient was a 15-year-old adolescent male who was referred to a physical therapist for a chief complaint of bilateral posterolateral lower-leg pain, which was worse in the right lower extremity than in the left. Due to findings that were concerning for a stress fracture, the patient was referred to a pediatric sports medicine physician. Subsequent radiographs revealed findings that were concerning for a stress fracture along the medial aspect of the midshaft of the right fibula. PMID:23277163

  11. Ulnar shaft stress fracture in a high school softball pitcher.

    PubMed

    Bigosinski, Krystian; Palmer, Trish; Weber, Kathleen; Evola, Jennifer

    2010-03-01

    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

  12. 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…

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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 m. 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.

  18. 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.

  19. 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.

  20. Transverse vibrations of embedded nanowires under axial compression with high-order surface stress effects

    NASA Astrophysics Data System (ADS)

    Zhang, Y. Q.; Pang, M.; Chen, W. Q.

    2015-02-01

    Implementing the high-order surface stress model into the Bernoulli-Euler beam theory, the transverse vibration of an axially compressed nanowire embedded in elastic medium is investigated. Closed-form expression is obtained for the natural frequency of a simply supported nanowire. The influences of compressive axial load, high-order surface stress and surrounding elastic medium on the natural frequency are discussed. Additionally, the analytical solution of axial buckling load for the simply supported nanowire is derived, which takes into account the effects of high-order surface stress and surrounding elastic medium. It is concluded from numerical results that the natural frequency of transverse vibration of the nanowire is dependent upon axial load, surrounding elastic medium, and high-order surface stress. Similarly, the dependences of the buckling load on surrounding elastic medium and high-order surface stress are significant.

  1. 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.

  2. 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…

  3. Effects of Electromagnetic Stirring on the Microstructure and High-Temperature Mechanical Properties of a Hyper-eutectic Al-Si-Cu-Ni Alloy

    NASA Astrophysics Data System (ADS)

    Jang, Youngsoo; Choi, Byounghee; Kang, Byungkeun; Hong, Chun Pyo

    2015-02-01

    A liquid treatment method by electromagnetic stirring was applied to a hyper-eutectic Al-15wt pctSi-4wt pctCu-3wt pctNi alloy for the piston manufacturing with diecasting process in order to improve high-temperature mechanical properties of the piston heads. The mechanical properties, such as hardness, high-temperature tensile stress, thermal expansion, and high-temperature relative wear resistance, were estimated using the specimens taken from the liquid-treated diecast products, and the results were compared with those of a conventional metal-mold-cast piston.

  4. 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

  5. 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.

  6. 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.

  7. High temperature oxidation behavior of FeAl intermetallics -- Oxide scales formed in ambient atmosphere

    SciTech Connect

    Xu, C.H.; Gao, W.; He, Y.D.

    2000-05-10

    Iron aluminides (Fe-Al) are intermetallic compounds that possess a number of advantages including low materials cost, conservation of Ni and Cr, relatively low densities, and good corrosion and oxidation resistances. The authors have studied the high temperature oxidation and sulfidation behaviors of Fe-Al, including isothermal and cyclic oxidation kinetics, scale structure and spallation tendency, and the reactive elements effects (REE) in an effort to use these materials in industries. This paper reports their results on the structures and formation mechanisms of the scales formed on Fe-Al during oxidation. The scales formed on alloys after exposure to high temperatures often have a complex structure and composition. It is known that when some alloys were oxidized in air at high temperatures, nitrides were formed underneath the oxide scale. It was reported that the oxidation of TiAl alloys in an ambient atmosphere led to the nitration of the base metal beneath the oxide scales. After a long exposure time a multilayered scale was formed which consisted of metal, Ti{sub 2}AlN, TiN, TiO{sub 2} and Al{sub 2}O{sub 3}. Cr was oxidized in air at 1,200 C, forming a Cr{sub 2}O{sub 3} scale with a layer of Cr{sub 2}N beneath the oxide. When binary Cr alloys containing Ti,Zr, or Nb were oxidized in air at 1,150 C, a layer or internally distributed Cr{sub 2}N formed beneath the oxide scales. However, the structures and formation mechanisms of these types of scales are not clear. The authors have also found that the scales formed on Fe-Al at 1,100 C in air have a complex structure containing nitrides. This paper reports the authors' studies on this subject.

  8. 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.

  9. 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.

  10. 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.

  11. Amorphous and nanocrystalline phase formation in highly-driven Al-based binary alloys

    SciTech Connect

    Kalay, Yunus Eren

    2008-10-15

    Remarkable advances have been made since rapid solidification was first introduced to the field of materials science and technology. New types of materials such as amorphous alloys and nanostructure materials have been developed as a result of rapid solidification techniques. While these advances are, in many respects, ground breaking, much remains to be discerned concerning the fundamental relationships that exist between a liquid and a rapidly solidified solid. The scope of the current dissertation involves an extensive set of experimental, analytical, and computational studies designed to increase the overall understanding of morphological selection, phase competition, and structural hierarchy that occurs under far-from equilibrium conditions. High pressure gas atomization and Cu-block melt-spinning are the two different rapid solidification techniques applied in this study. The research is mainly focused on Al-Si and Al-Sm alloy systems. Silicon and samarium produce different, yet favorable, systems for exploration when alloyed with aluminum under far-from equilibrium conditions. One of the main differences comes from the positions of their respective T{sub 0} curves, which makes Al-Si a good candidate for solubility extension while the plunging T{sub 0} line in Al-Sm promotes glass formation. The rapidly solidified gas-atomized Al-Si powders within a composition range of 15 to 50 wt% Si are examined using scanning and transmission electron microscopy. The non-equilibrium partitioning and morphological selection observed by examining powders at different size classes are described via a microstructure map. The interface velocities and the amount of undercooling present in the powders are estimated from measured eutectic spacings based on Jackson-Hunt (JH) and Trivedi-Magnin-Kurz (TMK) models, which permit a direct comparison of theoretical predictions. For an average particle size of 10 {micro}m with a Peclet number of {approx}0.2, JH and TMK deviate from each other. This deviation indicates an adiabatic type solidification path where heat of fusion is reabsorbed. It is interesting that this particle size range is also consistent with the appearance of a microcellular growth. While no glass formation is observed within this system, the smallest size powders appear to consist of a mixture of nanocrystalline Si and Al. Al-Sm alloys have been investigated within a composition range of 34 to 42 wt% Sm. Gas atomized powders of Al-Sm are investigated to explore the morphological and structural hierarchy that correlates with different degrees of departure from full equilibrium conditions. The resultant powders show a variety of structural selection with respect to amount of undercooling, with an amorphous structure appearing at the highest cooling rates. Because of the chaotic nature of gas atomization, Cu-block melt-spinning is used to produce a homogeneous amorphous structure. The as-quenched structure within Al-34 to 42 wt% Sm consists of nanocrystalline fcc-Al (on the order of 5 nm) embedded in an amorphous matrix. The nucleation density of fcc-Al after initial crystallization is on the order of 10{sup 22}-10{sup 23} m{sup -3}, which is 10{sup 5}-10{sup 6} orders of magnitude higher than what classical nucleation theory predicts. Detailed analysis of liquid and as-quenched structures using high energy synchrotron X-ray diffraction, high energy transmission electron microscopy, and atom probe tomography techniques revealed an Al-Sm network similar in appearance to a medium range order (MRO) structure. A model whereby these MRO clusters promote the observed high nucleation density of fcc-Al nanocrystals is proposed. The devitrification path was identified using high temperature, in-situ, high energy synchrotron X-ray diffraction techniques and the crystallization kinetics were described using an analytical Johnson-Mehl-Avrami (JMA) approach.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. High performance AlScN thin film based surface acoustic wave devices with large electromechanical coupling coefficient

    NASA Astrophysics Data System (ADS)

    Wang, Wenbo; Mayrhofer, Patrick M.; He, Xingli; Gillinger, Manuel; Ye, Zhi; Wang, Xiaozhi; Bittner, Achim; Schmid, Ulrich; Luo, J. K.

    2014-09-01

    AlN and AlScN thin films with 27% scandium (Sc) were synthesized by DC magnetron sputtering deposition and used to fabricate surface acoustic wave (SAW) devices. Compared with AlN-based devices, the AlScN SAW devices exhibit much better transmission properties. Scandium doping results in electromechanical coupling coefficient, K2, in the range of 2.0% 2.2% for a wide normalized thickness range, more than a 300% increase compared to that of AlN-based SAW devices, thus demonstrating the potential applications of AlScN in high frequency resonators, sensors, and high efficiency energy harvesting devices. The coupling coefficients of the present AlScN based SAW devices are much higher than that of the theoretical calculation based on some assumptions for AlScN piezoelectric material properties, implying there is a need for in-depth investigations on the material properties of AlScN.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Spatial distribution of deep level defects in crack-free AlGaN grown on GaN with a high-temperature AlN interlayer

    NASA Astrophysics Data System (ADS)

    Sun, Q.; Wang, H.; Jiang, D. S.; Jin, R. Q.; Huang, Y.; Zhang, S. M.; Yang, H.; Jahn, U.; Ploog, K. H.

    2006-12-01

    The deep level luminescence of crack-free Al0.25Ga0.75N layers grown on a GaN template with a high-temperature grown AlN interlayer has been studied using spatially resolved cathodoluminescence (CL) spectroscopy. The CL spectra of Al0.25Ga0.75N grown on a thin AlN interlayer present a deep level aquamarine luminescence (DLAL) band at about 2.6eV and a deep level violet luminescence (DLVL) band at about 3.17eV. Cross-section line scan CL measurements on a cleaved sample edge clearly reveal different distributions of DLAL-related and DLVL-related defects in AlGaN along the growth direction. The DLAL band of AlGaN is attributed to evolve from the yellow luminescence band of GaN, and therefore has an analogous origin of a radiative transition between a shallow donor and a deep acceptor. The DLVL band is correlated with defects distributed near the GaN /AlN/AlGaN interfaces. Additionally, the lateral distribution of the intensity of the DLAL band shows a domainlike feature which is accompanied by a lateral phase separation of Al composition. Such a distribution of deep level defects is probably caused by the strain field within the domains.

  2. High rate and selective etching of GaN, AlGaN, and AlN using an inductively coupled plasma

    NASA Astrophysics Data System (ADS)

    Smith, S. A.; Wolden, C. A.; Bremser, M. D.; Hanser, A. D.; Davis, R. F.; Lampert, W. V.

    1997-12-01

    The etching behavior of gallium nitride (GaN), aluminum gallium nitride (AlxGa1-xN), and aluminum nitride (AlN) has been systematically examined in an inductively coupled plasma (ICP) using Cl2 and Ar as the reagents. Etch rates were strongly influenced by ICP power and dc bias, while relatively insensitive to pressure, flow rate, and gas composition. Maximum etch rates of 9800 Å/min for GaN, 9060 Å/min for Al0.28Ga0.72N, and 7490 Å/min for AlN were attained. The etch profiles were highly anisotropic over the range of conditions studied. The dc bias had to exceed certain voltages before significant etch rates were obtained. These values were <-20 V for GaN, -40 V for Al0.28Ga0.72N, and >-50 V for AlN. As such, increasing selectivity for GaN over Al0.28Ga0.72N and AlN was achieved at dc biases below -40 V. At -20 V, the GaN etch rates were 38 times greater than AlN and a factor of 10 greater than Al0.28Ga0.72N. These results demonstrate the importance of ion bombardment in the etching of these materials.

  3. 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

  4. High novelty-seeking rats are resilient to negative physiological effects of the early life stress.

    PubMed

    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 stress - stress-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

  5. 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.

  6. Stress Fracture of the First Rib in a High School Weight Lifter

    PubMed Central

    Fujioka, Hiroyuki; Kokubu, Takeshi; Makino, Takeshi; Nagura, Issei; Toyokawa, Narikazu; Inui, Atsuyuki; Sakata, Ryosuke; Kurosaka, Masahiro

    2009-01-01

    A 17-year-old boy, who played a weight lifting in high school, sustained stress fracture of the first rib without any causes. We successfully treated first rib stress fracture with limitation of using the upper extremity and with using low-intensity pulsed ultrasound. Key points Stress fracture of the first rib in a weight lifter was successfully treated with limitation of sports activity and with LIPUS treatment. PMID:24149543

  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 novel since broadband luminescence emission normally shows severe thermal quenching. The tightly bound AlO6 octahedra in GdAlO3 results in a larger energy barrier to nonradiative decays than in other materials and therefore makes using broadband emission for temperature sensing possible at high temperatures. This approach results in a substantial increase in temperature capability. For example, the most commonly used Cr-doped crystal used for luminescence-based temperature measurements, ruby, has only been demonstrated up to 600 C, whereas the Cr:GdAlO3 optical thermometer under development has already been shown to exhibit useful luminescence up to 1,300 C. Because GdAlO3 is non-reactive and is stable in harsh, high-temperature environments, sensors composed of Cr:GdAlO3 will be very well suited for remote high-temperature measurements in engine or industrial environments where its intense high-temperature luminescence will stand out above significant thermal radiation background levels.

  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. AlGaN Ultraviolet A and Ultraviolet C Photodetectors with Very High Specific Detectivity D*

    NASA Astrophysics Data System (ADS)

    Albrecht, Björn; Kopta, Susanne; John, Oliver; Kirste, Lutz; Driad, Rachid; Köhler, Klaus; Walther, Martin; Ambacher, Oliver

    2013-08-01

    The development of AlGaN pin photodetectors sensitive in the UV range with different narrow band active regions is reported in this paper. Structures were grown by metalorganic vapor phase epitaxy on (0001) sapphire substrates using three-dimensional GaN as well as high temperature AlN nucleation. Very high specific detectivities of 1×1014 cm Hz0.5 W-1 can be achieved based on optimized growth conditions of undoped and doped AlGaN layers with an Al-content ranging from 0% up to 100%. The crack-free AlGaN layers have edge dislocation densities in the range of 5×109 cm-2. Based on the two different nucleation types, pin layer structures were grown and fabricated to UV-A (320 to 365 nm) and UV-C (< 280 nm) photodetectors. The electro-optical performance of these photodetectors measured on-wafer will be presented in this paper, supplemented by the data of a single photodetector chip mounted in a TO 18 package.

  10. Investigation of trap states in Al2O3 InAlN/GaN metal-oxide-semiconductor high-electron-mobility transistors

    NASA Astrophysics Data System (ADS)

    Zhang, Peng; Zhao, Sheng-Lei; Xue, Jun-Shuai; Zhu, Jie-Jie; Ma, Xiao-Hua; Zhang, Jin-Cheng; Hao, Yue

    2015-12-01

    In this paper the trapping effects in Al2O3/In0.17Al0.83N/GaN MOS-HEMT (here, HEMT stands for high electron mobility transistor) are investigated by frequency-dependent capacitance and conductance analysis. The trap states are found at both the Al2O3/InAlN and InAlN/GaN interface. Trap states in InAlN/GaN heterostructure are determined to have mixed de-trapping mechanisms, emission, and tunneling. Part of the electrons captured in the trap states are likely to tunnel into the two-dimensional electron gas (2DEG) channel under serious band bending and stronger electric field peak caused by high Al content in the InAlN barrier, which explains the opposite voltage dependence of time constant and relation between the time constant and energy of the trap states. Project supported by the Program for National Natural Science Foundation of China (Grant Nos. 61404100 and 61306017).

  11. 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.

  12. 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.

  13. 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.

  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. 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}.

  17. 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.

  18. Phase separation in equiatomic AlCoCrFeNi high-entropy alloy.

    PubMed

    Manzoni, A; Daoud, H; Völkl, R; Glatzel, U; Wanderka, N

    2013-09-01

    The microstructure of the as-cast AlCoCrFeNi high entropy alloy has been investigated by transmission electron microscopy and atom probe tomography. The alloy shows a very pronounced microstructure with clearly distinguishable dendrites and interdendrites. In both regions a separation into an Al-Ni rich matrix and Cr-Fe-rich precipitates can be observed. Moreover, fluctuations of single elements within the Cr-Fe rich phase have been singled out by three dimensional atom probe measurements. The results of investigations are discussed in terms of spinodal decomposition of the alloying elements inside the Cr-Fe-rich precipitates. PMID:23352803

  19. 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.

  20. 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)

  1. Stress-Strain Behaviors Simulation of High Chromium Steel at Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Liu, Ligang; Li, Qiang; Liao, Bo; Gao, Yukui; Wang, Yuhui; Ren, Xuejun; Yang, Qingxiang

    2010-10-01

    It is important but difficult to study the constitutive equations describing the mechanical properties of steels. In this work, a thermal/mechanical simulator was used in conjunction with the Anand model to obtain the stress-strain curves for a high chromium steel associated with different temperature/strain rate pairs. The finite element software, ANSYS, was used to simulate the stress-strain behavior of a high chromium steel during casting at the strain rates of 1, 0.1, and 0.01 1/s, and to validate the Anand model. The results show that the high-temperature deformation is mainly plastic and the von Mises stresses are small, the stresses introduced at elevated temperatures have little effect on the residual stress fields, and the simulation of the mechanical behavior of steels using an elastic-plastic model at low temperatures during cooling is acceptable.

  2. 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)

  3. Proteomic analysis of the response of Arabidopsis chloroplast proteins to high light stress.

    PubMed

    Phee, Bong-Kwan; Cho, Jin-Hwan; Park, Sebyul; Jung, Jin Hee; Lee, Youn-Hyung; Jeon, Jong-Seong; Bhoo, Seong Hee; Hahn, Tae-Ryong

    2004-11-01

    Light is an essential environmental factor in the progression of plant growth and development but prolonged exposure to high levels of light stress can cause cellular damage and ultimately result in the death of the plant. Plants can respond defensively to this stress for a limited period and this involves changes to their gene expression profiles. Proteomic approaches were therefore applied to the study of the response to high light stress in the Arabidopsis thaliana plant species. Wild-type Arabidopsis was grown under normal light (100 micromol photons.m(-2).s(-1)) conditions and then subjected to high light (1000 micromol photons.m(-2).s(-1)) stress. Chloroplasts were then isolated from these plants and both soluble and insoluble proteins were extracted and subjected to two-dimensional (2-D) gel electrophoresis. The resolved proteins were subsequently identified by matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) and comparative database analysis. 64 protein spots, which were identified as candidate factors that responded to high light stress, were then selected for analysis and 52 of these were successfully identified using MALDI-TOF-MS analysis. 35 of the 52 identified proteins were found to decrease their expression levels during high light stress and a further 14 of the candidate proteins had upregulated expression levels under these conditions. Most of the proteins that were downregulated during high light stress are involved in photosynthesis pathways. However, many of the 14 upregulated proteins were identified as previously well-known high light stress-related proteins, such as heat shock proteins (HSPs), dehydroascorbate reductase (DHAR), and superoxide dismutase (SOD). Three novel proteins that were more highly expressed during periods of high light stress but had no clear functional relationship to these conditions, were also identified in this study. PMID:15478214

  4. Stress Factors and Their Alleviation in Parents of High Risk Preterm Infants.

    ERIC Educational Resources Information Center

    Lowenthal, Barbara

    The word "stress" all too often describes the emotional state of a parent after the premature birth of a high risk infant. Research studies indicate specific reasons for parental stress in the context and settings associated with the premature birth of a child. Such reasons include lack of preparation for the early birth, the immature appearance…

  5. High Temperature Oxidation and Microstructural Evolution of Modified MCrAlY Coatings

    NASA Astrophysics Data System (ADS)

    Pulci, Giovanni; Tirillò, Jacopo; Marra, Francesco; Sarasini, Fabrizio; Bellucci, Alessandra; Valente, Teodoro; Bartuli, Cecilia

    2013-11-01

    Thermal sprayed MCrAlY coatings are widely used as a bond coat in thermal barrier systems to protect the substrate from corrosion and high temperature oxidation and to improve the compatibility between the ceramic top coat and metallic substrate. In this paper, the high temperature oxidation resistance of MCrAlY coatings with modified compositions was evaluated; in particular, the effect of the addition of reactive and refractory elements (Ta, Re, Si, and Hf) was investigated. MCrAlY coatings were obtained by high velocity oxygen fuel spray and vacuum plasma spray techniques; samples were exposed to air at 1423 K (1150 °C) and the oxidation kinetics were evaluated by measuring the thickness of the thermally grown oxide (TGO) scale at several exposure times. Experimental data confirmed that the oxidation resistance of MCrAlY coatings is strictly related to the amount of the reactive and refractory elements in the starting powders and that a thorough understanding of the microstructural modifications taking place during oxidation is essential for controlling TGO growth and thermal barriers' durability.

  6. Improvement in rolling workability of Fe3Al by high-speed rolling

    NASA Astrophysics Data System (ADS)

    Muraoka, A.; Utsunomiya, H.; Matsumoto, R.; Sakai, T.

    2012-08-01

    High-speed rolling is expected to improve the deformability of difficult-to-work alloys. In this work, high-speed rolling was applied to Fe3Al, and the rolling workability was investigated. Fe-28%Al was prepared by plasma arc melting and multi-pass hot-rolled to a sheet 2 mm in thickness, followed by heat-treatment. Both the hot-rolling and heat-treatment were carried out at 1173 K. These specimens were rolled in a one-pass operation with a thickness reduction of 30 % at 1000 m/min in the temperature range from 573 to 973 K. Rolling at 5 m/min was also conducted for comparison. Sound sheets without defects or cracks were obtained even at 673 K in the high-speed rolling, while sound sheets were obtained only above 1173 K in the low-speed rolling. EBSD analysis showed that fine grains were formed either after the high-speed rolling at 873 K or after the low-speed rolling at 1073 K. Vickers hardness is not sensitive to the rolling speed below 773 K and decreased above 773 K and 1173 K in the high-speed rolling and low-speed rolling, respectively. The rolling workability of Fe3Al was significantly improved by the high-speed rolling.

  7. Irradiation Resistance in Al x CoCrFeNi High Entropy Alloys

    NASA Astrophysics Data System (ADS)

    Xia, S. Q.; Yang, X.; Yang, T. F.; Liu, S.; Zhang, Y.

    2015-08-01

    The irradiation behavior of Al x CoCrFeNi (x = 0.1, 0.75, and 1.5) high entropy alloys was studied under 3 MeV Au-ions irradiation. The microstructural change and volume swelling due to irradiation were investigated using transmission electron microscopy and atomic force microscopy. The results showed that, with increasing the Al contents, the phase crystal structures of the as-cast samples evolved from face-centered cubic (FCC), to FCC + body-centered cubic (BCC), and BCC and irradiation-induced volume swelling increased. All alloys showed exceptional structural stability when irradiated up to over 50 displacement per atom at 298 K, and the irradiation-induced volume swellings in Al x CoCrFeNi HEAs were significantly lower than conventional nuclear materials under similar irradiation dosages.

  8. Highly uniform sheet resistance of the double-channel AlInN/GaN heterostructure

    NASA Astrophysics Data System (ADS)

    Zhang, S.; Yin, J. Y.; Feng, Z. H.; Li, M. C.; Wang, J. Z.; Zhao, L. C.

    2010-12-01

    A high uniformity of sheet resistance was achieved in the double-channel (DC) Al 0.82In 0.18N/GaN heterostructure by lowering the interface roughness scattering effect. The variation of the AlInN/GaN interface roughness as a key factor influenced the uniformity of the sheet resistance. In the DC heterostructure, the distribution of the two dimension electron gas (2DEG) was modified to reduce interface roughness scattering effect. As a result, the uniformity of the sheet resistance was enhanced, and the nonuniformity of the sheet resistance in the DC Al 0.82In 0.18N/GaN could be reduced to 0.7% after structure optimization.

  9. Botulinum toxin detection using AlGaN /GaN high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Wang, Yu-Lin; Chu, B. H.; Chen, K. H.; Chang, C. Y.; Lele, T. P.; Tseng, Y.; Pearton, S. J.; Ramage, J.; Hooten, D.; Dabiran, A.; Chow, P. P.; Ren, F.

    2008-12-01

    Antibody-functionalized, Au-gated AlGaN /GaN high electron mobility transistors (HEMTs) were used to detect botulinum toxin. The antibody was anchored to the gate area through immobilized thioglycolic acid. The AlGaN /GaN HEMT drain-source current showed a rapid response of less than 5s when the target toxin in a buffer was added to the antibody-immobilized surface. We could detect a range of concentrations from 1to10ng/ml. These results clearly demonstrate the promise of field-deployable electronic biological sensors based on AlGaN /GaN HEMTs for botulinum toxin detection.

  10. 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.

  11. The triclinic high temperature modification of the {alpha} phase of the Zn-Al system

    SciTech Connect

    Sandoval-Jimenez, A.; Negrete, J.; Torres-Villasenor, G.

    1999-12-01

    The structure of the {beta} phase of the Zn-Al system was reinvestigated. The X-ray diffraction (XRD) pattern of the Zn-21.0wt%Al after 9 h at 350 C clearly showed the splitting of some Bragg peaks. The triclinic structure permits a description of the spectra with a = 285.857, b = 285.283, c = 285.847 pm, {alpha} = 59.602{degree}, {beta} = 59.869{degree}, {gamma} = 59,716{degree}. This structure corresponds to a small distortion of the primitive R cell of the high temperature fcc solid solution {alpha}-(Al) when the Zn content reaches about 69.5 wt% at 350 C.

  12. 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.

  13. Rock Strength Anisotropy in High Stress Conditions: A Case Study for Application to Shaft Stability Assessments

    NASA Astrophysics Data System (ADS)

    Watson, Julian Matthew; Vakili, Abouzar; Jakubowski, Mateusz

    2015-03-01

    Although rock strength anisotropy is a well-known phenomenon in rock mechanics, its impact on geotechnical design is often ignored or underestimated. This paper explores the concept of anisotropy in a high stress environment using an improved unified constitutive model (IUCM), which can account for more complex failure mechanisms. The IUCM is used to better understand the typical responses of anisotropic rocks to underground mining. This study applies the IUCM to a proposed rock shaft located in high stress/anisotropic conditions. Results suggest that the effect of rock strength anisotropy must be taken into consideration when assessing the rock mass response to mining in high stress and anisotropic rock conditions.

  14. 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

  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. High density GaN/AlN quantum dots for deep UV LED with high quantum efficiency and temperature stability

    PubMed Central

    Yang, Weihuang; Li, Jinchai; Zhang, Yong; Huang, Po-Kai; Lu, Tien-Chang; Kuo, Hao-Chung; Li, Shuping; Yang, Xu; Chen, Hangyang; Liu, Dayi; Kang, Junyong

    2014-01-01

    High internal efficiency and high temperature stability ultraviolet (UV) light-emitting diodes (LEDs) at 308 nm were achieved using high density (2.5 × 109 cm−2) GaN/AlN quantum dots (QDs) grown by MOVPE. Photoluminescence shows the characteristic behaviors of QDs: nearly constant linewidth and emission energy, and linear dependence of the intensity with varying excitation power. More significantly, the radiative recombination was found to dominant from 15 to 300 K, with a high internal quantum efficiency of 62% even at room temperature. PMID:24898569

  17. Boechera species exhibit species-specific responses to combined heat and high light stress.

    PubMed

    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

  18. 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

  19. T91 cladding tubes with and without modified FeCrAlY coatings exposed in LBE at different flow, stress and temperature conditions

    NASA Astrophysics Data System (ADS)

    Weisenburger, A.; Heinzel, A.; Müller, G.; Muscher, H.; Rousanov, A.

    2008-06-01

    Corrosion tests of 2000 h duration are conducted on tubes consisting of the steel T91 in liquid metal loops containing eutectic lead-bismuth melt with 10 -6 wt% oxygen in solution. The experiments include tests at temperatures of 480-600° C, at liquid metal flow velocities of 1, 2 and 3 m/s and under mechanical stress due to an internal pressure of 15 MPa. The surface of tubes exposed to 600 °C and to different flow velocities are coated with a FeCrAlY alloy to examine its suitability as a protective coating for high loaded parts like cladding tubes. The coating was remelted by an electron pulse of GESA to homogenize the coating and improve its bonding to the bulk material. In all of the tests no liquid metal attack was observed. As received steel specimens developed multilayer oxide scales of a thickness increasing with temperature and internal pressure, while coated tubes had a thin protective alumina scale. Flow velocities above 2 m/s permanently removed formed magnetite at 550 °C. No influence of the flow velocity was observed for the coated surfaces which keep their stable thin alumina scale. The internal pressure of 15 MPa caused a strain of 0.7% in the tube wall, which obviously increases iron diffusion and enhances magnetite formation.

  20. 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.

  1. 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

    2016-02-01

    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.

  2. 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.

  3. 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.

  4. 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 of shock-induced chemical reaction occurring in the time-scale of the high-pressure state. TEM characterization of recovered shock-compressed (unreacted) Ni + Al multilayered foils exhibits distinct features of constituent mixing revealing jetted layers and inter-mixed regions. These features were primarily observed in the proximity of the undulations present in the alternating layers of the Ni + Al starting foils, suggesting the important role of such instabilities in promoting shock-induced intermetallic-forming reactions in the fully dense highly exothermic multilayered thin foils.

  5. Starbursts and high-redshift galaxies are radioactive: high abundances of 26Al and other short-lived radionuclides

    NASA Astrophysics Data System (ADS)

    Lacki, Brian C.

    2014-06-01

    Short-lived radionuclides (SLRs) like 26Al are synthesized by massive stars and are a byproduct of star formation. The abundances of SLRs in the gas of a star-forming galaxy are inversely proportional to the gas consumption time. The rapid evolution of specific star formation rate (SSFR) of normal galaxies implies they had mean SLR abundances 3-10 times higher at z = 2. During the epoch of Solar system formation, the background SLR abundances of the Galaxy were up to twice as high as at present, if SLR yields from massive stars do not depend on metallicity. If SLRs are homogenized in the gas of galaxies, the high SSFRs of normal galaxies can partly explain the elevated abundance of SLRs like 60Fe and 26Al in the early Solar system. Starburst galaxies have much higher SSFRs still, and have enormous mean abundances of 26Al (26Al/27Al ?10-3 for solar metallicity gas). The main uncertainty is whether the SLRs are mixed with the star-forming molecular gas: they could be trapped in hot gas and decay before entering the colder phases, or be blown out by starburst winds. I consider how variability in star formation rate affects the SLR abundances, and I discuss how SLR transport may differ in these galaxies. The enhanced 26Al of starbursts might maintain moderate ionization rates (10-18-10-17 s-1), possibly dominating ionization in dense clouds not penetrated by cosmic rays. Similar ionization rates would be maintained in protoplanetary discs of starbursts, if the SLRs are well mixed, and the radiogenic heating of planetesimals would likewise be much higher. In this way, galaxy evolution can affect the geological history of planetary systems.

  6. Growth and characterization of highly oriented AlN films by DC reactive sputtering

    NASA Astrophysics Data System (ADS)

    Panda, Padmalochan; Sravani, Bulusu; Ramaseshan, R.; Ravi, N.; Jose, Feby; Dash, S.; Tyagi, A. K.

    2015-06-01

    Wurtzite type AlN thin films were grown on Si (100) substrates at substrate temperatures (S.T.) varying from RT to 600 °C using DC reactive magnetron sputtering by keeping the parameters such as Ar/N2, power and target to substrate distance (TSD) constant. Evolution of preferred orientation of the deposited films was studied by GIXRD and a-axis orientation was observed at 400 °C. The residual stress measurement of these films was carried out by sin2ψ technique and they varied from tensile to compressive (R.T. to 600 °C). Highest hardness (HIT) was observed for 400 °C as 20 GPa, whereas highest modulus was observed for 600 °C as 264 GPa.

  7. Investigation on compressive behavior of Cu-35Ni-15Al alloy at high temperatures

    NASA Astrophysics Data System (ADS)

    Li, Cong; Chen, Jian; Li, Wei; Hu, Yongle; Ren, Yanjie; Qiu, Wei; He, Jianjun; Chen, Jianlin

    2014-08-01

    Microstructures and mechanical properties of Cu-35Ni-15Al alloy in cast and porous states were studied by scanning electron microscopy and compression tests. The influence of porosity, deformation temperature and loading rate on mechanical properties of the two kinds of alloys was investigated. The results show that the as cast alloy and porous alloys have almost the same phase constitution: Cu rich phase, Ni rich phase and K intermetallics. The yield strength of porous alloys increases continuously with decreasing porosity, the relationship between porosity and yield stress follows Gibson-Ashby equation. With decreasing deformation temperature, the yield strength of as cast alloy and porous alloy increase. With the increase of loading rate, the yield strength of these alloys shows an increasing trend. After compression, the microstructure of as cast alloy is more uniform, and porous alloys are more prone to have localized deformations.

  8. 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.

  9. Phase Diagrams of High-Entropy Alloy System Al-Co-Cr-Fe-Mo-Ni

    NASA Astrophysics Data System (ADS)

    Hsu, Chin-You; Juan, Chien-Chang; Chen, Shin-Tsung; Sheu, Tsing-Shien; Yeh, Jien-Wei; Chen, Swe-Kai

    2013-12-01

    The high-entropy alloy system Al-Co-Cr-Fe-Mo-Ni has been previously designed based on the Al x CoCrCuFeNi system and was demonstrated to have great improvements in toughness at high hardness level and in softening resistance at elevated temperatures. For this promising system, it is important to have phase diagrams for further efficient alloy design and research. The current study combines the results from scanning electron microscopy, transmission electron microscopy, room-temperature and high-temperature x-ray diffractometry, and differential thermal analysis to construct approximate phase diagrams by varying the content of each composing element. Thermodynamic calculation in considering both mixing enthalpy and entropy was also used to justify the simple phase fields in these phase diagrams.

  10. 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

  11. Evaluation of wheat chromosome translocation lines for high temperature stress tolerance at grain filling stage.

    PubMed

    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

  12. The Role of Stress in Causing High b-Value Regions in Aftershock Zones

    NASA Astrophysics Data System (ADS)

    Wiemer, S.; Toda, S.; Woessner, J.

    2004-12-01

    Aftershock zones present an ideal environment for studying physical mechanism influencing the earthquake size distribution, or b-value, because of the high seismic activity and the sudden changes caused by a mainshock. Several recent studies have documented dramatic temporal and spatial heterogeneity of b within aftershock sequences of recent large events such as Landers, Hector Mines, Denali and Western Tottori, with b-values ranging from 0.5 to above 1.5. To improve our understanding of the link between mainshocks slip, resulting stress changes, aftershocks occurrence and their size distribution, we investigate the fine scale b-value distribution within several aftershock zones and compare it with results from stress tensor inversions. Several recent studies have speculated that areas of high slip during mainshocks subsequently show high b-values and vice versa. A first order observation is also that regions of high slip during the mainshock are also regions of high heterogeneity, in agreement the heterogeneous postseimic stress field hypothesis defined by Michael. We then map the rotations of the stress field near the rupture zone, observing significant rotations which are consistent with the predicted coseismic rotations of the principal stress axes in an elastic half space under an assumption of a 30-bar uniaxial NE-SW compression. In contrast, a region wedged between the Landers and Joshua Tree rupture zones, in which Coulomb stress increases for pre-existing strike-slip faults, show less rotation and low b-values. We propose a conceptual model where stress perturbations caused by the main shocks are on the order of the background regional stress field, thus allowing faults or cracks near the rupture zone to be activated which are in principal unfavorably oriented for rupture given the regional stress field. These events, however, occurring in a heterogeneous stress field, are generally small, leading to high b-values. In contrast, stress transfer to the surrounding areas mainly beyond the edges of the source fault increases differential stress, which promotes ruptures of moderate-to-large scale matured faults that are consistent with the tectonic stress field. This results in low b-value. The recovery with time of the stress field near the rupture zone to a more homogeneous state, which would coincide with a decrease in the b-values, would depend on the local loading rate. For the Landers region this process is still ongoing 14 years after the mainshocks.

  13. The role of hydrogen in promoting Al sbnd Si interdiffusion in albite (NaAlSi 3O 8) at high pressures

    NASA Astrophysics Data System (ADS)

    Goldsmith, Julian R.

    1986-10-01

    The rate of Al/Si disorder in "dry" low albite is greatly enhanced at high pressures. This enhancement takes place in a P-T regime where the presence of water would induce melting; none was observed. The experimental work was carried out in piston-cylinder apparatus using NaCl pressure medium. Modification of the experimental conditions to avoid production of hydrogen by dissociation of moisture in the pressure medium, as well as to capture hydrogen with Fe 2O 3 and ZnO indicates that hydrogen is the active agent in promoting Al/Si diffusion at high pressures in NaAlSi 3O 8. A mechanism involving transient OH groups that stimulate coordinations greater than 4, simultaneously breaking Al sbnd O and Si sbnd O network bonds is proposed.

  14. 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.

  15. The interface debond stress in single and multiple SiC fiber/Ti-6Al-4V composites under transverse tension

    SciTech Connect

    Gundel, D.B.; Warrier, S.G.; Miracle, D.B.

    1997-03-01

    The cruciform specimen, which effectively eliminates the influence of the fiber-free surface intersection, has recently been introduced to characterize the transverse tensile response of fiber-reinforced composites. In the present study, extensive transverse tensile testing of single and multiple-fiber specimens of SCS-6 SiC fiber/Ti-6Al-4V composites was performed. Poor consolidation and specimen damage prior to the test, when present, caused the measured interface strength to be low. The debond stress was relatively insensitive to specimen thickness between 200 and 500 {micro}m. The average remote debond stress of well-consolidated, damage-free specimens was 322 {plus_minus} 14 MPa, while a Weibull analysis indicated that the characteristic strength was 328 MPa and the Weibull modulus was 27. Stress analyses suggest that, at this level of remote stress, the interface supports a tensile stress of approximately 120 MPa, which is much greater strength than previously thought. Multiple-ply, multiple-fiber specimens were found to have nearly the same remote debond stress as the single-fiber specimens.

  16. 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.

  17. Thermal peeling stress analysis of thin-film high-temperature superconductors using FEA

    SciTech Connect

    Gu, B.; Phelan, P.E.

    1996-12-31

    Thermal peeling stress between a thin film and the substrate is caused by the mismatch of thermal expansion coefficient under a temperature change. The thermal peeling stress resulting from the temperature decrease from ambient to operating conditions (cryogenic temperatures) between a thin-film high-temperature superconductor and its substrate is calculated using finite element analysis (FEA). The superconductor thin film is idealized as a long bridge on a large substrate. A two-dimensional FEA model is applied to calculate the tensile (peeling) stress at the thin film/substrate interface. Results are obtained for different geometries and temperature conditions, and these results are compared with analytical predictions. A stress singularity is found at the very edge of the thin film which is not predicted by the analytical prediction. The peeling stress can be very high due to this stress singularity, even if the temperature change is not very large. The singular stress area depends on the local geometry of the edge. One can prevent the high singular stress by appropriate geometry. Therefore, refining the geometry of the thin-film HTS device is important.

  18. 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

  19. 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

  20. 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.

  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. 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 ?-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 ?-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 ?-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.

  4. 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.

  5. 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.

  6. 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.

  7. Solar flare prediction using highly stressed longitudinal magnetic field parameters

    NASA Astrophysics Data System (ADS)

    Huang, Xin; Wang, Hua-Ning

    2013-03-01

    Three new longitudinal magnetic field parameters are extracted from SOHO/MDI magnetograms to characterize properties of the stressed magnetic field in active regions, and their flare productivities are calculated for 1055 active regions. We find that the proposed parameters can be used to distinguish flaring samples from non-flaring samples. Using the long-term accumulated MDI data, we build the solar flare prediction model by using a data mining method. Furthermore, the decision boundary, which is used to divide flaring from non-flaring samples, is determined by the decision tree algorithm. Finally, the performance of the prediction model is evaluated by 10-fold cross validation technology. We conclude that an efficient solar flare prediction model can be built by the proposed longitudinal magnetic field parameters with the data mining method.

  8. High temperature induces apoptosis and oxidative stress in pufferfish (Takifugu obscurus) blood cells.

    PubMed

    Cheng, Chang-Hong; Yang, Fang-Fang; Liao, Shao-An; Miao, Yu-Tao; Ye, Chao-Xia; Wang, An-Li; Tan, Jia-Wen; Chen, Xiao-Yan

    2015-10-01

    Water temperature is an important environmental factor in aquaculture farming that affects the survival and growth of organisms. The change in culture water temperature may not only modify various chemical and biological processes but also affect the status of fish populations. In previous studies, high temperature induced apoptosis and oxidative stress. However, the precise mechanism and the pathways that are activated in fish are still unclear. In the present study, we investigated the effects of high temperature (34°C) on the induction of apoptosis and oxidative stress in pufferfish (Takifugu obscurus) blood cells. The data showed that high temperature exposure increased oxygen species (ROS), cytoplasmic free-Ca(2+) concentration and cell apoptosis. To test the apoptotic pathway, the expression pattern of some key apoptotic related genes including P53, Bax, caspase 9 and caspase 3 were examined. The results showed that acute high temperature stress induced up-regulation of these genes, suggesting that the p53-Bax pathway and the caspase-dependent apoptotic pathway could be involved in apoptosis induced by high temperature stress. Furthermore, the gene expression of antioxidant enzymes (Cu/Zn-SOD, Mn-SOD, CAT, GPx, and GR) and heat shock proteins (HSP90 and HSP70) in the blood cells were induced by high temperature stress. Taken together, our results showed that high temperature-induced oxidative stress may cause pufferfish blood cells apoptosis, and cooperatively activated p53-Bax and caspase-dependent apoptotic pathway. PMID:26590470

  9. 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.

  10. 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.

  11. MCrAlY Bondcoats by High-Velocity Atmospheric Plasma Spraying

    NASA Astrophysics Data System (ADS)

    Mauer, G.; Sebold, D.; Vaßen, R.

    2014-01-01

    MCrAlY bondcoats (M = Co, Ni) are used to protect metallic substrates from oxidation and to improve adhesion of ceramic thermal barrier coatings for high temperature applications, such as in land-based and aviation turbines. Since MCrAlYs are prone to take up oxygen during thermal spraying, bondcoats often are manufactured under inert gas conditions at low pressure. Plasma spraying at atmospheric conditions is a cost-effective alternative if it would be possible to limit the oxygen uptake as well as to obtain sufficiently dense microstructures. In the present work, high-velocity spray parameters were developed for the TriplexPro 210 three-cathode plasma torch using MCrAlY powders of different particle size fractions to achieve these objectives. The aims are conflictive since the former requires cold conditions, whereas the latter is obtained by more elevated particle temperatures. High particle velocities can solve this divergence as they imply shorter time for oxidation during flight and contribute to coating densification by kinetic rather than thermal energy. Further aims of the experimental work were high deposition efficiencies as well as sufficient surface roughness. The oxidation behavior of the sprayed coatings was characterized by thermal gravimetric analyses and isothermal heat treatments.

  12. High resolution microstructure characterization of the interface between cold sprayed Al coating and Mg alloy substrate

    NASA Astrophysics Data System (ADS)

    Wang, Qiang; Qiu, Dong; Xiong, Yuming; Birbilis, Nick; Zhang, Ming-Xing

    2014-01-01

    High-resolution transmission electron microscopy (HR-TEM) has validated the intimate metallurgical (atomic) bond formed along the interface of a cold-sprayed Al coating upon an Mg-alloy (AZ91) substrate. The compressive impact led to the formation of nanostructured layers of about 300-500 nm into the substrate. A highly distorted lattice structure with the inclusion of small amorphous zones was observed at the periphery of the particle/substrate interface, as a result of adiabatic shear plastic deformation at a high strain rate.

  13. Double recessed AlInAs/GaInAs/InP HEMTs with high breakdown voltages

    SciTech Connect

    Hur, K.Y.; McTaggart, R.A.; LeBlanc, B.W.

    1995-12-31

    A double recessed T-gate process has been successfully utilized to increase gate-to-drain breakdown voltages of double pulse doped AlInAs/GaInAs/InP HEMTs. By varying lateral channel dimensions, breakdown voltages in the range 11-19 V can be tailored with maximum channel currents in the range 450-600 mA/mm. This combination of high breakdown voltages and high channel currents indicate that the double recess process is a promising approach for high power applications.

  14. 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.

  15. 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

  16. Synthesis and characterization of terephthalate-intercalated NiAl layered double hydroxides with high Al content.

    PubMed

    Arias, Santiago; Eon, Jean Guillaume; San Gil, Rosane A S; Licea, Yordy E; Palacio, Luz Amparo; Faro, Arnaldo C

    2013-02-14

    Terephthalate-intercalated nickel-aluminum layered double hydroxides (LDHs) were prepared by a co-precipitation method, with nominal x values in the general formula Ni((1-x))Al(x)(OH)(2)(C(8)H(4)O(4))(x/2) in the range 0.3-0.8. The materials were characterized by X-ray diffraction, X-ray fluorescence spectroscopy, CHN analysis, thermogravimetric analysis, FTIR spectroscopy, EXAFS at the Ni edge and (27)Al NMR spectroscopy. A combination of XRD, XRF and CHN analysis indicated that crystalline LDHs with true x values up to 0.5 were obtained, along with increasing segregation of an aluminum hydroxide phase with increasing aluminum content. The EXAFS analysis indicated an upper limit of ca. 0.6 for the atomic fraction of aluminum at the second nickel coordination sphere. The (27)Al NMR analysis suggested that a phase containing octahedrally co-ordinated Al(3+) is segregated for nominal x values from 0.6 upwards. PMID:23188191

  17. Stress effects on rats chronically receiving a highly palatable diet are sex-specific.

    PubMed

    Fachin, Andrelisa; Silva, Rachel Krolow S; Noschang, Cristie G; Pettenuzzo, Leticia; Bertinetti, Liane; Billodre, Mauro Nör; Peres, William; Busnello, Fernanda; Dalmaz, Carla

    2008-11-01

    The stress response is known to lead to behavioral and metabolic changes. Exposure to chronic stress can promote the development of physiological and behavioral dysfunctions, including alterations in feeding behavior. The aim of this study was to verify whether chronic restraint stress alters the consumption of a highly palatable, highly caloric diet (chocolate), chronically offered to the animals. Male rats ate more chocolate than females, and they also exhibited a higher weight gain, abdominal fat deposition, and higher plasma levels of total cholesterol, LDL-cholesterol and glucose. The stress exposure decreased body weight, increased adrenal weight and decreased plasma insulin levels. Overall, female rats had lower plasma insulin levels and chocolate consumption prevented the increased adrenal gland weight after exposure to chronic stress, suggesting a reduction of stress effects induced by palatable food consumption. Taken together, these results suggest a peculiar metabolic pattern, related to energy store and expenditure, in stressed animals receiving a palatable diet. Since these effects were sex-specific, we may also propose that females and males subjected to restraint stress and chocolate consumption are differentially affected. PMID:18524415

  18. Modeling of al Crystal Fracture Under High-Rate Strain Based on Atomistic Simulations

    NASA Astrophysics Data System (ADS)

    Kuksin, Alexey Yu.; Norman, Genri E.; Stegailov, Vladimir V.; Yanilkin, Alexey V.

    2007-12-01

    The kinetic model of fracture under high-rate strain based on the results of molecular dynamic (MD) simulations is presented. Kinetic parameters for the model as functions of strain and temperature are obtained via statistical averaging over sets of multiple MD runs of (a) void nucleation in a crystal and (b) void growth under stretching. Within the EAM model of single crystal Al at the temperature close to the melting point it is shown that: (a) the void formation is a two-stage process of crystal homogeneous melting and further cavitation in the melt formed; (b) lattice amorphisation predominates over dislocations emission in the mechanism of the void growth. With the help of the model developed dynamic spall strength of the defect free Al crystal is calculated. While the good agreement with the experimental data is observed in the high-temperature region, it becomes worse when temperature decreases. This fact could manifest the increasing role of defects.

  19. 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.

  20. Enthalpies of formation of CaAl4O7 and CaAl12O19 (hibonite) by high temperature, alkali borate solution calorimetry

    NASA Astrophysics Data System (ADS)

    Geiger, C. A.; Kleppa, O. J.; Grossman, L.; Mysen, B. O.; Lattimer, J. M.

    1988-06-01

    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.

  1. 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.

  2. 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.

  3. Investigation of smooth specimen scc test procedures; variations in environment, specimen size, stressing frame, and stress state. [for high strength aluminum alloys

    NASA Technical Reports Server (NTRS)

    Lifka, B. W.; Sprowls, D. O.; Kelsey, R. A.

    1975-01-01

    The variables studied in the stress-corrosion cracking performance of high strength aluminum alloys were: (1) corrosiveness of the environment, (2) specimen size and stiffness of the stressing system, (3) interpretation of transgranular cracking, and (4) interaction of the state of stress and specimen orientation in a product with an anisotropic grain structure. It was shown that the probability of failure and time to fracture for a specimen loaded in direct tension are influenced by corrosion pattern, the stressing assembly stiffness, and the notch tensile strength of the alloy. Results demonstrate that the combination of a normal tension stress and a shear stress acting on the plane of maximum susceptibility in a product with a highly directional grain cause the greatest tendency for stress-corrosion cracking.

  4. 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.

  5. High Pressure Form AlOOH and its Relation to Stishovite and Brucite

    NASA Astrophysics Data System (ADS)

    Kudoh, Y.; Kuribayashi, T.; Suzuki, A.; Ohtani, E.; Kamada, T.

    2001-12-01

    The specimen used in this study was a single crystal of δ -AlOOH synthesized by Suzuki et al. (2000) using a multi-anvil apparatus at conditions of 1000° C and 21 GPa . A set of X-ray diffraction intensities up to sinθ /λ =0.80 Å-1 were measured with a single crystal of 83x35x24 μ m using MoKα radiation (50 kV, 40mA). Al:Mg:Si ratio was measured by EDS with the same crystal used in the X-ray diffraction intensity measurement. EDS analysis showed a Al:Mg:Si ratio 0.84:0.07:0.09, yielding the chemical formula (Al0.84Mg0.07Si0.09)H0.98O2. Crystallographic data for δ -AlOOH obtained are; Orthorhombic, a=4.2060(6) Å, b=4.6975(8) Å, c=2.8327(4) Å, V=55.97(1) Å3, Z=2, Dcalc=3.553 g/cm3. For the space group of δ -AlOOH, Suzuki et al. (2000) reported P21nm from powder X-ray data but the systematic absence of reflections with h+l odd for h0l and k+l odd for 0kl observed in the present work indicated possible space group Pnn2 or Pnnm. The N(Z) test for a center of symmetry indicated an acentric space group. The non-centrosymmetric space group Pnn2 was therefore employed and was confirmed by the structural refinement. The agreement factors for 109 independent reflections (Io>3.0σ Io) were R=3.6% and Rw=6.3% with anisotropic temperature factors. The result of structural analysis showed 5 possible sites for H with O-H- - -O distances of 2.511 Å, 2.553 Å, 2.705 Å, 2.744 Å and 2.834 Å, indicating that the structure is affordable for various amount of H with substituting Al by Mg. The partial occupancy of Mg and Si atoms at Al site suggests the possibility of limited solid solution among δ -AlOOH, stishovite,SiO2 and hypothetical rutile-structured Mg(OH)2. The hypothetical rutile-structured Mg(OH)2 might be a possible candidate for high pressure form of brucite. By the extraporation of the unit cell volumes of δ -AlOOH and stishovite,SiO2, the unit cell volume of the hypothetical rutile-structured Mg(OH)2 is estimated to be V=61.5 A3, giving the density 3.149 g/cm3.

  6. Aftershocks are well aligned with the background stress field, contradicting the hypothesis of highly-heterogeneous crustal stress

    USGS Publications Warehouse

    Hardebeck, Jeanne L.

    2010-01-01

    It has been proposed that the crustal stress field contains small-length-scale heterogeneity of much larger amplitude than the uniform background stress. This model predicts that earthquake focal mechanisms should reflect the loading stress rather than the uniform background stress. So, if the heterogeneous stress hypothesis is correct, focal mechanisms before and after a large earthquake should align with the tectonic loading and the earthquake-induced static stress perturbation, respectively. However, I show that the off-fault triggered aftershocks of the 1992 M7.3 Landers, California, earthquake align with the same stress field as the pre-Landers mechanisms. The aftershocks occurred on faults that were well oriented for failure in the pre-Landers stress field and then loaded by the Landers-induced static stress change. Aftershocks in regions experiencing a 0.05 to 5 MPa coseismic differential stress change align with the modeled Landers-induced static stress change, implying that they were triggered by the stress perturbation. Contrary to the heterogeneous stress hypothesis, these triggered aftershocks are also well aligned with the pre-Landers stress field obtained from inverting the pre-Landers focal mechanisms. Therefore, the inverted pre-Landers stress must represent the persistent background stress field. Earthquake focal mechanisms provide an unbiased sample of the spatially coherent background stress field, which is large relative to any small-scale stress heterogeneity. The counterexample provided by the Landers earthquake is strong evidence that the heterogeneous stress model is not widely applicable.

  7. 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 size decreased with the prolongation of milling times, while the internal strain increased. A simple model is presented to illustrate the mechanical alloying of a ductile-brittle component system. A competition between the cold welding mechanism and the fracturing mechanism were found during powder milling and finally the above two mechanisms reached an equilibrium. The maximum relative density was obtained at 1500 Degree-Sign C. The harness of the sintered composite was decreased while the fracture toughness was improved after addition Al into alumina.

  8. 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.

  9. 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.

  10. Electronic origin of atomic-level stresses in High-Entropy Alloys

    NASA Astrophysics Data System (ADS)

    Odbadrakh, Khorgolkhuu; Egami, Takeshi; Ojha, Madhu; Nicholson, Don; Stocks, Malcolm

    High-entropy alloys are multi-component solid solutions in which four or more elements occupy the same crystallographic lattice sites with roughly equal compositions. The underlying chemical disorder gives rise to small local lattice distortions and atomic-level stresses, which are also disorders on their own. These disorders lead to radiation resistance and mechanical strength in high temperature environment, making HEAs alloys attractive candidates as nuclear materials. We report electronic origin of the atomic-level stresses based upon first-principles calculations using Locally Self-consistent Multiple Scattering theory method. Strong atomic-level stresses are present in HEAs due not only to the differences in the intrinsic atomic sizes but due to charge transfer among the elements. We suggest that the improved properties of HEAs originate mainly from the high magnitudes of atomic-level stresses in these complex disordered alloys.

  11. 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.

  12. Optimizing amorphous indium zinc oxide film growth for low residual stress and high electrical conductivity

    NASA Astrophysics Data System (ADS)

    Kumar, Mukesh; Sigdel, A. K.; Gennett, T.; Berry, J. J.; Perkins, J. D.; Ginley, D. S.; Packard, C. E.

    2013-10-01

    With recent advances in flexible electronics, there is a growing need for transparent conductors with optimum conductivity tailored to the application and nearly zero residual stress to ensure mechanical reliability. Within amorphous transparent conducting oxide (TCO) systems, a variety of sputter growth parameters have been shown to separately impact film stress and optoelectronic properties due to the complex nature of the deposition process. We apply a statistical design of experiments (DOE) approach to identify growth parameter-material property relationships in amorphous indium zinc oxide (a-IZO) thin films and observed large, compressive residual stresses in films grown under conditions typically used for the deposition of highly conductive samples. Power, growth pressure, oxygen partial pressure, and RF power ratio (RF/(RF + DC)) were varied according to a full-factorial test matrix and each film was characterized. The resulting regression model and analysis of variance (ANOVA) revealed significant contributions to the residual stress from individual growth parameters as well as interactions of different growth parameters, but no conditions were found within the initial growth space that simultaneously produced low residual stress and high electrical conductivity. Extrapolation of the model results to lower oxygen partial pressures, combined with prior knowledge of conductivity-growth parameter relationships in the IZO system, allowed the selection of two promising growth conditions that were both empirically verified to achieve nearly zero residual stress and electrical conductivities >1480 S/cm. This work shows that a-IZO can be simultaneously optimized for high conductivity and low residual stress.

  13. HIGH TEMPERATURE STRESS ON FLORAL DEVELOPMENT AND YIELD OF COTTON

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Because a number of reproductive processes must occur in highly concerted fashion during the progamic phase (from pollination to fertilization) for successful fertilization and seed production to occur, final yield in cotton is exceptionally sensitive to high temperatures during the flowering period...

  14. 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.

  15. 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 stability of nitrates and exposed Pt surface, gives the best NOx trapping capability.

  16. Assessing Cumulative Thermal Stress in Fish During Chronic Exposure to High Temperature

    SciTech Connect

    Bevelhimer, M.S.; Bennett, W.R.

    1999-11-14

    As environmental laws become increasingly protective, and with possible future changes in global climate, thermal effects on aquatic resources are likely to receive increasing attention. Lethal temperatures for a variety of species have been determined for situations where temperatures rise rapidly resulting in lethal effects. However, less is known about the effects of chronic exposure to high (but not immediately lethal) temperatures and even less about stress accumulation during periods of fluctuating temperatures. In this paper we present a modeling framework for assessing cumulative thermal stress in fish. The model assumes that stress accumulation occurs above a threshold temperature at a rate depending on the degree to which the threshold is exceeded. The model also includes stress recovery (or alleviation) when temperatures drop below the threshold temperature as in systems with large daily variation. In addition to non-specific physiological stress, the model also simulates thermal effects on growth.

  17. High Resolution Raman spectroscopy of GaAs, AlAs, and GaAs-AlAs superlattices

    NASA Astrophysics Data System (ADS)

    Poweleit, C. D.; Canonico, M.; Lopez, M.; Knox, M. A.; Menéndez, J.

    1997-03-01

    Recent theoretical work has demonstrated that phonon lifetimes in semiconductors can be predicted from first principles if the phonon decay process is dominated by third-order anharmonicity.(A. Debernardi, S. Baroni, E. Molinari, Phys. Rev. Lett. 75), 1819, (1995) Experimentally, the anharmonic lifetime of Raman-active phonons can be obtained from measurements of the linewidth of the Raman lines. We report such measurements for the Brillouin zone-center phonons in GaAs, AlAs and GaAs-AlAs superlattices. The experiments were performed using an ultrahigh-resolution double monochromator for which state-of-the-art CCD detection does not impose any significant resolution penalty. The linewidth and lineshift of the Raman lines were measured between 10 K and 500 K. Within this range, the anharmonic decay is dominated by third-order anharmonicity and can therefore be compared with theory.

  18. 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.

  19. Osmium Metal Studied under High Pressure and Nonhydrostatic Stress

    SciTech Connect

    Weinberger,M.; Tolbert, S.; Kavner, A.

    2008-01-01

    Interest in osmium as an ultra-incompressible material and as an analog for the behavior of iron at high pressure has inspired recent studies of its mechanical properties. We have measured elastic and plastic deformation of Os metal at high pressures using in situ high pressure x-ray diffraction in the radial geometry. We show that Os has the highest yield strength observed for any pure metal, supporting up to 10 GPa at a pressure of 26 GPa. Furthermore, our data indicate changes in the nonhydrostatic apparent c/a ratio and clear lattice preferred orientation effects at pressures above 15 GPa.

  20. 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.

  1. Life prediction of 808nm high power semiconductor laser by accelerated life test of constant current stress

    NASA Astrophysics Data System (ADS)

    Yao, Nan; Li, Wei; Zhao, Yihao; Zhong, Li; Liu, Suping; Ma, Xiaoyu

    2015-10-01

    High power semiconductor laser is widely used because of its high transformation efficiency, good working stability, compact volume and simple driving requirements. Laser's lifetime is very long, but tests at high levels of stress can speed up the failure process and shorten the times to failure significantly. So accelerated life test is used here for forecasting the lifetime of 808nm CW GaAs/AlGaAs high power semiconductor laser that has an output power of 1W under 1.04A. Accelerated life test of constant current stress based on the Inverse Power Law Relationship was designed. Tests were conducted under 1.3A, 1.6A and 1.9A at room temperature. It is the first time that this method is used in the domestic research of laser's lifetime prediction. Applying Weibull Distribution to describe the lifetime distribution and analyzing the data of times to failure, characteristics lifetime's functional relationship model with current is achieved. Then the characteristics lifetime under normal current is extrapolated, which is 9473h. Besides, to confirm the validity of the functional relationship model, we conduct an additional accelerated life test under 1.75A. Based on this experimental data we calculated the characteristics lifetime corresponding to 1.75A that is 171h, while the extrapolated characteristics lifetime from the former functional relationship model is 162h. The two results shows 5% deviation that is very low and acceptable, which indicates that the test design is reasonable and authentic.

  2. Complexity of physiological responses decreases in high-stress musical performance

    PubMed Central

    Williamon, Aaron; Aufegger, Lisa; Wasley, David; Looney, David; Mandic, Danilo P.

    2013-01-01

    For musicians, performing in front of an audience can cause considerable apprehension; indeed, performance anxiety is felt throughout the profession, with wide ranging symptoms arising irrespective of age, skill level and amount of practice. A key indicator of stress is frequency-specific fluctuations in the dynamics of heart rate known as heart rate variability (HRV). Recent developments in sensor technology have made possible the measurement of physiological parameters reflecting HRV non-invasively and outside of the laboratory, opening research avenues for real-time performer feedback to help improve stress management. However, the study of stress using standard algorithms has led to conflicting and inconsistent results. Here, we present an innovative and rigorous approach which combines: (i) a controlled and repeatable experiment in which the physiological response of an expert musician was evaluated in a low-stress performance and a high-stress recital for an audience of 400 people, (ii) a piece of music with varying physical and cognitive demands, and (iii) dynamic stress level assessment with standard and state-of-the-art HRV analysis algorithms such as those within the domain of complexity science which account for higher order stress signatures. We show that this offers new scope for interpreting the autonomic nervous system response to stress in real-world scenarios, with the evolution of stress levels being consistent with the difficulty of the music being played, superimposed on the stress caused by performing in front of an audience. For an emerging class of algorithms that can analyse HRV independent of absolute data scaling, it is shown that complexity science performs a more accurate assessment of average stress levels, thus providing greater insight into the degree of physiological change experienced by musicians when performing in public. PMID:24068177

  3. Solid-solution hardening of a high-Entropy AlTiVCrNbMo alloy

    NASA Astrophysics Data System (ADS)

    Firstov, S. A.; Rogul', T. G.; Krapivka, N. A.; Ponomarev, S. S.; Tkach, V. N.; Kovylyaev, V. V.; Gorban', V. F.; Karpets, M. V.

    2014-04-01

    The nature of solid-solution hardening of high-entropy alloys is discussed using an equiatomic bcc AlTiVCrNbMo alloy as an example. The hardening of the alloy is found to be characterized by an increase in the temperature dependence of the component of the critical shear strength and by anomalously high athermic hardening due to the perpendicular slip plane of the Burgers vector component. A relatively simple expression is proposed to estimate the detected hardening Δ H(Δσ).

  4. High-power AlGaAs channeled substrate planar diode lasers for spaceborne communications

    NASA Technical Reports Server (NTRS)

    Connolly, J. C.; Goldstein, B.; Pultz, G. N.; Slavin, S. E.; Carlin, D. B.; Ettenberg, M.

    1988-01-01

    A high power channeled substrate planar AlGaAs diode laser with an emission wavelength of 8600 to 8800 A was developed. The optoelectronic behavior (power current, single spatial and spectral behavior, far field characteristics, modulation, and astigmatism properties) and results of computer modeling studies on the performance of the laser are discussed. Lifetest data on these devices at high output power levels is also included. In addition, a new type of channeled substrate planar laser utilizing a Bragg grating to stabilize the longitudinal mode was demonstrated. The fabrication procedures and optoelectronic properties of this new diode laser are described.

  5. Microstructural Evolution of Ti-6Al-4V during High Strain Rate Conditions of Metal Cutting

    NASA Technical Reports Server (NTRS)

    Dong, Lei; Schneider, Judy

    2009-01-01

    The microstructural evolution following metal cutting was investigated within the metal chips of Ti-6Al-4V. Metal cutting was used to impose a high strain rate on the order of approx.10(exp 5)/s within the primary shear zone as the metal was removed from the workpiece. The initial microstructure of the parent material (PM) was composed of a bi-modal microstructure with coarse prior grains and equiaxed primary located at the boundaries. After metal cutting, the microstructure of the metal chips showed coarsening of the equiaxed primary grains and lamellar. These metallographic findings suggest that the metal chips experienced high temperatures which remained below the transus temperature.

  6. Creation of surface nanostructures in Al2O3 by slow highly charged ions

    NASA Astrophysics Data System (ADS)

    El-Said, A. S.; Wilhelm, R. A.; Heller, R.; Akhmadaliev, Sh.; Facsko, S.

    2013-12-01

    Al2O3 single crystals were irradiated with slow highly charged Xe ions of various charge states from an EBIT (Electron Beam Ion Trap) source at the Dresden two source facility. The irradiations were performed at room temperature and under normal incidence. Scanning force microscopy (SFM) was utilized to investigate the topography of the irradiated surfaces. The measurements showed that above a potential energy threshold, each ion creates a nanohillock protruding from the surface. These structures are compared to those created by swift heavy ions (SHI). The results are discussed in terms of potential energy deposition of highly charged ions (HCI) and electronic energy loss of SHI.

  7. Effects of annealing on texture evolution of cross shear rolled high-purity Al foils

    NASA Astrophysics Data System (ADS)

    Wang, L.; Liu, Y.; Song, X.; He, J.; Zuo, L.

    2015-04-01

    The effects of annealing on recrystallization texture of cross shear rolled high-purity Al foil were investigated by orientation distribution functions (ODFs) and electron backscattered diffraction (EBSD). The results show that the intermediate annealing is beneficial to the development of the cube texture. The cube texture can be promoted by annealing, and the critical annealing temperature is about 280 °C. The cubic orientation grains firstly nucleate, and then expand into other grains with a high growth speed, and large angle grain boundary ratio increases, finally can swallow up most of the original grains, which results in the cube texture

  8. Stress management as an enabling technology for high-field superconducting dipole magnets

    NASA Astrophysics Data System (ADS)

    Holik, Eddie Frank, III

    This dissertation examines stress management and other construction techniques as means to meet future accelerator requirement demands by planning, fabricating, and analyzing a high-field, Nb3Sn dipole. In order to enable future fundamental research and discovery in high energy accelerator physics, bending magnets must access the highest fields possible. Stress management is a novel, propitious path to attain higher fields and preserve the maximum current capacity of advanced superconductors by managing the Lorentz stress so that strain induced current degradation is mitigated. Stress management is accomplished through several innovative design features. A block-coil geometry enables an Inconel pier and beam matrix to be incorporated in the windings for Lorentz Stress support and reduced AC loss. A laminar spring between windings and mica paper surrounding each winding inhibit any stress transferral through the support structure and has been simulated with ALGORRTM. Wood's metal filled, stainless steel bladders apply isostatic, surface-conforming preload to the pier and beam support structure. Sufficient preload along with mica paper sheer release reduces magnet training by inhibiting stick-slip motion. The effectiveness of stress management is tested with high-precision capacitive stress transducers and strain gauges. In addition to stress management, there are several technologies developed to assist in the successful construction of a high-field dipole. Quench protection has been designed and simulated along with full 3D magnetic simulation with OPERARTM. Rutherford cable was constructed, and cable thermal expansion data was analysed after heat treatment. Pre-impregnation analysis techniques were developed due to elemental tin leakage in varying quantities during heat treatment from each coil. Robust splicing techniques were developed with measured resistivites consistent with nO joints. Stress management has not been incorporated by any other high field dipole research laboratory and has not yet been put to a definitive high-field test. The TAMU Physics Accelerator Research Laboratory has constructed a Nb 3Sn dipole, TAMU3, that is specially designed to provide a test bed for high-field stress management.

  9. Optimization of High Temperature Hoop Creep Response in ODS-Fe3Al Tubes

    SciTech Connect

    Kad, B.K.; Heatherington, J.H.; McKamey, C.; Wright, I.; Sikka, V.; Judkins, R.

    2003-04-22

    Oxide dispersion strengthened (ODS) Fe3Al alloys are currently being developed for heat-exchanger tubes for eventual use at operating temperatures of up to 1100 C in the power generation industry. The development challenges include (a) efforts to produce thin walled ODS-Fe3Al tubes, employing powder extrusion methodologies, with (b) adequate increased strength for service at operating temperatures to (c) mitigate creep failures by enhancing the as-processed grain size. A detailed and comprehensive research and development methodology is prescribed to produce ODS-Fe3Al thin walled tubes. Current single step extrusion consolidation methodologies typically yield 8ft. lengths of 1-3/8 inch diameter, 1/8 inch wall thickness ODS-Fe3Al tubes. The process parameters for such consolidation methodologies have been prescribed and evaluated as being routinely reproducible. Recrystallization treatments at 1200 C produce elongated grains (with their long axis parallel to the extrusion axis), typically 200-2000 {micro}m in diameter, and several millimeters long. The dispersion distribution is unaltered on a micro scale by recrystallization, but the high aspect ratio grain shape typically obtained limits grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloys requires an understanding and manipulating the factors that control grain alignment and recrystallization behavior. Current efforts are focused on examining the processing dependent longitudinal vs. transverse creep anisotropy, and exploring post-extrusion methods to improve hoop creep response in ODS-Fe3Al alloy tubes. In this report we examine the mechanisms of hoop creep failure and describe our efforts to improve creep performance via variations in thermal-mechanical treatments.

  10. Analysis of thermal residual stress in a thick-walled ring of Duralcan-base Al-SiC functionally graded material

    SciTech Connect

    Fukui, Yasuyoshi; Watanabe, Yoshimi

    1996-12-01

    A ring-cutting test and an elastic theory were applied to evaluate the macroscopic residual stress in a thick-walled ring made of Al-SiC functionally graded material (FGM). The FGM ring specimens, with outer diameter 90 mm, radial thickness approximately 8.4 to 10 mm, and width 30 mm, were fabricated by the centrifugal casting method from an ingot of Duralcan F3D.20S of Al-20 vol pct SiC master composite. Because of a difference in centrifugal forces of SiC particles and of molten aluminum alloy, the rings had a graded composition of SiC particles in the radial direction. The volume fractions of SiC particles in each ring specimen varied in the range of 0 to 43 vol pct from the inner to the outer surface of the ring, depending on the applied mold spin speed. A ring diametral compression test was performed to validate an analytical formula based on the curved beam theory that can account for the graded properties of the material. Excellent agreement between the theory that can account for the graded properties of the material. Excellent agreement between the theory and the experiment was found. The residual stress was found to be generated by a cooling of {Delta}T = 140 K, which was from half the melting point corresponding stress-free condition to the ambient temperature. The hoop residual stresses in the FGM ring varied in the range of {minus}50 to +35 MPa and from tension at the inner surface to compression at the outer space because of the graded composition. With an increase in wall thickness and/or composition gradation, the residual stresses were found to increase.

  11. High Temperature Strength and Stress Relaxation Behavior of Dilute Binary Mg Alloys

    NASA Astrophysics Data System (ADS)

    Abaspour, Saeideh; Cáceres, Carlos H.

    2016-03-01

    Monotonic compression and stress relaxation tests were carried out on specimens of 6 cast binary alloys with (at. pct) 2.5 Al, 0.6 Sn, 2.2 Zn, 0.9 Nd, 0.8 Gd and 1.3 Y, and of a similarly cast AZ91D alloy for reference. The solute concentration of the binary alloys was kept deliberately low to limit precipitation hardening effects during the testing, done in the solution heat treated and quenched condition. Compression testing was carried out at 298 K, 373 K and 453 K (25 °C, 100 °C and 180 °C) for all of the alloys and at 493 K and 523 K (220 °C and 250 °C) for the Nd-, Gd- and Y- containing ones. Stress relaxation was done at 453 K (180 °C) at either a predetermined strain (0.05) or stress (150 MPa). The Mg-Al and the AZ91 alloys softened considerably above 373 K (100 °C). The rest of the alloys exhibited increasing linear strain hardening in compression and reduced stress relaxation, in the order Sn, Zn, Nd, Gd and Y, an indication of a progressively stable dislocation substructure, hence of an increasingly extended athermal regime in the strength-temperature relationship. The overall strain hardening behavior matches that of commercial alloys involving the same solutes at comparable or higher concentrations, and can be accounted for through the respective tendency of the solute atoms to develop short range order. This tendency is lowest for the near-random solid solution introduced by Al, and highest for Nd, Gd and Y, in agreement with their respective phase diagrams. The implications for creep resistant alloy selection and design are discussed.

  12. High Temperature Strength and Stress Relaxation Behavior of Dilute Binary Mg Alloys

    NASA Astrophysics Data System (ADS)

    Abaspour, Saeideh; Cáceres, Carlos H.

    2016-01-01

    Monotonic compression and stress relaxation tests were carried out on specimens of 6 cast binary alloys with (at. pct) 2.5 Al, 0.6 Sn, 2.2 Zn, 0.9 Nd, 0.8 Gd and 1.3 Y, and of a similarly cast AZ91D alloy for reference. The solute concentration of the binary alloys was kept deliberately low to limit precipitation hardening effects during the testing, done in the solution heat treated and quenched condition. Compression testing was carried out at 298 K, 373 K and 453 K (25 °C, 100 °C and 180 °C) for all of the alloys and at 493 K and 523 K (220 °C and 250 °C) for the Nd-, Gd- and Y- containing ones. Stress relaxation was done at 453 K (180 °C) at either a predetermined strain (0.05) or stress (150 MPa). The Mg-Al and the AZ91 alloys softened considerably above 373 K (100 °C). The rest of the alloys exhibited increasing linear strain hardening in compression and reduced stress relaxation, in the order Sn, Zn, Nd, Gd and Y, an indication of a progressively stable dislocation substructure, hence of an increasingly extended athermal regime in the strength-temperature relationship. The overall strain hardening behavior matches that of commercial alloys involving the same solutes at comparable or higher concentrations, and can be accounted for through the respective tendency of the solute atoms to develop short range order. This tendency is lowest for the near-random solid solution introduced by Al, and highest for Nd, Gd and Y, in agreement with their respective phase diagrams. The implications for creep resistant alloy selection and design are discussed.

  13. Reliability of AlGaN/GaN high electron mobility transistors on low dislocation density bulk GaN substrate: Implications of surface step edges

    SciTech Connect

    Killat, N. E-mail: Martin.Kuball@bristol.ac.uk; Montes Bajo, M.; Kuball, M. E-mail: Martin.Kuball@bristol.ac.uk; Paskova, T.; Materials Science and Engineering Department, North Carolina State University, Raleigh, North Carolina 27695 ; Evans, K. R.; Leach, J.; Electrical and Computer Engineering Department, Virginia Commonwealth University, Richmond, Virginia 23284 ; Li, X.; Özgür, Ü.; Morkoç, H.; Chabak, K. D.; Crespo, A.; Gillespie, J. K.; Fitch, R.; Kossler, M.; Walker, D. E.; Trejo, M.; Via, G. D.; Blevins, J. D.

    2013-11-04

    To enable gaining insight into degradation mechanisms of AlGaN/GaN high electron mobility transistors, devices grown on a low-dislocation-density bulk-GaN substrate were studied. Gate leakage current and electroluminescence (EL) monitoring revealed a progressive appearance of EL spots during off-state stress which signify the generation of gate current leakage paths. Atomic force microscopy evidenced the formation of semiconductor surface pits at the failure location, which corresponds to the interaction region of the gate contact edge and the edges of surface steps.

  14. Surface modification by oil jet peening in Al alloys, AA6063-T6 and AA6061-T4: Residual stress and hardness

    NASA Astrophysics Data System (ADS)

    Grinspan, A. Sahaya; Gnanamoorthy, R.

    2006-11-01

    The life of structural members that experience cyclic loading is improved by the introduction of surface compressive residual stresses. A high-pressure oil jet is used for the introduction of surface compressive residual stresses in aluminum alloys, AA6063-T6 and AA6061-T4. The peening machine designed and developed in the laboratory is capable of generating high pressures using hydraulic oil. The magnitude of residual stress developed depends upon the stand-off distance and yield strength of the material. A hardened layer up to a depth of about 350 μm was developed in the materials investigated. The residual stresses and surface hardening induced are comparable to that produced by other peening processes. An analytical model is proposed to predict the impact pressure.

  15. 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

  16. High resolution sup 27 Al NMR spectroscopy of the aluminophosphate molecular sieve VPI-5

    SciTech Connect

    Wu, Y.; Chmelka, B.F.; Pines, A. ); Davis, M.E. ); Grobet, P.J.; Jacobs, P.A. )

    1990-08-01

    Aluminium plays an important part in determining the properties of many materials, such as the catalytic behavior of zeolites. Aluminophosphate molecular sieves, in particular, have useful applications as superlattice hosts in the fabrication of quantum-effect devices. Although nuclear magnetic resonance (NMR) spectroscopy is often a sensitive probe of solids, the use of {sup 27}Al NMR to investigate the structure of aluminosilicates and aluminophosphates has been severely limited because anisotropic second-order quadrupolar interactions, responsible for spectral broadening, cannot be eliminated by conventional magic-angle-spinning or multiple-pulse techniques. Here the authors report the first high-resolution NMR spectra of {sup 27}Al in a solid using double rotation and demonstrate its usefulness for probing subtle structural perturbations in the aluminophosphate molecular sieve VPI-5. From their results, they conclude that high-resolution {sup 27}Al NMR is capable of resolving discrete framework aluminium sites, permitting quantitative investigation of site-specific adsorbate interactions with the VPI-5 host.

  17. Study of surface leakage current of AlGaN/GaN high electron mobility transistors

    SciTech Connect

    Chen, YongHe; Zhang, Kai; Cao, MengYi; Zhao, ShengLei; Zhang, JinCheng; Hao, Yue; Ma, XiaoHua

    2014-04-14

    Temperature-dependent surface current measurements were performed to analyze the mechanism of surface conductance of AlGaN/GaN channel high-electron-mobility transistors by utilizing process-optimized double gate structures. Different temperatures and electric field dependence have been found in surface current measurements. At low electric field, the mechanism of surface conductance is considered to be two-dimensional variable range hopping. At elevated electric field, the Frenkel–Poole trap assisted emission governs the main surface electrons transportation. The extracted energy barrier height of electrons emitting from trapped state near Fermi energy level into a threading dislocations-related continuum state is 0.38 eV. SiN passivation reduces the surface leakage current by two order of magnitude and nearly 4 orders of magnitude at low and high electric fields, respectively. SiN also suppresses the Frenkel–Poole conductance at high temperature by improving the surface states of AlGaN/GaN. A surface treatment process has been introduced to further suppress the surface leakage current at high temperature and high field, which results in a decrease in surface current of almost 3 orders of magnitude at 476 K.

  18. Synthesis and structural characterization of Al-containing interlayer-expanded-MWW zeolite with high catalytic performance.

    PubMed

    Yokoi, Toshiyuki; Mizuno, Shun; Imai, Hiroyuki; Tatsumi, Takashi

    2014-07-21

    Treatment of the zeolitic layered precursor of Al-MWW, so-called Al-MWW(P), with diethoxydimethylsilane (DEDMS) in acidic media leads to the formation of an aluminosilicate-type interlayer-expanded zeolite MWW (Al-IEZ-MWW) with expanded 12-membered ring (12-MR) micropores. However, the silylation process under acidic conditions simultaneously causes dealumination from the MWW framework, resulting in a decrease in the acid amount. We have developed a method for preparing Al-IEZ-MWW without leaching of the Al species. The strategy is to conduct the silylation under weakly acidic conditions; the silylation was conducted in an aqueous solution of an ammonium salt, e.g., NH4Cl, instead of HNO3. Subsequent additional acid treatment led to the formation of Al-IEZ-MWW that shows a high catalytic performance in the acylation of anisole compared to typical Al-MWW as well as Al-IEZ-MWW directly prepared under acidic conditions. The change in the state of Al atoms during the preparation process was investigated by high-resolution solid-state (27)Al MAS NMR and (27)Al MQMAS NMR techniques. PMID:24798349

  19. A high performance InAlN/GaN HEMT with low Ron and gate leakage

    NASA Astrophysics Data System (ADS)

    Chunlei, Ma; Guodong, Gu; Yuanjie, Lü

    2016-02-01

    InAlN/GaN high-electron mobility transistors (HEMTs) with a gate length of 100 nm and oxygen plasma treatment were fabricated. A Si/Ti/Al/Ni/Au ohmic contact was also used to reduce the contact resistance. DC and RF characteristics of the devices were measured. The fabricated devices show a maximum drain current density of 2.18 A/mm at VGS = 2 V, a low on-resistance (Ron) of 1.49 ω·mm and low gate leakage current. An excellent frequency response was also obtained. The current cut-off frequency (fT) is 81 GHz and the maximum oscillation frequency is 138 GHz, respectively. Project supported by the National Natural Science Foundation of China (No. 61306113).

  20. A highly selective, chlorofluorocarbon-free GaAs on AlGaAs etch

    SciTech Connect

    Smith, L.E. . Solid State Technology Center)

    1993-07-01

    A highly selective reactive ion etching process using SiCl[sub 4], CF[sub 4], O[sub 2], and He is reported. The selectivity of the etch, which is adjustable, ranges from 308:1 to 428:1 for GaAs to Al[sub 0.11]Ga[sub 0.89]As. This variability in selectivity is achieved by adjusting the helium flow rate. One very attractive feature of this etch is that it uses no chlorofluorocarbons and therefore complies with future bans on these substances imposed at both federal and corporate levels. The etch is demonstrated on a GaAs field effect transistor structure with an underlying Al[sub 0.11]Ga[sub 0.89]As stop-etch layer. The etch can be used for both anisotropic and isotropic applications.