72 research outputs found
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Processing and properties of hot-forged bulk superconductors
(Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (Bi-2223) and TlBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (Tl-1223) bars were hot forged in air at 820--850C. Final stresses of 2--3 MPa were sufficient to produce >95% dense Bi-2223 bars. In contrast, stresses to {approx}42 MPa were able to produce only 75--80% dense Tl-1223 bars. The Bi-2223 bars were more phase-pure and exhibited much stronger c-axis textures than the Tl-1223. Maximum critical current densities at 77 K were 8 {times} 10{sup 4} A/cm{sup 2} for the Bi-2223 and 2 {times} 10{sup 4}/cm{sup 2} for the Tl-1223. Fracture strength and toughness values were 140 MPa and 2.9 MPa{radical}m for the Bi-2223 and 50 MPa and 0.5 MPa{radical}m for the Tl-1223
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Mechanical properties of nanocrystalline metals, intermetalics and multiphase materials determined by tension, compression and disk-bend techniques
The mechanical behavior of nanocrystalline metallic, intermetallic, and multiphase materials was investigated using tension, compression, and disk-bend techniques. Nanocrystalline NiAl, Al-Al{sub 3}Zr, and Cu were synthesized by gas condensation and either resistive or electron beam heating followed by high temperature vacuum compaction. Disk- bend tests of nanocrystalline NiAl show evidence of improved ductility at room temperature in this normally extremely brittle material. In contrast, tension tests of multiphase nanocrystalline Al- Al{sub 3}Zr samples show significant increases in strength by substantial reductions in ductility with decreasing grain size. Compression tests of nanocrystalline copper result in substantially higher yield stress and total elongation values than those measured in tensile tests. Implications for operative deformation mechanisms in these materials are discussed
Visualizing size-dependent deformation mechanism transition in Sn
Displacive deformation via dislocation slip and deformation twinning usually plays a dominant role in the plasticity of crystalline solids at room temperature. Here we report in situ quantitative transmission electron microscope deformation tests of single crystal Sn samples. We found that when the sample size was reduced from 450 nm down to 130 nm, diffusional deformation replaces displacive plasticity as the dominant deformation mechanism at room temperature. At the same time, the strength-size relationship changed from “smaller is stronger” to “smaller is much weaker”. The effective surface diffusivity calculated based on our experimental data matches well with that reported in literature for boundary diffusion. The observed change in the deformation mode arises from the sample size-dependent competition between the Hall-Petch-like strengthening of displacive processes and Coble diffusion softening processes. Our findings have important implications for the stability and reliability of nanoscale devices such as metallic nanogaps.National Science Foundation (U.S.) (CMMI-0728069)National Science Foundation (U.S.) (DMR-1008104)National Science Foundation (U.S.) (DMR-1120901)United States. Air Force Office of Scientific Research (FA9550-08-1-0325
Challenges and Opportunities of Health Care Supply Chain Management in the United States
An Analysis of N Nutrition on Yield and Yield Components for the Improvement of Rice Fertilization in Korea
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Liquid helium boil-off measurements of heat leakage from sinter-forged BSCCO current leads under DC and AC conditions
Liquid helium boil-off experiments are conducted to determine the heat leakage rate of a pair of BSCCO 2223 high-temperature superconductor current leads made by sinter forging. The experiments are carried out in both DC and AC conditions and with and without an intermediate heat intercept. Current ranges are from 0-500 A for DC tests and 0-1,000 A{sub rms} for AC tests. The leads are self-cooled. Results show that magnetic hysteresis (AC) losses for both the BSCCO leads and the low-temperature superconductor current jumper are small for the current range. It is shown that significant reduction in heat leakage rate (liquid helium boil-off rate) is realized by using the BSCCO superconductor leads. At 100 A, the heat leakage rate of the BSCCO/copper binary lead is approximately 29% of that of the conventional copper lead. Further reduction in liquid helium boil-off rate can be achieved by using an intermediate heat intercept. For example, at 500 K, the heat leakage rate of the BSCCO/copper binary lead is only 7% of that of the conventional copper lead when an intermediate heat intercept is used
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SAS1A: Computer code for the analysis of fast-reactor power and flow transients
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