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STRAIN RATE SENSITIVTTY OF POLYCRYSTALLINE AND SINGLE CRYSTAL NiAl

HSU Shuen , YANG Sycherng , HON Weipirn , WANG Chienyi LEE Tsangsheau (Chung-Shan Institute of Science and Technology , Lung-Tan , Taiwan , China) HSU Ichung(National Taiwan University , Taipei , Taiwan , China) CHIN Stephen , ANTON Donald L.(United Technologies Research Center , East Hartford. CT , USA)

金属学报(英文版)

The compressive and tensile strain rate sensitivities of polycrystalline and single crystal NiAl have been evaluated at 877 ℃ which is well above DBTT. Samples were prepared to specific sizes by hot press consolidation of appropriate powder sizes and minimizing past consolidation thermal exposures. NiAl single crystals were grown in the [100]orientation using a modified Bridgeman technique. The yield and tensile strength of polycrystalline NiAl as a function of grain size generally follows a Hall-Petch type relationship . A tensile strain rate effect was found at strain rate of 1 to 10-4 sec-1. The strain rate sensitivity coefficient, m,in the equation of σ = Kε is in the range of 0. 10 to 0. 13. The highest strain rate (1 sec-1) resulted in significantly higher strengths and little or no observed ductility. Compressive strain rate testing al strain rate of 10-5to 10-2 sec-1 and at temperature of 1050°to 1250°K was conducted both for polycrystalline and for single crystal NiAl. The calculated stress exponents and the activation energy for creep were compared with the reference data.

关键词: :strain rate sensitivity polycrystalline NiAl , null

Shape-Memory Intermetallics Development in Taiwan

S.K.Wu(Institute of Materials Science and Engineering , National Taiwan University Taipei , Taiwan 106 , China) H.C. Lin(Department of Materials Science , Feng-Chia University. Taichung. Taiwan 407. China)

金属学报(英文版)

In Taiwan, many groups engage in the development of TiNi SMAs. The two-stage martensitic transformations of and have been clarified for both TiNi binary and ternary alloys. The deformation behaviors have been investigated by cold-rolling, hot-rolling and wire drawing. Both shape memory effect and pseudoelasticity can be improved by some thermal-mechanical treatments. The damping characteristics of TiNi and TiNiX SMAs have also been systematically studied. Both B19'/B19 martensite (M)and R-phase(R) have high daming capacities due to the stress-induced movement of twin boundaries. Meanwhile, the addition of third elements-Fe and Cu-can largely increase the damping capacity.Recently, some high temperature shape memory alloys-TiHiPd and TiNi-.Au alloys-have also been intensively studied in Taiwan. All these potential investigations on the TiNi SMAs in Taiwan have attracted much attention and their important characteristics will be applied widely in the near future.

关键词: : TiNi shape memory alloys. research and development in Taiwan

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