Effects of Several Factors on the Ductility of the Ti-Ni Alloy

研究了镍浓度、试验温度、M_S温度和热处理等因素对钛镍合金塑性的影响。为了测量延伸率(断裂应变)，进行了拉伸试验。它主要用来衡量延性。为了了解上述因素对塑性的影响，测量了所有情况下诱发滑移变形和马氏体的临界应力。在MS温度、室温和473K下，分别测量了1273K固溶处理的试件的延伸率与Ni含量在50~52at%之间的关系。延伸率随Ni含量的增加而降低，50at%Ni的延伸率最高可达70%左右，52at%Ni的延伸率最低可达10%左右。在不同的镍浓度下，M的延伸率都是最大的，而473K的延伸率最小。由于在473K变形过程中没有发生马氏体相变，还发现马氏体相比母相更具延展性。在77~473K的不同温度下获得的延伸率表明，固溶处理的样品在M_S附近的延伸率最大，例如，在M_S附近的延伸率为70%，在77K和473K时的延伸率分别为50%和24%。然而，经时效处理的富镍试件的延伸率没有表现出任何的试验温度依赖性，在任何试验温度下延伸率都在20%左右。以上结果将主要根据滑移变形的临界应力来证明是合理的。

The effects of the following several factors on the ductility of the Ti-Ni alloy have been investigated : Ni-concentration, test temperature, M_S temperature and heat-treatment. Tensile tests have been carried out for measuring the elongation(fracture strain), . which was mainly used as the measure of the ductility. The critical stresses for inducing slip deformation and martensites were measured for all cases in order to understand the effects of the above factors on the ductility.The elongation was measured in specimens solution-treated at 1273K as a function of Ni-concentration ranging from 50 to 52at% at the MS temperature, room temperature and 473K, respectively. The elongation decreased with increasing Ni-concentration ; the maximum elongation being about 70% for 50at%Ni, while the minimum being about 10% for 52at%Ni. The elongation obtained at M., was always the largest for any Ni-concentration, while the elongation at 473K was the smallest. Since the martensitic transformation does not occur at 473K during deformation, it was also found that the martensite phase is more ductile than the parent phase. The elongation obtained at various test temperatures ranging from 77 to 473K showed that the elongation at around M_S was the maximum for the solution-treated specimen ; for example, 70% around M_S, 50% at 77K and 24% at 473K, respectively, for the Ti-51at%Ni. However, the elongation of the age treated Ni-rich specimen did not show any test temperature dependence, the elongation being about 20% at any test temperature.The above results will be shown to be rationalized mainly in terms of the critical stress for slip deformation.