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

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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.