抄録
Effects of the heat treatment on the characteristics of various types of stress-induced martensitic transformations and associated pseudoelasticity in single crystals with ⟨001⟩ orientation of Cu-14.1Al-4.2Ni and Cu-14.7Al-4.2Ni (mass%) alloys have been investigated. Three kinds of heat treatments were given, that is, (a) rapid quench from 1273 K, (b) normal quench from 1273 K and (c) aging at 523 K for 3.6 ks after the normal quench. As a result, various parameters characterizing the transformations have been found to vary with the heat treatment. Ms temperatures and critical stresses for inducing γ1′→β1″ and β1′(β1″)→α1′ transformations increase in the order of (a), (b) and (c), whereas critical stresses for inducing β1→γ1′ and β1→β1′ transformations decrease in that order. These variations indicate that a previously observed anomaly on the temperature dependence of critical stresses for inducing the β1′→α1′ transformation above 470 K is due to an aging effect, and further that the interphase boundaries in a phase diagram with the temperature-stress coordinate shift by the heat treatment. Elongations due to various transformations have also been found to vary not only with heat treatment but also with test temperature. This suggests that lattice constants of various martensite phases vary with heat treatment and temperature. The critical stress and the elongation for β1′(β1″)→α1′ transformation have been found to vary in an opposite direction with temperature and heat treatment, suggesting the existence of a critical point for the transformation.
