Temperature–stress phase diagram of strain glass Ti48.5Ni51.5

The temperature and stress dependence of the properties of a recently discovered strain glass Ti48.5Ni51.5, which is a glass of frozen local lattice strains, was investigated systematically. It was found that the ideal freezing temperature (T0) of the strain glass decreases with increasing stress. When the stress exceeds a critical value σc(T), the pseudo-B2 strain glass transforms into B19′ martensite. However, the stress–strain behavior associated with such a stress-induced transition showed a crossover at a crossover temperature TCR, which is ∼20 K below T0. Above TCR, the sample showed superelastic behavior; however, below TCR, the sample demonstrated plastic behavior. More interestingly, the σc vs. temperature relation for unfrozen strain glass obeys the Clausius–Clapyeron relationship, whereas that for frozen strain glass disobeys this universal thermodynamic law. A phenomenological explanation is provided for all the phenomena observed, and it is shown that all the anomalous effects come from the broken ergodicity of the glass system and a temperature-dependent relative stability of the martensitic phase. Based on experimental observations, a temperature–stress phase diagram is constructed for this strain glass, which may serve as a guide map for understanding and predicting the properties of strain glass.