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

Abstract The temperature and stress dependence of the properties of a recently discovered strain glass Ti 48.5 Ni 51.5 , which is a glass of frozen local lattice strains, was investigated systematically. It was found that the ideal freezing temperature ( T 0 ) of the strain glass decreases with increasing stress. When the stress exceeds a critical value σ c ( 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 T CR , which is ∼20 K below T 0 . Above T CR , the sample showed superelastic behavior; however, below T CR , the sample demonstrated plastic behavior. More interestingly, the σ c 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.