Strain glass in Fe-doped Ti–Ni Original Research Article

We report the existence of strain glass in Ti50Ni50−xFex, beyond a critical Fe doping level x > xc(5 < xc < 6). The strain glass state is confirmed by the appearance of a frequency-dependent anomaly in the AC mechanical modulus/loss at a freezing temperature T0 and by the breaking of ergodicity shown in a zero-field-cooling/field-cooling experiment. Based on the experimental results, a phase diagram is established in which both the normal martensitic transformations (for x < xc) and the strain glass transition (for x > xc) are indicated. The new phase diagram allows for explanations of two long-standing puzzles in Ti50Ni50−xFex and Ti–Ni alloys: (i) the origin of nano-domains present prior to the martensitic transformation (for x < xc) and (ii) the negative temperature dependence of electrical resistivity in abnormal non-transforming compositions (for x > xc).