Effect of annealing temperature on martensitic transformation of Ti49.2Ni50.8 alloy processed by equal channel angular pressing

The effect of annealing temperature on the martensitic transformation of a Ti49.2Ni50.8 alloy processed by equal channel angular pressing (ECAP) was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The as-ECAP processed and subsequently annealed Ti49.2Ni50.8 alloys consist of B2 parent phase, Ti4Ni2O phase and B19′ martensite at room temperature. Upon cooling, all samples show B2→R→B19′ two-stage transformation. Upon heating, when the annealing temperature is less than 400 °C, the samples show B19′→R→B2 two-stage transformation; when the annealing temperature is higher than 500 °C, the samples show B19′→B2 single-stage transformation. The B2–R transformation is characterized by wide interval due to the dislocations introduced during ECAP.