Stress-induced martensitic transformation in (Ni47Ti44)100-xNbx shape memory alloys with wide hysteresis

The effect of deformation via stress-induced martensitic transformation on the reverse transformation behavior of the (Ni47Ti44)100-xNbx(x=3, 9, 15, 20, 30, mole fraction, %) shape memory alloys was investigated in detail by differential scanning calorimetry (DSC) after performing cryogenic tensile tests at a temperature of Ms+30 °C. The results show that Nb-content has obvious effect on the process of stress-induced martensitic transformation. It is also observed that the stress-induced martensite is stabilized relative to the thermally-induced martensite (TIM) formed on cooling, and Nb-content in Ni-Ti-Nb alloy has great influence on the reverse transformation start temperature and transformation temperature hysteresis of stress-induced martensite(SIM). The mechanism of wide transformation temperature hysteresis was fully explained based on the microscopic structure and the distribution of the elastic strain energy of (Ni47Ti44)100-xNbx alloys.