Effect of aging on martensitic transformation and superelasticity of TiNiCr shape memory alloy

The effect of aging on microstructure, martensitic transformation and superelasticity of a Ti48.4Ni51.1Cr0.5 alloy was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) analysis and tensile tests. When the alloy was aged at 400 °C for 30 min, Ti3Ni4 precipitate appears. When aged at a temperature between 400 °C and 500 °C, the samples show a two-stage martensitic transformation. The aged Ti48.4Ni51.1Cr0.5 alloy exhibits a well-defined superelasticity at room temperature. The recovery ratio increases with increasing aging temperature from 300 to 450 °C. Further increase of aging temperature leads to the decrease of recovery ratio. The stress hysteresis shows the opposite dependence on aging temperature. The relationship between aging treatment and martensitic transformation and superelasticity can be rationalized by the evolution of Ti3Ni4 precipitate.