Influence of aging on phase transformation and microstructure of Ni50.3Ti29.7Hf20 high temperature shape memory alloy

We report the effect of aging on phase transformation temperature and mechanical strength of Ni50.3Ti29.7Hf20 high temperature shape memory alloy. Aging of the alloy at 550 °C and 650 °C increases the martensite phase transformation temperature. Transmission Electron Microscopy and quantitative investigation of microstructure by small-angle scattering confirm the improved hardness of the alloy on aging. Aging at 550 °C results in significant volume fraction of fine Ni-rich precipitates. Further, aging at 650 °C gives rise to coarsening of the precipitates vis-à-vis reduction in hardness.