Grain size effect on the martensitic transformation temperatures of nanocrystalline NiTi alloy

Abstract

© 2015 IOP Publishing Ltd. The grain size effect on B19′ martensitic transformation temperatures of a nanocrystalline Ti-50.2 at%Ni alloy was investigated by differential scanning calorimetry (DSC) analysis and (TEM) observation. It was found that the R → B19′ transformation temperature decreases with decreasing grain size in the range of 50-150 nm, whilst the reverse B19′ → R transformation temperature remains independent of grain size, leading to an increase of the hysteresis with decreasing grain size. The observed effects of grain size on the characteristics of the R 虠 B19′ transformation are attributed to variations of both the elastic and the irreversible energies of the martensitic transformation in the nanograin regime.