Effect of hydrostatic pressure on thermally induced phase transformation in NiTi alloy: A molecular dynamics study

Abstract

Molecular dynamics simulations are performed to study the influence of hydrostatic pressure P on the thermally induced phase transformations in NiTi alloy during thermal cycling between 500 K and 5 K. It is found that the martensitic transformation path shows strong dependence on the P: During cooling process, the NiTi alloy undergoes single transformation of B2 → B19′ at 0 ≤ P ≤ 3 GPa, two-step transformation of B2 → B2 + R → B19′ at 3 < P ≤ 5 GPa, and B2 → R at 5 < P ≤ 8 GPa. The martensite start temperature (Ms) decreases from 293 to 236 K with increasing P from 0 to 5 GPa, and the start temperature of R phase (Rs) decreases from 333 to 233 K with increasing P from 6 to 8 GPa. The shift of Ms or Rs can be explained by the Clausius-Clapeyron equation. Our work provides novel insights into the martensitic phase transformations in NiTi alloy.