Grain size effect on the temperature-dependence of elastic modulus of nanocrystalline NiTi

Abstract

The effect of grain size on temperature-dependent elastic modulus (TDEM) of polycrystalline NiTi over a temperature span of 200 °C was investigated by dynamic thermomechanical analysis (DMA). It is found that the TDEM rapidly reduced with grain size down to nanoscale. In-situ neutron diffraction and molecular dynamics (MD) simulation reveal that the volume fraction and thermal stability of austenite phase at low temperature gradually increased with the reduction of grain size due to the mechanical constraint of grain boundary, which results in the two-phase coexistence during cooling. The compensation of the intrinsic opposite TDEM of austenite and martensite leads to the overall reduced TDEM in nanocrystalline NiTi. This study strongly implies that the TDEM of shape memory alloy can be tailored by grain size.