The effect of Ni content on phase transformation behavior of NiTi alloys: An atomistic modeling study

In this study, the thermodynamic behavior of single- and poly-crystalline NiTi shape memory alloys (SMAs) with different Ni contents was investigated by molecular dynamics (MD) simulations. By employing the 2NN-MEAM potential, the influence of Ni content on phase transformation temperature is analyzed for single- and poly-crystalline NiTi. Our simulation results show that the characteristic phase transformation temperature increases and then decreases as the binary NiTi alloy changes from Ti-rich to Ni-rich state. In addition, the change of Ni content also dramatically affects the formation of martensite variants and twins, whereas it shows slight effect on the formed types of variants. According to the characteristic phase transformation temperature obtained by thermally induced phase transformation, temperatures of 500 K, 600 K, 700 K and 300 K, 400 K, 500 K, three for each type of alloys, are selected to discuss the superelastic effect of single- and poly-crystalline NiTi. By conducting uniaxial loading and unloading under different constant temperature conditions, corresponding stress–strain responses are obtained. The microstructure and grain orientation of each model are studied. The herringbone structure exists in nanocrystals with different Ni contents, but is not identified in single crystals, whether under thermally induced or stress-induced phase transformation conditions.