Effect of nanograin size on nanoformed NiTi alloys

The nanoforming process of single-crystal (SC) and nanocrystalline (NC) NiTi alloys is studied and compared using molecular dynamics simulations based on the many-body tight-binding potential. The effect of the grain size (GS) is evaluated in terms of atomic trajectories, slip vectors, potential energy, loading force, and elastic recovery. The simulation results show that for the SC NiTi alloy, the deformation proceeds through a series of nucleations and emissions of dislocations along the {1 1 0} close-packed plane, extending to the interior. The SC NiTi alloy has better filling ability than that of the NC NiTi alloys due to its lack of grain boundaries (GBs). The filling ability of the NC workpieces slightly increases with decreasing GS. For the NC NiTi alloys, dislocations nucleate and are emitted along the {1 1 0} close-packed plane in grains from the GBs. Emitted dislocations easily terminate at GBs. There is no clear relationship between elastic recovery and GS.