Atomistic simulation of microstructure evolution of NiTi single crystals in bending deformation

Abstract In order to explore the microstructure evolution of the equiatomic NiTi shape memory alloy during the bending deformation, molecular dynamics simulations based on the 2NN-MEAM potential were respectively carried out in the compressive zone, tensile-compressive zone (identified as “combined zone”) and tensile zone, which were divided according to the force analysis. Positive and negative strain rates or velocities with linear variations were applied in different zones during the bending deformation. The results show that the simulated lath martensites and dislocations during the bending deformation are highly consistent with the results of bending experiment. In the bending simulation, the martensitic transformation occurs in different degrees in the above three zones. The microstructure evolution under compressive stress conditions is different from that of tensile stress conditions, including stress-induced martensitic transformation, dislocation density and distribution, the formation of highly stressed austenites and Frenkel defect pairs. Additionally, during the stress-induced martensitic transformation, the morphology and structure of martensites strongly depend on the deformation methods, strain rate and Ni/Ti atomic ratio. The current simulation work reveals lots of micro information that cannot be observed and captured by experiments on an atomic scale, which is expected to grasp the information of the stress-induced martensitic transformation and the resultant defect structures during the bending deformation.