Plastic deformation mechanisms of NiTiFe shape memory alloy subjected to equal channel angular extrusion

Abstract

Abstract Based on equal channel angular extrusion (ECAE), NiTiFe shape memory alloy (SMA) was subjected to severe plastic deformation in order to obtain the refined microstructures. Finite element method (FEM), electron backscattered diffraction (EBSD) analysis and transmission electron microscopy (TEM) were used to investigate plastic deformation mechanisms of NiTiFe SMA subjected to ECAE. According to finite element simulation, equivalent stress and equivalent strain fields were obtained during ECAE of NiTiFe SMA, where larger shear stress at channel corner contributes to the refinement of the microstructures. Based on EBSD experiment and TEM observation, the grain refinement and even nanocrystlline grains were found in the NiTiFe SMA subjected to ECAE, and the mechanisms of grain refinement was revealed. It can be concluded that dislocation slip plays a significant role in plastic deformation of NiTiFe SMA subjected to ECAE. The sizes of the refined grains are related to the density of dislocations, so the refined grains possess various sizes due to the inhomogeneity of plastic deformation. The nanocrystalline grains are induced in the region with extremely high dislocation density.