Microstructure evolution and deformation mechanism of NiTiFe shape memory alloy based on plane strain compression and subsequent annealing

Microstructure evolution and deformation mechanism of NiTiFe shape memory alloy (SMA) are investigated during plane strain compression and subsequent annealing at 400 °C. In the case of various deformation degrees, an inhomogeneous plastic deformation occurs in the NiTiFe SMA undergoing plane strain compression. With increasing deformation extent, a mixture of nanocrystalline and amorphous phases can be generated. Annealing significantly influences the microstructures of NiTiFe SMA subjected to plane strain compression. Consequently, in the annealed NiTiFe SMA, the distributions of grain size, high angle grain boundary, subgrain boundary and geometrically necessary dislocation (GND) density are captured using electron backscatter diffraction (EBSD). The maximum Schmid factor of all the slip systems of each grain in NiTiFe SMA is obtained on the basis of <111>/{110}, <100>/{110} and <100>/{010} slip systems. It can be concluded that prior to mechanically-induced martensite phase transformation, dislocation slip is responsible for plane strain compression of NiTiFe SMA, where <111>/{110} slip system plays a dominant role.