Microstructure evolution and deformation behavior of as-cast NiTi shape memory alloy under compression

Abstract

The as-cast ingot of equiatomic nickel-titanium shape memory alloy (SMA) was prepared via vacuum consumable arc melting. Differential scanning calorimetry (DSC), X-ray diffraction (XRD) analysis, energy dispersive X-ray (EDX) measurement and microanalysis were adopted in order to understand the microstructure evolution and deformation behavior of the as-cast NiTi SMA under compression at various strain rates and temperatures. The microstructures of as-cast NiTi SMA composed of dendritic grains and equiaxed grains are inhomogeneous and show segregation. The as-cast NiTi SMA consists of B19′ martensite, B2 austenite and Ti2Ni phase simultaneously at room temperature. The as-cast NiTi SMA is sensitive to strain rate under compression at high temperature, at which NiTi SMA is characterized by dynamic recrystallization at strain rates of 0.1 and 0.01 s−1, but by dynamic recovery at strain rate of 0.001s−1. The strain rates have little influence on the true stress—strain curves as well as microstructure of NiTi SMA at room temperature and −100°C.