Phase transformation mechanisms of NiTi shape memory alloy during electromagnetic pulse welding of Al/NiTi dissimilar joints

The phase transformation mechanisms of NiTi shape memory alloy (SMA) during electromagnetic pulse welding (EMPW) of Al/NiTi dissimilar alloy joints were studied. Two types of amorphization behaviors were observed in the NiTi SMA of the Al/NiTi dissimilar joint. These are: i) fast cooling-induced amorphization of the joint interfacial reaction layer; and ii) severe deformation-induced amorphization. Additionally, the martensitic transformation was observed in the NiTi SMA during the high strain rate plastic deformation imposed by the EMPW process. The study shows that the formation of B19' martensite during high strain rate plastic deformation of NiTi SMA is influenced by both the strain rate and the peak pressure of the deformation during welding.