Microstructural Evolution of NiTi47.7Cu6.3 Alloy during Hot Deformation

In the present work, the hot workability and microstructural evolution of NiTi47.7Cu6.3 (at.%) shape memory alloy were investigated by using wedge-rolling test. The wedge specimens were subjected to hot rolling at the temperatures of 700–1000°C. The microstructural evolutions at the strains of 0.05, 0.15, 0.2, 0.25 and 0.3 were then characterized by optical microscopy and scanning electron microscopy (SEM) as well as energy dispersive spectrometry (EDS) technique. Depending on the deformation temperature and strain, the dynamic recrystallization (DRX) could occur, leading to the refining of the microstructure. At low temperatures of 700 and 800°C, there was no sign of DRX at all studied strains. At these temperatures, the formed fine needle-like precipitates pinned the grain boundaries and prevented them from bulging/migration. By contrast, at higher temperatures of 900 and 1000°C, the DRX took place at the critical strains lower than 0.25 and 0.15, respectively. However, at higher temperatures, strain-induced-boundary-migration (SIBM) mechanism resulted in the formation of DRX grains.