Difference in recrystallization between electropulsing-treated and furnace-treated NiTi alloy

The cold-rolled NiTi alloy was treated by electropulsing and muffle furnace at the same temperature for minutes, respectively. In order to find the difference between two methods for the recrystallization of the NiTi alloy, the hardness, electrical resistivity and microstructure of the NiTi alloy were investigated. The hardness and microstructure evolution of NiTi alloy indicates that electropulsing can reduce the recrystallization temperature of NiTi alloy by 200 degrees C owing to the enhancement of atom diffusion. Compared with the traditional heat treatment, electropulsing can easily refines grain of the NiTi alloy with an average size of about 41 nm, due to increases of the nucleation rate and limited grain growth. In addition, electropulsing can decrease resistivity of NiTi alloy to the minimum value at the low frequency of electropulsing for 2.5 min. For NiTi alloy treated by furnace annealing at 300 and 350 degrees C, the phase transition from martensite to austenite induces the hardness increase with increasing temperature and prolonging time. (C) 2015 Elsevier B.V. All rights reserved.