Abstract:Mechanical behavior of nickel-titanium shape memory alloy (NiTi SMA) under hot deformation was investigated according to the true stress—strain curves of NiTi samples under compression at the strain rates of 0.001-1 s^-1 and at the temperatures of 600-1000 °C. Dynamic recovery and dynamic recrystallization of NiTi SMA were systematically investigated by microstructural evolution. The influence of the strain rates, the deformation temperatures and the deformation degree on the dynamic recovery and dynamic recrystallization of NiTi SMA was obtained as well. NiTi SMA was characterized by the combination of dynamic recovery and dynamic recrystallization at 600 °C and 700 °C, but the complete dynamic recrystallization occurred at other deformation temperatures. Increasing the deformation temperatures or decreasing the stain rates leads to larger equiaxed grains. The deformation degree has an important influence on the dynamic recrystallization of NiTi SMA. There exists the critical deformation degree during the dynamic recrystallization of NiTi SMA, beyond which the larger deformation degree contributes to obtaining the finer equiaxed grains.

Key words: NiTi alloy; shape memory alloy; dynamic recovery; dynamic recrystallization; hot deformation