Constitutive equation and processing map of equiatomic NiTi shape memory alloy under hot plastic deformation
(1. School of Mechanical and Electrical Engineering, Harbin Engineering University, Harbin 150001, China;
2. Hubei Water Resources Research Institute, Wuhan 430070, China)
2. Hubei Water Resources Research Institute, Wuhan 430070, China)
Abstract: In order to describe the deformation behavior and the hot workability of equiatomic NiTi shape memory alloy (SMA) during hot deformation, Arrhenius-type constitutive equation and hot processing map of the alloy were developed by hot compression tests at temperatures ranging from 500 to 1100 °C and strain rates ranging from 0.0005 to 0.5 s-1. The results show that the instability region of the hot processing map increases with the increase of deformation extent. The instability occurs in the low and high temperature regions. The instability region presents the adiabatic shear bands at low temperatures, but it exhibits the abnormal growth of the grains at high temperatures. Consequently, it is necessary to avoid processing the equiatomic NiTi SMA in these regions. It is preferable to process the NiTi SMA at the temperatures ranging from 750 to 900 °C.
Key words: NiTi alloy; shape memory alloy; hot plastic deformation; constitutive equation; hot processing map