Simulation of dynamic recrystallization of NiTi shape memory alloy during hot compression deformation based on cellular automaton

摘要

Dynamic recrystallization (DRX) occurs in NiTi alloy during compression deformation at the strain rates of 0.001-1 s~(-1) and at the temperatures of 800-1000 °C. Cellular automaton (CA) model is used for understanding physical mechanism of DRX of NiTi alloy so that the microstructural evolution, the dislocation density, the flow stress and the grain size are simulated and predicted. The recrystallized grains firstly nucleate at the grain boundaries of the grains in the initial microstructure, where the dislocation density reaches the critical value. DRX is characterized by repeated nucleation and finite growth of the recrystallized grains. The dislocation density decreases with the increase in the deformation temperature, but increases with the increase in the strain rate. The fluctuation of the simulated stress-strain curve is almost the same as the fluctuation of the dislocation density, which is responsible for the competition between hardening and softening. The recrystallized grain size increases with the increase in the deformation temperature, but decreases with the increase in the strain rate. In the case of a given temperature and a given strain rate, the grain size in the initial microstructures has almost no influence on the grain size in the resultant DRX microstructures.