Research on energy dissipation and dynamic recrystallization microstructure evolution behavior of NiTi alloy during hot deformation

High-temperature compression tests, electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) observations are performed to investigate the effect of energy dissipation changes on the dynamic recrystallization microstructure of NiTi alloy during hot deformation. The Strain-Compensated Arrhenius-Type (SCAT) model and hot processing map of NiTi alloy are developed to predict the optimal processing window. The energy analysis of the dynamic recrystallization process is realized by combining the change of power dissipation rate (i) and the evolution of dynamic recrystallization. The results show that the dynamic recrystallization fraction of the alloy increased with the increase of energy dissipation. Rheological instability is mainly observed in the low i region, and the lowest dynamic recrystallization fraction is 23.49%. However, the i values fluctuate abnormally in the medium i region and the high i region. At 1000 degrees C, 1 x 10-2 s- 1, the highest dynamic recrystallization fraction is 38.59%. At 950 degrees C, 1 s-1, the dynamic recrystallization fraction decreased to 28.87%. The analysis shows that the dynamic recrystallization fraction is 33.68% and the microstructure is uniform at 850 degrees C, 1 x 10-2 s- 1, which is the optimal processing parameter. In addition, the critical strain kinetic model is developed, and the critical strain is 0.298 at 850 degrees C, 1 x 10-2 s- 1. The microstructure evolution of dynamic recrystallization under different strains (0.3-0.9) shows that discontinuous dynamic recrystallization and continuous dynamic recrystallization participate in the softening of NiTi alloy with the increase of strain. Different i areas have different energy for microstructure evolution. In the low i area, the main softening mechanism is discontinuous dynamic recrystallization. With the increase of i, the energy for microstructure evolution increases, and continuous dynamic recrystallization occurs. In the high i area, the main softening mechanism is continuous dynamic recrystallization.