Hot Deformation Behavior and Microstructure Evolution of New-Type Ni-Cr-Co Based Alloy

Hot deformation behavior of a new-type Ni-Cr-Co based alloy was investigated by thermal compression tests under the deformation temperature range of 1050 similar to 1250 degrees C and strain rate range of 0.001 similar to 1 s(-1). The electron backscatter diffraction (EBSD) technique was employed to investigate the effects of deformation temperature and strain rate on the microstructure evolution of the alloy and nucleation mechanisms of dynamic recrystallization. The result shows that the flow stress decreases with the increasing of the deformation temperature and the decreasing of strain rate. The Arrhenius constitutive equation and hot processing map of the alloy were established based on the hot deformation data, and the hot deformation activation energy was calculated as 520.03 kJ/mol. The optimum hot processing interval is at the temperature scope of 1175 similar to 1250 degrees C and the strain rate range of 0.006 similar to 1 s(-1) with the peak power dissipation efficiency of 45%. The fraction of dynamic recrystallization increases with the increasing of deformation temperature and the decreasing of strain rate. And during dynamic recrystallization, a large number of deformed grains are replaced by fine equiaxial grains and a high frequency of Sigma 3 twin boundaries generates. The dominant dynamic recrystallization nucleation mechanism is grain boundary bulging, which is a typical feature of discontinuous dynamic recrystallization. In the low temperature and high strain rate region, continuous dynamic recrystallization characterized by the rotation of subgrains is detected. However, continuous dynamic recrystallization is just an assistant nucleation mechanism for the alloy.