Hot deformation behavior and dynamic recrystallization of dual-phase (CrCoNi)94Al3Ta3 medium entropy alloy

The microstructural evolution and dynamic recrystallization (DRX) behavior of a dual-phase (CrCoNi)94Al3Ta3 medium entropy alloy (MEA) was studied using thermal simulated test machine at temperature ranging from 1000 degrees C to 1150 degrees C under strain rate of 0.001-1 s-1. The initial dual-phase microstructures were equiaxed grains with face-centered cubic structure (gamma) and L12 phase (gamma') precipitated homogeneously in the grain, besides a certain amount pinned at boundary. The stress-strain curves exhibited a typical DRX softening behavior, in which the flow stress was sensitive to deformation temperature and strain rate. The deformation activation energy was calculated to be 612.04 kJ/mol (gamma + gamma' dual-phase region) and 391.02 kJ/mol (gamma single-phase region) respec-tively. The appropriate hot deformation parameters of (CrCoNi)94Al3Ta3 MEA were 1100 degrees C/0.001 s-1 and 1150 degrees C/0.01 s-1 based on the hot processing map and deformation microstructure. The discontinuous DRX trans-formed to continuous DRX depended on deformation temperature, this was because that the interaction between precipitates and dislocation was weakened as the deformation temperature beyond the dissolution temperature of L12 phase.