Hot deformation behavior and microstructure evolution of a novel Mn-containing HEA

Abstract

The deformation behavior and microstructure evolution of a novel Mn-containing HEA were explored during the deformation temperature ranges of 800∼1100 °C, and strain rate ranges of 0.001∼1s−1. The study results indicate that the true stress-strain curves after work hardening exhibit continuous softening type at low strain rate ranges of 0.001–0.01 s−1, while softening then steady-state type at high strain rate ranges of 0.1∼1s−1, respectively. The activation energy (Q) and stress exponent (n) are calculated to as 404.6 kJ/mol and 4.9016, respectively. As the strain increases, the flow instability is prone to expand towards the regions of lower strain rate and higher deformation temperature, and the optical processing window is determined at 1050–1100 °C and 0.001–0.002 s−1. The strain and stress field distribution of the FEM simulations reveal the inhomogeneous deformation and the damage field distribution predict the crack region of deformation specimen. The critical (εc)/peak strain (εp) for DRX do not display a proportional relationship with strain rate and an inversely proportional relationship with deformation temperature, and the relationship between εc and εp can be expressed as: εc = (0.3–0.5) εp. Only the discontinuous dynamic recrystallization (DDRX) mechanism is activated in the whole range of deformation conditions, but it is not fully carried out. Because of the inhomogeneous stress distribution, the dynamic recrystallized grains show bimodal grain size. Furthermore, the recrystallized grains do not grow significantly due to the synergistic contribution of sluggish diffusion effect, high solution hardening effect and the trimodal B2 precipitate phase distribution.