The effect of thermomechanical treatment on the evolution of the grain boundary character distribution in a Cr_0.8MnFeNi high-entropy alloy

We have employed thermomechanical processing to optimize the grain boundary character distribution (GBCD) of a grain boundary engineered (GBE) microstructure in a face-centered cubic Cr_0.8MnFeNi high-entropy alloy (HEA). The influence of the annealing time and the degree of tensile deformation on the GBCD were investigated through electron backscatter diffraction (EBSD). The results show that a 5% tensile deformation followed by annealing at 1000 °C for 40 min led to the formation of a high fraction of low Σ (Σ ≤ 29) coincident site lattice (CSL) boundaries (81.9%), a high (Σ9 + Σ27)/Σ3 ratio (0.17), and a high twin-related domain size to grain size ratio (4.49), demonstrating that the optimization of the GBCD had been achieved. Extending the annealing time further led to a slight decrease in the fraction of low-ΣCSL boundaries. The degree of tensile deformation employed before annealing at 1000 °C/40 min also had a significant influence on the GBCD. As the degree of deformation was increased from 3% to 20%, the low-ΣCSL (Σ ≤ 29) boundaries fraction first increased and then decreased. Any strain-induced boundary migration (SIBM) occurred mainly within low deformation (≤10%) specimens, while any extensive recrystallization occurred within high deformation (20%) specimens. Thus, the optimization of the GBCD could be attributed to sufficient SIBM rather than to significant recrystallization in Cr_0.8MnFeNi HEA.