Enhanced strength-ductility synergy in NbC-reinforced FeMnCoCr high entropy alloy with heterostructure by adopting a novel process

We explored a novel heterostructure design strategy to simultaneously enhance the strength and ductility of NbC-reinforced FeMnCoCr high-entropy alloys by adopting grain-scale strain localization regulation coupling partial recrystallization annealing, and the effect of cold-rolled microstructure on annealed microstructure evolution and mechanical properties was studied. The transformation-induced plasticity (TRIP) effect and the dislocation density decreased as the grain size increased. The significant grain-scale strain localization and obvious Brass and A textures were observed in the cold-rolled microstructure of the large grain samples. Recrystallization preferentially occurred in the high-strain region during annealing leading to heterogeneous recrystallization nucleation. The recrystallization kinetics of A texture was slow and remained in the partially recrystallized microstructure. A heterostructure with a bimodal grain size distribution was formed in coarse-grained samples. The heterostructure with coarse un-recrystallized grains wrapped by recrystallized grains has good comprehensive mechanical properties. Its yield strength was 1.4 times that of a fine-grained microstructure sample, while maintaining excellent strain hardening capacity without decreasing elongation. The high yield strength was attributed to dislocation strengthening. The TRIP effect appeared earlier in the coarse un-recrystallized grains with low dislocation density under tension, and the back stress strengthening and TRIP effect improved the strain hardening capacity.