Re alloying-driven stacking fault energy decrease enabled strength-ductility synergy in NiCoCrFe high-entropy alloys

Metallic materials have long been enslaved in the dilemma of strength-ductility trade-off, which limits their potential applications. Here, we report on a new class of non-equiatomic Re-added Ni-Co-Cr-Fe face-centered cubic (FCC) high-entropy alloys (HEAs) with superior yield strength to those of Mo-added and other FCC HEAs without compromising ductility. The strengthening mechanisms of these HEAs were discussed in detail by experimental observation of the recrystallized microstructure, dislocation configuration and deformation substructure combined with theoretical evaluation of yield stress and stacking fault energy (SFE). It has been clarified that the unique work-hardening capacity and deformability of these HEAs is attributed to solid solution strengthening and the grain boundary strengthening caused by refined crystalline on the one hand. And what's more important, the appropriate addition of Re greatly reduces SFE so as to modulate the dislocation slip and dissociation behavior and promote phase transformation. It has been confirmed that the plastic deformation process was controlled by abundant microbands, multiple nanoscale deformation twins and phase transformation in the Re-added HEAs.