Chemical composition fluctuations simultaneously enhance the strain-hardening rate and ductility in refractory multi-principal element alloys

Refractory multi-component alloys (MPEAs) are promising high-temperature structural materials, but the limited uniform elongations restrict engineering applications. Here, the mesoscopic-scale chemical composition fluctuations (CCFs) were reported to increase the uniform elongation by 240 % and the fracture elongation by 44 %. CCFs effectively impede the dislocations movement and facilitate cross-slip. As strain rises, deformation-induced destruction of CCFs promotes the diffusion of Nb and Zr elements, releases local stress, and contributes to the multiplication of dislocations to achieve a uniform distribution and frequent cross-slip. Moreover, the local strength increasing from element diffusion also retards dislocation motion, providing additional self-hardening
capacity. The hardening from the destruction of CCFs competes with the softening from cross-slip, thus maintaining a high work-hardening rate at large strains while increasing ductility. This work demonstrates the unique effect of CCFs on the mechanical properties of refractory MPEAs and provides new insights for designing high strength-ductility alloys.