Dislocation Multijunction-Driven Plasticity in HfNbTiZr High-Entropy Alloys

Refractory high-entropy-alloys (HEAs) have emerged as promising structural materials for extreme environments, yet their practical application of body-centered-cubic (BCC)-HEAs is significantly hindered by the persistent deficiency in room-temperature ductility. Among various BCC-HEAs, the HfNbTiZr and its derivatives exhibit exceptional room-temperature tensile plasticity, though the mechanisms governing this behavior remain poorly understood. Through integrated experimental characterization and atomistic simulations, we reveal that the pronounced atomic size mismatch in HfNbTiZr generates substantial lattice distortions, which promote the formation of grid-like dislocation multijunctions. These unique features serve as effective nucleation sites for successive dislocation generation and enable massive dislocation multiplication─a remarkable phenomenon considering the inherent mobility limitations of both edge and screw dislocations in BCC-HEAs. Notably, the migration of these dislocation multijunctions generates abundant dislocation debris that functions as self-generated dynamic sources for mobile dislocations. This autocatalytic dislocation multiplication mechanism fundamentally underpins the intrinsic plasticity of HfNbTiZr across wide temperature ranges.