River-like dislocation channel unleashes high tensile ductility in as-cast refractory multi-principal element alloys

Abstract

Dislocations govern the plastic deformability of structural alloys. However, this beneficial role is compromised in refractory multi-principal element alloys (RMPEAs), where tensile ductility degrades owing to plastic strain localization via planar slip and dislocation channeling. We proposed a ductilization concept based on engineered dislocation channels to divert and dredge dislocations, achieving a notable tensile ductility of 21% and a yield strength exceeding the gigapascal mark in the as-cast RMPEA. To test the hypothesis that enhanced lattice distortion and chemical fluctuations act as dislocation diverters, we designed Ti₅₃V₁₅Hf₃₂ (V15) and Ti₄₁V₂₇Hf₃₂ (V27) RMPEAs with distinct volume misfit and Warren-Cowley parameters. In-situ synchrotron high-energy X-ray diffraction and transmission electron microscopy analyses revealed that increasing the volume misfit facilitates a transition in dislocation character from edge-based (V15) to screw-based (V27) under tensile loading. Atom probe tomography and high-angle annular dark-field scanning transmission electron microscopy characterizations further demonstrated that elevated V content engenders pronounced chemical fluctuations, inducing diversion of dislocation slip and the formation of river-like dislocation channels. These dislocation channels, on one hand, promoted dynamic strain hardening through dense intersections of the channel boundaries. On the other hand, they prevented premature necking and failure by enabling dislocations to proliferate and cross-slip within channels. Consequently, the river-like dislocation channels delayed plastic instability at ultrahigh yield strength, thereby enabling the RMPEA to unleash exceptional tensile ductility. These findings provide a dislocation-harnessing pathway for pursuing strength-ductility synergy in RMPEAs.