Damage-tolerance in high-entropy alloys

Damage-tolerance can be an elusive characteristic in structural alloys requiring strength and ductility, properties that are often mutually exclusive. High-entropy alloys are of interest here; CrMnFeCoNi and CrCoNi solid-solutions display strengths of ~1 GPa, ductilities of ~60-90%, and exceptional fracture toughness (K_JIc > 200 MPa√m). Using in situ straining in an aberration-corrected transmission electron microscope (TEM), we report on the salient atomistic to microscale mechanisms underlying the origin of these properties. In CrMnFeCoNi, we identify a synergy of deformation mechanisms, with the easy motion of Shockley partials, their interactions to form stacking-fault parallelepipeds, and arrest at planar-slip bands of un-dissociated dislocations. In CrCoNi, a 3-D twin network is developed at ambient temperatures to arrest dislocations that impinge on boundaries, yet also to provide pathways for the easy dislocation motion along these boundaries. Both deformation sequences act to concomitantly generate high strength and ductility through work hardening, which provides for the exceptional damage-tolerance of these alloys.