Nanoscale origins of the damage tolerance of the high-entropy alloy CrMnFeCoNi

TLDR

Damage tolerance, requiring both high strength and ductility, is often elusive, but high‑entropy alloys such as CrMnFeCoNi show promise. The study aims to uncover the atomistic to micro‑scale mechanisms responsible for the CrMnFeCoNi alloy’s exceptional damage tolerance. In situ straining in an aberration‑corrected TEM reveals a synergy of multiple deformation mechanisms—easy Shockley partial motion, stacking‑fault parallelepiped formation, and arrest at planar slip bands—that together produce high strength, work hardening, and ductility. The alloy attains ∼1 GPa tensile strength, 60–70 % ductility, and fracture toughness over 200 MPa√m, with crack propagation further impeded by twinned nanoscale bridges that shield the crack tip.

Abstract

Abstract Damage tolerance can be an elusive characteristic of structural materials requiring both high strength and ductility, properties that are often mutually exclusive. High-entropy alloys are of interest in this regard. Specifically, the single-phase CrMnFeCoNi alloy displays tensile strength levels of ∼1 GPa, excellent ductility (∼60–70%) and exceptional fracture toughness ( K JIc >200 MPa√m). Here through the use of in situ straining in an aberration-corrected transmission electron microscope, we report on the salient atomistic to micro-scale mechanisms underlying the origin of these properties. We identify a synergy of multiple deformation mechanisms, rarely achieved in metallic alloys, which generates high strength, work hardening and ductility, including the easy motion of Shockley partials, their interactions to form stacking-fault parallelepipeds, and arrest at planar slip bands of undissociated dislocations. We further show that crack propagation is impeded by twinned, nanoscale bridges that form between the near-tip crack faces and delay fracture by shielding the crack tip.