Nanoscale Origins of the Damage Tolerance of the High-Entropy Alloy CrMnFeCoNi

TL;DR

This study uncovers the atomistic mechanisms behind the exceptional damage tolerance of the high-entropy alloy CrMnFeCoNi, revealing a synergy of deformation processes and nano-scale crack shielding that contribute to its strength and ductility.

Contribution

It provides detailed atomistic insights into the deformation and crack-impeding mechanisms in CrMnFeCoNi, a high-entropy alloy with remarkable mechanical properties.

Findings

Multiple deformation mechanisms coexist, including Shockley partials and stacking faults.

Nano-scale bridges form at crack tips, delaying fracture.

Crack propagation is impeded by twinned structures, enhancing toughness.

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 (KJIc > 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, nano-scale bridges that form between the near-tip crack faces and delay fracture by shielding the crack tip.