Strong and ductile CrCoNi medium-entropy alloy via dispersed heterostructure

Here we advocate the strategic design of dispersed heterostructure to retain ductility and toughness in high-strength metals, using the equiatomic CrCoNi alloy as an example. Dispersed heterostructure, with nanograins and/or ultrafine grains (the hard zone) dispersed around micrometer-sized grain (the soft zone), is fabricated by cold-rolling followed by sequential flash-annealing at increasing temperatures. It displays a decent uniform elongation of similar to 20 % and an exceptional strain energy density limit up to similar to 240 mJ/mm(3) at the strength level of similar to 1.2 GPa, which is unattainable by its homogeneous as well as clustered heterogeneous counterparts. Grain size-dependent heterogeneous deformation evokes inter-zone interactions, which induce strain partitioning, activate additional mechanical twinning and promote developments of dislocation gradient and long-range internal stress near zone boundary sequentially, imparting a multistage work hardening with extraordinary strain hardening rate up-turn followed by slow attenuation. Dispersed heterostructure provides a higher density of zone boundary, ensuring more extensive inter-zone interaction and thus maximizing the extraordinary strain hardening to improve ductility. (c) 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

In this article, the strategic design of dispersed heterostructure is advocated to maintain ductility and toughness in high-strength metals, using the example of the equiatomic CrCoNi alloy. The dispersed heterostructure, composed of nanograins and/or ultrafine grains (the hard zone) dispersed around micrometer-sized grains (the soft zone), is fabricated through cold-rolling and sequential flash annealing at increasing temperatures. The dispersed heterostructure exhibits a decent uniform elongation of about 20% and an exceptional strain energy density limit of up to 240 mJ/mm(3) at a strength level of about 1.2 GPa, surpassing its homogeneous and clustered heterogeneous counterparts. Grain size-dependent heterogeneous deformation induces inter-zone interactions, leading to strain partitioning, additional mechanical twinning, and the development of dislocation gradient and long-range internal stress near the zone boundaries, resulting in a multistage work hardening with extraordinary strain hardening rate up-turn followed by slow attenuation. The dispersed heterostructure provides a higher density of zone boundaries, ensuring more extensive inter-zone interaction and maximizing the extraordinary strain hardening to improve ductility.