Chemical Short-Range Ordering in a CrCoNi Medium-Entropy Alloy

TL;DR

This study uncovers non-random short-range chemical orderings in CrCoNi medium-entropy alloys, revealing how nanocluster structures influence mechanical properties and can be tuned via heat treatments.

Contribution

It introduces a novel data-mining approach to identify short-range order in alloys, combining multiple techniques and first-principles models to understand nanocluster structures.

Findings

Identification of two types of short-range order in nanoclusters.

Short-range order influences deformation mechanisms.

Nanocluster ordering can be tuned by heat treatments.

Abstract

The exceptional mechanical strengths of medium and high-entropy alloys have been attributed to hardening in random solid solutions. Here, we evidence non-random chemical mixings in CrCoNi alloys, resulting from short range ordering. A novel data-mining approach of electron nanodiffraction patterns enabled the study, which is assisted by neutron scattering, atom probe tomography, and diffraction simulation using first principles theory models. Results reveal two critical types of short range orders in nanoclusters that minimize the Cr and Cr nearest neighbors (L11) or segregate Cr on alternating close-packed planes (L12). The makeup of ordering-strengthened nanoclusters can be tuned by heat treatments to affect deformation mechanisms. These findings uncover a mixture of bonding preferences and their control at the nanoscopic scale in CrCoNi and provide general opportunities for an atomistic-structure study in concentrated alloys for the design of strong and ductile materials.