Data-driven electron-diffraction approach reveals local short-range ordering in CrCoNi with ordering effects

Non-random chemical mixings that are intrinsic to medium- and high-entropy alloys are difficult to detect and quantify. Here the authors perform a diffraction data-mining analysis, revealing nanoclusters of short-range orders in a CrCoNi alloy, and their impacts on chemical homogeneity and dislocations slip. The exceptional mechanical strength of medium/high-entropy alloys has been attributed to hardening in random solid solutions. Here, we evidence non-random chemical mixing in a CrCoNi alloy, resulting from short-range ordering. A data-mining approach of electron nanodiffraction enabled the study, which is assisted by neutron scattering, atom probe tomography, and diffraction simulation using first-principles theory models. Two samples, one homogenized and one heat-treated, are observed. In both samples, results reveal two types of short-range-order inside nanoclusters that minimize the Cr-Cr nearest neighbors (L1(2)) or segregate Cr on alternating close-packed planes (L1(1)). The L1(1) is predominant in the homogenized sample, while the L1(2) formation is promoted by heat-treatment, with the latter being accompanied by a dramatic change in dislocation-slip behavior. These findings uncover short-range order and the resulted chemical heterogeneities behind the mechanical strength in CrCoNi, providing general opportunities for atomistic-structure study in concentrated alloys for the design of strong and ductile materials.

Automated summary

This study reveals the impacts of short-range ordering on chemical homogeneity and dislocation slip in a CrCoNi alloy using a diffraction data-mining analysis. The results show the existence of two types of short-range ordering in nanoclusters, which significantly affect the mechanical strength of the material. These findings provide important opportunities for atomistic-structure study and design in concentrated alloys.