Prediction of chemical short-range order in high-/medium-entropy alloys

Abstract

Chemical short-range orders (CSROs), as the built-in sub-nanoscale entities in a high-/medium-entropy alloy (H/MEA), have aroused an ever-increasing interest. With multi-principal elements in an H/MEA to form a complex concentrated solution, a variety of sub-systems of species exist to induce the metastable ordered compounds as candidates for ultimate CSROs. The issues remain pending on the origin of CSROs as to how to judge if CSRO will form in an H/MEA and particularly, what kind of CSROs would be stably produced if there were multiple possibilities. Here, the first-principles method, along with the proposed local formation energy calculation in allusion to the atomic-scale chemical heterogeneities, is used to predict the CSRO formation based on the mechanical stability, thermodynamic formation energy, and electronic characteristics. The simulations are detailed in an equiatomic ternary VCoNi MEA with three kinds of potential compounds, i.e., L11, L12, and B2, in the face-centered cubic matrix. It turns out that L11 is stable but hard to grow up so as to become the final CSRO. L11 is further predicted as CSROs in CrCoNi, but unable to form in FeCoNi and CrMnFeCoNi alloys. These predictions are consistent with the experimental observations. Our findings shed light on understanding the formation of CSROs. This method is applicable to other H/MEAs to design and tailor CSROs by tuning chemical species/contents and thermal processing for high performance.