Tunable stacking fault energies by tailoring local chemical order in CrCoNi medium-entropy alloys

TLDR

High‑entropy alloys are a new class of metallic materials with unique mechanical behavior, but compositional disorder hampers detailed understanding of their structure–property relationships. The study uses first‑principles calculations to investigate how local chemical order relates to intrinsic and extrinsic stacking fault energies in CrCoNi medium‑entropy alloys. First‑principles calculations were performed to model local chemical order and its effect on stacking fault energies in CrCoNi alloys. The calculations show that local chemical order strongly tunes intrinsic and extrinsic stacking fault energies, correlates with fcc–hcp energy differences, and indicates that short‑range order is thermodynamically favored, thereby providing a pathway to design HEAs with targeted mechanical behavior.

Abstract

High-entropy alloys (HEAs) are an intriguing new class of metallic materials due to their unique mechanical behavior. Achieving a detailed understanding of structure-property relationships in these materials has been challenged by the compositional disorder that underlies their unique mechanical behavior. Accordingly, in this work, we employ first-principles calculations to investigate the nature of local chemical order and establish its relationship to the intrinsic and extrinsic stacking fault energy (SFE) in CrCoNi medium-entropy solid-solution alloys, whose combination of strength, ductility and toughness properties approach the best on record. We find that the average intrinsic and extrinsic SFE are both highly tunable, with values ranging from -43 mJ.m-2 to 30 mJ.m-2 and from -28 mJ.m-2 to 66 mJ.m-2, respectively, as the degree of local chemical order increases. The state of local ordering also strongly correlates with the energy difference between the face-centered cubic (fcc) and hexagonal-close packed (hcp) phases, which affects the occurrence of transformation-induced plasticity. This theoretical study demonstrates that chemical short-range order is thermodynamically favored in HEAs and can be tuned to affect the mechanical behavior of these alloys. It thus addresses the pressing need to establish robust processing-structure-property relationships to guide the science-based design of new HEAs with targeted mechanical behavior.