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

Abstract

<p id="d7683379e194">Our work has revealed the nature of local chemical order and has established its significant relationship to the intrinsic and extrinsic stacking fault energy in CrCoNi medium-entropy solid-solution alloys, whose combination of strength, ductility, and toughness properties approaches the best on record. These findings highlight the general need to discern how critical the role of local chemical ordering is in dictating the mechanical of properties of medium- and high-entropy alloys. Our results highlight the possibility of tuning order in disorder to ultimately achieve the science-based design and optimization of new high-entropy alloy systems with specifically desired combinations of macroscale mechanical properties. </p><p class="first" id="d7683379e197">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 approaches the best on record. We find that the average intrinsic and extrinsic SFE are both highly tunable, with values ranging from −43 to 30 mJ⋅m ⁻² and from −28 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 ( <i>fcc</i>) and hexagonal close-packed ( <i>hcp</i>) 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. </p>