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

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 115; no. 36; pp. 8919 - 8924
• Main Authors: Ding, Jun, Yu, Qin, Asta, Mark, Ritchie, Robert O.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 04.09.2018; National Academy of Sciences, Washington, DC (United States)
• Subjects: Alloys; Ductility; Entropy; Entropy of solution; First principles; High entropy alloys; local chemical order; MATERIALS SCIENCE; Mechanical properties; Medium entropy alloys; Organic chemistry; Other Topics; Physical Sciences; Science & Technology; Short range order; Stacking; Stacking fault energy; transformation-induced plasticity; transformation-induced plasticity; local chemical order; medium-entropy alloys; stacking fault energy
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.1808660115

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 (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.