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

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 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 and from -28 to 66 mJ⋅m, 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 () and hexagonal close-packed () 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.

Cooperative deformation in high-entropy alloys at ultralow temperatures

“…This was a surprising finding because the first-principle calculations predicted a stable hcp phase at low temperatures for a solid solution with a random distribution of constituent elements (19,35). One possible explanation is that, as a recent theoretical study suggested, the SFE varies widely depending on the short-range chemical order and can even become positive depending on the local configurations (36). Another possibility, as Ma et al (35) argued, is that the fcc phase may be stabilized by kinetics at low temperatures.…”

Semiconducting SiGeSn high-entropy alloy: A density functional theory study

“…Recently, the SQS method has been widely used to simulate the structures of metallic HEAs with a solid solution phase [25]. In addition, an SQS structure also serves as an initial structure followed by a combination of MC and DFT simulations to examine the occurrence of CSRO, which has been reported to occur in typical metallic HEAs such as Cr-Co-Ni [58,59] and affect mechanical properties such as stacking fault and point-defect energies. We focus on the SiGeSn HEA with the highest Sn content (i.e., where the ratio of the three elements is 1:1:1).…”

“…We then examine if the HEA exhibits a chemical short-range order (CSRO) which is a tendency for atomic clustering (e.g., one Si atom prefers Si/Ge neighbors over Sn atoms). CSRO has been reported in numerous HEAs and dominates several of their properties [58,59]. Furthermore, because point defects are unavoidable in any material due to thermal vibrations, we study the most basic point defect in the SiGeSn HEA, i.e., single vacancies.…”

Solid solution strengthening theories of high-entropy alloys

“…Such SRO arises from interactions between alloy elements, and has been experimentally observed or theoretically predicted for some multicomponent alloys [66][67][68][69][70]. In dilute alloys, the effect of SRO on strengthening has been historically envisioned through the formation of pairs, triplets or clusters, due to solute/solute interactions.…”