Modulation of Phase Separation and High-Temperature Mechanical Properties by L12 Phase in AlCoCrFeMo₀.₀₅Ni₂ High-Entropy Alloy

Abstract

The high-temperature strengthening mechanism of the L1₂ phase in AlCoCrFeMo₀.₀₅Ni₂ high-entropy alloy (HEA) remains unclear. This study investigates the high-temperature mechanical response of the L1₂ phase in this HEA using atomistic simulations. A 2×2×2 supercell was used to represent L1₂-structured regions in the quinary HEA, circumventing the limitations of modeling it directly within a 4-atom unit cell. The ordered (OM) and disordered (DM) models, with similar compositions, were compared under high-temperature deformation. The results revealed stress-induced phase decomposition in the OM, consistent with experimental observations in the alloy. The DM, conversely, exhibited superior phase stability. Furthermore, the OM exhibited significantly higher strength and enhanced ductility compared to the DM. Specifically, the OM showed a significant increase in the length of Shockley partial dislocations and stair-rod dislocations. Additionally, the OM exhibited a reduced dislocation density during tensile deformation. These observations collectively demonstrate that the OM possesses lower resistance to dislocation expansion and a greater propensity for cross-slip and dynamic recovery. This resulted in a lower work-hardening rate and improved uniform elongation, ductility, and toughness in the OM.