Multiscale mechanisms of Ta-induced short-range ordering for improved high-temperature performance of Co-Ni-Cr-Al-Ti multi-principal-element alloys

This study systematically investigates the multiscale mechanisms that govern the high-temperature structural stability, oxidation resistance, and mechanical properties of Co₄₀Ni₃₀Cr₂₀Al₅Ti₄Ta₁ multi-principal-element alloys (MPEAs), with a particular emphasis on the role of tantalum (Ta)-induced short-range ordering (SRO). The results demonstrate that Ta promotes SRO within the L1₂ nanoprecipitates, which impedes solute diffusion, effectively suppressing precipitate coarsening and enhancing microstructural stability during thermal exposure. The incorporation of Ta significantly improves oxidation resistance by facilitating the formation of thermodynamically stable Ta-containing oxide layers, resulting in a 54 % reduction in scale thickness and notably slower oxidation kinetics at 1173 K. Additionally, Ta-induced SRO reshapes the energy landscape of planar defects by increasing the energy of antiphase boundaries (APBs) and decreasing stacking fault energy, which facilitates the activation of superlattice intrinsic stacking faults (SISFs), Lomer-Cottrell locks, and deformation twins. These mechanisms collectively form a stable and dense dislocation-fault network that synergistically enhances both strength and ductility during high-temperature deformation (973–1073 K). Notably, the Ta-containing alloy achieves a tensile strength of 1225 MPa and a uniform elongation of 24 % at 973 K, outperforming conventional polycrystalline alloys. These findings highlight the potential of Ta-induced SRO to enhance the stability and performance of MPEAs under extreme conditions, offering critical insights for the design of high-strength, thermally stable materials for demanding structural applications.

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