Microstructural evolution, nanoindentation creep response, and wear properties of Y₂O₃-modified CoCrFeNi high entropy alloys

The combined effects of wear and creep largely determine the long-term reliability of alloys in demanding thermal and mechanical environments, but conventional structural materials show limited resistance to these degradation mechanisms. High-entropy alloys (HEAs), though inherently robust, have gained attention as potential candidates for such environments, particularly when reinforced with stable oxide dispersions. In this study, oxide-dispersion-strengthened Co–Cr–Fe–Ni HEAs containing 1 and 4 wt% Y₂O₃ were synthesized through mechanical alloying and spark plasma sintering to evaluate this approach. Microstructural characterization using X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the retention of the fcc crystal lattice. Pronounced grain refinement was achieved, decreasing from 360 ± 70 nm in the unreinforced HEA to 95 ± 15 nm in the 4 wt% ODS composition, accompanied by a substantial increase in hardness to 685 ± 30 HV. Wear experiments revealed a fourfold reduction in specific wear rate. This improvement was accompanied by a transition in wear mode from extensive surface damage in the unreinforced HEA to predominantly oxidative and fatigue-assisted mechanisms in the ODS HEAs, facilitated by the formation of protective tribo-oxide layers. Nanoindentation creep analysis revealed a decrease in stress exponent from 16.05 to 5.72 with increasing Y₂O₃ content. This change signifies a transition toward dislocation-controlled creep and tunable creep resistance. Collectively, these findings establish that rare-earth oxide dispersion is an effective strategy for simultaneously enhancing surface durability and controlling time-dependent deformation in HEAs, thereby extending their potential for demanding structural and tribological applications.