D. Zhao; M. Chen; G. Wang; Y. Wang; Y. Wang; Q. Dong; Z. Cui; Z. Zhang; H. Cui
SSRN 6926139 (2026)
Stacking fault energy (SFE) is widely used to tune the strength-plasticity balance of FCC alloys, but its role in governing the wear response of nanocrystalline (NC) alloys remains unresolved. Here, NC CoxCr33Ni67-x medium-entropy alloy coatings with systematically varied SFE were fabricated on Al alloy substrates by rapid electrical-current activated sintering, and their micromechanical deformation and dry sliding wear responses were correlated with defect evolution in the worn subsurface. Micropillar compression shows that the near-equiatomic Co33Cr33Ni33 coating achieves the highest apparent yield strength (~3.4 GPa), sustains ~30% engineering strain without catastrophic collapse, and retains the most stable strain-hardening response through balanced nanotwinning and transformation-related stacking-sequence evolution. By contrast, the ultralow-SFE Co43Cr33Ni24 coating undergoes rapid FCC-to-HCP transformation; this initially strengthens the nanograins but rapidly saturates the FCC matrix and promotes deformation instability. During sliding, these distinct defect pathways produce opposite tribological outcomes. The Co33Cr33Ni33 coating exhibits the lowest wear rate (~0.94×10-5 mm3 /Nm), enabled by self-sustained dynamic grain refinement mediated by deformation twins and stacking faults. The Co43Cr33Ni24 coating instead develops a wear-induced nanocrystalline-to-amorphous transition, with cracks propagating along the amorphization front and causing fish-scale spallation. These results identify SFE as a governing parameter that determines whether sliding-induced defect activity promotes adaptive grain refinement or damage-inducing amorphization, providing a mechanistic design principle for wear-resistant nanostructured FCC alloy coatings.