Mo-regulated tribo-oxide stability and near-surface evolution in laser-clad AlCoCrFeNiMox high-entropy alloy coatings during high-temperature sliding

AlCoCrFeNiMo x high-entropy alloy coatings with different Mo contents (x = 0, 0.05, 0.15, 0.25, and 0.35) were fabricated on 316L stainless steel by laser cladding to improve its high-temperature sliding wear resistance. The effects of Mo addition on phase constitution, lattice distortion, microstructure, and hardness were investigated, and the tribological behavior of the coatings was evaluated at 600 °C, with emphasis on tribo-oxide-layer stability and post-wear near-surface evolution. All coatings were mainly composed of disordered A2 and ordered B2 phases. Increasing Mo content caused a low-angle shift of the main diffraction peaks and an increase in lattice parameter, indicating enhanced lattice distortion. Accordingly, the coating hardness increased monotonically, reaching 652.30 HV 0.5 for Mo0.35, approximately 230% higher than that of the 316L substrate. In contrast, wear resistance showed a non-monotonic dependence on Mo content. The Mo0.25 coating exhibited the lowest average coefficient of friction of 0.2241 and the lowest wear rate of 4.08 × 10 -6 mm 3 ·N -1 ·m -1 , corresponding to a reduction of approximately 98.8% relative to the substrate. Its superior wear resistance was attributed to improved load-bearing capacity and the retention of a continuous, compact tribo-oxide layer during sliding. Excessive Mo addition, although further increasing hardness, intensified Fe–Cr–Mo redistribution near grain boundaries and was accompanied by more pronounced σ-phase-related diffraction signals in the post-wear near-surface region, thereby reducing tribo-oxide-layer stability. These results indicate that the high-temperature sliding wear resistance of laser-clad AlCoCrFeNiMo x coatings is governed by the balance among Mo-induced strengthening, tribo-oxide-layer stability, and near-surface microstructural evolution.