Tribological Analysis of Laser-Cladded Martensitic and Mixed-Alloy Coatings: Correlating Microstructure, Hardness, and Wear Response

High-strength quenched and tempered steels such as EN 42CrMo4, widely used for marine shaft applications due to their high strength, toughness, and fatigue resistance, are nevertheless susceptible to surface degradation under severe dry sliding conditions. To enhance surface integrity and tribological performance, this study investigates laser-cladded AISI 410L and mixed AISI 410L/AISI 4140 (50/50 wt.%) coatings deposited on EN 42CrMo4 steel using a high-power diode laser (HPDL). Two-layer coatings were produced, and selected specimens underwent post-cladding stress-relief heat treatment to mitigate residual stresses and temper as-solidified microstructures. Microstructural characterization revealed refined dendritic and martensitic morphologies, while the mixed-alloy coatings showed increased carbide formation and improved hardness homogeneity. The mixed AISI 410L/AISI 4140 coatings achieved significantly higher microhardness values (≈530–555 HV) compared to single-alloy 410L coatings (≈310–420 HV). Tribological testing under dry sliding conditions (Al₂O₃ counterbody, 5 N load, 0.5 m/s sliding speed) demonstrated that the mixed-alloy coatings exhibited substantially lower steady-state friction coefficients (μ ≈ 0.65–0.69) and markedly reduced specific wear rates (≈11–17 × 10⁻¹⁴ m³/Nm) compared to the 410L coatings (≈150–175 × 10⁻¹⁴ m³/Nm). Post-cladding heat treatment further stabilized friction behaviour and reduced wear in the mixed-alloy system by tempering martensite and alleviating localized stress concentrations. Wear mechanism analysis revealed a transition from severe abrasive wear with fatigue-induced delamination in the 410L coatings to predominantly mild abrasive wear in the mixed-alloy coatings, accompanied by localized plastic deformation. Overall, the results establish clear correlations between microstructure, hardness, and tribological response, demonstrating that mixed-alloy laser cladding is an effective strategy for enhancing the dry sliding performance of EN 42CrMo4 steel in demanding marine applications.