Preparation and Mechanism Study of Plasma-Sprayed Metal–Ceramic Composite Coatings Based on Microstructure

To overcome the limitations of single-phase plasma-sprayed coatings, where ceramic coatings exhibit high hardness but poor toughness while metallic coatings possess good ductility but insufficient hardness, AT40/Al metal–ceramic composite coatings were prepared by atmospheric plasma spraying. In this study, Al2O3–40%TiO2 (AT40) ceramic was used as the hard phase and aluminum as the ductile phase. The effects of Al content (10%, 20%, and 30%) and key spraying parameters, including arc power (36–40 kW), spraying distance (85–130 mm), and gun traverse speed (400–1200 mm s−1), on the microstructure and mechanical properties of the coatings were systematically investigated. The coatings were characterized using SEM, XRD, and EDS, and grey relational analysis was employed to evaluate the influence of process parameters. The results show that the introduction of an appropriate amount of Al significantly improves coating densification. When the Al content is 10%, the coating porosity decreases to 3.2%, compared with 8.5% for the pure AT40 coating. The optimal spraying parameters were determined to be 38 kW arc power, 100 mm spraying distance, and 400 mm s−1 traverse speed, under which the coating exhibits a microhardness of 519.68 HV and a 45.3% improvement in impact resistance compared with the pure AT40 coating. Phase analysis indicates that partial transformation of α-Al2O3 to γ-Al2O3 occurs during spraying, while interfacial reactions between Al and TiO2 lead to the formation of Al2TiO5, enhancing the interfacial bonding strength. The improved performance of the composite coating is attributed to the combined effects of structural densification, interfacial strengthening, and the synergistic interaction between ceramic and metallic phases.