Influence of Spray Distance on Microstructure and Properties of Suspension Plasma Sprayed YSZ + Al₂O₃ + SiC Coatings

Suspension plasma sprayed YSZ composite ceramic coatings have broad application prospects in the surface protection of marine engine hot-end components due to their excellent thermal insulation performance and high-temperature stability. However, the hardness and wear resistance of single YSZ coating are still insufficient under harsh working conditions, making it difficult to meet the long-term service requirements in high-salt and high-humidity environments. In this study, YSZ+Al₂O₃+SiC composite ceramic coatings are prepared on the surface of the nickel-based superalloy using suspension plasma spraying technology. The connection between the microstructure and mechanical properties of the coating is analyzed to investigate the influence of spray distance on performances of the composite ceramic coating. The results show that the coatings prepared at different spray distances are composed of ZrO₂, Al₂O₃ and SiC phases. As the spray distance increases from 30 mm to 50 mm, the coating porosity increases from 17.34% to 20.90%. The coating prepared at a spray distance of 40 mm has the most uniform microstructure and the best comprehensive performance, with the average surface microhardness of 1 162.9HV0.2, the maximum cross section hardness of 692.0HV0.2, and the steady-state friction coefficient of approximately 0.33. The worn mechanism is dominated by abrasive wear. The coating remains complete after 900 °C molten salt corrosion, demonstrating excellent corrosion resistance. This research can provide theoretical references for the process optimization of surface protection coatings of marine engine hot-end components.