Study on the Microstructure and Wear Properties of Al2O3-3%TiO2-xAl Composite Coatings Prepared by Plasma Spraying

Al2O3-3% TiO2-xAl (x = 0, 20, 40, 60 wt.%) composite coatings were prepared on Q235 substrate by plasma spraying technology, and the effects of pure Al phase addition on the microstructure and wear properties of the coatings were compared and analyzed. The results show that a unique splash-like structure was formed on the surface of the coating, and this structure became more obvious with the increase in Al content. Cross-sectional analysis shows that the introduction of pure Al phase reduces the large pores and cracks in the coating, forming a slender band structure. XRD analysis shows that the addition of pure Al phase leads to a decrease in the diffraction peak intensity of α-Al2O3, while the diffraction peak intensity of Al phase and γ-Al2O3 gradually increases, especially in the coating with 40% Al content; the diffraction peak of γ-Al2O3 increases significantly. XPS analysis further confirms that with the increase in Al content, a new pure Al peak appears in the Al element spectrum, and the peaks of α-Al2O3 and γ-Al2O3 fluctuate. In addition, the porosity of the coating decreases first and then increases and then decreases again with the increase in Al content. The porosity of the coating with 60% Al content is the lowest, at only 5.14%. Microhardness test results show that with the increase in Al content, the microhardness of the coating gradually decreases, and the fracture morphology changes from brittle fracture to irregular fracture, with the appearance of pull-out areas, indicating that the pure Al phase effectively improves the brittleness of the coating. However, the friction and wear test results show that the friction coefficient of the coating increases with the increase in Al content. The pure Al2O3 coating has high hardness and excellent wear resistance, while the coating with 60% Al content has the highest friction coefficient and the most severe wear. Moreover, adhesive wear phenomena appear on the coating surface with high Al content.