High temperature microstructure evolution and thermal shock resistance of plasma sprayed Al₂O₃-ZrO₂-CeO₂ coatings

Al₂O₃-ZrO₂-CeO₂ composite coatings were prepared by plasma spraying Al₂O₃-ZrO₂ composite powders with and without CeO₂ addition. The microstructure and properties of the Al₂O₃-ZrO₂-CeO₂ coatings at high temperature and thermal shock resistance were investigated. The results show that an amorphous phase was formed in the plasma sprayed Al₂O₃-ZrO₂ and Al₂O₃-ZrO₂-CeO₂ coatings. The Al₂O₃-ZrO₂ coating consisted mainly of t-ZrO₂, α-Al₂O₃, and γ-Al₂O₃. The Al₂O₃-ZrO₂-CeO₂ coating consisted mainly of t-ZrO₂, α-Al₂O₃, γ-Al₂O₃, and CeO₂. The Al₂O₃-ZrO₂-CeO₂ coating was more uniform and denser than the Al₂O₃-ZrO₂ coating. The results after heat treatment showed that the two coatings were stable at 800 °C. With the increase of temperature, the coatings underwent phase transformation at high temperature (1000 and 1200 °C). At 1000 °C, the amorphous phase was obviously reduced, and the amorphous phase was crystallized to form nanocrystals. When the heat treatment temperature was raised to 1200 °C, the intensity of the diffraction peaks of t-ZrO₂ and α-Al₂O₃ increased, the amorphous phase was completely crystallized, and γ-Al₂O₃ was transformed into α-Al₂O₃. The porosity of the two coatings decreased and the hardness increased after heat treatment. The thermal shock resistance of the coatings on the TC4 titanium alloy substrate was better than that on the Q235 steel substrate. The thermal shock resistance of the Al₂O₃-ZrO₂-CeO₂ coating was better than that of the Al₂O₃-ZrO₂ coating.