Microstructure and properties of Al2O3-ZrO2 composite coatings prepared by air plasma spraying

Three kinds of Al2O3-ZrO2 composite coatings with different composition were prepared by air plasma spraying on titanium alloy substrates. The compositions of the coatings were Al2O3-35wt%ZrO2, Al2O3-40wt%ZrO2 and Al2O3-45wt%ZrO2. The microstructure, microhardness and toughness of the three Al2O3-ZrO2 composite coatings were characterized by X-ray diffraction, scanning electron microscope, energy dispersive spectrometer and micro-Vickers. The result showed that α-Al2O3 transformed to γ-Al2O3 during the process of plasma spraying Al2O3-ZrO2 composite powders. Meanwhile, amorphous phase was formed in the Al2O3-ZrO2 composite coatings due to the rapid cooling and solidification of plasma spraying and the proper composition. There was more amorphous phase in the Al2O3-40wt%ZrO2 coating compared with the other two composite coatings. The reason was that the composition of the Al2O3-40wt%ZrO2 composite coating was closer to the eutectic point of Al2O3-ZrO2 pseudo-binary system. The Al2O3-40wt%ZrO2 composite coating with more amorphous phase had denser microstructure and lower porosity. With increasing of the content of ZrO2 in the Al2O3-ZrO2 composite coatings, the microhardness of the coatings decreased. And the microhardness of the Al2O3-ZrO2 composite coatings was significantly higher than that of single phase Al2O3 coating and single phase ZrO2 coating. Vicker indention results showed that the Al2O3-ZrO2 composite coatings had high toughness.