Microstructure and properties of composite coatings prepared by plasma spraying ZrO2-B2O3-Al composite powders

The composite coatings containing ZrB2 were prepared by plasma spraying ZrO2-B2O3-Al system, and the effects of ZrO2 particles size on the microstructure and properties of the as-prepared coating were investigated. The results show that ZrO2, B2O3 and Al reacted with each other to form ZrB2 during the plasma spraying process. The reaction degree of ZrO2-B2O3-Al composite powders with nano-sized ZrO2 particles was greater than that of the micro-sized ZrO2 particles, and there was more ZrB2 formed in the coating plasma sprayed with nano-sized ZrO2 particles. The coating prepared by plasma spraying ZrO2-B2O3-Al composite powder with micro-sized ZrO2 showed the characteristics of stacking of partially melted or unmelted feedstock particles, loose microstructure, high porosity, and poor quality. However, the coating prepared by plasma spraying ZrO2-B2O3-Al composite powder with nano-sized ZrO2 displayed lamellar structure, homogenous distribution of ZrB2 particles, dense microstructure and better quality. The hardness of the coating prepared by nano-sized ZrO2 was much higher than that of the coating prepared by micro-sized ZrO2, which is attributed to the high density and the homogeneously distributed reinforcement phase ZrB2 formed in the coating. Meanwhile, the coating prepared by plasma spraying ZrO2-B2O3-Al composite powder with nano-sized ZrO2 possessed high toughness.