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

Highlights: • The coatings containing ZrB₂ was prepared by plasma spraying ZrO₂-B₂O₃-Al system. • ZrO₂, B₂O₃ and Al reacted with each other to form ZrB₂ during plasma spraying. • Reaction degree of ZrO₂-B₂O₃-Al system with nano-ZrO₂ was greater than micro-ZrO₂. • The coating prepared by ZrO₂-B₂O₃-Al system with nano-ZrO₂ showed good properties. • The microstructure evolution models of ZrO₂-B₂O₃-Al during spraying were established. 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.