Microstructure and High PV Wear Behavior of Novel Amorphous Al2O3-YAG Ceramic Coating Fabricated by Atmospheric Plasma Spraying

Abstract

The reliability and lifetime of mechanical systems often depend on their capacity to resist to friction and wear under high PV values (P contact pressure; V friction velocity). This study deals with plasma-sprayed amorphous Al2O3-YAG coatings that could be used under such conditions. Their phase transformation, microstructure stability and high PV wear behavior were investigated. The sprayable Al2O3/Y2O3 feedstock was obtained by spray-drying nano-sized Al2O3 and Y2O3 powders. In order to elucidate the effect of the original powder particle size on phase composition and anti-wear property of the coatings, micro-sized Al2O3 and Y2O3 powders were also utilized to produce Al2O3-Y2O3 coating. Simultaneously, Al2O3 coating was also deposited for performance comparison. The combination of coating microstructure analysis, solidification theory of deep eutectic system and practical plasma spraying conditions clarified the formation mechanism of amorphous Al2O3-YAG coating. Furthermore, amorphous Al2O3-YAG coating showed better wear-resistant performance than crystalline Al2O3 and Al2O3-Y2O3 coatings under severe conditions with high PV values, which indicate excellent engineering application potential of the former coating. The relationships between microstructure characteristics and high PV wear behavior of amorphous Al2O3-YAG coating were established, which contribute to deeply understand corresponding friction and wear mechanisms. The rapid solidification temperature (Te) in plasma spraying process is rather lower than the glass transition temperature (Tg) due to the cooling effects in the coating deposition. Amorphous phase is dominant in as-sprayed Al2O3-YAG coating. The amorphous Al2O3-YAG coating has better plastic deformation ability than Al2O3 and Al2O3-Y2O3 coatings. The amorphous Al2O3-YAG coating possesses greater crack propagation resistance.