Optimization on the bonding strength and microstructure of atmospheric plasma sprayed Y2O3 coatings by response surface methodology

Atmospheric plasma spraying (APS) is one of the most effective techniques for the preparing Y2O3 ceramic coatings. In order to investigate the effect of spraying parameters on the microstructure and the bonding strength of Y2O3 coatings, a response surface methodology (RSM) has been adopted to design the plasma spraying parameters. The results showed that the optimized bonding strength of the coating (23.72 MPa) was obtained at the current of 610.61 A, Ar flow rate of 48.23 L/min, spraying distance of 15.06 cm, which was supported by both RSM and experimental results. The optimized Y2O3 coating possessed the small grain size of 37.01 nm and the low porosity of 1.80%, which brought in the optimized bonding strength of the coatings. Meanwhile, the pore sizes of the Y2O3 coatings also affected the bonding strength of the coatings, in which pore size less than 10 μm were found to support a higher bonding strength. Therefore, the microstructure of the coatings strongly affected the bonding strength including the adhesive strength and cohesive strength of the coatings, which consequently dominated the fracture failure mechanism of the Y2O3 coatings. With decreasing the bonding strength of the coatings, the fracture failure mechanisms were that the fracture mainly appeared within the coating, the fracture appeared at the coating/substrate interface and within the coating, the fracture mainly appeared at the coating/substrate interface, respectively.