Gas-deposition mechanisms of 7YSZ coating based on plasma spray-physical vapor deposition

Variable microstructures of ZrO2-7 wt.% Y2O3 (7YSZ) coating can be achieved by plasma spray-physical vapor deposition (PS-PVD). Based on gas-phase prepared 7YSZ coating, the deposition mechanisms and their dependency on process conditions were investigated. When the spray distance was 950 mm, heterogeneous nucleation occurred on the surface of substrate. Porous oriented columnar coating could be obtained on the nickel-based superalloy at a substrate temperature of 850 °C. As the substrate temperature decreases to room temperature, porous columnar coating tends to be dense coating that is mainly made of randomly oriented fine grains. But when the substrate was replaced by graphite, columnar coating was observed again. As the spray distance increases from 950 to 2200 mm, homogenous nucleation occurs at the end of plasma plume leading to formation of cluster agglomerated by nano-sized grains. Finally, fine grain constituted coating was obtained on substrate at room temperature regardless of substrate materials.