Effect of surface roughness on properties of PS-PVD YSZ ceramic coating

YSZ ceramic coating was prepared by PS-PVD process on K417G superalloy prefabricated with NiCoCrAlYTa bond coating. The tensile bond strength, particle erosion resistance and high temperature oxidation resistance of PS-PVD YSZ ceramic coating were tested by the universal tensile testing machine, particle erosion device and static oxidation furnace. The SEM and EDS were used to analyze the surface, cross-section morphology and element distribution. The results show that surface roughness has great influence on tensile bond strength, particle erosion resistance and high temperature oxidation resistance of YSZ ceramic coating. The bonding strength is increased first and then decreased with the increase of surface roughness. The coating prepared on the surface of Ra=0.40 μm has the highest bonding strength of 23.5 MPa. The tensile fracture occurs in the interior of YSZ ceramic coating at a distance of 40-70 μm from the bond coating. The erosion rate is decreased first and then increased with the increase of surface roughness. The coating prepared on the surface of Ra=0.40 μm has the best particle erosion resistance, and the erosion rate is 2.8×10-3 g/g. Small surface fluctuations and low porosity are two important reasons for preventing fast particle erosion. The YSZ coatings prepared with different surface roughness can produce dense and continuous TGO layer. Larger surface roughness causes larger fluctuation of growing TGO layer, which is more likely to cause local thickening and stress concentration, thus leading to failure.