Effect of spraying powder characteristics on mechanical and thermal shock properties of plasma-sprayed YSZ thermal barrier coating

Spraying powder characteristics are one of the important parameters that directly affect the microstructure and properties of plasma-sprayed coating. In this research, three types of plasma-sprayed yttria partially stabilised zirconia (YSZ) thermal barrier coatings (TBCs) were prepared by atmospheric plasma spraying using micron spherical, micron irregular, and nano-agglomerated spraying powder. The microstructures, and mechanical and thermal shock properties of YSZ TBCs were investigated. The results showed that all three YSZ coatings were relatively dense and mainly composed of t-ZrO2 phase and a small amount of m-ZrO2 phase. Compared with the coating prepared with the micron spherical and irregular spraying powder, the nanostructured coating had higher porosity and bonding strength (9.01% and 59.2 MPa). The thermal conductivity of nanostructured YSZ ceramic coating was 1.08 W.m(-1).K-1 at 800 degrees C, around 10% lower than that of the other two coatings. The coating prepared by nano-agglomerated spraying powder did not begin to exfoliate from the edge of the sample until it had undergone 125 thermal-shock cycles at 1100 degrees C, which was better than the 72 cycles sustained by the coating with micron spherical powder and the 76 cycles sustained when coating with irregular powder. After 155 thermal-shock cycles at 1100 degrees C, only a small amount of nanostructured YSZ TBCs were stripped layer-by-layer, while the other two YSZ TBCs had failed due to brittle fracture of the ceramic layer, suggesting that the coating prepared by nano-agglomerated powder exhibited the best thermal shock performance among the three YSZ TBCs at 1100 degrees C. The main failure mode of plasma-sprayed YSZ TBCs under water-quenching thermal shock at 1100 degrees C involved separation and exfoliation of the ceramic layer.