Deposition and CMAS Corrosion Mechanism of 7YSZ Thermal Barrier Coatings Prepared by Plasma Spray-Physical Vapor Deposition

Using agglomerated and sintered ZrO sub(2)-7wt%Y sub(2)O sub(3) (7YSZ) powders as raw materials, columnar thermal barrier coatings (TBCs) were prepared by plasma spray-physical vapor deposition (PS-PVD) at substrate temperature of 850 [degrees]C. The microstructures of columnar coating were analyzed by field emission-scanning electron microscope (FE-SEM). Based on the theory of atoms together, the formation and growth process of 7YSZ nucleus were investigated and the deposition mechanism of columnar coating was also analyzed. Besides, under the temperature of 1200 [degrees]C, the CMAS (CaO-MgO-Al sub(2)O sub(3)-SiO sub(2)) corrosion of columnar 7YSZ coating was examined and its failure mechanism was also discussed. During the deposition process of columnar 7YSZ coating, the 7YSZ gas molecules were firstly absorbed on substrate, then through diffusion and migration, the critical nucleus formed rapidly. Besides, the critical nucleus further grew up forming crystal island by absorbing other molecules. Then after following four steps of island formation, union formation, channel formation and continuation, the columnar coating formed eventually. When above melting temperature, the CMAS could penetrate into porous columnar coating by capillary force and react with the 7YSZ coating. Finally, the cracks appeared in the coating due to thermochemical and thermomechanical interaction.