Preparation of Micro-Nano Hierarchical Microstructure of Thermal Barrier Coatings and Its Performance against CMAS Wetting

The application of thermal barrier coatings (TBCs) is greatly limited by calcium-magnesium-alumina-silicate (CMAS) attack. The surface microstructure of TBCs is demonstrated its fundamental effect on the wetting behavior of molten CMAS, thus further influencing CMAS resistance of TBCs. In this study, hierarchical microstructure was innovatively fabricated by suspension plasma spray technology (SPS) on air plasma spraying (APS) coating surface, where cauliflower-like microstructures formed by the stacking of numerous micron and nanometer particles were densely distributed. And the wetting behavior of the melt on the coating surface was investigated and compared. Results indicated that SPS coatings showed a superior excellence of repelling the molten CMAS wetting compared with conventional APS coating, resulting from its micro-nano surface microstructure. After kept at 1300 ^oC for 5 min, the contact angle of melt on SPS coating was 115.1°, which was more than twice that on APS coating (52.1°), and that on SPS coating was 3.2 times larger than that on APS coating after 10 min. The effectiveness of SPS coating in repelling the melt was illustrated by theoretical analysis to be attributed to its micro-nano multi-scale microstructure. Also, air stored in the porous microstructure of SPS coating played a vital role in lifting CMAS droplet during the wetting process.