AFM Study of the Faceting of Ceramic Splats during Thermal Exposure for designing high sintering-resistance TBCs

Thermally sprayed TBCs usually exhibits much lower thermal conductively than their sintered bulk counterparts. During thermal exposure, the surface of adjacent splats becomes faceting and then the grain bridging occurs in the inter-lamellar pores. These phenomena results in disappearance of the lamellar structure and consequently change of thermal conductivity and mechanical properties. In this study, an atomic force microscopy (AFM) was carried out to precisely examine the evolution of surface faceting of atmospheric plasma sprayed YSZ, La₂Zr₂O₇, La₂Ce₂O₇ and Al₂O₃ splats with series thermal exposure durations and temperatures. Results show that the roughness of the splats increases with the thermal exposure temperature and tends to become saturated to certain value under a certain temperature, which suggests that larger 2D pores than twice of faceting height can survive from sintering. The high temperature exposure of coatings was conducted to correlate the survivable 2D pores with the survived pores in the coatings.