Effect of hollow spherical powder size distribution on porosity and segmentation cracks in thermal barrier coatings

The effect of characteristics of hollow spherical (HOSP) powders on porosity and development of segmentation cracks in plasma-sprayed thick thermal barrier coatings (TBCs) was investigated. Three powders with particle size ranges of 20-45, 53-75, and 90-120 mu m were selected from a commercial HOSP powder feedstock for spraying the TBCs. The 20-45 mu m powder has a higher deposition efficiency and a greater capability of producing segmented coatings than the other larger powders. Diagnostics of in-flight particles show that the average surface temperature and velocity of the particles sprayed from the fine powder is higher by 250 degrees C and 50 m/s compared with those sprayed from the 90 to 120 mu m powder, respectively, due to its greater ratio of surface area to mass. The lower porosity of the coating sprayed from the fine powder is mainly attributed to the decreased volume of intersplat gaps and voids.