Sintering Characteristics of Thermal Barrier YSZ Coatings Made by Suspension Plasma Spraying

Thermal barrier coatings (TBCs) deposited by suspension plasma spraying (SPS) are recognized as a potent method to increase efficiency and extend the life of gas turbines. The unique microstructure of the SPS coatings provides exceptional mechanical and thermal properties, but on the other hand, affects sintering of the TBCs what could lead to undesirable changes in properties and premature failure. This study attempts to characterize changes occurring in the SPS deposited TBCs during high-temperature exposure. Several SPS yttria-stabilized zirconia coatings were deposited with various spraying parameters including plasma gas composition, standoff distance and suspension. Then, the SPS coatings were subjected to temperature of 1150oC. It turned out that sintering shrinkage of SPS coatings was higher by a factor of 2-4 than APS coating. Detailed analysis of microstructural changes showed that the coatings with limited porosity at high temperature tend to form arrays of fine pores, while the coatings with higher initial porosity formed large spherical pores. Most of the SPS coatings showed a non-typical change of mechanical properties-a decrease in the Young's modulus and toughness. It was shown that peculiar evolution of mechanical properties can be associated with the porosity changes and interactions between pores and propagation crack.