Influence of Process-Induced Architectures on the Resistance of Thermal Barrier Coatings to Incipient CMAS Interactions under Simulated Attack

As gas turbine engines continually move toward higher operating temperatures for the sake of greater operating efficiency, the need for protective Thermal Barrier Coatings (TBCs) to improve subsequently rises. With higher operating temperatures, ingested siliceous debris (CMAS) are more likely to melt inside the engine and deposit onto the surfaces of these TBCs. Depending on the chemistry and microstructure of the attacked TBC, the CMAS particulates are either able to flow freely into the microstructure or are arrested at the surface. In particular, Yttria Stabilized Zirconia (YSZ) TBCs do not possess the same infiltration-resisting thermochemical reactions to CMAS as Gadolinium Zirconate (GZO) TBCs. In addition, a highly porous coating (>20%) might have a different infiltration rate as compared to a coating that is highly dense (<5%) and/or contains large vertically-oriented cracks at the surface. This study seeks to understand this interplay between chemistry, microstructure, and CMAS infiltration behavior. Different YSZ and GZO coatings were fabricated using Plasma Spray processes and exposed to CMAS in simulative conditions. A thermal gradient rig was built at Stony Brook University to allow simultaneous gradient exposure and CMAS attack. Results to be discussed include the interplay between TBC chemistry, microstructure, and CMAS infiltration.