Faculty Sponsor's Department(s):
Thermal barrier coatings (TBCs) are ceramic layers that allow gas turbine engines to operate at higher temperatures, with concomitant benefits to their fuel efficiency. However, current TBCs are susceptible to degradation and failure owing to the infiltration of molten silicate (CMAS) into their porosity that is needed to enable coating compliance. Infiltration of the TBC can be stopped when exposure to CMAS causes a rapid reaction forming new solid phases near the TBC surface. Quick dissolution and diffusion rates are necessary to enable prompt saturation, which is required for reaction between the CMAS and the TBC; therefore, understanding the kinetics between the two processes is critical. To quantify these kinetics, dense TBC oxides were placed in a 1D diffusive contact against different compositions of CMAS. The diffusion couples are heated to 1300°C for a prescribed, typically short time, to obtain concentration profiles before crystallization occurs, and rapidly cooled to retain the high-temperature configuration. Quantification of dissolution and diffusion rates is enabled by analyzing the TBC element concentration profiles in the CMAS, using an electron microprobe. Reaction products from the TBC-CMAS interaction were observed using electron microscopy to understand the reaction mechanisms. This research provides knowledge of the kinetic differences between traditional and new TBC materials (e.g., Gd2Zr2O7). It is evident that the Gd2Zr2O7 reacts faster with CMAS than the traditional TBC material because of enhanced dissolution and crystallization rates. The enriched understanding of dissolution, diffusion, and crystallization behaviors of TBCs, provides insight to guide novel TBC design.