Advanced Thermal Barrier Coatings for Industrial Gas Turbine Engines

Executive Summary 3 Thermal barrier coating (TBC) ceramic topcoats made from Y 2 O 3-stabilized ZrO 2 (YSZ) have been used successfully in gas-turbine engine applications for more than 30 years. YSZ derives its favorable performance from a combination of properties that include low thermal conductivity, high thermal expansion coefficient, and phase stability to relatively high temperatures. With advanced engine requirements of improved performance and increased durability, a new generation of thermal barrier coatings is needed that will provide greater insulation (lower thermal conductivity) and permit higher operating temperatures. To that end, the objectives of this project were: (i) to identify potential low-thermal conductivity ceramic TBC candidates, (ii) to measure and to analyze their thermal conductivities, (iii) to evaluate their hot-corrosion behavior, (iv) to prepare TBCs out of those ceramics, (v) to evaluate the thermo-mechanical performance of the TBCs, and (vi) to identify their failure mechanisms. All these objectives were achieved successfully in this project. This effort also resulted in the education of two Ph.D. students and two undergraduate research assistants, and the publication of five referred-journal publications. ceramics is not available in the literature. To that end, powders of the three types of rear-earth zirconates were prepared using the co-precipitation method, which were then hot-pressed to produce fully-dense ceramics. The thermal conductivities of these monoliths were measured as a function of temperature. It was found that the thermal conductivities of these ceramics are about the same, and they all are about 30% lower than the thermal conductivity of fully-dense 7wt% Y 2 O 3-stabilized ZrO 2 (7YSZ). The effect of phase ordering within Gd 2 Zr 2 O 7 (pyrochlore or fluorite) on the thermal conductivity was also investigated, and it was found that ordering has no effect on the thermal conductivity in the temperature of interest.