Perspectives on Thermal Gradients in Porous ZrO2-7-8 wt.% Y2O3 (YSZ) Thermal Barrier Coatings (TBCs) Manufactured by Air Plasma Spray (APS)

Porous (similar to 10-20%) ZrO2-7-8 wt.% Y2O3 (YSZ) thermal barrier coatings (TBCs) manufactured via air plasma spray (APS) and exhibiting a thickness range of similar to 250-500 mu m, provide thermal insulation from the hot combustion gases to the metallic parts located in the hot stationary sections of gas turbine engines (e.g., combustion chambers of aerospace turbines). The objective of this paper was to measure and report the thermal gradient values in a benchmark porous (similar to 15%) APS YSZ TBC, working within the known acceptable maximum temperature envelop conditions of a TBC/substrate system, i.e., T-ysz similar to 1300 degrees C and T-sub similar to 1000 degrees C. In order to accomplish this objective, the following steps were performed. A benchmark APS YSZ TBC exhibiting two distinct thicknesses (similar to 260 and similar to 460 mu m) was manufactured. In addition, a thermal gradient laser-rig was employed to generate a temperature drop (Delta T) along the coated coupon, with the target operate within the acceptable maximum temperature capabilities of this type of TBC/substrate architecture. This target was achieved, i.e., T-ysz values were not higher than similar to 1300 degrees C while the substrate temperatures did not reach values above similar to 1000 degrees C. The Delta Ts for the similar to 260 and similar to 460 mu m YSZ TBCs were similar to 280 and similar to 465 degrees C, respectively. The thermal gradient value for both YSZ TBCs was similar to 0.90 degrees C/mu m, which falls within those reported in the literature for porous APS YSZ TBCs.