Thermally grown oxide growth behavior and spallation lives of solution precursor plasma spray thermal barrier coatings

The effects of thermally grown oxide (TGO) growth rate and bond coat oxidation behavior on the spallation lives of thermal barrier coatings (TBCs) have been investigated. Yttria partially stabilized zirconia (7YSZ) coatings have been applied to various bond coat/superalloy substrate combinations using the Solution Precursor Plasma Spray (SPPS) process. The coatings have been furnace thermal cycled at 1121 °C, using one hour cycles. A large variation in the spallation lives, from 125 to 1230 cycles, has been observed and are attributed to (a) the spatially averaged TGO growth rate, (b) the maximum localized TGO thickness, (c) the formation of non-alumina oxides with weak interfaces, and (d) the formation of yttrium aluminate stringers in low pressure plasma spray (LPPS) processed bond coat. Of these four factors, the average TGO thickness is the most important. Surprisingly vacuum plasma sprayed bond coated samples consistently had shorter cyclic live compared to air plasma sprayed bond coated samples.