Microstructure design for blended feedstock and its thermal durability in lanthanum zirconate based thermal barrier coatings

Abstract

The effects of microstructure design on the lifetime performance of lanthanum zirconate (La2Zr2O7; LZO)-based thermal barrier coatings (TBCs) were investigated through various thermal exposure tests, such as furnace cyclic thermal fatigue, thermal shock, and jet engine thermal shock. To improve the thermal durability of LZO-based TBCs, composite top coats using two feedstock powders of LZO and 8 wt.% yttria-doped stabilized zirconia (8YSZ) were prepared by mixing in different volume ratios (50:50 and 25:75, respectively). In addition, buffer layers were introduced in layered LZO-based TBCs deposited using an air-plasma spray method. The TBC with the double buffer layer showed the best thermal cycle performance among all samples in all tests. For applications with relatively slow cooling rates, the thermal durability in single-layer TBCs is more effectively enhanced by controlling a composition ratio in the blended powder, better than introducing a single buffer layer. For applications with relatively fast cooling rates, the thermal durability can be effectively improved by introducing a buffer layer than controlling a composition in the top coat, since the buffer layer provides fast localized stress relief due to its high strain compliance. These research findings allow us to control the TBC structure, and the buffer layer is efficient in improving thermal durability in cyclic thermal environments.