Thermal shock performance and microstructure of advanced multilayer thermal barrier coatings with Gd2Zr2O7 topcoat

Abstract

Thermal shock behavior of multilayer thermal barrier coatings with yttria-stabilized zirconia (YSZ) and gadolinium zirconate (GZO) top layers was comprehensively investigated to compensate the demand for higher efficiency gas turbine engines. Here, four types of coatings comprised of three-layer and advanced four-layer with HVOF and LPPS bondcoats along with two types of topcoats (YSZ and GZO) were produced and exposed to thermal shock tests at 1100 and 1200 °C. In this regard, the microstructure of GZO, interlamellar and interfacial TGO morphologies, the ratcheting rate and its features, consumption of aluminum, the interdiffusion between bondcoat and the substrate and, ultimately, the performance of layers and their constitutions were evaluated in the multilayered coatings. According to the results, the bimodal microstructure of the top layer GZO assists with improving the sintering resistance and durability of the coating. Moreover, although the four-layer advanced coating with a GZO top layer exhibited a much higher lifetime, for the enhanced performance to keep on, the strength of GZO/YSZ interface and the structure of bondcoat-APS must be improved.