Thermal shock behavior of multilayer and functionally graded micro- and nano-structured topcoat APS TBCs

Abstract

Performance of air plasma sprayed (APS) thermal barrier coatings (TBCs) with multilayer and functionally graded topcoat were investigated in thermal shock conditions. Ceria-yttria stabilized zirconia (CSZ) and micro- and nano-structured yttria stabilized zirconia (YSZ and YSZ-N) were used to produce coating samples. The samples were classified into four families, namely single-layer, double-layer, triple-layer and functionally graded (FG). To measure thermal shock resistance, the heating/water quenching cycles were repeated 70 times and 30% destruction of the coating was considered its functionality limit. Thus, cycles did not continue for those coatings that were destroyed more than 30%. At the end of each cycle, the surface and edge damage were determined from the photos of samples. Furthermore, scanning electron microscope (SEM) images and energy-dispersive spectrometer (EDS) analysis of samples’ cross-section were taken before and after the test. After collecting the experimental data, effects of various factors on outputs were investigated. The results showed that YSZ-N single-layer coating and triple-layer with CSZ as a top layer, has less thermally grown oxide (TGO) thickness and best performance in thermal shock conditions.