Microstructural evaluation of YSZ/NiCrAlCo-Y2O3 coatings after isothermal oxidation at 1050°C

Abstract

In this study, the microstructure of the bond coat of the YSZ/NiCrAlCo-Y2O3 systems after isothermal oxidation was examined. The ceramic top coating (YSZ) and bond coat (NiCrAlCo-Y2O3) were manufactured by atmospheric plasma spraying (APS) process and were sprayed onto Inconel 718 superalloy. The thickness of the NiCrAlCo-Y2O3 bond coat was 140 ± 10 μm. Isothermal oxidation tests were performed at 1050 °C during 100 and 200 h in static air. The thermally grown oxide (TGO) layer was formed at the interface between the top coat and the bond coat as a consequence of the isothermal oxidation tests. Cross-section samples after isothermal oxidation were evaluated using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The analysis of EDS was performed to the TGO and the lamellas of bond coat near to the TGO. The results showed that the TGO layer was composed mainly of chromium and oxygen as resulting from its diffusion and oxidation. The analysis of the lamellas near to the TGO showed elements such as Ni, Cr, and Co, which are related to the chemical composition of the bond coat. Additionally, Inconel 718 alloys constituents such as Fe and Nb were found in the same area as the result of the diffusion of these elements through the bond coat.