Microstructural evolution of a NiCoCrAlY coating on an IN100 substrate

The microstructure of a NiCoCrAlY bond coat (BC) of a thermal barrier coating (TBC) system is investigated in dependence on the heat treatment temperature between 770 and 980 °C by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Besides the major γ and β phases, additionally γ′ precipitates within the γ phase, α-Cr precipitates within the β phase, grains of the Cr-rich intermetallic σ phase and M23X6 phase occur. The γ′ precipitates are observed within the bond coat up to a certain distance from the substrate depending on the temperature. This range decreases with temperature between 920 and 800 °C linearly. At higher temperatures, almost no γ′ precipitates are detected. The α-Cr precipitates within the β grains are found within all β grains for heat treatment temperatures below 770 °C. For higher temperatures up to 860 °C, they exist only within β grains near the substrate and are not proven for temperatures higher than 890 °C. grains are abundant after heat treatment at 770 °C, decreasing in number with increasing temperature until disappearing after heat treatment at 980 °C. For the M23X6, no temperature dependence was observed. crostructural evolution of the NiCoCrAlY coating is suggested to be used as post mortem temperature indicator.