Formation of a Continuous β-NiAl Layer Near the Interface in a γ+β MCrAlY

A thermal cycling test was carried out in an EB-PVD MCrAlY – superalloy system, the result of which showed that a continuous β-NiAl layer formed in the MCrAlY coating near the coating–superalloy interface. Since β phase can be as a reservoir of Al, the formation of the β layer, in which much Al is reserved, is probably beneficial to the coating’s life. An oxidation-diffusion model was adapted to simulate the development of the microstructures in the coating-superalloy system. The simulation results indicate that the formation of the β layer was strongly related to the high Al activity in the substrate; if the Al activity of the substrate was high enough, a β layer could be built up in the coating near the coating-substrate interface.