Effect of interdiffusion between Ni-Al coating and substrate on microstructure stability of single crystal superalloy

The coatings applied on gas turbine blade of single crystal superalloy are required to have a high adhesive strength with the substrate. The interdiffusion between coatings and substrate alloys is concerned due to its impact on the microstructure stability of the superalloy substrates. In view of the importance of the interdiffusion behavior, Ni-Al coatings with 10.90%(mass fraction), 14.30% and 17.60% Al respectively are prepared on the second generation single crystal superalloy René N5 by electron beam-physical vapor deposition (EB-PVD). Correspondingly, the coatings are composed of γ+γ′ two phases, γ′ single phase and γ′+β two phases, respectively. The effect of the interdiffusion between Ni-Al coatings and single crystal substrate on the microstructure stability of the superalloy substrate is investigated. It is found that the γ/γ′ coherent structure of the single crystal substrate is destroyed by inward diffusion of Al. However, the depth of the destroyed zone in the substrate has not positive correlation with Al concentration. For the coating with 14.30% Al, the interdiffusion induced damage of the substrate is most severe. The increasing of Al concentration in the Ni-Al coatings promotes the formation of TCP phase in the diffusion zone of the substrate.