Microstructure evolution of cobalt aluminide coating on nickel-based superalloys during exposure at 1050 °C

•CoAl coating was deposited by low pressure chemical vapor deposition.•Degradation rate of the CoAl coating vary with substrate superalloys.•γ′ or γ incline to initially grow in the interface between precipitates and matrix.•Initial precipitates have a morphological heredity-effect (MHE) to final γ phase.

Cobalt aluminide coating was deposited onto two directionally solidified Ni-based superalloys (DZ 466 and DS GTD111) by low-pressure chemical vapor deposition. Interdiffusion behaviors of the two coating/superalloy systems were examined during long-term thermal exposure at 1050 °C. It was observed that the inward diffusion of Al and Co from the coating to the substrate and the outward diffusion of Ni and refractory elements such as W, Ta and Cr etc. from the substrate occurred during annealing. This phenomenon induced the degradation of coating matrix and several precipitations of chromium containing phases. Degradation rate and precipitate categories are of great differences for the two studied superalloys. The initial precipitates presented in the coating system had a morphological heredity-effect (MHE) to the final γ phase microstructure. Mechanism referred to elements distribution was discussed.