Elemental diffusion and microarea evolution of YSZ/NiCoCrAlYHf coated single crystal superalloy after thermal exposure

The interaction between the bond coat (BC) and superalloy substrate under thermal conditions is a significant factor contributing to the failure of thermal barrier coating (TBC) systems. In this paper, specimens of Yttria-stabilized zirconia (YSZ)/NiCoCrAlYHf coated single crystal superalloy DD6 were thermally exposed at 1050 °C for up to 300 h, and the evolution of the interface area was investigated through the analysis of composition-microstructure-induced performance changes. Microstructural characterization shows the initial γ+γ′ IDZ transforming into a single γ structure and extending into the substrate, which is related to the elemental diffusion. Characteristics of microstructure were further quantified using image recognition and labeling based on Cellpose algorithm. The results visually demonstrate the coarsening of γ′ in the BC/substrate interface area. Diffusion kinetics calculations indicated that the BC and the adjoining areas exhibited higher diffusivity. By combining creep performance metrics and physical models of creep, the creep resistance degradation in the interface region were explained. Ultimately, a mechanism of the performance degradation in the interface region due to elemental diffusion and microstructural evolution was proposed.