Microstructure Evolution and Element Diffusion Behavior of DD6 - Thermal Barrier Coating System in Oxidation Environment

A NiCoCrAlYHf metallic bond coat was deposited on a DD6 nickel-based single crystal superalloy substrate using vacuum arc deposition technology. After heat treatment, a YSZ ceramic layer was deposited on the bond coat by employing electron-beam physical vapor deposition technology for preparing a DD6 - thermal barrier coating system. High-temperature oxidation experiments were conducted on the DD6 - thermal barrier coating system at 1050 ℃ to study the microstructural evolution and element diffusion behavior of the system during oxidation. The results reveal that the thermally grown oxide layer is thickened gradually as the oxidation proceeds, following a parabolic growth law. The oxidation rate constant at 1050 ℃ is 0.26 μm⁻²·h⁻¹. During the oxidation process, the growth of the thermally grown oxide drives the upward diffusion of Al in the bond coat, resulting in the formation of an Al-depleted zone in the metallic bond coat. The thickness of this zone is proportional to the oxidation time. Due to the change in the elemental difference between the bond coat and the single-crystal substrate, Al-depleted zones and γʹ phase-depleted zones are formed in the single crystal substrate. Both zones expand in thickness with the increase of oxidation time. These findings can provide certain guidance for assessing damage and failure of the DD6 - thermal barrier coating system.