Characterization and oxidation behavior of NiCoCrAlY coating fabricated by electrophoretic deposition and vacuum heat treatment

Electrophoretic deposition (EPD) was showed to be a feasible and convenient method to fabricate NiCoCrAlY coatings on nickel based supperalloys. The microstructure and composition of the NiCoCrAlY coatings after vacuum heat treatment were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDAX). Isothermal-oxidation test was performed at 1100 °C in static air for 100 h. The results show that the major phases in electrophoretic deposited and vacuum heat treated NiCoCrAlY coating are γ-Ni and γ′-Ni3Al phases, also there is an extremely small quantity of Al2O3 in the coating. Composition fluctuations occur in the coating and a certain amount of titanium diffuse from the superalloy substrate to the top of the coating during vacuum heat treatment. The oxidation test results exhibit that the oxidation kinetics of this coating has two typical stages. The protective oxide layer is mainly formed in the initial linear growth stage and then the oxide layer hinders further oxidation of the coating in the subsequent parabolic growth stage. The coating can effectively protect the superalloy substrate from oxidation. A certain amount of rutile TiO2 is formed in the coating during oxidation and it is adverse to the oxidation resistance of the coating.

Research highlights▶ Electrophoretic deposition (EPD), a low cost technique, was shown to be a feasible and convenient method to fabricate NiCoCrAlY coatings on nickel based supperalloys. ▶ The microstructure and composition of the NiCoCrAlY coatings were characterized by XRD, SEM and EDAX, then the dispersal behavior of some elements and other characteristics were expounded. ▶ Isothermal-oxidation tests were performed at 1100 °C in static air for 100 h. The isothermal-oxidation kinetics and oxidation products of this coating were investigated.