Oxidation Property of CoNiCrAlY Coatings Prepared by Various Thermal Spraying Techniques

To protect various gas turbine components against high temperature in the hot sections of power generation plants and aircraft engines, thermal barrier coatings (TBC’s) have been developed and widely used. Conventional TBC’s consist of a MCrAlY (M: Ni, Co, NiCo, etc,) bond coating for oxidation resistance and a ceramic top coating for thermal insulation. High quality coatings of MCrAlYs have been produced mostly by low pressure plasma spraying but other more economical processes are also used depending on the operating conditions of the component to be coated. In this study, CoNiCrAlY powders were deposited on Inconel 718 substrate with three types spraying system, i.e., low pressure plasma spraying, high velocity oxy-fuel spraying, and atmosphere plasma spraying. Specimens were isothermally tested for up to 100 h in air at 1373 K. Mass gain of the coatings was measured. Microstructure of the coating cross sections and the surface oxides were observed with SEM. To identify the crystal structure of the formed oxides, the specimens were analyzed by XRD from the surface.