CHARACTERIZATION OF ELECTRODEPOSITED ZIRCONIA MODIFIED NiCoCrAlY COMPOSITE COATINGS ISOTHERMALLY OXIDIZED AT 1000∘C

Abstract

The objective of this study is to evaluate the electrodeposited zirconia (ZrO2)-modified NiCoCrAlY composite coatings subjected to isothermal oxidation at 1000∘C under atmospheric conditions for 24 h. NiCoCrAlY composite coatings with 0, 10, 40, and 60[Formula: see text]wt.% of cobalt contents have been compared. The oxidation studies have revealed that the doping of yttrium (Y) and ZrO2 results in a significant reduction in weight gain, thereby imparting improved oxidation resistance. The morphology of the oxides formed on the surface is analyzed using field emission scanning electron microscope and the phases are identified by X-ray diffraction studies. The major oxidation products formed on the surface of NiCrAlY and Ni10CoCrAlY coatings consist of NiO. In contrast, the surface of Ni40CoCrAlY coating comprises of predominantly CoO and small amount of NiCo2O4. Cobalt oxide (CoO) is formed as the major phase on the surface of the Ni60CoCrAlY coating. The grains on the surface of ZrO2-modified NiCoCrAlY composites are faceted, while such grains are not seen in the case of unmodified coatings. The texture analysis reveals that cooling rate is the deciding factor for the facet formation. The coatings have been characterized extensively using X-ray photoelectron spectroscopy to get in-depth understanding.