High Temperature Oxidation Resistance of Two Ni(Co)CrAlYSi(Hf) Overlay Coatings
Two MCrAlY overlay coatings (NiCrAlYSi and NiCoCrAlYHf) were deposited on a DS superalloy of Ni-Al-Cr-Co-W-Mo-Ta-Hf system by vacuum arc deposition method. The two coatings show a good protection for the DS superalloy during the isothermal oxidation test at 1150 for 100 h. A continuous alumina-based scale was formed at the surfaces of the coated specimens after oxidation. Y2O3, NiO and SiO2 are also detectable in the oxide scale. For the Hf-bearing coating, some HfO2 particles exist at the interface between the coating and the substrate. But after the cyclic thermal oxidation at 1100°C, the Hf-free coating exhibited better oxidation resisitance than the Hf-bearing coating. The HfO2 blocks between the coat and the substrate may be the crack initiation which leads to the failure of the coating.
T. Chandra, K. Tsuzaki, M. Militzer , C. Ravindran
Z. H. Huang et al., "High Temperature Oxidation Resistance of Two Ni(Co)CrAlYSi(Hf) Overlay Coatings", Materials Science Forum, Vols. 539-543, pp. 1146-1152, 2007