Characterization of oxide scales formed on oxyfuel-sprayed Ni-Co-Cr-Al-Y plus ReTa coatings

A high-velocity oxyfuel-sprayed 30 wt.% Ni-20 wt.% Co-30 wt.% Cr-10 wt.% Al-2 wt% Y4 wt.% Re-4 wt.% Ta coating was oxidized between 1000 and 1200 degrees C for up to 200 h in air, and the oxide scales were examined. The dense, sprayed coating consisted mainly of Cr3Ni2, Ni3Al, Ni3Ta, Ni, NiO, Al5Y3O12, and Cr2O3. Intermetallics and some oxides formed during spraying. During oxidation, mainly alpha Al2O3, along with some Al5Y3O12, CoAl2O4, CoCr2O4, Ta2O5, and Ta2O2.2 formed on the coating. The preferential oxidation of Al to form the Al-rich scales resulted in the formation of an Al-depleted region beneath the scales. Rhenium, being the most noble element, was distributed throughout the oxide scale and the coating, without forming any independent oxides.