Characterization of Oxide Scales Formed on HVOF-Sprayed NiCoCrAlY+(Re, Ta) Coatings
J. H. Ko, J. H. Lee, D. B. Lee
METALS AND MATERIALS International
Abstract
High velocity oxy-fuel sprayed NiCoCrAlY+(Re or Ta) coatings were oxidized between 1000 and 1200 C o in air, and the oxide scales were examined by XRD, SEM/EDS, and EPMA. The unoxidized NiCoCrAlY+Re coating consisted mainly of Ni3Al with some Ni, Cr3Ni2, and Cr3O2, while the unoxidized NiCoCrAlY+Ta coating consisted of Ni3Al with some Ni, Ni3Ta, and Cr3Ni2. During oxidation, -Al2O3, CoAl2O4, CoCr2O4, and Al5Y3O12 formed on NiCoCrAlY+Re, while -Al2O3, CoAl2O4, Al5Y3O12, Ta2O5, and Ta2O2.2 formed on NiCoCrAlY+Ta. For both coatings, -Al2O3 formed easily from the initial oxidation stage. Beneath the oxide layer, an Al-depleted zone existed owing to the significant consumption of Al in the oxide layer.
Key words: Oxidation; Coating; Tantalum; NiCoCrAlY; Rhenium
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