Isothermal oxidation behavior of nicocraltay coating deposited by high velocity air-fuel spraying

The performance of thermal barrier coatings is influenced by the high temperature oxidation behavior of the bond coat. In this paper, NiCoCrAlTaY bond coat was deposited by high velocity air-fuel (HVAF) spraying, and the microstructure and surface morphology of the bond coat before and after oxidation were examined to aim at developing high performance thermal barrier coatings. Results showed that the HVAF sprayed NiCoCrAlTaY coating presented a dense microstructure and some partially melted particles with a near spherical morphology were deposited on the coating surface. A uniform α-Al ₂O ₃ scale was formed on the HVAF sprayed MCrAlY coating surface after the pre-oxidation treatment in an argon atmosphere. A small fraction of nodular-shaped mixed oxides was formed when the MCrAlY coating was oxidized for 100 h at 1000 °C. The amount of the mixed oxides increased less significantly after 200 h oxidation. A homogeneous α-Al ₂O ₃ oxide scale was maintained over the large particles on the bond coat surface after 200 h oxidation at 1000 °C in air. A model is proposed to explain the formation of nodular-shaped mixed oxides.