The performance of a thermal barrier coating is influenced by the high temperature oxidation behavior of 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. Results show that the HVAF sprayed NiCoCrAlTaY coating presented a dense microstructure and some partially melted particles in a near spherical morphology were deposited on the coating surface. A uniform α-Al 2 O 3 oxide 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 at 1000°C for 100 h. The amount of the mixed oxides did not significantly increase after 200 h oxidation. The large particles on the bond coat surface maintained homogeneous α-Al 2 O 3 oxide scale in 200 h oxidation at 1000°C in air. A model is proposed to explain the formation of nodular-shaped mixed oxides.

Surface morphology of MCrAlY bond coats is one of the factors that affect the oxidation behavior and the thermal stability of thermal barrier coatings. In the present study, the isothermal oxidation behavior of cold sprayed MCrAlY bond coat was investigated at three surface conditions: as-sprayed, polished and shot-peened conditions. The MCrAlY bond coat with sputters adhered weakly on the surface prepared by low-pressure plasma spraying was also employed. The above four types of surface conditions were employed to investigate the effect of the surface morphologies of MCrAlY (M=NiCo, Ni) bond coats on their oxidation behavior. MCrAlYs with the compositions of Ni20Cr10AlY and Ni23Co20Cr8.5Al5.0Ta0.6Y were employed for bond coat deposition. Cold-sprayed Ni20Cr10AlY exhibited a higher oxidation rate than that of the cold-sprayed Ni23Co20Cr8.5Al5.0Ta0.6Y bond coats. After 10 hrs oxidation, the TGO on the as-cold-sprayed bond coat surface was merely constituted by Al 2 O 3 , while the TGO on the bond coat surface attached with sputters was composed of Al 2 O 3 and spinel. After 500 hrs oxidation, Cr 2 O 3 and porous spinel appeared in the TGO on the two surfaces of as-cold-sprayed bond coat. The growth of Ni/Cr-oxides was attributed to the Al depletion. The content of spinel on cold-sprayed NiCrAlY decreased after shot-peening.