Oxidation behavior of HVOF sprayed nanocrystalline NiCrAlY powder

This paper describes recent progress on the research into improving the oxidation behavior of the bond coat using a HVOF nanostructured NiCrAlY coating. Commercially available NiCrAlY powder was mechanically cryomilled and HVOF sprayed onto Ni-based alloy to form a nanocrystalline bond coat. The powder and coating structure were characterized by XRD, SEM, and TEM. Oxidation experiments were performed on the coating to form the thermally grown oxide layer (TGO). After heat treatment at 1000 degreesC for 24 and 95 h, a homogeneous alpha-Al2O3 layer was formed on top of the bond coat. The oxide layer was analyzed and compared to the coating sprayed using the as-received powder. As shown in the results, the nanostructured characteristic of the coating and the presence of Al2O3 within the cryomilled powders (oxidation occurred during cryomilling process) seem to affect the nucleation of the alumina layer on the top of the coating. The formation of a continuous TGO layer protects the coating from further oxidation and avoids the formation of mixed oxide protrusions, such as those presented in the coating sprayed using the as-received powder. (C) 2002 Elsevier Science B.V. All rights reserved.