An in-situ formed ceramic/alloy/ceramic sandwich barrier to resist elements interdiffusion between NiCrAlY coating and a Ni-based superalloy

Abstract

NiCrAlY coatings are widely applied on various alloy components to enhance oxidation and/or corrosion resistance at high temperatures. However, elements interdiffusion occurs between them due to composition difference. Although various diffusion barriers (DBs) are reported, this problem is still far from completely solved as most ceramic barriers suffer from poor adherence, while the metallic barriers play a limited role. In this study, NiCrAlY coating was deposited onto a second-generation single-crystal superalloy by arc ion plating. A novel simple method is provided to address elements interdiffusion. By pre-oxidation at a moderate temperature, a thin scale of Ni(Co)O forms at the alloy surface. It transforms to be an alumina/NiCoCr alloy/alumina sandwich by an in-situ reaction with the overlaying NiCrAlY coating and the alloy substrate at high service temperatures, which offers good barrier ability in conjunction with strong adhesion. In the presence of such an alumina/alloy/alumina DB, the NiCrAlY coating provides high resistance to oxidation and scale spallation for the alloy substrate.