Investigation of Cold Sprayed Bond Coat: Microstructure and Oxidation Behavior

MCrAlY bond coating (M for Ni, Co, or a combination thereof) are widely used to protect the hot components, e.g., blade and vanes, in gas turbines. When the operating temperature of the components is not too high, the coatings are required to provide resistance against the hot corrosion attack. Bond coats are typically manufactured using thermal spray deposition techniques such as air-plasma, low-pressure plasma and high-velocity oxygen-fuel spraying. A common feature for these deposition processes is that they all require significant heating of the sprayed material to achieve either partial or total melting of the feedstock powder particles. The predominant drawback to these techniques is that their inherent high temperatures inevitably lead to changes in the coating microstructure throughout the deposition process. Additionally, the coating oxide content can be considerable due to in-process surface oxidation of the sprayed material. Unlike thermal spray process, the recent development of cold spray technology has made possible the deposition of dense and oxide-free coating; with good adhesion and with almost no degradation on the microstructure of the coated materials. The present study is part of an ongoing research project that aims to develop high performance MCrAlY bond coats by means of cold spray process in order to have complete control of the bond coat material microstructure. The objective of the work presented in this paper comprises two parts: (1) To perform a detailed investigation of cold sprayed MCrAlY bond coats in order to assess any changes in the microstructure of the coatings compared to the original feedstock powder. (2) To investigate the oxidation behavior of MCrAlY coatings manufactured by cold spray, using isothermal oxidation testing. Different analytical technics, including SEM, EDS, XRD, were used to conduct such study