Development of APS MCrAlY Dense Bond Coats

The objective of this study was to mimic the microstructure of MCrAlY coatings sprayed using HVOF (High Velocity Oxy-Fuel) processes by using an Air Plasma Spray (APS) process in order to improve oxidation and spallation life of MCrAlY APS coatings. Figure 1 shows the typical microstructures obtained when spraying bond coats using the (a) HVOF process, and (b) the APS process. The microstructures developed by each process are very different. The HVOF process produces a dense coating that protects the substrate material against oxidation and also serves a bond coat for the top Thermal Barrier Coating (TBC) coating. APS MCrAlY coatings typically contain more internal defects (pores, oxides, particle splat boundaries) and do not provide the same level of oxidation protection as a dense HVOF coating. APS coatings add-in thermal expansion mismatch and adhesion when used as a bond coat layer between the substrate and the TBC.