Effect of Spray Parameters on MCrAlY In-Flight Particle Oxidation and Coating Microstructure Deposited by Internal Diameter High Velocity Air Fuel (ID-HVAF)

Aircraft gas turbine blades operate in aggressive, generally oxidizing, atmospheres. A solution to mitigate the degradation and improve the performance of such components is the deposition of thermal barrier coatings (TBCs). Specifically for bond coats in aerospace applications, High Velocity Air Fuel (HVAF) is very efficient for coating deposition. However, internal diameter (ID) HVAF has received little attention in the literature and could be a promising alternative to limit oxidation during spraying when compared to conventional methods. The main objective of this study is to analyze how the ID-HVAF process influences the microstructure of NiCoCrAlY coatings. To that end, an i7 ID-HVAF torch is used to deposit NiCoCrAlY splats on a steel substrate with different stand-off distances. The deposited splats showed the presence of craters, and both partially melted and deformed particles at the surface. The particle velocity data was recorded, and the splat deformation and amount of particles deposited was shown to be directly corelated to the stand-off distance. The material composition analyzed and quantified by Energy Dispersive Spectroscopy (EDS) did not reveal any traces of in-flight of particle oxidation, but further investigation is required. This study provided a preliminary understanding towards the importance of stand-off distance on the splat deformation and in-flight oxidation.