Internal Diameter Coating Processes for Bond Coat (HVOF) and Thermal Barrier Coating (APS) Systems

Current developments in different industrial sectors show an increasing demand on thermally sprayed internal diameter (ID) coatings. But up to now, the focus of research is mainly on conventional processes such as arc spraying and plasma transferred wire arc spraying (PTWA), especially for cylinder and liner surfaces. However, also efficient HVOF and APS torches are available meanwhile for ID applications. Thus, in the present work, the focus of research is on the ID spraying of bond coats (BC) and thermal barrier coatings (TBC) for high temperature applications. An HVOF ID gun IDCoolFlow mono with a N₂ injection was used to spray dense BCs (MCrAlY). The TBCs (YSZ) were sprayed applying an SM-F100 Connex APS torch. As substrates, steel tubes with an internal diameter of 202.74 mm were used. The morphology and properties of the sprayed ID coating systems were investigated with respect to the substrate pretreatment and the combination of different HVOF and APS spray parameter sets.