Nowadays, high velocity oxyfuel flame spraying (HVOF) can replace low pressure plasma spraying (LPPS) processes in most applications for hot corrosion protective MCrAlY coatings in hot stage turbine parts.
Compared to LPPS coatings, state-of-the-art HVOF sprayed MCrAlY coating systems show competitive hot corrosion protective properties. Low investment costs of HVOF facilities and a stable, easy process control show a high potential and many advantages in terms of application of the HVOF technology.
Besides protective single layer hot corrosion coatings, HVOF coating systems are often used as bond coatings for ceramic TBC top layers. But the sprayed coatings show a comparatively low surface roughness which leads to a poor adhesion of the ceramic top layer, restricting the application area of HVOF.
This paper deals with a development project which aims on roughness enhancement of HVOF sprayed MCrAlY coatings in order to improve the bonding properties.
In the project’s framework, several HVOF systems and different spray powders were investigated. Parameter sets were developed considering a high surface roughness on the one hand and little coating defects on the other hand.