Innovative solutions for roughness problems related to MCrAlY coatings manufacturing by HVOF I: Base Material/Bond Coat Interface
C. Giolli, D. Russo, A. Lanzi, M. Spagnoli, G. Rizzi, A. Giorgetti, A. Scrivani
MCrAlY (where M is Ni, Co or NiCo) coatings are used as single overlay coating or as bond coat for thermal barrier coating (TBC) systems. Vacuum plasma spray (VPS) McrAlY coatings are considered today to be a state of the art. Nevertheless, high velocity oxygen fuel (HVOF) sprayed MCrAlY coating is gaining in popularity due to its quality and cost effectiveness. On the other hand, HVOF process has some limits: It requires heavy sand blasting of the substrates to obtain an adequate base metal roughness for the good adhesion of the deposited MCrAlY coatings and this causes high interface pollution. Moreover, HVOF process allows to obtain relatively low surface roughness of the MCrAlY coatings, which leads to a poor adhesion of the ceramic yttria partially stabilized zirconia (YPSZ) top coat. Studies performed by the authors tried to resolve these two problems by providing an adequate pollution free interface between substrate and coating and a rough surface of the HVOF coating in order to be used as bond coat for overlaying TBC coating. This paper is the first part of two and addresses the development of a surface preparation method, in order to obtain a completely pollution free surface of the substrate with an adequate roughness to be coated afterwards with HVOF. A new surface preparation process, name eXclen, was set up and HVOF was used to apply MCrAlY coating on the prepared base material. Optical and electronic microscopies were used to evaluate the quality of the interface Base Material (BM)/Bond Coat (BC). It was possible to observe the absence not only of foreign entrapped particles, but also of any chemical contamination or alteration of both coating and substrate materials. The BM/BC interface quality and MCrAlY coating adhesion resulted to satisfy the Original Equipment Manufacturer (OEM) requirements.