Gabriele Rizzi

Chemical stripping of ceramic films of titanium aluminum nitride from hard metal substrates

We report here the result of a study of different chemical stripping methodologies for ceramic coatings deposited by PVD on hard metal substrates. We show that an approach based on the study of the system by surface science techniques leads to the possibility of developing effective stripping methods as well as guidelines for improving the process. We will report about two methods tested for the stripping of layers of titanium aluminum nitride (TINALOX) deposited by Physical Vapor Deposition (PVD) on hard metal substrates. The methods were based on (i) the combination of hydrogen peroxide and potassium oxalate in alkaline conditions, and (ii) potassium permanganate in a concentrated sulfuric acid solution. Of the two methods, the second (permanganate and sulfuric acid) appears to be the most promising, although further studies will be needed to optimize the process.

Development, Characterization and Testing of MCrAlY HVOF Coating Used as Bond Coat for YPSZ Top Coat

MCrAlY coatings (where M stands for Co, Ni, or CoNi) are used as a single overlay coating or as bond coat for thermal barrier coating (TBC) systems. Low Pressure Plasma Spray (LPPS) or Vacuum Plasma Spray (VPS) MCrAlY coatings are considered nowadays the state of the art, nevertheless High Velocity Oxygen Fuel (HVOF) MCrAlY coating is gaining more and more importance due to its quality and to the possible cost reduction in comparison to the state of the art LPPS/VPS coatings. On the other hand the HVOF process tends to have a relatively low surface roughness, which hinders the possibility to act as bond coat for a TBC coating layer. In this work, a HVOF deposition process was developed to obtain a rough MCrAlY coating which can be used as bond coat for yttria partially stabilized zirconia (YPSZ) top coat. Developed parameters were used to apply a TBC system on a stage 2 blade. TBC sections on the same blade have successfully passed thermal fatigue testing according to the specification of an important OEM.Copyright