Thermisch gespritzte Korrosionsschutzschichten für sulfidierende Atmosphären (Thermal Sprayed Coatings for Reducing Sulfidizing Atmospheres at High Temperatures)

Thermal sprayed coatings of the intermetallic TiAl were applied on ferritic steels using plasma spraying and HVOF spraying methods. The specimens were investigated under reducing sulfidizing conditions in an Ar-H2-H2S- and a CH4-CO-CO2-H2-H2S-atmosphere. The experiments were carried out at 700°C for up to 1000 h. A very good corrosion resistance could be achieved in the Ar-H2-H2S-atmosphere. The coating remained well adherent and free of cracks or spallation. On the surface and along the coating lamellae slow growing Al- and Ti-oxides and Ti-sulfides had formed. The substrate material remained free of attack. The high carbon activity of the CH4-containing atmosphere led to a deposition of carbon within the coating lamellae and to subsequent formation of Ti-carbides which caused a severe degradation of the coating due to their high growth rate. In this case a sealing of the surface porosity e.g. by laser treatment has to be applied. Paper text in German.