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.

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