Bauteiloptimierung von dünnwandigen Strukturen für den Hochtemperatureinsatz

Coatings improve the high temperature corrosion resistance of materials by enriching the subsurface zone with elements that form protective oxide scales, which increases the material lifetime. Coatings of interest are aluminum (Al) diffusion coatings formed in a pack cementation process on austenitic steels. The coating procedure may lead to the risk of crack formation within the coating because of the detrimental combination of the brittleness of the Al-rich intermetallic phases that form, the coating thickness, and the mismatch of the coefficients of thermal expansion (CTE) between the material and the coating. By means of a new coating design, Al diffusion coatings consisting of less brittle intermetallic phases with a CTE closer to that of the substrate can be applied with a controlled coating thickness. For this purpose, the required coating manufacturing parameters such as process temperature, process time and powder composition are predicted by a coating design model. The coating design model combines thermodynamic and kinetic considerations on the pack cementation process. The thermodynamic considerations focus on the difference in Al activity between the pack and the intermetallic phases (FeAl, Fe₂Al₅) of the coating, which results in an Al-rich high aluminum (HA) or an Al poorer low aluminum (LA) coating. The kinetic considerations focus on the resulting coating thickness, based on the Al activity determined in the thermodynamic considerations. Further work is under way to extend the coating design to other austenitic materials and nickel base alloys.

Das IGF-Vorhaben Nr. 16881 BG/3 der Forschungsvereinigung DECHEMA e.V., Theodor-Heuss-Allee 25, 60486 Frankfurt am Main wurde über die AiF im Rahmen des Programms zur Förderung der industriellen Gemeinschaftsforschung (IGF) vom Bundesministerium für Wirtschaft und Energie aufgrund eines Beschlusses des Deutschen Bundestages gefördert.