Design model for diffusion coatings formed via pack cementation

A. Naji, M.C. Galetz, M. Schütze

Coatings improve the high temperature corrosion resistance of materials by enriching the subsurface zone with elements that form protective oxide scales, which increase the material lifetime. Interesting coatings are aluminum (Al) diffusion coatings formed in a pack cementation process e.g., on austenitic steels. The coating procedure may lead to the risk of crack formation within the coating because of the detrimental combination of high 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 the presented coating design model.

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