Kinetic Study of Aluminization of Iron by Using the Pack Cementation Technique

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Abstract
The kinetics of the aluminization of pure iron using the pack cementation technique at 900°C under both argon and 5% atmosphere have been studied. A low Al‐activity master alloy with a composition of 60 atom percent (a/o) Al‐40 a/o Fe was used to avoid the formation of intermetallic phases at the substrate surface. The substrate was wrapped with an alumina fiber sheath to achieve a particle‐free surface and to superimpose a constant porous diffusion barrier for gaseous species. The pack was continuously rotated to tumble the pack contents and eliminate any chemically depleted zone near the substrate. In this simplified system, the rate limiting step for the aluminizing process was series control by gaseous transport from the pack to the substrate surface and solid‐state diffusion in the substrate. , , and activators were studied in the coating processes. Based on the properties of the activators, models were proposed and used to predict the Al uptake as a function of time. Reasonable agreement between the theoretical calculations and the experimental data was demonstrated for the activator where the model was satisfied experimentally. The lack of agreement for and activators occurred for readily demonstrated reasons.

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