51316-7840-Diffusion Modeling of Aluminide Coatings

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Product Number: 51316-7840-SG

ISBN: 7840 2016 CP

Author: Vilupanur Ravi

Publication Date: 2016

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The deleterious effects of corrosion are mitigated by the application of coatings that can form a protective oxide layer. Halide Activated Pack Cementation (HAPC) is one such coating method in which a halide vapor is generated within a pack and undergoes reactions that ultimately result in the coating element e.g. Al being deposited and diffusing into the substrate. In this study the solid state diffusion of aluminum into stainless steel substrates was modeled using a popular computing environment i.e. MATLAB.UNS S30400 austenitic stainless steelwas aluminized for various times at 850°C. Samples were cross-sectioned for analysis by optical microscopy and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS). The coating thickness for each layer was measured and concentration profiles were determined. The Boltzmann-Matano method was applied to each concentration profile to determine the diffusion coefficients of aluminum in the coating and substrate phases assuming a semi-infinite substrate. The Boltzmann-Matano method was further refined following the approach of Dayananda to determine an error function solution to Fick’s Second Law in a multicomponent solid solution. The experimental results were found to be consistent with the model predictions. This model can be utilized to predict coating thickness the aluminum concentration profile and phases in the coating at 850°C as a function of time.