Abstract
The assumptions involved in Wagner's original treatment of alloy depletion profiles are examined and found to be acceptable for many situations. Finite difference analyses do not result in profiles which are significantly different from those obtained by the much simpler analytical solution once steady-state parabolic growth is established. Consequently an analytical solution is preferred and its combination with the classical Wagner expression for scale growth leads to a unified description of alloy oxidation when only the least noble metal is oxidized. The description is tested for an Fe-27.4wt.% Cr alloy oxidized at 1273°K and agreement between theoretical and experimental results is satisfactory. Alternative treatments of alloy oxidation which require that there be no recession of the alloy-scale interface are discussed and it is concluded that this assumption is unnecessarily restrictive in many cases. Suggestions that the oxidation of austenitic steels is controlled by diffusion in the alloy and that an interfacial transfer step is of importance in determining the oxidation rate in some cases are shown to be based on invalid assumptions. An analytical solution to the diffusion equation is developed for the case when a phase change occurs in the alloy because of less noble metal depletion and an expression is also presented for the profile developed in the limiting case where depletion is determined by scale evaporation.
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Bastow, B.D., Whittle, D.P. & Wood, G.C. Alloy depletion profiles resulting from the preferential removal of the less noble metal during alloy oxidation. Oxid Met 12, 413–438 (1978). https://doi.org/10.1007/BF00612088
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DOI: https://doi.org/10.1007/BF00612088