Effects of Nickel on Interface Morphology during Oxidation of Fe-Cu-Ni Alloys
Steel produced in Electric Arc Furnaces (EAF) contain a high amount of copper that causes a detrimental surface cracking phenomenon called hot shortness. Studies have found that nickel can alleviate hot shortness by increasing copper solubility in the Fe phase, decreasing oxidation rate and promoting occlusion [1-3]. Occlusion is a phenomenon whereby the copper-rich phase becomes incorporated into iron oxides. Nickel promotes occlusion by causing an uneven interface and increasing the number of internal oxides. The uneven interface is likely a result of the two concentration fields resulting from ternary diffusion of nickel, copper and iron in the Fe phase. This work is aimed at explaining why nickel causes wavy oxide/liquid-Cu and liquid-Cu/Fe interfaces. Constitutional super-saturation criterion  was applied to explain uneven interfaces caused by nickel. A model simulating diffusion behaviors of copper and nickel in Fe was developed by coupling Comsol Multiphysics® and Matlab®. Interface concentrations of copper and nickel and perturbation criterion values were calculated as a function of time. Modeling results show that (i) the nickel interface concentration first increases to a peak value then decreases slowly during oxidation process as a result of the change in oxidation rates, and (ii) the alloys with higher nickel contents have more potential for interface breakdown and this occurs within the initial linear oxidation regime.
Andreas Öchsner, Graeme E. Murch, Ali Shokuhfar and João M.P.Q. Delgado
L. Yin et al., "Effects of Nickel on Interface Morphology during Oxidation of Fe-Cu-Ni Alloys", Defect and Diffusion Forum, Vols. 297-301, pp. 318-329, 2010