Conversion of copper and manganese metallic films to spinel coating

Oxidation of copper + manganese metallic thin films on UNS 430 stainless steel was studied at temperatures of 600–950 °C. The Cu–Mn metallic films were converted to Cu–Mn spinel coating in the temperature range of 600–950 °C as confirmed by X-ray diffraction. Conversion mechanisms of metals to the spinel were investigated. Examination by SEM showed that negligible oxidation of the substrate alloy occurred in the coated samples at temperatures up to 750 °C; a transition layer formed between the substrate and spinel coating at higher temperatures. Cu–Mn spinel coating can provide protection to the metallic substrate at temperatures up to 850 °C. Formation of the spinel coating was due to reactions of CuO, which formed through outward diffusion of copper, with manganese oxides, which formed through inward diffusion of oxygen.