Oxidation of a CeO2-Dispersed-Al Chromium Coating

In this study, a novel CeO2-dispersed-Al modified chromium coating was produced by chromizing the electrodeposited Ni-10.7 wt% Al-CeO2 composites at 700°C for 8 h. For comparison, samples without CeO2 particles were also prepared. Oxidation at 900°C indicated that the beneficial effect of CeO2 is slight in the initial 10 h and becomes obvious with oxidation in the as-deposited state. During the pack cementation, the inward diffusion of Cr and outward diffusion of Al caused the formation of surface Cr2Al brittle layer, which spalled at 900°C. The accumulation of Al caused the formation of Al-rich-γ’-Ni3Al inner layer, which inversely inhibited the growth of the chromium coating. For Ni-Al-CeO2 composites, the accumulation of CeO2 during chromization at the chromium coating/Al-rich-γ’-Ni3Al interface acted as a diffusion barrier to inhibit the growth of chromium coating, which significantly decreased the diffusion distance of Al from Al-rich-γ’-Ni3Al inner layer to oxidation front and thereby promoted the selective oxidation of Al to form a continuous alumina scale below the outer chromia scale. The CeO2 effects on the chromium coating formation and the oxidation resistance of the as-deposited Ni-Al composites before and after chromization are discussed in detail.