Effect of Y2O3 on Oxidation Resistance of Ni-Al Composite Coatings Before and After Low-Temperature Chromizing

Ni-Al/Ni-Al-Y(2)O(3)composite coatings with 10.5 wt% Al were first developed by the codeposition of Ni and Al/Y(2)O(3)particles, then chromized at 700 degrees C for 8 h to produce a novel Y2O3-modified-/free-Al-containg chromium coating. The oxidation resistance of Ni-Al/Ni-Al-Y(2)O(3 )composite before and after chromization was compared at 900 degrees C for 50 h. The results indicated that Y(2)O(3 )slightly decreased the scaling rate of the electrodeposited alumina-forming Ni-10.5 wt% Al composite coatings, and the reduction effect increased with the extended oxidation time. The inward diffusion of Cr and outward diffusion of Al caused the formation of the surface Cr2Al layer above an Al-depleted area. At the same time, the gradual enrichment of Al in the inner area caused the formation of gamma'-Ni3Al inner layer, which inversely inhibited the inward Cr diffusion due to lower Cr solution in gamma'-Ni3Al. Mixture oxides of (Cr-1-Al-x(x))(2)O-3 formed on the surface Cr2Al spell at 5 h due to lower spallation resistance. After that, Y(2)O(3 )significantly decreased the scaling rate of chromium coatings. The effects of Y(2)O(3 )on the chromium coating formation and the oxidation behavior of the as-deposited alumina-forming Ni-Al composite coatings before and after chromization are discussed in detail.