The oxidation of two ternary Ni–Cu–10 at.% Al alloys in 1 atm of pure O2 at 800–900 °C

The oxidation of the ternary alloys Ni-45Cu-10Al and Ni-30Cu-10Al has been studied at 800-900 degreesC under 1 atm O-2. The presence of 10 at.% Al reduces significantly the oxidation rate of the corresponding Cu-Ni alloys during the initial oxidation stages, even before the establishment of a complete Al2O3 layer. The weight of individual sample of the two ternary NiCu-10Al alloys at 800 degreesC increases more rapidly than at 900 degreesC during the initial oxidation stage. As oxidation proceeds, the weight gain at 800 degreesC slows down to a degree that the total weight gain after 24 h oxidation at 800 degreesC is less than that at 900 degreesC. Due to a faster formation of the Al2O3 layer, which suppresses earlier the further oxidation of Cu and Ni, the external region of the scales grown on Ni-45Cu-10Al contain much less Cu and Ni oxides than those grown on Ni-30Cu-10Al. The transition from the internal oxidation to the selective external oxidation of the most reactive component Al in Ni-Cu-Al alloys is favored by higher values of the Al content, of temperature and of the Cu/Ni ratio. (C) 2003 Elsevier Ltd. All rights reserved.