The development of internal and intergranular oxides in nickel-chromium-aluminium alloys at high temperature |
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| Authors: | F.H. Stott G.C. Wood Y. Shida D.P. Whittle B.D. Bastow |
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| Affiliation: | 1. Corrosion and Protection Centre, University of Manchester Institute of Science and Technology, Manchester, U.K.;2. Present address: Central Research Laboratories, Sumitomo Metal Industries Limited, Amagasaki, Japan;3. Lawrence Berkeley Laboratory, University of California, Berkeley, California, U.S.A.;4. British Nuclear Fuels Ltd., Windscale and Calder Works, Sellafield, Seascale, Cumbria, U.K. |
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| Abstract: | The development of internal oxides, intergranular oxides and internal voids in Ni-15.1Cr-1.1Al and Ni-28.8Cr-1.0Al during oxidation in 1 atm oxygen at 1000° to 1200°C has been studied. In both cases, the formation of an external Cr2O3-rich scale causes vacancies to be generated in the alloy due to the different diffusion rates of chromium towards the alloy-scale interface and of nickel back into the bulk alloy. At 1000°C, condensation of these vacancies at the alloy grain boundaries facilitates formation of intergranular oxides while, at 1200°C, the vacancies condense to give voids in the grains and grain boundaries. Internal oxides are formed at both temperatures. The internal and intergranular oxides are mainly α-Al2O3, although some Cr2O3-rich oxides are produced near the alloy-scale interface. Possible mechanisms for the development of the internal and intergranular oxides in these alloys are discussed and related to the observed oxide morphologies and compositions. |
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