The influence of yttrium additions on the oxidation resistance of a directionally solidified Ni-Al-Cr3C2 eutectic alloy |
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Authors: | F. H. Stott G. C. Wood J. G. Fountain |
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Affiliation: | (1) Corrosion and Protection Centre, University of Manchester Institute of Science and Technology, Manchester, England |
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Abstract: | Isothermal oxidation of a directionally solidified Ni-Al-Cr3C2 eutectic alloy results in development of an external -Al3O3-rich scale. However, this scale breaks down after relatively short times at temperature and a less protective Cr2O3-rich scale is formed, together with substantial internal oxide in the alloy. In an attempt to maintain the external -Al2O3-rich scale and prevent damaging subscale oxidation, modified yttrium-containing directionally solidified alloys have been developed. The oxidation resistance of these alloys at 1000 and 1100°C in flowing air has been investigated and found to be considerably better than that of the corresponding yttrium-free alloy. At both temperatures an external -Al2O3-rich scale is produced and is retained for much longer periods than on the yttrium-free alloys during isothermal and thermal cycling oxidation. Some scale breakdown does occur during thermal cycling at 1100°C, but -Al2O3 is able to re-form as the surface oxide. However, although external -Al2O3-rich scales are retained for long periods on these alloys, some oxide penetration into the alloy beneath these scales does occur where coarse carbide fibers intersect the alloy surface. This is associated with relatively poor scale integrity at these intersections. |
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Keywords: | oxidation yttrium additions directionally solidified eutectic alloys |
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