The effect of preoxidation on the sulfidation of Ni-20Cr (2–5)Al Alloys |
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Authors: | S W Kim K Ohla H Fischmeister E Fromm |
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Affiliation: | (1) Institut für Werkstoffwissenschaft, Max-Planck-Institut für Metallforschung, Seestraße 92, D-7000 Stuttgart 1, Germany |
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Abstract: | Ni-20Cr alloys with 2, 3.5, and 5 wt.% Al have been preoxidized up to 100 hr at 1000°C in dry H2, in H2/23% H2O and in air and subsequently exposed to an H2/5% H2S atmosphere at 750° C. During the preoxidation treatment different types of oxide scales were formed which affect the sulfidation protection in different ways. Optimum results were obtained for alloys with 3.5 and 5 wt.% Al after 20 hr exposure to dry H2 at 1000°C. A thin Al2O3 scale is formed which decreases the sulfur attack by more than one order of magnitude. Preoxidation conditions for Ni-20Cr-2Al alloys in H2 and for Ni-20Cr-2Al and Ni-20Cr-3.5Al in H2/H2O were observed to be less effective. No improvement was found for preoxidation in air or for Ni-20Cr-5Al alloys preoxidized in H2/H2O. |
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Keywords: | nickel-base alloys sulfidation preoxidation Al2O3 scales Cr2O3 scales |
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