An analysis of the internal oxidation of binary M-Nb alloys under low oxygen pressures at 600–800°C |
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Authors: | F Gesmundo Y Niu F Viani F C Rizzo |
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Affiliation: | (1) Istituto di Chimica, Facolta' di Ingegneria, Universita' di Genova, Fiera del Mare, Pad. D, 16129 Genova, Italy;(2) Corrosion Science Laboratory, Institute of Corrosion and Protection of Metals, Academia Sinica, Wencui Road 62, 110015 Shenyang, China;(3) Departmento de Ciência dos Materiais e Metalurgia, Pontificia Universidade Católica do Rio de Janeiro, Caixa Postal 38008, 22453-900 Rio de Janeiro, Brasil |
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Abstract: | The corrosion of M–Nb alloys based on iron, cobalt, and nickel and containing 15 and 30 wt% Nb has been studied at 600–800°C under low oxygen pressures (10–24 atm at 600°C and 10–20 atm at 700–800°C). Except for the Co–Nb and Ni–Nb alloys corroded at 800°C, which formed external scales of niobium oxides, corrosion under low O2 pressures produced an internal oxidation of niobium. This attack was much faster than expected on the basis of the classical theory. Furthermore, the distribution of the internal oxide in the alloys containing two metal phases was very close to that of the Nb-rich phase in the original alloys. These kinetic, microstructural, and thermodynamic aspects are examined by taking into account the effects of the limited solubility of niobium in the various base metals and of the two-phase nature of the alloys. |
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Keywords: | niobium alloys oxidation high temperatures |
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