High temperature oxidation of Nb, NbC and Ni3Nb and oxygen enhanced crack growth

Previous studies have shown that oxygen increased the rates of crack growth in Ni base superalloys at high temperatures (> 800 K) by up to four orders of magnitude over those observed in an inert environment for alloys such as inconel 718, Rene-95 and x 750. In this study, high temperature oxidation studies of pure Nb, NbC and Ni{sub 3}Nb using XPS were undertaken (a) to provide direct confirmation of the oxidation of NbC, (b) to explore the possible role of Ni{sub 3}Nb and (c) to assess the relative reactivity of the latter two phases, along with Nb, with oxygen. Nb, NbC and Ni{sub 3}Nb were oxidized as a function of temperature and constant oxygen exposure, and the results are presented in this communication.

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