Abstract
The isothermal oxidation of Co-Cr alloys containing 0–30% Cr in 760 Torr oxygen at 1000° C has been studied kinetically and by appropriate physical techniques. Chromium additions to cobalt increase the parabolic oxidation rate to an almost constant level from 2 to 15% Cr, while further additions to 20–30% Cr decrease the rate. All the alloys produce a virtually pure CoO layer outside a layer containing Co-Cr spinel particles in a Cr3+ -doped CoO matrix. The variation of oxidation rate with alloy chromium content is explained in terms of the complex interplay of doping, blocking of cation transport by voids and spinel particles and short circuiting by transport of dissociative oxygen across these voids and other processes, internal oxidation making a negligible direct contribution to weight gain. Complete spinel layers are never quite developed under the conditions studied, although formation of spinel does slow the oxidation rate. The improved protection eventually obtained at higher chromium levels is produced by the tendency to form a Cr2O3 healing layer.
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Wright, I.G., Wood, G.C. The isothermal oxidation of Co-Cr alloys in 760 Torr oxygen at 1000°C. Oxid Met 11, 163–191 (1977). https://doi.org/10.1007/BF00606542
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DOI: https://doi.org/10.1007/BF00606542