Oxygen permeability of Fe‐Ni‐Cr alloys at 1100 and 1150 °C under carbon‐free and carbon‐containing gases

Abstract

Wagner's model of internal oxidation allows the prediction of an alloy's critical concentration of oxide forming metal required to achieve a protective oxide scale at high temperatures. The model depends on oxygen permeability in the alloy, but this parameter has not been evaluated for the Fe‐Ni system, and the influence of carbon‐bearing gases is unknown. Oxygen permeability measurement by internal oxidation of Fe‐Ni‐Cr alloys, reacted at 1100 and 1150 °C is described. Exposures in Rhines packs and flowing CO‐CO 2 gas mixtures serve to assess the influence of carbon on oxygen permeability at the Fe‐FeO equilibrium oxygen potential. Oxygen permeability in Fe‐Ni increases with iron content in a non‐ideal manner in both gas environments. Higher permeability is found in carbon bearing gases for iron‐rich alloys, and the size of this effect increases with temperature.