Air Oxidation Behavior of CrNiCo Alloys at High Temperature

Equimolar CrNiCo alloys present promising mechanical properties. For high temperature applications, a candidate alloy would also require good oxidation resistance. Here, we compared the isothermal oxidation response in laboratory air at 1100 °C of CrNiCo and a variant of the same alloy containing additional alloying elements that include Ti, Nb, and Al. This alloy corresponds to the non oxide-dispersion strengthened variant of the novel GRX-810 alloy. While both alloys formed a continuous chromia scale capped with a spinel layer during the transient oxidation stage, non-ODS GRX-810 exhibited faster overall oxide growth kinetics compared to non-ODS CrNiCo. The presence of Ti in carbo-nitride particles located at alloy grain boundaries was correlated with the acceleration of localized outward scale growth during the transient oxidation stages. The behavior of Nb is less clear. Although the carbo-nitrides, which included Nb, oxidized during the transient oxidation stages, its characteristic incorporation into the scale was not apparent. While solid-solution Al enriched the chromia at the metal-oxide interface, the Al content in non-ODS GRX-810 was not sufficient to counteract the deleterious effects of the Ti/Nb-based carbo-nitrides.