Isothermal oxidation of bulk dense Fe2AlB2 and Mn2AlB2 phases in 700–1000 °C temperature range

Abstract

Herein, the isothermal oxidation of Mn2AlB2 and Fe2AlB2 MAB phases in air was studied. When oxidized at 700 °C, the weight gain kinetics for Mn2AlB2 are sub-cubic up to 96 h as a result of the formation of a Mn2-xAlxO3 protective layer. Severe spallation of the oxides formed was observed at 800 °C and 900 °C, limiting its service temperature. The oxidation kinetics at 900 °C, for Fe2AlB2 become sub-parabolic beyond 60 h due to the formation of a passivating Αl4Β2Ο9 with excellent corner adherence. At both 800 °C and 1000 °C, however, the oxidation is rapid and severe. Therefore, both Mn2AlB2 and Fe2AlB2 may be used in practical application up to 700 °C and 900 °C, respectively. As far as we are aware, Fe2AlB2 is the second transition metal boride that is oxidation resistant at 900 °C; the first, MoAlB, is also a MAB phase.