Improved oxidation behavior of M–20Cr–20Ta (M: Ni, Fe, Co) ternary alloys by formation of complex Cr–Ta-based oxides

The oxidation behavior and microstructural evolution of M–20Cr–20Ta (M: Ni, Fe, Co) alloys are investigated at 1000◦C and 1200◦C in Ar–20 vol% O2. High-temperature oxidation results in growth of bi-layered oxide scales, featuring an outer Cr₂O₃ layer and an inner Cr–Ta oxide layer. The Cr–Ta oxide layer consists of two distinct phases: CrTaO₄ and CrTa₂O₆. Significant improvements in oxidation resistance are found for Co and Fe alloys, in consequence of formation of the Cr–Ta oxides. At 1200◦C, oxidation kinetics approach a cubic growth law after an initial transient stage, underscoring the exceptional protective capabilities of the Cr–Ta oxides.