LAUSR

The oxidation characteristics of Co-17Re-Cr-Ni alloys with varying Cr (18 at.% and 23 at.%) and Ni (8 at.%, 15 at.%, and 25 at.%) concentrations have been investigated at 1000°C in air. The corrosion resistance of the Co-17Re-23Cr- x Ni alloys improved with increasing Ni concentration, in turn facilitating the formation of a protective chromia layer. This observation can be attributed to an enhanced Cr diffusivity, as quantitatively confirmed by the determination of the Cr diffusion coefficients of the Co-17Re-18Cr- x Ni alloys. Reduction of the Cr concentration from 23 at.% to 18 at.% deteriorated the oxidation behavior, as mass loss was detected. Unexpectedly, the alloy with intermediate Ni concentration exhibited the best oxidation behavior among the various Co-17Re-18Cr- x Ni alloys studied. Accelerated σ phase formation in the Co-17Re-18Cr-25Ni alloy trapped a significant amount of Cr, lowering its concentration in the alloy matrix and, thus, decelerating the Cr 2 O 3 formation.