High temperature oxidation of γ/γ′-strengthened Co-base superalloys

Isothermal oxidation was carried out on new γ/γ′ Co-base superalloys of the system Co–Al–W–B. Appropriate B-contents lead to improved oxidation resistance and oxide layer adhesion. Oxidation at 800 and 900 °C results in formation of Co3O4, CoO, and complex oxides (containing Co, Al, and W). A continuous and protective inner alumina layer forms only at 800 °C. Furthermore, oxidation leads to phase transformation (γ/γ′ to γ/Co3W microstructure) at the matrix/oxide layer interface due to Al-depletion. The effect of additional alloying elements such as Ta, Cr, Nb, Si, V, Mo, and Ir on the oxidation behaviour was also investigated.

► Isothermal oxidation on new γ/γ′ Co-base superalloys of the system Co–Al–W–B in air. ► Appropriate B-content leads to improved oxidation resistance and layer adhesion. ► Oxidation at 800 °C leads to the formation of a protective inner alumina layer. ► Phase transformation at the matrix/oxide layer interface due to aluminium depletion.