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

Isothermal oxidation was carried out on new gamma/gamma ' 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 degrees 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 degrees C. Furthermore, oxidation leads to phase transformation (gamma/gamma ' to gamma/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 It on the oxidation behaviour was also investigated. (C) 2011 Elsevier Ltd. All rights reserved.