Effect of B and Cr on the high temperature oxidation behaviour of novel γ/γ′-strengthened Co-base superalloys

Isothermal oxidation was carried out on new gamma/gamma'-strengthened Co-base superalloys of the system Co-Al-W-B and Co-Al-W-B-Cr at 800 and 900 degrees C in air. ToF-SIMS investigations show that boron accumulates in the inner oxide layer which improves the oxidation behaviour and oxide layer adhesion considerably. B-rich precipitations can be observed in the alloy matrix, as well. Appropriate amounts of chromium as additional alloying element lead to further improvement of the oxidation resistance due to the formation of protective inner Al(2)O(3) and Cr(2)O(3) scales. (C) 2011 Elsevier Ltd. All rights reserved.