Corrosion properties of novel γ′-strengthened Co-base superalloys

Electrochemical properties of gamma'-strengthened Co-base superalloys with the composition Co-Al-W-B and Co-Al-W-B-Y are studied in comparison with pure Co at ambient temperature in 0.5 M NaCl aqueous solution (pH 5.8). The different materials exhibit comparable corrosion resistance with a limited initial passivation followed by severe pitting corrosion at higher potentials. Oxide layers, formed under isothermal oxidation at 800 and 900 degrees C, provide exceptional protection against pitting corrosion. No breakdown events are observed, even for thin layers formed during short-term oxidation (1 h at 900 degrees C). Si as alloying element further improves the corrosion behaviour of the oxidised alloy in NaCl. (C) 2012 Elsevier Ltd. All rights reserved.