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

Abstract Electrochemical properties of γ′-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 °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 °C). Si as alloying element further improves the corrosion behaviour of the oxidised alloy in NaCl.