Corrosion behaviour of Ni-Cr alloys in mixed oxidising gases at 650 °C

Abstract

Binary Ni-Cr alloys containing 5−30 wt% Cr were exposed to Ar-20O2, Ar-20O2-20H2O, Ar-20CO2, Ar-20CO2-20H2O and Ar-20H2O (vol.%) at 650 °C. In dry/wet O2, and dry CO2, 5−25 Cr alloys formed a three-layered structure: an external NiO layer, an inner oxide layer and an internal oxidation zone. The Ni-30Cr alloy formed a continuous chromia layer, with local outer NiO islands in dry/wet O2, but a continuous Ni-rich outer layer in dry CO2. In wet CO2/water vapour alone, all alloys underwent internal oxidation, nickel metal expulsion and NiO formation. Gas composition effects on the Cr concentration required for chromia formation are discussed.