Effects of alloyed Mn on oxidation behaviour of a Co-Ni-Cr-Fe alloy between 1050 and 1250 °C

The effects of Mn content on the oxidation behaviour of a Co-base superalloy with compositions of Co-29Cr-21Ni-23Fe-2.2Nb-1.6Si-xMn (x = 0, 0.5, 1, 2) (Co22 alloy for short, wt.%) have been studied. Isothermal oxidation behaviour was investigated, and it showed kinetics of the Mn-containing samples followed a two-stage parabolic law. In the absence of Mn, scales on Co22 alloys consisted mainly of Cr2O3 and SiO2, and small amounts of Fe-Cr, Ni-Cr spinel nodules formed on the surface. When Mn was added, a triple oxide layer could be observed, consisting of Mn-Cr spinel as outer layer, Cr2O3 as middle layer and SiO2 in the innermost layer.