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– x Mn ( 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 Cr 2 O 3 and SiO 2 , 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, Cr 2 O 3 as middle layer and SiO 2 in the innermost layer.