Effects of alloyed Mn on oxidation behaviour of a Co Ni Cr Fe alloy between 1050 and 1250 degC
Abstract 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.