Study On The High Temperature Oxidation Behaviors Of Annealed Ni-Based Superalloy Sheet Prepared By EB-PVD

The oxidation kinetics, surface topography, composition of the oxide film formed by oxidation treatment of original and vacuum heat-treated states at 800℃, 900℃, 1000℃were investigated on 72.8Ni20.3Al4.6Cr2.1Co superalloy sheet deposited by Electron Beam-Physical Vapor Deposition (EB-PVD), by means of TG, SEM with EDS, SAXD and XPS.The results indicated that the weight reduction of the specimen caused by the split and desquamation of oxides from matrix in the environment of cold and heat alternation of the heat-treated alloy was less conspicuous than original. The integrity of the oxide film composed by NiO, Cr2O3 was getting better as the time prolonged and it was more compact of heat-treated alloy.The split and desquamation of the surface oxides is bad for the oxidation resistance. It was because of the symmetrical structure that it showed better oxidation resistance of the heat-treated alloy.At the initial stage, the isothermal oxidation kinetics of the heat-treated alloy was quartic power law at 800℃, cubic power law at 900℃. Because of the split and desquamation of the surface oxides at 1000℃, it appeared weight reduction at the initial stage, but continuous gain from then on. At the posterior stage, the oxidation kinetics was all parabolic power law at 800℃, 900℃and 1000℃. The activation energy of the heat-treated alloy was 23.929kJ/mol, which was larger than the original state. The oxide film composed by NiO, Cr2O3,α-Al2O3, NiCr2O4, CoCr2O4 and NiAl2O4 granule with the shape of samdwich, rounded protuberance and spinel etc developed by the way that the spinel foemed as the 2nd phase on the substrate with large coverage. It comprised almost no Al2O3 at 800℃and a little at 900℃, but a great deal at 1000℃.