Study On The High Temperature Oxidation Behaviors Of NiCrAlCo Superalloy Sheet Prepared By EB-PVD

By means of SEM with EDS,AFM and Small Angle X-ray Diffraction,oxide's surface topography, phase composition and section topography with composition profiles were investigated on Ni20.3Cr2.1Al4.6Co,Ni23.5Cr1.5Al 2.7Co,Ni12.9Cr7.8Al6.5Co superalloy sheet for 0.3mm thickness, which prepared by Electron Beam-Physical Vapor Deposition (short for EB-PVD) and oxidation treatment at 800℃,900℃,1000℃for different time.The results indicated that the oxidation kinetics curves of the three materials were parabola power law at the initial stage, cubic power law at 800℃,900℃and 4 power law at 1000℃for the long time oxidation, the rate constant of oxidation k were between 1.94×10^-10 and 3.65×10^-9 kg²m^-4s^-1 at the initial stage and 10-13 order of magnitude at 800℃,900℃, 10^-15 at 1000℃. The weight change was less than 1%. According to the theory of the oxidation kinetics, the activation energy of the three materials were 38.305,61.085,47.725 kJ.mol^-1 at the initial stage. They had excellent oxidation resistance and the Ni23.5Cr 1.5Al2.7Co at 900℃was the best of the three materials.According the surface topography SEM they formed a compact oxidation except Ni20.3Cr2.1Al4.6Co. The oxidation was composed by granule of polyhedron, disciform and spinel and so on. They grow up as the time prolonged. The spinel increased in number and grew up as samdwich could be observed from the pictures; there were a lot of oxidation getting together and became a big one at last, it was of structure of spinel.According to the Small Angle X-ray Diffraction, a great deal of Cr₂O₃, NiO made up of a compact layer and there were a lot of NiCr₂O₄,CoCr₂O₄ spinel on the surface. There wasn't any Al₂O₃ observed at 800℃but at 900℃,1000℃. According to section topography SEM the thickness of the oxidation became thick as the time prolonged. Next to the base a continual layer of Al₂O₃ or Cr₂O₃ was formed, the middle layer was the mixed layer of Al₂O₃ and Cr₂O₃ or Cr₂O₃ and NiO, the outer layer was NiO and oxidation of Co. Moreover, the O element diffused into Ni-base and combined with the Al element and divided the base into...