Oxidation Behaviors of Microcrystalline As-deposited Ni-23.5Cr-2.66Co-1.44Al Superalloy Sheet Fabricated by Electron Beam Physical Vapor Deposition at 1000 °C

摘要

The superior performance of superalloys were well known for their applications at high temperature and under severe environmental conditions. Isothermal oxidation of microcrystalline as-deposited Ni-17.78Cr-19.85Fe-0.52Al(wt%) superalloy sheet fabricated by Electron Beam Physical Vapor Deposition (EB-PVD) exposed at 1000 °Cin air up to 100 hours was investigated. The characterization of the surface morphology and cross-sections were performed on samples isothermally oxidized for different exposure times. Surfaces and cross-sections of the oxidized specimens were studied by scanning electron microscopy (SEM). Phase identification of the oxide scale was performed by glancing angle X-ray diffraction (GAXRD) and energy dispersive X-ray microanalysis (EDX). The results showed that the oxidation kinetics of microcrystalline Ni-23.5Cr-2.66Co-1.44Al(wt%) superalloy sheet followed a cubical power law at initial oxidation stage and fourth power law for long oxidation terms. It was found that the oxide scales consisted mainly of an outer Cr2O3 oxide layer, and inner, mixed of NiO and NiCr2O4 oxides. Al2O3 layer formed at the scale/substrate interface after long time oxidation. This showed that Cr atoms outwards diffused was quicker than that of Ni atoms. And the Al atoms outwards diffused was slowest in this kind sheet at 1000°C.