Oxidation Behavior of Microcrystalline Ni-11.5Cr-4.5Co-0.5Al Superalloy Sheet Fabricated by Electron Beam Physical Vapor Deposition (EB-PVD) at 900°C

摘要

The superior performance of superalloys is well known for their applications at high temperature and under severe environmental conditions. The grain size of the superalloy affects the morphology, the composition of the oxide scale as well as the size, composition and formed on the alumina scale, and has influence in the kinetics. The isothermal oxidation behavior of microcrystalline Ni-11.5Cr-4.5Co-0.5Al superalloy sheet fabricated by Electron Beam Physical Vapor Deposition (EB-PVD) at 900°C up to 96hs in air was investigated in this paper. Mass-gain curves were obtained on testing the alloy in dry air. And characterization of the surface morphology and cross-sections was 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 experiment results indicated that this kind of superalloy sheet showed low oxidation rate. And the very thin oxide scale observed. The oxide scales consisted mainly of mixed oxides. The oxidation kinetics of microcrystalline Ni-11.5Cr-4.5Co-0.5Al superalloy sheet obeyed fourth power law, not parabolic power law predicted by lattice or volume diffusion, which was attributed to the form and growth of density microcrystalline oxide on the surface of microcrystalline Ni-11.5Cr-4.5Co-0.5Al superalloy. The oxide grains were much smaller on microcrystalline Ni-11.5Cr-4.5Co-0.5Al superalloy thereby higher density of grain boundary acted as the routes of the short circuit diffusion could be existed in the oxide scale than that on coarse crystalline alloy.