Journal
SURFACE & COATINGS TECHNOLOGY
Volume 188, Issue -, Pages 20-26Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.surfcoat.2004.07.111
Keywords
MCrAlY coatings; oxidation behaviour; EB (electron beam) remelting
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Alloys and coatings designed to resist oxidizing environments at high temperatures should be able to develop a surface oxide layer, which is thermodynamically stable, slowly growing and adherent. During oxidation in the temperature range 850-1300 degreesC, MCrAlY coatings should form Al2O3-rich scales, which are reasonably effective for long-term applications under isothermal or thermal cyclic oxidation conditions. This study is concerned with the isothermal oxidation behaviour of high-velocity oxygen fuel (HVOF)-sprayed CoNiCrAlY coatings containing 12 wt.% aluminium. Specimens treated in different ways (ground, polished and EB-remelted) were oxidized at 950 degreesC in synthetic air for various periods of time. Oxidation studies include thermogravimetric weight gain measurements under isothermal conditions in order to quantify the parabolic oxidation rate constant. The microstructure and morphology of as-sprayed and of oxidized coatings were characterised by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The ground and polished samples show internal oxidation as well as relatively high values of the oxidation rate constants. In the case of EB-remelted coatings, the oxide-scale growth rate is substantially smaller and no internal oxidation was observed. (C) 2004 Elsevier B.V. All rights reserved.
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