AbstractAbstract
[en] Microstructural changes in a metallic oxidation protection coating (Ni-Co-Cr-Al-Y) applied on a nickel base superalloy were investigated by means of scanning and transmission electron microscopy. The changes are due either to thermal mechanical fatigue testing under high thermal gradients or to defined isothermal heat treatments. The coated specimens were quenched from temperatures between 840 and 1100 deg. C to ambient temperature. The resultant phases, their local distribution and compositions were determined by energy dispersive X-ray (EDX) spectroscopy and electron diffraction. Phase equilibria at respective temperatures were determined by thermodynamic calculations based on the CALPHAD method. The calculated and experimentally determined phase distributions were compared. A particular microstructural feature, namely the existence and spatial distribution of spherical γ' Ni3Al precipitates in the coating and the diffusion zone between substrate and coating, was used as a postmortem indicator for the maximum temperature experienced by the specimen during testing. This paper gives a road map for developing a microstructural-based temperature calibration for complex metallic materials using thermodynamic simulations
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S0921509304007385; Copyright (c) 2004 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
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Materials Science and Engineering. A, Structural Materials: Properties, Microstructure and Processing; ISSN 0921-5093; ; CODEN MSAPE3; v. 384(1-2); p. 162-171
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AMBIENT TEMPERATURE, CALIBRATION, COATINGS, ELECTRON DIFFRACTION, FATIGUE, HEAT RESISTING ALLOYS, HEAT TREATMENTS, MICROSTRUCTURE, NICKEL, OXIDATION, PHASE DIAGRAMS, PRECIPITATION, SPATIAL DISTRIBUTION, SPHERICAL CONFIGURATION, TEMPERATURE GRADIENTS, TESTING, TRANSMISSION ELECTRON MICROSCOPY, X RADIATION
ALLOYS, CHEMICAL REACTIONS, COHERENT SCATTERING, CONFIGURATION, DIAGRAMS, DIFFRACTION, DISTRIBUTION, ELECTROMAGNETIC RADIATION, ELECTRON MICROSCOPY, ELEMENTS, HEAT RESISTANT MATERIALS, INFORMATION, IONIZING RADIATIONS, MATERIALS, MECHANICAL PROPERTIES, METALS, MICROSCOPY, RADIATIONS, SCATTERING, SEPARATION PROCESSES, TRANSITION ELEMENTS
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[en] We have measured the oxygen self-diffusivity in mullite ceramics via gas/solid exchange experiments in an atmosphere enriched in the rare stable isotope 18O. The resulting 18O isotope depth distributions were measured by SIMS depth profiling. Our investigation showed that grain boundary diffusion coefficients are about five orders of magnitude higher than lattice diffusivities. While the pre-exponential factors differ by about two orders of magnitude, the activation enthalpies in the volume (433±21 kJ/mol) and in the grain boundaries (363±25 kJ/mol) are surprisingly close to each other
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S0169433202006414; Copyright (c) 2002 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
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CHEMICAL ANALYSIS, DIFFUSION, DISTRIBUTION, ELEMENTS, EVEN-EVEN NUCLEI, INORGANIC ION EXCHANGERS, ION EXCHANGE MATERIALS, ISOTOPES, LIGHT NUCLEI, MATERIALS, MICROANALYSIS, MICROSTRUCTURE, MINERALS, NONDESTRUCTIVE ANALYSIS, NONMETALS, NUCLEI, OXIDE MINERALS, OXYGEN ISOTOPES, PHYSICAL PROPERTIES, SPECTROSCOPY, STABLE ISOTOPES, THERMODYNAMIC PROPERTIES
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[en] Spallation sensitive as-coated EB-PVD TBC systems on Nimonic 75 substrates were investigated by transmission electron microscopy (TEM). Decohesion was observed within the thermally grown oxide (TGO) layer between NiCoCrAlY bond coat and TBC. The TGOs consisted of unexpected oxide phases. In one case the TGO consisted of stratified layers containing spinel phase and chromia. In another case the TGO contained a vitreous Ca-silicate and a crystalline Y-silicate two-phase interlayer. The generation of the respective oxides is initiated by preceeding processing steps before TBC deposition. Suggestions for the manufacture of more confident TBC systems are presented. (orig.)
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4. international symposium on high temperature corrosion and protection of materials; 4. Colloque International sur la Corrosion et la Protection des Materiaux a Haute Temperature; Les Embiez (France); 20-24 May 1996; 12 refs.
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[en] The absence of a chemical reaction at an interface is conventionally thought to be an important criterion in producing a tough ceramic matrix composite (CMC). As a result of this criterion, interphases in CMCs were chosen on the basis of their chemical reactivity. A weak interface results in crack deflection, crack bridging, and, in fiber-reinforced ceramics, fiber pullout, resulting in an increased fracture toughness. In this paper, the authors present microstructural observations on alumina (Al2O3)-barium zirconate (BaZrO3) laminated composites wherein the reaction products that develop during processing resulted in sharp interfaces and appear to be weak enough to deflect cracks. These in situ reaction products in Al2O3-BaZrO3 laminated composites were characterized with the use of a scanning electron microscope, an electron microprobe, and a transmission electron microscope. The phases that develop, ZrO2, BaO·Al2O3, and BaO·6 Al2O3, produced sharp interfaces and are arranged in a sequence that could be predicted by using information from the phase diagram
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