The Ni-base superalloy, IN-718, has been coated with alumina sols. Coated surfaces, carrying alumina layers having thicknesses between 0.6 μm and 3.6 μm show a significantly reduced oxidation rate when compared with uncoated reference surfaces, even if heating temperature is increased up to 900 °C and heating time is extended to 800 h. Alumina layers were prepared via sol-gel processing using a modified Yoldas procedure to obtain alumina sols. No change in rheological sol behavior was observed for more than 1 year of aging under static conditions at room temperature. Depending on pH value, modified Yoldas sols contain a manifold of Al species, among them Al13 polycations. Thermal evolution of sol derived alumina powders depends on Al speciation of parent sols. Depending on sol composition, both gamma-Al2O3 and eta-Al2O3 occur as intermediate transition aluminas. Phase composition and gas phase velocity influence oxygen permeability of thin layers prepared with modified Yoldas sols.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa.de:bsz:105-8553447 |
| Date | 23 July 2009 |
| Creators | Dressler, Martin |
| Contributors | TU Bergakademie Freiberg, Maschinenbau, Verfahrens- und Energietechnik, Dr. sc. nat. Marianne Nofz, Prof. Dr.-Ing. habil. Christos G. Aneziris, Prof. Dr.-Ing. habil. Horst Biermann, Dr. sc. nat. Marianne Nofz |
| Publisher | Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola" |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis |
| Format | application/pdf |
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