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Tuesday, June 03, 2008, Auditorium 2 4:00 PM Junior Session This session will deal with different topics, most promising young talents, both from industry and universities will report shortly about their work. This session is accompanied by a special poster exposition. All visitors of this session are allowed to elect their favorite contribution, the winner will be anounced on the awards banquet |
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A comparative microstructural investigation of nanostructured and conventional Al2O3 coatings deposited by plasma spraying |
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Dimitris Zois* / University of Ioannina, Greece Michalis Vardavoulias / Pyrogenesis S.A, Greece Aggeliki Lekatou/ University of Ioannina, Greece Ioannis Panagiotopoulos/ University of Ioannina, Greece Athanasios Vazdirvanidis/ Hellenic Centre for Metal Research, Greece |
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Nanostructured and conventional Al2O3 powders have been plasma sprayed, under the same parameters, to produce coatings. The nanostructured powder was derived by mechanical attrition techniques and composed of agglomerates of nanoparticles, whereas the conventional powder consisted of solid granules. In order to keep the beneficial effect of the nanostructure in the final coating, a fraction of the powder?s nanostructure should be retained in coating after spraying Dissimilarities were noticed between the two types of coating, concerning porosity, roughness, deposition efficiency and á Al2O3 to ã Al2O3 proportions, which are related with the different percentages of semimolten particles in the structure of the coatings. The nanocoatings retained a higher percentage of semimolten particles than the conventional coatings, due to the microporosity of the nanoparticle agglomerates, compared to the conventional solid granules. The molten part of both conventional and nanostructured coatings consisted of ã Al2O3 of columnar structure. In order to investigate the mechanism of the melting front advance towards the particles interior during their presence inside the plasma stream, the particles were sprayed directly into distilled water. The nanostructured particles formed mainly hollow spheres, whereas the conventional particles formed mainly compact spheres. The internal porosity of the solidified nanoparticle agglomerates, which affected the overall coating?s porosity, was linked to the hollow sphere phenomenon. |