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1300 |
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Tuesday, June 03, 2008, Room 08 11:50 AM Nanomaterials 1 Most coating materials gain superior coating performance when applied as nanostructured coating, new designed materials and optimized processes show promising results for this |
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Fabrication of bulk nanocrystalline ceramic materials |
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Tomas Chraska* / Czech Academy of Sciences, Czech Republic Karel Neufuss / Institute of Plasma Physics, ASCR, Czech Republic Jiri Dubsky/ Institute of Plasma Physics, ASCR, Czech Republic Pavel Ctibor/ Institute of Plasma Physics, ASCR, Czech Reoublic Mariana Klementova/ Institute of Inorganic Chemistry, ASCR, Czech Republic |
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An alternative method to produce bulk nanocrystalline materials and avoid the powder compaction step is to produce amorphous material by rapid solidification followed by controlled heat treatment to introduce nanocrystalline structure. The extremely high cooling rates in plasma sprayed particles give rise to formation of nonequilibrium phases, which may become amorphous for certain materials. Five different materials studied in this work are based on near-eutectic mixtures of alumina, zirconia and silica. The powder feedstock materials have been plasma sprayed using water stabilized plasma torch (WSP®) and subsequently heat-treated to prepare nanocomposite materials with varying nanocrystallite size. The as-sprayed materials have very low open porosity and are mostly amorphous as determined by XRD. DTA and thermo-mechanical analysis determined that the as-sprayed amorphous materials crystallize at temperatures around 950ºC with an associated volume shrinkage of 1-2%. Short annealing times at the crystallization temperature bring about very fine microstructure with average grain size as small as twelve nanometers. The very fine microstructure was confirmed by transmission electron microscopy. The resulting structure is best described as nanocomposite with very small crystallites embedded in inter-crystallite network. Role of the silica compound on phase composition, microstructure, and mechanical properties of the as-sprayed and annealed materials is discussed. Elastic properties were measured for the nanocrystalline materials. The as-sprayed amorphous materials exhibit high hardness and high abrasion resistance. Both properties are significantly improved in the heat treated nanocrystalline samples thus making the bulk nanocrystalline materials suitable for many applications. |