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MECHANOSYNTHESIS OF NANOSTRUCTURED MATERIALS


In Lilliput, Gulliver noted that 'there are some laws and customs in this Empire very peculiar', an observation which might be appropriate for nanophased materials too. Nanophased materials behave indeed differently from their macroscopic counterparts because their characteristic sizes are smaller than the characteristic length scales of physical phenomena occurring in bulk materials. Hereafter, we shall focus on consolidated nanomaterials or on powdered materials whose particle sizes are large as compared to the mean crystallite size which is required to be lower than 100 nm, a conventional limit used for structural materials. Nanostructured materials are bulk solids with a nanometer-scale microstructure in which the chemical composition, the atomic arrangement and/or the size of the building blocks (e.g. crystallites) forming the solid vary on a length scale of a few nanometers throughout the bulk. Nanostructured materials have then a significant fraction of atoms residing in defect environments (grain boundaries, interfaces, interphases). The volume fraction associated with grain boundaries is for instance of ~20 % for a grain boundary thickness of ~0.7 nm and a grain size of 10 nm. They are produced by a large variety of methods, among which high-energy ball-milling has attracted much attention. This interest stems from a fortunate combination of technical simplicity and of complexity both of phenomena occurring during grinding and of mechanosynthesized materials. Mechanical alloying (MA), which is a dry and high-energy milling process, has been used to synthesize all kinds of materials, often with non-equilibrium structures: amorphous, quasicrystalline and nanocrystalline phases, extended solid solutions, alloys of immiscible elements, all sorts of compounds and composites. Mechanical alloying of mixtures of powders of pure elements or of powders of already partially combined elements differs from grinding of materials whose chemical composition remains the same during milling but whose structure or 'microstructure' is expected to evolve. High-energy ball-milling is indeed a way of inducing phase transformations in solids: amorphization or polymorphous transformations of compounds, disordering of ordered alloys are examples among others. High-energy ball-milling is moreover a means of modifying the reactivity of as-milled solids or of inducing chemical reactions between ground reactants at temperatures and at rates at which they would normally not occur (and references therein). High-energy ball-milling offers thus supplementary degrees of freedom in the choice of possible routes for synthesizing new materials. After having evoked some basic features of high-energy ball-milling, we shall present a few selected examples to illustrate its flexible use in the synthesis of nanophased materials and to stress the influence of the competition between damaging and restoring processes on the final state of ground powders.......

【作者名称】: G. LE CAEER, S. BEGIN-COLIN, P. DELCROIX
【作者单位】: Groupe Mailere Condensee et Materiaux, U.M.R. CNRS 6626, Universite de Rennes-1, Campus de Beaulieu, Batiment 11 A, F-35042 Rennes Cedex, France
【关 键 词】: MECHANOSYNTHESIS OF NANOSTRUCTURED MATERIALS
【会议名称】: NATO Advanced Research Workshop on Material Research in Atomic Scale by Moessbauer Spectroscopy Jun 1-6, 2002 Smolenice, Slovak Republic
【期刊论文数据库】: [DBS_Articles_01]
【期刊论文编号】: 101,777,663
【摘要长度】: 2,971
【会议地点】: Smolenice(SK)
【会议组织】: Groupe Mailere Condensee et Materiaux, U.M.R. CNRS 6626, Universite de Rennes-1, Campus de Beaulieu, Batiment 11 A, F-35042 Rennes Cedex, France
【会议时间】: 2002
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【下篇论文】: 外文会议 - SHAPE DISTORTION SIMULATIONS OFCARBON EPOXY COMPOSITES USING A SIMPLIFIEDMECHANICAL CONSTITUTIVE MODEL

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