Structure and properties of nanocrystalline materials |
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Authors: | C Suryanarayana |
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Affiliation: | (1) Institute for Materials and Advanced Processes, University of Idaho, 83844-3026 Moscow, ID, USA |
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Abstract: | The present article reviews the current status of research and development on the structure and properties of nanocrystalline
materials. Nanocrystalline materials are polycrystalline materials with grain sizes of up to about 100 nm. Because of the
extremely small dimensions, a large fraction of the atoms in these materials is located at the grain boundaries, and this
confers special attributes. Nanocrystalline materials can be prepared by inert gas-condensation, mechanical alloying, plasma
deposition, spray conversion processing, and many other methods. These have been briefly reviewed.
A clear picture of the structure of nanocrystalline materials is emerging only now. Whereas the earlier studies reasoned out
that the structure of grain boundaries in nanocrystalline materials was quite different from that in coarse-grained materials,
recent studies using spectroscopy, high-resolution electron microscopy, and computer simulation techniques showed unambiguously
that the structure of the grain boundaries is the same in both nanocrystalline and coarse-grained materials. A critical analysis
of this aspect and grain growth is presented.
The properties of nanocrystalline materials are very often superior to those of conventional polycrystalline coarse-grained
materials. Nanocrystalline materials exhibit increased strength/hardness, enhanced diffusivity, improved ductility/toughness,
reduced density, reduced elastic modulus, higher electrical resistivity, increased specific heat, higher thermal expansion
coefficient, lower thermal conductivity, and superior soft magnetic properties in comparison to conventional coarse-grained
materials. Recent results on these properties, with special emphasis on mechanical properties, have been discussed.
New concepts of nanocomposites and nanoglasses are also being investigated with special emphasis on ceramic composites to
increase their strength and toughness. Even though no components made of nanocrystalline materials are in use in any application
now, there appears to be a great potential for applications in the near future. The extensive investigations in recent years
on structure-property correlations in nanocrystalline materials have begun to unravel the complexities of these materials,
and paved the way for successful exploitation of the alloy design principles to synthesize better materials than hitherto
available. |
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Keywords: | Nanocrystalline materials synthesis gas condensation mechanical alloying spray conversion structure of grain boundaries properties diffusion mechanical properties ductility improvement electrical properties specific heat thermal expansion optical properties magnetic properties corrosion behaviour catalytic properties applications |
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