Abstract

The mechanical properties of two types of nanocomposite thin films, artificially multilayered thin films and granular metal thin films, are reviewed. Because of the small microstructural length scales characteristic of these materials, it would be expected that these materials display plastic properties markedly different from bulk solids. Also, because a significant fraction of the atoms in these materials are at interfaces, it might be expected that the elastic properties of nanocomposite thin films would be different from bulk materials. Artificially multilayered thin films, which are composed of alternating layers of two different materials, can display up to 50% enhancements or reductions in certain elastic moduli when the bilayer repeat length is reduced below about 5 nm. Significant enhancements in the hardness are also observed in this range of bilayer repeat length. Granular metal films, which are composed of a ceramic matrix embedded with metal granules of diameters as small as a few nanometers display novel mechanical behavior as a function of metal volume fraction. The hardness behavior suggests that there is a change in deformation mechanism at the metal percolation threshold. In addition, these materials display an enhancement in the apparent elastic compliance as measured by low-load indentation methods which also appears to be correlated with the percolation behavior of the metal.

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