New findings on metallic glass

Metallic glass is interesting for electrical conductors and superhard coatings. Researchers in Linköping and Uppsala have now shown that completely amorphous metal carbides can be grown in thin films.

Unlike metals and most alloys, amorphous materials, like glass, do not have a crystalline structure and thus no “seams”. This property is desirable for applications including the wear surfaces on tools.

The latest discovery by materials physicists Martin Magnusson, Linköping University, and Ulf Jansson, Uppsala University, and their colleagues is that metallic glass can consist of a mixture of two internal structures: a carbon matrix and a carbide phase. In a study published in the Journal of Physics: Condensed Matter they have managed to examine in detail the chemical bonding and structure of amorphous two-phase films of chromium and carbon.

In amorphous materials the structure and the positions of the atoms cannot be studied with current diffraction methods. Instead the researchers employed a combination of high-resolution electron microscopy in Linköping and synchrotron radiation spectroscopy at Maxlab in Lund.

One important part of the study was to examine the distance between different atoms in the materials and how it is affected by the composition and charge transfer between the constituent elements. At low carbon contents the material was completely amorphous. When the carbon content increased, graphene-like structures were formed between amorphous areas, where the distance between the atoms is greater. These differences are important for the properties of the films, like hardness, elasticity, and electrical resistance.

Examples of multifunctional applications for these amorphous carbides are materials with resistance to oxidation, wear and corrosion; decorative purposes; and electrical contacts.

Unlike transparent art glassware and window glass, which are made from silica sand, metallic glass has a shiny, anthracite-grey surface.

Article: Electronic structure and chemical bonding of amorphous chromium carbide thin films, Martin Magnuson, Matilda Andersson, Jun Lu, Lars Hultman and Ulf Jansson. J. Phys. Condens. Matter 24, May 2012

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