ICMCTF2008 Session D3-2: Carbon-Based Nanostructured Composite and Nanolaminated Films

Carbon based coatings are widely used for numerous applications spreading from specialized cutting tools for wood processing, through medical equipment and implants to optical instruments and data storage media. The coatings afford high hardness, low friction coefficient, high wear resistance and chemical inertness.

Their properties become still more attractive when carbon is combined with hard carbides of refractory metals (W, V, Mo, Ti). Composite coatings containing nanocrystalline carbides, embedded in relatively softer carbon matrix, show extraordinary combination of properties like low friction and wear rate, high hardness and toughness. An increase in hardness of composites in comparison to that of single phase coatings is based on the suppression of dislocation propagation. Oxidation resistance of these attractive materials can be improved by addition of silicon.

Alternatively, introduction of soft metal inclusions (Ag, Au, Cu, Ni, Co), usually inert or showing low reactivity to carbon, leads not only to intrinsic stress reduction but also results in improved adhesion to industrially accepted substrate materials. A nanocomposite structure containing conductive metal clusters (Cu, Ag, Au) in insulating, amorphous carbon matrix has shown high k properties whereas introduction of ferromagnetic clusters (Ni, Co) results in attractive magnetic properties. A large variety of methods allows deposition of carbon based nanocomposite films. Mostly used are PVD techniques (magnetron sputtering, filtered arc deposition). In parallel, several plasma enhanced CVD and hybrid methods have been developed.

Nanocomposite thin films comprising nanocrystalline TiC embedded in an amorphous SiC matrix (nc-TiC/a-SiC) are promising as electrical sliding contacts¹. The thin film material is multifunctional as it combines good electrical contact properties, ductility, chemical stability, and wear resistance. With these properties a wide range of applications for such thin films are suggested, for instance in electronics. This field requires controlled synthesis of the material preferably at low temperatures (≤300°C) to enable growth on commercial substrate materials. An outstanding question is, however, how the nanocomposite deposition process will be influenced when scaled up to an industrial level, and what will be the microstructure of the resulting thin films. In this study, we have deposited nc-TiC/a-SiC by DC magnetron sputtering in a pilot-plant scale system onto different substrate materials (including silicon, steel and electro-plated Ni on a Cu cylinder) held at 270°C from a Ti₃SiC₂ compound target. Deposition rates of more than 15µm/h are demonstrated which should enable a high throughput for the coated details. The resulting thin films are analyzed with respect to microstructure, resistivity and mechanical properties by using XRD, SEM, TEM, ERDA, nanoindentation, resistivity and resistance measurements. We find that the nanocomposite thin films are dense and consist of 15-23nm TiC grains with a (111) texture in a minority phase matrix of a-SiC, depending on the deposition rate.

¹Per Eklund et al., J. Vac. Sci. Technol.B, 2005, Vol. 23, 2486-2495.