Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Final Activity Report Summary - NANODIAMOND (Advanced technological applications of nanocrystalline diamond/amorphous carbon composite films)

Recently, nanocrystalline diamond films, either in pure form, or as a composite with NCD particles embedded in an amorphous matrix, have attracted considerable interest as such coatings retain to a large extent the extreme properties of polycrystalline diamond films but overcome one of their major disadvantages, i.e. the great surface roughness. Industry has already indicated strong interest into NCD/a-C films for a number of applications. However, in almost all investigations up to now, irrespective of the deposition route used for their preparation, the films are not thoroughly characterised, especially regarding the amounts of the crystalline and the amorphous phase, the nature and the properties of the matrix, and how the nature of the matrix influences the properties of the nanocomposite material. Thus, intensive fundamental research is required before industrial applications can be thought of.

The scientific objectives of the project included the development of a technique for deposition of NCD/a-C coatings and the establishment of process parameters dependence of their properties; the detailed investigation of the basic film properties, and evaluation of the application relevant properties as wear resistant coatings, for biomedical purposes and as a new material with extreme properties for nanostructures and MEMS.

The most important results and achievements of the project can be summarised by the following major points:

nanocrystalline diamond films composed of diamond crystallites (3-5 nm) embedded in an amorphous carbon matrix were deposited by microwave plasma chemical vapour deposition (MWCVD) and the parameter window for the preparation of NCD was established;
the films were rather smooth, with rms roughnesses down to 12 nm, which makes them appropriate for a number of applications;
the average hardness of the NCD films was ca. 40 GPa, the indentation modulus ca. 390 GPa, and the elastic recovery about 75%. A possible reason for the somewhat low values (as compared to bulk diamond) may be the presence of the amorphous matrix with a volume fraction of 40-50%. On the other hand, the tribological performance of a wear protecting coating is not only determined by its hardness; rather, the toughness is of even higher importance. Here, the presence of the amorphous matrix may even be of advantage as it can help to prevent fatal brittle failure;
the friction coefficient was on the order of 0.1 or even lower. No delamination of the coatings (neither inside nor alongside the wear track) took place during the tribo-tests even after 10,000 laps, revealing their good tribological properties;
nano-scratch tests performed with progressive loading showed that the NCD films are well adherent to the substrates. In some cases full delamination did not take place even at the final load. In those areas where delamination had occurred, the underlaying substrate was heavily damaged, which proved the protecting nature of the NCD coating;
the NCD/a-C coatings are not cytotoxic and do not induce adverse effects on cell health which is prerequisite for their biomedical applications;
simulated body fluid tests revealed that the NCD films are bioinert, i.e. no deposition of hydroxyapatite was observed after the contact with a solution possessing a similar composition as blood plasma; this makes the NCD films appropriate for the coating e.g. of cardiovascular artificial components.

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