Modified diamond-like carbon coatings

Diamond-like carbon (DLC) coatings are of high technological interest due to their outstanding properties such as high hardness (up to 6000 HV), very low friction and wear, chemical inertness, high thermal conductivity as well as biocompatibility. Improved lifetime has been obtained for ceramic sliding bearings, for forming tools, for precision instruments as well as for magnetic hard discs. Good adhesion of the coating is an essential requirement for any technical application. The main disadvantage of these films is their thermal instability. At temperatures exceeding 350 degrees C the internal structure of the films starts to deteriorate by successive transformation into graphite. DLC films containing different amounts of adequate elements opens the additional possibility of, within a certain range, continuously adapting properties such as thermal stability, hardness, internal stress, tribological properties, electrical conductivity, surface energy, and biological reactions of the cells in contact with the surface (cell growth, cell differentiation). Nanoscale multilayers, consisting of alternating layers of hard and soft DLC are produced by a modulation of the self bias voltage in the plasma activated chemical vapor deposition (PACVD) process. A dependence of the tribological behavior from the thickness of the single layers and the type of hardness transition between the consecutive layers (stepwise / continuous) could be observed.