Application-oriented modifications of deposition processes for diamond-like-carbon-based coatings

Abstract

Hydrogenated amorphous carbon films (a-C:H) exhibit some “diamond-like” properties as high wear resistance and low electrical conductivity. However, to fulfil requirements for special applications, e.g. high wear resistance combined with high electrical conductivity or low surface energy, the films had to be modified. These modifications can be realized by the incorporation of other elements (metals, F, O, N or Si) into the a-C:H network structure either by co-sputtering of metals or by adding adequate reactive gases to the working gas. It was found that the surface energy of a-C:H films can be definitely changed by the incorporation of elements such as F, N, O or Si into the films, using a mixture of acetylene with, for example, fluorinated hydrocarbons, nitrogen or silicon-based hydrocarbons as a working gas. Hard coatings with decreased or increased wetting angles against water were prepared. For example a Teflon ®-like material with low adhesion forces could be deposited, while the tribological properties of this coating are similar to those of diamond-like carbon coatings. Metal-containing amorphous hydrocarbon (M-C:H) films with 15 at.% metal (e.g. Ta, W, Ti or Nb) or less have nearly the same wear resistance and friction coefficient as a-C:H, but their electrical conductivities are several orders higher. The variation in the metal concentration in such coatings has to be kept under good control to increase the adhesion forces to the substrate material by the use of metallic interface layers. We have developed a reactive d.c. magnetron sputtering technique for the preparation of M-C:H films with well-defined metal contents in the graduated interface and in the functional top coat respectively. A reproducible preparation of coatings with desired metal contents was achieved for different industrial components.