SUPERHARD TI-B-C-N COATINGS

In order to advance the development of extremely hard coatings, new homogeneous and metastable films within the Ti-B-C-N system were prepared by magnetron sputter ion plating using a TiB2 target in the d.c. mode. Multicomponent layers of different compositions and structures were deposited by varying the reactive gases methane (CH4) and nitrogen (N2) and the dominant process parameters (e.g. sputtering power and substrate bias). X-ray diffraction studies of the coatings revealed either an amorphous structure or crystallization in a hexagonal lattice. The lattice parameters were strongly influenced by the quantity of carbon and nitrogen incorporated. Electron microprobe analysis was used to determine the coating compositions. Evaluation of the characteristic light element X-ray spectra provided initial qualitative data on chemical bonding properties. Auger electron spectroscopy confirmed the constitution of the films. The Palmquist method and hertzian indentations were used to characterize film toughness. The remaining mechanical coating properties were investigated by means of microhardness measurements and the CSEM scratch test. Scanning electron microscopy indicated an extremely dense coating structure. Superhardness up to values of 7000 HV 0.05 was the dominant property. Coating thicknesses ranging from 6 to 25-mu-m were realized. Behaviour of the Ti-B-C-N layers in abrasive wear tests was favourable.