Preparation and properties of hard i-C and i-BN coatings

Abstract

The state of the art in preparing and investigating hard i-C films is discussed in the context of new experimental results. Such films, which are characterized by unusual hardness and high electrical resistivity, can be produced by using deposition techniques, such as plasma, ion beam or ion plating methods, in which ionized film-forming and/or inert species of sufficient energy are involved. Although crystalline fractions may occur, the basic structure of the layers was found to be amorphous. The results of electron diffraction analysis and electron energy loss spectrometry in conjunction with the relatively low mass density of the films suggest a structural model consisting of puckered n-fold carbon rings (where n = 3−8) with presumably tetrahedral cross-links. The physical properties of i-C coatings are reviewed with particular emphasis on microhardness, frictional behaviour, wear and corrosion protection. First results obtained for BN deposits indicate that similar i-BN structures can be prepared. Widespread applications of i-C and i-BN coatings, eventually in the form of composite layers together with other hard materials, are anticipated.