Deposition of TiC coatings is usually carried out by chemical vapour deposition. Recently deposition by sputtering and activated reactive evaporation has been reported. The ion plating technique (conventional and reactive), so far, does not seem to be successful. However, the present investigation using a third variation, chemical ion plating, produced adherent, uniform, dense, microcrystalline Tic coatings on steel substrates, characteristics expected when ion plating is used. Deposition took place on the cathode in an argon assisted glow discharge using gaseous reactants (TiC14, C2H2 and H2). The parameters investigated were: the pressure, voltage and current of the discharge, the reactants ratio and indirectly the temperature of the substrate. It was found that the factor governing the deposition was the discharge current, heating the substrate to temperatures where the reaction is thermodynamically feasible. The coatings were characterized by X-ray diffraction techniques. Their microstructure, thickness, uniformity and surface topography were studied by optical and scanning electron microscopy. The X- ray diffraction pattern showed only TiC with mean lattice parameter of 4.347 +/- 0.009 A which is higher than the corresponding value in the literature (4.328 A) probably due to the stresses accumulated during deposition and the presence of Cl impurities. Electron probe micro- analysis showed that the coatings consist of Ti, Cl (4%) and C in greater than stoichiometric proportions, as was confirmed also by chemical analysis. Oxygen was not detectable. The C was not detected as a second phase because it was non-crystalline and because the coating was very fine grained (below 1000 A). The properties of the coatings changed with composition. Vickers microhardness values reached 2700 - 3000 kgmm-2, the values accepted for Tic, at high concentrations of C. The good adhesion between coatings and substrate, observed on qualitative basis, was assessed by the frequently used scratching test and was best at high C content. However, at high C contents partial spalling occurred which was avoided at low C contents or when carburized steel substrates were used. Deposition rate increased as the C content increased. Finally the friction coefficient of coatings against a stainless steel counter-face decreased at high C contents (from 0.28 to 0.18).
|Date of Award||1976|