Pyrolytic laser-based chemical vapour deposition of TiC coatings
TiC layers have been successfully deposited locally on D2 tool steel specimens and miniature industrial tools with the aim to improve their mechanical and chemical surface properties. The deposition process was based on a pyrolytically-induced chemical reaction of TiCl4 and CCl4 compounds combined with an atomic hydrogen source. Local heating of the substrate was achieved by means of a 100 W CO2 laser controlled by a microcomputer-based feedback loop system, involving on-line substrate temperature monitoring. Scanning electron microscopy, energy-dispersive X-ray analysis, X-ray diffraction, and transmission electron microscopy analysis showed that close-stoichiometric TiC (fcc structure, lattice constant a = 4.2 Angstrom) was deposited in the films with a nanocrystalline structure. The microhardness of the coatings was in the range 2500-3200 HK.