TiC and TiN coatings formed on Si 3N 4TiC composite ceramics by chemical vapour deposition

Abstract

Titanium carbide (TiC) and titanium nitride (TiN) films were deposited on Si 3N 4TiC composite cutting tools by chemical vapour deposition using TiCl 4CH 4H 2 and TiCl 4H 2N 2 gas mixtures respectively. An Auger electron spectroscopy survey was performed in order to find out the non-metal to metal ratio of the coated layer at various deposition conditions. The non-metal to metal ratio of deposit increases with increasing m C: Ti (mole ratio of CH 4 to TiCl 4 in the input) for TiC coatings and m N: Ti (mole ratio of N 2 to TiCl 4 in the input) for TiN coatings. Nearly stoichiometric films could be obtained with m C:Ti = 1.15−1.61 for TiC and with m N:Ti = 25–28 for TiN. Also, maximum microhardness of the coatings can be obtained in these ranges. An interfacial region between the coated layer and the substrate was investigated by Auger depth profile analysis. The interfacial region of TiC coatings on Si 3N 4TiC ceramics is wider than that of TiN coatings according to Auger depth profile analysis, which indicates good interfacial bonding for TiC. The microstructure and thermal shock resistance of the coated layer were also investigated. Experimental results show that TiC coatings have an equiaxed structure and TiN coatings have a columnar structure with a (220) preferred orientation. Also, TiC coatings on Si 3N 4TiC ceramics have more resistance to thermal shock than do TiN coatings.