DEPOSITION OF AND ANNEALING EFFECT ON TI(C, N) COATINGS

The influence of annealing environment such as temperature and atmosphere on the microhardness of Ti(C, N) coatings has been studied. Complete solid solution between TiC and TiN was obtained on steel substrates by ion plating. The composition of the coatings was close to stoichiometric. A linear relationship between the hardness and the carbon content in the coatings was obtained. The values of the Vickers hardness varied from 2100 (TiN) to 5300 (TiC) which was harder than the reported values of bulk TiC. The possible origins of such high values of the hardness are the fine grains, the crystallographic orientation, high compressive residual stresses or the dense defect-free structure of the coatings. The hardness of the TiC coatings dropped rapidly after annealing in air at 673 K although Ti(C, N) coatings maintained their hardness even at 773 K. Titanium oxide was formed at the surface of annealed samples whose values of hardness rapidly decreased. It is suggested that this softening is due to formation of soft oxides such as TiO2. The oxidation was dependent upon the chemical composition of the coatings. The Ti(C, N) coatings which included larger amounts of TiN component could be more oxidation resistant and maintained a very hard surface.