Effect of the carbon content on the structure and mechanical properties of Ti-Si-C coatings by cathodic arc evaporation

Ti-Si-C coatings with various carbon contents were synthesized on cemented carbide substrates by a TiSi (88:12 at.%) alloy cathode in acetylene (C2H2) plasma atmosphere with a flow rate of 15 to 40 sccm using a dual source cathodic arc evaporation system. Experimental results showed that the structure and the mechanical and wear properties of Ti-Si-C coatings were strongly dependent on the carbon content (or acetylene flow rate). When the carbon content is lower than 46 at.%, the Ti-Si-C coating was comprised of an fcc NaCl-type TiC phase, a small volume fraction of Ti3SiC2 metallic phase, and an amorphous SiC phase. When the carbon content was increased above 50 at.%, the Ti3SiC2 metallic phase was reduced and nanocrystalline TiC (nc-TiC) and amorphous SiC (a-SiC) and carbon phases (a-C) were observed. The coatings could be characterized as TiC nanocrystallites imbedded in an amorphous SiC, C and free carbon matrix, resulting in the hardness evidently enhanced to 40 GPa as the carbon content was increased at about 52 at.%. When the carbon content was further increased to above 54 at.%, the volume fraction of amorphous carbon significantly increased, the fraction of the crystalline phases decreased, and both the hardness and the wear resistance decreased.