Effects of carbon content and annealing temperature on the microstructure and hardness of super hard Ti–Si–C–N nanocomposite coatings prepared by pulsed d.c. PCVD

Novel quaternary Ti–Si–C–N coatings composed of nanocrystalline Ti(C, N), amorphous phases of Si3N4 and C, and occasionally free Si and nanocrystalline TiSi2 were deposited on high-speed steel (HSS) substrate at 550 °C using pulsed d.c. plasma chemical vapor deposition (PCVD) technique from TiCl4, SiCl4, CH4, N2, H2 and Ar mixtures. It was found that the hardness increased with the increase of C content and reached the maximum value of approximately 48 GPa at the C content of 38.6 at.%. However, the crystallite size decreased to a minimum value of approximately 7 nm at the content of 38.6 at.% C. It could be detected that crystallite size and hardness almost remained stable during annealing up to 900 °C for Ti–Si–C–N coatings. However, a sharp decrease in the hardness was observed after annealing at 1000 °C due to the growth of grain. A shift of the diffraction peaks was towards higher 2θ for Ti–Si–C–N coatings after annealing at increasing temperatures because of evaporation of COx and resultant loss of C from coating at elevated temperature. In addition, SiOx, TiOx were detected in Ti–Si–C–N coatings after annealing at 1100 °C.