Transmission electron microscopy microstructural characterization of Ti-Si-C-N coatings

A new type of Ti-Si-C-N coatings deposited on high-speed steel substrate by means of pulsed direct current (dc) plasma-enhanced chemical vapor deposition was investigated. The as-deposited coatings were characterized systematically by using energy-dispersive x-ray spectroscopy, x-ray diffraction (XRD), transmission electron microscopy (TEM), and microhardness with particular attention paid to the microstructure of the coatings. It has been shown that C content has a profound effect on the microstructure and hardness of coatings. TEM and XRD analyses revealed that these coatings consist of the dominate Ti(C, N) with a silicide (TiSi2, Si3N4, or SiC, depending on the C content in the coatings). The crystallite sizes are in the range of 8-35 nm, which decrease with increasing C content. The Ti-Si-C-N coatings with high C content (25.2-38.6 at.%) possess superhardness (41-48 GPa). This can be attributed to the grain refinement/grain boundary hardening and dispersion hardening of the hard, nanosized crystalline Si3N4 or SiC formed in the deposition.