The effect of NH3 plasma pre-treatment on the properties of TiN coatings produced by plasma-enhanced chemical vapor deposition (PECVD)

Abstract

TiN coatings were deposited on high-speed steel (HSS) by plasma-enhanced chemical vapor deposition using a gas mixture of TiCl 4 , NH 3 , H 2 and Ar. Prior to deposition, the substrate was pre-treated by NH 3 plasma in the same deposition chamber. The structure and composition of the coatings were analyzed by X-ray diffraction, energy-dispersive spectroscopy and Auger electron spectroscopy . The mechanical properties of the coatings, such as hardness, adhesion strength and wear resistance, were also investigated. It was found that CrN is formed on the substrate surface after the NH 3 treatment. Iron nitrides, which are known to deteriorate the adhesion property of the coating, were not observed. The lattice parameters of the HSS and the coatings increased after pre-treatment. The adhesion strength of the coatings with NH 3 pre-treatment of the substrate was improved compared with that without pre-treatment. It is supposed that the improvement in adhesion was caused mainly by the removal of oxide from the substrate surface. The formation of an inter-diffusion layer of iron, nitrogen, chromium and titanium, and a decrease in the stress gradient at the interface, worked as secondary effects for the improvement of adhesion properties. In addition, the microhardness of the coatings with pre-treatment increased. As a consequence, the wear resistance also increased owing to a higher hardness and a higher adhesion strength.