Evaluation of the corrosion behaviour of wear-resistant PACVD coatings

The deposition of wear-resistant coatings by means of plasma-assisted CVD (PACVD) provides a successful means of depositing homogeneous pinhole-free coatings on substrates with complex shapes. In applications such as chemical apparatus processing and the food industry, however, the mechanical loads occurring are superimposed by corrosive attack. In this study, layer types of the system Ti–C–N were deposited by means of pulsed d.c. PACVD using either a Cl-containing or an organometallic metal donor. The coatings were characterized by XRD, SEM, EDS, WDS, XPS and SAM. Further, hardness, adhesion and friction tests as well as cyclovoltammetric and impedance measurements in relevant media were carried out. The PACVD technique permits the deposition of dense and pinhole-free coatings with high hardness and an apparent corrosion resistance. Stoichiometric TiN is electrochemically stable in most electrolytes. If the formation of micropores is not suppressed by the optimal choice of deposition parameters, the low alloyed steel substrate corrodes, causing a detachment of the coating. On layers deposited on stainless steel, no sign of substrate corrosion could be detected. A comparison of Ti(C,N) coatings deposited from Cl-containing and Cl-free precursors did not reveal any difference with regard to their corrosion behaviour. High Cl-containing TiC coatings still exhibit an excellent corrosion resistance.