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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.

Titanium nitride TiN, titanium boronitride Ti(B,N) and titanium carbonitride Ti(C,N) coatings were deposited by PA-CVD on tempering and stainless steel substrates. The deposition process can be supervised by OES. The coatings were characterized by XRD, SEM and WDS as well as hardness, adhesion and friction tests. Electrochemical impedance measurements and cyclic voltammetry in praxis relevant media were carried out. Mechanical and corrosion properties of the coatings can be controlled by the PA-CVD process parameters. The incorporation of chlorine in the coating can be varied by the process parameters with TiCl 4 or completely avoided using metallo-organic precursors. No influence of the chlorine content on the corrosion behavior was observed. Even coatings with extremely high chlorine content still exhibit an excellent corrosion resistance. Thus, the microstructure of the coating is the key to the corrosion properties of hard coatings on steel. A new micro electrochemical scanning droplet technique with a lateral resolution of 150 μm allows the investigation of TiN-coated substrates of complex geometry. The PA-CVD technique permits the deposition of dense and pinhole free coatings. On structures with simulated aspect ratios less than 3, a dense protective coating is proved. However, if the formation of micro pores is not suppressed by the optimal choice of deposition parameters, low-alloyed steel substrates corrode through pores, causing a detachment of the coating. On layers deposited on stainless steel, no sign of substrate corrosion could be detected. A model for the corrosion mechanism is given in Fig. 17.