CORROSION PERFORMANCE OF LAYERED COATINGS PRODUCED BY PHYSICAL VAPOR-DEPOSITION

Potentiodynamic methods were used to investigate the relative corrosion protection provided on 304 stainless steel by various coating and pretreatment routes designed to isolate the substrate from the environment. These include combinations of plasma oxidizing, plasma nitriding and chromium, nickel and titanium nitride coatings produced by triode ion plating methods. It is shown that optimization of the layer structure and galvanic coupling are vital where a combination of wear and corrision resistance is required. Nickel interlayers under TiN, for example, are shown to provide improved protection against corrosion. Attempts to increase corrosion resistance by producing a passive layer through a d.c. plasma processing stage on the substrate were not so successful, and the reasons for this are discussed.