Corrosion Properties of Cathodic ARC evaporated Nitride Coatings

The use of thin hard metal nitride coatings reactively deposited by Physical Vapour Deposition (PVD) is well established in many engineering applications, specifically operations utilising cutting tools and metal forming dies. The PVD coatings offer enhanced tribological properties at the tool surface which is of paramount importance for wear control and to enhance productivity. One of the drawbacks that have restricted the use of cathodic arc PVD coatings as corrosion barriers is the macro-particle induced defects that occur during the arc evaporation process. Incorporation of spherical or lenticular macroparticles of 0.1-5 μm diameter results in a high degree of porosity in thin PVD coatings through void formation and generation of pinholes which leads to reduced corrosion resistance. However, it is anticipated that reducing the number of macro-particles and associated morphological defects would therefore lead to improved corrosion resistance. One route to achieving this is by the use of a pulsed arc current as opposed to a constant DC source in the arc evaporation process.