Improvement of the corrosion resistance of PVD hard coating–substrate systems

Hard coatings play a continuously increasing role in the field of tribology as well as for decorative applications. In both areas they are often exposed to corrosive environments. While especially hard coatings exhibit a high corrosion resistance for themselves, hard coating–substrate systems may suffer from a severe corrosion attack due to the defects in the coating structure (pores, pinholes) resulting from the PVD-typical film morphology. In contrast to the huge number of investigations on the structure, properties and tribological performance of hard coatings, only limited studies exist on the corrosion behaviour of hard coating–substrate systems and attempts to improve their corrosion resistance. This paper briefly describes the corrosion mechanisms and reports characteristic examples of the system behaviour. Special emphasis is put on recent investigations in order to improve the corrosion resistance by alloying, interlayers and multilayered coating structures.