DECORATIVE HARD COATINGS - NEW LAYER SYSTEMS WITHOUT ALLERGY RISK

Combinations of physically vapour deposited (PVD) coatings and electroplated layers are widely used for decorative applications. The electroplated layer beneath the PVD coating acts as a diffusion barrier. Conventionally electroplated barrier layers make use of nickel which has to be replaced in allergy-free systems by for example Ni/NiPd and CuSn(Zn). The PVD coating has to meet a variety of requirements: attractive colour, high wear resistance and good corrosion resistance. Within the scope of the search for new colours a number of nitrides of binary IVa metal-based alloys such as (Ti,V)N, (Zr,V)N, (Zr,Al)N, (Zr,Cr)N, (Zr,Y)N were deposited by reactive magnetron sputtering. To describe the colour the CIE L*a*b* system was used. Spectroscopic ellipsometry (SE) was introduced to determine material related parameters. In general, both the stoichiometry and the structure can influence the colour of a coating. The correlation between colour, stoichiometry and structure was determined by surface analytical methods (glow discharge optical spectroscopy, Auger electron spectroscopy, X-ray diffraction). Proper selection of process parameters (target composition, N2 flow rate, etc.) results in coatings with colours exceeding the conventional spectrum of decorative coatings. As an example of structural and stoichiometric influences on colour, ZrN and (Zr,Y)N coatings are discussed.