Decorative Coatings Formed by Anodic Oxidation of PVD Niobium Layers
Current techniques for depositing decorative and/or protective metal coatings onto metal substrates either involve 'wet' methods, thermal spraying or commercial PVD. Wet methods such as electroplating are used to deposit metals such as platinum, nickel and chromium.
There is no technique available that will allow these coatings to develop primary colours, and so there is only a limited range of colours available, such as white, silver, black and gold. Electroplating is also very difficult on fine-featured items such as jewellery, whereas PVD methods do not have this limitation. Cathodically deposited lacquers can produce a range of coloured finishes on conducting substrates, but these do not have the durability of a PVD or electroplated coating.
Current commercial PVD coating techniques are used to deposit wear resistant coatings onto implements such as cutting tools and also to deposit hard wearing 'gold' coloured titanium nitride coatings for decorative purposes. It has been shown that, with modern unbalanced magnetron sputtering systems (the new PVD method), the deposition of multi-layered metal and oxide coatings may be realised.
Dense niobium (Nb) coatings have only recently been deposited and primarily investigated for their corrosion resistance. Our recent research work has demonstrated controllable anodic oxidation of strongly adherent niobium layers to give an attractive coloured coating.