Ni-free alloys as final coatings: white bronze coatings on copper

Abstract

The problem of allergies arising from the presence of Ni in alloys used for decorative objects coming into contact with the skin has become increasingly important over the past five to ten years. As an alternative, “white bronze” has been shown to be an effective solution even from an aesthetic point of view. This work investigates the corrosion behaviour of copper treated with two different techniques: electroplating and ion beam mixing. To this end copper has been electroplated with a thin (0.3 and 0.04 µm) coating of white bronze (Cu 66, Sn 23, Zn 10, Pb 1 wt%), the high brightness (as a noble metal) and corrosion resistance of which allow it to be used in decorative industries for jewellery, watches, etc. The bronze coating was ion beam mixed through bombardment with an argon ion beam. The corrosion behaviour of the bronze coatings was compared with that of pure copper through two method of analysis: a) electrochemical analysis, aimed at measuring the corrosion rate in a alkaline solution (pH = 12.4); and b) surface analysis intended to verify the thickness, homogeneity and composition of coatings through Rutherford backscattering spectroscopy (RBS) and scanning electron microscopy (SEM). The implanted bronze electroplated copper showed the best corrosion behaviour. Electrochemical tests showed low corrosion rates and a corrosion mechanism similar to that of more noble coatings.