Influence of the Ag content on the tribocorrosion behaviour of TaN-xAg multilayer coatings on the AISI316L Stainless steel for biomedical applications

摘要

Surface modifications constitute a well-established practice for improving the functional properties of materials such as corrosion resistance or biocompatibility, specifically in the biomedical field. TaN-xAg multilayer coatings have been developed as an attempt to improve the durability of biomedical devices. However, its corrosion and tribocorrosion behavior should be analyzed because the resulting material will be subjected to the combine action of corrosion and wear during its operating conditions. The aim of this work is to determine the effect of the Ag addition on the tribocorrosion behavior of TaN-xAg multilayer coatings deposited by reactive dc magnetron sputtering on a stainless steel. To do that, first an AISI 316L substrate was nitrided by plasma at 450°C, secondly a Ta adhesion monolayer was deposited to improve the adhesion of the multilayer coating, in a third step a TaN matrix ceramic coating was formed by injection of N_2 into de reactor and doped with Ag to low power applied to target. The final step consisted in a final deposition of a TaN layer diffusion by applying different bias voltage to control the refinement degree of the coating structure. Thermal treatment at 200°C during 4 minutes under a controlled nitrogen atmosphere was carried out in order to promote silver diffusion across the multilayer coatings. The tribocorrosion behavior of the resulting materials was studied in a ball-on-disc tribometer, rubbing against an alumina ball, coupled to a potentiostat under open circuit potentials in a phosphate buffer solution. Although the silver content in the coatings was very similar, its surface distribution was different among them, so different potential evolution with time were observed during the tribocorrosion tests. Ag sites act as cathodic catalyzer thus enhancing the cathodic reaction and then provoking a larger decay in the open circuit potential during rubbing. In some cases, several potential decays were observed during one test coinciding with the total and/or partial delamination of the different layers of the coatings.