Corrosion and wear-corrosion studies of nitrides coatings obtained by reactive sputtering

Ceramic coatings such as TiN, or other nitrides and carbides produced by physical vapour deposition (PVD) are frequently used to increase the service life of tools. In the literature it is possible to fmd many articles about the wear or corrosion resistance of these materials but very few works which regard wear and corrosion phenomena occurring at the same time. In this work we have studied TiN and (Ti,Cr)N with 1 mu m thickness coatings deposited by reactive sputtering on stainless steel. In order to minimise coating porosity and defects some samples were prepared as a multilayer coating with a 2000 Angstrom thick Ti first layer and a 8000 Angstrom nitride top layer. At first the corrosion resistance properties were evaluated in acid and in sodium chloride aerated solutions using potentiodynamic plots. The chromium presence in coatings increases corrosion resistance. Later the samples' corrosion behaviour was characterised during wear. An appropriate machine was used which permitted electrochemical measurements during wear testing. By monitoring E-corr and electrochemical impedance spectroscopy during testing time, the effect of various loads and counterface types on corrosion behaviour can be observed. The influence of the presence of chromium in coatings and of a titanium underlayer can also be observed. (Ti,Cr)N deposits, which have the best corrosion resistance, prove to be the least resistant coatings to the wear-corrosion process as confirmed by microscopical observation.