Corrosion and wear protection of mild steel substrates by innovative PVD coatings

Abstract

Today, innovative coatings must ensure wear protection and corrosion resistance for engineering materials with high corrosion susceptibility, e.g. mild steels, as well as the current sustainability criteria in terms of environment protection and health.PVD technology fulfils most of these demands, but unfortunately, the corrosion protection performance is unsatisfactory due to the typically low coating thicknesses of only few micrometres.One solution to overcome the corrosion problem are TiMgREN (RE = Rare Earth) based coatings, which were developed by the authors. Even with 5 μm thick monolithic TiMgGdN coatings a corrosion resistance of at least 800 h could be achieved in the salt spray test without any macroscopic corrosion attack.In the present work, the influence of the coating composition, the substrate material and the surface roughness on the corrosion properties was examined. Besides, the application of Gd as alloying element, the influence and the effect of other rare earth metals (La, Ce) on the corrosion performance were investigated.As benchmark, the TiMgGdN coatings were compared with industrial standard PVD coatings, DLC and electroplated Cr regarding the corrosion and the wear performance.The coatings were characterized concerning their microstructural, mechanical and chemical properties. Salt spray tests as well as electrochemical measurements were carried out to examine the corrosion properties of the coated specimens. Furthermore, ball on disk wear tests were conducted by reciprocal dry sling tests by using a SRV 3 tribometer.It was shown that by variation of the deposition parameters, the coating properties could be improved concerning both, corrosion and wear performance. Furthermore, the effect of the used rare earth metal type and the rare earth metal content on the coating properties was investigated. The TiMgGdN coatings exhibit superior corrosion properties in comparison to the industrial standard coatings.