Establishing PVD-coatings for the corrosion protection of mild steel substrates for complex tribological and corrosive stresses

Due to the health hazard, emanating from chromium trioxide based coating processes, the longtime approved hard chromium platings have to be replaced by alternative coating systems in future. Therefore, the development of PVD coatings, which protect mild steel substrates from both, corrosive and tribological stresses, is a key demand for the PVD coating industry. These coatings have to achieve comparable properties for wear protection and corrosion resistance like chromium platings and also must fulfill the current sustainability criteria in terms of environment protection and health. Recently, the authors developed a TiMgGdN coating system with improved corrosion properties for steel substrates. The superior corrosion properties of TiMgGdN was initially discovered for surface protection of magnesium alloys, which is the most corrosive construction metal (Hoche et al., 2014). In the present work, the TiMgGdN coating concept was applied to mild steel substrates. The coating composition and the deposition parameters were varied to optimize the coatings for steel substrates. The coatings were deposited by using both, DC and HiPIMS sputtering. The influences of the chemical composition, the deposition parameters, the substrate roughness and the sputter mode on the corrosion properties were examined. 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, the electrochemical properties as well as the open circuit potentials of the coating materials themselves were determined.