Corrosion and scratch resistance of DLC coatings applied on chromium molybdenum steel

Diamond-like carbon (DLC) coatings found many industrial applications in various fields, such as in aerospace, automotive bearing and electronic applications. DLC coatings performances are strictly correlated to their structure and composition which can be optimized controlling the substrate bias voltage (SBV). In this research, the corrosion and scratch resistance of DLC coatings applied on chromium molybdenum steel has been evaluated by electrochemical, microscopical and spectroscopical techniques. It has been observed that increasing the SBV leads to harder and more protective coatings, but decreases the resistance to delamination during scratch testing. Corrosion was always triggered at local defects of the Cr/C gradient interlayer, where the DLC layer was easily delaminated, exposing the chromium molybdenum steel substrate. The results of this study suggest that a better control of the Cr/C deposition parameters are necessary to further enhance corrosion resistance. •The paper explores the properties of DLC coatings obtained with different applied bias voltages.•A correlation was found between the structure of DLC and the corrosion/wear resistance of the material.•The local corrosion properties were studied by using glass capillary tubes.•The corrosion mechanism was identified as delamination of the DLC coating at defective locations of the Cr/C interlayer.