A progressive type of tungsten-doped DLC coating was applied to a quenched and tempered 100Cr6 steel with the aim to improve the wear and corrosion properties in simulated seawater conditions and to compare the performance to conventional DLC coating. Tungsten doping caused a shift of the corrosion potential (E_corr) to a lower negative value of −172 mV, while the conventional DLC exhibited an E_corr of −477 mV. In dry conditions, the W-DLC coefficient of friction is slightly higher than that of the conventional DLC (0.187 for the W-DLC vs. 0.137 for the DLC), but in cases of a saltwater environment, this difference becomes almost negligible (0.105 for the W-DLC vs. 0.076 for the DLC). The conventional DLC coating also started to show marks of deterioration when exposed to a combination of wear in a corrosive environment, while the W-DLC layer still maintained its integrity.

The work focused on evaluating the tribological, corrosion, and fatigue properties of a Diamond like Carbon (DLC) coating and a duplex CrN/DLC coating in a 3.5% NaCl solution simulating the aggressive environment of seawater. C55 steel was selected as the substrate material due to its widespread industrial application in the production of highly stressed machine components and its relatively low resistance to corrosion damage. The experimental results demonstrated that the application of DLC and CrN/DLC coatings significantly improved the tribological and corrosion properties of the investigated material in a chloride corrosive environment. At the same time, it was shown that the duplex CrN/DLC coating not only eliminated the negative effect of the corrosive environment on the fatigue properties of C55 steel but even led to their improvement. The fatigue limit of C55 steel with the CrN/DLC coating reached 717 MPa, representing an increase of 3.3% compared with the base material and 29.2% compared with uncoated C55 steel after 72 h of corrosion exposure in a 3.5% NaCl solution. The superior fatigue performance of the CrN/DLC system was associated with its improved adhesion and barrier properties provided by the duplex coating architecture and the CrN interlayer.