Influence of application technology on the erosion resistance of DLC coatings

Various components need protection against superimposed corrosion and wear (abrasion, erosion) loading, e.g. in off-shore applications. The goal of the research has been to develop a PVD multilayer coating by systematically altering the layer architecture in order to protect components against corrosive environments and erosive loadings. Our approach regarding the coating architecture has been to apply a diamond-like carbon (DLC) layer on top of a multilayer coating system, to ensure an excellent erosion resistance while providing a good corrosion protection. vestigation is focused on the influence of the application technology (PVD or PECVD) and the resulting coating properties of the DLC top-layer. The investigated PECVD-top-layer was produced by a mixture of acetylene and hydrogen gas, whereas the PVD-top-layers were deposited from a graphite-target and different mixtures of acetylene and argon gas. The applicated DLC top-layers are characterized by hardness values between 11 and 23 GPa and similar adhesion properties. Note that hardness has been determined by nano-indentation and adhesion characterized by scratch testing. Residual stresses of the DLC-top-layers were determined by means of focused ion beam milling and tracking of the resulting relaxation strains by digital image correlation. Residual compressive stresses up to 2 GPa have been determined. Under loading in an erosive environment (combination of abrasive and fatigue loading) the abrasive degradation of the investigated coatings has been found to depend mainly on coating hardness. As expected, the hardest DLC top-layer (PECVD) shows least abrasive degradation. However, when tested under cyclic loading, the coating exhibiting the highest hardness values (PECVD) show the most severe fatigue damage of all DLC coatings investigated.