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174 GPa for the film with a Cu content of 28 at.%. In parallel, a 50% drop in the nanohardness from about 28 GPa towards 14 GPa is observed for these coatings. An increase in the Cu content also produces an increment of the coefficient of friction in reciprocating sliding tests performed against a corundum ball counterbody. As compared to the metal free film, a nearly four times higher coefficient of friction value is detected in the case of a Cu content of 28 at.%. Nevertheless, the carbon-copper composite coatings produced a clear surface protection of the substrate evidenced by a reduced wear loss for Cu contents below 5 at.%.

The use of lightweight materials, such as ultra-high-strength aluminium alloys, is in high demand in the automotive and aerospace industries where weight savings are critical. The tool materials used for high-speed cutting of these aluminium alloys are subjected to severe conditions that promote premature failure of cutting tools. The application of polycrystalline diamond (PCD) coatings provides cutting tools with increased mechanical and thermal fatigue resistance and improved tribological performance. Despite these good properties, their high cost remains a major limitation in this sector. Super-hard Diamond-Like Carbon (DLC) coatings offer a technologically and economically feasible alternative to PCD-coated tools for cutting and machining non-ferrous materials. In this paper, the machining performance of coated and un-coated hard metal inserts in the turning of 7075 aluminium alloy has been explored. The surface quality of machined parts, the cutting tool wear resistance and the vibrations generated during turning of un-coated, PCD and super-hard thin DLC coatings on tungsten carbide inserts were compared. The results obtained demonstrate that DLC coatings are a potentially interesting alternative to PCD coatings for machining ultra-high-strength aluminium alloys, where surface component finish is a key factor.

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