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To address modern tribological challenges—reducing friction and wear to conserve resources while minimising environmental impact—cobalt-doped DLC (Co-DLC) coatings were developed. These nanometric multilayer coatings, designed to retain key properties such as hardness, reduced modulus, and substrate adhesion, were fabricated using non-reactive DC magnetron sputtering (DCMS). The multilayer structure was achieved by controlling the planetary substrate holder's rotational speed. Characterisation of microscopic, chemical, structural, and mechanical properties was performed using techniques including FEI-SEM, EDS, XRD, TEM, Raman spectroscopy, scratch adhesion testing, and nanoindentation. Tribological performance was evaluated under boundary and fully flooded lubrication using PAO4 base oil and formulations with ashless, sulphur-free AW and EP additives. The coatings exhibited a granular surface morphology, columnar cross-sections, and amorphous structure. Increased dopant concentrations slightly enhanced graphitisation and significantly improved adhesion, though hardness and reduced modulus decreased. Tribological testing revealed superlubricity in several coating–oil combinations and significantly reduced wear rates with higher dopant levels and new additives. A phosphate ester additive without an amine group achieved the lowest COF values, while one with an amine group yielded minimal wear rates. These findings highlight the potential of Co-DLC coatings and tailored additives to minimise friction and wear effectively. [ABSTRACT FROM AUTHOR]

With low friction and high hardness, diamond-like carbon (DLC) coatings are a prominent surface engineering solution for tribosystems in various applications. Their versatility stems from their varying composition, facilitated by different deposition techniques, which affect their properties. However, environmental impact is often overlooked in coating design. The objective of this paper is to assess the resource efficiency of four different common deposition techniques, thus identifying critical factors for sustainable DLC deposition. The coatings were deposited in one single chamber, enabling a direct comparison of the resource consumption of each technology. Expenditure of electric energy and consumables per volumetric output accounted for the environmental impact of manufacturing the coatings, which was evaluated across the indicators of damage to human health, damage to ecosystems, and resource scarcity. Electric energy use, dictated by deposition rate, was demonstrated to be the most significant factor contributing to the environmental impact. The environmental impact of PECVD and μW-PECVD was comparable and remarkably lower than that of dcMS and HiPIMS, the latter being the least energy efficient process, with the lowest output rate but highest energy expenditure. Thus, μW-PECVD could be considered the 'greenest' production method. These findings are consequential for coaters to efficiently produce good-quality DLCs with low environmental impact. [ABSTRACT FROM AUTHOR]