Friction and wear of DLC films deposited on additive manufactured AlSi10Mg: the role of surface finishing

The recent introduction of Additive Manufacturing in the vehicle industry paves the way for advanced cus-tomization and optimized consumption of resources in components production. However, the poor surface fin-ishing typical of additively manufactured parts hinders their practical use without further processing. Controlling roughness is particularly important when applying coatings, but may imply a considerable increase in the manufacturing costs, depending on the required finishing level. In this work, the still unexplored combination of Diamond-Like Carbon (DLC) coatings with additive manufactured metallic materials is investigated. In partic-ular, substrates are adopted in the form of discs of AlSi10Mg aluminium alloy built by Selective Laser Melting. The effectiveness of the coatings is studied from the tribological point of view, with focus on the effects produced by the surface topography. For the purpose, the AlSi10Mg discs are processed with different combinations of finishing techniques, and coated with a-C DLC deposited by magnetron sputtering. The resulting films are 1.7 mu m thick with root mean square roughness ranging from 0.28 to 2.67 mu m. Ball-on-disc friction tests reveal that, with respect to uncoated samples, the presence of the films produces a significant decrease of both the friction co-efficient and the wear rate, which reach values as low as 0.15 and 1 center dot 10-6 mm3 (N m)-1, respectively. Most noticeably, both friction and wear exhibit a minimum if plotted against the coating roughness. Such a behaviour, explained in terms of abrasive and adhesive mechanisms, indicates the existence of an intermediate range of roughness that minimizes friction and wear, hence suggesting that high levels of finishing are not necessary to achieve good tribological performances.