Friction and wear characteristics of DLC-terminated coatings deposited on AlSi10Mg alloy produced by Additive Manufacturing

Al–Si alloys are attractive materials for the fabrication of mechanical components, mainly because of their high strength-to-density ratio. Though the advent of Selective Laser Melting (SLM) has potentially expanded the range of their applicability, their poor tribological performances limit their effective use. Identifying post-processing protocols and coating strategies enhancing these properties and compatible with large-scale production is fundamental to the industrial uptake of SLM-fabricated Al–Si parts. This work tests the possibility of depositing self-lubricating Diamond-Like Carbon (DLC)-terminated films on AlSi10Mg built by SLM and subjected to different surface finishing processes. The applied coating architectures consist of an electroless nickel-phosphorus buffer layer deposited on the AlSi10Mg surface, plus a series of interlayers and a DLC top film grown by Plasma Assisted – Chemical Vapor Deposition. The wear resistance and frictional behavior of the samples are evaluated for different substrate pre-treatments and coating assemblies under two applied loads. Cast substrates, processed and coated in a similar way, are also studied for comparison. The DLC film lends good tribological performances to all the coating-substrate combinations explored, being mechanically assisted by the underlying Ni–P layer. The friction coefficients stabilize around 0.20 at the lowest load, independently of the sample surface roughness (Sq), which spans the range 0.47–4.6 μm. Conversely, the counterpart wear rates increase with roughness up to 10􀀀 5 mm3/(N⋅m). Both tribological parameters decrease by nearly 20 % and 70 %, respectively, after a tenfold increase in load. These results indicate that DLC-terminated multilayers are extremely efficient on AlSi10Mg even in the presence of significant roughness. Their application requires a limited number of wellestablished processing steps also in the case of SLM grown parts.