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 mu m. Conversely, the counterpart wear rates increase with roughness up to 10-5 mm3/(N & sdot;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.