Influence of nano-sized WC addition on the microstructure, residual stress, and tribological properties of WC-Co HVAF-sprayed coatings

Selective Laser Melting (SLM) opens new opportunities for the use of Al-Si alloys in mechanical parts. Besides simplifying the fabrication of complex components, this Additive Manufacturing technique also helps improve the mechanical properties of Al- Si alloys, making them attractive for applications where low or moderate load carrying capacity is required and significant weight reduction is desirable. However, the tribological properties of these components are generally inadequate and the optimization of dedicated post-processing protocols and coating strategies becomes mandatory. This work tests the possibility of depositing self-lubricating Diamond Like Carbon (DLC)-based films on an AlSi10Mg alloy built by SLM, with methods suitable for large-scale production. The resulting wear resistance and frictional behavior are evaluated under various applied loads, using substrates prepared with different pre- treatments. Cast samples are also considered for comparison. The applied coatings are multilayer architectures produced with industrial techniques, consisting of an electroless nickel-phosphorus buffer layer deposited on the AlSi10Mg surface plus a DLC top thin film grown by Plasma Assisted - Chemical Vapor Deposition (PA-CVD). The buffer layer assists coating adhesion while the DLC termination lends improved tribological performances. At 1 N load, the friction coefficients stabilize in the range 0.18-0.22 for different coating-substrate combinations whose surface roughness (Sq) varies between 0.47 and 4.6 µm. Even lower values are obtained when increasing the load to 10 N, similarly to what is found for the counterpart wear rate, which passes from 10-6-10-5 to 10-7-10-6 mm3/(N∙m). These results indicate that DLC-terminated coating architectures are extremely efficient on conventionally made samples as well as on SLM grown samples even in the presence of significant roughness. At the same time, industrial processes such as PA-CVD prove to be a viable solution for depositing on SLM components after standard finishing procedures have been applied on their surfaces.