Study of the critical issues related to the deposition of Ni-P + DLC multilayer coating on PBF-LB AlSi10Mg components with complex geometries and lattice structures

Complex structures in AlSi10Mg alloy produced by Powder Bed Fusion-Laser Beam (PBF-LB) show high specific strength and an advantageous surface-to-volume ratio. However, in the as-built condition they are characterized by a high roughness that may worsen their performance. To overcome this limitation, a multilayer coating was applied, comprising: (i) an electroless Ni-9%P interlayer to mitigate surface defects and optimize topography, and (ii) a hydrogenated amorphous carbon (a-C:H (DLC)) topcoat deposited via PA-CVD. After manufacturing, tumbling was carried out to improve the surface quality before the deposition of the Ni-P interlayer. The features of the coated system were evaluated by optical profilometry, FEG-SEM/EDS observations, micro/nanoscale hardness tests, and scratch test. This comprehensive analysis enabled the identification of critical challenges associated with the deposition of the Ni-P + DLC multilayer coating on PBF-LB AlSi10Mg complex-shaped components. The corrosion behavior was studied using potentiodynamic tests to determine the corrosion potential and current density, and immersion tests to evaluate the influence of surface defects and critical geometries. Corrosion mechanisms were investigated by FEG-SEM/EDS analyses.