Search

The integration of metals and polymers in the same component to couple the best properties and advantages of both these classes of materials can be useful for engineering applications. In this scenario, the aim of this paper is to integrate additive manufacturing of composites with cold spray deposition of metal particles: in particular, 3D-printed carbon fibre-reinforced plastics (CFRP) panels were coated with aluminium particles to couple the lightweight and high mechanical properties of CFRP with high wear resistance and hardness of metals. CFRP panels have been produced by using the Fused Filament Fabrication (FFF) technology, then the panels have been coated with aluminium particles by using a low pressure cold spray facility. Panels with various stratification sequences have been produced to investigate the feasibility of the process and to highlight the influence of the lay-up strategy on the whole process; the parameters of the cold spray process have been also optimized to ensure an effective deposition. Adhesion tests, distortion measurements, cross-section observations and surface coverage measurements have been chosen as response outputs to evaluate the effectiveness of the process and to assess the influence of the process parameters. The integration between FFF of CFRPs and cold spray deposition of aluminium particles has been proved, values of surface coverage close to 100% and good values of adhesion strength (close to 4 MPa) have been achieved; moreover, the presence of the fibres, giving a higher stiffness to the substrate, avoids the occurrence of distortion phenomena during the deposition. It was also proved that the printing parameters influence the deposition: an increase in the infill density from 30% to 50% leads to an increase in the adhesion strength up to 40%. In summary, the results obtained proved the feasibility of the process and allowed to enucleate directions of future research.

Surface metallization is amongst the recent trends in the polymer and polymer matrix composites (PMCs) research industries to improve the electrical and thermal properties and exploit the subsequent utilization in the aerospace sector. Specifically, polymer matrix composites have been subjected to the limitations in form of high temperature exposure and substrate deterioration. The present study encompasses a new strategy in the manufacturing and metallization process. The first stage in the manufacturing of hybrid thermoplastic-thermoset composite was the hot compaction which comprised of primary preform preparation enabling the partial impregnation of the thermoplastic resin through the fabric reinforcement layer. The subsequent stage entailed the preform vacuum bagging and conducting catalyzed thermoset resin impregnation. The vacuum resin infusion step included a cocuring cycle to generate a fiber reinforced composite comprising of thermoplastic and impregnated thermoset resin with improved adhesion. Resin flow front movement was analyzed during the resin infusion process. Composite metallization was achieved through cold spray (CS). CS process parameters influence on the coating quality and characterization of laminates through microstructural analysis and results have been reported. The hybrid composite with thermoset resin through thickness and in-plane impregnation was achieved with the intact adherent thermoplastic layer after the curing cycle. In the CS metallization, the effective operative window of stand-off distances (SoD) and temperature has been determined.

In this research activity, the manufacturing of metallic coatings on polymer-based panels through the low pressure cold spray technique was studied. Aluminium particles were sprayed for the metallization and carbon fibre composite materials with thermoplastic matrix (PP, PA66) were used as substrates. Different deposition parameter combinations have been set to investigate the feasibility of the process; SEM analyses were carried out to study the coating surface morphology and the interface interaction between particle and substrate. The results showed that the CS process is an effective technique to create aluminium coatings on polymeric matrix composite materials: compact coatings can be obtained if the process parameters are properly set.

The Cold Gas Dynamic Spray technology, generally referred as Cold Spray, is a relatively new additive manufacturing technique able to produce fully dense coatings through the deposition of particles on a substrate. Fine powders are accelerated to high velocity and projected onto a substrate, upon impact with the target surface, conversion of kinetic energy to plastic deformation occurs and the solid particles deform and bond together. During the cold spray deposition process, the particles remain in a solid state during the deposition, resulting in high-quality coatings with low residual stresses and oxide inclusions. The relative lower process temperatures allow the cold spray to manufacture coatings on high temperature-sensitive materials. It could also be a valid method for deposition of a wide variety of materials, from metallic alloys up to ceramics and composites. Depending on the materials employed as substrate and coating, different bonding mechanisms can occur during the deposition. The present review aims to summarise the main bonding theories proposed up to now for the cold spray, focusing on both the particle deformation behaviour during the contact with the surface and the interfacial bonding mechanisms. The available theories for different substrate/coating configurations will be discussed and compared. The effects of deposition parameters, the substrate’s surface and microstructure of feedstock powders on the bonding mechanism will also be discussed.