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By the term, lattice structures are intended topologically ordered open-celled structures consisting of one or more repeating unit cells. Technological development and especially the growth of the additive manufacturing (AM) industry allows innovative structural design, including complex lattice structure. Selective laser melting (SLM) is an AM process that enables the manufacture of space filling structures. This work investigated the influence of the most important process parameter settings on lattices printability, focusing on the geometrical accuracy, the quantity of powders adhered to the main frame (satellites) and their compression behaviour. The process parameters such as the laser power, scan speed and layer height affect vigorously the design, quality and mechanical properties of the part. The aim of the paper is to evaluate how different parameter combinations affect the cellular structures’ printing. Twenty-four lattice structures with cubic and rhombic dodecahedron unit cells made of stainless steel 17-4PH (AISI-630) were printed using different combinations of SLM process parameters. Each structure was analysed considering its geometrical, topological and mechanical properties. Finally, the best parameter combination was evaluated comparing results achieved. Although this work investigated the 17-4PH stainless steel, physical principles related to the printing process described are generally true for the SLM process. Therefore, the adopted approach could still be suitable also for all the other materials commonly used with this AM technology.

In this work, the effect of different mixing techniques on thermal and mechanical properties of graphene nanoplatelets (GNPs) and graphene nanofibers (GANFs) loaded epoxy nanocomposites was investigated. Three dispersion methods were employed: a high shear rate (HSR), ultrasonication (US) and the fluidized bed method (FBM). The optical microscopy has revealed that the most suitable dispersion, in terms of homogeneity and cluster size, is achieved by implementing the US and FBM techniques, leading to nanocomposites with the largest increase of glass transition temperature, as supported by the DMA analysis data. The fracture toughness results show a general increase of both the critical stress intensity factor (KIC) and the critical strain energy release rate (GIC), likely due to the homogeneity and the low scale dispersion of the carbonaceous nanostructures. Based on the nanocomposite fracture toughness improvements and also assuming a potential large scale up production of the nanocomposite matrix, a single mixing technique, namely the FBM, was employed to manufacture the carbon fiber reinforced composite (CFRC). This method has resulted in being less time-consuming and is potentially most suitable for the high volume industrial production. The CFRCs were characterized in terms of tensile, flexural and interlaminar fracture toughness properties and the results were analyzed and discussed.

A customized Al-Cu-Mg-Si alloy is successfully processed by selective laser melting. AlSi10Mg powder, used as a master alloy, has been mixed with pure Cu powder through a fluidized bed and the obtained powder mix was used as feedstock material for the printing process. To investigate the feasibility of the process and to discuss the effect of the process parameters, a two-step experimental campaign has been carried out: in the first batch of experiments the energy density has been varied to frame the processing window while in the second batch the energy density has been kept constant and the main process parameters have been varied to highlight their influence on the process. Density, porosity, and microhardness have been chosen as output to evaluate the success of the process. The microstructure and composition phase were studied through scanning electron microscopy and X-ray elemental mapping, respectively. A maximum relative density of 97% has been obtained while a predominant role of the laser beam power has been observed.

The in-situ contour strategy during Laser-Powder Bed Fusion (L-PBF) process remains one of the most promising solutions to improve the poor surface quality of the parts. On the other hand, it is well established that contour step affects the formation of sub-surface defects. The aim of this work is to assess the entity of sub-surface defects during the Laser-Powder Bed Fusion of Inconel 718 samples for which different contour processing conditions are considered. Cubic samples with 10 mm side were produced through L-PBF using a Concept Laser Cusing M2 L-PBF machine. The samples were printed with fixed bulk laser parameters, adopting a layer thickness of 30 μm and a chessboard laser scanning strategy. The in-situ contour conditions were changed in terms of laser scanning speed and hatch zone border. Afterwards, the samples were analyzed in terms of surface roughness (Sa) and sub-surface density through confocal microscopy. The results revealed that the surface roughness was the most affected output as a function of the varied process parameters, including the sample position on the building platform, with values ranging from 13 to 32 μm. On the other hand, the sub-surface density was always higher than 99%.

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.

International audience; Composite materials are widely used as main parts and structural components in different fields, especially for automotive and military applications. Although these materials supply different advantages comparing to the metals, their implementation in engineering applications is limited due to low electrical and thermal properties and low resistance to erosion. To enhance these above-mentioned properties, the metallization of composite materials by creating a thin metal film on their surface can be achieved. Among different coating deposition techniques, Cold Spray appears to be the most suitable one for the metallization of temperature-sensitive materials such as polymers and composites with a thermoplastic matrix. This process relies on kinetic energy for the formation of the coating rather than on thermal energy and consequent erosion and degradation of the polymer-based composite can be avoided. In the last years, a new method to produce composite materials, as known as Fused Filament Fabrication (FFF), has been developed for industrial applications. This technique consists of a 3D printing process that involves the thermal extrusion of thermoplastic polymer and fibers in the form of filaments from a heated mobile nozzle. The implementation of this new technique is leading to the manufacturing of customized composite materials for the cold spray application. In the presented experimental campaign, Onyx material is used as a substrate. This material is made of Nylon, a thermoplastic matrix, and chopped carbon fibers randomly dispersed in it. Aluminum powders were cold sprayed on the Onyx substrate with a low-pressure cold spray (LPCS) system. This study aims to investigate the possibility of the metalizing 3D-printed composite material by cold spray technology. For this purpose, optical and microscopical analyses are carried out. Based on the results, the feasibility of the process and the influence of the morphology of the substrate are discussed, and optimal spraying conditions are proposed.

The deposition of steel powders on glass fiber reinforced polymer (GFRP) with the Cold Spray technique is investigated. Metallization of composite materials is still challenging when high-strength and dense powders, such as steel, are used due to excessive erosion of the polymer or disruption of the fibers during the deposition. To overcome these issues, low-pressure cold spray equipment has been used for the experimental campaign shown in this paper. Different coatings were obtained by using nitrogen as the carrier gas and different sets of pressure and standoff distance. Optimization of the process parameters, including the stratification of the laminate, has been carried out. Results of an initial study of the feasibility of the process and the influence of the different chosen spray conditions are exposed. In particular, the bonding mechanisms of steel powders and their morphology are discussed.

Cold spray deposition of aluminum powders on polyethylene reinforced with glass fibers has been studied. Different processing conditions, including different stratifications of the fiber-reinforced polymer used as a substrate, have been investigated to better understand the deposition mechanism. The experimental campaign has been conceived and tailored to highlight the influence of several process parameters on the deposition of the first layer of particles. The results obtained allowed to highlight and clarify the influence of standoff distance and gas pressure and also gave some insights concerning the effect of the substrate stratification. Guidelines regarding the design of the manufacturing process have been also released.

The customization of material characteristics in combination with extreme design flexibility represents the most intriguing scope of Additive Manufacturing. In this context, this work investigated the feasibility of the Laser-based Powder Bed Fusion process (L-PBF) of pre-mixed Inconel 718-Cu powder blends, exploring the effects of the laser-related process parameters and Cu addition, in order to develop alloys able to combine excellent mechanical properties under severe operating conditions with good thermal and electrical conductivity. More specifically, this work investigated the effects of using a layer thickness of $\boldsymbol{30 \mu \mathrm{m}}$ on the process quality in terms of density, microhardness, microstructure and surface roughness. Results showed that cubic samples with 10 mm side were successfully produced, with a relative density always greater than 98 percent. The resulting microhardness was from 290 to 340 HV, decreasing as a function of the Cu addition and keyhole defects development. The latter were the main defects observed in the microstructure, characterized also by heterogeneous crystalline grains for all the investigated conditions. Finally, the surface roughness (Sa) was from 7 to $\boldsymbol{25 \mu \mathrm{m}}$ , in line with the typical values of L-PBF products.

In this work, the mechanical behaviour of natural composite fibre sandwich panels is experimentally investigated. The composite sandwich panels are composed of a natural core made of Posidonia dried leaves reinforced with aluminium skins. The introduced material system is characterized by good structural behaviour (due to the aluminium skins) combined with the good thermal and acoustical insulation provided by the Posidonia core. Flexural and impact tests, characterized by different impact energies, have been performed on specimens with and without the aluminium skins, to preliminary assess the influence of the Posidonia core densities on the natural fibre sandwich mechanical behaviour.

Additive Manufacturing (AM), applied to metal industry, is a family of processes that allow complex shape components to be realized from raw materials in the form of powders. The compaction of the powders is achieved by local melting of bed. Electron Beam Melting (EBM) is an additive manufacturing process in which a focalized electron beam is the heat source that allows the powders to be compacted. By EBM it is possible to realize complex shape components; this feature is of particular interest in titanium industry where numerous efforts are done to develop near net shape processes. One of the limits of EBM based AM process is the difficulty to realize large dimension parts. Due to this limit the study of joining processes of different parts is of great interest. In the present work the microstructure evolution of sheets of TI6Al4V made by EBM and joined by Linear Friction Welding (LFW) is analyzed in details. The bulk microstructure of the specimen is fine lamellar; lamellae are enclosed in alpha colonies. Different types of porosities are observed. In the joint a Thermo Mechanical Affected Zone (TMAZ) and Weld Bead (WB) are evident. In TMAZ a partial recrystallization occurs and the parent microstructure is deformed. Complete recrystallization occurs in WB whose structure is martensitic.

The effects of different heat treatments on Inconel 718 parts produced through selective laser melting were investigated. Different heat treatments, carried out by varying both temperature and time, were performed on 10x10x10 mm3 cubes. Aiming to study the effects of the treatments, microhardness measurements, optical and SEM observations were carried out on both the treated and the untreated samples. The results obtained proved the effectiveness of the treatment, if the conditions are properly set, in producing the typical microstructure of the cast Inconel 718 that is the starting point for the conventional heat treatments. A predominant influence of the temperature was also highlighted.The effects of different heat treatments on Inconel 718 parts produced through selective laser melting were investigated. Different heat treatments, carried out by varying both temperature and time, were performed on 10x10x10 mm3 cubes. Aiming to study the effects of the treatments, microhardness measurements, optical and SEM observations were carried out on both the treated and the untreated samples. The results obtained proved the effectiveness of the treatment, if the conditions are properly set, in producing the typical microstructure of the cast Inconel 718 that is the starting point for the conventional heat treatments. A predominant influence of the temperature was also highlighted.

In this activity, customized panels for the CS deposition have been produced and aluminium has been deposited using air as a carrier gas. The custom-made panels were made with different matrix thicknesses on the surface in order to point out the influence of the fibres in the deposition and to study the feasibility and the growth of the coating. The polymer chosen for the matrix is polypropylene, widely used in the automotive sector, while for the reinforcements glass fibres have been used. Different process parameters have been examined in order to point out the influence of temperature, stand-off distance and pressure chosen, on the compaction and densification of the coating produced. In addition, morphological investigations were performed to further characterize the coatings deposited. It has been noticed that aluminium powders can be effectively deposited on polypropylene panels, leading to significantly better results when the thickness of the matrix is ​​sufficient to prevent the powders bouncing elastically on the fibres, while benefiting from the stiffening effect of the latter.

Cemented carbides, also known as Widia, are hard metals produced by sintering process and widely used in mechanical machining. They show high cutting capacity and good wear resistance; consequently, they result to be excellent materials for manufacturing cutting tools and sandblast nozzles. In this work, the wear resistance of WC-Co carbides containing Eta-phase, a secondary phase present in the hard metals when a carbon content deficiency occurs, is analyzed. Different mixtures of carbide are prepared and sintered, with different weight percentages of carbon, in order to form Eta-phase and then analyze how the carbon content influences the wear resistance of the material. This characterization is carried out by abrasive wear tests. The test parameters are chosen considering the working conditions of sandblast nozzles. Additional information is gathered through microscopic observations and the evaluation of hardness and microhardness of the different mixtures. The analyses highlight that there is a limit of carbon content below which bad sintering occurs. Considering the mixtures without these sintering problems, they show a wear resistance depending on the size and distribution of the Eta-phase; moreover, the one with high carbon content deficiency shows the best performance.

As a result of the increasing environmental awareness, the concern for environmental sustainability and the growing global waste problem, the interest of bio-composites materials is growing rapidly in the last years in order to use them in various engineering fields. Tremendous advantages and opportunities are associated with the use of these materials. On the other hand, some issues are related to the superficial properties of the bio-laminates, in particular the wear properties, the flame resistance and the aesthetic appearance have to be improved in order to extend the application fields of these materials. Aiming to these goals this paper deals with the study of the deposition of aluminum coating through cold spray process on hemp/PLA bio-composites manufactured by using the compression molding technique. Therefore, SEM observations, roughness analyses, bending tests, pin on disk and scratch tests were carried out in order to study the feasibility of the process and to investigate on the properties of the coated samples. The experimental results proved that when the process parameters of the deposition process are properly set, no damages are induced in the composite panel and that the aluminum coating, under specific load conditions, resulted to be able to protect the substrate.

Cemented carbides present some characteristics that ensure high performances for cutting and wear-resistant tools. The aim of the work is to evaluate the influence of Chromium Carbide and Nickel on the properties (wear and friction) of a cemented carbide constituted by a hard phase of tungsten carbide and a binder phase of cobalt. Different tests were carried out by varying the percentage of Cr3C2 and, for one only case, also Nickel was added. The tests were carried out by a pin-on-disk apparatus and diamond abrasive sheet. The experimental campaign provided tests for different values of load and relative velocity. Friction coefficient was directly evaluated by the apparatus and data on the wear were obtained by measuring the loss of weight of the samples (parallelepipeds with hemispherical head). The tests allowed to determine the percentage of Cr3C2 that ensure an improvement of the aforementioned properties and to highlight the irrelevance of Nickel.

The use of hard metals, in particular for cutting tools, is becoming wider. Their manufacturing cost, higher than traditional steel, is compensated by an increased lifetime. This work involves the rheological characterization of a WC–Co compound, in order to evaluate its viscosity for different values of strain rate. Following this characterization, the data are implemented in a FEM code, in order to simulate the extrusion processes of such compounds to manufacture hard metal bars. This study highlights the importance of an accurate viscosity evaluation of these mixtures and the correct setting of FEM parameters in order to predict successfully extrusion processes. As an example, an analysis is presented for the case of cutting tools with helical holes for the passing of fluid coolant.

Cold roll forming is a process for plastic deformation, which allows realizing profiles, with a defined section and established length, from the plastic deformation of a metal sheet. The sheet is induced to cross several stands of rolls, arranged along the same axis of advancing. The rolls induce plastic deformation in the sheet and then lead it to the desired geometric configuration. In order to control the geometric parameters of the plate during the profiling, it was created a FEM model to simulate the final stage of the technological process, developed by an industrial production line of a company located in Naples (Italy), that sells tubes with several cross sections. In this phase, the semi-finished product, having a circular cross section, is forced to cross through four stands of rolls. In this way, it changes the geometric condition of the cross section from circular to square. The model was carried out using a non-linear calculation code, which allows analyzing the parameters of interest in the different process steps. The results, obtained numerically, were compared with the experimental ones through the measurement of five specimens, obtained directly from technological process. The values of percentage deviation, regarding the external dimension and the thickness, for each step of advancement, do not exceed the 3% of error. Then, the analysis results denote the capability to simulate the cold roll forming process using finite element method.