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2016 - 2017, The research activity was devoted to the study of the composite materials manufacturing processes. In particular, the liquid composite molding (LCM) processes were the object of the performed study. In recent years LCM processes have gained a widespread diffusion in different industrial fields, from civil to automotive and aerospace due to their several advantages compared to the conventional autoclave processes. However, some disadvantages related to a not uniform preform impregnation due to a local variation of the preform permeability, fibers bundles misalignment, that would results in dry zones or matrix richer areas, affect the LCMs limiting their usage in industrial full scale. Other limits are due to a limited pressure driving force as well as a reduced pressure compaction influencing the final volume fraction achievable with detrimental effects on the mechanical properties of the composite material product. A more deep knowledge of the phenomena involved in the manufacturing of the composite materials are required to implement proper control action on the parameters (e.g. pressure, resin flow rate, thermal cycle as well as inlet/vent locations) to optimize the process. In order to improve the impregnation of the preform and reduce the time required to fully fill the mold cavity an in-line microwave preheating system was developed. The aims was to couple a microwave generator upstream the LCM mold to heat up the resin prior the entry into the mold. Indeed, the temperature increasing reduces the liquid viscosity allowing the resin to flow more freely through the dry preform. To perform a thorough study on the effectiveness of the proposed approach a laboratory scale apparatus for liquid composite molding processes was designed. The system was instrumented with ad-hoc designed sensors to monitor the resin flow during the process. Cheaper dielectric sensors are designed, produced and installed on the mold. A numerical model was also developed to simulate the resin flow through the fibers preform. The numerical model proved to able to deal with the dual-scale nature of the textile preform commonly used in the LCMs, that are characterized by two different regions (inter- and intra-tow) with different values of permeability. The numerical outcomes were also used to validate the data obtained from the dielectric sensors. They demonstrated to be able to monitor the both the impregnation and the saturation of the fiber preform. The developed microwave heating system proved to be effective to both reduce the total infusion time as well as improve the wetting of the fibers, achieving a more uniform impregnation with a limited amount of residual voids.[edited by Author], XVI n.s. (XXX ciclo)

This paper deals with the study of the enhancement of the tribological properties of AA2024 through the deposition of a titanium coating. In particular two different coatings were studied: (1) untreated titanium coating; and (2) post-deposition laser-treated titanium coating. Titanium grade 2 powders were deposited onto an aluminium alloy AA2024-T3 sheet through the cold gas dynamic spray process. The selective laser post treatment was carried out by using a 220 W diode laser to further enhance the wear properties of the coating. Tribo-tests were executed to analyse the tribological behaviour of materials in contact with an alternative moving counterpart under a controlled normal load. Four different samples were tested to assess the effectiveness of the treatments: untreated aluminium sheets, titanium grade 2 sheets, as-sprayed titanium powders and the laser-treated coating layer. The results obtained proved the effectiveness of the coating in improving the tribological behaviour of the AA2024. In particular the laser-treated coating showed the best results in terms of both the friction coefficient and mass lost. The laser treatment promotes a change of the wear mechanism, switching from a severe adhesive wear, resulting in galling, to an abrasive wear mechanism.

Cold Gas Dynamic Spray is an emerging coating technology based on the use of a supersonic gas jet to accelerate (up to 1000 m/s) and to impact a powder, with size ranging from 1 to 50 μm in diameter, on a substrate. Due to the high speed, during the impact, the powder undergoes a severe plastic deformation such that it adheres on the substrate. Thanks to this method, it is possible to produce up to fully dense metallic coatings on substrates of different materials. With this technology, different kinds of powder (metals, polymers, ceramics, composite materials and nanocrystalline powders) or their mixing can be deposited. Among the various possible powders that can be deposited by cold spray, titanium is one of the most attractive materials thanks to its potential applications. A titanium layer produced onto a softer materials (i.e. aluminium alloys) could improve both the corrosion resistance and the wear properties of the components. However, the coating made with this technique could be affected by several problems, such as porosity, high roughness and low mechanical properties. A possible solution for this issues is the use of laser remelting post-deposition treatment. The present investigation deals with the application of a continuous wave diode laser in order to change the coating properties and metallographic structure. With this aim, laser remelting of a titanium cold sprayed layer were carried out on samples of grade 2 titanium alloy, 5 mm thick, obtained by cold spray technique, by using a 220 W diode laser at different scan speed. In order to avoid the influence of the particular substrate, the laser remelting process was carried after the detachment of the coating from the substrate. After laser treatments, light and SEM microscopy were carried out to analyze the geometry of remelted zone and the evolution of its microstructure morphology. Moreover, micro-hardness measurements were made to evaluate the mechanical properties. Three different metallurgical structures corresponding to the remelted zone, the heat affected zone and base material were observed. The remelted zone showed an elliptical shape, with a depth up to 0.7 mm and a martensitic microstructure. Furthermore, in this zone, hardness higher than the base material (more than threefold) was found. In conclusion, it is possible to affirm that the laser remelting is a promising technique to improve the superficial properties of titanium cold sprayed layers.