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Direct metal laser sintering (DMLS) is an additive manufacturing technique for the fabrication of near net-shaped parts directly from computer-aided design data by melting together different layers with the help of a laser source. This paper presents an investigation of the surface roughness of aluminum samples produced by DMLS. A model based on an L orthogonal array of Taguchi design was created to perform experimental planning. Some input parameters, namely laser power, scan speed, and hatching distance were selected for the investigation. The upper surfaces of the samples were analyzed before and after shot peening. The morphology was analyzed by means of field emission scanning electron microscope. Scan speed was found to have the greatest influence on the surface roughness. Further, shot peening can effectively reduce the surface roughness. [ABSTRACT FROM AUTHOR]

Abstract: Silicon carbide multilayered composites containing short carbon fibres were prepared by tape casting followed by pressureless sintering. The dispersion of fibres into the SiC slurry was studied either by ultrasonics or by mechanical agitation, choosing the best solvent-dispersant couple that was compatible with the requirements of the tape casting technique. The effect of sintering temperature was studied, using carbon and boron as sintering aids, and mechanical properties were measured on composites containing from 5 vol.% to 25 vol.% of short carbon fibres. The results show that carbon fibres inhibit the complete densification of the sintered samples, and mechanical properties suffer from the high residual porosity. Since tape casting demonstrated to be a good technique to align the fibres along the casting direction, different architectures were tested for the composites, studying the effect of fibres alignment direction on the mechanical properties. [Copyright &y& Elsevier]

Laser powder bed fusion (LPBF) process allows to manufacture customized metal porous 3D parts known to have many interesting combinations of physical and mechanical properties. Therefore, the minimum resolution obtainable by this process is of high importance in the design of porous functional parts e.g. thin walls. Knowledge of the relationship between process parameters and material employed is fundamental to obtain these kinds of structures with LPBF. A series of experiments were carried out with a laser-melting system with laser power up to 200 W and a spot of 100 μm to analyze the influence of the manufacturing strategy in the construction of thin walls in AlSi10Mg alloy. The results showed that it is possible to have well defined dense thin walls using appropriate building strategies, providing also useful information for the design rules definition of the LPBF process. The results also showed that the energy density is not able to provide information on the complexity that involves the melt pools formation and propagation. A mathematical model was also developed to build well defined thin walls directly through the process parameters and to reduce the mismatch between as-designed and as-manufactured thin wall structures. The verification of such model was made building thin walls in AlSi10Mg and then comparing them to the as-designed structures. [ABSTRACT FROM AUTHOR]

• Corrosion resistance of as-built AlSi10Mg lower than that of polished samples. • Chloride concentration played a key role in the initiation of localized corrosion. • Selective dissolution of the α-Al phase observed, especially at melt pool edges. • Si-rich particles acted as cathodes to promote preferential attack of Al. Potentiodynamic tests were performed on AlSi10Mg alloy produced using laser powder bed fusion. As corrosion depends on the surface conditions, we compared the rough as-built surface with that formed after mechanical polishing and passivation in air. The as-built samples showed lower pitting potentials than polished samples. Corrosion initiation depended heavily on the chloride concentration. The higher potential of Si particles compared to the Al matrix provided the driving force for selective dissolution of the α-Al phase. The potential difference between the Si particles and α-Al phase was higher at the melt pool edges, resulting in preferential attack of these regions. [ABSTRACT FROM AUTHOR]

Abstract Laser powder bed fusion (LPBF) is one of the most widespread additive manufacturing (AM) technologies for metals, in which the components are built additively layer upon layer along the z-axis (the building direction) perpendicular to the building platform (xy-plane). Here, we evaluated the effect of post-processing heat treatments at 200, 300, and 400 °C on the corrosion resistance of AlSi10Mg alloy manufactured by LPBF for two orientations in the building chamber (XY – parallel to the building plane or XZ – perpendicular to the building plane). Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests were conducted at the constant chloride ion concentration of 0.02 M and 23 °C for the as-built and heat-treated specimens. All specimens were polished on the surface and displayed similar behaviors in the EIS tests. The pitting potential results were widely scattered and therefore analyzed using a statistical approach. Statistical data analysis based on analysis of variance technique (ANOVA) was performed. The results confirmed that the population significantly differs only by considering the heat treatments and the building direction plays only minor role. The cumulative distribution curves of pitting potentials showed a decrease in pitting resistance as the temperature of heat treatment increases. Graphical abstract Effect of heat treatment temperature on the pitting potentials of AlSi10Mg obtained by means of laser powder bed fusion. Image 1 Highlights • Pitting potentials of AlSi10Mg present a wide experimental variability. • Cumulative frequency of pitting potentials shows a deleterious effect of the temperature of post-processing heat treatment. • Corrosion attack take place at the edge of melt pool up to 300 °C of heat treatment temperature. [ABSTRACT FROM AUTHOR]

Additive manufacturing technologies have been increasingly applied to the development of radio frequency components in the past few years. Indeed, the free-form capability of these processes allows for the design of novel components, whose actual implementation through conventional machining is rather complex or even not possible. This paper describes a monolithic WR51 component integrating three radio frequency functionalities, namely, bending, twisting, and filtering. Three aluminum prototypes with different bending/twisting radii have been manufactured through the selective laser melting process. They exhibit a measured rejection higher than 60 dB in 17.5 and 21.2 GHz, and a measured return loss better than 20 dB in 12.5 and 15 GHz. Significant mass and envelope reductions (higher than 60% depending on the bending/twisting radius) with respect to the reference subsystem with distinct waveguide components are achieved. These results assess the effectiveness of 3-D metal printing in the miniaturization and integration of waveguide systems. [ABSTRACT FROM PUBLISHER]

Selective laser melting (SLM) process, an additive manufacturing (AM) technology, has had a rapid growth in the biomedical and aerospace markets because of the ability to manufacture complex designs directly from computer-aided design (CAD) using materials such as titanium and aluminum alloys. Although this technology allows designers to fabricate geometries not achievable with conventional manufacturing, it has some restrictions. The paper presents the technological problems and restrictions resulting in the production of structures in aluminum alloy by SLM. In particular, it analyzed the input file of the process, .STL file, and the dimensional limits of geometries with sharp edges as a simple parallelepiped with a square base since the understanding of the limitations can help the designer in the creation of new components. The creation of function-independent design rules, easily transferrable on individual part designs, could allow a wide industrial usage and a better knowledge of AM technologies. The results presented in this paper showed that the choice of parameters of conversion from the CAD model to .STL file could be a restriction for the software for preprocessing part but also affects the surface roughness. Moreover, if a SLM machine with a laser beam of 100 μm is used, it is not possible to produce geometries with sharp edges with size base below 0.8 mm in an aluminum alloy. [ABSTRACT FROM AUTHOR]

The paper investigates the corrosion behavior of AlSi10Mg alloy produced by direct metal laser sintering (DMLS). Potentiodynamic tests were performed in aerated diluted Harrison solution, on specimens with different orientation with respect to the building plane. Different surface finishing were analyzed, covering rough surfaces as produced by DMLS and after polishing by means of emery papers and alumina slurry or chemical polishing with phosphoric and nitric acid bright dipping (BD). A conversion treatment by short immersion in Ce(III) salt solution was evaluated in order to improve corrosion resistance of both as-produced surface and polished surface. Selective attack of α-Al phase occurs at the border of the melting pools, typical of DMLS process, and slightly reduces on transversal planes, perpendicular to the building plane. Acid pickling slightly improves the corrosion resistance of as-produced surface, but no positive effects were noticed on polished one. The Ce(III) conversion treatment does not inhibit corrosion on as-produced specimens. Its effectiveness is higher on polished and pickled specimens. On polished surface, the effectiveness of conversion treatment mainly depends on plane orientation. [ABSTRACT FROM AUTHOR]

The paper deals with the effect of heat treatments on corrosion resistance of an AlSi10Mg alloy obtained by means of Direct Metal Laser Sintering. The tests were performed on as-processed alloy and after different post-heat treatment, covering stress relieving, annealing at high temperature and water quenching. Potentiodynamic and electrochemical impedance spectroscopy tests were carried out in aerated Harrison solution. The results show localized corrosion and selective penetrating attack at the border of melt pools on untreated or only stress relieved specimens. The selective attack was not observed after high temperature annealing. Modification of EIS plot evidenced galvanic coupling with silicon coarse particles that extensively precipitate during high temperature annealing. The morphology of precipitates is described in order to evidence their relevance in terms of rising selective penetrating attack and galvanic coupling. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) technologies are gaining increasing attraction for biomedical applications due to the granted customizability and optimal surface topography for osteointegration. Ti-6Al-4V is one of the most promising materials due to its biocompatibility. However, excessive ions release can occur, leading to a relevant immunologic response in the surrounding tissues. Despite the corrosion behavior of the conventionally-manufactured material being well known, it should be assessed for AM-processed components, as the effect of the unique superficial and microstructural features granted by the process is still quite unknown. The aim of this paper is the electrochemical evaluation of the passive current density of the laser powder bed fusion (LPBF)-processed Ti-6Al-4V alloy via potentiostatic tests, carried out at typical in-service potentials for biomedical implants. This parameter is correlated with the ion release rate of the alloy, a fundamental phenomenon to address to prevent possible inflammations caused by the implant. Different manufacturing conditions (surface finishing, heat treatment) and exposure time (0, 60 and 6000 h) were considered. The importance of performing these measurements over a long period (> 8 months) was demonstrated. In fact, despite the initial current densities being significantly affected by the surface and microstructural differences, the ion release rates converged for long-time exposures. The results also underlined the good corrosion resistance of the material. Poor corrosion performances, alongside with significant current densities development, were observed in the as-built condition. A pickling treatment demonstrated to mitigate such effect without compromising the unique surface finishing granted by the manufacturing technology. [ABSTRACT FROM AUTHOR]

In the present work, the fabrication and characterization of non-curling, free-standing TiO2 nanotube mem- branes and their integration in front-side illuminated dye-sensitized solar cells are reported. Vertically oriented TiO2 nanotube arrays were fabricated by anodic oxidation of a titanium foil. Nanotube membranes were detached from the metallic foil, transferred and bonded on transparent fluorine-doped tin oxide/glass substrates employing a TiO2 sol as a binder. Crystalline phase and morphology of the film were investigated, evidencing the formation of a highly ordered 1D nanotubes carpet, with a pure anatase crystalline structure. TiO2 nanotube-based DSCs were fabricated using reversible microfluidic architecture. The cell performances were studied by I-V electrical characterization, incident-photon-to-electron conversion effciency, electrochemical impedance spectroscopy and open circuit voltage decay measurements, showing an increase in electron lifetime compared to nanoparticle-based dye- -sensitized solar cells. [ABSTRACT FROM AUTHOR]

Additive manufacturing has emerged as a promising method for developing new Ti-based alloys. However, very few works have been dedicated to the in-situ synthesis of Ti-Cu alloys using Laser powder bed fusion (LPBF) method. The current work investigates the correlations between the volumetric energy density (VED) and some structural features of the in-situ Ti-5 wt.% Cu alloys produced by LPBF of the elemental powders. The results highlighted the importance of selecting the size of constituents in accordance with their thermophysical properties. It was also shown that crystallite size and lattice distortion of the α phase increased with increasing the VED. These were attributed to the higher temperature and lower cooling rate of the melt pools as well as improved particles melting and copper dissolution in the titanium lattice at higher VEDs. Isotropy of the microstructure was also improved at higher VEDs. Image 1 • In-situ Ti-5%Cu alloy was produced by Laser Powder Bed Fusion of elemental powders. • Correlations between Volumetric Energy Density and microstructures were investigated. • Crystallite size and lattice distortion of α phase increased with increasing VED. • Isotropy of the microstructure was improved at higher VEDs. • Constituents size must be chosen in accordance with their thermophysical properties. [ABSTRACT FROM AUTHOR]