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Additive manufacturing technologies have several well-known advantages; however, the surface quality of the printed parts is poor, compromising the corrosion and mechanical properties. Thus, surface finishing treatments are necessary. The most post-processing treatments proposed in the literature are mechanical or chemical. The formers are contact techniques and cannot be suitable for complex geometry, while the latter use strong and dangerous reagents. This paper is aimed to investigate the effect of the electropolishing treatment, a contactless technique, using an eco-friendly electrolytic solution in reducing the roughness and improving the fatigue properties of Ti6Al4V specimens produced by electron beam melting technology. Several parameters affecting the effectiveness of the electropolishing treatment have been investigated, as interelectrode distance, stirring rate and duration time. An optimal combination of them allowed a uniform surface treatment and a significant roughness reduction (64% of Sa reduction for cylindrical specimens). Under sinusoidal loading conditions with a maximum stress of 378 MPa and a stress ratio equal to R = 0.1, the mean fatigue life of electropolished dog-bone specimens was 250% longer than that of as-built specimens.

This paper introduces a numerical tool developed for the design and optimization of axial-symmetrical hybrid composite/metal structures. It is assumed that the defined structures are produced by means of two different processes: Additive Layer Manufacturing (ALM) for the metallic parts and Filament Winding (FW) for the composite parts. The defined optimization procedure involves two specific software: ANSYS and ModeFrontier. The former is dedicated to the production of the geometrical and FE models, to the structural analysis, and to the post-process, focusing on the definition of the Unit Cells for the modelling of the metal part. The latter is dedicated to the definition of the best design set and thus to the optimization flow management. The core of the developed numerical procedure is the routine based on the Ansys Parametric Design Language (APDL), which allows an automatic generation of any geometrical model defined by a generic design set. The developed procedure is able to choose the best design, in terms of structural performance, changing the lattice metallic parameters (number of unit cells and their topology) and the composite parameters (number of plies and their orientation). The introduced numerical tool has been used to design several hybrid structures configurations. These configurations have been analysed in terms of mechanical behaviour under specific boundary conditions and compared to similar conventional metal structure.

Additive manufacturing (AM), applied to metal industry, is a family of processes that allows complex shape components to be realized from raw materials in the form of powders. Electron beam melting (EBM) is a relatively new additive manufacturing (AM) technology. Similar to electron-beam welding, EBM utilizes a high-energy electron beam as a moving heat source to melt metal powder, and 3D parts are produced in a layer-building fashion by rapid self-cooling. By EBM, it is possible to realize metallic complex shape components, e.g. fine network structures, internal cavities and channels, which are difficult to make by conventional manufacturing means. This feature is of particular interest in titanium industry in which numerous efforts are done to develop near net shape processes. In the field of mechanical engineering and, in particular, in the aerospace industry, it is crucial for quality certification purpose that components are produced through qualified and robust manufacturing processes ensuring high product repeatability. The contribution of the present work is to experimentally identify the EBM job parameters (sample orientation, location of the sample in the layer and height in the build chamber) that influence the dimensional accuracy and the surface roughness of the manufactured parts in Ti6Al4V. The repeatability of EBM is investigated too.

The advent of additive manufacturing technologies significantly encouraged the development and usage of lattice structures. This paper aims to experimentally investigate the influence of dimension, building position, and orientation on the mechanical properties of Ti6Al4V trusses, manufactured by electron beam melting process, to be used in lattice cells. Specimens were manufactured considering the following parameters: truss diameter (1, 1.5, 2 mm), growth orientation (0°, 45°, 90°), and specimen position inside the building chamber. Trusses with diameter of 1 mm showed inconsistent mechanical properties caused by the poor manufacturing quality. Specimen position was found to influence the analyzed mechanical properties. Unmelted powders were observed to affect the outer surfaces of all specimens and the whole cross-sections of specimens manufactured at 0°. Specimens manufactured at 45° with diameter of 2 mm demonstrated the best performances, whereas specimens manufactured at 90° with diameter of 2 mm displayed the highest elongation at fracture.

Electron Beam Melting (EBM) is an emerging additive manufacturing technique for the fabrication of titanium alloy Ti-6Al-4V for orthopedic applications. Here, a hybrid manufacturing technique viz. EBM with Friction Stir Processing (FSP) has been proposed to enhance implant surface properties. The surface modification using FSP reduces the roughness generated by the EBM technique from ~44.77 μm to ~15.82 μm. Simultaneously, FSP improves the biological and mechanical properties of the Ti-6Al-4V substrates. The roughness, wettability, amounts of ions released, and surface microhardness were measured to analyze the stability of the substrates. The effect of the hybrid processing strategy on cell viability was tested against mouse fibroblast cells NIH3T3 through MTT assay, and we found that the friction stir processed substrate (EBM-F) showed the highest cell viability. The EBM-F surface displays a two-fold increase in the cell-viability as compared to the unprocessed EBM surface after 24 h of cell-seeding. The FSP substrate allows human cervical cells HeLa to adhere onto its surface while selectively preventing the attachment of E.coli bacterial cells. These observations towards cells signify biocompatible surface characteristics of the FSP EBM substrate.

Electron Beam Melting is an Additive Manufacturing technology that allows the production of items using metal powder as raw material. The main advantage of Additive Manufacturing (AM) is realizing complex shape components; however one of the main defects is the poor quality of the surface. To this aim, different post processing treatments have been proposed such as machining, surface laser melting, sand blasting, etc. The main drawback of these technologies is the necessity to use tools that makes complex shape item difficult to handle. This inconvenient does not occur in chemical machining, since a chemical solution can operate in an undifferentiated way on the whole surface of a component. In this work some components in Ti6Al4V obtained through AM have been treated in acidic solutions containing HF and HNO3 with different HF/HNO3 molar ratio. All the solutions employed have proven to be effective in smoothing the metal surface, but the best results have been obtained with solutions with high content of HNO3. It should be noted that the process causes changes in the surface composition with respect to the received samples with an impoverishment of Al. This effect is partially mitigated by the passivating action of HNO3.

Additive layer manufacturing (ALM) is increasingly attracting the research and industry community interest due to the several benefits provided by the layer-by-layer production approach. With respect to the surface finish, process parameters influence significantly the surface roughness. According to the State of the Art, it is found out that the roughness level may affect the structural performance of ALM products by both quasi-static and fatigue points of view. In this paper, an experimental investigation is proposed, showing that the roughness level plays a more influent role for thin components, with respect to the quasi-static response. The investigated ALM process concerns the electron beam melting technology.

Additive manufacturing of titanium alloy Ti-6Al-4?V has significantly increased over the past few years, primarily due to its broad application over the conventional manufacturing process for complex and near net shape production. However, difficulties arise while printing complex and huge structures and therefore, the components need a suitable joining process. We study the feasibility of friction stir welding of Ti-6Al-4?V plates made by electron beam melting, performing both microstructural and mechanical analysis. Microstructures for all the welds reveal lamellar (??+??) phase and very fine equiaxed ? grain with the prior ? phase at grain boundaries in the stirred zone. Microhardness at different depths of the joint is measured and the strength of the joint is determined using a tensile test. The results obtained prove the feasibility of the process and provide the necessary processing conditions., by Amit Kumar Singha, Bhoopendra Kumara, Kaushal Jha, Astarita Antonello, Squillace Antonino, Stefania Franchitti and Amit Arora