Electron Beam Melting (EBM) is an Additive Manufacturing technique which can be used to fabricate complex structures from alloys such as Ti6Al4V, for example for orthopaedic applications. Here we describe the use of EBM for the fabrication of a novel Ti6Al4V structure of a regular diamond lattice incorporating graded porosity, achieved via changes in the strut cross section thickness. Scanning Electron Microscopy and micro computed tomography analysis confirmed that generally EBM reproduced the CAD design of the lattice well, although at smaller strut sizes the fabricated lattice produced thicker struts than the model. Mechanical characterisation of the lattice in uniaxial compression showed that its behaviour under compression along the direction of gradation can be predicted to good accuracy with a simple rule of mixtures approach, knowing the properties and the behaviour of its constituent layers.

Electron Beam Melting (EBM) as a means of Additive Manufacturing (AM), is of interest for the fabrication of intricate geometries for cellular materials in areas where complex architectures are needed, e.g. biomedical implants. Most studies have focused on specific geometries and so the effect of the structure on mechanical performance is not well understood. Many kinds of micro- and macro-scale defects can arise in additively manufactured components, so assessment of their influence on properties is needed. In this work, lattices of Ti-6Al-4V having a cubic structure have been manufactured by EBM, and the effect of heat treatments above and below the β-transus temperature on microstructure and compression response have been investigated. The former modifies only slightly the α+β structure and mechanical performance whereas the latter leads to coarse alternating α and β lamellae packets and α at the prior grain boundaries with a 10% loss in yield strength. The variation in the compressive yield stress with strut diameter is in good accord with simple models based on compressive deformation rather than shearing or buckling. Internal pores for struts aligned with the build direction are found around the edges of the solid form, in regions which seem to be associated with the EB scan pattern. Struts normal to the build direction show more significant defects but their redundancy means that they do not compromise the compressive performance in the build direction. Using a particle size in the range 45–100 μm minimum weld-track sizes were experimentally and numerically identified to be 176 and 148 μm in depth respectively with a depth-to-width ratio of 0.55. This produced a beam pass of the order of 300 μm oversizing small features (struts of 0.4 and 0.6 mm nominal diameter) when a contour around the strut periphery was applied

An investigation on the additive manufacturing and the experimental testing of 3D models of tensegrity\ud prisms and columns is presented. An Electron Beam Melting facility (Arcam EBM S12) is employed to 3D\ud print structures composed of tensegrity prisms endowed with rigid bases and temporary supports, which\ud are made out of the titanium alloy Ti6Al4V. The temporary supports are removed after the additive man-\ud ufacturing phase, when Spectra cross-strings are added to the 3D printed models, and a suitable state of\ud internal prestress is applied to the structure. The experimental part of the study shows that the examined\ud structures feature stiffening-type elastic response under large or moderately large axial strains induced\ud by compressive loading. Such a geometrically nonlinear behavior confirms previous theoretical results\ud available in the literature, and paves the way to the use of tensegrity prisms and columns as innovative\ud mechanical metamaterials and smart devices

The Electron Beam (EBM) additive manufacturing process is well suited to fabricating complex structural designs in Ti–6Al–4V because of the design freedoms it offers combined with strong and consistent material properties. However it has been observed that complications may arise when manufacturing truss-like structures (such as those produced via structural topology optimization) in the form of undersized features on the finished part. The issue appears to affect truss members that are not aligned with the vertical build direction, with an apparent lack of material on the negative surfaces. This effect appears to worsen with a greater angle between the truss member and the build direction, even with the use of support structures. This investigation has characterized and measured the dimensional errors that result from this issue through 3D scanning techniques. Process modifications have then been made which result in significant improvements in dimensional accuracy. This investigation highlights the importance of heat management at features with negative surfaces to yield parts that are dimensionally accurate without introducing excessive internal melt defects in the form of voids and porosity