A study on the mechanical properties of micro-truss Ti-6Al-4V materials fabricated by Electron Beam Melting

Electron beam melting (EBM) has been used to manufacture Ti-6Al-4V micro-truss materials for light weight mechanical applications. Several structures were examined, including a cubic lattice, a diamond structure and randomly-structured foams. The “As-built" material, after the selection of processing parameters and fabrication, has been characterised at a micro and macro level through optical microscopy (OM) and x-ray tomography (XCT) respectively. In order to assess the beam penetration and dimensions of the material after the deposition, a numerical method was employed to study the heat source interaction with the metal to be melted. Fabricated structures were evaluated after compression testing, identifying the collapse behaviour. The influence of the microstructure was investigated in the “As-built" condition and after post-builds heat treatments at lower and higher temperatures than the beta-transus. From this study, is it suggested that the incidence of volumetric defects from the additive manufacturing (AM) process influences the mechanical resistance and performance more dramatically than the bulk material properties. Additionally, due to the nature of the alloy system with work hardening and low heat conductivity, the observed failure mode was related to the development of adiabatic shear bands. This type of failure was characterised by deformation at high strain rates through Hopkinson bar tests.