Effect of Energy Density of Incident Beam on Mechanical Property of Titanium Alloy Products Fabricated by Electron Beam Melting (EBM) Method

Abstract

Electron beam melting (EBM) is a promising fabrication technique for directly producing metal products from powder as the starting material. Powders are provided as a thin layer (~100 μm) and melted layer by layer with an electron beam. In this study, the effects of the energy density of the incident beam on the mechanical properties of Ti–6 mass% Al–4 mass% V alloy products fabricated through EBM were examined. The products were fabricated using an electron beam at various energy densities depending on the electron beam current. The microstructures and crystallographic orientations were observed using optical microscopy and electron backscatter diffraction (EBSD), respectively. Compression tests were carried out in 2 loading directions using a mechanical testing machine equipped with strain gauges, one perpendicular (x–y direction) and the other parallel (z direction) to the stacking direction. In principle, the microstructure consisted of an acicular-shaped α phase (hcp lattice) and a small-volume β phase (bcc lattice). In addition, columnar grains elongated toward the z direction appeared during the repeated melting and solidification that occurred during the EBM process. An increase in the beam current of the incident beam enlarged the α grains and increased the relative density, resulting in the related Young’s modulus of the products. The energy density caused by the beam current also introduces anisotropy in the deformation behavior depending on the loading axis toward the stacking direction. This is closely related to the cast defect arranged along the stacking layers. It was concluded that the mechanical properties of the Ti–6 mass% Al–4 mass% V alloy products formed through EBM were very sensitive to the incident beam current and stacking direction, resulting in the exhibition of anisotropic deformation behavior within a limited range of energy density.