Effects of growth direction on fatigue behaviour of EBMed Ti6Al4V specimens

Electron Beam Melting (EBM) is an additive manufacturing process able to produce near-net-shape Ti6Al4V components, but the resulting anisotropic microstructure can lead to directionally dependent mechanical properties. This study investigates the influence of build orientation on the fatigue crack growth (FCG) behaviour of EBM-fabricated Ti6Al4V. Compact Tension specimens were manufactured in three distinct orientations relative to the build direction: horizontal (HH), vertical-horizontal (VH), and vertical-vertical (VV). FCG tests were conducted according to ASTM E647. The results revealed a strong FCG anisotropy. The VV configuration exhibited superior fatigue resistance, characterised by the lowest crack growth rates. Conversely, the HH orientation demonstrated the poorest performance, with significantly faster crack propagation. Fractographic analysis via SEM confirmed that the worst behaviour of the HH specimen was due to a low-energy, transgranular quasi-cleavage mechanism, exacerbated by process-induced porosity. These findings highlighted that building orientation is a critical design parameter that must be optimised to ensure the structural integrity and service life of fatigue-critical EBM components in demanding applications.