Enhanced Mechanical Anisotropy from Lack‐of‐Fusion Voids in a Low‐Strength Near‐Alpha Titanium Alloy Fabricated by Electron Beam Additive Manufacturing

The mechanisms governing mechanical anisotropy in additively manufactured titanium alloys containing pore defects remain incompletely understood. This study investigates such phenomenon in a low‐strength near‐α titanium alloy fabricated by electron beam powder bed fusion (EB‐PBF), focusing on the unique role of lack‐of‐fusion (LOF) flat voids. In contrast to high‐strength counterparts, the studied alloy exhibits a pronounced ductility anisotropy: the transverse elongation‐to‐fracture reaches 10.5%, 2.5 times that of the vertical direction, while strength anisotropy remains negligible. Analyses of slip bands, stress/strain fields, and fracture characteristics attribute this anisotropy to the synergistic effects of strongly anisotropic stress concentrations and significant variations in the effective load‐bearing area caused by the flat voids. Under vertical loading, accelerated stress concentration and the formation of micro shear bands adjacent to the flat voids lead to premature fracture. In contrast, highly dense samples display only minor anisotropy with a reversed trend, primarily governed by intense deformation mismatch between columnar grains. These findings elucidate the critical role of LOF flat voids in controlling anisotropic mechanical behavior of EB‐PBF titanium alloys.