Comparative Metrological Characterization of Ti-6Al-4V Lattice Structures Produced by Laser-Powder Bed Fusion

Additive manufacturing technologies, such as laser-powder bed fusion, enable the fabrication of metallic lattices with a wide range of topologies and size scales. The possibility of manufacturing these materials into complex shapes with good property-to-weight ratios stimulates a growing interest in several industrial sectors. Nevertheless, such small-scale structures often suffer from various morphological defects that can lead to a marked deviation from the nominal geometry and, consequently, impact the mechanical, transport, and thermal properties. An accurate characterization of the lattice geometry and dimensions is thus of paramount importance for a reliable prediction of the lattice properties. The most adopted characterization techniques for as-built lattices are X-ray computed tomography (CT), scanning electron microscopy, and optical microscopy. Contrary to the other methods, CT provides full three-dimensional data including inaccessible geometries and features, in a nondestructive way, but it requires expensive equipment and considerable expertise. Scanning electron microscopy and optical microscopy can be faster and less expensive but are nondestructive only when limited to the outer surface of the lattice. Instead, when combined with metallographic analysis, they require destructive, careful, and time-consuming specimen preparation, and the analysis is confined to selected sections. In this work, the three aforementioned techniques are used to characterize laser-powder bed fusion Ti-6Al-4V regular cubic lattices of a 4-mm unit cell size and circular cross-section struts 0.760 mm in diameter. The results of strut cross-section measurements obtained with the different techniques are compared and the effect of the size of the analysis domain on the compatibility of the results is investigated by comparing lattice subvolumes of different sizes. Via a thorough statistical analysis, it is shown that CT and metallographic characterizations lead to similar results, while the microscope imaging method can overestimate the strut thickness compared to the other methods.