Geometrical accuracies, defects and compressive mechanical failure of hollow Ti-6Al-4V alloy cylinders printed by laser powder bed fusion using X-ray microcomputed tomography

While 3D metal printing is widely used for making complex structures, the printing quality of internal structures and defects are difficult to assess due to technical challenges. This study used X-ray microcomputed tomography (micro-CT) to reveal geometrical accuracies, defects and mechanical failure of Ti-6Al-4V alloys printed by laser powder bed fusion. Ti-alloy cylinders of 10 mm height and 5 mm diameter containing either a circular or a square internal central hole of a cross-sectional area of 1 mm², were printed horizontally and vertically. The printed metal structures were scanned using high-resolution (7 μm voxel size) micro-CT. The cylinders were then subjected to compression tests to evaluate their compressive mechanical properties, including Young’s modulus, ductility, compressive strength and yield strength. Fractured cylinders were re-scanned by micro-CT to investigate failure behaviors. The results show that all printed Ti-6Al-4V structures had imperfect quality with malforms, dimensional errors, porosities, and unconsolidated powder. Vertical printing achieved higher form and dimension accuracies than horizontal printing. Pore defects and unconsolidated powder concentrated within internal peripheries of printed cylinders. The Young’s moduli and strength were significantly affected by internal structures and defects, and printing directions. Vertically and horizontally printed cylinders with square internal holes exhibited a more ductile brittle fracture mode and suffered from compression-induced catastrophic shear failures compared to the ones with circular internal holes. This research provides a micro-CT detection technique which can be used for the quality assurance of hollow 3D-printed metal structures.