Abstract:The defects formed inside the additive manufactured (AM) part have a detrimental effect on the mechanical performance of the printed component. The effect of defects on the performance of parts varies with their geometry features. The characteristics of porosity defects in 36 bulk Ti6Al4V specimens with different printing parameters were investigated via X-ray computed tomography (XCT). The porosity defects are classified into four types: spherical- shaped, elliptical-shaped, elongated-shaped and irregularly-shaped pores, based on their geometric characteristics. Elongated-shaped defects account for the largest proportion of defects with all printing parameters, and the proportion of irregularly-shaped defects enhances with the increase of scanning speed. The characteristics of gradual accumulation of defects in single-track and multi-track samples were also analyzed. Porosity may gradually accumulate with the overlay of layers, while the appropriate overlapping rate may melt the pores between the tracks. The formation of defects is greatly influenced by surface roughness and pool wetting.

Key words: selective laser melting; X-ray computed tomography; porosity defect; 3D geometric morphology; formation mechanism; Ti6Al4V alloy