In Situ Visualization of Bubble Formation During Selective Laser Melting of an Alumina Powder Bed

The behavior of bubble and pore formation during selective laser melting of ceramics remains unclear. In this study, in situ observations of a single laser scan over an alumina powder bed were performed using a simple near-infrared visualization system. A CO 2 laser was scanned over a pressurized powder bed under various irradiation conditions, and the interior of the molten pool was recorded with a high-speed camera. The solidified beads were then analyzed by X-ray computed tomography. The observations revealed bubbles forming at the solid–liquid interface and migrating within the molten pool, which were ultimately trapped as pores in the solidified structure. In addition, a qualitative correlation was established between the pore distribution in the solidified structure and the bubble distribution observed in situ. The influence of laser irradiation conditions on pore formation behavior was systematically clarified. These results demonstrate the effectiveness of near-infrared observation techniques in selective laser melting of oxide ceramics.