Near-infrared in situ observation of bubble migration and crystal growth behavior in a laser-induced Al2O3 molten pool

Abstract The dynamics of defect formation during the melting and solidification process in the selective laser melting and laser fusion welding of ceramics remain unclear. In this study, we propose a simple visualization method using near-infrared light to directly observe fundamental phenomena in the molten pool of ceramics under laser irradiation. Submillimeter Al 2 O 3 samples with varying density ratios were irradiated with a CO 2 laser, and the interior of the molten pool was visualized using an 850-nm near-infrared light source and a bandpass filter. Observations of bubble migration captured with a high-speed camera indicated that some of the bubbles move along the Marangoni convection depending on their diameter. The three-dimensional motion of bubbles was observed from two distinct angles. The bubbles approximately 3 μm in diameter were observed under high magnification. In addition, crystal growth behavior was observed during the solidification process. The efficacy of the proposed method was demonstrated by visualizing the effect of the material density ratios on bubble diameter and its distribution inside the molten pool. Graphical abstract