Distribution control and formation mechanism of gas inclusions in directionally solidified Al₂O₃-Er₃Al₅O₁₂-ZrO₂ ternary eutectic ceramic by laser floating zone melting

Distribution control and formation mechanism of gas inclusions formed in directionally solidified Al₂O₃-Er₃Al₅O₁₂-ZrO₂ eutectic ceramic rods are explored during laser floating zone melting. In atmospheric environment, highly-dense bubble-free eutectic rods are well fabricated at low solidification rate (<25 μm/s). Gas inclusions form intermittently when the solidification rate is in the range of 25−50 μm/s, but produce continuously at higher solidification rates (100−200 μm/s). The gas inclusions exhibit an elongated finger-like pattern along the growth direction, which of the maximum value of diameter first increases and then decreases with increasing the solidification rate. Meanwhile, the volume fraction of gas inclusions increased gradually with the solidification rate. Based on the effect of surface tension gradient, heterogeneous nucleation of gas bubbles is evaluated to be the primary formation mechanism of gas inclusions.