Study of the stability of the molten zone and the stresses induced during the growth of Al_2O_3-Y_3Al_5O_(12) eutectic composite by the laser floating zone technique

摘要

A series of analytical calculations is used to study both the effect of the thermal gradients and the stability of the molten zone in the laser floating zone growth of Al_2O_3-Y_3Al_5O_(12) eutectic composite. The thermal gradients in the solidification interface have been calculated and the axial gradient compared with the experimental one of 4.5 X 10~5 K/m. For these calculations the coefficients of heat transfer from the molten zone to the ambient at the solid-melt interface have been previously obtained. The thermal stresses generated by the high thermal gradients can induce crack formation during the cooling depending on the rod diameter. The theory predicts that it is possible to grow rods free of cracks up to R = 1.7 mm, at low rates (10 mrn/h) in close agreement with the experimental critical radius of 1.6 mm. The dependence of the zone length on the input laser power used to carry out the growth is shown. The study of the floating zone profile allows determining the maximum stable zone length, verifying the stability criterion established by some authors.