Influence of withdrawing speed on the porous structures of Gasar ingots fabricated by Bridgman method

The pore straightness of Gasar ingots was investigated through experiments and numerical simulation. The pore growth direction changes from diverging to convergent as the withdrawing speed increases, and straight pores are obtained when the solid/liquid interfaces are almost planar. The optimum withdrawing speed to obtain straight pores increases as the sample size decreases. Under optimum conditions, the average pore diameter of the small ingot is smaller than that of the large ingot, while the penetrative porosity of the large ingot is superior. The shape of the solid/liquid interfaces at the bottom of the ingot can be improved effectively by modifying the structure of the mold. Bridgman method is applicable for the fabrication of Gasar ingots with large size and high quality, and suitable sample size should be considered for different structural requirements.