Fabrication of Gasar ingots with straight parallel pores by a Bridgman method

Multi-step withdrawal schemes with varying speeds of Bridgman method were designed and studied by numerical simulation and experimental methods in order to improve the pore straightness and parallelism of Gasar ingots. When the starting withdrawal speed v is larger than the expected reference v of 1 mm/s, a subsequent decelerated withdrawal process is necessary, and v should go down to cross 1 mm/s. When the starting v is smaller than 1 mm/s, a hybrid-speed withdrawal process with a quickly accelerating stage first and a gradually decelerating stage afterwards is necessary, and v should also cross 1 mm/s. The optimized varying speed withdrawal schemes should conform to the natural decreasing trend of the solidification rate. Compared with the optimized constant speed withdrawal scheme, the optimized varying speed withdrawal schemes can not only improve the pore straightness, but also adjust the pore structure of Gasar ingots.