Ti-Al合金定向凝固过程中胞/枝晶间距选择的计算机模拟

Numerical Simulation of Cellular/Dendrite Arm Spacing Selection During Unidirectional Solidification of Ti-Al Alloy

利用溶质扩散控制模型对Ti-Al合金定向凝固初始阶段变速冷却过程中胞/枝晶转变过程进行了数值模拟。在给定的冷却速率下,枝晶臂间距大于胞晶臂间距,而在过渡区,枝晶间距达到最大。另外,模拟结果也显示,晶核数量对柱状晶间距产生影响,随着植入晶核数量的增加,柱状晶间距非均匀化程度明显减小。出现过渡区的原因与枝晶生长所引起固/液界面前沿成分波动有关。模拟与试验结果吻合较好。

Solute diffusion controlled solidification model was applied to simulate the initial stage cellular to dendrite transition of Ti55Al45 alloys during directional solidification at different velocities. The simulation results show that the dendrite spacing is larger than that of cellular spacing at a given rate, the columnar grain spacing sharply increases to a maximum as solidification advance to coexistence zone. In addition, simulation also revealed the numbers of the seeds also exert an influence on the grain spacing, with increasing the numbers of the seeds; the uniform degree of the columnar grain spacing tends to increase. Lastly the main influence factors ：of affecting celluladdendritic transition were analyzed, which could be dendrite growth resulting in slight fluctuations of liquid composition occurred at growth front. The simulation results also are in reasonable agreement with experiment observation at low cooling rates.