定向凝固过程中NH_4Cl-H_2O枝晶生长的数值模拟

SIMULATION OF NH_4Cl-H_2O DENDRITIC GROWTH IN DIRECTIONAL SOLIDIFICATION

建立了一种改进的元胞自动机模型(MCA),通过考虑成分过冷、曲率过冷、择优取向系数、温度梯度和抽拉速度等因素,模拟了不同温度梯度方向、不同择优取向及不同抽拉速度对柱状晶形态的影响.模拟结果较好地刻画了温度梯度和生长方向夹角的变化对一次枝晶臂间距的影响,不同择优生长取向的柱状晶竞争生长过程以及柱状晶尖端分叉机制.为了验证模型的可靠性,使用NH_4Cl-H_2O透明合金进行了定向凝固实验,实验结果和模拟结果吻合较好.

Studying the microstructure evolution mechanism of directional solidification by numerical simulation has the directive significance in the solidification theory and practical production. Taking account of constitutional undercooling,curvature undercooling,preferred growth orientation coefficient,temperature gradient and pulling velocity,a modified cellular automaton（MCA）model has been developed to simulate the influence of different temperature gradient directions,different preferred growth orientations and different pulling velocities on the morphologies of columnar dendrites. The simulation results well describe the influence of inclination angle between temperature gradient and growth direction on primary dendrite arm spacing（PDAS）.Meanwhile the simulation results also reproduce the competitive growth of columnar dendrites with different preferred growth orientations and the splitting of the columnar dendritic tips.For the purpose of verifying this model,the relevant experiments have been carried out on an NH_4Cl-H_2O solution.The experimental results are compared critically with the simulation ones from the MCA model.