对流作用下枝晶形貌演化的数值模拟和实验研究

Simulation and experimental research of melt convection on dendrite morphology evolution

合金凝固过程中存在于枝晶尖端液相区的强制对流和自然对流均能改变溶质扩散层厚度,从而会对枝晶形貌产生较大影响.在元胞自动机模型基础上,耦合液体流动方程、热传导方程和溶质对流扩散方程,建立了新的计算微观组织演化的数值模型,并利用该模型研究了强制对流和自然对流对枝晶生长的影响.三维数值模拟结果再现了强制对流作用下等轴枝晶的生长过程,揭示了强制对流对枝晶生长速率和尖端半径的影响特点.同时利用该模型模拟了NH4Cl-H2O溶液定向凝固过程中自然对流对柱状晶生长的影响,并采用相应的实验进行验证.模拟结果与实验结果符合良好,从而证明该模型是可靠的,可推广到实际合金系中.

The existence of forced and natural melt convections in the liquid in front of dendritic tip will Change the thickness of diffusion layer,which can significantly influence the dendrite morphology.Using the cellular automaton method and considering the influences of melt convection and heat transfer on microstructure evolution,a new numerical model is established by coupling the Navier-Stokes equations,the heat transfer equation and the solute convection and diffusion equation.The influences of forced and natural melt convection on dendrite morphology evolution are investigated by this model.The three-dimensional simulations reproduce the equiaxed dendrite growth,and reveal the influence of convection on dendritic growth rate and tip radius.The effect of natural convection on columnar dendrite growth during directional solidification of NH4Cl-H2O solution is simulated via the model.Experimental validation of this solidification process is performed and compared with simulation results.The simulation results accord well with experimental measurements.Hence,the model is reliable and can be extended to the prediction of the behavior of dendrite growth in real alloys.