中文摘要：

通过耦合温度场模型、溶质扩散方程以及枝晶生长动力学方程等重要因素，建立了一种改进的元胞自动机模型。该模型通过采用偏心算法消除网格各向异性，实现了二维尺度上任意角度枝晶生长的模拟，同时适用于模拟三维尺度上枝晶的生长过程。利用建立的模型开展了定向凝固枝晶竞争生长过程的数值模拟。为了体现本模型的有效性，模拟了透明合金的竞争生长过程，并与实验结果符合良好。镍基高温合金汇聚竞争和发散竞争的模拟结果清楚地展现了不同抽拉速度和枝晶优先生长角度下枝晶的竞争生长过程，并且模拟结果与理论模型相符合。三维枝晶生长的模拟结果表明本模型可以用来模拟三维枝晶一次臂间距的调整过程。

英文摘要：

Investigating the dendritic competitive growth mechanism is of great importance for directional solidification, and the numerical simulation technique is regarded as an effective approach to a description of microstructural evolution. Therefore, a modified cellular automaton model with decentered square algorithm is developed for quantitatively simulat-ing the dendritic competitive growth process. The model takes into account the simplified thermal field, solute diffusion, growth kinetics, etc., and the solid fraction increment calculation is achieved through local level rule method. The model is successfully used to describe the dendrites with various growth orientations and its availability in simulating dendritic competitive growth is verified by comparing with the experimental results of transparent alloy. For the nickel-based superalloy, the simulated results reveal that in the case of converging dendrites, the unfavorably oriented dendrite is able to overgrow the favorably oriented dendrite, which is dependent on the preferential growth angle. For the divergence case, the favorably oriented dendrite can overgrow the unfavorably oriented dendrite through side branching at the grain boundary. The competitive growth process is mainly controlled by the pulling rate and the preferential growth angle. Furthermore, the model is successfully extended to the simulation of three-dimensional dendritic competitive growth.