垂直定向凝固条件下通道偏析形成过程的数值模拟

建立了描述合金凝固过程热－溶质对流和宏观偏析形成过程的数学模型。模型中耦合求解了凝固过程中质量、动量、能量和溶质守恒方程；同时，基于固液两相区中温度和成分的耦合关系建立了固相分数场的更新方法。利用该模型模拟了底部冷却的二维矩形区域内Fe-C合金凝固过程中通道偏析的形成和发展过程。模拟结果表明，垂直定向凝固条件下通道偏析形成于液相线前沿附近，而不是两相区内部。这一结果很好地支持了文献中基于实验观察提出的通道偏析形成机理。

NUMERICAL SIMULATION ON CHANNEL SEGREGATION IN VERTICALLY UNIDIRECTIONAL SOLIDIFICATION PROCESS

A mathematical model for describing the thermosolutal convection and macrosegrega-tion evolution in solidification of multicomponent alloys is developed, in which the macroscopic mass, momentum, energy and species conservation equations are solved simultaneously. The solid fraction field is updated by using an approach based on complete coupling of the temperature and concentration through thermodynamic equilibrium in the mushy zone. By using this model, the origination and evolution of channel segregation in solidification of a Fe--C alloy in a bottom-chilled two-dimensional rectangular domain a.re numerically simulated. The simulation results show that in vertically unidirectional solidification process the channel segregation originates near the liquidus front instead of in the mushy zone, which supports the proposed formation mechanism of the segregation based on experimental observations.