边界热通量作用下枝晶生长相场模型的有限元法模拟

Phase field simulation of dendrite growth with boundary heat flux by finite element method

基于Beckermann和Karma枝晶生长相场模型,建立耦合溶质场、温度场的相场模型,采用有限元法对控制方程进行求解,研究凝固过程Al-3.0%(质量分数)Cu合金在边界热通量作用下的枝晶生长行为。结果表明,边界热通量作用能够显著改变凝固前沿的传热和传质,影响枝晶生长形貌。在边界抽热条件下,枝晶前沿温度降低,实际过冷度增大,从而促进二次枝晶生长发育,界面前沿溶质扩散层薄,枝晶微观偏析严重。而边界加热条件下,枝晶前沿温度升高,实际过冷度减小,抑制枝晶生长发育,界面前沿扩散层厚,枝晶微观偏析减弱。

Based on the phase model reported by Beckermann and Karma, a phase-field approach which incorpo- rates both solute and heat equations was built. Finite element method is used to solve such equations numerical- ly. The various dendritic growth patterns with the boundary heat flux of Al-3.0wt% Cu alloy were studied. It is found that the boundary heat flux significantly alters the local heat and solute transfer at the solidification front, thus the dendrite morphology was influenced. Under heat flux extraction from the boundary, owing to the grea- ter actual undercooling, there is a stronger tendency for the dendrite to grow faster and a thin diffusion layer in front of the growth dendrite, leading to serious microsegregation of dendrite. However, under heat flux input from the boundary, owing to the less actual supercooling, there is inhibition of dendrite growth and forming a thick diffusion layer, leading to weakening of dendrite microsegregation.