强制对流和高各向异性对枝晶生长的影响

摘要

Based on the new regularized Wheeler model that couples the concentration field, temperature field and flow field, the phase field model was established to simulate dendrite growth of Ni-Cu alloys with strong anisotropy in a forced flow. The results show that corners appear at the tip of smooth dendrite and the tip grow velocity at steady state first increased and then decreased with increases of anisotropy strength in the range of 0.06-0.2. In the case of strong anisotropy, the crystals grow into an equiaxial dendrite without flow and into an asymmetrical dendrite with flow. Under forced flow with flow velocity of 6.43 m/s, the upstream dendrite grows faster because of the undercooled melt flushing, the tip velocity at steady state increases by about 12.61% compared to the case without flow. The heat and solute are congregated in the downstream, which makes the dendrite grow slowly, the tip velocity at steady state decreases by about 14.62% compared to the case without flow.%基于修正的Wheeler相场模型，建立耦合溶质场、温度场和流场的相场模型，研究Ni-Cu合金凝固过程中高各向异性作用下的枝晶生长行为。结果表明：各向异性强度在0．06-0．2之间取值时，随着各向异性强度增加，光滑主枝尖端出现棱角，枝晶尖端生长速度先增加后减小。在高各向异性条件下，有无对流时晶粒分别以不对称枝晶和等轴枝晶方式生长。在流速为6．43m·s-1的强制对流作用下。逆流侧枝晶受过冷熔体冲刷，逆流枝晶生长迅速，与纯扩散时相比稳态生长速度增加了12．61％；热量和溶质在顺流侧聚集，顺流枝晶生长缓慢，与纯扩散时相比稳态生长速度减小了14．62％。