非均匀温度场下枝晶生长状态

Dendrite Growth State Under Non-uniform Temperature Field

为了掌握非均匀温度场下微观组织的演变规律,本工作采用改进的元胞自动机模型,在完成算法验证的基础上,对比微观组织在均匀温度场和非均匀温度场下组织演变的异同,并系统研究微观组织在非均匀温度场中的枝晶形貌、尖端生长速率和域内溶质分布以及多晶组织的演变规律。研究结果表明:该模型仿真结果与CA-FD模型结果误差范围在1.4%以内;枝晶凝固末端尖端速率在温度均匀场内趋于稳定,而在非均匀场内表现为持续上升;固相溶质浓度在非均匀场内随着枝晶臂的延展而增大,在均匀场内则保持不变。对于非均匀温度场内单枝晶生长,冷速达到10 K/s时,枝晶臂的长度达到1030μm,较均匀场增加49.3%,当冷速达到30 K/s时,枝晶臂长度达到1460μm,同比增加了111.6%;冷速的加强使枝晶内部固相溶质浓度增加,出现更多侧向枝晶臂,使固/液界面区域溶质出现波动,呈现不规则分布;多晶组织在非均匀温度场内平均溶质浓度随冷速的增大而上升,且域内合金在凝固结束后固相比例随冷速的增加由45%增加到65%,同时观察到域内溶质富集,多次枝晶臂的产生和枝晶臂粗化等现象。

In order to grasp the evolution of microstructure under non-uniform temperature field,this work adopted a modified meta-cellular automata model to compare the similarities and differences of microstructure evolution under uniform and non-uniform temperature fields on the basis of completing the algorithm verification,and systematically studied the evolution of dendrite morphology,tip growth rate and solute distribution in the domain as well as the evolution of polycrystalline structure in non-uniform temperature field.The results show that the simulation results of the model is within 1.4%of the error range of the CA-FD mode.The tip rate at the solidification end of the dendrite tends to be stable in the uniform temperature field,while it shows a continuous increase in the non-uniform field.The solid phase solute concentration increases with the extension of the dendrite arm in the non-uniform field,but remains constant in the uniform field.For single dendrite growth in the non-uniform temperature field,the length of dendrite arms reaches 1030μm when the cooling rate reaches 10 K/s,an increase of 49.3%compared to the uniform field.And the length of dendrite arms reaches 1460μm when the cooling rate reaches 30 K/s,an increase of 111.6%.The strengthening of the cooling rate increases the solid-phase solute concentration inside the dendrite,and more lateral dendrite arms appear,causing the fluctuation of the solute at the solid/liquid interface,showing an irregular distribution.The average solute concentration in the non-uniform temperature field of the polycrystalline structure increases with the increase of the cooling rate,and the proportion of solid phase in the domain increases from 45%to 65%at the end of solidification with the increase of the cooling rate.While solute enrichment in the domain,multiple dendrite arm generation and dendrite arm coarsening are observed.