定向凝固糊状区枝晶粗化和二次臂迁移的实验和模拟  

Dendrite Coarsening and Secondary Arm Migration in the Mushy Zone During Directional Solidification:Experiment and Simulation

作　　者：方辉 薛桦 汤倩玉 张庆宇[1] 潘诗琰[2] 朱鸣芳[1] FANG Hui;XUE Hua;TANG Qianyu;ZHANG Qingyu;PAN Shiyan;ZHU Mingfang(Jiangsu Key Laboratory of Advanced Metallic Materials,School of Materials Science and Engineering,Southeast University,Nanjing 211189,China;School of Materials Science and Engineering,Nanjing University of Science and Technology,Nanjing 210094,China)

机构地区：[1]东南大学材料科学与工程学院江苏省先进金属材料高技术研究重点实验室,南京211189 [2]南京理工大学材料科学与工程学院,南京210094

出　　处：《金属学报》2019年第5期664-672,共9页Acta Metallurgica Sinica

基　　金：国家自然科学基金项目Nos.51371051;51501091;中央高校基本科研业务费专项资金项目No.2242016K40008;东南大学优秀博士论文培育基金项目No.YBJJ1627~~

摘　　要：采用透明合金原位观察实验和元胞自动机(CA)模拟,对丁二腈-丙酮(SCN-ACE)合金在定向凝固过程中糊状区的枝晶形貌演化进行了分析研究。实验和模拟均观察到了由于小枝晶臂重熔、相邻枝晶臂从尖端或根部合并的3种枝晶臂粗化模式,以及由于温度梯度区域熔化(TGZM)效应所引起的二次枝晶臂向高温方向的迁移现象。结果表明,枝晶臂的迁移速率随温度梯度的提高而加快;随保温时间的延长,枝晶臂的迁移速率降低。实验值和解析解吻合良好。通过模拟证实了必须有熔化效应才能实现枝晶臂迁移和小枝晶臂重熔的粗化模式。此外,熔化效应对由相邻枝晶臂合并引起的粗化模式也有显著的促进作用。Directional solidification is a common and important process in both scientific research and industrial practice.Dendrites are the most frequently observed microstructures in the directional solidification.It is known that dendrite coarsening in mushy zones is an unavoidable phenomenon that influences microstructures and thereby properties significantly.Moreover,the presence of temperature gradients during directional solidification leads to temperature gradient zone melting(TGZM),which yields dendrite arm migration towards higher temperatures.In the present work,the evolution of dendrite microstructures in the mushy zone during directional solidification is investigated through in situ experiments and cellular automaton(CA) simulations for a transparent succinonitrile-acetone(SCN-ACE) alloy.The phenomena of dendrite coarsening and the secondary dendrite arm migration toward high temperature direction due to TGZM have been observed by both experiment and simulation.Dendrite coarsening is found to be caused by three modes,including the remelting of small dendrite arms,and dendrite arm coalescence through the advancement of interdendritic grooves and joining of dendrite arm tips.The experimental measurements indicate that the average migration velocity of the secondary dendrite arm increases with increasing the temperature gradient.For a fixed temperature gradient,dendrite arm migration becomes slower with time.The experimental data agree reasonably well with the analytical predictions.The present CA model involving the mechanisms of both solidification and melting can effectively reproduce the typical features of secondary dendrite arm migration and dendrite coarsening as observed in experiments.The simulation results show that the local liquid concentrations near the lateral side of big arms and in the "valleys" between side arms are relatively higher than that at the tips of small arms.This drives solute diffusion and leads to the dissolution of small arms,the growth of thick arms,and advancement of interdendrit

关 键 词：定向凝固 枝晶 温度梯度区域熔化 元胞自动机 

分 类 号：TG113.12[金属学及工艺—物理冶金] TG111.4[金属学及工艺—金属学]