[1]李喜,任忠鸣.静磁场下热电磁效应及其对凝固组织的影响[J].中国材料进展,2014,(6):349-354.[doi:10.7502/j.issn.1674-3962.2014.06.05]
　LI Xi,REN Zhongming.Thermoelectric magnetic effect and its effect on the solidification structure under static magnetic fields[J].MATERIALS CHINA,2014,(6):349-354.[doi:10.7502/j.issn.1674-3962.2014.06.05]
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静磁场下热电磁效应及其对凝固组织的影响()
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中国材料进展[ISSN:1674-3962/CN:61-1473/TG]

卷:
期数:
2014年第6期
页码:
349-354
栏目:
特约研究论文
出版日期:
2014-06-30

文章信息/Info

Title:
Thermoelectric magnetic effect and its effect on the solidification structure under static magnetic fields
作者:
李喜; 任忠鸣
上海大学，材料科学与工程学院
Author(s):
LI Xi;  REN Zhongming
Department of Materials Engineering, Shanghai University
关键词:
静磁场; 定向凝固; 热电磁效应; 凝固组织
DOI:
10.7502/j.issn.1674-3962.2014.06.05
文献标志码:
A
摘要:
由于塞贝克效应，当一个温度梯度被施加时，在凝固界面将会产生一个热电流。在磁场下定向凝固过程中热电流和静磁场相互作用将会产生一个显著的热电磁力。此磁力将会诱发各种现象，比如在液体中搅拌，固相运动以及固相受力。由于在金属的凝固的过程中常常存在温度梯度，这些效应将会普遍存在。在较小和适度的磁场下热电磁力将促进液体的流动，在较强的磁场下将抑制液体的流动。另外，热电磁流有多尺度效应，尺度越小，抑制液体流动所需的磁场越高。至今，已经完成了大量涉及多种合金的实验，所有的实验结果表明在凝固前沿和糊状区均都存在热电磁流。热电磁流动显著地影响微观和宏观偏析，凝固组织以及晶间。热电磁流动的方向以及相应的偏析可以通过改变磁场的方向而被控制。另一方面，作用于固相的热电磁力也将显著地影响凝固组织，表现为固相所受的热电磁力导致枝晶的断裂、枝晶碎片的运动和柱状晶-等轴晶转变等现象。近来，同步辐射X射线成像技术被应用实时观测在横向磁场下定向凝固过程中枝晶的生长行为，观察到在磁场下枝晶发生断裂和枝晶碎片沿一定方向运动的行为，这进一步证实了热电磁效应在磁场下凝固过程中将显著地影响凝固组织。
Abstract:
The thermo-electric currents are due to the Seebeck effect when temperature gradients exist in the material. Thermo-electric currents in the presence of static magnetic fields generate significant electromagnetic forces (TEM forces). Those forces may produce various phenomena like pumping, stirring in liquid metals as well as solid motions, stresses in the solid metal. Those effects may be encountered especially during the solidification of metallic materials because of the existence of significant temperature gradients. In liquid metals the application of a static magnetic field enhances TEM convection at moderate intensity but also damps it when it is strong enough. Moreover, it has been found that the thermoelectric magnetic effect own muti-scales effect, the smaller the length scales are (for example when primary or secondary dendrite arm spacings are considered), the higher the magnetic field strength which is needed to damp the TEM convection. So far, many solidification experiments on various types of alloys have been carried out. The experiments have shown that TEM convection occurs both in the liquid bulk but also in the deep mushy zone. TEM convection may strongly influence the meso-macrosegregation patterns, the solidification structures and the grain boundaries leading to the striking grain boundary structure of the mushy zone. The flow pattern and accordingly the segregations may be controlled by changing the orientation of the applied magnetic field, i.e., axial or transverse. Furthermore, the TEM forces on the solid promote the appearance of direct Columnar-to-Equiaxed Transitions thanks to the possible enhanced fragmentation of the dendrites. Such mechanisms have been recently partly observed by X-ray in situ observations, where channel formation effects as well as detachment of grains along with horizontal motions were observed. This further confirms that there exists a significant influence of the thermoelectric magnetic effects on the solidification structure during directional solidification under the magnetic field.
更新日期/Last Update: 2014-05-28