交变电磁场在晶体生长与凝固方面的应用

Application of Alternative Electromagnetic Field in Crystal Growth and Solidification

在合金凝固过程中施加时变电磁场,导电熔体在洛仑兹力的驱动下产生的强迫对流可有效控制合金溶质的再分配过程。在材料凝固与晶体生长过程中施加电磁场有助于深入研究其热物理性质、相平衡、亚稳态、组织形成、成分过冷和形核。人们对重力环境下合金的凝固过程已进行了大量深入详尽的实验探究,利用电磁场手段对凝固前沿进行有效干预并在晶体组织结构、成分偏析等方面取得了一定的进展。而微重力环境下浮力对流减少,为在宏观和微观尺度上获得成分更为均匀的半导体或合金材料提供了一个独特的平台,目前的研究表明在微重力环境下合金的凝固特征与在重力环境下的有所不同。从理论与实验的角度阐释了在微重力及重力环境下电磁场引起的强迫对流强度及方向对晶体生长过程中的宏观偏析、微观偏析、晶体形态以及金属间化合物的生长模式及空间分布的影响规律。

In the solidification process of alloys,forced convection produced by time-varying electromagnetic fields can effectively control the redistribution process of alloy solute. The application of electromagnetic field in the solidification and growth process of materials can be conductive to the research of its thermophysical properties,phase equilibrium,metastable state,microstructure formation,component undercooling and nucleation. The solidification process of alloy in the gravitational environment has been studied in details. The electromagnetic field method has been used to intervene the solidification front effectively and some results have been obtained in the crystal structure and segregation. Microgravity condition provides a technique for obtaining semiconductors or alloys with more uniform composition at both macroscopic and microscopic scales.The current research shows that the solidification characteristics of alloys under the microgravity environment are different from that under the gravitational condition. In this paper,the effects of forced convection on the macro-segregation,microsegregation,crystal morphology and the growth pattern and spatial distribution of intermetallic compounds in the process of crystal growth under both microgravity and gravitational condition,are discussed in terms of the theoretical and experimental perspectives.