微重力与电磁场对凝固过程的影响

Influence of Microgravity and Electromagnetic Field on the Solidification of Metallic Alloys

欧洲空间局两项材料领域课题MICAST和CETSOL均涉及微重力科学相关研究.通过等轴晶柱状晶转变(CET)分析了微重力环境对材料凝固过程的影响;介绍了一项在地面施加行波电磁场的标准(Benchmark)凝固实验,其温度场演化及微观凝固组织和浓度偏析均展示了磁控受迫对流对金属材料凝固过程的显著作用.

Solidification or crystal growth of metallic alloys is crucially determined by flow,heat and mass transfer,whilst the external imposed fields like electromagnetic field or gravitational environment can significantly influence these transfer processes.In this paper,two experiments are briefly presented to exhibit above influence on the microstructure evolution of metallic alloys,particularly on the Columnar-Equiaxed Transition（CET）.Firstly,a sound rocket-based experiment demonstrates the effect of microgravity by comparison with that of ground-based experiment,and the quite different microstructure reveals that the natural convection plays an essential role in the solidification.Secondly,a quasi-two-dimensional solidifying experimental benchmark is presented to exhibit the natural and forced convection on the micro/macro segregation of the metallic alloys.The natural convection has been observed through the evolution of temperature field measured in real time,and this experiment exhibit the solute segregation naturally formed in the liquid and mushy zones.The forced convection driven by a traveling electromagnetic field interferes with solute segregation directly.Lastly,their influence mechanisms are analyzed and perspective of China＇s research strategy for material science in space is addressed.