物理学报2017，Vol.66Issue(13)：214-223,10.DOI:10.7498/aps.66.136401
电磁悬浮条件下液态Fe50Cu50合金的对流和凝固规律研究
Fluid convection and solidification mechanisms of liquid Fe50Cu50 alloy under electromagnetic levitation condition
摘要
Abstract
In the electromagnetic levitation experiment, the liquid flow in the undercooled liquid alloy remarkably affects the relevant thermodynamic property measurement and solidification microstructure. Therefore, it is of great importance to understand the fluid convection inside the undercooled melt. Theoretical calculation and electromagnetic levitation experiment have been used to investigate the internal velocity distribution and rapid solidification mechanism of Fe50Cu50 alloy. Based on axisymmetric electromagnetic levitation model, the distribution patterns of magnetic flux density and inducted current for levitated Fe50 Cu50 alloy are calculated together with the mean Lorenz force. The Navier-Stokes equations are further taken into account in order to clarify the internal fluid flow. The results of the theoretical calculation reveal that the fluid velocity within levitated melt is strongly dependent on three factors, i.e., current density, current frequency and melt undercooling. As one of these factors increases, the maximum fluid velocity decreases while the average fluid velocity increases. Meanwhile, the area with fluid velocity larger than 100 mm·s?1 is significantly extended. Furthermore, the fluid flow within levitated melt displays an annular tubular distribution characteristic. The Fe50Cu50 alloy melt is undercooled and solidified under electromagnetic levitation condition. In this undercooling regime ?T <69 K, solidification microstructures are composed of dendrites, and a morphology transition of "coarse dendrites →refined dendrites" is observed with the increase of melt undercooling. Comparing with the critical undercooling of metastable liquid phase separation in the glass fluxing experiment, the forced flow within the Fe50Cu50 alloy melt has suppressed phase separation substantially. Once the undercooling attains a value of 150 K, metastable phase separation leads to the formation of layered pattern structure consisting of floating Fe-rich zone and sinking Cu-rich zone. A core-shell macrosegregation morphology with the Cu-rich zone distributed in the center and outside of the sample and Fe-rich zone in the middle occurs if the undercooling increases to 204 K. With the enhancement of undercooling after phase separation, the grain size of α-Fe dendrites in Cu-rich zone presents a decreasing trend. In contrast to the phase separated morphology of Fe50Cu50 alloy under the glass fluxing condition, the phase separated morphologies show obviously different characteristics. In such a case, the forced convection induced by electromagnetic stirring results in the formation of wavy interface between Fe-rich and Cu-rich zones, the distorted morphology of the Cu-rich spheres distributed in the Fe-rich zone, and the increased appearance probabilities of Cu-rich spheres at the upper part of electromagnetically levitated sample. Experimental observations demonstrate that the distribution pattern of Cu-rich spheres in Fe-rich zone is influenced by the tubular fluid flow inside the melt.关键词
电磁悬浮/对流/深过冷/相分离Key words
electromagnetic levitation/forced convection/high undercooling/phase separation引用本文复制引用
林茂杰,常健,吴宇昊,徐山森,魏炳波..电磁悬浮条件下液态Fe50Cu50合金的对流和凝固规律研究[J].物理学报,2017,66(13):214-223,10.基金项目
国家自然科学基金(批准号: 51401167, 51327901)和中央高校基本科研业务费专项资金(批准号: 3102015ZY097)资助的课题. Project supported by the National Natural Science Foundation of China (Grant Nos. 51401167, 51327901), and Fundamental Research Funds for the Central Universities, China (Grant No. 3102015ZY097). （批准号: 51401167, 51327901）
