Phase selection and microstructure formation in undercooled Co–61.8 at.% Si melts under various containerless processing conditions
Phase selection and microstructure formation in undercooled Co–61.8 at.% Si melts under various containerless processing conditions
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DOI：
10.1016/j.actamat.2013.04.061
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发表时间：
2013-08
期刊：
影响因子：
9.4
通讯作者：
Yong Zhang;Jianrong Gao;M. Kolbe;S. Klein;Chunzheng Yang;H. Yasuda;D. Herlach;C. Gandin
中科院分区：
文献类型：
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作者：
Yong Zhang;Jianrong Gao;M. Kolbe;S. Klein;Chunzheng Yang;H. Yasuda;D. Herlach;C. Gandin
对亚共晶成分Co-61.8at.%Si分别采用电磁悬浮、静磁场悬浮、静电悬浮和玻璃熔剂等方法进行过冷凝固。样品通常表现出两个热事件，根据过冷度的不同，热事件要么分开，要么连续。用高速相机对这两个热事件进行了现场监测，发现在88K的临界过冷度时，初生相的枝晶生长速度突然降低。对凝固样品的扫描电子显微镜研究表明，CoSi化合物和CoSi2化合物分别在低过冷度和高过冷度时作为主相形核。样品的微观结构不仅与过冷度有关，还与第二次热事件的起始温度或延迟时间有关。熔体对流对过冷熔体的初生相选择没有影响，但对延迟时间有显著影响，从而对深过冷度样品的显微组织形成有显著影响。
The hypoeutectic composition Co–61.8at.% Si was undercooled and solidified using electromagnetic levitation, electromagnetic levitation under a static magnetic field, electrostatic levitation and glass-fluxing. The samples generally showed two thermal events, either separated or continuous depending on undercooling. In situ monitoring of the two thermal events with a high-speed camera revealed a sudden decrease of dendritic growth velocities of primary phases at a critical undercooling of 88K. Scanning electron microscopy studies of the solidified samples showed that the CoSi compound and the CoSi2compound nucleate as the primary phase for low and high undercoolings, respectively. The microstructure of the samples depends not only on undercooling, but also on the onset temperature or delay time of the second thermal event. Melt convection has no effect on the primary phase selection in undercooled melts, but it has a significant effect on the delay time and therefore on microstructure formation of the samples for high undercoolings.