Experimental evidence of crystal fragmentation from highly undercooled Ni99B1 melts processed on an electrostatic levitator
Experimental evidence of crystal fragmentation from highly undercooled Ni99B1 melts processed on an electrostatic levitator
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DOI：
10.1007/s11661-005-0097-0
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发表时间：
2005-11
期刊：
影响因子：
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通讯作者：
Mingjun Li;T. Ishikawa;S. Yoda;K. Nagashio;K. Kuribayashi
中科院分区：
文献类型：
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作者：
Mingjun Li;T. Ishikawa;S. Yoda;K. Nagashio;K. Kuribayashi
采用静电悬浮器（ESL）和CO2激光加热装置，在深过冷条件下对Ni99B1块体进行无容器凝固，观察到晶粒细化的微观组织。通过电子背散射衍射（EBSP）和孪晶方向的分析，揭示了在宏观毫米尺度上具有胞状结构的初生生长痕迹。与在电磁悬浮器上处理的样品中的强机械电磁搅拌相比，ESL为熔体提供了相当静止的状态，这使得能够识别凝固后的初级生长痕迹。实验结果表明，Ni99B1合金在深过冷区的细化是由于初生晶体的破碎而不是动态形核。
Employing an electrostatic levitator (ESL) equipped with a CO2laser heating setup, we solidified Ni99B1bulk crystals through containerless processing at high undercoolings and observed grain-refined microstructures. The electron backscatter diffraction pattern (EBSP) and analysis of the twin directions were accomplished, from which the primary growth traces with a cellular-like structure were revealed on a macro-millimeter scale. In comparison with the strong mechanical electromagnetic stirring in a sample processed on an electromagnetic levitator, the ESL provides a quite quiescent state for the melt, which enables identification of the primary growth traces after solidification. The present observation supplied experimental evidence that the refined microstructure in the Ni99B1alloys at the high undercooling regime was due to fragmentation of the primary growth crystal, rather than dynamic nucleation.