Multi-transformations in rapid solidification of highly undercooled hypoeutectic Ni–Ni_3B alloy melt
Multi-transformations in rapid solidification of highly undercooled hypoeutectic Ni–Ni_3B alloy melt
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DOI：
10.1557/jmr.2015.295
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发表时间：
2015-11
影响因子：
2.7
通讯作者：
Junfeng Xu;Di Zhang-;Feng Liu;Z. Jian
中科院分区：
文献类型：
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作者：
Junfeng Xu;Di Zhang-;Feng Liu;Z. Jian
采用高速摄像和显微组织分析方法研究了Ni-3.3 wt% B合金的过冷凝固过程。在中等初始过冷度（Δ Tp = 75 K）下，初次相变的凝固界面呈平面枝晶形状，具有恒定的生长速度，而共晶相变的凝固界面呈多枝晶形状，呈间歇生长，恒定的生长速度不能准确描述界面。这些差异表明，初生相凝固受远距离扩散控制，而共晶凝固受近距离扩散控制。在大过冷度（Δ T _p = 262 K）下，组织中出现了一种由多相组成的“白色枝晶”，共晶相由内到外依次由点相（异常组织）→不规则共晶→规则共晶，表明“白色枝晶”中心可能是共晶反应的形核区。
The solidification of undercooled Ni–3.3 wt% B alloy was studied by high-speed video analysis and microstructural analysis. For moderate initial undercooling (Δ T _p = 75 K), the solidification interface for primary phase transformation manifests a shape of a planar dendrite, and possesses an constant growth velocity, for eutectic transformation whereas the interface presents multi-dendrite shape and spasmodic growth, so that a constant velocity cannot describe the interface exactly. These differences suggest that primary phase solidification is controlled by far-distance diffusion while eutectic solidification by short-distance diffusion. For large initial undercooling (Δ T _p = 262 K), a kinds of large “white dendrites”, which is in fact composed of multiple phases, were found in the microstructure, from inside to outside of which, the eutectic phase changes from dot phases (anomalous structure) to irregular eutectic and then to regular eutectic, indicating that the center of “white dendrites” may be the nucleation zone of eutectic reaction.