Solidification of Highly Undercooled Hypereutectic Ni-Ni3B Alloy Melt
Solidification of Highly Undercooled Hypereutectic Ni-Ni3B Alloy Melt
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高度过冷过共晶Ni-Ni3B合金熔体的凝固
DOI：
10.1007/s11661-014-2460-5
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发表时间：
2014-10-01
影响因子：
2.8
通讯作者：
Jian, Zengyun
中科院分区：
文献类型：
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作者：
Liu, Feng;Xu, Junfeng;Jian, Zengyun
采用玻璃熔剂技术研究了过冷Ni-4.5wtPctB合金熔体的凝固过程。合金熔体过冷至Delta T(P)-245K(245A℃)，得到α-Ni枝晶、Ni3B枝晶、棒状共晶和析出物的混合物。如果Delta T(P)为千分之175K+/-A10K(175A+/-A10A℃)，则凝固路径为初生相变和共晶转变(L->；Ni3B和L->；Ni/Ni3B)，如果Delta T(P)为千分之175K+/-A10K(175A+/-A10A℃)，则凝固路径为亚稳态共晶转变、亚稳定相分解和残余液态凝固(L->；Ni/Ni23B6，Ni23B6->；Ni/Ni_3B和L；Ni/Ni_3B)。采用高速摄像系统对每一次转变的凝固前沿进行观察。结果表明，残余液态凝固时的凝固前沿速度与共晶转变时的凝固前沿速度相同，但比亚稳态共晶转变时的凝固前沿速度大一个数量级，证实了该反应为L-r->；Ni/Ni_3B，并发现凝固前沿速度随Delta T(R)的增大而减小，这可以用残余液体分数的减少和Ni_(23)B_6分解速率的降低来解释。
The solidification of undercooled Ni-4.5 wt pct B alloy melt was investigated by using the glass fluxing technique. The alloy melt was undercooled up to Delta T (p) -245 K (245 A degrees C), where a mixture of alpha-Ni dendrite, Ni3B dendrite, rod eutectic, and precipitates was obtained. If Delta T (p) < 175 K +/- A 10 K (175 A degrees C +/- A 10 A degrees C), the solidification pathway was found as primary transformation and eutectic transformation (L -> Ni3B and L -> Ni/Ni3B); if Delta T (p) a parts per thousand yen 175 K +/- A 10 K (175 A degrees C +/- A 10 A degrees C), the pathway was found as metastable eutectic transformation, metastable phase decomposition, and residual liquid solidification (L -> Ni/Ni23B6, Ni23B6 -> Ni/Ni3B, and L-r -> Ni/Ni3B). A high-speed video system was adopted to observe the solidification front of each transformation. It showed that for residual liquid solidification, the solidification front velocity is the same magnitude as that for eutectic transformation, but is an order of magnitude larger than for metastable eutectic transformation, which confirms the reaction as L-r -> Ni/Ni3B; it also showed that this velocity decreases with increasing Delta T (r), which can be explained by reduction of the residual liquid fraction and decrease of Ni23B6 decomposition rate.