Growth velocity-undercooling relationship and structure refinement mechanism of undercooled Ni-Cu alloys
Growth velocity-undercooling relationship and structure refinement mechanism of undercooled Ni-Cu alloys
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DOI：
10.1016/j.jallcom.2018.09.228
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发表时间：
2019-01
影响因子：
6.2
通讯作者：
Xinming Xu;Zhao Yanliang-;H. Hou
中科院分区：
文献类型：
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作者：
Xinming Xu;Zhao Yanliang-;H. Hou
利用高速热成像技术对深过冷Ni-Cu合金样品的生长速度-过冷度关系进行了系统的测量。结果表明，Ni 80 Cu 20合金与Ni 95 Cu 5合金的生长速度基本一致，Ni 85 Cu 15合金与Ni 90 Cu 10合金的生长速度基本一致，这一结果在浓固溶体合金中尚未见报道。凝固速度随过冷度的增大而增大，直到达到最大值。目前的枝晶生长模型可以很好地描述枝晶生长速度。在临界过冷度下，生长速度-过冷度曲线出现明显的不连续性。速度-过冷曲线的不连续性可归因于生长枝晶之前的本体液体中的溶质扩散的有限速度。这些样品中的显微结构证据表明发生了树枝状断裂。利用光学显微镜和EBSD分析的显微组织分析表明，再结晶伴随着在高过冷度的晶粒细化。此外，在高过冷度，退火孪晶的高密度的凝固样品中，表明发生再结晶的凝固微观结构和高密度的亚晶粒的淬火样品中观察到的微观结构内，这表明发生了广泛的恢复，结果以前没有报道的样品凝固从高度过冷熔体。
The growth velocity-undercooling relationship as a function of bulk undercoolings was systematically measured using high speed thermal imaging of highly undercooled Ni-Cu alloy samples. It was found that the growth velocity of Ni80Cu20 alloy was almost coincident with that of Ni95Cu5 alloy and the growth velocity of Ni85Cu15 alloy was almost coincident with that of Ni90Cu10 alloy, which was a new result that was unreported previously for concentrated solid solution alloys. It was also found that the solidification velocity increased smoothly with undercooling up to the maximum value. Growth velocity can be adequately represented by the current dendritic growth model. A clear discontinuity in the growth velocity-undercooling curve was observed at a critical undercooling. This discontinuity in the velocity-undercooling curve can be attributed to the finite speed of solute diffusion in the bulk liquid ahead of the growing dendrite. Microstructural evidences in these samples indicative the occurrence of dendritic fragmentation. Microstructural analysis using light microscopy and EBSD analysis reveals that recrystallization accompanies the grain refinement at high undercoolings. Furthermore, at high undercoolings, a high density of annealing twins in the as solidified samples indicates the occurrence of recrystallization in the solidification microstructure and a high density of subgrains in the quenched samples are observed within the microstructure, which indicates the occurrence of extensive recovery, a result previously unreported in samples solidified from highly undercooled melts.