Probing interdendritic flow and hot tearing during solidification using real time X-ray imaging and droplet tracking
Probing interdendritic flow and hot tearing during solidification using real time X-ray imaging and droplet tracking
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DOI：
10.1016/j.actamat.2022.118298
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发表时间：
2022-09-06
期刊：
影响因子：
9.4
通讯作者：
Grant, P. S.
中科院分区：
文献类型：
--
作者：
Liotti, E.;Lui, A.;Grant, P. S.
众所周知，在合金铸件中控制收缩引起的液体流动对于避免在凝固的最后阶段形成灾难性的热撕裂是非常重要的，但是在实际条件下对金属液态流动和热撕裂形成的直接实验测量却很少。我们使用同步x射线获得了单晶Al-Pb合金凝固的射线成像视频序列，其中Pb液滴形成为细尺度乳液。我们跟踪和测量了成千上万的Pb液滴的速度，因为它们在凝固的最后阶段由于液体到固体收缩的影响而穿过枝晶间区域，直到热撕裂形成的点。基于液滴速度，我们分析了随着固体分数的增加枝晶间液体的速度，以及收缩压降对流动的驱动作用。该分析应用于在冷却速率范围内获得的等轴和柱状显微组织的视频序列。我们对热撕裂形成的临界收缩诱导压力的测量结果与先前基于模型和理论的建议一致。讨论了液态金属流动液滴跟踪测量的局限性和前景。(c) 2022 materials Inc.Elsevier Ltd.出版。版权所有。
Despite the well-known importance of controlling shrinkage-induced liquid flow in alloy castings to avoid the formation of catastrophic hot tears during the final stages of solidification, there has been little direct experimental measurement of liquid metal flow and hot tear formation under practical conditions. We use synchrotron X-rays to obtain radiographic video sequences of the solidification of monotectic Al-Pb alloys in which Pb droplets form as a fine-scale emulsion. We track and measure the velocity of thousands of Pb droplets as they move through interdendritic regions due to the effect of liquid to solid shrinkage during the final stages of solidification, up to the point of hot tear formation. Based on the droplet velocities, we present an analysis to estimate the interdendritic liquid velocity as solid fraction increases, and thus the shrinkage pressure drop driving the flow. The analysis is applied for video sequences obtained for both equiaxed and columnar microstructures, each under a range of cooling rates. Our measurements of the critical shrinkage-induced pressure for hot tear formation agree well with prior model-based and theoretical suggestions. The limitations and prospects for droplet tracking measurements of liquid metal flows are discussed. (c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.