Comparison of Channel Segregation Formation in Model Alloys and Steels via Numerical Simulations
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CHANNEL segregation, which is characterized by strip regions of chemical inhomogeneity, is a common phenomenon in various alloys and has been studied widely and deeply through experimental and numerical simulation approaches. Consensus has been established that channel segregation stems from thermosolutal convection in the mushy zone.[1] To date, to predict the chemical variations and inhomogeneities in ingots, a large number of mathematical models have been developed and built, primarily based on this theoretical framework. In these models, the conservation equations for mass, solute, energy, and momentum at the system scale are coupled with microstructural solidification dynamics. Benefiting from these developments of theoretical models, profound numerical simulations have been carried out, such as the multicomponent simulation,[2] three-dimensional simulation,[3] multiphase simulation,[4,5] and even microstructural level simulation.[6,7] As the pioneering work of quantitative understanding of macrosegregation, Flemings and coworkers[8,9] deduced the local solute redistribution equation (LSRE), in which only solidification shrinkage flow was considered initially. Based on this model, Mehrabian et al.[10,11] further extended the LSRE, including the interdendritic Y.F. CAO, Ph.D Student, Y. CHEN, Associate Professor, D.Z. LI, Professor, H.W. LIU, Associate Professor, and P.X. FU, Associate Professor, are with the Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, Liaoning, 110016 P.R. China. Contact e-mail:chenyun@ imr.ac.cn Manuscript submitted April 27, 2015. Article published online March 8, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
flow that is induced by gravity. They revealed that the gravity-driven flows could lead to local remelting of solidified dendrites in some cases and cause persistent channel segregation eventually. Nevertheless, considering that the LSRE model depends on the local solidification conditions, direct prediction of macrosegregation in an ingot using that model is intricate and hardly feasible in practice. Attempts to calculate the macrosegregation with the so-called multidomain models have been made by coupling energy, solute, and momentum fields simultaneously across the moving boundaries between different phases.[12,13] To further tackle the problem of tracking the boundaries between the solid, mushy zone, and bulk liquid, Bennon and Incropera[14] developed the first continuum macrosegregation model. Almost at the same time, another promising volume-averaged approach to solve the set of continuum equations was developed by Beckermann and Viskanta.[15] With these developments of the macrosegregation models, direct prediction of channel or freckle formation can be accomplished.[16–19] To accurately consider the effects of the microscopic phenomena on the macroscopic transport that were ignored previously, Ni and Beckermann[20] further addressed the macroscopic transport equations in the solid and liquid phases separately u
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