Solidification under Forced-Flow Conditions in a Shallow Cavity
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past 50 years, many attempts have been made to design special techniques with the purpose of improving and controlling the final solidified structure by forced flow. When one considers any particular casting system, one can see that the flow is present from the early stages of the process. During the casting, flow generally occurs in the bulk liquid and in the semi-solid regions. Some of the techniques have been successfully used in academic research with the aim of studying the fundamentals of solidification under forced-flow conditions: gravity flow-through systems,[1] mechanical stirring,[2] centrifugal casting,[3] application of a magnetic or electromagnetic field creating the Lorenz force,[4,5] etc. As experimental research has developed over the last 50 years, computational modeling and simulation have been widely used in the last two decades as cost-saving tools for the prediction and interpretation of the results. Using these two approaches in combination leads to a deeper understanding of the effects of melt flow as a result of natural and forced convection on the solidification phenomenon in metallic alloys, i.e., (1) the morphology of grains and their deflection toward incoming flow,[1–5] (2) the columnar-to-equiaxed transition and grain morphology,[4] and (3) the change of segregation pattern.[4,5,6] Forced flow applied to the bulk of the molten metal interacts with the growing solid producing the distortion of the solid-liquid interface,[1] altering the shape of the mushy zone[7] and affecting the solidification parameters.[8] Depending on the nature of the flow and the initial velocity, oscillation (vortices) of various magnitudes may occur at the solidification front. A.N. TURCHIN, Ph.D. Student, D.G. ESKIN, Senior Scientist, are with the The Netherlands Institute for Metals Research, 2628CD, Delft, The Netherlands. Contact e-mail: [email protected] L. KATGERMAN, Professor, is with the Department of Materials Science and Engineering, Delft University of Technology, 2628CD, Delft, The Netherlands. Manuscript submitted December 13, 2006. Article published online June 26, 2007. METALLURGICAL AND MATERIALS TRANSACTIONS A
However, many questions are still far from being understood completely. How does the forced flow and, in particular, the vorticity at the solidification front affect the macrostructural features? How does the forced flow influence the microstructure evolution? The present study is aimed at analyzing the effects of macroinstabilities at the solidification front on macroand microstructural features. The solidification under forced-flow conditions in the chill with a shallow rectangular cavity is proposed to create the vortex structure at the solid-liquid interface while solidification progresses. The combined approach based on fluid dynamics calculations and experimental work is implemented to determine quantitatively the solidification parameters, i.e., the local solidification time, rate, and thermal gradient, depending on the flow and heat regimes. In addition, the correlations between the structural parameters, the as
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