Simultaneous Observation of Melt Flow and Motion of Equiaxed Crystals During Solidification Using a Dual Phase Particle
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SOLIDIFICATION is a multidisciplinary field involving thermodynamics, fluid dynamics and solid mechanics, heat and mass transfer, and other disciplines.[1–3] One of the most challenging problems in solidification modeling is the complex interactions between physical phenomena occurring at different length scales ranging from atomic rearrangement over single crystal-melt interactions to heat extraction, momentum and species transport at the system level. An important phenomenon in solidification is the simultaneous occurrence of melt flow and crystal motion. Solidification takes place either by a growing columnar front and/or by the growth of equiaxed crystals. Columnar growth happens in the form of cells or dendrites from the mold walls into the bulk melt due to heat extraction from outside. In equiaxed solidification, globular or dendritic crystals form by nucleation or fragmentation and subsequent growth into the surrounding melt. When equiaxed solidification is present, the phases (liquid and equiaxed crystal) interact with each other through momentum and energy exchange. The resulting solid–liquid multiphase flow pattern strongly depends on the microstructure of the equiaxed crystals, which in turn is governed by grain nucleation and growth mechanisms. Because the coupled liquid– solid flow causes structural and chemical heterogeneities in the final solidified products, a fundamental understanding of the multiphase transport phenomena ABDELLAH KHARICHA, Research Team Leader, MIHAELA STEFAN-KHARICHA, Ph.D. Student, ANDREAS LUDWIG, Professor, MENGHUAI WU, Associate Professor, are with the Department of Metallurgy, University of Leoben, Leoben, Austria. Contact e-mail: [email protected] Manuscript submitted March 23, 2012. Article published online September 19, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
coupled with the grain nucleation and growth mechanisms is required. The occurrence of dispersed two-phase flows in nature and industrial applications is abundant. The present topic shows the interaction of solid particles (equiaxed crystals) and the melt flow. However, there is a lack of consistent data to support the numerous theories for flow-particle interaction that have been developed in recent years.[4–9] Due to its transparency, the H2O-NH4Cl solution was used for many experimental studies in the past[1–3,6,10] as the perfect analog for metallic alloys solidification. Beckermann’s group used hypereutectic alloys of H2ONH4Cl to study the solidification and the convection phenomena.[11–13] The shadowgraph technique was used in this publication[11] for qualitative comparison between experimental measurements and numerical simulations. On the other hand, a carefully applied analysis of shadowgraph images could as well provide information about the distribution and sizes of grains in the liquid melt at least for small fractions of solid. A brief introduction to the PIV technique is given elsewhere.[14–17] The current authors described in more detail the principals of the PIV technique in Part I o
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