Abstract
The random packing of equiaxed dendritic grains in metal-alloy solidification is numerically simulated and validated via an experimental model. This phenomenon is characterized by a driving force which is induced by the solid-liquid density difference. Thereby, the solid dendritic grains, nucleated in the melt, sediment and pack with a relatively low inertia-to-dissipation ratio, which is the so-called Stokes number. The characteristics of the particle packed porous structure such as solid packing fraction affect the final solidified product. A multi-sphere clumping Discrete Element Method (DEM) approach is employed to predict the solid packing fraction as function of the grain geometry under the solidification conditions. Five different monodisperse noncohesive frictionless particle collections are numerically packed by means of a vertical acceleration: a) three dendritic morphologies; b) spheres and c) one ellipsoidal geometry. In order to validate our numerical results with solidification conditions, the sedimentation and packing of two monodisperse collections (spherical and dendritic) is experimentally carried out in a viscous quiescent medium. The hydrodynamic similarity is respected between the actual phenomenon and the experimental model, that is a low Stokes number, o (10−3 ). In this way, the experimental average solid packing fraction is employed to validate the numerical model. Eventually, the average packing fraction is found to highly depend on the equiaxed dendritic grain sphericity, with looser packings for lower sphericity.
Highlights
During metal alloy solidification solid and liquid phases co-exist since solid grains are nucleated in the melt
We focus on the modeling of the random packing phenomenon of the equiaxed dendritic solid grains during solidification and essentially the study of the geometrical influence though sphericity on the packing fraction
We model the equiaxed dendritic grain deposition and packing under solidification conditions
Summary
During metal alloy solidification solid and liquid phases co-exist since solid grains are nucleated in the melt. The solid phase density is slightly higher than that of the melt so the solid particles tend to settle and pack, e.g. aluminum and steel alloys. This forms a porous dendritic network [1] whose properties such as its solid packing fraction are important to better understand in order to improve the solidification macrosegregation modeling of metallic alloys [2, 3]. The packing is characterized by particles whose morphology is equiaxed dendrite-like and by a low driving force which is the apparent weight of the solid grains immersed in the melt [4]
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