Mushy zone

P. Lehmann, R. Moreau, D. Camel, R. Bolcato. A simple analysis of the effect of convection on the structure of the mushy zone in the case of horizontal Bridgman solidification. Comparison with experimental results. J Cryst Growth 183 690, 1998. 

In the classical Stefan formulation of phase change problems, solidification occurs at a well defined front which moves though the material (Aziz 2003). This is appropriate for simple materials, but not for chocolate which is a multi-component mixture of triglycerides which displays a spread of melting points. A front is therefore difficult to define. Instead a mushy zone exists instead where solid and liquid co-exist the process is described as continuous solidification (Voiler, Swaminathan and Thomas 1990). 

The solute elements of Nb-V containing steel are in the balance status at the initial stage of solidification. With the temperature decreasing, solute segregation occur in the mushy zone which can be explained by the diffusion coefficient of solute elements is smaller than temperature diffusivity during solidification process. Thus, solute redistribution is characterized by segregation factor which can be expressed as follow c," /C = Cj /tc ... 

Felicelli et al. [54] used a fixed finite element algorithm to calculate macrosegregation and the formation of channels and freckles in Pb-Sn alloys. They assumed that the mushy zone is a porous medium with an isotropic permeability and considered superficial velocity components for the fluid velocities in the mushy region. The superflcial velocities are... 

Schneider MC, Beckermann C (1995) A numerical study of the combined effects of microsegregation, mushy zone permeabriity and flow, caused by volume contraction and thermosolutal convection, on macrosegregation and eutectic formation in binary alloy soUdiflcation. Int J Heat Mass Transf 38 3455-3473... 

Ilegbusi OJ, Mat MD (1998) Modeling flowabriity of mushy zone with a hybrid model utilizing coherency solid fraction. Mater Sci Eng A A247 135-141... 

Paradies CJ, Smith RN, GUcksman ME (1997) The influence of convection during solidification on fragmentation of the mushy zone of a model alloy. Metall Mater Trans A 28A 875-883... 

HiUs RN, Loper DE, Roberts PH (1983) A thermodynamically consistent model of a mushy zone. Q J Mech Appl Math 36 505-539... 

Flow in porous media plays an important role in many areas of science and engineering. Examples of the application of porous media flow phenomena are as diverse as flow in human limgs or flow due to solidification in the mushy zone of liquid metals. 

Local freezing temperature along the growing sample. The temperature ahead of the solidification interface must increase at least at the mte shown by Gi to stabilize the plane front growth interface. If the thermal gradient is insufficient, as illustrated by slope Gz, the growth interface breaks down into a dendritic structure with a mushy zone (mixture of solid dendrites and interdendritic fluid) that extends to the point where the temperature is above the local freezing point. 

Long-range segregation can result either from changes that occur in the liquid before the solidification front has proceeded very far or as the result of fluid motion in the mushy zone behind the solidification front. 

A further temperature decrease causes two phenomena to take place. First, there is an increase in the quantity of solid phase and a decrease in the quantity of liquid phase. The fluidity of the alloy is reduced and the material takes on the consistency of a paste or mush (i.e., slush) hence, this two-phase region is often referred to as the pasty range or the mushy zone. Second, there is a change in the respective compositions of the Uquid and sohd phases. For example, when the temperature of the alloy drops to that of point C, 195 ° C, the composition of the newly formed... 

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