Solidification segregation

Ohashi T. et al., A study on solidification, segregation and fluid flow of molten steel in continuously cast slabs. Trans ISIJ, 15 (1975) 571-579... 

Blanc G. Tricot R., Solidification, segregation et homogeneisation des aciers inoxydables austenitiqu-es contenant de la ferrite delta. Mem. Sci. Rev. Met., 68(1971), 735-753... 

Powder Techniques. Highly alloyed materials made by the processes described are particularly susceptible to segregation of alloying elements during solidification both on a macro- and a microscale. Much plastic working was necessary to minimise this susceptibiUty before service appHcations. 

S. Coriell, R. Boisvert, R. Rehm, R. Sekerka. Lateral solute segregation during unidirectional solidification of a binary alloy with a curved solid-liquid interface. J Cryst Growth 54 167, 1981. 

The formation of the microstructure involves the folding of linear segments of polymer chains in an orderly manner to form a crystalline lamellae, which tends to organize into a spherulite structure. The SCB hinder the formation of spherulite. However, the volume of spherulite/axialites increases if the branched segments participate in their formation [59]. Heterogeneity due to MW and SCB leads to segregation of PE molecules on solidification [59-65], The low MW species are accumulated in the peripheral parts of the spherulite/axialites [63]. The low-MW segregated material is brittle due to a low concentration of interlamellar tie chains [65] and... 

In practice, of course, few alloys are homogeneous in composition, the segregation produced during solidification being reduced but not... 

For an alloy droplet, the post-recalescence solidification involves segregated solidification and eutectic solidification. 619 Droplet cooling in the region (1),(2) and (6) can be calculated directly with the above-described heat transfer model. The nucleation temperature (the achievable undercooling) and the solid fraction evolution during recalescence and post-recalescence solidification need to be determined additionally on the basis of the rapid solidification kinetics. 154 156 ... 

DICTRA (Diffusion simulation software) (Borgenstam et al. 2000). DICTRA (coupled with Thermo-Calc) is a software for the simulation of diffusion in multi-component alloy systems (processes which can be simulated are for example the homogenization of alloys, micro-segregation during solidification, carburizing, and decarburizing, of steels, etc.). 

Unfortunately, the dilute solution model is limited in its applicability to concentrated solutions. This causes problems for alloys such as Ni-based superalloys, high alloy steels, etc., and systems where elements partition strongly to the liquid and where solidification processes involve a high level of segregation. It is also not possible to combine dilute solution databases which have been assessed for different solvents. The solution to this problem is to use models which are applicable over the whole concentration range, some of which are described below. 

The phase-field simulations reproduce a wide range of microstructural phenomena such as dendrite formation in supercooled fixed-stoichiometry systems [10], dendrite formation and segregation patterns in constitutionally supercooled alloy systems [11], elastic interactions between precipitates [12], and polycrystalline solidification, impingement, and grain growth [6]. 

As a reasonable approximation, the dendritic structure may be represented by the diagram in Fig. 22.4. The solidification in the interdendritic space can be described by constructing the cell (shown dashed) and assuming that solidification proceeds in a manner similar to the plane-front solidification of a bar (as discussed in Section 22.1). Under typical casting conditions, kf k. Therefore, the segregation... 

Defects that must be appraised continuously include white spot" and "freckle. While spot is an area of alloy depleted in the lower melting-point alloying additions. Freckle is a mid-radial channel segregation resulting from a deep mcli pool and a steeply sloping liquidus profile. This segregation develops in the liquid before solidification. 

A major complication in the analysis of convection and segregation in melt crystal growth is the need for simultaneous calculation of the melt-crystal interface shape with the temperature, velocity, and pressure fields. For low growth rates, for which the assumption of local thermal equilibrium is valid, the shape of the solidification interface dDbI is given by the shape of the liquidus curve Tm(c) for the binary phase diagram ... 

For a semi-crystalline polymer the solidification model of Fischer [11] predicts that the chain dimensions are frozen in at Tm if crystallization occurs sufficiently fast so as to prevent the disentanglement of chains by unravelling and/or their segregation according to their mass. For a series of polyethylene samples Michler [12] has accomplished an instructive comparison between the dimensions of molecular coils and the thickness of crystalline lamellae (Fig. 4). 

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