Solidification solute segregation

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. 

Subramanian S. V. Haworth C. W. Kirkwood D. H., Growth morphology and solute segregation in the solidification of some iron alloys. JISI, 206 (1968), 1027-1032... 

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 ... 

Z. Z. Cai, M. Y. Zhu, Influence of Solute Segregation on Crack Susceptibility at Solidification Front of Continuous Casting Strand , Foundry Technology, 30(11) (2009),... 

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. 

From our example, we could see that for our lab-scale furnace with only one impurity element, the segregation follows closely to the ideal case. The difference between the ideal case measured in the Czochralski material, where the stirring and resulting transport of solutes from the interface is good, and our casting furnace with relatively low melt velocities (V 1.5-2 mm s 1 Meese et al. [20]) is due to the build up of impurities during the solidification due to low transport of solute from the interface to bulk and due to recirculation... 

To prevent grain boundary segregation, methods based on the conelation of enrichment ratio with the inverse of solid solubility have been used in several cases. Johnson et al., for example, ) proposed doping nickel-based alloys with additives such as hafnium, zirconium or lanthanum in order to remove sulfur from solution by the formation of sulfides during solidification thus preventing segregation and subsequent embrittlement. 

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