The Contribution of Constitutional Supercooling to Nucleation and Grain Formation

The concept of constitutional supercooling (CS) including the term itself was first described and discussed qualitatively by Rutter and Chalmers in order to understand the formation of cellular structures during the solidification of tin, and then quantified by Tiller et al . On that basis, Winegard...

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Bibliographic Details
Published in:Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 2015-11, Vol.46 (11), p.4868-4885
Main Authors: StJohn, D. H., Prasad, A., Easton, M. A., Qian, M.
Format: Article
Language:English
Subjects:
Alloys
Characterization and Evaluation of Materials
Chemistry and Materials Science
Cooling
Formations
Grains
Materials Science
Mathematical models
Metallic Materials
Metallurgy
Nanotechnology
Nucleation
Physical metallurgy
Structural Materials
Supercooling
Surfaces and Interfaces
Symposium: ICASP-4 (International Conference on Advanced Solidification Processing)
Temperature
Thin Films
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Summary:The concept of constitutional supercooling (CS) including the term itself was first described and discussed qualitatively by Rutter and Chalmers in order to understand the formation of cellular structures during the solidification of tin, and then quantified by Tiller et al . On that basis, Winegard and Chalmers further considered ‘supercooling and dendritic freezing of alloys’ where they described how CS promotes the heterogeneous nucleation of new crystals and the formation of an equiaxed zone. Since then the importance of CS in promoting the formation of equiaxed microstructures in both grain refined and unrefined alloys has been clearly revealed and quantified. This paper describes our current understanding of the role of CS in promoting nucleation and grain formation. It also highlights that CS, on the one hand, develops a nucleation-free zone surrounding each nucleated and growing grain and, on the other hand, protects this grain from readily remelting when temperature fluctuations occur due to convection. Further, due to the importance of the diffusion field that generates CS, recent analytical models are evaluated and compared with a numerical model. A comprehensive description of the mechanisms affecting nucleation and grain formation and the prediction of grain size is presented with reference to the influence of the casting conditions applied during the practical casting of an alloy.
ISSN:1073-5623
1543-1940
DOI:10.1007/s11661-015-2960-y