Bridgman Crystal Growth of an Alloy With Thermosolutal Convection Under Microgravity Conditions

James E. Simpson, Suresh V. Garimella ISchool of Mechanical EngineeringPurdue UniversityWest Lafayette, Indiana 47907-1288Phone: (765) 494-5621; Fax: (765) 494-0539sureshg@ecn.purdue.eduHenry C. de Groh IIINASA Glenn Research CenterCleveland, Ohio 44135Reza AbbaschianDepartment of Materials Science and EngineeringUniversity of FloridaGainesville, Florida 32611ABSTRACTThe solidification of a dilute alloy (bismuth-tin) under Bridgman crystal growth conditions isinvestigated. Computations are performed in two dimensions with a uniform grid. The simulationincludes the species concentration, temperature and flow fields, as well as conduction in theampoule. Fully transient simulations have been performed, with no simplifying steady stateapproximations. Results are obtained under microgravity conditions for pure bismuth, and for Bi-0.1at.%Sn and Bi-l.0 at.%Sn alloys, and compared with experimental results obtained from crystalsgrown in the microgravity environment of space. For the Bi-l.0at.%Sn case the results indicate that asecondary convective cell, driven by solutal gradients, forms near the interface. The magnitude of thevelocities in this cell increases with time, causing increasing solute segregation at the solid/liquidinterface. The concentration-dependence of the melting temperature is incorporated in the model forthe Bi-l.0 at.%Sn alloy. Satisfactory correspondence is obtained between the predicted andexperimental results in terms of solute concentrations in the solidified crystal.§ Submitted for possible publication in ASME Journal of Heat Transfer, October 1998 and in revisedform, April 25, 2000¶ Associate Professor, author to whom correspondence should be addressed