Bridgman crystal growth of an alloy with thermosolutal convection under microgravity conditions

The solidification of a dilute alloy (bismuthtin) tender Bridgman crystal g rowth conditions is investigated. Computations are pe formed in two dimensi ons with a uniform grid. The simulation includes the species concentration, temperature and flow fields, as well as conduction in the ampoule. Fully t ransient simulations have been performed, with no simplifying steady state approximations. Results tire obtained under microgravity conditions for pur e bismuth, and for Bi-0.1 at. % Sn and Bi- 1.0 at. % Sn alloys, and compare d with experimental results obtained from crystals grown in the microgravit y, environment of space. For the Bi-1.0 at. % Sn case the results indicate that a secondary convective cell, driven by solutal gradients, forms near t he interface. The magnitude of the velocities in this cell increases with t ime, causing increasing solute segregation tit the solid/liquid interface. Finally, a comparison between model predictions and results obtained from a space experiment is reported. The concentration-dependence of the alloy me lting temperature is incorporated in the model for this case. Satisfactory correspondence is obtained between the predicted and experimental results i n terms of solute concentrations in the solidified crystal.