Rapid solidification: in situ diagnostics and theoretical modelling

We report on progress in direct experimental investigations of non-equilibrium crystallization in undercooled melts. Containerless processing is applied for undercooling and is combined with diagnostic means. The results of such experiments are utilized to critically assess physical models for rapid solidification. Existing models of rapid growth of solid into undercooled melts are reviewed. The sharp interface model is applied to quantitatively describe rapid dendrite growth of metals and alloys. It is extended to include effects of fluid flow in liquids induced by forced convection in electromagnetically levitated drops. Morphological transitions resulting in grain refinement via instabilities of growing dendrites are analyzed and used to evaluate the effect of fluid flow on grain refinement. Theoretical predictions given by sharp-interface model are compared with results of phase-field modeling and with new data of crystal growth dynamics measured with high accuracy. Depending on the undercooling prior to solidification the effects of solute diffusion, convective flow, solute trapping and microstructure evolution are demonstrated. (c) 2006 Elsevier B.V. All rights reserved.