Comparison of dendrites of a pure material with thermal alloy dendrites: An experimental method to estimate the T-0-temperature

Complete solute trapping during alloy solidification is considered to be a process which takes place under extreme non-equilibrium conditions. To show how thermodynamic considerations are used in the theoretical description o f solute trapping, the relation between the temperature at the interface T and the growth velocity V is derived for pure materials and for binary dilu te alloys. It is shown that in alloy solidification with complete solute tr apping the T-V relation is similar to that of a pure material with a hypoth etical "melting point" given as the T-0-temperature. Here, T-0 is defined a s the temperature at which the free energy of liquid and solid, both with t he same concentration, is equal and the solid/liquid interface is at rest. From the comparison of bath undercoolings necessary to achieve similar dend ritic growth velocities during pure material growth and complete solute tra pping growth of dilute alloys, an experimental method to estimate T-0 is di scussed. The comparison of T-0 estimated by this method with the theoretica l predictions shows reasonable agreement. (C) 2001 Acta Materialia Inc. Pub lished by Elsevier Science Ltd. All rights reserved.