Solute Trapping in Highly Undercooled Succinonitrile-Acetone Alloys

Abstract

Pure succinonitrile and three dilute succinonitrile-acetone alloys were undercooled in long and fine capillary tubes up to the hypercooling limit. Solidification was externally triggered and growth into the undercooled melt optically monitored. The undercooling dependence of the growth velocity was measured systematically for the pure material and the three alloys. It was found that above ΔT = 10 K all V-ΔT curves were parallel. Motivated by this observation it is shown that with freely growing alloy dendrites the only mechanism for parallel V-ΔT curves is complete solute trapping. From the parallel shift of the curves the T 0 -temperature can be estimated. Although in the presented experiments thin surface dendrites grow along the tube wall, and therefore the results for free growing dendrites cannot be adapted directly, the agreement between the theoretically estimated T 0 -temperatures and the temperatures estimated from the measurements is remarkable. From this observation and three additional assumptions it is proposed that in the succinonitrile-acetone system complete solute trapping occurs above a growth velocity of V = 0.4 m/s.