Solidification Mechanism of Highly Undercooled Metal Alloys

Abstract

ABSTRACTThis paper describes the results of experiments on metal droplet undercooling, and presents a preliminary analysis of the structures obtained. Work was conducted with Sn-25wt%Pb and Ni-34wt%Sn alloys. To achieve the required high degrees of undercooling, emulsification treatments were utilized following techniques described by Perepezko and co-workers.Experiments show the fraction of supersaturated primary phase is found to be a function of the amount of undercooling, as is the fineness of the structures. The solidification behavior of the tin-lead droplets during recalescence was analyzed using three different hypotheses; 1) solid forming throughout recalescence is of the maximumthermodynamically stable composition, 2) partitionless solidification below the “To” temperature, and solid forming thereafter is of the maximum thermodynamically stable composition, and 3) partitionless solidification below the “To” temperature with solid forming thereafter that is of the maximum thermodynamically metastable composition that is possible.