On the operative mechanisms in the solidification of undercooled melts

Abstract

The role of undercooling in controlling the operative mechanisms of solidification and in promoting the formation of extended solid solutions in the Ag---Cu and Cd---Zn systems is discussed. Use is made of a novel expression for the free energy of an undercooled liquid in arriving at several characteristic temperatures controlling the mechanism of solidification. The temperature T₀, of equal free energy of solid and liquid phases, the temperature T_f at which fluctuations in the liquid state can become potent nucleants and the temperature T_a at which the driving forces for the processes of solute redistribution and of diffuionless solidification become equal are determined for the two systems. The prominent role of the entropy of fusion in determining the mixing parameters from phase diagram data is highlighted.