Critical solidification behavior of undercooled Ag-Cu alloys

Publisher Website
Google Scholar
Abstract
Melts of Ag, Cu, and four different Ag‐Cu alloys, including the eutectic composition, with masses between 1 and 2.5 g were undercooled by the glass flux method, and the temperature of the specimen was measured with a pyrometer during cooling and recalescence. For each composition the maximum recalescence rate was determined as a function of the undercooling. Comparison of the results for Ag and Cu with published measurements of the dendrite growth velocities in these metals showed that the maximum recalescence rate provides a good semiquantitative measure of the growth rate. For the Ag‐Cu alloys there is a critical solidification temperature—close to T0—at which the maximum recalescence rate rises abruptly by about two orders of magnitude, accompanied by significant changes in the microstructure. It is shown that this behavior can be explained theoretically on the basis of a transition from diffusion‐controlled growth of the eutectic or the primary dendrites to dendritic growth of a supersaturated phase, provided that interface kinetics and growth‐rate‐dependent partition coefficients are taken into account.