Dynamics of core-shell particle formation in drop-tube processed metastable monotectic alloys

We examine the apparent size of the core and shell as a function of cooling rate in core-shell particles of the metastable monotectic alloy Co-50 at% Cu, finding that the volume fraction of the core systematically increases with cooling rate and hence undercooling. A model for this variation is proposed. A Monte-Carlo simulation is used to correct for sectioning effects allowing the true core: shell volume ratio to be estimated. From this, and the observation of a second, spinodal, episode of liquid phase separation we are able to estimate the undercooling at solidification. This permits a calculation of the time available following liquid phase separation for the migration giving rise to the observed core-shell structure to occur and hence the required Marangoni velocity required to such migration. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.