Real time observation of equiaxed growth of Sn-Pb alloy under an applied direct current by synchrotron microradiography

The equiaxed growth of Sn-50 wt% Pb alloy with an applied direct current (DC) was investigated using an updated synchrotron radiation imaging technique, i.e. the diffraction enhanced imaging (DEI). Without DC, dendrites grew in an irregular manner due to the gravity-driven fluid flow; while imposing DC, the dendrites grew in an isotropous manner and more equiaxed morphology of grains was finally obtained. The electromagnetic flow induced by DC decreased the pileup of solute ahead of the growing solid/liquid interface and promoted the growth of the dendrites situated aside and below. Quantitative analysis on the growth rate of dendrites indicated that the interactions between dendrites were strengthened when imposing DC. It was thus believed that, with DC treatment, the formation of finer and more equiaxed grain structure is mainly attributed to the suppressed growth and strengthened interaction of growing grains. (C) 2012 Elsevier By. All rights reserved.