In-situ characterization of dendrite tip radius in Sn-base alloys

The solidification processes for Sn2Ag alloy and Sn2Ag0.6Zn alloy have been directly observed insitu using timeresolved Xray imaging at SPring8. In case of low cooling rate, the solidification condition is in coupled zone, the primary（βSn）has been overgrown by the eutectic structure. In case of other cooling conditions, the solidification of primary（βSn）dendrites and inter-dendritic eutectic structure have been observed. The dendrite tip radii have been characterized. It was found that the dendrite tip radius decreased as the growth velocity increased. The tip radius in Sn2Ag0.6Zn alloy is found to be smaller than that in Sn2Ag alloy, when the growth velocity is the same. The values of tip radius agreed well with the previous results which were obtained using the unidirectional solidification and quenching technique.