Rapid solidification of Ag-Si eutectic alloys in drop tube

Rapid solidification has been investigated on Ag-2.5% Si hypoeutectic, Ag-3.1% Si eutectic, and Ag-5% Si (weight percentage) hypereutectic alloys in a 3-m drop tube. The irregular eutectic microstructures vary with droplet size and composition. Grain refinement has occurred to primary Ag dendrites, and to primary and eutectic Si with the decrease of droplet diameter. The interphase spacing was measured experimentally and calculated theoretically based on the modified Jackson-Hunt and Trivedi-Magnin-Kurz eutectic growth models. The growth velocity was also predicted by these two models. The operating range parameter φ has been obtained approximately to be 2.614. It is presumed that Marangoni convection may be responsible for the central distribution of primary Si blocks in the hypereutectic alloy. Appearance of primary Ag phase in the eutectic alloy and a novel microstructure characterized by primary Ag grains with a few Si blocks distributing in the fine globular eutectic matrix in small droplets of Ag-5% Si hypereutectic alloy is interpreted by the skewed-coupled zone.