Solidification interface morphology in narrow channel during unidirectional solidification

Directional solidification studies have been carried out in Succinonitrile -0.04 to 3.0mol% acetone alloy in small channels at the condition from planer to dendritic interface growth in order to clarify the solutal and geometrical influences of narrow fibers interstices on the microstructure of matrix alloys and to optimize high-performance Metal Matrix Composites. The specimens were designed to have an inner composite region and an outer un-reinforced bulk region in order to make a comparison of the interfacial morphology under the same thermal conditions. In the composite region of the specimens, the tip radius of cell increased with increasing the tube diameter and decreasing the number of cell, The concentration of acetone at the cell tips in 200 urn diameter-tube is estimated three times higher than bulk composition, and the tip composition increases as the tube diameter becomes smaller. The solutal undercooling is estimated to be 1.8K by the tip radius, that indicates the trapped solutal diffusion field might govern the cell tip undercooling and tip radius. Secondary dendrite arm spacing stabilized more uniformly in the glass tubes, when the tube size is designed less than primary dendrite arm spacing. Solute pile-up between the dendrite tip and inner wall of tube interrupts the secondary dendrite arm coarsening. However, the coarsening of secondary dendrite arm becomes remarkable if the tube diameter is larger than the primary arm spacing and no interference of any other dendrites occurs.