Competitive growth of Si and YSi₂ phases in a eutectic Si-Y alloy prepared by the Bridgeman method

A directionally solidified Si-YSi₂ alloy was prepared by the Bridgman method at different withdrawal rates. The microstructures of longitudinal section and cross section were investigated. We observed that as the withdrawal rate increased from 0.5 mm/min to 2 mm/min, the morphology of YSi₂ phase changed from fine, long strips to islands and finally to blocks distributed along the thick primary Si phase. By calculating the interface growth temperatures of each phase, we found the interface growth temperatures of Si phase and YSi₂ phase both decreased with withdrawal rate increasing while that of eutectic structure was almost unchanged. Beyond that the interface growth temperature of Si phase was always higher than that of YSi₂ phase. We determined two critical withdrawal rates of V_C1= 0.96 mm/min and V_C2= 1.57 mm/min. Coupled growth was predominant when the withdrawal rate was slower than V_C1 and primary Si phase disappeared. Primary Si phase began to form as the withdrawal rate was greater than V_C1 and could be obviously thicker as the withdrawal rate was greater than V_C2.