Directional solidification microstructures of Cu-55Sn hypo-peritectic alloy

Effects of solidification structure and solidified rate on structural morphology, interfacial temperature and phase constituent of Cu-55Sn hypo-peritectic alloy have been investigated with directional solidification rate in the range of 0.5~100 μm. The results show that directional solidified phase constituent is composed of primary ε phase, peritectic η phase and eutectic (η + Sn) phase. Bulky peritectic η phase is embedded in primary ε phase in the directional solidification Cu-55Sn hypo-eutectic alloy with directionally solidified rate in the range of 0. 5~1 μm / s while with solidified rate more than 5 μm, the solidification structure remains the conventional plate structure, where peritectic η phase coats primary ε phase. Coupled growth in isothermal interface for peritectic η phase and primary e phase can not be formed because primary ε phase is prior phase, which is in accordance with analysis of top-interface temperature growth theory. Major peritectic η phase is directionally formed from the liquid phase during direction solidification process. In addition, with increasing in cooling rate and decreasing in solidification time, peritectic η phase content is firstly increased then decreased, and the peak content of the peritectic η phase can be observed with the directional solidification rate of about 10 μm.