Research On The Directionally Solidified Microstructure Of Cu-Sn Peritectic Alloys

Peritectic solidification is a very important phase transformation involved in many structural materials and functional materials. Recently, many aspects of peritectic solidification have been investigated including nucleation and growth, banded structure, coupled growth and phase selection. However, the effects of solidification condition on the microstructure characteristic scales, such as primary dendrite arm spacing, size and volume fraction of each phase, deserve further study, which is helpful to improve the property of materials.In this paper, hyperperitectic Cu-Sn alloys with three composition as, Cu-69wt.%Sn, Cu-73wt.%Sn and Cu-75wt.%Sn were studied by directional solidification with drawing velocity range from 1um/s to 5000um/s. The microstructure were analyzed in order to obtain the variation of primary dendrite arm spacing of primary ε phase, thickness of ε and peritectic phase n. and volume fraction of eutectic structure with the solidification velocity.The results show that there exists transition region at the beginning of all samples. The microstructure and length of transition region vary with solidification condition. When the velocity between 1um/s and 1000um/s, the plate-like primary phase is envelopped in the secondary phase in the steady state region. With increasing of growth velocity, the primary ε of Cu-69wt.%Sn becomes more and more thinner. The relation between primary dendrite arm spacing of primary ε andsolidification velocity satisfies λV0.312= 176um1.312-0.312S at low velocity whileλV0.528= 678um1.528-1.528S at high velocity. The volume fraction of eutecticstructure first increases with increasing V and then decreases. The thickness of peritectic phase n rapidly decreases at low velocity and slightly reduces at high velocity. The peritectic transformation mechanism in Cu-Sn is dominant at low velocity.