Morphologies of intermetallic compound phases in Sn-Cu and Sn-Co peritectic alloys during directional solidification

Abstract

The morphologies of intermetallic phases (IMCs) during directional solidification of the Sn-Cu (L+Cu3Sn→Cu6Sn5) and Sn-Co (L+CoSn→CoSn2) peritectic systems were analyzed. The primary Cu3Sn and peritectic Cu6Sn5 phases in Sn-Cu alloy are IMCs whose solubility ranges are narrow, while both the primary CoSn and peritectic CoSn2 phases in Sn-Co alloy are IMCs whose solubility ranges are nil in equilibrium condition. The experimental results before acid corrosion shows that the dendritic morphology of both the Cu6Sn5 and CoSn2 phases can be observed. The investigation on the local dendritic morphology after deep acid corrosion shows that these dendrites are composed of small sub-structures with faceted feature. Faceted growth of the primary Cu3Sn and CoSn phases is also confirmed, and a faceted to non-faceted transition in their morphologies is observed with increasing growth velocities. Further analysis shows that the dendritic morphology is formed in the solidified phases whose solubility range is larger during peritectic solidification.