Phase Equilibria of Sn-Co-Ni System and Interfacial Reactions in Sn/(Co, Ni) Couples

Abstract

Sn-Co-Ni alloys of 25 different compositions have been prepared and equilibrated at 250 °C. A new ternary (Ni, Co)Sn4 phase is found, and all the binary compounds have very significant mutual solubilities between Co and Ni. According to the ternary equilibrium phase data and the constituent binary phase diagrams, the 250 °C isothermal section of the Sn-Co-Ni system is proposed. In the Sn-CoSn-Ni3Sn4 corner, there are nine two-phase regions and five tie-triangles. Interfacial reactions between molten Sn and Ni-1.0 at. pct Co, Ni-3.0 at. pct Co, Ni-5.0 at. pct Co, Ni-20.0 at. pct Co, and Ni-40.0 at. pct Co substrates are examined. It has been found that the interfacial reactions in Sn/Ni-1.0 at. pct Co are similar to those in Sn/Ni couples, and only the Ni3Sn4 phase is formed. The (Ni, Co)Sn4 phase is formed in the couples prepared with Ni-3.0 at. pct Co, Ni-5.0 at. pct Co, and Ni-20.0 at. pct Co substrates. It grows very fast and has a faceted and unique morphology.