Abstract
Sn-Co-Cu ternary alloys are promising lead-free solders, and isothermal sections of Sn-Co-Cu phase equilibria are fundamentally important for the alloys' development and applications. Sn-Co-Cu ternary alloys were prepared and equilibrated at 523 K, 1073 K, and 1273 K (250 °C, 800 °C, and 1000 °C), and the equilibrium phases were experimentally determined. In addition to the terminal solid solutions and binary intermetallic compounds, a new ternary compound, Sn 3 Co 2 Cu 8 , was found. The solubilities of Cu in the α-CoSn 3 and CoSn 2 phases at 523 K (250 °C) are 4.2 and 1.6 at. pct, respectively, while the Cu solubility in the a-Co 3 Sn 2 phase is as high as 20.0 at. pct. The Cu solubility increases with temperature and is around 30.0 at. pct in the β-Co 3 Sn 2 at 1073 K (800 °C). The Co solubility in the ν-Cu 6 Sn 5 phase is also significant and is 15.5 at. pct at 523 K (250 °C). © 2012 The Minerals, Metals & Materials Society and ASM International.