Due to toxicity of the lead in the Pb-Sn alloys, the development of lead-free solders is of high importance in the electronics industry. The Sn-Zn based alloys are quite attractive for the solder materials because of its low-cost and the appropriate melting point, and for this reason, some Sn-Zn based alloys have been put into practical use. In the present study, we selected the Sn-Zn-Ti ternary system as the candidate for such solders, and the phase equilibria in the ternary system have been studied experimentally and using thermodynamic calculations.

The phase equilibria of the Zn-Ti binary system is not well established, and thus the phase boundaries were determined using differential scanning calorimetry as well as the diffusion couples method. In addition, the formation energies for some stoichiometric compounds were obtained by using the first principle band energy calculations. For the ternary system, some alloys were prepared by homogenizing at 873K and the compositions of the precipitates were analyzed using the electron probe microanalyser (EPMA). Thermodynamic analysis was performed on the basis of the information, adopting the reported values for the thermodynamic properties of the Sn-Zn and Sn-Ti binary systems.

The microstructure observation showed that the compound with the composition of Sn₃Zn₁₂Ti₅ exists in the ternary system. Five kinds of invariant reactions in the Sn-rich liquidus surface of the ternary system were predicted by the calculation of the phase diagrams. The ternary eutectic point falls at 8.67%Zn, 0.0005%Ti and 466K. Based on these results, a non-equilibrium solidification process using the Scheil model was simulated.