Phase Equilibria of the Ternary Sn-Zn-Co System at 250A°C and 500A°C

The isothermal sections of the ternary Sn-Zn-Co system (< 60 at.% Co) at 250A degrees C and 500A degrees C have been experimentally determined. A series of Sn-Zn-Co alloys of various compositions were prepared and annealed at the respective temperatures to reach phase equilibrium. The equilibrium phases in these alloys were examined metallographically and characterized by electron probe microanalysis and x-ray diffraction. In this system, the ternary solubilities of all the binary Sn-Co and Co-Zn intermetallic compounds (IMCs) are very limited. For the phase equilibria at 250A degrees C, two ternary IMCs, T-1 and T-2, were found, whose compositions were Sn-25 at.%Zn-25 at.%Co and Sn-15 at.%Zn-41 at.%Co, respectively. For the phase equilibria at 500A degrees C, in addition to the T-2 phase, another ternary IMC, namely T-3 (Sn-18 at.%Zn-37 at.%Co), was also found. Moreover, the phase stability of the T-1 and T-3 phases was investigated at temperatures of 260A degrees C to 400A degrees C in detail. The equilibrium phase was the T-1 phase below 300A degrees C, and changed to the T-3 phase at 400A degrees C. The crystal structures of these three ternary IMCs were also studied. The T-1 phase has a cubic structure (Pm3m), and the T-2 and T-3 phases are orthorhombic in space group Cmcm and Pnma, respectively.