Structural and thermal properties of Sn–Ag alloys

Abstract

Microstructure and thermal properties of slowly cooled Sn–10% Ag and Sn–20% Ag alloys were experimentally investigated in this study. It was found that microstructure of the studied alloys is composed of large, plate-like grains of Ag3Sn intermetallic phase in the Sn-rich eutectic matrix. Phase transition temperatures and corresponding heat effects were experimentally determined and compared with the results of thermodynamic and phase equilibria calculations using the CALPHAD (CALculation of PHAse Diagrams) method and optimized thermodynamic parameters from literature. The xenon flash method was employed for the measurements of thermal diffusivity and determination of thermal conductivity in the temperature range from 25 to 150 °C. The results show that the thermal diffusivity and thermal conductivity gradually decrease with increasing temperature. The determined values of thermal conductivities of the investigated alloys are very close to each other and only slightly higher than that of pure tin. The contributions of electrons and phonons to the thermal conductivity of the studied alloys at room temperature were determined using the Wiedemann-Franz law and the obtained values of the thermal and electrical conductivities. The percentage contributions of the phonon component to the thermal conductivity for Sn–10% Ag and Sn–20% Ag alloys at 25 °C were found to be 20.5% and 28.9%, respectively.