Thermal expansion and elastic properties of high gold-Tin Alloys

The Au-Sn eutectic alloy, composed of the ζ and δ phases, has been used for many years in the sealing of hermetic parts. Recently, it was shown that the ζ phase undergoes an ordering transformation to ζ′. Since this transformation may affect hermeticity, measurements of density, linear thermal expansion coefficient, elastic moduli, and Poisson’s ratio were made on ζ-phase, eutectic, and δ-phase specimens. Measurements were made over a temperature range that includes the ζ → ζ′ transformation. Abrupt changes in these thermophysical properties, near the phase transformation temperature, are noted for ζ and eutectic specimens but not for the δ specimen.