Mechanism of Bi Precipitation in Sn65.4Bi34.6 Eutectic System

The macroscopic Bi precipitation process in highly heterogeneous Sn65.4Bi34.6 eutectic alloy is investigated on an atomic scale by positron annihilation spectroscopy. High concentration of vacancy-sized free volumes are located at interfaces among short-range ordered phases. Along with Bi precipitation, the chemical surroundings around the free volumes are changed from Bi- to Sn-rich environment and the concentration of free volume increases. The results demonstrate that free volume-intermediated atomic diffusion at the interfaces is responsible for macroscopic Bi precipitation in Sn65.4Bi34.6.