Wetting transition of grain boundaries in the Sn-rich part of the Sn-Bi phase diagram

The microstructural evolution of tin-rich Sn-Bi alloys after the grain boundary wetting phase transition in the (liquid + beta-Sn) two-phase region of the Sn-Bi phase diagram was investigated. Three Sn-Bi alloys with 30.6, 23, and 10 wt% Bi were annealed between 139 and 215 A degrees C for 24 h. The micrographs of Sn-Bi alloys reveal that the small amount of liquid phase prevented the grain boundary wetting transition to occur during annealing close to the solidus line. The melted area of the grain boundary triple junctions and grain boundaries increased with increasing the annealing temperature. When the amount of liquid phase exceeded 34 wt% during annealing, increasing temperature has not affected the wetting behavior of grain boundaries noticeably and led only to the increase of the amount of liquid phase among solid grains in the microstructure. The XRD results show that the phase structure and crystallinity remained unchanged after quenching from various annealing temperatures.