Gravity-induced sedimentation during melting and liquid phase sintering of Pb–Sn alloys Original Research Article

Gravity-induced phase separation during melting of Pb–Sn alloys results in a macroscopic concentration gradient that must be eliminated before phase equilibrium is established. When Pb–Sn alloys are heat treated in solid-plus-liquid regions (akin to liquid phase sintering), recession of the mushy (solid-plus-liquid) region accompanies elimination of the concentration gradient. Sedimentation apparently ceases as phase equilibrium is approached. Some solid-plus-liquid alloys do not sediment. These have a solid volume fraction sufficient to sterically hinder the gravity-induced phase separation. This critical volume fraction is about 0.50 for hypoeutectic (Pb-rich) alloys and about 0.75 for hypereutectic (Sn-rich) alloys.