The liquidus and solidus temperatures and enthalpy of fusion for Ag-Sn alloys are systematically measured within the whole composition range by differential scanning calorimetry (DSC). The measured enthalpy of fusion is related to Sn content by polynomial functions, which exhibit one maximum value at 52 wt%Sn and two minimum values around 21 wt%Sn and 96.5 wt%Sn, respectively. The liquidus slope, the solidification temperature interval, the solute partition coefficient and the entropy of fusion are calculated on the basis of the measured results. The undercoolability of those liquid Ag-Sn alloys solidifying with primary (Ag) solid solution phase is stronger than the other alloys with the preferential nucleation of ζ and ε intermetallic compounds. Morphological observations reveal that peritectic reactions can rarely be completed, and the peritectic microstructures are always composed of both primary and peritectic phases.
The dynamic solidification of ternary Ag38.5Cu33.4Ge28.1 eutectic alloy within a 35 kHz ultrasonic field is investigated and compared with both its equilibrium solidification by DSC method and its rapid solidification in drop tube.The volume fractions of the primary(Ge) phase and pseudobinary(Ag+ε2) eutectic solidified within ultrasonic field are larger than those formed under equilibrium state,whereas that of ternary(Ag+ε2+Ge) eutectic exhibits the reverse trend.During rapid solidification,the liquid alloy droplet directly solidifies into ternary(Ag+ε2+Ge) eutectic if its diameter is smaller than 350 m.The ultrasound stimulates the nucleation of alloy melt and prevents the bulk undercooling.With the increase of sound intensity,the primary(Ge) phase transfers from faceted dendrites to nonfaceted blocks with blunt edges,and its grain size is remarkably reduced.Both pseudobinary(Ag+ε2) and ternary(Ag+ε2+Ge) eutectics experience a morphological transition from regular to anomalous structures.This indicates that their cooperative growth mode is replaced by independent growth of eutectic phases under the combined effects of cavitation and acoustic streaming.The ultrasound also shows a prominent coarsening effect to the pseudobinary(Ag+ε2) and ternary(Ag+ε2+Ge) eutectics.
