The morphology and crystallography of directionally solidified pb-sn eutectic alloys

Directional solidification of Pb-Sn eutectic alloys at high temperature gradients has shown that two distinct eutectic morphologies occur, a regular lamellar structure and a wavy lamellar structure, termed degenerate. An electron channelling technique was used to characterize the crystallography of the two morphologies. The degenerate grains grow in advance of the regular grains and are the preferred growth morphologies in spite of the fact that coarsening experiments revealed that the degenerate grains possessed a higher lamellar interface energy. This result conflicts with the Zener model of eutectic growth. A possible rationalization of this conflict based on the anisotropy of thermal conductivity in Sn is presented.