The evolution of liquid lead (Pb) inclusions at grain boundaries in
aluminum (Al) was investigated by direct in situ TEM observation in the
temperature range from 330°–643°C, In agreement with earlier
reports on quenched alloys, the characteristic contact angle of the
lens-shaped grain boundary inclusions was found to be near 120°. This
angle remained approximately constant over the entire temperature range,
ruling out the possibility of a wetting transition. Coarsening of grain
boundary inclusions was observed to proceed mainly by Ostwald ripening,
although coalescence could also be observed. Inclusions at grain
boundaries, at triple junctions, and at the intersection of grain
boundaries with the foil surfaces adopted characteristic shapes that were
shown to be equilibrium forms. At the highest temperatures, the grain
boundaries were observed to detach from the inclusions and the interaction
of a migrating grain boundary with inclusions could be observed.