In situ transmission electron microscope measurements of solid Al-solid Pb and solid Al-liquid Pb surface-energy anisotropy in rapidly solidified Al-5% Pb (by mass)

Alloys of Al-5% Pb and Al-5% Pb-0.5% Si (by mass) have been manufactured by rapid solidification and then examined by transmission electron microscopy. The rapidly solidified alloy microstructures consist of 5-60 nm Pb particles embedded in an Al matrix. The Pb particles have a cube-cube orientation relation with the Al matrix, and are cuboctahedral in shape, bounded by {100}$_{Al, Pb}$ and {111}$_{Al, Pb}$ facets. The equilibrium Pb particle shape and therefore the anisotropy of solid Al-solid Pb and solid Al-liquid Pb surface energies have been monitored by in situ heating in the transmission electron microscope over the temperature range between room temperature and 550 $^\circ$C. The anisotropy of solid Al-solid Pb surface energy is constant between room temperature and the Pb melting point, with a \{100\}$_{Al, Pb}$ surface energy about 14% greater than the {111}$_{Al, Pb}$ surface energy, in good agreement with geometric near-neighbour bond energy calculations. The {100}$_{Al, Pb}$ facet disappears when the Pb particles melt, and the anisotropy of solid Al-liquid Pb surface energy decreases gradually with increasing temperature above the Pb melting point, until the Pb particles become spherical at about 550 $^\circ$C.