Anisotropy of interfacial free energy of some hexagonal close-packed metals

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Abstract
The equilibrium shapes of inert gas bubbles in zinc were determined by annealing foils which had been supersaturated with argon by ion bombardment. The anisotropy of solid-vapour surface free energy in the temperature range 130-300°C was evaluated by studying bubble shape as a function of annealing temperature. At 300°C the equilibrium bubbles are bounded by basal, {1011} pyramidal and {1010} prismatic facets, and from the mean aspect ratio of the bubbles, it was determined that γ(1010)/γ(0001) = 1.55. At lower temperatures the extent of the prismatic bubble faces is reduced, whereas aspect ratio increases somewhat to 1·75 at 130°C. From these results, the free energy of (0001) zinc surfaces has been determined to be ∼ 600 ergs/cm2, or about six times higher than values obtained by cleavage techniques. Our results are correlated with other experimental data concerning the anisotropy both of solid-vapour and of solid-liquid interfacial free energy in h.c.p. metals. The data for solid vapour interfaces have been obtained from the observed shapes of inert gas bubbles in zinc, magnesium and beryllium, whereas data for solid-liquid interfaces have been obtained from the shapes of droplets of alloy liquid entrained within cadmium, zinc and magnesium. In each case, the experimentally determined γ plots are compared with those based upon pairwise-interaction theory.