Studies of voids in neutron-irradiated aluminium single crystals III. Determination of void surface properties

Abstract

Anisotropio small-angle scattering has been measured with 8 Å neutrons from an aluminium single crystal containing a volume fraction of 0·8% octahedral voids created by exposure to a fluence of 1·7 × 10²¹ n/cm² (> 0·18 MeV) at 55°C. The scattering law in the (111) directions follows ⁻², while in (100) it follows ⁻² after correction for the contribution from a small (0·0014%) volume fraction of cubic voids. From the ratio of the intensity in these two directions, as determined in an experiment where the data were recorded at a fixed scattering vector length while the crystal was rotated about [110], the mean truncation parameter of the octahedra was found to be 0·19 ± 0·02. From this value, the ratio of the specific surface free energy for these two planes is γ₁₀₀/γ₁₁₁ = 1·40 ± 0·03. The discrepancy between this value and the value 1·03 determined for aluminium containing helium bubbles by Nelson, Mazey and Barnes (1965) is associated with contamination of the surfaces by transmutation-produced Si.