Internal oxidation of CuFe—I. Small angle x-ray scattering study of oxide precipitation

Abstract

The combination of 3D-small-angle X-ray scattering, anomalous small-angle X-ray scattering and X-ray diffraction was used to characterize the nature and morphology of iron-oxide precipitates formed by internal oxidation of CuFe single crystals. Two types of iron-oxides with spinel structure were identified. The first type, Fe 3O 4 (90% of the total amount of precipitates), forms plates on {111}-planes of the copper lattice, whereas the other, with a composition close to γ-Fe 2O 3, forms plates on {100}-planes. The occurrence of plate-like precipitates on well defined habit planes is attributed to the large elastic misfit between matrix and precipitates. The fact that two oxides with very similar structure grow on different habit planes is interpreted as a bifurcation between two possible orientation relations during nucleation of the oxide.