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(Meta‐)stable phases and pre‐Guinier–Preston zones in AlCu alloys constructed from ab initio relaxed atomic positions – Comparison to experimental methods

Vacancies on different sublattices in the stable and meta‐stable Al2Cu phases Θ and Θ′ have been studied by ab initio calculations. We calculate their formation energies and relaxation features. These phases exist in over‐aged dilute AlCu alloys and have to grow under Al‐rich conditions. Our calculations show that the preferred site for structural vacancies is on the Cu sublattice. Characteristic for early stages of aging dilute AlCu alloys are pre‐Guinier–Preston (GP) zones. Here, we calculated the atomic arrangements of small clusters of Cu atoms in the aluminum matrix (Cu platelets on the {100}‐planes of Al). Strong – energy lowering – relaxations of Al atoms toward the habit plane of Cu atoms possibly explain the stability of these planar configurations favored over three‐dimensional agglomerations in real materials. The ab initio atomic positions for Θ‐ and Θ′‐phases as well as for pre‐GP zones have been finally used to calculate both X‐ray absorption fine structure spectra and positron annihilation data – namely positron lifetimes and momentum distributions. Comparisons to the few existing experimental data are discussed and suggestions for further experiments are given.