Segregation of alloying elements to stabilize θ′ phase interfaces in Al-Cu based alloys

Interactions of alloying elements (Si, Mg, Mn, Zr, Zn) and vacancies with coherent interfaces of theta' phase in Al-based alloys have been systematically studied by means of ab initio supercell calculations. The interface structure with a half-filled interfacial Cu layer is calculated to be lower in energy (by 0.1 eV per structural vacancy) than the structure with a filled Cu layer; the degree of interface reconstruction depends on the availability of vacancies. The presence of vacancies in the interfacial Cu layer plays a crucial role in the interaction of solutes with coherent theta' phase interfaces. The solute-interface interaction energies are calculated to be much weaker for elements having closed (Cu, Zn) or empty (Mg, Si) d-electron shells than for d-transition metals (Mn, Zr). To clarify the roles of alloying elements and interface structure in the stability of theta' phase precipitates, we analyze the solute-interface interactions in terms of electronic-structure and atomic-size contributions to interatomic bonding. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.