An analytical bond-order potential for the aluminum copper binary system

Abstract

Al-rich Al1−xCux alloys are important structural materials in the aerospace industry due to their high strength to density ratio. They are also emerging materials for hydrogen containing structures due to their potentially high resistance to hydrogen embrittlement. To enable accurate simulations of the mechanical behavior of Al1−xCux alloys that can guide material improvement, we have developed a high-fidelity analytical bond-order potential (BOP) for the Al-Cu system (the code is publically available in molecular dynamics package LAMMPS). The formalism of the potential is derived from quantum mechanical theories, and the parameters are optimized in an iteration fashion. The iterations begin by fitting properties of a variety of elemental and compound configurations (with coordination varying from 1 to 12) including small clusters, bulk lattices, defects, and surfaces. Following the fitting process, crystalline growth of important equilibrium phases is checked through molecular dynamics simulations of vapor deposition. It is demonstrated that this Al-Cu bond-order potential has unique advantages relative to existing literature potentials in reproducing structural and property tends from experiments and quantum-mechanical calculations, and providing good descriptions of melting temperature, defect characteristics, and surface energies. Most importantly, this BOP is the only potential currently available capable of capturing the Al-rich end of the Al-Cu phase diagram. This capability is rigorously verified by the potential's ability to capture the crystalline growth of the ground-state structures for elemental Al and Cu, as well as, the θ and θ′ phases of the Al2Cu compound in vapor deposition simulations.