Atomistic simulation of alumina grain boundary structure and diffusion

• Applicant: Professor Dr. Ralf Drautz
• Subject Area: Computer-Aided Design of Materials and Simulation of Materials Behaviour from Atomic to Microscopic Scale ; Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 536664308

Oxide scales on Al- or Cr-containing alloys provide efficient and inexpensive corrosion protection. However, key atomic scale mechanisms in oxide scale formation are unknown or disputed, which limits insight and understanding and blocks the computational design of optimal alloys and oxide scales. Atomistic simulation of mechanisms in oxide scale formation is difficult. Firstly, an accurate representation of the potential energy surface is required that enables the simulation of complex atomic rearrangements in grain boundaries and includes the contribution of charge transfer to the energy. Secondly, the simulation cells need to comprise thousands of atoms to sample realistic geometries and simulations need to be run for sufficiently long times to observe atomic rearrangements and diffusion. While density functional theory (DFT) is sufficiently accurate, it is unable to simulate that many atoms. On the other hand, simulations with sufficient atoms are possible by employing classical interatomic potentials, but these potentials are generally not sufficiently accurate or transferable, even when including a model of charge transfer. Only recently a class of accurate interatomic potentials, often termed machine-learning potentials, became prominant, which describe a potential energy surface with near-DFT precision. Within this category the approach we favour is the Atomic Cluster Expansion (ACE), in which we are incorporating charge transfer. It is fast and systematically improvable. With this approach we propose to develop accurate and transferable interatomic potentials for the aluminium-oxygen system. We will employ these potentials for the simulation of diffusion in grain boundaries of the oxide scale and extract from our simulations the atomic scale mechanisms and diffusion coefficients that are decisive for understanding the growth rates of oxide scales. Our project will be the first to our knowledge which tackles the problem of atomic scale diffusion mechanisms and rates in oxide grain boundaries at high temperature, laying the foundations for atomic scale design of protective scales.

• DFG Programme: Research Grants