Berlin 2024 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 3: Topical Session: Sustainable metallurgy

MM 3.8: Talk

Monday, March 18, 2024, 12:30–12:45, C 130

Order-disorder transitions on alloy surfaces: Full Monte Carlo thermodynamic averages versus Calphad inspired analytical models — Jing Yang, •Mira Todorova, and Jörg Neugebauer — Max-Planck-Insitut für Eisenforschung GmbH, Max-Planck-Strasse 1, D-40237 Düsseldorf, Germany

In this work, we propose an analytical thermodynamic model to describe the order-disorder transition on the surface of a metal alloy with substitutional defects. We apply this model on the system of Mg surface with Ca substitutions. First, we show the occurrence of a surface phase transition by using Monte Carlo simulations coupled with cluster expansion. Specifically, the system undergoes a transition from a disordered phase at high temperature and Ca-poor conditions to an ordered phase with 1/3 monolayer Ca coverage at low temperature and Ca-rich conditions. Then we show that with an analytical model which assumes Boltzmann distribution of the phase fractions, it is possible to accurately reproduce the critical transition condition. Last, we compare our method to the sublattice model, which is commonly used in the CALPHAD approach to describe solution phases with ordering. The proposed method provides a simplified model for describing order-disorder transition and is potentially applicable also to constructing bulk phase diagrams.

Keywords: alloy; surface; Monte Carlo; thermodynamics