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MM: Fachverband Metall- und Materialphysik
MM 44: Developement of Calculation Methods II
MM 44.4: Talk
Wednesday, March 20, 2024, 16:30–16:45, C 264
Extracting Gibbs free energies from local composition fluctuations in atom probe data — Jianshu Zheng1, Rüya Duran1, Marvin Poul2, Guido Schmitz1, and •Sebastian Eich1 — 1Institute for Materials Science, University of Stuttgart, Germany — 2Department of Computational Alloy Design, Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany
While thermodynamic fluctuation theory has been applied to liquids for decades to obtain Gibbs free energies from local composition fluctuations, the present work extends this theory to solids by considering an additional elastic work term. This theory is firstly verified via atomistic embedded-atom simulations in an exemplary Cu–Ni system using Monte Carlo techniques. Composition fluctuations, which are evaluated for various-sized subvolumes, reveal a systematic dependence on the size of the evaluation volume, but extrapolation to an infinitely large subvolume leads to perfect agreement with the prediction by the extended theory. Thus, recovering Gibbs free energies becomes indeed possible also in solids. In a second step, this method is now applied to experimental atom probe tomography (APT) data with high chemical and spatial resolution, enabling the analysis of local composition fluctuations. From these data, the Gibbs free energy is recovered and remarkable agreement is found between our approach and the latest CALPHAD representation of the miscibility gap. This methodology is therefore believed to efficiently improve the accuracy of thermodynamic information (e.g. miscibility gap, mixing/demixing tendencies, critical solution temperature) from direct APT measurements.
Keywords: Gibbs free energy; Small systems; Nanothermodynamics; Thermodynamic fluctuations