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MM: Fachverband Metall- und Materialphysik
MM 41: Topical Session: Defect Phases III
MM 41.7: Vortrag
Donnerstag, 30. März 2023, 17:45–18:00, SCH A 216
Ga Induced Defect Phase Transformations in the Σ7 Mg Grain Boundary — •Prince Mathews1, Siyuan Zhang1, Christina Scheu1, Tilmann Hickel1,2, and Jörg Neugebauer1 — 1Max-Planck-Institut für Eisenforschung, D-40237 Düsseldorf — 2Federal Institute for Materials Research and Testing (BAM), D-12489 Berlin, Germany
The design of tailored materials requires to understand not only bulk phases but also the stability of various defect phases. Grain boundaries (GBs) form one class of defects that directly influence the properties of the material. Therefore, GB phase transformations introduced by alloying can alter mechanical performance. In this work, the Σ7 [0001] | 21.78° (sym. plane 12-30) GB in hcp Mg is investigated, for which an A- and a T-type is known. Ab-initio simulations as a function of stress and temperature (using quasi-harmonic approximation) are performed, and show the presence of a phase transformation. Based on the computed Gibbs energies, the defect phase diagram as a function of the Ga chemical potential is determined. To this end, a complete set of Ga configurations at the GB is first screened with an empirical potential, before accurate ab initio calculations are performed for the low-energy configurations. Ga is not only found to trigger a transformation between T and A type, but a systematic transition of the preferred segregation sites is also seen with an increasing number of Ga atoms at the GB. The results qualitatively agree well with experimental results from high-resolution transition electron microscopy (HR-TEM). Physical mechanisms are provided to explain remaining discrepancies.