Prince Mathews

S. Zhang1, C. Scheu1, R. Janisch2, J. Neugebauer1, T. Hickel1,3

1Max-Planck-Institut für Eisenforschung, Düsseldorf, Germany:  2ICAMS, RU-Bochum; 3BAM, Berlin

Ga Induced Defect Phase Transformations in the Σ7 Mg Grain Boundary

Designing of tailored materials requires the studying of various defects and defect transformations along with the bulk phases. Grain boundaries (GBs) is one such defect that directly influence the properties of the material. Alloy additions can further introduce defect phase transformations and alter mechanical properties. In this work, the defect under consideration is the Ʃ7 [0001] 21.78° (sym. plane 12-30) GB in the Mg hcp system, with the defect phases being A- and T-type, differing in atomic arrangement at the GB. Ab-initio simulations are performed to determine the stability of the 2 defect phases for the case of pure Mg with respect to stress and temperature (using quasi-harmonic approximation). Experimental evidence shows T-type configuration in pure Mg, and A-type configuration with Ga decoration at the GB. Hence, using a MEAM potential, all configurations for Ga atoms up to the number of Ga atoms as seen experimentally are investigated and prescreened for DFT simulations. Using these energies, a workflow for constructing the defect phase diagram has been developed which can be further extended to investigate multiple defects. A systematic transition of preference of segregation sites is seen with increasing number of Ga atoms at the GB. The stability of different configurations as a function of coverage (column occupancy of a site occupied by Ga) is also discussed to explain the discrepancy between lowest energy configuration obtained from DFT simulations and the experimentally observed configuration.

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