Dresden 2009 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 5: Materials Design I

MM 5.1: Talk

Monday, March 23, 2009, 10:15–10:30, IFW D

Using ab initio calculations in designing bcc Mg-Li alloys for ultra light-weight applications — William Art Counts, •Martin Friák, Dierk Raabe, and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Strasse 1, 402 37, Düsseldorf, Germany

Ab initio calculations are becoming increasingly useful to engineers interested in designing new alloys because these calculations are able to accurately predict basic material properties only knowing the atomic composition of the material. In order to explore the suitability of this approach in identifying potential candidates for ultra-light-weight applications we studied bcc Mg-Li alloys. In a first step, the fundamental physical properties (like formation energy and elastic constants) of an extensive set of bcc Mg-Li compounds are calculated using density-functional theory (DFT) and compared with available experimental data. These DFT-determined properties are in turn used to calculate engineering parameters like (i) specific Young’s modulus (Y/ρ) or (ii) bulk over shear modulus ratio (B/G) differentiating between brittle and ductile behavior. In a second step, these engineering parameters are used to identify alloys that have optimal mechanical properties needed for a light-weight structural material. It was found that the stiffest bcc magnesium-lithium alloys contain about 70 at.% Mg while the most ductile alloys have 0-20 at.% Mg. An Ashby map containing Y/ρ vs. B/G shows that it is not possible to increase both Y/ρ and B/G by changing only the composition of a binary alloy (W. A. Counts, M. Friák, D. Raabe, J. Neugebauer, Acta Mater 57 (2009) 69).