Ab Initio Guided Design of bcc Ternary Mg–Li–X Alloys for Ultra-Lightweight Applications
In this project we conduct together with Dr. Sandlöbes at RWTH Aachen and the department of Prof. Neugebauer ab initio calculations for designing new Mg – Li alloys. Ab initio calculations can accurately predict basic structural, mechanical, and functional properties using only the atomic composition as a basis.
Figure Ashby map of Y/r versus G/B of bcc Mg–Li alloys. The vertical dotted line separates the ductile and brittle regions.
In this project, fundamental physical properties (such as formation energies and elastic constants) of a set of bcc Mg–Li and Mg–Li-based compounds are calculated using density functional theory (DFT). These DFT-determined properties are in turn used to calculate engineering parameters such as (i) specific Young’s modulus (Y/r) or (ii) shear over bulk modulus ratio (G/B) differentiating between brittle and ductile behavior. These parameters are then used to identify those alloys that have optimal mechanical properties for lightweight structural applications. First, in case of the binary Mg–Li system, Ashby maps are designed containing Y/r versus G/B shows that it is not possible to increase Y/r without simultaneously increasing G/B (i.e., brittleness) by changing only the composition of a binary alloy. In an attempt to bypass such a fundamental materials-design limitation, a set of Mg–Li–X ternaries (X standing for Ca, Al, Si, Cu, Zn) based on stoichiometric Mg–Li with CsCl structure is studied.
