Mechanical, thermal, and physical properties of Mg-Ca compounds in the framework of the modified embedded-atom method.

Interatomic potentials for pure Ca and the Mg-Ca binary have been developed in the framework of the second nearest-neighbors modified embedded-atom method (MEAM). The validity and the transferability of the Ca MEAM potential was performed by calculating physical, mechanical, and thermal properties. These properties were compared to experimental data and numerical data obtained from existing Ca potentials, and a good agreement was found. In addition, the dissociation of the edge dislocation into two Shockley partials aligns with the linear elasticity solution. Furthermore, the velocity of an edge dislocation under static and dynamics loading conditions predicted in Ca using the MEAM formalism reproduces the expected behavior of an edge dislocation in fcc crystal structures. The Ca MEAM potential was then coupled to an existing Mg MEAM potential to describe the properties of the Mg-Ca alloys. Heat of formation, structural energy difference, and elastic constants were calculated for several ordered Mg-Ca compounds containing different concentrations of Ca. As expected from first-principle calculations based on DFT, Mg2Ca with the Laves phase C14 was found to be the most stable structure with the lowest heat of formation compared to compounds with other Ca concentrations (Mg3Ca, MgCa, and MgCa3). Moreover, the mechanical stability was recovered for the different tested compounds and is in agreement with first-principle data.