Atomistic modeling of the effect of calcium on the yield surface of nanopolycrystalline magnesium-based alloys

•The mechanical behavior of Mg–Ca nanopolycrystal is discussed.•Grain boundaries are the favorable locations for embrittlement of Ca in Mg alloys.

The change of mechanical properties resulting from the addition of Ca alloying elements in nanopolycrystalline Mg-based alloys was investigated using molecular dynamics in the framework of the modified embedded-atom method. Using an energetic approach, it was demonstrated that grain boundaries and their vicinity are the favorable locations for substitutional Ca atoms in nanopolycrystalline Mg with average grain diameter in the order of 12 nm. Based on the McLean theory, a concentration around 8 at% of Mg can be substituted by Ca atoms at the grain boundaries. Thus, by increasing the concentration of substitutional Ca atoms from 1 at% to 5 at% in a nanopolycrystalline Mg sample, we demonstrated that the addition of Ca in Mg-based alloys leads to a systematical decrease of the yield surface. Moreover, a microstructural analysis was performed to identify the relation between the deformation mechanisms and the change in yield surface revealed by the addition of substitutional Ca atoms. It was found that the addition of substitutional Ca leads to (i) a decrease of the activity of 〈a〉 dislocations, (ii) an increase of the activity of non-basal dislocations, and (iii) an enhancement of the intergranular fracture.

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