Molecular dynamics and DFT simulations on the effect of impurities and metallic dopants on the strength of Cu grain boundaries.

Non-metallic impurities introduced in metals during deposition along with metallic dopants are expected to affect the properties of grain boundaries (GBs) and, thus, can be detrimental to the performance of the material [1]. However, the exact effects that these elements can have on the properties of the GBs are not yet fully understood. Moreover, simulations of such systems using quantum mechanical approaches are constrained to models with less than 1000 atoms.

To enable large-scale simulations of polycrystalline Cu including millions of atoms, we tested the applicability and accuracy of a range of interatomic potentials (IPs). Different types of potentials were examined to determine the effects of impurities and dopants on the strength of GBs. The results were compared with our DFT calculations to determine the accuracy of the examined potentials. The tested Bond Order (BOP) and Modified Embedded Atom Method (MEAM) potentials were found to accurately reproduce the relaxation effects and segregation energies of metallic dopants, namely Al, Ti, Mg and Fe. All metallic dopants were found to segregate in the center of symmetry of the Sigma5 GBs. All the examined non-metallic impurities were found to segregate as substitutional atoms at the same position where the formation energy of a mono vacancy was the lowest. The reason for such a preference was attributed to the ability of impurities to attract negative charges in these sites. Also, the presence of impurities like H was found to reduce the work of separation of the examined GBs. The presence of Ti was found to increase the work of separation and the yield strength of the crystal. Also, Al was found to reduce the relaxation effects introduced due to the presence of H. These results indicate that the doping of Cu with Al or Ti could potentially reduce the degradation effects due to hydrogen embrittlement.

References

[1] Huang, Z. et al. 2019. Acta Materialia, 166, pp.113-125.