Molecular dynamics study of the effect of extended ingrain defects on grain growth kinetics in nanocrystalline copper

Vladimir V Dremov,Pavel V Chirkov,Alexey V Karavaev

doi:10.1038/s41598-020-79861-3

Abstract

The paper presents results of a large-scale classical molecular dynamics study into the effect of ingrain defects on the grain growth rate of face centered cubic nanocrystalline material under thermal annealing. To do this, two types of virtual MD samples are used. The samples of the first type are constructed artificially by filling Voronoi cells with atoms arranged in fcc lattice essentially with no ingrain defects. The other samples are obtained by natural crystallization from melted material and contain numerous extended ingrain defects. These samples with a high concentration of ingrain defects imitate nanocrystalline material produced by severe plastic deformation via high pressure torsion or equal channel angular extrusion. The samples of both types are subjected to long-time zero pressure isothermal annealing at Tapprox 0.9T_m (T_m is melting temperature) which leads to grain coarsening due to recrystallization. Direct molecular dynamics simulations of the annealing of different samples show that at the same conditions recrystallization goes two times faster in the samples with a high concentration of extended ingrain defects than in the defect-free samples. That is, to increase the thermal stability of nanostructured material the technologies used for forming nanocrystalline structures should be developed so as to avoid the thermomechanical treatment regimes leading to the formation of structures with high concentration of ingrain defects.

Highlights

The paper presents results of a large-scale classical molecular dynamics study into the effect of ingrain defects on the grain growth rate of face centered cubic nanocrystalline material under thermal annealing
The samples of the second kind are aimed to imitate nanocrystalline material produced by severe plastic deformation, for example, by high pressure torsion or equal channel angular extrusion
State-of-the-art supercomputing technologies allow addressing the problem of materials design and their properties change due to processing, storage and exploitation in direct large-scale molecular dynamics simulations

Summary

Virtual nanocrystalline samples generation

Atomistic simulations of recrystallization process were carried out with submicrocrystalline samples of copper. A special procedure is applied to provide for proper sintering of grains at boundaries[16] to allow the use of periodic boundary conditions in all directions The advantage of this option is the construction of samples composed of nanocrystallines which have the required average size and are almost free of ingrain defects (see Fig. 1). Concentrations of the vacancies and interstitials reach 10−4 and 10−5 respectively just after crystallization decrease rapidly and stay nearly constant at the level ∼ 4.5 × 10−5 for vacancies and ∼ 2 × 10−6 for interstitial atoms during annealing at T ≈ 0.9 Tm. The samples prepared with the crystallization-from-melt technique are designated hereafter as M-type samples. Of randomly orientated grains as well as random spatial distribution of grain centres, i.e. similar grain size distribution at the beginning of annealing (see Fig. 3)

Results and discussion

Conclusion

Author contributions

Additional information