Diffusive molecular dynamics and its application to nanoindentation and sintering

Abstract

The interplay between diffusional and displacive atomic movements is a key to understanding deformation mechanisms and microstructure evolution in solids. The ability to handle the diffusional time scale and the structural complexity in these problems poses a general challenge to atomistic modeling. We present here a new approach, called Diffusive Molecular Dynamics (DMD), which can capture diffusional time scale while maintaining atomic resolution, by coarse-graining over atomic vibrations and evolving a smooth site-probability representation. The model is applied to nanoindentation and sintering, where intimate coupling between diffusional creep, displacive dislocation nucleation and grain rotation are observed.

Finding activation pathway of coupled displacive-diffusional defect processes in atomistics: Dislocation climb in fcc copper

“…Due to omission of the noise term in the master equation 8 , kinetics in DMD is only downhill and therefore, it cannot capture uphill phenomena in the mass-action space. Hence, to overcome the critical activation energy corresponding to the nucleation of a loop on a partial, a "3-vacancy roughness" was created on a randomly chosen partial (here δB) by reassigning c i = 0.001 to three sites in a row at the end of the extra half-plane {220} as shown in the inset of Fig.…”

“…Diffusive Molecular Dynamics DMD method is described in Ref. 8 . Here, it may suffice to say that compared to 6N variables in MD, the atomic positions and the momenta {x i , p i }, for i = 1 .…”

“…2(a) and (b), and the dissociation width was found to be 1.82 nm, the cores being located by means of coordination number plot. This configuration was subsequently taken to 1200 K using equilibrium lattice parameter and equilibrium {α i } for copper at this temperature 8 and was subjected to a constant 0.5% uniaxial compressive strain (∼ 950 MPa, volume averaged virial in Eq. 4) in u x direction.…”

Adaptive-boost molecular dynamics simulation of carbon diffusion in iron

“…Such a bootstrapped {∆V } database not only allows one to visualize the physics of diffusion, but would also accelerate subsequent simulations in the following way. For instance, when we simulate more complex thermomechanical processes where thousands of diffusional hops need to happen for the microstructure to evolve significantly 27 , one could first try to match the local atomic environment with those stored in the database. If a highly matching environment is found (after considering translational and rotational transforms), one could use the stored ∆V form (probably somewhat scaled in amplitude and arguments) as the initial boost potential, without the bootstraping from zero.…”

Deformation-Diffusion Coupled Analysis of Long-Term Hydrogen Diffusion in Nanofilms

“…However, these two computational methods are limited to relatively small material samples and to time windows of microseconds at best. Considerable efforts have been devoted to accelerating MD and MC methods, such as accelerated MD [5,6] and diffusive MD [7]. However, no computationallytractable atomistically-based models appear to be available to study deformation-diffusion coupled problems with the vast disparity of length and time scales described above.…”