Molecular Dynamics Simulation of Defect Substructure Evolution and Mechanisms of Plastic Deformation in Aluminium Nanocrystals

YG Gordienko, METALLOFIZIKA I NOVEISHIE TEKHNOLOGII, 33, 1217-1247 (2011).

The change of plastic deformation mode is qualitatively investigated by molecular dynamics simulation in Al nanocrystals with orientations < 011 > 011 and < 010 >010 under severe plastic strain: from homogeneous (laminar) mode (based on easy dislocation glide) to heterogeneous localized (hydrodynamic) mode (based on correlated displacement of groups of atom vacancy or highly excited states). These results are complemented by quantitative analysis of generalized parameters (temperature, pair-interaction energy, and pressure) and compared with the results for other f.c.c. metals (Al, Cu, Ag, Au, Ni, Pt, and Pd). Using the new technology of high-performance computation on the base of Service Grid and Desktop Grid infrastructures, the massive computer simulations of plastic-deformation processes are carried out for the very high number of Al nanocrystals. Statistical analysis (as well as moment analysis and bootstrapping analysis) of the defect-density distribution over an ensemble of all nanocrystals for the certain strain levels shows that such a change of plastic-deformation mode is accompanied with the change of defect-density distribution type over an ensemble of nanocrystals. For stacking faults, the ensemble distribution is changed from normal distribution to Weibull one (10% < epsilon < 20%) and then to Gumbel distribution (epsilon > 20%); for point defects and their aggregates, normal distribution is changed to Weibull one (epsilon > 20%). This evidences that some bound local zones (namely, chain links according to the 'chain with a weak link' model) of correlated (hydrodynamic) plastic flow appear in a nanocrystal, which manifests itself as collective displacements of point defects and their, aggregates in the 'weak link' with power-law (scale-invariant or fractal) basic distribution of defects density over links of the chain.

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