A molecular dynamics study of the shock-induced defect microstructure in single crystal Cu

P Wen and G Tao and CQ Pang and SQ Yuan and Q Wang, COMPUTATIONAL MATERIALS SCIENCE, 124, 304-310 (2016).

DOI: 10.1016/j.commatsci.2016.08.010

Molecular dynamics simulations of shock compression are carried out over a range of pressures (from 22 GPa to 75 GPa) to investigate the shock- induced defect microstructure in single crystal Cu. The results show that under increasing shock pressure, we can detect three distinct phases of the defect regimes for single crystal Cu: dislocations -> stacking faults -> twins. We show the evolution processes of different defect microstructures. According to the analyses of these evolution processes, the formation mechanisms of various defect microstructures are studied. When the shock pressure is less than 30 GPa, the motion of dislocations is a significant mechanism in single crystal Cu under the shock compression. The motion between various dislocations and loops widely exists on the (111) close-placed plane. The interesting dislocation loops are obtained at a relatively low pressure, and a new mechanism of nucleation and development of the dislocation loop is proposed. When the shock pressure is greater than 30 GPa, a large number of intersecting stacking faults are formed. On the (001) surface, stacking faults align along the 220 and (2) over bar 20 directions at exactly 90 degrees, and they are present roughly in the same proportion. The stacking fault spacing decreases with the increase of shock pressure, and shock-induced plasticity increases as a function of shock strength. The structure of the simulation, based on the topology, matches extremely well with that found in recent transmission electron microscopy studies of single crystal Cu recovered from laser shock experiments. At a relatively high pressure (61 GPa), we find that the stacking faults and twins exist together in single crystal Cu. It is shown that two types of stacking faults with vertical directions are the competitive mechanism. When one of them dominates, twins will be formed from this type of stacking fault. Thus, the directions of twins are randomly distributed in the initial stage. Rotation and combination of twins are significant mechanisms, and these mechanisms lead to the final formation of twins. At 75 GPa, twins elongate along 1 (2) over bar1 and (1) over bar(2) over bar(1) over bar directions on the ((1) over bar 01) surface. The configuration and direction of the twins are in agreement with experimental results. (C) 2016 Elsevier B.V. All rights reserved.

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