Molecular Dynamics Simulation Of The Mechanical Behavior Of Nanotwinned Copper

Based on the theory of dislocations and molecular dynamics simulation, this study is focused on the mechanical behavior of nanotwinned copper under uniaxial tension and indentation. The deformation mechanism of twin boundaries (TBs) is the main research point because they improve both the strength and ductility of metals. Different TB orientations lead to very different deformation mechanism and different Young's modulus values. It is investigated whether TB can serve as dislocation source. In addition, the effects of voids on elastic modulus and yield stress are simulated and investigated in detail.The results indicate that perfect TBs can't serve as dislocation sources under homogeneous deformation. However, TB steps and pinning stacking faults break the coherency of TBs, which turns the TBs into potential dislocation sources. Dislocations can nucleate from these steps and propagate in the crystalline to the other side of TBs.Normal stress has no effect on TB migration. When the resolved shear stress reaches the critical value, TB will migrate along its normal direction.Simulation results also reveal that TBs can act as obstacles to dislocation motions that lead to the strengthening of nanotwinned materials. Leading partial dislocation is impinged on the TBs which causes dislocations pile up. With dislocations accumulating, the strong interactions between leading partial dislocations and TBs can break the coherency of the TBs and some step shape partial dislocations emit from these TBs. These partial dislocations can glide easily along TBs contributing primarily to the plastic strain or ductility of nanotwinned metals.Additionally, the effect of voids with different sites on elastic mechanical behavior of nanotwinned copper is also studied and analyzed thoroughly. It is found that, when the diameter of void is small (less than 4nm), as the diameter increases the material's strength reduces rapidly, but the Young's modulus decreases slowly. Simulation results reveal that when the diameter of the void is veiy small (about 1nm), the plastic deformation is dominated by the slip of stacking faults. In the whole process of plastic deformation, no dislocations can be nucleated from the edges of void.when the diameter of void is not small(more than 4nm), as the diameter increases the material's Young's modulus decreases rapidly, but the strength reduces slowly. Simulation results reveal that, at first stage of plastic deformation, dislocations can be nucleated from the edges of void.