| The strength of nano-layered materials is dictated by dislocation confinement at interfaces, when an external stress is applied. In materials composed of nano-layered duplex structures, several factors influence the maximum value of the externally-applied stress before dislocations can move across the interface, and thus slip confinement is lost. The strengthening effect is a result of elastic modulus mismatch across the interface (the Koehler barrier), lattice resistance mismatch influencing the core structure (the gamma surface effect), and any coherency strains.; Recently, it has been experimentally shown that nano-twinned copper can be produced by pulsed electro-plating, and that the strength is several GPa without significant loss of electrical conductivity.; The objective of our research is to use large-scale Molecular Dynamics modelling methods to study the mechanisms of dislocation motion in multi-layer nano-structure and the interactions of dislocation with interfaces and twin boundaries. Those methods used the Embedded Atom Method for the calculation of potentials of Cu, Ni.; We present here studies of dislocation motion in Cu/Ni nano-layers utilizing Molecular Dynamics (MD) simulations, where we observed that the interfaces act as barriers for dislocation transmission, which accelerate or decelerate the motion of its partials.; We present another study of the mechanism of twin boundary migration (TBM) in copper crystals with a nano-twinned structure. We show that the mechanism of twin boundary migration is a consequence of the nucleation and motion of Schockley partial dislocations across the twin boundary.; We also studied the size effects on the deformation of nano-twinned copper. The deformation behaviors of nano-twinned Cu with different twin thickness are compared under several loading methods. The stacking fault density and the number of nucleated dislocations are compared for different size lamellae of twin structures. The present simulations reveal the origins of strengthening caused by nano-twins as the restriction of dissociated dislocation loop motion in narrow channels. A Critical twin thickness for the maximum strength in twinned copper is found to be around 4 nm.; After the introduction of the background, we presents a literature review on the theory of Molecular Dynamics Modelling and the applications of MD on the Nano-materials. The research progress and results will be discussed next and followed by a Conclusion and Summary. |
