Molecular dynamic simulations of the mechanical properties of crystalline/crystalline and crystalline/amorphous nanolayered pillars

By properly introducing interfaces and boundaries to nanomaterials, good plasticity can be obtained without sacrificing the strength. Nanolayered crystalline/crystalline (C/C) Cu/Zr and crystalline/amorphous (C/A) Cu/CuZr with and without twin boundaries (TBs) are investigated by large scale molecular dynamic simulations. By characterizing the plastic deformation on atomic scale, the simulation results show that the C/C interfaces, C/A interfaces, grain boundaries (GBs) and TBs have different effects on the deformation behaviors of nanolayered pillars. In C/C pillars, partial dislocations slip in the columnar nano-crystals of Cu layers and diffusion and motion of GBs take place in Zr layers. The dislocations entrapped within the C/C interfaces and the diffusion and motion of GBs in Zr layers lead to strain softening. TBs can effectively improve the yield stress of C/C pillars but not that of C/A pillars. The dominant deformation mechanisms in C/A pillars are the activations of the shear transformation zones (STZs) and the interplay of dislocations and STZs at the interfaces, which, in conjunction with the strain compatibility of the amorphous layers, contribute the less strain softening responses in C/A pillars.