Nanoscale deformation of crystalline metals: Experiments and simulations

In the present work, we performed experiments and molecular dynamic simulations to study the atomic physical process and deformation mechanism involved in nanoscale deformation of crystalline metals. By contact deforming bulk metals using hard molds with different cavity sizes at various temperatures and different stress levels, the flow of metals (e.g., Au and Ag) into nanocavities is quantified by the aspect ratio of molded micro-/nanorods, based on which the dependence of deformability on cavity size, temperature and stress is revealed. It is found that the critical forming pressure is determined by the entering barrier. Once the entering barrier can be overcome, quantified by the aspect ratio of metal nanorods, the molding efficiency increases with the cavity size decreasing. Moreover, three deformation modes are uncovered in the nanoscale plastic flow of metals and directly related with the atomic physical processes, i.e. atomic diffusion, dislocation nucleation, multiplication and movement. In the dislocation dominated temperature regime, a transition of deformation mode from burst growth to continuous growth is observed as the cavity size increases. When the mold cavity size is very small (100-101 nm), the metal atoms flowing in a mold cavity will arrange amorphously even at low temperature, which usually only occurs at high temperature for large cavity sizes. Therefore, reducing the size shows the same effect as increasing the temperature, making nanomolding easier.