Thermoplastic deformation and structural evolutions in nanoimprinting metallic glasses using molecular dynamics analysis

We perform simulations on nanoimprinting metallic glasses to investigate the thermoplastic deformation and structural evolutions via molecular dynamics analysis. The atomic diffusion mechanisms, including single atomic and highly collective hopping, are observed in metallic glass block. Mold filling speed is significantly affected by the initial metallic glass film thickness, and the film with the thickness approaching the width of the pattern on mold is optimal to shorten mold filling time and save materials. With the support of a modified equation of plane Poiseuille flow, we analyze the resistance of boundary condition and capillary force, which have reasonably explained the thickness effect. We then show the structural evolutions to assess the impact of the mold filling process on the short-range and the middle-range orders in metallic glasses. Lower fractions of icosahedra and icosahedra-like clusters and smaller aggregated clusters have been detected in the processed structure than in the billets, showing that the processed metallic glasses are more symmetrical and have more disorder. The results further suggest that the mold filling process has broken the original structures in metallic glasses, resulting in less icosahedra and bond networks, which lead to a better plasticity in the processed metallic glasses. (C) 2015 Elsevier B.V. All rights reserved.