Rheological behavior during thermoplastic deformation of metallic glasses: A molecular dynamic simulation

Nanoimprint is a low-cost and effective method to manufacture nanostructures for metallic glasses with a precision replication of the mould shape and control of size. However, the atomic structure of the materials changes during the processing, which affects the practical application and the performance of the nanostructures. This crucial issue has not been addressed as thoroughly as it deserves. Here, we investigate the rheological behaviors of metallic glasses under the deformation with different temperatures and strain rates via molecular dynamic simulation. We find an abnormal rheological mode change in the non-Newtonian region, which is attributed to the evolution of short- and medium-range ordered structures. Mechanical deformation leads to the destruction and regeneration of atomic short-range ordered structures at all strain rate ranges. Their total amount and distribution remain at a similar level when the strain rate is low. When the strain rate exceeds a critical value, the deformation accelerates the relaxation by shortening the β-relaxation, resulting in the decrease of the total amount of short-range ordered structure and reorganization in the medium-range ordered structure. Furthermore, the results show a significant inheritability from the sample during deformation to the cooled-down sample, demonstrating the influence of deformation history on the properties of materials manufactured with the nanoimprint. The deformation during the nanoimprinting could reduce the ultimate strength and increase the plasticity of the materials, which provides a potential method to precisely turn the properties of metallic glasses by controlling the rheological process in the nanoimprint possessing.