Metallic glass nanolaminates with shape memory alloys

We model the deformation behavior of metallic amorphous Cu_64Zr_36/crystalline B2 CuZr nanolaminate systems using molecular-dynamics computer simulations. Amorphous-crystalline nanolaminates with shape memory alloys may be a material class which is combining the advantageous properties of metallic glasses with large-strain homogeneous flow at low temperatures and high stresses. We find that the deformation of the glassy and crystalline phases is a coupled process: martensitic transformation leads to shear band formation while the stress at the shear band tip induces martensitic transformation in the shape memory crystal. Moreover, the martensitic transformation changes the shear band morphology, stabilizes the shear flow and avoids a runaway instability. Finally, the critical volume fraction of the B2 layer for which the composite laminate shows a brittle-to-ductile transition is identified. The value of the critical volume fraction can be further decreased when the structure of the metallic glass is rejuvenated. Therefore, tailoring the architecture of metallic glass laminates with shape memory phases may allow the development of materials that exhibit large tensile ductility

Deformation behavior of bulk and nanostructured metallic glasses studied via molecular dynamics simulations

In this study, we characterize the mechanical properties of Cu64Zr36 nanoglasses under tensile load by means of large-scale molecular dynamics simulations and compare the deformation behavior to the case of a homogeneous bulk glass. The simulations reveal that interfaces act as precursors for the formation of multiple shear bands. In contrast, a bulk metallic glass under uniaxial tension shows inhomogeneous plastic flow confined in one dominant shear band. The results suggest that controlling the microstructure of a nanoglass can pave the way for tuning the mechanical properties of glassy materials

From nanoglasses to bulk massive glasses

Molecular dynamics simulations are presented that provide evidence for the existence of diluted interfaces in nanoglasses, which is a class of material that can be synthesized by consolidating glassy nanoparticles. By comparing simulations of a covalently bonded Ge nanoglass and a metallic CuZr nanoglass, we show that the delocalization of the excess free volume initially located within the interfaces depends on the flow strain of the material. Our results suggest that the density distribution within a nanoglass can be controlled by the initial particle size and the annealing conditions. Therefore, nanoglasses represent an alternative route for controlling the properties of glassy materials