Manage local deformation by patterning structural heterogeneity: Controlling toughness in honeycomb patterned metallic glass composites

Metallic glass is a macroscopically brittle material that can fail catastrophically without the protection mechanisms such as work hardening in most metallic materials. How to control local deformation and enhance toughness becomes one of the most challenging engineering as well as scientific problems facing materials research community. Here, using a finite element method we tested the hypothesis in a new design of the metallic glass composite by pattern the inclusions in the form of connected network boundaries in a honeycomb lattice. We show that the harder (Figs. a) and softer (Figs. b) inclusion boundaries function differently in mechanism in enhance the toughness. The hard boundary composite strengthens and toughens the composites via divide-and-conquer mechanism by containing the local shear deformation inside the cells as shown by the free volume distribution (a1) and local shear strain (a2), while the soft boundary composite toughens the composite by redistributing the local free volumes (b1) and local strains (b3), and shear bands, along the boundaries. In the former, the harder boundaries are the primary stress carrier (a2), whereas the stress in the latter is redistributed throughout the sample (b2). • We proposed a new design idea to pattern softer metallic glass regions in the form of honeycomb lattice to enhance toughness of metallic glasses. • We tested and validated the design by finite element modeling that matches the size and length scales accessible to experimenters. • We revealed that the working mechanism to achieve toughness is due to redistribution of local shears and shear bands. • Connected network pattern is an essential design criterion for inclusions such as the boundaries of the honeycomb lattice metallic glass composite. Shear band dominated strong strain localization is known for causing brittleness in metallic glasses. By pre-patterning glassy regions with different mechanical properties in the geometry of a honeycomb lattice, we show that the brittleness can be alleviated or even eradicated. The underlying mechanisms in this new design of composite with structural heterogeneity relate to the new microstructure parameters such as the width and the mechanical properties of the patterned regions. The optimal toughness can be achieved through redistributing the heterogeneous structural components such that the local shear is distributed heterogeneously during deformation. This finding points to a new design principle for toughening metallic glass composites that have been synthesized by far in ad hoc fashion by dispersing inclusions randomly.