The fracture toughness of glassy materials remains poorly understood. In large part, this is due to the disordered, intrinsically non-equilibrium nature of the glass structure, which challenges its theoretical description and experimental determination. We show that the notch fracture toughness of metallic glasses exhibits an abrupt toughening transition as a function of a well-controlled fictive temperature (Tf), which characterizes the average glass structure. The ordinary temperature, which has been previously associated with a ductile-to-brittle transition, is shown to play a secondary role. The observed transition is interpreted to result from a competition between the Tf-dependent plastic relaxation rate and an applied strain rate. Consequently, a similar toughening transition as a function of strain rate is predicted and demonstrated experimentally. The observed mechanical toughening transition bears strong similarities to the ordinary glass transition and explains the previously reported large scatter in fracture toughness data and ductile-to-brittle transitions.

No abstract

A combination of lithography and thermoplastic forming allows us to fabricate honeycombs from bulk metallic glass (BMG) precisely and to manipulate its structure selectively. Characteristics of the honeycomb such as the ligament length, thickness, and radius of curvature at the joints of the cells are varied to determine how changes in these characteristics affect properties under uniaxial in‐plane compression testing. It is found that the deformation behavior of BMG honeycombs can be controlled through microstructural design, from brittle to ductile, by changing the length to thickness ratio of the ligaments. The ability to absorb energy of BMG honeycombs exceeds honeycombs of most other materials due to the utilization of a size effect, which result in plasticity. Besides the usage for BMG honeycombs, the technique provides a general method to effectively characterize complex microstructural architectures and tailoring these architectures to the specifications of the material used.

No abstract

Nanoimprinting by thermoplastic forming has attracted significant attention due to its promise of low-cost fabrication of functionalized surfaces and nanostructured devices, and metallic glasses have been identified as a material class ideally suited for nanoimprinting. In particular, their featureless atomic structure suggests that there may not be an intrinsic size limit to the material's ability to replicate a mould. Here we demonstrate atomic-scale imprinting into a platinum-based metallic glass alloy under ambient conditions using atomic step edges of a strontium titanate single crystal as a mould. The moulded metallic glass replicates the 'atomic smoothness' of the strontium titanate, with identical roughness to the one measured on the mould even after multiple usages and with replicas exhibiting an exceptional long-term stability of years. By providing a practical, reusable, and potentially high-throughput approach for atomic imprinting, our findings may open novel applications in surface functionalization through topographical structuring.

No abstract

3D Metallic glass structures (3DMGs) are fabricated through thermoplastic forming (TPF)-based patterning of MG sheets combined with a parallel joining technique. To demonstrate this capability and benchmark 3DMGs, we have fabricated honeycomb-like MG architectures covering a wide range of relative densities. 3DMGs exhibit high elasticity of up to 40% loading strain, high elastic energy storability, and high energy absorption which is superior compared to those made from other materials such as conventional metals and ceramics, based on our theoretical analysis. The combination of MG properties and introduced versatile fabrication method suggest the possibility of developing a wide range of 3DMGs with excellent performance for specific applications.

A method is introduced to determine notch toughness of bulk metallic glasses (BMGs). Through thermoplastic replication of Si molds, unprece-10 dented control in fabricating BMG toughness samples can be achieved and influences such as cooling rate, thermal history, residual stress, sample geometry, and notch precision are drastically reduced. For the 20 Zr 44 Ti 11 Cu 10 Ni 10 Be 25 BMG samples, we measured a notch toughness of 109 ± 3 MPa ffiffiffi ffi m p . Such a much smaller scatter than the previously reported suggests reliable properties of BMGs when thermoplastically formed.