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INTELHYB Report Summary

Project ID: 340025
Funded under: FP7-IDEAS-ERC
Country: Germany

Mid-Term Report Summary - INTELHYB (Next generation of complex metallic materials with intelligent hybrid structures)

In a modern society, metallic materials are crucially important (e.g. energy, safety, infrastructure, transportation, health, medicine, life sciences, IT). However, so much of our technology is limited by materials performance! Contemporary examples with inherent challenges to be overcome are the design of ultrahigh specific strength materials. The present time of challenges in clean power generation and other aspects of sustainability may yet be materials science’s finest hour, when solutions emerge in the form of new materials and new processing routes: and there bulk metallic glasses with intelligent hybrid structures will surely have a prominent role. The key concept behind INTELHYB is to define new routes for creation of tailored metallic materials based on scale-bridging intelligent hybrid structures enabling property as well as function optimization. The intrinsic properties of advanced alloy systems can be altered by changing their microstructural features. We defined a highly efficient method to produce and characterize structures with systematically-designed pores embedded inside. The fabrication stage involves a combination of photolithography and deep reactive ion etching of a Si template replicated using the concept of thermoplastic forming. Pt- and Zr-based bulk metallic glasses were used as test materials. Furthermore, length-scale effects on the mechanical behavior of porous BMGs were explored.
When reducing the size of metallic glass samples, a wide range of failure modes ranging from brittle to ductile ones were observed. Simulations on the deformation behavior of nanoscaled metallic glasses reported an unusual extended strain softening and are not able to reproduce the brittle-like fracture deformation as found in experiments. Using large-scale molecular dynamics simulations we provided an atomistic understanding of the deformation mechanisms of metallic glass nanowires and differentiate the extrinsic size effects and aspect ratio contribution to plasticity. Furthermore, we developed a model for predicting the critical nanowire aspect ratio for the ductile-to-brittle transition. Then we showed that the structure of brittle nanowires can be tuned to a softer phase characterized by a defective short-range order and an excess free volume upon systematic structural rejuvenation, finally leading to enhanced tensile ductility.
Tailoring the intrinsic length-scale effects in bulk metallic glasses necessitates a systematic analyzing strategy. Although various achievements were made in the past years to structurally enhance the properties of different alloys, the influence of short-term annealing at moderate temperatures (i.e. few hundreds degrees Celsius) on the relaxation kinetics was not fully covered. INTELHYB aims for unraveling the connection between the physical, thermo/ mechanical and structural changes as a function of selected pre-annealing temperatures and time scales. The controlled formation of nanocrystals below 50 nm with homogenous distribution inside the matrix phase via thermal treatment increase the material’s resistance to strain softening by almost an order of magnitude. Our work established the design aspects of metallic glasses with enhanced mechanical properties via nanostructural modifications, while postulating a counterargument to the intrinsic property degradation accounted for long-term annealing.

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