Research
Our research focuses on chemistry-structure-processing-property relationships in a wide range of materials and scientific phenomena. Materials of focus are metallic glasses, high entropy alloys, functional alloys, materials for additive manufacturing, and nanocrystalline metals. The scientific phenomena that we are researching are glass formation, single crystal formation, metastability, nanoscale effects, deformation mechanisms, mechanical response and nucleation and growth. To study such relationships, we use state-of-the-art materials synthesis and characterization methods, combinatorial synthesis paired with fast screening techniques, data science and artificial intelligence and nanofabrication techniques. Further, we explore novel materials processing techniques for additive manufacturing, nanomolding, and thermoplastic net-shaping.
Combinatorial Material Science
We use combinatorial strategies for materials science and discovery. One technique that we are focusing on for combinatorial synthesis is combinatorial sputtering, which allows us to synthesis large compositional regions, approximately 1000 alloys, simultaneously. To effectively characterize these compositional libraries, we have been developing high throughput characterization methods which allow fast screening for a range of properties. We have been employing combinatorial methods to identify new metallic glasses, stable nanocrystalline alloys, quasicrystal formation, biocompatible and degradable alloys, and to understand glass formation and phase selection in high-entropy alloys.
Nanofabrication
Nanofabrication is a crucial requirement to develop solutions for a broad range of problems including water de-salination, batteries, fuel cells, cellular response, antibacterial, hydrophobic, de-icing, plasmonic, photovoltaics, biosensors, catalytic, adhesion regulation, flexible electronics, storage devices and quantum materials.
Our focus is on developing Nanofabrication techniques based on molding. Such Nanomolding is highly versatile, precise, and scaleable. Typically, we use hard molds which we fill under the influence of temperature and pressure. We have shown that metallic glasses can be nanomolded based on viscous flow. For crystalline metals and ordered phases, Nanomolding is based on atomic diffusion or dislocation movements. Nanomolding leaves the metastable structure of the metallic glass unaffected and results in an equilibrium state for crystalline metals where single crystals are formed.
Processing
Materials Processing is key to realize desired atomic structure and associated properties during the formgiving process, particularly in the late-stage materials’ development process to enable commercial applications. Versatility of shapes, scalability, cost, speed, robustness, and repeatability are all to be considered and tied into the material-property relationship.
Our lab has developed several novel processing techniques for metallic glasses which utilize the supercooled liquid state to mold geometries that were previously impossible for metals. We developed and patented a thermoplastic forming (TPF) method, which allows to mold metals as if they were plastics while maintaining superb mechanical properties. TPF based blow-molding and compression molding has allowed us to precisely fabricate metallic glasses with miniature, micro, nano, and sub-nano scale features, laying the foundation for atomic imprinting.
While exploring how to apply these ideas to more diverse materials classes, we discovered nanomolding through atomic diffusion. This thermomechanical nanomolding (TMNM) allows nanomolidng of any material and has already been demonstrated with metals, alloys, ordered phases, superconductors, semiconductors, phase change materials, and quantum materials like topological insulators.
Structure Property Relationships
The holy grail of materials science is to relate the materials’ structure to properties. So-called structure-property relationships are rooted in the quantum mechanical interaction of atoms. For simple properties and materials such interactions can be calculated through ab initio methods by solving the Schroedinger equation over involved atoms. For complex materials however, other approaches are required, as the number of involved atoms is by many orders of magnitude too high for today’s computing power to be solved through ab initio calculations.
Examples of material classes encompassing complex materials are glasses and materials with microstructure. In these cases, experimental strategies are often required that isolate structural variations and can quantify its effect on properties. Of specific importance is often the effect of processing on the structure and hence properties. Developing specific strategies has allowed us to understand fracture toughness in metallic glasses, understanding flaw tolerance as part of the natural selection in biological evolution, revealed a flaw tolerance behavior in metallic glasses, identified rejuvenation strategies and revealed a mechanical glass transition.