Materials World Network: Nanoscale studies of fundamental mechanisms of deformation in amorphous materials

Conventional metallic alloys can be shaped by forming processes. This ability to undergo 'plastic deformation' is exploited in making components, but is also important in making the materials resistant to cracking. Plastic deformation is facilitated by the crystalline structure of the metals within which planes of atoms can slide over each other mediated by defects called 'dislocations'. The dislocation mechanisms of plastic deformation have been very widely studied and are well understood. In contrast, conventional glasses (amorphous solids) do not have a crystalline structure. While glasses can flow when softened by heating, when they are stressed at room temperature they typically show brittle fracture by cracking. Yet, if cracking is avoided, glasses are strong. There is much current interest in developing glasses into materials with usable strength so that their engineering applications could be increased. A starting point is metals with glassy rather than crystalline structure ('metallic glasses'). These materials they do show some plasticity, but unfortunately their deformation under loading is not uniform. The plastic deformation is instead localised in very thin 'shear bands'. But it has gradually become clear that while deformation is concentrated in the bands, there must be substantial flow of the apparently undeformed material between them. This opens up a whole new field of study of plastic deformation of glassy materials. This project aims to develop a fundamental understanding of the mechanisms of such deformation by comparing different types of glass ranging from metallic glasses to amorphous silicon (in essence comparing the effects of metallic and covalent bonding). The research involves sensitive tests of mechanical properties using techniques such as nanoindentation and deformation of micropillars. Such probes are useful for studying deformation mechanisms and can be used over a wide range of temperature. They form the heart of the UK-based work, which is however just part of an international collaboration with partners in the USA (Johns Hopkins University, Baltimore) and Japan (Tohoku University, Sendai). Work on these other laboratories will focus on high-resolution studies of the structures of the deformed materials and on atomistic modelling based on the concept of 'shear transformation zones'. Overall complementary expertise has been assembled to elucidate the mechanisms of plasticity in the absence of crystalline structure. In this way, there is the prospect of developing glasses of whatever kind with greatly improved mechanical properties, enabling their wider exploitation as engineering materials with outstanding performance.

New Materials The proposed research is on fundamental mechanisms, so the likely benefits are in the medium-to-long term. Those benefits, however, are potentially large - in effect being to extend to glassy materials the reliability of properties, and the ability to control those properties, that are taken for granted with engineering alloys. Glasses can then become structural engineering materials in the full sense. We expect new materials that are stronger, tougher and more resistant to fatigue. It is important to emphasise that the project builds on some progress already made - for example, metallic glasses are starting to show (with special compositions and processing treatments) combinations of high strength and high toughness that are simply not matched by any conventional engineering material. However, this project is not confined to metallic glasses, but considers glassy materials more generally. Who will benefit? With a family of new materials, the benefits are likely to be distributed widely and difficult to quantify. The most obvious opportunities are for industry. In this regard, it is of interest to note that the oxide glass industry (in which, of course, the UK has a sizable stake) is currently very interested in Usable Glass Strength , see http://www.gmic.org/Strength%20In%20Glass.html In the USA, the Glass Manufacturing Industry Council (GMIC, see above site) is studying the potential impact on society of having glasses with increased strength. They conclude that improving usable glass strength is critical for a vibrant glass industry in the future and that the potential for breakthrough success is high! How will they benefit? Improved materials bring a broad benefit to individuals and institutions in lower-cost devices with improved functionality. They can provide (through their manufacture, or their usage) a competitive edge to UK industry. For likely industrial benefits, we can again look to the preliminary studies of the GMIC (based in the USA, but with an international reach) on the possibilities for stronger glass. They have, for example, held prize competitions around the question: So, what would YOU do with stronger glass? . Among Realistic Applications , the GMIC lists: structural glass, stronger solar panels, thin solar panels, skyscraper agriculture, glass roofs. And under the heading Future applications can change the way we live , the GMIC lists: aeronautics, transportation, buildings, energy storage, light pipes, food and drink containers, telecommunications. Among potential advantages, the GMIC notes that glasses can have a theoretical strength higher than steel with one third the weight, that they can be corrosion proof, with attractive & engineered appearance. The potential for industry is great, with corresponding benefits for the consumer across the range of sectors noted above as well as biomedical. The potential for better exploitation of glassy materials (of all types) in MEMS devices is particularly high. UK industry in advanced materials has much to gain, in the medium-to-long term, from the advent of fully engineered glasses with improved and controlled mechanical properties. Research and Professional Skills: Staff on the project will be trained in state-of-the-art techniques, involving structural characterization, measurement of mechanical properties and atomistic modelling of fundamental mechanisms - an unusually broad range that will equip them well. The analytical skills would be useful not only in many technical (scientific/engineering) areas, but also in finance and administration, the ability to model quantitatively and to analyse mechanisms being particularly important.