The project focused on the following topics:
Material Processing
We have developed new compositions of metallic glasses. Our novel aluminium-based glassy alloys are precursors to nanoscale partially and fully crystallized materials that show exceptional ratios of strength to density and excellent thermal stability. Our development of iron-based high-entropy metallic glasses has been fruitful in extending the composition range of glass formation, and in obtaining very stable nanoscale structures that show ultra-high hardness without any obvious embrittlement.
We have demonstrated that constrained uniaxial compression gives extreme rejuvenation of metallic glasses ― this progress exceeds our expectations at the start of the project: see ‘Progress beyond the state of the art’, below.
A key idea underlying the project was that temperature cycling (mostly from room temperature down to liquid-nitrogen temperature, 77 K) would change the structures of metallic glasses. This idea has been amply verified by subsequent work. The effects of cryothermal cycling on metallic glasses have now been explored much further – and it is clear that remarkable improvements in properties (especially in mechanical properties such as toughness) can be achieved.
We have shown that electrical Joule heating can achieve ultrafast heat treatments and thermal cycling of metallic glasses. Heating rates of over 100,000 K/s can be reached, and thousands of thermal cycles can be performed. The base temperature is 77 K (liquid-nitrogen bath), and heating can be up to the melting point of the metallic sample.
We have shown that ultrafast heating is useful to obtain glass/crystal nanocomposites with some remarkable properties, such a high strength maintained to high temperature. Our results open up possibilities for further alloy development.
Materials Characterization
We have shown that high-resolution transmission electron microscopy can be used to detect nanoscale phase separation and voiding, and to obtain quantitative information on the degree of relaxation/rejuvenation of metallic glasses.
Modelling and Atomistic Simulation
We have used atomistic simulation to detect new ‘atomic rattling’ ultrafast relaxation processes, relevant for the onset of plastic flow.
We have shown that classical nucleation theory can account for an unrecognised crystal nucleation regime in a glass-forming system. This is needed to understand a wide range of phenomena and in planning future research, for example to optimize glass-forming ability.
Magnetic materials
In the final phase of the project, we explored the prospects for obtaining ‘tetrataenite’ in a metallic-glass-forming alloy. Tetrataenite is an iron-nickel phase that is potentially a good permanent-magnet material. As it does not contain rare-earths, it has attracted much interest. It is found in some meteorites, but no way has so far been found to manufacture it at scale on earth. A possible synthesis route (simple casting) had been reported in the literature. Our aim was to build on that work by developing better optimized compositions and processing. After much detailed investigation, we concluded that the interpretation of the results in the published work was wrong. Although disappointing, this has helped to clarify research in this area and to suggest directions for future research.
Overview of exploitation and dissemination
There is as yet no commercial exploitation of the results. But links have been made (small-scale ongoing research and consulting) in two areas: (i) soft-magnetic iron-based metal glasses for transformers cores and device applications; (ii) precious-metal-based bulk metallic glasses for jewellery. In area (i), the interest is in making metallic glasses less brittle, especially after the heating treatments necessary to optimize the magnetic properties. In area (ii), the interest is in developing hallmark-standard alloys for jewellery (including watches) that are scratch-resistant and tarnish-resistant.
So far the project researchers (other than the PI himself) appear as co-authors on a total of 36 papers in print in international scientific journals. The researchers have also brought prominence to the project through face-to-face presentations at international conferences (an average of 3 per year, except in the depth of the COVID lockdown (when there were roughly 2 on-line meetings per year).
