Periodic Reporting for period 4 - ExtendGlass (Extending the range of the glassy state: Exploring structure and property limits in metallic glasses)
Periodo di rendicontazione: 2021-04-01 al 2023-03-31
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 ― the progress made on this much 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. There is much more work to do in this area.
Materials Characterization
We have shown that high-resolution transmission electron microscopy 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 a hitherto unrecognised crystal nucleation regime in a glass-forming system. Such analyses are useful in understanding a wide range of phenomena and in planning future research, for example to optimize glass-forming ability.