Metallic glasses are fascinating materials that consist of mixtures of metallic atoms that do not have long-range translational order, which are of interest as structural materials due to their high strength, hardness and wear resistance. The drawbacks of metallic glasses are low ductility and thermodynamic stability. Here, we investigate the structural parameters that control these properties by using colloidal synthesis to make nickel-boron metallic glass nanoparticles with tunable size, composition and mechanical behavior.
These nanoparticles are found to have high ductility and homogeneous deformation at room temperature. X-ray photoelectron spectroscopy and mass spectroscopy are used to determine the composition, and bonding states within the nanoparticles. In situ transmission electron microscopy compression testing reveals that nanoparticles either deform homogeneously, or through a slowly propagating slip event reminiscent of shear banding. Scanning electron microscope compression testing shows that nanoparticles of 89 to 263 nm in size show an inverse size effect, in which larger nanoparticles are more likely to exhibit homogeneous deformation, while smaller nanoparticles are more likely to exhibit shear banding. Cyclic testing reveals a Bauschinger‚Äôs effect, in which a hysteresis is observed upon unloading and re-loading. We determine that the mechanical behavior of the metallic glass nanoparticles is related to local atomic arrangements within the glass and its nanoscale size.
Phase stability at high pressure are investigated by placing nanoparticles inside of a diamond anvil cell and compressing the particles to ~10 GPa pressure. The internal structure of the nanoparticles is monitored using synchrotron X-ray diffraction. At elevated pressures, the nanoparticles gradually compress and eventually form a hexagonal close-packed crystalline phase. The particles are recovered after compression, and examined using TEM, which confirms the formation of a crystalline phase. The thermodynamics and kinetics of this phase transition are analyzed by considering strain energy, chemical potential and surface energy.

Mechanics and Phase Stability of Colloidal Nano-Metallic Glass

The Virtual Technical Meeting of the Society of Engineering Science 2020 is the first fully virtual meeting of the SES community to envision and connect during the hiatus created by Covid-19, providing a platform for the exchange of ideas, and to showcase the latest research in the field of engineering science.

[Visit the Programme](https://drive.google.com/file/d/1BoCPBzrr1IQFANuzQI8a-paXCJoOcCkB/view?usp=sharing) | [Visit the Prerecorded Video/Poster List](https://drive.google.com/file/d/1XHLeEXJxEFjCSsNScuLDfMwy1X7oy7oJ/view?usp=sharing) | [View the Session Grid](https://drive.google.com/file/d/1VeDOC-Ev5m_ymYjXnjaXSZHR3_DARiLt/view?usp=sharing)