Nanoengineering metallic glasses through chemical and structural heterogeneities – Super-Glasses

Wider research context
The design of high-performance materials requires combining often mutually exclusive properties, such as high yield strength and ductility. Metallic Glasses (MGs) with amorphous structure have high strength, but usually poor ductility with catastrophic failure due to the formation of thin (~10 nm) shear bands (SBs), hindering their application as structural materials. Introducing local heterogeneities at the atomic level, by the addition of non-metallic elements and by controlling the structural state, represents an effective way to improve their mechanical properties promoting a more homogeneous deformation. Nevertheless, the complex interplay between local chemical heterogeneities (such as the addition of covalent elements) or the free volume limits a physical understanding. Therefore, to date the control of mechanical properties using SB nanoengineering is often limited to a trial-error approach.

Objectives
In this context, this project aims to provide guidelines to produce strong and ductile MGs through a systematic novel nanoengineering approach, where chemistry, oxygen alloying and structure are controlled independently. Multi-length scale characterization techniques from the atomic up to the mm, paired with scale-bridging modelling are envisioned.

Methods
The project will rely on the synthesis of thin film MGs, offering the possibility to test a wide compositional range and implement a tailored nanoscale design involving a deep control of local heterogeneities with the addition of a defined amount of oxygen and the precise tuning of the free volume content through relaxation. A systematic synthesis of MGs combined with multiscale modelling and experiments will lead to design strategies. These will be scaled up to produce bulk MGs with optimized mechanical behavior.

Innovation
The project will combine for the first time multiscale experimental and numerical approaches spanning from the atomic to the mm scale. Thin film MG systems enable to tune structure, chemistry and O content in a more systematic way, while a controlled free-volume reduction will make them ideal model system for the development of bulk counterparts with improved properties.

Primary researchers involved
The joint French-Austrian team merges two recognized institutions with expertise in different fields of materials science and their deep knowledge of MGs and thin films, the Laboratoire des Sciences des Procédés et des Matériaux (LSPM) - CNRS and the Erich Schmid Institute of Materials Science (ESI) – ÖAW. Their complementary expertise includes ab initio molecular dynamics simulations and machine learning force fields coupled with VASP, MD with LAMMPS (coordinated by Dr. Salman, LSPM), synthesis of thin films, in situ SEM micromechanics, opto-acoustics (coordinated by Dr. Ghidelli, LSPM) and 4D STEM, in situ TEM mechanical characterization, advanced bulk and thin film synthesis routes (coordinated by Dr. Gammer, ESI).