The ultrastable state of metallic glasses and its role in the structural pathway of ageing

Project Information

PathAge

Grant agreement ID: 101063523

DOI

10.3030/101063523

Project closed

EC signature date 13 June 2022

Start date 1 October 2022

End date 30 September 2024

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 189 687,36

Coordinated by

BUNDESANSTALT FUER MATERIALFORSCHUNG UND -PRUEFUNG
Germany

Periodic Reporting for period 1 - PathAge (The ultrastable state of metallic glasses and its role in the structural pathway of ageing)

Reporting period: 2022-10-01 to 2024-09-30

Summary of the context and overall objectives of the project

Metallic glasses (MGs) are a class of advanced materials with a disordered atomic structure. Their unique combination of metallic strength and elasticity makes them highly promising for cutting-edge applications like micro-motors and biomedical tools. An extraordinary state of MGs, called the ultrastable state, can be achieved by specific processing techniques. It shares similarities with the ultrastable state found in molecular glass-formers, as widely used in OLED displays, involving enhanced kinetic and thermodynamic stability. To unlock the full potential of ultrastable MGs, such as their use in extreme environments, a deeper understanding of their underlying structure is crucial. The PATHAGE project aims to address this challenge by focusing on two main questions:
What are the structural characteristics of conventional and ultrastable MGs?
What mechanisms govern the structural evolution in MGs?
By answering these questions, PATHAGE will contribute significantly to the advancement of our understanding of ultrastable MGs and their potential applications.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Nano-mechanical Characterization and Structural Analysis

Nano-mechanical mapping techniques, such as high-resolution nanoindentation (HR-NI) and atomic force microscopy (AFM), were employed to investigate the mechanical properties of metallic glasses on a nanoscale level. Here, HR-NI data revealed heterogeneity length scales within the material. These findings shed light on the elastic heterogeneity of metallic glasses.
Advanced electron microscopy techniques, including 4D-STEM, were utilized to study the local atomic arrangements of both conventional and ultrastable metallic glasses. The results, currently under preparation for publication, provide valuable information about the distribution of structural motifs, their evolution during annealing, and the relationship between the ultrastable and the annealed state of metallic glasses.
Synchrotron-based investigations, including x-ray photon correlation spectroscopy (XPCS), were pursuit to delve deeper into the structural details of metallic glasses. These studies aim to uncover the mechanism of structural evolution based on underlying atomic-scale rearrangements. As a major achievement, intermittent structural dynamics signatures could be set in context to cluster-related dynamics, another indication for the existence of a topological network.

Correlating Experimental and Simulation Results

The experimental results obtained from 4D-STEM were compared with molecular dynamics (MD) simulations to gain insights into the atomic-scale processes governing the structural evolution of metallic glasses. Analyzing the distribution of local structural units aims to understand the factors influencing the stability and properties of these materials.
The combination of experimental and simulation techniques has also been employed to investigate the impact of annealing on the structural dynamics of metallic glasses as observed by XPCS. The results highlight the significant changes in the material's properties and the underlying structural transformations that are induced by annealing and that lead to the formation of an extended topological network of amorphous character.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The main scientific achievement of PathAge is the experimental validation of the existence of an amorphous, yet heterogeneous microstructure, whose extend strongly depends on the preparation and annealing state of the sample.
This microstructure, consisting of a topological network of reoccurring more-stable local motifs and surrounding regions of more-frustrated structures, evolves with thermal annealing and also seems to be connected to the ultrastable state of MGs. Evidence for this behaviour was achieved by experimental XPCS measurements conducted during isothermal annealing [Nature Communications 15 (2024) 6595] in concert with MD-simulations including a virtual XPCS-approach [Acta Materialia 267 (2024) 119730]. The findings suggest that a transformation from an overall more homogeneous structure towards the amorphous microstructure of a percolative network and more-frustrated regions occurs as a consequence of local rearrangements. The understanding of this network was substantiated further by measurements of the structural dynamics under mechanical excitation in the so-called elastic response regime, which clearly demonstrates how the percolative network is responsible for a globally elastic response followed by flow initiation at the material’s yield point, while the more-frustrated regions lead to a dynamic response that suggests that the material admits microplastic responses even at lowest stress amplitudes [publication under review]. Finally, nano-mechanical mapping of metallic glasses in the elastic response regime reveals that the elastic structure develops a stress-driven heterogeneity connected to a length scale, that is depending on the annealing state of the sample [Materials & Design 229 (2023) 111929; Scripta Materialia 255 (2025) 116380]. This serves as another measure of the underlying amorphous microstructure of metallic glasses.
The existence of such a topological, percolative network is a meaningful breakthrough as it reflects an important and distinguished extension of the state-of-the-art scientific progress made in the field. Over the recent years, the amorphous structure of metallic glasses had been described as consisting of soft spots and a surrounding matrix, but the distinct identification of an elastically stiff percolative system-spanning network had been missing. PathAge is now providing a microstructural picture and provides reasoning for experimental observations that is not provided by the existence of individual soft spots or liquid-like spots.
These insights allow for new measures in the field of metallic glass applications and as a consequence, tailoring of material's properties can be based on this enhanced understanding of the amorphous microstructure.