Related Experiment Video
Updated: Apr 1, 2026
08:55
Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
Published on: June 7, 2018
9.0K
On the correlation between microscopic structural heterogeneity and embrittlement behavior in metallic glasses
Weidong Li1, Yanfei Gao1,2, Hongbin Bei2
1Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996.
Scientific Reports
|October 6, 2015
Summary
Annealing Zr-based bulk metallic glasses (BMGs) transforms ductile materials into brittle ones by reducing structural defects. This embrittlement is linked to decreased fracture energy and can be modeled by defect density changes.
Area of Science:
- Materials Science
- Metallurgy
- Solid State Physics
Background:
- Bulk metallic glasses (BMGs) are advanced materials with unique mechanical properties.
- Understanding the relationship between microstructure and mechanical behavior in BMGs is crucial for their application.
- Annealing can significantly alter the properties of BMGs, often leading to embrittlement.
Purpose of the Study:
- To investigate the effect of annealing on the microstructure and mechanical properties of a Zr-based BMG.
- To establish a quantitative relationship between structural defects and fracture behavior.
- To develop a model explaining the ductile-to-brittle transition in annealed BMGs.
Main Methods:
- Systematic annealing of Zr-based BMG at temperatures ranging from 100 to 300 °C.
- Measurement of mechanical properties (ductility, fracture energy, elastic constants) and thermal properties (crystallization temperature, enthalpy).
- Nanoindentation pop-in tests and ultrasonic elastic constant measurements.
- Application of a stochastic defect model and development of a ductile-versus-brittle behavior (DBB) model.
Main Results:
- Annealing induced a transition from ductile to brittle behavior, with fracture energy approaching zero.
- Differential scanning calorimetry showed no significant changes in crystallization, confirming the amorphous state.
- Elastic constants showed minor variations, consistent with empirical relationships.
- Nanoindentation revealed microscopic structural heterogeneities, with defect density decreasing exponentially with annealing time/temperature.
- Defect density was found to be exponentially related to fracture energy.
Conclusions:
- Annealing Zr-based BMGs leads to embrittlement primarily due to a reduction in structural defect density.
- The developed DBB model successfully identifies structural heterogeneity and defect-crack tip interactions as origins of embrittlement.
- The findings provide a mechanistic understanding of property changes in metallic glasses under thermal treatment.
Related Concept Videos
01:24Stress-Strain Diagram - Brittle Materials
5.2K
Brittle materials, including glass, cast iron, and stone, exhibit unique characteristics. They fracture without considerable change in their elongation rate, indicating that their breaking and ultimate strength are equivalent. Such materials also show lower strain levels at the point of rupture. The failure in brittle materials predominantly results from normal stresses, as evidenced by the rupture created along a surface perpendicular to the applied load. These materials do not display...
5.2K
01:29Imperfections in Crystal Structure: Non-Stoichiometric Defects
76
Non-stoichiometric defects refer to a type of defect in the crystal structure of a compound where the ratio of its constituent elements deviates from the ideal stoichiometric ratio. There are two main types of non-stoichiometric defects: metal excess defects and metal deficiency defects.Metal excess defects occur when there is a slight surplus of metal ions than what is required by the stoichiometric ratio of the compound. For example, heating a sodium chloride crystal in sodium vapor results...
76
01:24Stress-Strain Diagram - Ductile Materials
2.6K
The stress-strain relationship in ductile materials such as structural steel or aluminium is intricate and progresses through several stages. When a specimen is loaded, it initially exhibits a linear length increase, depicted by a steep straight line on the stress-strain diagram. It indicates the material is elastically deforming and will return to its original shape once unloaded. However, when a critical stress value is reached, plastic deformation begins. This stage sees substantial...
2.6K
01:26Imperfections in Crystal Structure: Stoichiometric Point Defects
86
Schottky defects arise when some lattice points in a crystal, such as those in NaCl, remain unoccupied, creating lattice vacancies without disturbing the overall electrical neutrality of the crystal. This defect is common in ionic crystals where the positive and negative ions are similar in size, as seen in sodium chloride and cesium chloride. The presence of Schottky defects enables the crystal to conduct electricity to a small extent through an ionic mechanism. Electric fields cause nearby...
86
01:25Yield Criteria for Ductile Materials under Plane Stress
731
In designing structural elements and machine parts using ductile materials, it is crucial to ensure that these components withstand applied stresses without yielding. Yielding is initially determined through a tensile test, which evaluates the material's response to uniaxial stress. However, tensile stress is insufficient when components face biaxial or plane stress conditions This condition requires advanced criteria to predict failure.
The Maximum Shearing Stress Criterion, also known as...
The Maximum Shearing Stress Criterion, also known as...
731
01:25Imperfections in Crystal Structure: Point, Line and Plane Defects
95
A perfect crystal, in theory, has a uniform structure with the same unit cell and lattice points throughout. However, any deviation from this periodic arrangement is known as an imperfection or defect. These defects can be categorized into three types: point, line, and plane defects.Point defects occur when there is a deviation from the ideal due to missing atoms, displaced atoms, or additional atoms. These imperfections might occur due to imperfect packing during crystallization or because of...
95