Nanostructures in Metallic Glass
Revolution in Materials Science
Introduction to the World of Metallic Glasses
In the world of modern materials, there exists a special category of substances that combine seemingly incompatible properties - the strength of steel and the structure of glass. These unique materials, known as bulk metallic glasses (BMG), open new horizons in aerospace, medicine, and precision instrument engineering. A special place among them is occupied by the Cu47Ni8Ti34Zr11 alloy, also known as Vit101, whose amazing properties are revealed during a special type of heat treatment - liquid-state isothermal quenching.
This technology overcomes the limitations of traditional casting methods, allowing for the creation of larger and more complex parts from metallic glasses.
Amorphous Structure
Disordered atomic arrangement similar to glass
High Strength
Exceptional mechanical properties
Thermal Processing
Controlled transformation through precise heating
Key Concepts and Terminology
Metallic glasses, or amorphous metals, are materials that have a disordered atomic structure characteristic of glasses but are composed of metallic elements. Unlike conventional metals with a regular crystal lattice, atoms in metallic glasses are arranged chaotically, giving them a unique combination of high strength, elasticity, and corrosion resistance.
Isothermal quenching is a specialized heat treatment method in which molten metal is rapidly cooled to a specific temperature and then held at that temperature for controlled transformation of its structure 5 . In the case of Vit101 alloy, this process occurs directly from the liquid state, allowing bypassing crystallization and forming an amorphous or nanocrystalline structure.
A key difference of isothermal quenching from traditional methods is the replacement of diffusionless martensitic transformation with diffusion intermediate transformation, which proceeds gradually and simultaneously throughout the material cross-section . This significantly reduces internal stresses and minimizes the risk of crack formation and deformations.
Critical cooling rate (CCR) is the minimum cooling rate at which molten metal can be transformed into an amorphous state without crystallization 6 . For zirconium BMGs, this indicator is approximately 1-100 K/s, but the presence of oxygen in the alloy can increase CCR to 1.4 × 10⁴ K/s 6 .
Vit101 alloy, although having a somewhat lower glass-forming ability, demonstrates higher strength and economic efficiency compared to zirconium analogs.
Experimental Methodology: Precise Structure Control
The research team led by Lysenko undertook a systematic study of the structure formation of Vit101 alloy during liquid-state isothermal quenching. The methodology combines numerical modeling and experimental validation to establish correlations between thermal regimes and the resulting microstructure.
Experimental Procedure
Sample Preparation
Cu47Ni8Ti34Zr11 (Vit101) alloy was placed in a specially designed quenching setup.
Heating and Temperature Maintenance
The alloy was heated to liquid state with precise temperature control.
Casting into Heated Mold
The melt was poured into a preheated copper mold, whose temperature varied in different experiments 2 .
Isothermal Holding
After filling the mold, a constant temperature was maintained for a specified time to ensure isothermal solidification conditions.
Cooling
After completion of transformation, samples were air-cooled to room temperature.
Measurement Methods and Analysis
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Thermographic MeasurementsFor temperature fields
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Microstructural AnalysisFor structural components
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Kinetic CalculationsFor nucleation rates
| Component/Equipment | Purpose and Functions |
|---|---|
| Cu47Ni8Ti34Zr11 (Vit101) Alloy | Main research material, has high amorphization ability upon quenching |
| Copper Mold | Provides intensive cooling of the melt due to high thermal conductivity of copper |
| Heating Furnace | Provides heating of the alloy to liquid state and maintenance of precise temperature |
| Temperature Control System | Records and maintains mold temperature with accuracy of several degrees |
| Vacuum Chamber | Provides controlled atmosphere, preventing oxidation of the alloy at high temperatures |
| High-Speed Pyrometer | Measures temperature profiles with frequency up to 25 kHz in range 673-1473 K 6 |
Results and Analysis: From Amorphous State to Nanocrystals
Influence of Mold Temperature on Alloy Structure
The study revealed a direct relationship between the initial temperature of the casting mold and the final microstructure of the obtained ingots. Scientists established that under certain temperature conditions, it is possible to form amorphous, amorphous-crystalline, and completely crystalline states 4 .
The most significant discovery was the determination of the temperature interval 676-674 K, at which an isothermal solidification regime is established and primary nanocrystalline structures are formed 2 . Under these conditions, crystallization occurs with extremely high crystal nucleation rates (~10¹⁵-10¹⁸ m⁻³·s⁻¹) and very low growth rates (~10⁻¹³-10⁻⁸ m/s) 2 .
| Mold Temperature, K | Average Crystal Size, nm | Structure Type |
|---|---|---|
| 676-674 | 63-240 | Nanocrystalline |
| Above interval | Micrometer range | Crystalline |
| Below interval | Variable | Amorphous-crystalline |
| Parameter | Isothermal Quenching | Regular Quenching |
|---|---|---|
| Structure | Bainite/Nanocrystals | Martensite |
| Internal Stresses | Minimal | Significant |
| Risk of Cracks | Low | High |
| Applicability | High-alloy steels, BMG | Carbon steels |
Visualization of Crystal Formation Process
Crystal Size vs. Mold Temperature
Interactive chart showing relationship between processing temperature and resulting crystal size
Conclusion: Prospects and Opportunities
The study of structure formation in Cu47Ni8Ti34Zr11 alloy under conditions of liquid-state isothermal quenching opens new possibilities in controlling the microstructure of metallic materials.
Establishing precise temperature intervals that ensure the formation of nanocrystalline structures with controlled grain sizes is of significant interest for modern technologies.
The method of liquid-state isothermal quenching overcomes fundamental limitations of traditional methods for producing bulk metallic glasses, allowing the creation of larger products with complex geometry. This is especially relevant in the context of additive technologies, such as selective laser melting (PBF-LB/M), where control of thermal history is a key factor for preventing unwanted crystallization 6 .
Aerospace
Lightweight, high-strength components
Automotive
Durable, wear-resistant parts
Medical
Biocompatible implants and instruments
Further development of this direction promises revolutionary changes in the production of high-strength, wear-resistant, and corrosion-resistant materials where the combination of strength, lightness, and reliability is crucial.
References
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