Metallic glass, also known as an amorphous metal, is a metallic material in which the atoms do not possess the long-range, regularly repeating arrangement found in ordinary crystalline metals. Instead, the atoms are arranged in a disordered or amorphous structure.
Metallic glasses are generally produced by cooling a molten alloy very rapidly, so that the atoms do not have sufficient time to arrange themselves into a crystalline lattice.
Structure of Metallic Glass
In ordinary metals, atoms are arranged in an ordered crystal lattice. In metallic glass, there is no long-range periodic order, although short-range atomic order may still exist. This amorphous structure gives metallic glasses several unusual physical, magnetic, and mechanical properties.
Preparation of Metallic Glass
Metallic glasses are commonly prepared by rapid solidification of a suitable molten alloy. The cooling rate must be sufficiently high to prevent crystallization.
- A suitable alloy is heated until it becomes completely molten.
- The molten alloy is subjected to very rapid cooling.
- Rapid cooling prevents the atoms from attaining an ordered crystalline arrangement.
- The resulting solid material has an amorphous structure and is called metallic glass.
Common Methods of Preparation
- Single-roll melt spinning: A thin stream of molten alloy is brought into contact with a rapidly rotating cooled wheel, producing a thin metallic-glass ribbon.
- Planar-flow casting: Molten metal is rapidly cooled between a moving cooled surface and another controlled surface to produce continuous ribbons.
- Rapid quenching: Small quantities of molten alloy are cooled at extremely high rates to suppress crystallization.
Properties of Metallic Glass
- They lack long-range crystalline order.
- They generally have no conventional grain boundaries.
- They possess high strength and hardness.
- They often show good resistance to corrosion and wear.
- Some metallic glasses exhibit useful soft-magnetic properties.
- They can have relatively high elastic limits compared with many conventional metals.
- They generally have low electrical resistivity temperature coefficients compared with crystalline metals.
- They are often brittle at room temperature, although some compositions can show appreciable plasticity.
Examples
Metallic glasses are commonly based on alloys containing elements such as iron, cobalt, nickel, zirconium, titanium, copper, and aluminium. Examples include iron-based and cobalt-based amorphous alloys, as well as zirconium-based bulk metallic glasses.
Applications of Metallic Glass
- Transformer and magnetic-core materials
- Magnetic sensors and electronic components
- Corrosion-resistant coatings
- Wear-resistant engineering components
- Sports and precision equipment
- Special-purpose structural materials
Metallic Glass vs. Ordinary Crystalline Metal
| Metallic Glass | Crystalline Metal |
|---|---|
| No long-range periodic atomic arrangement | Atoms have long-range periodic arrangement |
| Generally lacks conventional grain boundaries | Usually consists of grains separated by grain boundaries |
| Produced by sufficiently rapid solidification | Normally forms through crystallization during solidification |
| Often shows high strength and hardness | Properties depend strongly on crystal structure and microstructure |
Conclusion
Metallic glass is an amorphous metallic alloy produced by suppressing crystallization, usually through rapid cooling of a molten alloy. Its combination of high strength, hardness, corrosion resistance, and useful magnetic properties makes it important in specialized engineering and electronic applications.