If you work with advanced materials, you’ve probably seen terms like metallic glass, amorphous metal, glassy metal, and bulk metallic glass used almost interchangeably. It’s easy to think they all mean the same thing — but they don’t.

The difference looks small, but it matters when you start making real parts. Simply put, “bulk” means the material can be made thick enough to actually use.

Metallic Glass vs. Bulk Metallic Glass

Metallic Glass vs. Bulk Metallic Glass

The Main Points

Same meaning: Amorphous metal, metallic glass, and glassy metal all describe metals without a crystalline structure.
Main distinction: Bulk metallic glass (BMG) can be made in sections thicker than about 1 mm.
Processing difference: Traditional metallic glasses need very fast cooling, while BMG alloys can stay amorphous even with slower cooling.
Why it matters: The bulk form allows real parts to be made with high strength, good elasticity, and corrosion resistance.

The Basis: Amorphous Metal - What's It?

Most everyday metals — steel, aluminum, copper — are crystalline, meaning their atoms follow a repeating pattern, a bit like bricks in a neatly stacked wall.

Amorphous metals behave differently. Their atomic structure is disordered, more like a pile of scattered bricks with no long-range pattern, even though the material is still solid.

This glass-like structure forms when a molten alloy cools so quickly that atoms don’t have time to arrange into crystals. They essentially “freeze” in a liquid-like configuration, which is why terms like metallic glass or glassy metal are used.

Explaining the Terms: A Simple Guide

Amorphous Metal vs. Metallic Glass vs. Glassy Metal

These three terms are essentially interchangeable. All describe metallic alloys that lack a crystalline structure.

Amorphous metal — the most technical and descriptive term
Metallic glass — commonly used in research and industry
Glassy metal — less common but still equivalent

In most contexts, choosing one over another is a matter of preference rather than meaning.

What Is Bulk Metallic Glass (BMG)?

This is where the terminology starts to diverge. A bulk metallic glass is still an amorphous metal, but it can be produced in much thicker sections.

Early metallic glasses could only be made as thin ribbons because they required extremely high cooling rates — sometimes around one million Kelvin per second. Only very thin material could solidify quickly enough to remain amorphous.

BMG alloys changed that. Carefully designed multi-component compositions slow down crystal formation, allowing amorphous structures to form even with much lower cooling rates. As a result, components several millimeters — or even centimeters — thick can be cast.

At a Glance: A Quick Comparison

The table below compares conventional metals, traditional metallic glasses, and BMGs.

Characteristic	Conventional Crystalline Metals	Traditional Metallic Glass	Bulk Metallic Glass (BMG)
Atomic Structure	Ordered, repeating (crystalline)	Disordered, random (amorphous)	Disordered, random (amorphous)
Required Cooling Rate	Slow (not critical)	Extremely high (~1,000,000 K/s)	Low to moderate (1 to 100 K/s)
Maximum Thickness	Virtually unlimited	< 1 millimeter	> 1 millimeter, up to centimeters
Strength	Good to high	Very high	Extremely high
Elastic Limit	Low (~0.2%)	High (~2%)	High (~2%)
Corrosion Resistance	Variable, prone to weak points	Excellent	Excellent

The Manufacturing Process: Cooling and Confusion

What really separates conventional metallic glass from BMGs is how quickly the alloy must be cooled. Traditional metallic glasses are typically produced by melt spinning, where molten alloy is rapidly solidified on a rotating copper wheel. The cooling rate is extremely high, which prevents crystal formation but limits thickness.

BMG alloys are designed differently. Multi-component compositions slow down crystal nucleation, allowing the material to remain amorphous even at much lower cooling rates. This makes it possible to cast parts several millimeters — or even centimeters — thick.

The production process of amorphous ribbon

The production process of amorphous ribbon

Why BMGs Can Be Made in Bulk

Traditional metallic glass production often uses melt spinning. Molten alloy is ejected onto a rapidly rotating copper wheel, where it solidifies in milliseconds. The cooling rate is extremely high, which prevents crystal formation but limits thickness.

BMGs rely on a different approach. Complex multi-element alloys, often with different atomic sizes, make it harder for atoms to organize into crystals — sometimes referred to as a “confusion” effect. Because crystal formation is slowed, the alloy can cool more gradually and still remain amorphous.

This slower cooling rate makes bulk casting possible.

Amorphous Alloy Strip: The Traditional Form of Metallic Glass

Amorphous alloy strips are one of the earliest forms of metallic glass. They are produced by rapid cooling, usually through melt spinning, which creates very thin ribbons.

Compared with traditional strip production, the process is shorter and uses less energy. These strips are widely used in transformer cores and other magnetic components because of their low energy loss.

Although they cannot be made thick like bulk metallic glass, amorphous strips remain important for electrical applications.

Amorphous ribbon materials manufactured by Hongwang

Amorphous ribbon materials manufactured by Hongwang

Properties of Bulk Metallic Glass

Because they lack grain boundaries, BMGs tend to show a different set of mechanical and chemical properties:

High strength and hardness
Without grain boundaries, there are fewer weak points where deformation can start.

Large elastic limit
BMGs can elastically deform much more than conventional metals before yielding.

Corrosion resistance
The uniform structure reduces localized corrosion.

Thermoplastic formability
Within a certain temperature range, BMGs soften and can be molded like plastics.

These properties make BMGs attractive across several industries. For example, a biomedical engineer designing a long-lasting implant may find zirconium-based BMGs particularly useful. These include stents or surgical tools that resist corrosion.

In consumer electronics, designers use the high strength of BMGs for luxury watch cases and for robust smartphone cases. Research groups, including those at Caltech, have demonstrated many of these applications in recent years.

Conclusion: Clarity in a Disordered World

In practice, the terminology is fairly straightforward. "Amorphous metal," "metallic glass," and "glassy metal" are typically used interchangeably to describe metals with a disordered atomic structure.

The key difference comes with "bulk metallic glass" (BMG), which refers to amorphous alloys that can be produced in much thicker sections. This becomes possible through alloy compositions that slow down crystal formation, allowing the material to remain amorphous at lower cooling rates.

In practical terms, “bulk” means the amorphous structure can be maintained in thicker sections — making real components feasible.

Frequently Asked Questions (FAQ)

Is metallic glass transparent just like regular glass?

No. The term “glass” refers to the disordered atomic structure, not optical transparency. Metallic glasses are opaque and have a metallic luster, just like conventional metals.

What is the strongest metallic glass?

Some palladium- and platinum-based metallic glasses have demonstrated exceptionally high strength and toughness, although zirconium-based BMGs are more commonly used in practice.

Why isn't bulk metallic glass used more widely?

The primary barriers include the cost of materials, limited sizes, and difficulties in production. Many of the BMGs that are produced contain elements such as zirconium, beryllium, and palladium and are thus expensive. Furthermore, though "bulk" may be a great improvement compared to thin ribbons, making parts larger than a few inches is still a struggle. Therefore, it has lower usage than steel or aluminum.

Can metallic glass be welded?

Metallic glass welding is very challenging. The concentrated heat from typical welding will cause the material to form crystals at the weld site. This would make the material lose its properties and become brittle. Specialized methods such as friction stir welding or ultrasonic welding are being researched. They join them without such crystal formation.

What is Vitreloy?

Vitreloy is the commercial trade name for a series of zirconium-based bulk metallic glasses. These were some of the very first BMGs commercialized. They were developed in research at Caltech in the last decades. For this reason, the name is often used to refer to those popular and early BMGs.

Metallic Glass vs. Bulk Metallic Glass: What’s the Difference and Why It Matters

Amorphous vs. Crystalline Materials: Structure, Trade-Offs, and When to Use Each

Why Amorphous Metals Make Sense for Low-Loss Magnetic Cores

How Amorphous Materials Form, Soften, and Eventually Crystallize

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