Metallic Glasses – Types, Production, Properties, and Application

There are many new engineering materials like Metallic Glasses, Nanomaterial, Shape memory alloys, and biomaterials. In this lecture, we are going to learn about the Metallic glasses and then the other materials will be discussed in the next lectures.

Introduction

With the advent of Material science and Engineering, so many new Engineering materials have been discovered. The newly discovered engineering materials find major applications in industries. In general, the materials are classified as metals and alloys, ceramics, glass, glass ceramics, composites, polymers, and semiconductors.

To design new engineering materials with the required properties for specific applications, low cost, and safety factor consideration, a sound knowledge of the structure, properties, processing, and composition is required.

Metallic Glasses

Metallic Glasses are newly developed engineering materials. Metallic glasses share the properties of both metals and alloys.

Most metals and alloys are crystalline, i.e., their atoms are arranged in a regular pattern that extends over a long distance. In contrast, glass is an amorphous (non-crystalline), brittle, and transparent solid.

Thus, metallic glasses are metal alloys that are amorphous. That, they do not have a long-range atomic order. The major advantages of such glasses are they are generally homogeneous in composition and offer strong and superior corrosion resistance.

To have this peculiar property, metallic glasses are to be cooling s molten metal rapidly at a rate of 2 \times 10^{60} Cs^{-1}. During this process of solidification, the atoms do not have enough time or energy to rearrange for crystal nucleation. Thus, the liquid upon reaching the glass transition temperature Tg solidifies as a metallic glass. A gain, upon heating metallic glasses shows a reversible glass-liquid transition at Tg.

Also Read: Thermal Conductivity

Types of Metallic Glasses

Metallic glasses are two types based on their base materials used for preparation.

1. Metal-Metal Glasses
2. Metal-Metalloid Glasses

1. Metal-Metal Glasses

• Examples: Ni – Nb, Mg – Zn, and Cu – Zr

2. Metal-Metalloid Glasses

• Transition metals like Fe, Co, and Ni, and metalloids like B, Si, C, and P are used.

• Examples: Fe₆₇ Co₁₈ B₁₄ Si, Fe₄₀ Ni₃₈ Mo₄ B₁₈, Fe₇₈ B₁₃ Si₉ and Co₆₆ Fe₄ Ni, B₁₄, Si₁₅, etc.

Also Read: Miller Indices

Preparation for Metallic Glasses

Various rapid cooling techniques such as spraying, spinning, and laser deposition are used for the production of metallic glasses.

1. Melt-Spinning Process Technique

• The melt-spinning process technique involved in the preparation of metallic glass is illustrated in the figure below.

• In this technique, there is a spinning disc made of copper. In order to prepare a metallic glass of a particular type, a suitable combination of metal-metal or metal-metalloid alloy in its stoichiometric ratio is taken in a refractory tube having a fine nozzle as its bottom. The nozzle side of the tube is placed just over the spinning disc.

• An induction heater attached to the refractory tube melts the alloy. This melt is kept above its melting point till it gets transformed into a homogeneous mixture. An inert gas such as helium is made to flow through the tube containing the homogenous mixture. As a result, the melt gets ejected through the nozzle. The ejected melt is cooled at a faster rate with the help of the spinning cooled copper disc. The ejection rate can be increased by increasing the pressure of the inert gas. Thus a glassy alloy ribbon starts getting formed over the spinning disc.

• The thickness of the glassy ribbon may be varied by increasing or decreasing the speed of the spinning disc.

2. Twin Roller System

• In the Twin roller system technique, a molten alloy is passed through two rollers rotating in opposite directions.

3. Melt Extraction System

• In the Melt extraction system technique a fast-moving roller sweeps off molten droplets into a strip from a solid rod.

Also Read: CRYSTAL SYSTEMS AND BRAVAIS LATTICES

Properties of Metallic Glasses

1. The strength of metallic glasses is very high (nearly twice that of stainless steel) but they are lighter in weight.
2. They are ductile, malleable, brittle, and opaque. The hardness is very high.
3. The toughness is very high, i.e., the fracture resistance is very high (more than in ceramics).
4. They have high elasticity, i.e., the yield strength is high.
5. They have high corrosion resistance.
6. They do not contain any crystalline defects like point defects, dislocation, stacking faults, etc.
7. They are soft magnetic materials. As a result, easy magnetization and demagnetization are possible.
8. Magnetically soft metallic glasses have a very narrow hysteresis loop. Thus, they have very low hysteresis energy losses.
9. They have high electrical resistivity which leads to a low eddy current loss.

The last two properties of metallic glasses make it possible for them to be used as a transformer core.

Also Read: Josephson Effect

Application of Metallic Glasses

• Metallic glasses are used as transformer core material in high-power transformers.

• Because of their high electrical resistivity and nearly zero temperature coefficient of resistance, these materials are used in making cryo-thermometers, magnetoresistance sensors, and computer memories.

• As the magnetic properties of the metallic glasses are not affected by irradiation they are used in making containers for nuclear waste disposal.

• These materials are used in the preparation of magnets for fusion reactors and magnets for levitated trains etc.

• Metallic Glasses can also be used for making watch cases to replace Ni and other metals which can cause allergic reactions.

• The excellent corrosion resistance property makes these materials ideal for cutting and making surgical instruments. In addition, they can be used as a prosthetic material for implantation in the human body.

• In the future, the usage of metallic glasses in the electronics field can yield stronger, lighter, and more easily molded casting for personal electronics products.

• Metallic glasses are used in tap recorders as heads, in the manufacture of springs and standard resistance.

Frequently Asked Questions (FAQs)

Also Read

• Engineering Materials | Classification Of Engineering Materials
• Superconductivity | Properties of superconductivity |Types of superconductors | Application of superconductivity