Metallic Glasses: A Revolution in Material Science

Swadhin Kumar Patel, Biswajit Kumar Swain, Ajit Behera and Soumya Sanjeeb Mohapatra

## Abstract

Metallic glasses represent one kind of advanced material, very popular in recent decades. These materials are very adaptable like plastics for their manufacturability in very complex shapes. TPF (Thermoplastic forming) based processes seem very good method to process them. These materials can compete with plastics but have metallic properties. They behave as magnetic materials with less hysteresis loss and less eddy current loss making them suitable for transformer and MEMS (Micro-Electromechanical System) applications. These materials exhibit good corrosion resistance, hardness and toughness. Based on the property and application, metallic glasses are good rivals to plastics, metals and ceramics. Chemical composition and kinetics of supercooling of these materials are the areas where young researchers can focus attention with a view to their improvement.

Keywords: metallic glass, crystalline and amorphous structure, supercooling, TPF-based processing

### 1. Introduction

In our day-to-day life, we use several types of products made from different materials. Based on the area of application, the desired properties of equipment for their production and processing can vary. According to this, material selection takes place in the way to supply the best possible outcomes compared to others. In recent decades, aluminum, steel and plastics have been the most commonly used materials. The aluminum is considered as the best choice for automobile and structural object for its low density and high specific strength, whereas, due to good strength and cost-effectiveness, steel is the most preferred material for structural applications like construction, railway industry etc. Likewise, plastics are used for various home and kitchen appliances and also for the interior design of buildings, vehicles etc. Plastics are very adaptable materials because of their easy processing, but characterized by low strength compared to metals. On the other hand, aluminum and steel lose the battle with plastics in area of their processing in order to produce very intricate shapes. Because of the high processing temperature, metal products may have more defects over plastics. In this sense, metallic glasses compete with both metals and plastics. These materials have good strength and toughness compared to plastics and can be formed in any desired intricate design compared to metals. Also they possess high corrosion and wear resistance. So, we can say that metallic glasses are the materials having the good properties of metals (like steel and aluminum) as

### Metallic Glasses

well as good adaptability like plastics. In metallic glasses, during deformation, dislocation movements occurs, shearing a localization of atoms, but in the case of crystalline materials several defects occur weakening them [1].

1.multicomponent BMG systems must consist of at least three or more elements;

According to atomic arrangement, we can categorize the existing and man-made solid materials into two main groups: crystalline and amorphous. When there is a proper ordered arrangement of atoms then we say it is a crystalline material. If there is a random arrangement of atoms, then the material is called amorphous. The atomic arrangements of crystalline and amorphous materials are shown in Figure 1. To get such randomness, the sizes of the atoms are very important. Much difference in the atomic radius of the components leads to more randomness in the atomic arrangement. Glass forming is majorly concerned with the study of crystallization of materials in order to avoid crystallization. When metallic alloys are cooled at a very fast rate, possibilities of getting an ordered arrangement are poor [5]. The glass transition temperature (Generally denoted as "Tg") characterizes amorphous/glass nature of materials. This is more easily understood in the case of a polymer. If we cool a polymer from its liquid state, initially it undergoes cooling and it gets a rubbery state and then after crossing the Tg, it becomes brittle. This kind of phenomenon occurs in amorphous metals too. In case of metallic glasses, we can say that Tg is the temperature at which material gets soft from hard upon heating or get hard upon cooling. This definition for polymers and metals looks similar but it is restricted to amorphous and semicrystalline metals only. The best way to explain the process of getting an amorphous metal or metallic glass is by supercooling the metal from its liquid state. In Figure 2 Tf is the freezing temperature. During cooling, the liquid goes beyond the freezing point and is known as supercooled metal which can have an amorphous structure [6]. In this way, we can get a metallic glass. In the absence of supercooling, the liquid has a tendency to crystallize [6]. During the formation of glass, the material should avoid the route of crystallization. Crystallization happens during the cooling of material below its liquidus temperature. The difference in Gibbs free energy between liquid and crystalline state is an important factor for the ability of a metal to crystallize or to become amorphous. Whenever there is a transformation between liquid to the solid-state of a material,

2.atomic size of the constituent elements should have a significant size

difference (greater than 12%);

Metallic Glasses: A Revolution in Material Science DOI: http://dx.doi.org/10.5772/intechopen.90165

Figure 1.

13

2. General description of metallic glasses

3.heat of mixing of the elements should be negative.

The atomic arrangement of (a) single crystal, (b) polycrystal and (c) amorphous structures.

As promising materials for different applications, metallic glasses are preferred over metals, ceramics, magnetic and some other types of existing materials due to their enhanced properties. Some of the important reasons for which we consider these glasses for specific applications are discussed in the followings.


The good adaptation of these materials for different industrial applications is a consequence of combinations of those properties. All those applications are discussed later.

The discovery of metallic glass in 1960 motivated scientists to research and manufacture this kind of materials [2]. They were first manufactured in California Institute of Technology, USA. The researchers got the non-crystalline structure in Au-Si alloys. Rapid quenching of those alloys from their liquid state was conducted by the gun technology. They formed a very thin layer of metallic glass over a cold copper substrate. The reason to take copper as the substrate is because of its good thermal conductivity. After that, people are continuously discovering various metallic glasses with different compositions of elements [2]. After 2000 AD, people are making varieties of metallic glasses and its demand is increasing for industrial applications. In the 1990s, the development of different BMGs (Bulk Metallic Glasses) based on late transition metals (LTM) started. A. Inoue et al. successfully developed the Fe–Al–Ga–P–C–B BMGs in 1995 [3]. Today the availability and costeffectiveness are the two major factors in selecting and production of such materials.

For the stabilization of a supercooled metallic liquid the three rules were proposed [4]:

well as good adaptability like plastics. In metallic glasses, during deformation, dislocation movements occurs, shearing a localization of atoms, but in the case of

1.As discussed earlier metallic glasses have no long-range of ordering like crystalline materials. It develops more homogeneity inside the material because defects like point defects, dislocations and stacking faults are absent.

2.These materials possess very high strength in the elastic region. It can be declared as a good yielding strength of the material which is higher than steel.

3.Because of the good homogeneity of atoms in metallic glasses, very good corrosion resistance is achieved along with good wear resistance.

5.These materials have good luster and mirror effects but they are opaque.

6.The metallic glasses are very hard materials and their fracture resistance is

7.Because of the metallic atoms, these glasses possess significant magnetic effects. It helps to easily magnetize or demagnetize these materials. Metallic glasses with soft magnetism have very small hysteresis loop. Due to the narrow

8.Because of the amorphous structure of metallic glasses, their electrical

consequence of combinations of those properties. All those applications are

resistivity is higher resulting in less eddy current loss during its application.

The good adaptation of these materials for different industrial applications is a

The discovery of metallic glass in 1960 motivated scientists to research and manufacture this kind of materials [2]. They were first manufactured in California Institute of Technology, USA. The researchers got the non-crystalline structure in Au-Si alloys. Rapid quenching of those alloys from their liquid state was conducted by the gun technology. They formed a very thin layer of metallic glass over a cold copper substrate. The reason to take copper as the substrate is because of its good thermal conductivity. After that, people are continuously discovering various metallic glasses with different compositions of elements [2]. After 2000 AD, people are making varieties of metallic glasses and its demand is increasing for industrial applications. In the 1990s, the development of different BMGs (Bulk Metallic Glasses) based on late transition metals (LTM) started. A. Inoue et al. successfully developed the Fe–Al–Ga–P–C–B BMGs in 1995 [3]. Today the availability and costeffectiveness are the two major factors in selecting and production of such materials. For the stabilization of a supercooled metallic liquid the three rules were

hysteresis, in these glasses hysteresis loss is minimized.

4.Ordinary silica glasses are brittle in nature unlike the metallic glasses which are

As promising materials for different applications, metallic glasses are preferred over metals, ceramics, magnetic and some other types of existing materials due to their enhanced properties. Some of the important reasons for which we consider

crystalline materials several defects occur weakening them [1].

very tough materials.

Metallic Glasses

discussed later.

proposed [4]:

12

much better compared to ceramics.

these glasses for specific applications are discussed in the followings.

