Preface

The term "metallic glasses" is widely used to denote the amorphous alloys obtained by rapid quenching techniques. These materials, characterized by short range atom ordering, have found application in a variety of modern industries due to their favorable magnetic, electrical, mechanical, and anti-corrosion properties.

Kinetic and thermodynamic metastability is one of the main characteristics of metallic glasses. Inevitably, these materials tend to transform to more stable forms by crystallization, under conditions of high temperature or pressure, or during prolonged application at moderate temperatures. Their thermal stability is mainly determined by their chemical composition, while the functional properties are determined by both the chemical composition and microstructure of the material.

Thermally induced microstructural transformations could result in deterioration or improvement of the functional properties, as a consequence of the formation of hybrid amorphous/nanocrystalline structure with appropriate crystalline volume fraction and diameter of the formed crystals. Accordingly, functional properties of metallic glasses as well as their thermal stability, mechanism, and kinetics of microstructural transformations, represent topics of considerable interest for the practical application of metallic glasses.

> **Dragica M. Minić and Milica M. Vasić** University of Belgrade, Faculty of Physical Chemistry, Serbia

**1**

metals;

least 12%;

**Chapter 1**

Glasses

**1. Introduction**

Introductory Chapter: Metallic

Fast-growing technological development imposes a need for new functional materials with improved physical and mechanical properties. Since their first synthesis in 1960 [1], amorphous alloys, also known as metallic glasses, have been a focus of numerous investigations due to their advanced mechanical, electrical, magnetic, and anti-corrosion properties, related to their isotropic structure and

Generally speaking, metallic glasses are multi-component systems involving different metals (MI-MII) or metal and non-metal, i.e., metalloid (M-NM) components [7–9]. For the MI-MII systems, the metals belong to the groups of transition, rare-earth or alkaline metals, or are uranium, neptunium, or plutonium [2, 10, 11]. The M-NM systems can be represented by the general formula M75–85NM15–25 (at.%), where M is one or more metal elements, usually the transition or noble one, and NM is one or more metalloid or non-metal elements, most commonly B, Si, Ge, C, or P. The metallic glasses are solid materials without structural translational periodicity, characteristic for a crystalline structure. From the atomic aspect, the structure of metallic glasses is analogous to the structure of liquids, characterized by macroscopic isotropy, nonexistence of the long-range atomic ordering, but existence of a short-range ordering at the atomic level. The short-range ordering of the atoms means that each atom is surrounded by the same atoms positioned at similar distances, where the lines drawn between the atom centers form similar angles, as a consequence of chemical bonds keeping the atoms together in solid state. Variation in inter-atomic distances and angles means the variation in the strength of chemical bonds, causing the softening of material in defined temperature interval instead of

The ability of a liquid alloy to transform into the metallic glass is called the glass-forming ability (GFA). The GFA is determined by structural, thermodynamic, and kinetic parameters characterizing the system, i.e., chemical composition, geometrical arrangement of atoms, bonding and atomic size effects, cooling rate, and crystallization kinetics [5]. So far, many empirical criteria were proposed with the aim of predicting and explaining the GFA [5, 13–15]. The empirical criteria for easier

1. alloy is multi-component containing at least three elements, two of which are

2. atomic radii difference among the three constituent elements should be at

3.heats of mixing among the main three elements should be negative;

*Dragica M. Minić and Milica M. Vasić*

short-range atomic arrangement [2–6].

melting at defined temperature [12].

glass formation can be expressed in five points as follows:
