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The topics discussed in this book focus on fundamental problems concerning the structural relaxation of amorphous metallic alloys, above all the possibility of studying it on the basis of viscous flow behavior and its relation to rheological anomalies, such as bend stress relaxation, thermal expansion, specific heat, density changes, and crystallization. Most relaxation studies deal with the relaxation changes of a single definite material property, and not with a wider spectrum of physical properties integrated into a common framework. This book shows that it is possible to describe these property changes on the basis of a more comprehensive theoretical understanding of their mechanism.



1. Production, Properties and Applications of Glassy Metals

A brief overview about the production properties and applications of amorphous metallic alloys is given. The possibility of synthesis and production of bulk amorphous alloys is discussed. The most important properties of application of metallic glasses are discussed. The ways for control change of physical and application properties of metallic glasses are presented. The main author’s objectives of this book are presented.

Krassimir Russew, Liljana Stojanova

2. Most Important Methods for Production of Amorphous Metallic Alloys

The most frequently used methods for production of amorphous metallic alloys via rapid solidification from the melt, chill block melt spinning, and planar flow casting are presented and discussed. The influence of technological production parameters are taken under consideration. The dependence of the geometrical dimensions of ribbonlike glassy metals upon the melt ejection pressure and peripheral velocity of the quenching substrate (disk) is theoretically subjected to analysis and experimental proof. The authors’ experience upon the production of bulk amorphous alloys is presented and discussed. A brief description about other methods for production of amorphous metallic materials is presented. An overview about the bibliography in the form of more than 90 cited references is proposed.

Krassimir Russew, Liljana Stojanova

3. Experimental Methods for Determination of the Magnitude and Temperature Dependence of the Viscosity of Amorphous Metallic Alloys

The importance of knowing the magnitude and the temperature dependence of glassy metals viscosity is presented. The possibility for estimation of the critical cooling rate for obtaining the metallic alloys in amorphous state via rapid cooling from the melt is analyzed. An overview about the bibliographic sources devoted to the determination of glassy metals viscosity under isothermal and nonisothermal experimental conditions is proposed. The experimental techniques are taken under consideration. A thorough analysis of the method for precise determination of glassy metals viscosity under nonisothermal conditions is presented. A real estimation of the critical cooling rate with Fe–B glassy alloy as an example is demonstrated.

Krassimir Russew, Liljana Stojanova

4. Viscous Flow Behavior of Amorphous Ribbonlike Metallic Alloys Depending on Different Factors

An attempt has been made to provide an information about the experimental evidence, as obtained by the authors, for the existence of a definite interrelation between the viscous flow features and the chemical composition of binary metal-metal, metal-metalloid, ternary metal-metal-metalloid, and quaternary glassy alloys. The thermal prehistory of metallic glasses and the influence of technological conditions by rapid quenching from the melt are also considered. An estimation of the critical quenching rate and its reliability for predicting the glass transition will also be given.

Krassimir Russew, Liljana Stojanova

5. Basic Concepts of the Free Volume Model: Structural Relaxation and Viscosity in the Framework of the Model

The basic concept and ideals of the free volume model (FVM) of Turnbull and Cohen are considered. The relation between structural relaxation and atomic free volume in amorphous condensed matter is pointed out. The viscosity temperature dependence of amorphous metallic alloys in the framework of the free volume model, as considered by F. Spaepen, A. van den Beukel, P. Duine, etc., is presented and discussed. The contribution of the authors to the extension of the FVM ideas for describing the viscosity temperature dependence of glassy metals under nonisothermal experimental conditions is presented. An experimental proof of the correctness of this FVM extension is given.

Krassimir Russew, Liljana Stojanova

6. Glass Forming Ability, Crystallization, and Viscosity of Rapidly Solidified Amorphous Cо100-xZrx and Cu100-xZrx Alloys

The glass forming ability (GFA) of glassy alloys with Cо-Zr and Cu-Zr as examples is studied, considered, and discussed in relation to their nonisothermal viscous flow and crystallization behavior. The glass forming ability (GFA) and melt fragility number of Angell and its Moynihan interpretation are presented. An FVM interpretation of the melt fragility numbers of Angell and Moynihan is proposed and experimentally proven. It is demonstrated that the exact viscosity measurement of glassy metals allows the determination of FVM parameters describing its temperature dependence. In this way it is possible to calculate the melt fragility number of Angell and to estimate the glass forming ability (GFA) of metallic alloys.

Krassimir Russew, Liljana Stojanova

7. Bend Stress Relaxation of Amorphous Metallic Alloys Under Isothermal and Nonisothermal Heating Conditions

A model analysis about the relation between the viscosity and the relaxation of bend stresses of ribbonlike amorphous metallic alloys, both under isothermal and nonisothermal conditions, is presented. Additionally, an experimental proof of the theoretical considerations based on the free volume model (FVM) is given. The experimental proof upon a study of the nonisothermal viscous flow behavior of Fe40Ni40Si6B14 amorphous metallic glass, in the high temperature range around its glass transition temperature, is performed. Additionally a study of the (nonisothermal and isothermal) relaxation of bend stresses in the same ribbonlike alloy at considerably lower temperatures is carried out. It is shown that the FVM interpretation of the two kinds of experimental data is possible with practically one and the same common set of FVM parameters. A new method for quantitative experimental separation of viscous flow caused plastic and anelastic deformations, respectively, is developed. It is shown that the relaxation of the anelastic deformation can be very well described by the empirical equation of Kohlrausch–Williams–Watts.

Krassimir Russew, Liljana Stojanova

8. Structural Relaxation in Various Amorphous Metallic Alloys Studied via Direct Viscosity and Bend Stress Relaxation Measurements

This book section is a continuation of those presented in Chap. 7, theoretical bend stress relaxation considerations with respect to their relation to the viscosity. The chapter provides additional experimental proof with the aid of viscosity and bend stress relaxation measurements on Pd77.5Cu6Si16.5, Аl25La50Ni25, and Al7.5Cu17.5Ni10Zr65 glassy alloys.The FVM interpretation of the two kinds of experimental data is possible with practically one and the same set of FVM parameters. A new method for quantitative experimental separation of viscous flow caused plastic and anelastic deformations, respectively, is developed. It is shown that the relaxation of the anelastic deformation, both under isothermal and nonisothermal conditions, can be very well described by the empirical equation of Kohlrausch-Williams-Watts.

Krassimir Russew, Liljana Stojanova

9. Thermal Expansion and Heat Capacity of Amorphous Metallic Alloys: Interpretation of Their Anomalous Behavior in the Framework of FVM

A free volume model analysis upon the thermal expansion and specific heat relaxation peculiarities of glassy metals has been carried out. It has been shown, both theoretically and experimentally, that the processes of viscous flow and relaxation caused by anomalies in thermal expansion and specific heat of glassy metals are governed by one and the same mechanism of structural changes based upon annihilation and/or production of atomic excess free volume.

Krassimir Russew, Liljana Stojanova

10. Relation Between the Density Changes and Thermal Expansion Anomalies in the Amorphous Metallic Alloys

The structural relaxation of bulk samples of the amorphous metals with Pd40Cu30Ni10P20 bulk glassy alloy as an example, by the determination of the temperature dependences of the thermal expansion at a constant heating rate of 10 K/min and isothermal measurement of the density changes, has been studied. An expression for the theoretical description of density changes of amorphous metallic alloys as a function of the heat treatment conditions in the framework of the free volume model (FVM) has been derived. Experimental determination of the density changes of a Pd40Cu30Ni10P20 glassy alloy is carried out. A good agreement between the experimental data and the FVM theoretical expectations is established. Calculated using the derived theoretical description via inserting in it the experimentally obtained thermal expansion, experimental data have been carried out. They are in good agreement with the experimental data for the density changes of the same system.

Krassimir Russew, Liljana Stojanova

11. Crystallization Kinetics of Bulk Amorphous Metallic Alloys and Its Relation to the Forgoing Relaxation Processes

The crystallization behavior of undercooled liquid Pd40Cu30Ni10P20 metallic alloy has been studied with the aid of differential scanning calorimetry, optical metallography, and electron microscopy methods. The crystallization occurs as a single-stage process starting preferably on the surface of casting voids in the sample volume and on the outer sample cutting planes. The linear crystal growth velocity of crystallizing cells was measured at several constant temperatures in the range of 590–620 K. It is constant at constant temperatures and its temperature dependence is in good agreement with the theoretical concepts of Uhlmann calculated using the temperature dependence of the experimentally determined viscosity temperature dependence of the alloy studied. Differential scanning calorimetry study of isothermal overall volume transformation kinetics of samples pre-annealed at 600 K for 600 s has been also carried out at several constant temperatures. The experimental data are interpreted on the basis of the equation of Kolmogorov–Avrami–Johnson–Mehl for the case of 3D growth of fixed number of preexisting nuclei. The possibility to re-vitrify the crystallized samples by their melting in differential scanning calorimeter, followed by quick cooling with cooling rate of 5 K s−1 is shown. The volume transformation kinetics of re-vitrified samples has been also studied.

Krassimir Russew, Liljana Stojanova

12. Mechanical Properties of Amorphous Metallic Alloys and Their Relation to the Viscosity Characteristic Parameters

The unified theoretical equation of B. Yang et al. on the relation between the mechanical strength and viscous flow behavior of glassy metals is presented and discussed; it is shown that the equation of Yang can be successfully used for estimation of fraction strength of various ribbonlike glassy metals, provided that their viscous flow behavior is precisely determined under nonisothermal experimental conditions. The viscous flow and mechanical properties of Co100-x Zrx and Cu100-xZrx glassy alloys are presented and discussed, together with their comparison with the data existing in the bibliography. A relation between the estimated fraction strength of glassy alloys and their Vickers microhardness is established.

Krassimir Russew, Liljana Stojanova

13. Properties and Applications of Amorphous Metallic Alloys

An extensive overview upon the application of amorphous metallic alloys in relation to their properties is presented. Their commercial production in the USA, Europe, and Russia with their trademarks and most important application properties in tabular form is presented and discussed.

Krassimir Russew, Liljana Stojanova

14. Quick Reference to the Viscous Flow Behaviour of Glassy Alloys at a Heating Rate of 20 K/min

This chapter provides selected information about the viscosity temperature dependence at a heating rate of 20 K/min of about 30 binary and multicomponent amorphous metallic alloys, representative for the variety of glassy metals studied and considered in this book. Numerical data for the values of FVM parameters are also given, which makes it possible to calculate the viscosity temperature dependences of these glassy alloys at other heating rates chosen by the user of this book.

Krassimir Russew, Liljana Stojanova


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