Viscosity of Amorphous Materials during Glass-Forming: More from the Adam-Gibbs Law

2013 ◽  
Vol 535-536 ◽  
pp. 223-226 ◽  
Author(s):  
H.H. Ruan ◽  
Liang Chi Zhang
Keyword(s):  
Amorphous Materials ◽  
Arithmetic Mean ◽  
Amorphous Selenium ◽  
Macroscopic System ◽  
Glass Forming ◽  
Amorphous System ◽  
Viscosity Variation ◽  
Microscopic Origin ◽  
Viscosity Changes ◽  
Fundamental Mechanism

This study aims to investigate the microscopic origin of viscosity by simplifying an amorphous system to a mixture of many independent atomic subsystems. The response of the macroscopic system is then taken as an ensemble average of the relaxations of such subsystems. The result shows that with the reduction of temperature, the overall viscosity changes from the harmonic mean of the subsystems, which is dominated by the fast relaxations, to the arithmetic mean governed by the slowest relaxation. The successful application of our model to the amorphous Selenium indicates the model captures the fundamental mechanism of the viscosity variation.

Strong Liquid Behavior of Zr-Ti-Cu-Ni-Be Bulk Metallic Glass Forming Alloys

1996 ◽  
Vol 455 ◽  
Author(s):  
Ralf Busch ◽  
Andreas Masuhr ◽  
Eric Bakke ◽  
William L. Johnson
Keyword(s):  
Glass Transition ◽  
Melting Point ◽  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Supercooled Liquid ◽  
Glass Transition Region ◽  
Glass Forming ◽  
Liquid Behavior ◽  
Metallic Liquids ◽  
Microscopic Origin

ABSTRACTThe viscosities of the Zr46.75Ti8.25Cu7.5Ni10Be27.5 and the Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass forming liquids was determined from the melting point down to the glass transition in the entire temperature range of the supercooled liquid. The temperature dependence of the viscosity in the supercooled liquid obeys the Vogel-Fulcher-Tammann (VFT) relation. The fragility index D is about 20 for both alloys and the ratio between glass transition temperature and VFT temperature is found to be 1.5. A comparison with other glass forming systems shows that these bulk metallic glass formers are strong liquids comparable to sodium silicate glass. Furthermore, they are the strongest among metallic glass forming liquids. This behavior is a main contributing factor to the glass forming ability since it implicates a higher viscosity from the melting point down to the glass transition compared to other metallic liquids. Thus, the kinetics in the supercooled liquid is sluggish and yields a low critical cooling rate for glass formation. The relaxation behavior in the glass transition region of the alloys is consistent with their strong glassy nature as reflected by a stretching exponent that is close to 0.8. The microscopic origin of the strong liquid behavior of bulk metallic glass formers is discussed.

scholarly journals Microscopic origin of the logarithmic relaxation in molecular glass-forming liquids

2018 ◽  
Vol 98 (9) ◽  
Author(s):  
Changjiu Chen ◽  
Rithin P. Krishnan ◽  
Kaikin Wong ◽  
Dehong Yu ◽  
Fanni Juranyi ◽  
...  
Keyword(s):  
Glass Forming ◽  
Molecular Glass ◽  
Microscopic Origin

Physical evolution and glass forming tendency of Ge1 − xSnxSe2.5 amorphous system

Vacuum ◽  
1998 ◽  
Vol 49 (1) ◽  
pp. 25-30 ◽  
Author(s):  
SS Fouad ◽  
SA Fayek ◽  
MH Ali
Keyword(s):  
Glass Forming ◽  
Amorphous System

Structure of Glass and Liquid Studied with a Conical Nozzle Levitation and Diffraction Technique

2007 ◽  
Vol 539-543 ◽  
pp. 2012-2017 ◽  
Author(s):  
Akitoshi Mizuno ◽  
Shinji Kohara ◽  
Seiichi Matsumura ◽  
Masahito Watanabe ◽  
J.K.R. Weber ◽  
...  
Keyword(s):  
Amorphous Materials ◽  
High Energy ◽  
Conical Nozzle ◽  
Atomic Configuration ◽  
X Ray Diffraction ◽  
Synchrotron Source ◽  
X Ray ◽  
3 Dimensional ◽  
Glass Forming ◽  
The Third

Two topics are described for structure analyses of glass and liquid using a combination of conical nozzle levitation (CNL) technique and diffraction experiments. The structure of high-purity bulk forsterite (Mg2SiO4) glass synthesized by a CNL technique has been determined by a combination of high-energy x-ray, neutron diffraction, and reverse Monte Carlo (RMC) modeling technique. The 3-dimensional atomic configuration derived from RMC modeling revealed that unusual network structure. In order to study structures of high-temperature and undercooled liquids, a CNL system has been developed and integrated with the two-axis diffractometer for glass, liquid, and amorphous materials at SPring-8, which is one of the third-generation synchrotron source. High-energy x-ray diffraction experiments were performed to obtain reliable diffraction data for the liquid phase of metallic glass-forming Zr-Cu binary alloys.

Glass Forming Ability of Bulk Amorphous Materials in Cu-Zr-Ag Ternary Alloy Systems

2012 ◽  
Vol 729 ◽  
pp. 373-378 ◽  
Author(s):  
Dóra Janovszky ◽  
F. Tranta ◽  
J. Sólyom ◽  
A. Roósz
Keyword(s):  
Ternary Alloy ◽  
Amorphous Materials ◽  
Amorphous Material ◽  
Alloy System ◽  
Glass Forming Ability ◽  
Maximum Temperature ◽  
Material Structure ◽  
Kinetic Properties ◽  
Liquid Region ◽  
Glass Forming

The glass forming ability (GFA) of the Cu-Zr-Ag alloy system was investigated on the basis of the thermal stability, and the structural, thermodynamic and kinetic properties of the material. We changed the concentration of the alloys, as we departed from the Cu58Zr42 composition and produced three different eutectic points in the Cu-Zr-Ag ternary system, in accordance with the results published in the respective literature. We produced various test pieces of Cu-Zr-Ag amorphous alloys with different Ag contents (0-70%), by casting the material into wedge-shaped copper moulds. In such ternary alloy system there is only a limited concentration range where amorphous materials can be produced: in the event that the Ag content of the material exceeds 35 at%, no amorphous material structure will develop. In our experiment the maximum temperature range of the supercooled liquid region (ΔTx) was 75 K. The calculated four GFA parameter values are not in perfect harmony and fail to point out the optimal composition available; however, based on γ and the reciprocal value of ω, the best compositions from the GFA aspect are Cu42.5Zr37.5Ag20and Cu40Zr37.5Ag22.5. The decrease of the maximum thickness of the bulk metallic glasses is influenced more by the oxygen content than the composition changes within the Cu-Zr-Ag system.

scholarly journals The Role of Casting Temperature in Preparation of Bulk Metallic Glasses

2010 ◽  
Vol 638-642 ◽  
pp. 1671-1676
Author(s):  
Hao Wang
Keyword(s):  
Metallic Glasses ◽  
Crystalline Phase ◽  
Amorphous Materials ◽  
Bulk Metallic Glasses ◽  
Processing Condition ◽  
Past Research ◽  
Glass Forming Ability ◽  
Casting Temperature ◽  
Glass Forming ◽  
Controlling Parameter

In the past research on bulk metallic glasses (BMGs) has been concentrated on searching for alloy composition to obtain high glass forming ability. Very few studies are on the effect of processing condition on glass forming ability of BMGs. In this study, we have prepared CuZr-based BMGs at different casting temperatures. Increasing casting temperature increases glass forming ability and decreases the amount of the crystalline phase during BMG solidification. At a high casting temperature 1723 K, fully amorphous sample is obtained at a size of 2 mm in diameter. While under the lower casting temperatures (1523 K and 1323 K), crystalline CuZr phases exist. The formation of the crystalline phase is attributed to the initial crystals or cluster survived in the BMG melt during ingot remelting. The study indicates that casting temperature can be used as the controlling parameter to produce purely amorphous materials or crystalline CuZr-phase reinforced BMG composites, and the mechanical properties and thermal stability of the BMG composites can be tailored by the amount of the crystalline phase existed in the materials.

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