Criteria For Glass Formation Research Articles

Effects of Rare-Earth Metals on the Thermal Stability and Glass-Forming Ability of Al–Ni–Co–R Amorphous Alloys

Al86Ni4Co4R6 and Al86Ni6Co2R6 (R = Nd, Sm, Gd, Tb, or Yb) metallic ribbons were produced by planar flow spin casting. The glass-transition and phase-transformation temperatures of these alloys were determined in crystallization kinetic studies. Glass-forming criteria for these alloys were calculated from differential scanning calorimetry (DSC) and differential thermal analysis (DTA) data. The rare-earth metals and combinations of transition metals useful to enhance the thermal stability and glass-forming ability of the alloys were found.

Thermokinetic behavior of Ga-doped GeTe4 glasses

Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) were used in conjunction to study thermokinetic behavior of (GeTe4)y(GaTe3)100-y bulk infrared glasses (for y between 40 and 100). The DSC data were utilized to describe the glass transition and crystallization kinetics in terms of the Tool-Narayanaswamy-Moynihan and Šesták-Berggren models, respectively. The kinetic data are of sufficient quality to enable predictions utilizable for preparation of Ge-Ga-Te ceramics and glass-ceramics. Whereas the compositional evolution of the positions of glass transition and crystallization effects was found to be small, the activation energies obtained for the two processes have shown that in case of the crystallization process the applied heating rate q+ has large influence on the position of the corresponding kinetic peak on the temperature axis (Tc) and, consequently, on the values of glass stability and glass-forming criteria calculated by using this value. For this reason, a new viscous-flow-related criterion, which utilizes the joint DSC and TMA measurements and is independent from applied q+, was derived to consider the thermal stability of the glassy materials with regard to their processing (fiber-drawing or shape-molding). Based on the newly developed criteria, the (GeTe4)67(GaTe3)33 glass (positioned near the eutectic) was found to be optimal with respect to the fiber-drawing procedure.

Investigating the Applicability and Limitations of Glass-Forming Criteria Based on Bond Parameters on Thermal Stability in Mg-Based Multicomponent Bulk Metallic Glasses

In this paper, correlation of thermal stability ( $$ \Delta {T_x} $$ ) with the bond parameters such as electronegativity ( $$ \Delta x $$ ), atomic radius mismatch ( $$ \delta $$ ), and valence electron concentration ( $$ \Delta {n^{1/3}} $$ ) for Mg-based multicomponent bulk metallic glasses (BMGs) have been evaluated. A statistical approach of regression analysis has been adopted to investigate correlations among these parameters. Available experimental data have been used for the systematic investigation from ternary to multicomponent Mg-based BMGs. In addition, the applicability of the criteria has been assessed for the systems with and without rare earth (RE) elements. We have found that BMG systems containing RE group elements have significant effect on width of supercooled liquid region. Results obtained from our modified empirical equation have been compared with that of earlier models and have shown better correlations.

Metallic glass formation at the interface of explosively welded Nb and stainless steel

The interface between explosively welded niobium and stainless steel SUS 304 was studied using scanning electron microscopy, transmission electron microscopy and energy dispersive X-Ray spectroscopy. The wavy interface along which vortex zones were located was observed. The vortex zones formed due to the mixing of materials typically had amorphous structure. Inoue’s criteria of glass formation were used to explain this result. The effect of the composition, cooling rate and pressure on the glass formation are discussed. The conditions of deformation, heating, and cooling as well as shockwaves propagation were numerically simulated. We show that the conditions of vortex zone formation resemble the conditions of rapid solidification processes. In contrast to the “classical” methods of rapid solidification of melt, the conditions of metastable phase formation during explosive welding are significantly complicated by the fluctuations of composition and pressure. Possible metastable structures formation at the interface of some common explosively joined materials is predicted.

Kinetic criteria of glass-formation, pressure dependence of the glass-transition temperature, and the Prigogine–Defay ratio

An analysis of some current topics of discussion in the theoretical modeling of the glass transition and of glass properties is given. In the first part, a general model-independent kinetic criterion of glass-formation is formulated. Its interrelation with other attempts of formulation of such criteria is discussed and some consequences not studied so far in detail are analyzed. It is shown that the value of the glass transition temperature depends not only on system properties and rates of change of external control parameters but, as a rule, also on the property of the system measured for its specification. In addition, systems described by several structural order-parameters may exhibit multiple glass transitions. The respective glass transition temperatures are shown to depend on the spectrum of relaxation times of the respective structural order-parameter and the degree of deviation of the system from the thermodynamic equilibrium state. Employing mentioned kinetic criteria, further on general equations for the pressure dependence of the glass transition temperature and the value of the viscosity at the glass transition temperature in dependence on cooling rate are formulated. In the second part, existing different approaches to the theoretical determination of the Prigogine–Defay (PD) ratio in glass transition are critically reviewed. As shown, following the kinetic approach to the determination of the glass transition temperature Tg, the analysis of the pressure dependence of Tg does not lead to any generally valid predictions for the value of the PD-ratio. It is demonstrated further that some recent attempts to question it do not affect the basic result of earlier analysis (J. W. P. Schmelzer and I. Gutzow, J. Chem. Phys. 125, 184511/1-11 (2006)) concerning the possibility to predict theoretically values of the PD-ratio larger than one when only one structural order-parameter is employed to describe kinetic freeze-in at glass transition.

Crystallization kinetics accountability and the correspondingly developed glass-forming criteria: A personal recollection at the forty years anniversaries

The meaning of experimentally determined characteristic temperatures is analyzed in terms of Hruby glass forming criterion. Despite various analyzed modifications it reveals that the sensitivity of original criterion is unsurpassable. The applicability of Sestak-Berggren empirical equation for the description of crystallisation kinetics is comparable with the classical modelling based on Johnson-Mehl-Avrami equation. Their employment is certainly dependent to the purpose of evaluation showing their substitution ability and limits.

A critical analysis of the glass-forming ability of alloys

Several empirical rules have been proposed during the past few years to synthesize bulk metallic glasses. But, the real reasons for the improved glass-forming ability of these alloys are still not clear and the ability to design alloy compositions to enable synthesis of larger diameter rods has not improved. The present work conducts a critical analysis of the existing data in terms of the different glass-forming criteria and concludes that the available parameters cannot satisfactorily predict the GFA and explain all the observed data. Reasons for this failure have been suggested.

Bulk metallic glasses

Amorphous alloys were first developed over 40 years ago and found applications as magnetic core or reinforcement added to other materials. The scope of applications is limited due to the small thickness in the region of only tens of microns. The research effort in the past two decades, mainly pioneered by a Japanese- and a US-group of scientists, has substantially relaxed this size constrain. Some bulk metallic glasses can have tensile strength up to 3000 MPa with good corrosion resistance, reasonable toughness, low internal friction and good processability. Bulk metallic glasses are now being used in consumer electronic industries, sporting goods industries, etc. In this paper, the authors reviewed the recent development of new alloy systems of bulk metallic glasses. The properties and processing technologies relevant to the industrial applications of these alloys are also discussed here. The behaviors of bulk metallic glasses under extreme conditions such as high pressure and low temperature are especially addressed in this review. In order that the scope of applications can be broadened, the understanding of the glass-forming criteria is important for the design of new alloy systems and also the processing techniques.

Amorphization and nanostructure synthesis in Al alloys

The recent innovations in metallic glasses have led to new alloy classes that may be vitrified and a re-examination of the commonly used criteria for glass formation and stability. In one case large, bulk volumes may be slowly cooled to the glassy state that signifies a nucleation-controlled synthesis. The other important case is represented by Al and Fe based marginal glass formers that have been synthesized under growth controlled kinetic conditions mainly by rapid solidification processes. With marginal glass forming alloys the termination of the amorphous state upon heating is often characterized by a primary crystallization reaction that yields a high number density in the range of 1021–1022 m−3 of Al nanocrystals (15–20 nm in diameter) dispersed within a residual amorphous matrix. At the same time the results from alternate synthesis strategies involving intense cold rolling reveal that the primary crystallization reaction can be bypassed during deformation alloying of elemental multilayers or enhanced during deformation bonding of amorphous ribbons. The kinetics analysis of the crystallization behavior provides insight into the origin of the dispersed nanocrystal and amorphous matrix microstructures, the important influence of heterogeneous catalysts and an effective assessment of the overall stability that are essential for microstructure control.

Synthesis and Stability of Amorphous Al Alloys

AbstractThe recent innovations in metallic glasses have led to new alloy classes that may be vitrified and a re-examination of the commonly used criteria for glass formation and stability. The new alloy classes are usually at least ternary systems and often higher order that can be grouped into two general categories. In one case large, bulk volumes may be slowly cooled to the glassy state which signifies a nucleation controlled synthesis. The other important class is represented by Al and Fe based glasses that can be synthesized only by rapid solidification processes such as melt spinning. These glasses are often called marginal glass formers that are synthesized under growth controlled kinetic conditions. With marginal glass forming alloys the termination of the amorphous state upon heating is often not characterized by a clear glass transition signal, Tg, but instead by the rapid onset of a primary crystallization reaction that represents the partial crystallization into a high number density of nanocrystals of the major component (i.e. Al or Fe) dispersed within a residual amorphous matrix. However, a closer examination by modulated or dynamic differential scanning calorimetry (DDSC) has identified a true reversible Tg signal that confirms the amorphous state and has revealed additional low temperature annealing behavior that impacts the overall thermal stability and microstructure evolution. At the same time alternate synthesis strategies involving deformation alloying by intense cold rolling reveals that the primary crystallization reaction can be bypassed. Alternatively other approaches have demonstrated that by suitable alloying it is possible to innoculate the primary crystallization reaction and increase the density of primary nanocrystals by about an order of magnitude. These developments represent a major level of microstructure control that have an impact on the structural performance and stability.

Effect of composition on the glass-forming tendency of barium aluminosilicate gels derived from metal alkoxides

The effect of composition on the glass-forming tendency of barium aluminosilicate gels derived from metal alkoxides with compositions near the theoretical composition of barium feldspar was studied. Results indicated that, in the experimental range, larger SiO 2 content and larger BaO/Al 2O 3 ratio were advantageous to glass formation. A criterion for glass formation in the studied system was established as ( b+3−4 y)/(2 y+ s(1+ b)/(100− s))< J c, where b is the BaO/Al 2O 3 ratio, s the mol percentage of SiO 2, y the fraction of four-coordinated aluminum over the total amount of aluminum, and J c is a constant for a definite experimental condition. The criterion showed good fitness with the experimental results.

Synthesis and properties of GeS 2–Ga 2S 3:NdCl 3 and GeS 2–Ga 2S 3:Nd 2O 3 glasses

High purity (GeS 2) 80− x (Ga 2S 3) 20· xNdCl 3 ( x=1, 2, 3) and (GeS 2) 79(Ga 2S 3) 20·Nd 2O 3 glasses were prepared and their thermal and optical properties measured. The GeS 2–Ga 2S 3 glasses can dissolve relatively large amounts of NdCl 3 and Nd 2O 3 (≤3 mol%) and still form stable glasses. They are optically transparent in the range from 19000 cm −1 to 800 cm −1. The glass transition temperature ( T g≅378°C) and the glass-forming criteria are only slightly changed by Nd doping (Δ T=147°C, H r=0.78; H′=0.39, S=4.10 K, where Δ T= T c− T g, H r is Hruby's criterion, H r=( T c− T g)/( T m− T c), H′=( T c− T g)/ T g, and S=( T c− T x)( T c− T g)/ T g). The short-wavelength absorption edge lies near 2.7 eV, doping with Nd creates new absorption bands which can be assigned to electron transfer from the 4 I 9/2 level to 4 G 7/2, 4 G 9/2, 2 K 13/2, 2 G 5/2, 2 G 7/2, 2 H 11/2, 4 F 9/2, 4 F 7/2, 4 S 3/2, 2 H 9/2, 4 F 5/2, 4 F 3/2, 4 I 15/2, 4 I 13/2 and 4 I 11/2 levels. In doped glasses, several broad luminescence bands, near 910, 1080 and 1360 nm, were found, which can be assigned to the transitions from 4 F 3/2 to 4 I 9/2, to 4 I 11/2 and to 4 I 13/2 electron levels. The long-wavelength absorption edge was found near 1000 cm −1 and is due to multiphonon Ge–S and Ga–S vibrations.

Synthesis and physical properties of the system (GeS 2) 80− x(Ga 2S 3) 20: xPr glasses

High purity (GeS 2) 80− x (Ga 2S 3) 20· xPrCl 3 ( x= 1,2,3), (GeS 2) 79(Ga 2S 3) 20Pr 6O 11 glasses were prepared and their basic thermal and optical properties were detemuned. The glass transition temperature T g is in the region 399–404°C. The glass-forming criteria (Δ T ∈ (123–128°C), H r ∈ (0.59–0.66), S ∈ (2.37–3.29) are changed by Pr doping only a little. The short-wavelength absorption edge lies near 2.7 eV, the doping by Pr creates new absorption bands which can be assigned to the 3H 4- 3H 6, 3H 4- 3F 3, 3H 4- 3F 4, 3H 4- 3P 0 and 3H 4- 3P 1 electron transitions. The experimentally found oscillator strengths calculated from absorption spectra lies between those of Pr doped halide and chalcohalide glasses. The long-wavelength absorption edge was found near 800–1000 cm −1 and it corresponds to multiphonon Ge-S and Ga-S vibrations. The far-IR diffuse reflectance spectra were measured and the spectrum revealed by Kubelka-Munk method. The spectrum was deconvoluted into several bands which can be assigned to GeS 4 and GaS 4 tetrahedra vibrations. The narrow luminescence bands corresponding to electron transitions in Pr 3+ ions (20000, 17857, 15873, 15220, 14326, 13947 and 13459 cm −1) with the most intensive band near 15220 cm −1 were found. These bands can be assigned to the transitions from the 3P 0 and 1D 2 levels to 3F 4, 3F 3, 3F 2, 3H 6, 3H 5 and 3H 4 levels. The most intensive band corresponds to the 3P 0- 3F 2 transitions.

Theoretical estimation of the possibility of glass formation in sulfate, phosphate, and sulfate-phosphate systems

The possibility of preparing glasses in sulfate, phosphate, and sulfate-phosphate systems is estimated from nine criteria of glass formation. It is shown that if these criteria concern only the first coordination sphere (i.e., the formation of PO4 and SO4 groups), glass formation in the systems should be considered possible. The majority of the criteria of glass formation have a defect consisting of the fact that their use is necessary but not sufficient for predicting the possibility of preparing glasses in a wide class of systems.

Local atomic structure of amorphous and crystalline alloys: Computer simulation

The microscopic stresses defined at each atom, or the atomic level stresses, are effective parameters to describe the local variations in the atomic arrangement in liquids and glasses. We have calculated them for model binary alloy systems both in the amorphous and in the crystalline (fcc and bcc) states. It was found that alloying two elements does not change the average atomic level stresses in the amorphous state when normalized by the elastic modulus, while in the crystalline state alloying sharply increases the stresses, in agreement with the theoretical prediction. Some of the basic issues regarding the nature of the amorphous alloys, namely the glass transition and the criteria for glass formation, are discussed based upon these results.

The Identification of the Metallic Glass State

AbstractDavid Turnbull has been the most prominent figure in the identification of the metallic glass state. This paper reviews his many contributions: the free volume model for transport in simple liquids, the demonstration of a substantial crystal nucleation barrier in liquid metals, the prediction of the universality of the glass transition, the formulation of criteria for glass formation, the first demonstration of the characteristic glass transition phenomena in a metallic glass, and important contributions to the study of the structure and physical properties.

Time-Resolved Laser Induced Transformations In Crystalline Te Thin Films

ABSTRACTWe report on time-resolved measurements of laser-induced transformations in Te thin films. Rapid thermal transformations are effected utilizing a KrF excimer laser (12 ns duration, 249 nm). The kinetics of the transformation is investigated utilizing transient conductance and infrared absorption measurements as well as reflectivity and transmissivity changes at 633 nm. The threshold for melting is accurately determined as well as melt velocities pertinent to the recrystallization kinetics of the molten films. Criteria for glass formation of Te are also discussed.