Ability Of Metallic Glasses Research Articles

Short-to-medium range structure and glass-forming ability in metallic glasses

In this paper, we investigate the clustering model and glass-forming ability (GFA) in response to variant compositions and cooling rates. The structural units are obtained by molecular dynamics and hierarchical clustering. In the clustering model, a nesting relationship from small- to large-scale units, i.e., from short- to medium-range order, is observed during the hierarchical clustering. Furthermore, the packing efficiency of short-range units is applied to depict the GFA, and the result suggests that the packing efficiency is not strictly increased with respect to cooling rate. A positive correlation between a high packing efficiency and a large skewness is found, which validates that alloys with the stronger GFA have a more disordered structure.

Maximizing the degree of rejuvenation in metallic glasses

As the reverse process of relaxation, rejuvenation is the structural excitation process that can bring metallic glasses (MGs) to a higher energy state and usually increases their free volume. Here, using a dilution procedure conducted by randomly removing atoms from the modeled glass matrix, the degree of rejuvenation can be systematically controlled and the maximum rejuvenation threshold of MGs is identified. The structural relaxation is activated during the rejuvenation process and the dynamic balance between free volume creation and annihilation defines the rejuvenation ability of MGs. The highest degree of rejuvenation correlates to the flow strain of the materials and the structure is similar to that found in shear bands.

Surface reactivation of FeNiPC metallic glass: A strategy for highly enhanced catalytic behavior

With intrinsically disordered atomic structure, metallic glasses (MGs) have been extensively studied as advanced catalysts. Although the nature of widely tunable atomic composition in MGs facilitates accommodation in different catalytic environments, it may also induce the decline of catalytic activity due to surface effect. The role of surface of MGs is still not fully understood. In this work, an Fe50Ni30P13C7 (FeNiPC) glassy ribbon was found to have a strong-binding surface layer with the superior anticorrosion but low catalytic ability. Nevertheless, an effective elimination of surface layer by chemical dealloying could highly promote the catalytic ability of FeNiPC glassy ribbons from 20 min to only 10 min for brilliant black BN dye degradation. Further investigation revealed that chemical dealloying could effectively dissolve the surface layer of FeNiPC glassy ribbons induced reactivation of surface that was previously buried under the strong oxide layer, instead of generating nano-porous structured surface. The reactivation of ribbon surface effectively optimized active reaction sites and the re-exposure of Fe, Ni and P with zero-valent state formed galvanic cells by atomic clusters leading to the acceleration of catalysis. The insight and revelation of intrinsic surface activity in this work provide an effective way to highly promote the catalytic ability of MGs.

Fe73.5Si13.5B9Cu1Nb3 metallic glass: Rapid activation of peroxymonosulfate towards ultrafast Eosin Y degradation

Discovering functional applications of metallic glasses (MGs) as heterogeneous catalysts is a fundamental and essential topic. This work reports the rapid production of sulfate radicals (SO4−) from peroxymonosulfate (PMS) using Fe73.5Si13.5B9Cu1Nb3 glassy ribbons as catalysts for Eosin Y (EY) dye wastewater treatment. The reaction rates (k) from the experimental data reveal that the EY degradation is well fitted with the pseudo-first-order kinetic model. The strong electron transfer ability is characterized by electrochemical methods, presenting an advanced catalytic performance for EY degradation. Various experimental parameters, including dye concentration, catalyst dosage, PMS concentration, light intensity, pH and reaction temperature as well as the saline and natural inorganic effects, are fully investigated. The results show that the color removal of EY dye could achieve nearly 100% within 20min. The quenching experiments are performed to verify the production of reactive species, suggesting that both OH and SO4− are produced from PMS and play significant roles in EY degradation. This critical study reveals that using Fe73.5Si13.5B9Cu1Nb3 MGs as catalysts exhibits a superior reactivity on PMS activation in wastewater treatment. The discoveries shed lights into the study of electron transfer ability for MGs, presenting extensive prospects in the application of dye wastewater treatment.

Correlation between the Arrhenius crossover and the glass forming ability in metallic glasses

The distinctive characteristic of the metallic glass-forming system is that the variation in viscosity with temperature obeys Vogel-Fulcher-Tammann (VFT) relationship in the undercooled state and Arrhenius relationship in the high temperature region. A dimensionless index has thus been proposed based on the Arrhenius-VFT crossover and the classical nucleation rate and growth rate theory to evaluate the glass-forming ability (GFA). The indicator G(a) is expressed with the combination of Tg, the glass transition temperature, Tx, the onset crystallization temperature, Tl, the liquidus temperature, T0, the VFT temperature, and a a constant that could be determined according to the best correlation between G(a) and the critical cooling rate (Rc). Compared with other GFA indexes, G(a) shows the best fit with Rc, with the square of the correlation coefficient (R2) being 0.9238 when a = 0.15 for the 23 various alloy systems concerned about. Our results indicate the crossover in the viscosity variation has key effect on GFA and one can use the index G(a) to predict Rc and GFA for different alloys effectively.

Hidden topological order and its correlation with glass-forming ability in metallic glasses

Unlike the well-defined long-range periodic order that characterizes crystals, so far the inherent atomic packing mode in glassy solids remains mysterious. Based on molecular dynamics simulations, here we find medium-range atomic packing orders in metallic glasses, which are hidden in the diffraction data in terms of structure factors or pair correlation functions. The analysis of the hidden orders in various metallic glasses indicates that the glassy and crystalline solids share a nontrivial structural homology in short-to-medium range, and the hidden orders are formulated by inheriting partial crystalline orders during glass formation. As the number of chemical components increases, more hidden orders are often developed in a metallic glass and entangled topologically. We use this phenomenon to explain the geometric frustration in glass formation and the glass-forming ability of metallic alloys.

Thermodynamic behavior of glass-forming metallic supercooled liquids

We analyze the enthalpy of crystallization Hx and fusion Hm, and calculate the average difference of the heat capacity between supercooled liquid and equilibrium crystalline solid ΔCave in a series of glass-forming metallic supercooled liquids. It is found that ΔCave is close to a constant 13.2J/mol/K which is an important feature for glass-forming metallic supercooled liquids, and there is no obvious correlation between the parameter φ(=1−Hx/Hm) and the glass-forming ability. The ratio of ΔCave to the entropy of fusion is an important parameter in determining the glass-forming ability in metallic glasses.

Atomic and cluster level dense packing contributes to the high glass-forming ability in metallic glasses

The microstructure features of a representative Zr48Cu45Al7 bulk metallic glass (BMG) were investigated via a series of simulations and calculations coupled with the synchrotron radiation-based experiments. It was revealed that bond shortening occurs in the atomic pairs, due to the strong interaction between the Al dopant atoms and their neighbors. The bond shortening leads to the atomic and cluster level dense packing in the local structures, which should be the structural mechanism of the high glass-forming ability in Al-microalloyed BMGs. This work not only reveals the atomic and cluster level microstructures in this class of glass materials, but also has implications for developing other BMGs with relatively large critical sizes.

Atomic-Scale Mechanisms of the Glass-Forming Ability in Metallic Glasses

The issue, composition dependence of glass-forming ability (GFA) in metallic glasses (MG), has been investigated by systematic experimental measurements coupled with theoretical calculations in Cu-Zr and Ni-Nb alloy systems. It is found that the atomic-level packing efficiency strongly relates to their GFA. The best GFA is located at the largest difference in the packing efficiency of the solute-centered clusters between the glassy and crystal alloys in both MG systems. This work provides an understanding of GFA from atomic level and will shed light on the development of new MGs with larger critical sizes.

Glass Forming Ability of Ca-Based Bulk Metallic Glasses

Knowledge of glass forming ability (GFA) of amorphous metallic alloys is very important from both theoretical and practical point of view. Thermodynamically, the Gibbs free energy difference, ΔG between the undercooled liquid and the corresponding crystalline state is driving force for crystallization. As a consequence, it is a good indicator for glass forming ability of metallic glasses. A novel expression for ΔG has been used to estimate the GFA of recently developed Ca-based bulk metallic glasses viz. Ca53Mg23Cu24,Ca65Mg15Cu20,Ca40Mg25Cu35, Ca50Mg22.5Cu27.5 and Ca55Mg15Cu30. Different GFA criteria are also evaluated for systems taken up in the study and effect of addition of variation in composition of Ca-Mg-Cu system is also investigated. Present work suggests that among different GFA criteria, ΔG is the best criterion for the prediction of GFA for Ca-based bulk metallic glasses.

Investigation on Correlation between the Modified Criterion and the Glass-Forming Ability for Metallic Glasses

A modified criterion γ’ (=Tx/(1.5Tg+Tl) of glass-forming ability (GFA) for metallic glasses is suggested on the basis of present criterion γ (=Tx/(Tg+Tl) that correlates well with some systems including metallic glasses, some glassy oxides and some cryo-protective aqueous solutions. Results show that the modified criterion γ’ shows stronger correlation with the critical cooling rate Rc for metallic glasses than the criterion γ, which is demonstrated by a value increase in the statistical correlation parameter R2 from 0.9022 to 0.9037. Furthermore, a modified equation is given to reflect the relationship between γ’ and Rc.

An electronic structure perspective on glass-forming ability in metallic glasses

Through systematic study of glass-forming ability (GFA) and the electronic specific heat coefficient in typical ternary (Cu50Zr50)100−xAlx bulk metallic glasses, we provide compelling experimental evidence that the density of electronic energy states at the Fermi level indeed is closely correlated with the GFA of metallic glasses, and the best GFA can be obtained when the Fermi surfaces nearly touch the quasi-Brillouin boundaries, as predicted by the nearly free electron model. Our results highlight the significance of electronic structural effects on the formation of metallic glasses.

Glass Formation and Mechanical Properties of Ti–Cu–Ni Alloys with High Ti Content

Abstract A series of Ti–Cu–Ni alloys with Ti content as high as 50–70 at. % expected to possess potential high glass-forming ability (GFA) was designed according to the ε criterion (Xia, M. X., Zhang, S. G., Ma, C. L., and Li, J. G., “Evaluation of Glass-Forming Ability for Metallic Glasses Based on Order-Disorder Competition,” Appl. Phys. Lett. Vol. 89, 2006, pp. 091917-1–091917-3) and were prepared by melt spinning and suck casting methods. The samples were examined by X-ray diffractometry, differential scanning calorimetry, optical microscopy, scanning electronic microscopy, and quasistatic compression test. The GFA of the melt-spun ribbons is enhanced with increasing ε. Ti58Cu32Ni10 alloy with the maximum designed ε value of 0.542 exhibits best GFA with a glass transition temperature of 627 K and a wide supercooled liquid region of 45 K. However, this alloy failed to form a fully glassy rod of 1 mm in diameter. Room temperature compression tests reveal that the 1 mm diameter Ti58Cu32Ni10 glass composite exhibits work-hardening characteristic, with ultimate compressive stress of 2418 MPa, yielding stress σ0.2 of 1448 MPa and about 7.8 % plastic strain. The combination of high strength and ductility was attributed to a dendritic TiCu(Ni) network embedded in the hard glass matrix.

Viscous flow recovery in bulk metallic glasses by heat treatment

It is commonly accepted that the ability of metallic glasses to undergo viscous flow sharply and ineversibly drops with increasing duration and temperature of annealing, which is related to an increase in the degree of “irreversible” structural relaxation. The results of isothermal creep measurements show that this ability can be recovered almost completely by means of short-term heating to a temperature above that of the glass transition.

Calculations of dominant factors of glass-forming ability for metallic glasses from viscosity

Abstract The calculation models in which the viscosity is used as a main parameter are proposed for the estimation of the three glass-forming ability (GFA) factors: critical cooling rate ( R c ) for formation of glassy phase, reduced glass transition temperature ( T g / T m ) and supercooled liquid range (Δ T x ≡ T x − T g ), where T g , T m and T x are the glass transition, melting and crystallization temperature, respectively. The R c and T g / T m were analyzed on the basis of the homogeneous nucleation and growth theory by the construction of a time-transformation diagram for the crystallization of metallic glass. On the other hand, Δ T x was calculated on the basis of a free volume theory proposed by Beukel and Sietsma, and then was related with R c calculated from the time–transformation curve. The calculations were carried out for Fe-, Pd-, Pt-, Zr-, Mg-based metallic glasses for which the viscosity is expressed by Vogel–Fulcher–Tammann equation or the Doolittle equation. The calculated results summarized in R c − T g / T m and R c −Δ T x diagrams agree with the experimental data qualitatively. It was shown that all the GFA factors of metallic glasses can be calculated from viscosity. These results indicate that the viscosity is the key parameter for the determinations of R c , T g / T m and Δ T x .