Relaxation In Glasses Research Articles

Rejuvenation by enthalpy relaxation in metallic glasses

Structural relaxation can be induced by annealing and usually leads to embrittlement in metallic glasses (MGs). Here, we show that a relaxed MG obtained by annealing an as-cast MG at a temperature (annealing temperature, Ta) below its fictive temperature can be suitably rejuvenated by a thermal treatment of the relaxed MG at a temperature higher than Ta. The effect is driven by enthalpy relaxation, an endothermic reaction upon heating relaxed MG. This rejuvenation lifts the energy state of the relaxed MG towards that of the as-cast MG. Importantly, we found that the plasticity and fracture toughness of the optimally rejuvenated samples exceed those in the as-cast sample, reversing the relaxation-induced embrittlement in the relaxed sample. An analysis of the structural changes shows that the packing density, rather than the ordering of the atomic structure, is responsible for the effects of rejuvenation. The observed rejuvenation may originate from the recovery of loosely packed regions in the MG atomic structure that were densified during annealing. Our findings are significant for tailoring the mechanical properties of MGs.

Micro-drilling of alkali-silicate glass with ultraviolet picosecond laser

The low efficiency of UV-laser ablation of transparent alkali-silicate glass has been increased by means of irradiation by 60Co γ-quanta to doses 104 −107 Gy to induce intensive UV-visible coloration. Varying the picosecond pulse energy of Nd:YAG laser at 4-harmonics 266 nm within 1−9 mJ and pulse number, arrays and grids of holes were drilled with diameters from 9 to 40 µm on area up to 1×1 cm2 . Shock waves of 4−5 µm were generated by expanding plasma around ablated holes at focused pulse energy density >108 J/m2 and nanoscale crystallization occurred there. Besides, a submicron hole was drilled aside the central micron hole due to generation of vacuum UV harmonics. The combined effect of γ-irradiation followed by UV laser drilling has resulted in decrease of silicon and oxygen contents, and generation of fluorine that may be caused by photonuclear reactions 28Si14→19F9+ 33Т1; 16O8→44He2; 16О8+3Т1→19F9. Because of glass viscosity and relaxation during 2 months at 300 K, the exit diameter of drilled holes has increased up to the entry one. Such micro-scale grids can be used for separating liquid mixtures or cleaning water.

Reply to "Comment on 'Deformations, relaxation, and broken symmetries in liquids, solids, and glasses: A unified topological field theory' ".

We reply to the Comment by Bryk etal. [Phys Rev. E 106, 036601 (2022)10.1103/PhysRevE.106.036601] on our paper [Phys. Rev. E 105, 024602 (2022)2470-004510.1103/PhysRevE.105.024602].

Comment on "Deformations, relaxation, and broken symmetries in liquids, solids, and glasses: A unified topological field theory".

We discuss a field-theoretical approach to liquids, solids, and glasses, published recently [Phys. Rev. E 105, 034108 (2022)10.1103/PhysRevE.105.034108], which aims to describe these materials in a common formalism. We argue that such a formalism contradicts the known hydrodynamic theory of classical liquids. In particular, the authors miss the important particle-number conservation law and the density fluctuations as a hydrodynamic slow variable. This results in an exotic mechanism of hydrodynamic sound instead of the standard hydrodynamic one due to combined particle-number and momentum conservation, a fact well documented in fluid-mechanics textbooks.

Controlling the relaxation versus rejuvenation behavior in Zr-based bulk metallic glasses induced by elastostatic compression

Elastostatic compression (ESC) has received considerable research attention as a tool to study rejuvenation and relaxation processes for bulk metallic glasses (BMGs). However, little is understood about the conditions that control whether rejuvenation or relaxation will occur, and whether conditions exist that can give structural stability. We address these questions by applying ESC at 90% of the yield stress to both cast and laser powder bed fusion (LPBF) manufactured Zr-based BMG samples in the as-cast, as-built, and different annealed states. The structural state and mechanical properties for each material condition were characterized by differential scanning calorimetry and microhardness, respectively, and two representative groups were also used for compression testing. Initial relaxation or rejuvenation was observed for elastostatically compressed as-cast samples, and the behavior reversed over 72 h of ESC. In contrast, no ESC effect was observed for the as-built LPBF samples. It was found that the onset of either relaxation or rejuvenation by ESC could be better predicted if samples were annealed into a controlled initial state. Five different types of initial response to ESC were observed, corresponding to different initial energy state ranges. Materials in the highest and lowest initial energy states were stable against structural changes by ESC. Close to the highest energy state, rejuvenation was dominant, while relaxation took place close to the lowest energy state. At intermediate initial energy states, both relaxation and rejuvenation were observed after ESC loading, suggesting that the glass structure easily finds different local minima in the potential energy landscape. In all cases, relaxation was associated with BMG hardening and rejuvenation was associated with softening. Overall, the results of this study provide new insights into how ESC impacts the structural state and mechanical properties of BMGs.

Gamma relaxation in Dy-based metallic glasses and its correlation with plasticity

The discovery of secondary relaxation in metallic glass (MG) breaks the longstanding cognition that MG, as a simple glassy system, exhibits only α relaxation and contributes significantly to the understanding of the structure and mechanical properties of MG. In this work, two independent fast secondary relaxation peaks corresponding to γ and β′ relaxation were detected by dynamic mechanical measurement in several Dy-based MGs at temperatures far below the glass transition temperature. Compared with β′ relaxation, the novel γ relaxation is activated at lower temperatures and possesses smaller activation energy approximately 2/3 of that for β′ relaxation. By exciting γ relaxation, loosely packed regions evolve into vein-like patterns in the fracture surface, leading to unusual plasticity at cryogenic temperatures. Furthermore, a holistic relaxation spectrum including boson peak, fast γ and β′ relaxation, slow β relaxation and primary α relaxation in MG was depicted.

Evolution of the distribution of flow units of a metallic glass under cyclic loading

Dynamic mechanical relaxation processes (i.e., β relaxation and α relaxation) are closely connected with the mechanical and physical properties of metallic glasses. In the current work, the β relaxation of La60Ni15Al25 metallic glass was studied in sequential heating and cooling experiments by dynamic mechanical analysis. The values of the loss modulus peak were found to reach a relatively stable state during the progress of the heating-cooling cycles. The evolution of the flow unit distribution during thermal cycling was revealed by stress relaxation tests. The experimental results of stress relaxation were well described by a generalized Maxwell model, allowing the analysis of the underlying relaxation time and activation energy distributions. We also show here a suppressed relaxation behavior observed under repeated loading cycles, which is attributed to the annihilation of flow units and the modification of the relaxation time spectrum obtained in the framework of the generalized Maxwell model.

Structural rearrangements during sub-Tg relaxation and nucleation in lithium disilicate glass revealed by a solid-state NMR and MD strategy

Structural rearrangements taking place during relaxation and crystal nucleation in lithium-disilicate (LS2) glass have been investigated by a comprehensive set of solid-state nuclear magnetic resonance (NMR) experiments, supported by molecular dynamics (MD) simulations. Samples were subjected to heat treatments at 435 °C, i.e., 20 K below the laboratory glass transition temperature (Tg). Raman and NMR data indicate that under these conditions both relaxation and nucleation occur without detectable changes in the network former unit distribution of the glassy silicon-oxide network. Instead, relaxation of the frozen supercooled melt and nucleation of LS2 crystals occur principally in terms of a changing lithium local environment: 7Li spin-echo decay NMR indicates average Li-Li distances, characterized by homonuclear dipolar second-moment measurements, are reduced after very short heat treatments and approach those found in the isochemical crystal. This finding is supported by molecular dynamics (MD) simulations predicting a dependence of the Li+ ion distribution on the melt-cooling rate. In addition, the structural reorganization also impacts the distribution of electric field gradients as detected by 7Li satellite transition NMR spectroscopy. Finally, crystal nucleation becomes most evident by the appearance of minor amounts of sharp 29Si MAS resonances and a significant change in the 7Li NMR satellite transitions, as visualized by difference spectroscopy. This study defines a new NMR strategy, generally applicable for investigating the structural relaxation process accompanying the internal crystallization of ion-conducting frozen supercooled melts containing suitable NMR active nuclear probes (7Li, 23Na, 133Cs, etc.).

Rejuvenation behaviors of recovery-annealed Cu–Zr metallic glass with different thermal treatment conditions: a molecular dynamics study

The recovery annealing process, which reheats the relaxed metallic glass (MG) to a certain temperature above glass transition temperature and subsequently rapid quenched, could tailor the sample to a less relaxed state, called as rejuvenation process. During the recovery annealing process, the final cooling rate, isothermal time and annealing temperature all affect the obtained rejuvenated state. In the present study, we investigated the changes of configurational potential energy and atomic structure of Cu–Zr MG under various different parameters by using molecular dynamics simulation. We found that when the final cooling rate after recovery annealing exceeds the cooling rate of the as-cast sample, a transition point from ageing to rejuvenation exists in the annealing temperature ranging from 900 to 1000 K. Meanwhile, the degree of ageing when annealed at 900 K, as well as the degree of rejuvenation when annealed at 1000 K, improves with a longer isothermal time. The transition behavior from ageing to rejuvenation at different annealing temperatures is mainly caused by the variation of proportions of Cu-centered and Zr-centered polyhedra in the supercooled liquid region. This work provides a profound understanding of the change in configurational potential energy and atomic structure during recovery annealing with different thermal parameters.

Transient nature of fast relaxation in metallic glass

Metallic glasses exhibit fast mechanical relaxations at temperatures well below the glass transition, one of which shows little variation with temperature known as nearly constant loss (NCL). Despite the important implications of this phenomenon to deformation, the origin of the relaxation is unclear. Through molecular dynamics simulations of a model metallic glass, Cu64.5Zr35.5, we implement molecular dynamics dynamical mechanical spectroscopy (MD-DMS) with system stress decomposed into atomic-level stresses to identify the group of atoms responsible for NCL. This work demonstrates that NCL relaxation is due to transient groups of atoms that revert to the typical atomic-level viscoelastic behavior over picosecond timescales. They are homogenously distributed throughout the glass and have no outstanding features, rather than having defect-like local structure as previously reported.

Pressure effects on the dynamics and glass formation of Cu-Ag eutectic melt

The effects of pressure on the dynamic property and glass transition of Cu54.2Ag45.8 eutectic melt were systematically studied by extensive molecular dynamics simulations. It is shown that an increasing external pressure can slow down the dynamics of the melt and enhances the dynamic heterogeneity. As the pressure increases, the dynamic crossover temperature and glass transition temperature monotonously increase. Application of an external pressure to the melt is conducive to formation of <0, 3, 6, 4> and <0, 3, 6, 3> polyhedrons in the metallic glass, but unfavorable for formation of <0, 0, 12, 0> clusters. The increase of pressure results in an inverse structure-energy relationship in the relaxed glass, i.e., the potential energy increases with increasing atomic packing density, because the relaxation of local structure into the low-energy configuration is restricted. Finally, the effects of temperature and pressure on the microstructure evolution during glass formation were compared.

Crystallization Study of Pb Additive Se-Te-Ge Nanostructured Alloys using Non-isothermal Differential Scanning Calorimetry

Nanotechnology started a new era in research and continuous escalations due to its potential applications. In modern optoelectronics, Pb additive nano-chalcogenides are becoming promising materials. For a memory and switching material, the thermal stability and glass-forming ability are vital, and the glass should be thermally stable from a technological point of view. This research article investigates the thermal behaviour of bulk (Se80Te20)94-xGe6Pbx (x = 0, 2, 4 and 6) samples synthesized using the melt quench procedure non-isothermal differential scanning calorimetry at four heating rates from 5 to 20°Cmin-1. Further, the overall crystallization study, which includes thermal stability, ease of glass formation, fragility, glass relaxation and glass-crystallization transformation kinetics of investigated alloys using different empirical formalisms, is reported and discussed. Compositional and heating rate dependence of recorded characteristic temperatures and other deduced parameters of reheated alloys are also discussed. The correlation between deduced parameters is also established to define the utility of these materials in practical applications.

Revealing the nature of glass by the hyperquenching-annealing-calorimetry approach

C. Austen Angell has been a great inspiration for liquid and glass scientists including myself. He was a close collaborator of mine on glass dynamics and thermodynamics, particularly on the sub- T g relaxation in glass. Here, in memory of his seminal contributions to science and our collaboration, I revisit our published data and analyze our unpublished data, as well as review some of important results reported recently in the literature, concerning the sub- T g relaxation in glass, a field on which Austen has profoundly impacted. I highlight new insights into the dynamics, thermodynamics, and structural heterogeneity in glass far from equilibrium, based on the hyperquenching-annealing-calorimetry (HAC) experiments. I describe key extensions and applications of the HAC approach in glass research. Finally, I present the perspectives and challenges regarding the sub- T g relaxation in glasses with fictive temperatures well above T g . • The hyperquenching-annealing-calorimetry approach is used to solve glass problems. • The above-mentioned approach is named the ‘energy bird’ approach. • The ‘energy bird’ proved to be very sensitive to structural heterogeneity in glass. • The origin of the ‘shadow’ glass transition is discussed through literature data.

Influence of magnetic interaction on configurational-entropy-suppressed β -relaxations in FeNi-based metallic glasses

In this article, we studied the effect of magnetic interaction on β-relaxations of FexNi72−xSi4.8B19.2Nb4 (x = 0, 10, 30, 50, 72) metallic glasses (MGs). It is found that, with the substitution of Fe by Ni, the β-relaxation changes from a shoulder to an excess wing, suggesting an entropic effect on the suppression of β-relaxation. A peak caused by ferromagnetic transformation appears in the loss modulus curve of Fe30Ni42Si4.8B19.2Nb4 MG with suppressed β-relaxation, which is sensitive to stress and strain. In addition, the β-relaxation can be further varied by annealing under a transverse or longitudinal magnetic field. The results suggest that the entropy-suppressed β-relaxation in MGs can be affected by magnetic interaction that could help to improve their mechanical properties.

Structural, shear and volume relaxation in a commercial float glass during aging

Density, Raman spectroscopy and viscosity measurements are utilized to probe, respectively, the volume, structural and shear relaxation behavior of a Na-Ca-Mg silicate glass of standard commercial float composition at ∼80 °C below its calorimetric glass transition. The results, when taken together, indicate that the lowering of fictive temperature of the glass during aging results in a Q-species disproportionation of the type Q2+Q4→2Q3, and all three relaxation processes are characterized by stretched exponential kinetics with similar average timescale (〈τ〉∼ 300 h) and stretching exponent (β ∼ 0.4), implying a close mechanistic relationship. It is hypothesized that the coexistence of strongly and weakly constrained domains or structural moieties in the network of a glass or supercooled liquid can give rise to a temporal decoupling between the structural and shear relaxation processes, as has been reported in some of the recent studies in the literature.

Atomistic study on simultaneous achievement of partial crystallization and rejuvenated glassy structure in thermal process of metallic glasses

ABSTRACT The relaxation state and partial crystallization are crucial factors that affect the material properties of metallic glasses. Rejuvenation induces a less relaxed glass state and hence facilitates the control of the relaxation state. The rejuvenation and crystallization during thermal processing are associated closely with the phase changes of metallic glasses upon heating. Most nanocrystalline metallic glasses formed via conventional thermal annealing have a relaxed glassy matrix. In this molecular dynamics study, we investigate the feasibility of thermal processing to simultaneously realise both partial crystallization and rejuvenation using model alloy system. Dynamic mechanical analyses reveal relaxation behaviours and local deformation features of metallic glasses composed of a crystalline phase and a rejuvenated glass matrix. The crystalline phase increases the macroscopic shear stiffness of the composite model over a wide temperature range, whereas it does not significantly affect the internal friction of the rejuvenated glass matrix. In addition, dispersed nanocrystals suppress the development of sharp and concentrated shear localisation in the rejuvenated glass matrix. The simultaneous adjustment of the relaxation state and crystalline phase in the glass matrix is discussed from a viewpoint of the microstructure design of metallic glasses.

On the shear modulus and thermal effects during structural relaxation of a model metallic glass: Correlation and thermal decoupling

Pd40Ni40P20 (at.%) samples with different enthalpy states were fabricated through high-pressure torsion or sub-Tg annealing of the as-cast material. Subsequently, the underlying structural relaxation was studied by in-situ shear modulus measurements and modulated differential scanning calorimetry. The results show that high-pressure torsion leads to shear modulus softening and an increase of the nonreversible exothermic enthalpy, indicating a significant structural rejuvenation, while sub-Tg annealing causes shear modulus hardening and a decrease of the nonreversible exothermic enthalpy. The reversible endothermic effect which can reflect the fractional change of supercooled liquid with temperature was found to be almost identical for all samples, and independent of deformation or thermal history. The total heat flow can be well correlated with the shear modulus within the framework of interstitialcy theory. Furthermore, we demonstrate that the structural relaxation below Tg decouples into internal stress relaxation and β-relaxation. In addition, this work indicates that the processes of α-relaxation and β-relaxation in the metallic glass are of similar structural origin but occur on different spatial scales.

Confinement Effects on the Spatially Inhomogeneous Dynamics in Metallic Glass Films.

This work develops the elastically collective nonlinear Langevin equation theory to investigate, for the first time, the glassy dynamics in capped metallic glass thin films. Finite-size effects on the spatial gradient of structural relaxation time and glass transition temperature (Tg) are calculated at different temperatures and vitrification criteria. Molecular dynamics is significantly slowed down near rough solid surfaces, and the dynamics at location far from the interfaces is sped up. In thick films, the mobility gradient normalized by the bulk value obeys the double-exponential form since interference effects between two surfaces are weak. Reducing the film thickness induces a strong dynamic coupling between two surfaces and flattens the relaxation gradient. The normalized gradient of the glass transition temperature is independent of vitrification time scale criterion and can be fitted by a superposition function as the films are not ultrathin. The local fragility is found to remain unchanged with location. This finding suggests that one can use Angell plots of bulk relaxation time and the Tg spatial gradient to characterize glassy dynamics in metallic glass films. Our computational results agree well with experimental data and simulation.

Deformations, relaxation, and broken symmetries in liquids, solids, and glasses: A unified topological field theory.

We combine hydrodynamic and field theoretic methods to develop a general theory of phonons as Goldstone bosons in crystals, glasses, and liquids based on nonaffine displacements and the consequent Goldstone phase relaxation. We relate the conservation, or lack thereof, of specific higher-form currents with properties of the underlying deformation field-nonaffinity-which dictates how molecules move under an applied stress or deformation. In particular, the single-valuedness of the deformation field is associated with conservation of higher-form charges that count the number of topological defects. Our formalism predicts, from first principles, the presence of propagating shear waves above a critical wave vector in liquids, thus giving a formal derivation of the phenomenon in terms of fundamental symmetries. The same picture provides also a theoretical explanation of the corresponding "positive sound dispersion" phenomenon for longitudinal sound. Importantly, accordingly to our theory, the main collective relaxation timescale of a liquid or a glass (known as the α relaxation for the latter) is given by the phase relaxation time, which is not necessarily related to the Maxwell time. Finally, we build a nonequilibrium effective action using the in-in formalism defined on the Schwinger-Keldysh contour, that further supports the emerging picture. In summary, our work suggests that the fundamental difference between solids, fluids, and glasses has to be identified with the associated generalized higher-form global symmetries and their topological structure, and that the Burgers vector for the displacement fields serves as a suitable topological order parameter distinguishing the solid (ordered) phase and the amorphous ones (fluids, glasses).

Evident glass relaxation at room temperature induced by size effect

Probing the relaxation dynamics of glasses at temperatures far below the glass transition remains challenging owing to the extremely slow relaxation characteristic and the lack of appropriate experimental techniques. We utilized a sensitive laser reflection curvature method to probe the slow relaxation dynamics of metallic glassy (MG) films of different thicknesses at room temperature. It was found that the relaxation dynamics of MG films can be dramatically accelerated by the thickness reduction, similar to the role of temperature. We also compared the size-induced relaxation of MG films to the relaxation of MG ribbons at varying temperatures. Similar effects of size and temperature on the relaxation dynamics are revealed. We show that a MG film with a thickness of $\ensuremath{\sim}10$ nm at room temperature has a fast relaxation dynamics equivalent to that of a bulk MG near the glass transition temperature within an observation time scale of 1 s, indicating that the liquidlike behavior in glass can be induced by size reduction. Our observation for MGs, similar to that of polymer glasses reported previously, suggests that the size-induced enhanced relaxation dynamics and glass transition is universal in glassy materials.