Properties Of Metallic Glasses Research Articles

Ellipsometric analysis of isothermally devitrified metallic glasses

Effects of devitrification in metallic glasses are of particular interest for their utilization in various applications as the phase transformation from amorphous to crystalline state is known to significantly change their properties. In this work, we study the effect of devitrification on the optical properties of metallic glasses using the spectroscopic ellipsometry technique. Ellipsometry measurements on isothermally crystallized samples at controlled temperatures between the glass transition temperature and the crystallization temperature revealed characteristic dependence of the complex index of refraction on the controlled devitrification temperature, suggesting an effective optical approach which can be prospectively used for characterization of structural changes during devitrification. The crystallinity of devitrified samples was verified using a combination of differential scanning calorimetry and X-ray diffraction measurements.

Surface functionalization of Zr-based metallic glass by direct nanosecond laser texturing

The functional properties of metallic glasses (MGs) can be enhanced by introducing special micro/nano-structures on their surface. In this study, a nanosecond pulsed laser was used to texture micro-convex array structures with different pitches (P) on a Zr-based MG surface to enrich its engineering applications. The reflection characteristics and wettability of polished and textured surfaces were compared. The experimental results showed that unlike the bright spot reflected from the polished surface, the light reflected from the textured surface would induce a well-defined diffraction pattern. In addition, the wettability of the surfaces covered with micro-convex array structures was also different from that of the polished surface. That is, without post-processing, the textured array structures would promote hydrophilicity; while after exposing in the air for 100 days or fluoroalkylsilane modification, the textured array structures facilitated hydrophobicity.

Tailoring microstructure of metallic glass for delocalized plasticity by pressure annealing: Forward and inverse studies

As an extreme processing condition, pressure annealing has a great potential in tailoring the microstructure of metallic materials to improve their mechanical properties. Determining the process-microstructure-mechanical properties relationship with high-pressure and high-temperature is thus of scientific importance. Herein, we propose an approach of pressure annealing in tuning the structure and mechanical behavior of a prototype of Fe80P20 metallic glass (MG) through a combination of experiments, molecular dynamics (MD) simulations, and machine learning. The experimental results show that pressure annealing can induce structural rejuvenation and more distributed deformation in Fe80P20 MG. Inspired by this, forward studies from experiments to MD simulations are carried out to systematically investigate the effects of pressure annealing on the mechanical properties and microstructure of the Fe80P20 MG for a broad pressure and temperature range, followed by inverse studies from machine learning to experimental verification that enable us to capture the hiding structural feature affecting the mechanical behavior of pressure-annealed Fe80P20 MG. We demonstrate that pressure annealing can endow a MG having a transition of deformation mode from localized to delocalized, which is predominantly governed by pressure-annealing-induced variations in an atomic packing structure. Our work proposes a promising route for fine-tuning the mechanical properties of MGs, and provides insights into the current understanding of the relationship between the microstructure and mechanical behaviors of Fe80P20 MG with pressure annealing.

Linear magnetization dependence and large intrinsic anomalous Hall effect in Fe78Si9B13 metallic glasses

The origin of anomalous Hall effect (AHE) in ferromagnetic metallic glasses (MGs) is not yet understood completely. Here, the AHE is explored in Fe78Si9B13 MGs. We find the behavior of resistivity at low temperature seems to be more likely due to structure effect rather than Kondo-type effect. More importantly, we firstly find the primitive experiment anomalous Hall conductivity ({\sigma}AH) without separation of extrinsic contribution has a linear magnetization (Mz) dependence when temperature is changing, which is another feature of intrinsic mechanism and indicates intrinsic contribution is dominated. Furthermore, the {\sigma}AH normalized by Mz is independent of longitudinal conductivity ({\sigma}xx), which shows the characteristic of dissipationless intrinsic mechanism. We suggest the intrinsic contribution can be understood from the density of Berry curvature integrated over occupied energies proposed for aperiodic materials recently, and the linear magnetization dependence can be understood qualitatively from the fluctuations of spin orientation and the proportional relationship between Berry curvature and magnetization. Moreover, based on the recent theory report of topological amorphous metals, we make a prediction that the large intrinsic {\sigma}AH (616 S/cm) in Fe78Si9B13 MGs implies some topological properties of MGs waiting for further discovery.

Characteristic of dynamic mechanical relaxation processes in Cu46Zr46Al8 and La43.4Ce18.6Ni24Al14 metallic glasses

Dynamic mechanical relaxation processes are very important to understand physical and mechanical properties of metallic glasses. In the current work, dynamic mechanical behaviors of La43.6Ce18.4Ni24Al and Cu46Zr46Al8 metallic glasses were investigated by mechanical spectroscopy. Unlike Cu46Zr46Al8 metallic glass, La43.6Ce18.4Ni24Al14 glassy system shows an evident slow β relaxation process. In addition, physical aging below the glass transition temperature Tg induces a reduction of intensity of the β relaxation. Evolution of the concentration of “defects” of metallic glasses was analyzed in the framework of Interstitialcy theory. Our research provides a new insight on understanding of the correlation between the structural heterogeneity and β relaxation of metallic glasses.

Chemical heterogeneous structure and internal record of deformation behavior in Cu-Fe-Zr metallic glasses

Although chemical structural heterogeneities were induced into metallic glasses (MGs) to improve their ductility, the nature of the influence of the heterogeneous structure on their deformation behavior is still unclear. Here, by using microalloying elements to tailor the microstructure in Cu-Fe-Zr MGs, the formation of heterogeneous structure and the correlation between the heterogeneous structure and the deformation behavior are discussed. The results show that a honeycomb-like heterogeneous structure is formed in the (Cu0.5Fe0.5)40Zr59X1 (XNb and Ta) alloys. From a viewpoint of dynamic, the nature of the microalloying effect on the microstructure has been analysed. The deformation behavior of (Cu0.5Fe0.5)40Zr59X1 MGs with a high population of nanoscale glassy particles (NGPs) is investigated by nanoindentation and bending test. These glassy particles play an interesting role in the internal record of the local structure evolution. It was found that NGPs contiguous to shear bands (SBs) coarsen by Ostwald ripening. However, NGPs within SB would dissolve due to direct mechanical shearing and mixing. It indicates that the volume of shear transformation zone decreases obviously in the heterogeneous MGs due to the high fraction of interfaces. This work is of significance in understanding the relationship between structure and property of MGs.

Metallic Nanoglasses with Promoted β-Relaxation and Tensile Plasticity.

The secondary (β) relaxation is an intrinsic feature of glassy systems and is crucial for the mechanical properties of metallic glasses. However, it remains puzzling what structural features control the β-relaxation fundamentally. Here, we use the recently developed nanoglasses exhibiting well-defined structural features at the nanometer scale to interrogate such structure-dynamics relations. We show that an electrodeposited Ni77.5P22.5 nanoglass exhibits promoted β-relaxation and enhanced microscale tensile plasticity over the most rapidly melt-quenched metallic glass with the same composition. Structurally, the β-relaxation is sensitive to the interfacial regions among grains in the nanoglasses. Our results reveal a clear correlation between the amorphous nanostructures and the β-relaxation. It seems that the nanostructuring represents a novel route to obtain high-energy glassy states, that is, the inverse problem of the ultrastable glass.

Nanoglass and Nanocrystallization Reactions in Metallic Glasses

Strategies to change the properties of metallic glass by controlling the crystallization and the glass transition behavior are essential in promoting the application of these materials. Aside from changing the composition approaches to stabilize the glass and frustrate the nucleation and growth of crystals, new strategies at a fixed glass composition are of special interest. In this review, some recent work is summarized on new strategies to tune the properties of metallic glasses without changing composition. First, the nanocrystallization strategy is introduced that is based on the nanocrystallized microstructures such as those that develop in marginal Al-based metallic glasses. The heterogeneous and transient nucleation effects in the nanocrystallization reactions in Al-based metallic glasses are systematically investigated and can be assessed by the determination of delay time based on Flash DSC measurements. These results provide a basis to understand the strong effect of minor alloying additions on the onset of primary Al nanocrystallization and to design the novel Al-based composites with improved properties. Secondly, by an optimal annealing treatment, a liquid-cooled Au-based metallic glass can achieve very high kinetic stability to yield a large increase in glass transition temperature of 28 K and this is 3-5 times larger than the increase usually reported. The measured enthalpy decrease is about 50% of the difference between the as-cooled glass and the equilibrium crystalline state and reaches the extrapolated enthalpy of the supercooled liquid. Finally, the nano-glass strategy makes an Au-based nanoglass show ultrastable kinetic characters at low heating rate (e.g., 300 K/s) compared to a melt-spun ribbon, which is attributed to the kinetic constraint effect of nanoglobular interfaces. These results indicate that the nanoglass microstructure can act to increase metallic glass stability and provide another mechanism for the synthesis of ultrastable glass. These developments open new opportunities to improve the stability and properties and largely increase the application potentials of metallic glasses.

Acoustic properties of metallic glasses at low temperatures: Tunneling systems and their dephasing

The low temperature acoustic properties of bulk metallic glasses measured over a broad range of frequencies rigorously test the predictions of the standard tunneling model. The strength of these experiments and their analyses is mainly based on the interaction of the tunneling states with conduction electrons or quasiparticles in the superconducting state. A new series of experiments at kHz and GHz frequencies on the same sample material essentially confirms previous measurements and their discrepancies with theoretical predictions. These discrepancies can be lifted by considering more correctly the line widths of the dominating two-level atomic-tunneling systems. In fact, dephasing caused or mediated by interaction with conduction electrons may lead to particularly large line widths and destroy the tunneling sytems' two-level character in the normal conducting state.

Effect of Raw Material Purity on Structure and Properties of Metallic Glasses

Zirconium base metallic glasses [Zr0.73(Cu0.59Ni0.41)0.27]87Al13 was fabricated by industrial zirconium with low purity and high purity zirconium according to different quality ratios in order to study the effect of raw material purity on the structure and properties of metallic glasses. The results showed that the complete metallic glasses was failed to be fabricate with low purity zirconium. And the compression process was typical brittle fracture with low compressive strength and without plastic strain. The glasses forming ability of low purity zirconium metallic glass with different purity was significantly improved after the addition of yttrium element. The compression experiments showed that the compressive strength and plasticity of metallic glasses were improved, and the microhardness was also increased. It indicates that yttrium element can eliminate the adverse effect of impurity in low purity zirconium on the glasses forming ability of the alloy and improve the structural properties of the metallic glasses.

Decoupling between calorimetric and dynamical glass transitions in high-entropy metallic glasses

Glass transition is one of the unresolved critical issues in solid-state physics and materials science, during which a viscous liquid is frozen into a solid or structurally arrested state. On account of the uniform arrested mechanism, the calorimetric glass transition temperature (Tg) always follows the same trend as the dynamical glass transition (or α-relaxation) temperature (Tα) determined by dynamic mechanical analysis (DMA). Here, we explored the correlations between the calorimetric and dynamical glass transitions of three prototypical high-entropy metallic glasses (HEMGs) systems. We found that the HEMGs present a depressed dynamical glass transition phenomenon, i.e., HEMGs with moderate calorimetric Tg represent the highest Tα and the maximum activation energy of α-relaxation. These decoupled glass transitions from thermal and mechanical measurements reveal the effect of high configurational entropy on the structure and dynamics of supercooled liquids and metallic glasses, which are associated with sluggish diffusion and decreased dynamic and spatial heterogeneities from high mixing entropy. The results have important implications in understanding the entropy effect on the structure and properties of metallic glasses for designing new materials with plenteous physical and mechanical performances.

Correlations between the hierarchical spatial heterogeneity and the mechanical properties of metallic glasses

Understanding the spatial heterogeneity originated from the inherent atomic packing mode in glassy solids is one of the central problems in condensed-matter physics and materials science. Here, based on Fourier analysis, we establish an analysis protocol to measure the spatial heterogeneity of metallic glasses quantitatively. Our method reveals an interesting hierarchy of the spatial heterogeneity, ranging from atomic scale to nanoscale, in metallic glasses inherited from the thermal processes. The trends of the spatial heterogeneity change under mechanical loadings provide valuable information about the onset of the shear instability. More importantly, a positive correlation between the initial nanoscale heterogeneity and the material ductility is found that is consistent with the previously reports. The analysis protocol proposed here provides a new way to explore the structure-property relationship for disordered matters.

Relation of the fragility and heat capacity jump in the supercooled liquid region with the shear modulus relaxation in metallic glasses

Fragility constitutes a major parameter of supercooled liquids. The phenomenological definition of this quantity is related to the rate of a change of the shear viscosity η at the glass transition temperature. Although a large number of correlations of the fragility with different properties of metallic glasses were reported, an adequate understanding of its physical nature is still lacking. Attempting to uncover this nature, we performed the calculation of the fragility within the framework of the interstitialcy theory (IT) combined with the elastic shoving model. We derived an analytical expression for the fragility, which shows its relation with the high-frequency shear modulus G in the supercooled liquid state. To verify this result, specially designed measurements of η and G were performed on seven Zr-, Cu- and Pd-based metallic glasses. It was found that the fragility calculated from shear modulus relaxation data is in excellent agreement with the fragility derived directly from shear viscosity measurements. We also calculated the heat capacity jump ΔC sql at the glass transition and showed that it is related to the fragility and, consequently, to shear modulus relaxation. The ΔC sql-value thus derived is in a good agreement with experimental data. It is concluded that the fragility and heat capacity jump in the supercooled liquid state can be determined by the evolution of the system of interstitial-type defects frozen-in from the melt upon glass production, as suggested by the IT. This connection is mediated by the high-frequency shear modulus.

Atomistic investigation on the mechanical properties of 3D nanoporous metallic glasses under uniaxial tension and compression

Nanoporous metallic glasses (NPMGs) have a combination of superior properties of metallic glasses and porous structures. Comprehending the inherent deformation and failure mechanisms of NPMGs subjected to complex loading conditions is of great importance to transferring it from scientific research to realistic multifunctional applications, as well as optimize the bottom-up design of NPMGs working in extreme conditions. However, deficiencies in state-of-the-art positioning characterization methods and the microstructure complexity remain tremendous obstacles for the in-situ investigation of deformation processes completely based on real experiments. In this work, molecular dynamics simulations of tensile and compressive tests of 3D NPMGs with diamond and gyroid structures are presented to investigate the mechanical behaviors, as well as deformation processes at the atomic level. Our results suggest that the 3D NPMGs have excellent properties such as lightweight, high strength, and enhanced ductility, which is distinct from bulk metallic glasses lacking global-plasticity. The mechanical behaviors of NPMGs strongly depend on the relative density and ligament size. A tension-compression asymmetry is observed due to the non-negligible surface effects in NPMGs. The influence of surface stress on the mechanical properties becomes slighter with the increment of relative density. This work reveals an atomic-level understanding of the inherent deformation modes of NPMGs, promoting the multifunctional applications of metallic glasses-based materials.Subject Areas: material science, computational material

Atomistic modelling of thermal-cycling rejuvenation in metallic glasses

Cycling of a metallic glass between ambient and cryogenic temperatures can induce higher-energy states characteristic of glass formation on faster cooling. This rejuvenation, unexpected because it occurs at small macroscopic strains and well below the temperatures of thermally induced structural change, is important, for example, in improving plasticity. Molecular-dynamics simulations elucidate the mechanisms by which thermal cycling can induce relaxation (reaching lower energy) as well as rejuvenation. Thermal cycling, over tens of cycles, drives local atomic rearrangements progressively erasing the initial glass structure. This arises mainly from the heating stage in each thermal cycle, linked to the intrinsic structural heterogeneity in metallic glasses. Although, in particular, the timescales in MD simulations are shorter than in physical experiments, the present simulations reproduce many physically observed effects, suggesting that they may be useful in optimizing thermal cycling for tuning the properties of metallic glasses and glasses in general.

Revealing the structural heterogeneity of metallic glass: Mechanical spectroscopy and nanoindentation experiments

Microstructural heterogeneity is an important issue in understanding the mechanical and physical properties of metallic glasses (MGs). Theoretically, physical aging below the glass transition temperature relax the MGs systems to a lower potential energy state on the potential landscape (PEL) while the cold rolling rejuvenates MGs to a higher potential energy state. In the current work, we systemically turned the structural heterogeneity through dynamic mechanical relaxation and rejuvenation. Correlations among the structural heterogeneity, internal friction, and shear transformation zones (STZs) of the model alloy was connected. Based on the cooperative shear model and statistical analysis, the scale variation of the STZs was revealed. This study demonstrated that the spatial structural heterogeneity can be enhanced by severe plastic deformation which can reduce the energy barrier for STZs activation. And we proposed the barriers decrease and more nucleation sites of STZs from physical aging to rejuvenation, which may be potential mechanism for improving the plasticity in MGs.

From brittle to ductile transition: The influence of oxygen on mechanical properties of metallic glasses

Metallic glass is a brittle solid macroscopically but has tremendous ductility in nano and mesoscopic scales. Oxygen is generally considered to be the major culprit in causing the brittleness by inducing crystallization. Since oxygen is omnipresent in the making and applications of metallic glasses, how to avoid, and even take advantage of oxygen, becomes materials scientists’ wild dream. Here we demonstrate using atomistic simulation that the brittle solid can be turned ductile in a model Al-based metallic glass with oxygen addition. There are two major underlying mechanisms found here, one is to keep the oxides in small size and the other is to preserve the free volumes in the surroundings of the oxide clusters. The relatively loosely packed neighboring regions of the nanosized oxide clusters make the glass softer and thereby improves deformability and thus ductility. The finding challenges experimentalists to explore and discover new class of glasses that are not only oxygen tolerant but beneficial in mechanical properties.

Pressure-induced spin crossover in a Fe78Si9B13 metallic glass

The pressure effect on structures and properties of a Fe78Si9B13 metallic glass was investigated by in situ high-pressure synchrotron Fe Kβ x-ray emission spectroscopy and x-ray diffraction, and electrical resistivity measurements up to ∼51 GPa. The study reveals a reversible and continuous pressure-induced high- to low-spin crossover of Fe atoms in an amorphous structure. The changes of the local spin moment can be scaled to match its average atomic distance shrinkage very well during compression. The crossover of electronic spin states in the Fe78Si9B13 metallic glass resembles that of typical crystalline Fe-bearing materials but without a sharp atomic volume collapse and an abrupt electrical resistivity jump. These findings could help guide applications of Fe-based metallic glasses as a soft ferromagnetic material at extreme conditions and also improve our understanding of magnetism and coupling of its changes with disordered atomic structures and other properties in metallic glasses.

Visco-elasticity and mechanical relaxation behavior in La-based metallic glasses

Dynamic mechanical relaxation process is one of the important issues to understand mechanical/physical properties of metallic glasses. In the current research, dynamic mechanical relaxation behavior of La62Al14(Cu5/6Ag1/6)20(Ni1/2Co1/2)4 and (La0.7Ce0.3)65Al10Co25 bulk metallic glasses were investigated by mechanical spectroscopy. Unlike the typical Zr- or Cu-based metallic glasses, (La0.7Ce0.3)65Al10Co25 metallic glass shows an evident β relaxation process. On the other hand, La62Al14(Cu5/6Ag1/6)20(Ni1/2Co1/2)4 metallic glass presents a “shoulder” relaxation process. Physical aging below the glass transition temperature Tg induces a decrease of the concentration of “defects”, which corresponds to a reduction of the intensity of the β relaxation. During aging process, the amplitude of β relaxation (△E") decreases, while the relaxation time (τβ) increases. In organic glasses, it was reported that the changes of In(τβ) and In(△Emax) are linearly correlated with In(τβ)=b-a In(△E"max), this correlation has also been found in metallic glass. This behavior is discussed in the framework of the asymmetric double well potential (ADWP) model, and U and △ are used to characterize ADWP. It is suggested that during the aging process, the U/△ ratio remains basically unchanged, which is close to the coefficient describing the linear correlation between In(τβ) and In(△Emax) (U/△~a).

Unveiling correlation between α2 relaxation and yielding behavior in metallic glasses

Relaxation processes usually influence the mechanical properties of glassy materials. Recently, a so-called ${\ensuremath{\alpha}}_{2}$ relaxation has been identified in metallic glasses, caused by the mobility decoupling between different constituting atoms. It locates between the primary ($\ensuremath{\alpha}$) relaxation and the secondary ($\ensuremath{\beta}$) relaxation and behaves as an additional $\ensuremath{\alpha}$ relaxation. In this paper, we show that ${\ensuremath{\alpha}}_{2}$ relaxation influences the yielding behaviors of a model ${\mathrm{Al}}_{90}{\mathrm{Sm}}_{10}$ metallic glass. In particular, the transition from the stress overshoot to nonovershoot yielding and ${\ensuremath{\alpha}}_{2}$ relaxation follow the same time-temperature relation and microscopic origin. Our results suggest that ${\ensuremath{\alpha}}_{2}$ relaxation provides an additional way to control the mechanical properties of metallic glasses.