Metallic Glass-forming Liquids Research Articles

Viscosity and surface tension of the Zr56.5Ti13.3Ni13.6Cu9.6S7 bulk metallic glass-forming liquid

The viscosity of the Zr56.5Ti13.3Ni13.6Cu9.6S7 bulk glass forming alloy was measured in equilibrium liquid at low and high temperatures. Low temperature measurements were conducted in the vicinity of the glass transition using a thermomechanical analyzer, covering a viscosity range between 109 and 1014 Pa s. The high-temperature experiments were carried out by electromagnetic levitation of a spherical droplet in microgravity during a parabolic flight campaign (TEMPUS), ranging in viscosity from 50 to 800 mPa s. The viscosities were individually modeled using the Vogel–Fulcher–Tammann equation to obtain the fragility parameter D*, which displays a strong liquid behavior of 25.8 and 19.6 for the low and high temperature region, respectively. The Mauro–Yue–Ellison–Gupta–Allan viscosity model was additionally applied, revealing an even more accurate description across the whole temperature range. Next to viscosity, TEMPUS measurements allow the determination of surface tension. With a value of 0.9 N m−1, it is significantly lower than that of other Zr-based metallic glasses without the element sulfur.

Evolution of coupling modes between α and β relaxations in metallic glass-forming liquids revealed by nano-calorimetry

The coupling behavior of α and β relaxations in supercooled liquids (SLs) is a key scientific issue that relates to the essence of glass transition and the modulation of glass properties. Here, we observe the evolution of α and β relaxations in Au50Ag7.5Cu17.5Si25 alloys from glass to SLs by nano calorimetric technique. We find that all the β participates in α relaxation in these metallic glasses (MGs) upon heating. Two typical coupling (or decoupling upon cooling) modes of α and β relaxations in Au-based MG SLs have been discovered, dependent on the degree of coupling between α and β relaxations in glasses. The coupling degree increases during the isothermal annealing process as the energy state of the glass decreases. Above a critical degree the decoupling mode changes from “β splits from α” to “α splits from β”. A survey including metallic glasses, polymer glasses and oxide glasses shows the general existence of the critical degree of coupling in glasses. The differences in local structure feature in glasses with different coupling degree is elucidated by analysis on atomic nonaffine displacements using molecular dynamics simulations. Further our work demonstrates that the plasticity of MGs can be effectively modulated by altering the coupling behavior between α and β relaxation.

An intrinsic connection between the liquid-liquid transition and fragile-to-strong transition in soft magnetic Fe-based metallic glasses: Comparisons with other metallic glasses

There are two significant abnormal transitions observed in metallic glass forming liquids (MGFLs), i.e., liquid-liquid transition (LLT) above liquidus temperature and fragile-to-strong (F-S) transition in supercooled region. In this study, we focus on the correlation between LLT and F-S transition in Fe-based soft magnetic metallic glasses (MGs) for the first time. We find that the more distinct the LLT is, the weaker is the F-S transition, and the smaller is the glass forming ability (GFA). By employing molecular dynamics simulation, we identify that this relationship is due to the inherent correlated evolution trends of crystal-like clusters between the LLT and the F-S transition regions. Moreover, we analyze a general rule regarding the LLT and F-S transition in MGs, along with their composition-dependent peculiarities. This work sheds light on the process of liquid-solid inheritance of different MGs, and deepens the understanding of the liquid dynamics of MGs and their following GFA.

Effect of chemical short-range ordering on thermodynamics, structure, and dynamics of ZrCu-based metallic glass-forming liquids

Chemical-ordering in metallic liquid alloys affects important structural, thermodynamic, and dynamical factors governing the kinetics of the glass formation process and the glass-forming ability. The present study on Zr50Cu50, Zr50Cu45Al5, and Zr50Cu45Ag5 metallic glass-forming liquids reveal that minor addition of Al/Ag in Zr50Cu50 leads to different chemical short-range orders due to the hetero-coordination tendency of Al in Zr50Cu45Al5 and homo-coordination tendency of Ag in Zr50Cu45Ag5. Different chemical short-range ordering causes qualitatively different topological short-range orders in the two ternary alloys. Results of inherent structure energy and excess entropy indicate modification of the potential energy landscape such that the local minima (metabasins) on the landscape of Zr50Cu45Al5 become deeper and less rugged, whereas the metabasins become shallower and more rugged in Zr50Cu45Ag5. Single-particle dynamics investigations clearly demonstrate the effect of difference in the chemical-ordering, topological short-range order, and the potential energy landscape on the atomic diffusion, structural relaxation, and dynamic heterogeneities in the ternary alloys. It signifies that the dynamics of the studied glass-forming alloys is closely linked with the structure and thermodynamics. The study also provides a very useful insight of the correlation between the chemical-ordering and the short-time dynamical features in the studied metallic glass-forming liquids.

Universal basis underlying temperature, pressure and size induced dynamical evolution in metallic glass-forming liquids

The dramatic temperature-dependence of liquids dynamics has attracted considerable scientific interests and efforts in the past decades, but the physics of which remains elusive. In addition to temperature, some other parameters, such as pressure, loading and size, can also tune the liquid dynamics and induce glass transition, which makes the situation more complicated. Here, we performed molecular dynamics simulations for Ni50Zr50 bulk liquid and nanodroplet to study the dynamics evolution in the complex multivariate phase space, especially along the isotherm with the change of pressure or droplet size. It is found that the short-time Debye–Waller factor universally determines the long-time relaxation dynamics no matter how the temperature, pressure or size changes. The basic correlation even holds at the local atomic scale. This finding provides general understanding of the microscopic mechanism of dynamic arrest and dynamic heterogeneity.

Viscosity anomaly of a metallic glass-forming liquid under high pressure

Viscosity, as a critical property closely associated with the glass-forming ability of a liquid, has been extensively studied with varying temperatures. However, its pressure dependence has not been well explored yet due to experimental difficulties. Here, we measured the viscosity of a metallic glass-forming liquid, Zr46Cu37.6Ag8.4Al8, at pressures up to 6.1 GPa above the melting points by falling-sphere viscometry with ultrafast synchrotron x-ray imaging. Overall, the viscosity increases with pressure, while surprisingly, there is an abrupt drop between 3.2 GPa and 3.7 GPa, indicating the possible existence of a pressure-induced liquid-to-liquid transition. Pressure could change the short- and medium-range orders in the multicomponent glass-forming liquid, as suggested by the different crystalline outcomes after cooling to room temperature at high- and low-pressure ranges. Our work extended the viscosity investigation of metallic glass-forming liquids to the high-pressure regime, which will expand our understanding of liquid-liquid transitions and metallic glass formation.

Structural decomposition retarded crystal growth in the undercooled liquid of Zr70Al12.5Fe17.5 metallic glass-forming alloy

The recent attention on crystallization of undercooled glass-forming metallic liquids has been directing to the intriguing viscosity behaviors. The present study discloses that structural decomposition of the grown-out crystalline products plays a part in the crystal growth kinetics. In the supercooled liquid of Zr70Al12.5Fe17.5 metallic glass, the polymorphically crystallizing metastable τ2-Zr6Al2Fe phase decomposes into τ2 + τ2′ (space group:Amm2, a = 6.895 Å, b = 3.368 Å, c = 5.119 Å), and retards crystal growth. The structure decomposition also occurs in the solidified bulk alloys.

Strong-to-fragile transition in a metallic-glass forming supercooled liquid associated with a liquid–liquid transition

Liquid–liquid transitions are present in a variety of substances. However, investigating the liquid–liquid transitions occurring in a supercooled liquid is difficult because of the interference from rapid crystallization. Here, we report a strong-to-fragile transition in a Pd32Ni52P16 metallic glass-forming supercooled liquid associated with a liquid–liquid transition. Since the liquid–liquid transition takes place at temperatures smaller than the crystallization temperature, the liquid viscosity can be acquired by creep experiments conducted at temperatures close to the glass transition temperature without interference from crystallization. The strong-to-fragile transition results in a 37% increase of the fragility index and a 56% elongation after thermal-plastic processing. An investigation on the loss-modulus peaks by a dynamic mechanical analyzer implies that the enhanced thermal plasticity is contributed by both glass transition and strong-to-fragile transition. This work highlights how liquid–liquid transition affects liquid fragility and how it may aid the thermal-plastic processing of metallic glass.

A fractal structural feature related to dynamic crossover in metallic glass-forming liquids.

The dynamic crossover in supercooled liquids initially predicted by model coupling theory has been widely accepted, but its underlying structural origin is still an open issue for glass-forming liquids. By molecular dynamics simulations of binary CuZr liquids, the present work verifies that high pressure could enhance this crossover, facilitating the studies on the structural features at the crossover temperature Tc. We discover that the topological connectivity of icosahedral clusters is responsible for this dynamic crossover, rather than all clusters. Tc is the temperature at which the connectivity degree between these clusters reaches a maximum and the dynamic heterogeneity begins to keep stable. Below Tc, the fractal topological structures appear in the medium-range order scale. The icosahedral clusters with a certain connectivity pattern can be regarded as a fractal structural unit. By employing the established fractal analysis method, the fractal dimension D of the icosahedral network is calculated. Our results indicate that the D value increases monotonically with increasing pressure and the fractal behavior of the icosahedral network is an inherent feature of metallic glasses. We also find similar fractal behavior in clusters with high local five-fold symmetry. Our findings shed light on the origin of a dynamic crossover in the deep supercooled region of metallic glasses and also demonstrate the important role of icosahedral clusters in uncovering the fractal behavior of metallic glass.

Unsupervised machine learning study on structural signature of glass transition in metallic glass-forming liquids

As a liquid is quenched into glassy state, characterizing the glassy order responsible for glass transition in disordered liquid structures is a longstanding challenge. Here, an unsupervised machine learning method, affinity propagation clustering was developed, which is able to automatically classify disordered structures by using purely atomic distances in disordered structures at a given temperature in training set, without any prior input of local symmetry, atomic packing, or dynamical information. Surprisingly, the clustering models successfully identify the liquid- and glass-like atoms in metallic glass-forming liquids and predict their temperature evolution in whole cooling process. This demonstrates that a liquid or glass structure possesses all atomic structure information from high-temperature liquid states to low-temperature glassy states. Moreover, the glassy order formed by glass-like atoms increases with a power-law form followed by a linear one below a crossover point which is quite close to glass transition temperature. Meanwhile, the atomic structures of glassy order percolate in glass transition. These results manifest the structural signature of glass transition. Furthermore, the liquid- and glass-like structural characteristics show excellent correlation with properties in metallic liquids and glasses, such as structural relaxation, shear modulus and dynamic propensity. Our results provide a new machine-learning strategy for characterizing disordered structures and unraveling structure-property relationship in glass-forming systems.

Pressure weakening unusual-caged dynamics of La80Al20 metallic glass-forming liquid

Caged dynamics is the precursor of β-relaxation and is part of the complex relaxation dynamics of metallic glasses. However, limited by the lack of suitable experimental techniques, the pressure dependence of the caged dynamics of glass-forming metallic liquids and its underlying mechanism are still an open question to date. An unusual caged dynamics manifests a sudden drop near 0.1 ps in the partial non-Gaussian parameter of Al atoms in metallic alloy La80Al20 liquid was recently found by molecular dynamics simulations. The present work investigates the caged dynamics of the La80Al20 liquid with strong atomic interactions under different pressures again by molecular dynamics simulations. It is found that the dominant polyhedra are transformed from the stable icosahedral-like polyhedra to the unstable ones that are compatible with crystal symmetry, resulting in the promotion of the rearrangement of atoms. These changes in turn cause the central Al atoms to be less hindered by the surrounding atoms, enhancing the cage-breaking motion and weakening the unusual caged dynamics. In addition, the applied pressure not only increases the diversity of vibrational frequencies but also weakens the difference in atomic vibrational amplitudes, leading to the weakening of the unusual caged dynamics. These findings provide new insights into the caged dynamics under pressure from the perspective of microstructure and vibrational properties.

Structural Changes in Metallic Glass-Forming Liquids on Cooling and Subsequent Vitrification in Relationship with Their Properties.

The present review is related to the studies of structural changes observed in metallic glass-forming liquids on cooling and subsequent vitrification in terms of radial distribution function and its analogues. These structural changes are discussed in relationship with liquid’s properties, especially the relaxation time and viscosity. These changes are found to be directly responsible for liquid fragility: deviation of the temperature dependence of viscosity of a supercooled liquid from the Arrhenius equation through modification of the activation energy for viscous flow. Further studies of this phenomenon are necessary to provide direct mathematical correlation between the atomic structure and properties.

Boosting Oxygen-Evolving Activity via Atom-Stepped Interfaces Architected with Kinetic Frustration.

A highly active interface is extremely critical for the catalytic efficiency of an electrocatalyst; however, facilely tailoring its atomic packing characteristics remains challenging. Herein, a simple yet effective strategy is reported to obtain copious high-energy atomic steps at the interface via controlling the solidification behavior of glass-forming metallic liquids. By adjusting the chemical composition and cooling rate, highly faceted FeNi3 nanocrystals are insitu formed in an FeNiB metallic glass (MG) matrix, leading to the creation of order/disorder interfaces. Benefiting from the catalytically active and stable atomic steps at the jagged interfaces, the resultant free-standing FeNi3 nanocrystal/MG composite exhibits a low oxygen-evolving overpotential of 214mV at 10mAcm-2 , a small Tafel slope of 32.4mVdec-1 , and good stability in alkaline media, outperforming most state-of-the-art catalysts. This approach is based on the manipulation of nucleation and crystal growth of the solid-solution nanophases (e.g., FeNi3 ) in glass-forming liquids, so that the highly stepped interface architecture can be obtained due to the kinetic frustration effect in MGs upon undercooling. It is envisaged that the atomic-level stepped interface engineering via the physical metallurgy method can be easily extended to other MG systems, providing a new and generic paradigm for designing efficient yet cost-effective electrocatalysts.

Shear-accelerated crystallization of glass-forming metallic liquids in high-pressure die casting

• Solidification behavior of Zr 55 Cu 30 Ni 5 Al 10 glass forming liquid under various flow rates was investigated. • Flow-induced crystallization was observed in glass forming liquid as injection rate exceeds 1.1 m/s. • The accelerated crystallization behavior is mainly ascribed to the abrupt perturbation at the end filling stage. • Flow related effect on glass forming ability must be considered in bulk metallic glasses produced by high pressure die casting. As one of the most important forming technologies for industrial bulk metallic glass (BMG) parts with complex shapes, high-pressure die casting (HPDC) can fill a die cavity with a glass-forming metallic liquid in milliseconds. However, to our knowledge, the correlation between flow and crystallization behavior in the HPDC process has never been established. In this study, we report on the solidification behavior of Zr 55 Cu 30 Ni 5 Al 10 glass forming liquid under various flow rates. Surprisingly, the resulting alloys display a decreasing content of amorphous phase with increase of flow rate, i.e. increase of cooling rate, suggesting that crystallization kinetics of glass-forming metallic liquids in the HPDC process is strongly dependent on the flow field. Analysis reveals that the accelerated crystallization behavior is mainly ascribed to the rapid increase in viscosity with a decreasing temperature as well as to the huge shear effect in the glass-forming liquid at the end stage of the filling process when the temperature is close to the glass-transition point; this results in a transition from diffusion- to advection-dominated transport. The current investigation suggests that flow-related crystallization must be considered to assess the intrinsic glass-forming ability of BMGs produced via HPDC. The obtained results will not only improve the understanding of crystallization dynamics but also promote the high-quality production and large-scale application of BMG parts.

Understanding the unusual-caged dynamics from the microstructure and interatomic interactions in binary metallic glass-forming liquids

The caged dynamics appears at time shorter than the β-relaxation but longer than the boson peak. Due to the limitations of experimental conditions, the mechanism of caged dynamics is not well studied in metallic glasses. We study a model La65Al35 glass-forming liquid with strong atomic interactions that presents an unusual caged dynamics, and the La65Ni35 GF liquid is also studied to clarify the underlying mechanisms of caged dynamics. There is a sudden drop near 0.1 ps in the partial non-Gaussian parameter of Al atoms, reflecting the development of caging of the Al atoms with time. A similar feature is also found in Ni80P20, Sm80Al20, Pd80Si20, and Y80Mg20 metallic GF liquids. The chemical order, Voronoi polyhedra, and covalent-like bonds are all related to the cage-breaking behavior of the central atoms, in turn regulating the unusual caged dynamics. These findings shed light on the complex relaxation dynamics of GF liquids.

High-precision nuclear magnetic resonance probe suitable for in situ studies of high-temperature metallic melts

High-temperature nuclear magnetic resonance (NMR) has proven to be very useful for detecting the temperature-induced structural evolution and dynamics in melts. However, the sensitivity and precision of high-temperature NMR probes are limited. Here we report a sensitive and stable high-temperature NMR probe based on laser-heating, suitable for in situ studies of metallic melts, which can work stably at the temperature of up to 2000 K. In our design, a well-designed optical path and the use of a water-cooled copper radio-frequency (RF) coil significantly optimize the signal-to-noise ratio (S/NR) at high temperatures. Additionally, a precise temperature controlling system with an error of less than ± 1 K has been designed. After temperature calibration, the temperature measurement error is controlled within ± 2 K. As a performance testing, 27Al NMR spectra are measured in Zr-based metallic glass-forming liquid in situ. Results show that the S/NR reaches 45 within 90 s even when the sample’s temperature is up to 1500 K and that the isothermal signal drift is better than 0.001 ppm per hour. This high-temperature NMR probe can be used to clarify some highly debated issues about metallic liquids, such as glass transition and liquid–liquid transition.

Comparative Study of the Measured and Two Ideal Glass Transition Temperatures Corresponding to the Limit of Infinitely Slow Heating Rate and the Infinite Barriers with Respect to Flow in Metallic Glasses and Glass-Forming Liquids

Comparative Study of the Measured and Two Ideal Glass Transition Temperatures Corresponding to the Limit of Infinitely Slow Heating Rate and the Infinite Barriers with Respect to Flow in Metallic Glasses and Glass-Forming Liquids

Pressure Effects in the Unusual-Caged Dynamics of La80al20 Metallic Glass-Forming Liquid

Pressure Effects in the Unusual-Caged Dynamics of La80al20 Metallic Glass-Forming Liquid

Common structural basis of short- and long-time relaxation dynamics in metallic glass-forming liquids

Classical molecular dynamics simulations were performed for five model metallic glass-forming liquids to investigate the structure correlation with both short-time β and long-time α relaxation dynamics. It is found that Debye-Waller factor characterizing the short-time β relaxation decreases with increasing five-fold local symmetry in atomic clusters, following a power-law behavior. It is also found that the equation of Debye-Waller factor and α-relaxation time, which is widely studied in polymer systems, is applicable in metallic glass-forming systems as well. Furthermore, a new equation is derived for the five-fold local symmetry and α-relaxation time, which describes the simulated data very well. These findings indicate that there exist a common structural basis for both the short-time β-relaxation and the long-time α-relaxation dynamics.

Changes in the crystallization sequence upon sulfur addition in the Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glass-forming liquid revealed by in situ high-energy x-ray diffraction

Bulk metallic glasses (BMGs) surpass the strength of steels and possess the elasticity and formability of polymers. The key to obtain these properties is to conserve the amorphous structure of a metallic melt and avoid crystallization during processing. In this work, a change in the crystallization sequence in the widely used BMG ${\mathrm{Zr}}_{52.5}{\mathrm{Cu}}_{17.9}{\mathrm{Ni}}_{14.6}{\mathrm{Al}}_{10}{\mathrm{Ti}}_{5}$ (Vit105) upon the addition of sulfur (${\mathrm{Zr}}_{51.45}{\mathrm{Cu}}_{17.54}{\mathrm{Ni}}_{14.31}{\mathrm{Al}}_{9.8}{\mathrm{Ti}}_{4.9}{\mathrm{S}}_{2}$; Vit105 ${\mathrm{S}}_{2}$) is revealed by in situ high-energy x-ray diffraction, both upon heating from the glassy state and upon cooling from the liquid state during electrostatic levitation. This methodology proves to be a powerful tool to elucidate the complete crystallization behavior of complex BMG-forming liquids. The experiments show that the addition of sulfur changes the crystallization sequence and phases in a different manner upon cooling from the liquid state than upon heating from the glassy state. The thermal stability at low temperatures upon heating is increased, as the supercooled liquid region is extended from 60 to 77 K and the glass transition temperature increases from 671 to 692 K. However, the thermal stability is decreased upon cooling, causing a reduced glass-forming ability.