Metallic Glass-forming Alloys Research Articles

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.

Simulation of phase evolution in a Zr-based glass forming alloy during multiple laser remelting

Additive manufacturing by laser-based powder bed fusion is a promising technique for bulk metallic glass production. But, reheating by deposition of subsequent layers may cause local crystallisation of the alloy. To investigate the crystalline phase evolution during laser scanning of a Zr-based metallic glass-forming alloy, a simulation strategy based on the finite element method and the classical nucleation theory has been developed and compared with experimental results from multiple laser remelting of a single-track. Multiple laser remelting of a single-track demonstrates the crystallisation behaviour by the influence of thermal history in the reheated material. Scanning electron microscopy and transmission electron microscopy reveals the crystalline phase evolution in the heat affected zone after each laser scan. A trend can be observed where repeated remelting results in an increased crystalline volume fraction with larger crystals in the heat affected zone, both in simulation and experiment. A gradient of cluster number density and mean radius can also be predicted by the model, with good correlation to the experiments. Prediction of crystallisation, as presented in this work, can be a useful tool to aid the development of process parameters during additive manufacturing for bulk metallic glass formation.

Yttrium Enhanced Glass-Forming Ability of Zr-Based Metallic Glasses

Thermodynamic behavior of Zr56-xCo28Al16Yx (0, 2, 7, 10) bulk metallic glass-forming alloys has been studied using an analytical approach where some of the key thermodynamic quantities such as ΔH, ΔS and ΔG has been estimated using a hyperbolic temperature dependence of specific heat difference ΔCp in the supercooled liquid region. The study is focused on understanding the effect of Yttrium-doping on the thermodynamics of the alloys in the supercooled region and on the glass-forming ability of these alloys. The analytical approach has been found to give estimates of ΔG in a wide supercooled liquid region in excellent agreement with the experimental results. Estimated ΔG values are found to be minimum for Y concentration of 7 and 10% which is consistent with the observed high GFA for these compositions. Fundamental elemental properties such as atomic size, electronegativity, the heat of mixing have been found to play an important role in governing the thermodynamics of the alloys in the supercooled liquid region.

Effect of Al addition on structure and dynamics of Zr-Cu-Al glass-forming alloy

Classical molecular dynamics study of metallic glass-forming alloys, Zr36Cu64 and Zr47Cu46Al7, is carried out to acquire atomic level understanding of the microalloying effect of Al atoms on the structure and dynamics of the alloy. The results indicate that in comparison to hard sphere-like atomic packing in the binary alloy, microalloying of Al brings in a fundamental modification in the atomic packing due to soft sphere-like Cu-Al bonding due to chemical short-range ordering (CSRO). In the ternary alloy, CSRO is found to homogenize the topological packing of the icosahedra (<0,0,12,0 > ). Microalloying also impacts the single particle dynamics at the timescale of β-relaxation and could have important implications on the mechanical properties of the glasses prepared from this alloy.

Observation of an apparent first-order glass transition in ultrafragile Pt–Cu–P bulk metallic glasses

An experimental study of the configurational thermodynamics for a series of near-eutectic Pt80-x Cu x P20 bulk metallic glass-forming alloys is reported where 14 < x < 27. The undercooled liquid alloys exhibit very high fragility that increases as x decreases, resulting in an increasingly sharp glass transition. With decreasing x, the extrapolated Kauzmann temperature of the liquid, T K , becomes indistinguishable from the conventionally defined glass transition temperature, T g For x < 17, the observed liquid configurational enthalpy vs. T displays a marked discontinuous drop or latent heat at a well-defined freezing temperature, T gm The entropy drop for this first-order liquid/glass transition is approximately two-thirds of the entropy of fusion of the crystallized eutectic alloy. Below T gm , the configurational entropy of the frozen glass continues to fall rapidly, approaching that of the crystallized eutectic solid in the low T limit. The so-called Kauzmann paradox, with negative liquid entropy (vs. the crystalline state), is averted and the liquid configurational entropy appears to comply with the third law of thermodynamics. Despite their ultrafragile character, the liquids at x = 14 and 16 are bulk glass formers, yielding fully glassy rods up to 2- and 3-mm diameter on water quenching in thin-wall silica tubes. The low Cu content alloys are definitive examples of glasses that exhibit first-order melting.

Thermodynamics of polymorphism in a bulk metallic glass: Heat capacity measurements by fast differential scanning calorimetry

The Au-based bulk metallic glass-forming alloy Au70Cu5.5Ag7.5Si17 is the first atomic system in which monotropic polymorphism has been experimentally found. In this study, strategies for measuring thermodynamic quantities such as heat capacity, transformation enthalpy and entropy, and Gibbs free energy for stable and metastable phases are evaluated based on this system. The transformation enthalpies between phases are determined via differential scanning calorimetry (DSC); the corresponding heat capacities are measured via stochastic temperature-modulated DSC (TOPEM); and the equilibrium melting temperatures of metastable phases, only detectable at high rates, are determined via fast DSC (FDSC). Whereas the slow heating rate of conventional DSC limits the characterization of metastable phases, the combination of both DSC and FDSC allows for their detailed heat-capacity determination. Furthermore, various approximation functions that have previously been used to determine the temperature dependence of the thermodynamic driving force for nucleation and crystallization are compared with the experimental data.

Long-Range Mass Transport during Structural Transitions in Metallic Glass-Forming Melts

We investigate the structure and dynamics of the bulk metallic glass-forming alloys Zr_{41.2}Ti_{13.8}Cu_{12.5}Ni_{10}Be_{22.5} and Zr_{58.5}Cu_{15.6}Ni_{12.8}Al_{10.3}Nb_{2.8}. Combining insitu synchrotron x-ray diffraction and quasielastic neutron scattering with electrostatic levitation, we directly observe an abrupt change in the temperature dependence of the first structure factor maximum of these melts. We find that the kinetics of this liquid-liquid transition during cooling are on the order of tens of seconds, whereas its onset temperature depends only weakly on the applied cooling rate. Such slow transition kinetics require long-range mass transport, which is incompatible with a transition mechanism involving only local structural changes as in oxides or molecular liquids.

Assessing continuous casting of precious bulk metallic glasses

This study describes investigations of continuous casting for the bulk metallic glass-forming alloys Pd43Ni10Cu27P20 and Pt57.3Cu14.6Ni5.3P22.8, respectively. Continuous casting of the Pd-based alloy readily produced fully amorphous rods of 10 mm diameter and >500 mm length. In contrast, the Pt-based alloy always underwent crystallization during the casting process, even at smaller rod diameters down to 2 mm. In search of the reason for this difference, we simulated the process using ProCAST. Via adapting the heat transfer coefficients for all the relevant interfaces of the continuous casting setup we obtained good agreement between the experimental temperature data and the simulations. The calculations revealed that the maximum cooling rates achievable with this industrial setup ranged from 15 K/s to 17 K/s. This is well above the critical cooling rate for glass formation of the Pd-based alloy, but below that of the Pt-based alloy, as inferred from literature data and corroborated by fast differential scanning calorimetry. These findings illustrate how detailed casting simulations can predict the feasibility of semi-industrial bulk metallic glass production techniques.

Indications for a fragile-to-strong transition in the high- and low-temperature viscosity of the Fe43Cr16Mo16C15B10 bulk metallic glass-forming alloy

Viscosity of the Fe-based bulk metallic glass-forming liquid Fe43Cr16Mo16C15B10 is measured around the glass transition and in the stable liquid. Low-temperature measurements are conducted using three-point beam bending in a thermomechanical analyzer, and high-temperature data are obtained from the damping behavior of an oscillating droplet which is electromagnetically levitated in microgravity on a reduced-gravity aircraft. The alloy displays an intermediately strong liquid behavior (D* = 15.1) at low temperatures and a fragile behavior (D* = 7.9) at high temperatures. Hence, the temperature dependence of viscosity changes drastically between the high- and the low-temperature regime, which suggests the existence of a fragile-to-strong liquid-liquid transition in the supercooled liquid. Furthermore, viscosity and fragility data are discussed with respect to the glass-forming ability of the alloy.

How closely do many-body potentials describe the structure and dynamics of Cu-Zr glass-forming alloy?

Molecular dynamics investigations of the structure and dynamics of Cu64.5Zr35.5 metallic glass-forming alloy have been carried out using five different semi-empirical, many-body interaction potentials based on the Finnis-Sinclair model [M. I. Mendelev et al., J. Appl. Phys. 102, 043501 (2007) (MSK); M. I. Mendelev et al., Philos. Mag. 89, 967 (2009) (MKOSYP); L. Ward et al., e-print arXiv:1209.0619 (2012) (WAFW)] and the embedded-atom model [Y. Q. Cheng et al., Phys. Rev. Lett. 102, 245501 (2009) (CMS) and N. Jakse et al., Phys. Rev. B 85, 174201 (2012) (JNP)]. Although the total static structure factor of the alloy for all the five interaction potentials is, in general, found to be in good agreement with the experimental results, the investigation of a local structure in terms of icosahedral short-range order reveals that the effect of the interaction potential (especially the cohesive part) on the structure of the alloy is not as trivial as it seems. For MSK and JNP potentials, the self-intermediate scattering function Fs(q, t), q-dependence of the structural relaxation time τα in the low-q region, and the self-diffusion coefficient, Ds, for Cu-atoms in the alloy are in excellent agreement with the experimental results. The results for MKOSYP, CMS, and WAFW potentials deviate significantly from the experiment and suggest the dynamics of the alloy to be faster. The difference in the description of the dynamics of the alloy by different potentials is found to be due to the difference in the relevant energy scales corresponding to the temperature scales. τα and Ds exhibit Arrhenius temperature dependence in the high temperature regime above the melting temperature. We also suggest that the attractive forces influence the dynamics of the liquid alloy significantly, which is against the mere perturbative role assigned to the attractive forces in the van der Waals picture of liquids that has been challenged in the recent years. As the five interaction potentials are frequently employed to study thermodynamic, mechanical, and transport properties of Cu-Zr alloys, our study also provides a suitability check for these potentials.

Development of Mo‐Ni‐Si‐B metallic glass with high thermal stability and H versus E ratios

We report a novel Mo‐Ni‐Si‐B metallic glass which can be solidified into fully amorphous state by melt-spinning process, with high crystallization onset temperature of over 1100K, extremely high Vickers hardness of 27.5±2.2GPa and relatively low Young's modulus of 364.3±6.6GPa. The dense cluster-packing model suggests that the addition of boron up to 10at.% can occupy vacant cluster-interstices of (Mo, Ni)-Si cluster arrays, which results in a more efficiently dense-packed cluster structure, destabilizes the formation of nanocrystalline phases, and systematically increases the glass-forming ability (GFA) in Mo‐Ni‐Si‐B alloys. The GFA parameters that do not directly rely on Tg, such as ΔT* and ε parameter, show greater reliability to evaluate GFA for Mo‐Ni‐Si‐B metallic glass exhibiting no clear Tg. The H/E and H2/(2E) ratios of the newly developed Mo‐Ni‐Si‐B metallic glass, which reflect wear resistance and resilience, exhibit the highest values among various hard ceramic materials as well as metallic glass-forming alloys developed up to now. These advantages of Mo‐Ni‐Si‐B metallic glass can be used more widely to form a high temperature wear-resistant coating layer on various substrates. Furthermore, the same idea might be used to form a metallic glass-nitride nanocomposite coating layer by reactive deposition in N2 ambient, with highly lubricative property and high wear-resistance, especially at high temperature.

Atomic-scale simulation to study the dynamical properties and local structure of Cu-Zr and Ni-Zr metallic glass-forming alloys.

Molecular dynamics simulation with well-developed EAM potentials was carried out to investigate the transport properties and local atomic structure of Cu-Zr and Ni-Zr metallic glasses and supercooled liquids. It is found that Cu or Ni atoms have much faster dynamics than Zr atoms in relaxation timescales, while Zr atoms display faster dynamics in the Cu-Zr system than in the Ni-Zr system. A dynamical crossover phenomenon from Arrhenius to super-Arrhenius behavior in the transport properties was observed for the Cu65Zr35 system at Tx ≈ 1250 K and the Ni65Zr35 system at Tx ≈ 1500 K, respectively. Further structural analysis suggests that the dominant interconnected clusters in Cu65Zr35 and Ni65Zr35 systems are 〈0, 0, 12, 0〉, 〈0, 1, 10, 2〉, 〈0, 2, 8, 2〉 and 〈0, 3, 6, 4〉. To directly characterize and visualize the correlated dynamics, we regard the full icosahedra as the microscopic origin responsible for the formation of metallic glasses in the Cu65Zr35 system, while the metallic glass formation in the Ni65Zr35 system can be attributed to the slow dynamics of 〈0, 3, 6, 4〉, 〈0, 2, 8, 2〉 and 〈0, 1, 10, 2〉 Ni-centered Voronoi polyhedra. The local atomic order and dynamics for Cu65Zr35 and Ni65Zr35 systems are remarkably different, and these differences are presumed to hinder crystal nucleation and growth, hence promoting the largely different bulk glass-forming ability.

Retraction: Atomic-scale simulation to study the dynamical properties and local structure of Cu-Zr and Ni-Zr metallic glass-forming alloys.

Retraction of 'Atomic-scale simulation to study the dynamical properties and local structure of Cu-Zr and Ni-Zr metallic glass-forming alloys' by M. H. Yang et al., Phys. Chem. Chem. Phys., 2016, 18, 7169-7183.

Viscosity and fragility of the supercooled liquids and melts from the Fe–Co–B–Si–Nb and Fe–Mo–P–C–B–Si glass-forming alloy systems

The dynamic viscosity of four Fe-based bulk metallic glass-forming alloys, [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 (alloy A), {[(Fe0.5Co0.5)0.75B0.2Si0.05]0.96Nb0.04}99.5Cu0.5 (alloy B), Fe74Mo4P10C7.5B2.5Si2 (alloy C) and (Fe0.9Ni0.1)77Mo5P9C7.5B1.5 (alloy D), was investigated as a function of temperature in the supercooled liquid region, as well as above the melting point. The alloy B is Cu-added alloy A, while the alloy D was obtained upon fine-tuning the alloy C composition. All these alloys may form bulk metallic glasses upon copper mold casting. The viscosities in the supercooled liquid region were calculated using the data obtained upon parallel plate rheometry measurements, as well as upon differential scanning calorimetry (DSC). The values of the supercooled fragility parameter m, 61, 66, 52 and 60 for the alloys A, B, C and D respectively, indicate that these alloys are intermediate glass formers. The behavior of the same alloys, in the molten state, was studied using a high temperature torsional oscillation cup viscometer. The values of the corresponding fragility parameter M was calculated as 5.03, 5.91, 4.25, 4.93 for the alloys A, B, C and D, respectively. They confirm the supercooled liquid behavior and predict that the alloys A and C may form glasses easier than the fine-tuned compositions B and D. Angell plot is constructed for the entire range of viscosities and the values from both regions, i.e. above melting point and supercooled liquid region, fit well with the model.

A study on the surface photovoltage property of flower-like nanobelt film

The microstructure and photoelectric response property of a Zr-doped titanate nanobelt film synthesized by hydrothermal-dealloying of Ti-based metallic glass-forming alloy are studied. A dense and uniform flower-like nanobelt film grows on the surface of the Ti-based alloy substrate during a hydrothermal process. Furthermore, the nanobelt film shows prompt and reversible surface photo-voltage response with irradiation wavelength in the range of 300–350nm. This work may provide a facile way to fabricate flexible shaped nanomaterial films with unique photoelectric properties using alloy as precursors.

Early stage crystallization kinetics in metallic glass-forming alloys

Abstract The crystallization kinetics and structural changes of a few metallic glassy alloys were monitored using X-ray diffraction, transmission electron microscopy, differential scanning and isothermal calorimetry methods. Microstructural observations were used to estimate the nucleation and growth rates. A clear comparison of the differences in the crystallization kinetics in the metallic glassy samples is observed at the early and later crystallization stages.

Influence of Copper Addition on Glass Forming Ability, Thermal Stability, Structure and Magnetic Properties of Fe-Co-Based BMGs

The aim of the paper was investigation of the effect of Cu addition on glass forming ability (GFA), thermal stability, structure and magnetic properties of Fe-Co-based bulk metallic glasses (BMGs). The raw materials used in this experiment for the production of BMGs were pure Fe, Co, Cu and industrial Fe-B, Fe-Si, Fe-Nb ferroalloy. Investigations were carried out on BMGs in rods shaped with square section with side of 1.5mm. The structure of the investigated BMGs in rod form is amorphous. The addition of small amounts of Cu is effective in changing GFA and magnetic properties. The melting temperature - Tm remained almost constant for both investigated alloy. Two alloy compositions are at or very close to the eutectics, what according to ref. [1] should guarantee the best metallic glass-forming alloys. The investigated alloys have good soft magnetic properties. The successful synthesis of the Fe36.00Co36.00B19.00Si5Nb4 and Fe35.75Co35.75B18.90Si5Nb4Cu0.6 alloys with high GFA and good soft magnetic properties by using starting industrial alloys are encouraging for the future industry applications.

Measurements of volume, thermal expansion, and specific heat in Zr57Cu15.4Ni12.6Al10Nb5 and Zr58.5Cu15.6Ni12.8Al10.3Nb2.8 liquids and glasses

The temperature dependence of the specific volume, thermal expansion coefficient, and specific heat in the equilibrium, supercooled liquids, and glasses of the bulk metallic glass-forming alloys Zr57Cu15.4Ni12.6Al10Nb5 and Zr58.5Cu15.6Ni12.8Al10.3Nb2.8 are determined using the containerless electrostatic levitation technique. Such measurements have not been possible thus far because of rapid crystallization from the supercooled metastable liquids. The results show a decrease in the thermal expansion coefficient with decreasing temperature before the onset of the glass transition. The difference in the rate of decrease between the two alloys indicates larger structural contributions to the thermal expansion for the stronger liquid at high temperatures.

Wetting of WC by a Zr-base metallic glass-forming alloy

Wetting of hot-pressed polycrystalline WC substrates by a Zr55Cu30Al10Ni5 bulk metallic glass (BMG)-forming alloy was investigated at 1133–1253 K in a high vacuum using a modified sessile drop method. The alloy melt spread rapidly on the WC surface, reaching no more than 30° within 3 s, and then slowly (at T < 1213 K) or even remained steady (at T ≥ 1213 K) in the subsequent isothermal dwelling stage. The final equilibrium contact angles were between 11° and 20°, slightly increasing with rising temperature and thus presenting an appreciably anomalous temperature-dependent behavior. The reaction between WC and the Zr-base melt was moderate, slightly enhancing with increasing temperature, and yielded W, ZrC and W5Zr3 at the interface. The wetting, in principle, was driven by the formation of a precursor film in front of the triple line as a result of the adsorption of active atoms (primarily Zr) rather than by the interfacial reaction. From the viewpoint of the wettability and reactivity, WC is a good reinforcement for the preparation of the Zr-base BMG matrix composites.

Effects of Re microalloying on glass formation and mechanical properties of Zr–Cu–Al alloys

The effect of microalloying with rhenium on a metallic glass-forming alloy (Cu46Zr46Al8)100− x Re x (x = 1, 2) was investigated. Re possesses a positive enthalpy of mixing within the Cu–Re terminal system. Splat quenched foils of ≈40 µm in thickness display an amorphous structure. Their crystallisation temperature increases from T x = 504 to 513°C with addition of Re at nearly constant glass formation temperature T g = 445°C for the amorphous samples. In contrast, injection cast rods consist of B2-CuZr type phase dendrites, minor fractions of a cubic phase CuZrAl, and randomly distributed small particles of a Re-rich phase. This represents a novel concept in microalloying where Re-rich precipitates trigger the B2 phase formation. It leads to a unique combination of mechanical properties for as-cast rods, which display high strength at sizeable plastic deformation up to ε p ≈ 4% and an extended range of work-hardening prior to failure.