Zr-based Metallic Glass Research Articles

Zr-based metallic glasses Hugoniot under laser shock compression and spall strength evolution with the strain rate (> 107 s-1)

We investigate the mechanical response of Zr50Cu40Al10 and Zr60Cu30Al10 metallic glasses under laser shock compression to reproduce hypervelocity impact conditions such as high longitudinal stresses and high strain rates in an unknown range of 106−107s−1. Hugoniot curves and strength parameters (spall strength and strain rate) are obtained from free surface velocity profiles and compared with previous studies on the mechanical behaviour of Zr-based metallic glasses under plate impact experiments. We established Hugoniot curves for both compositions up to 100 GPa, corresponding to a particle velocity of 1.8 km/s, and consistent with literature up to 75 GPa. Concerning the strength parameters, we studied the evolution of the spall strength with the strain rate and obtained data unreached up to now from 1.7×106s−1 to 2.7×107s−1. This range of data correspond to strain rates of hypervelocity impacts of small debris (≈0.1−1mm) on space infrastructure shields. Moreover, we highlight a strong dependency of the spall strength with the strain rate starting from 2×106s−1. Indeed, the spall strength increases from 2.6 GPa, close to its quasi-static tensile strength value, up to 13.6 GPa.

Enhanced pitting corrosion resistance of a Zr-based metallic glass by ultraviolet light irradiation

Enhanced pitting corrosion resistance of a Zr-based metallic glass by ultraviolet light irradiation

Towards the additive manufacturing of Zr-based metallic glasses using liquid phase sintering: Reactivity and phase transformation kinetics at the crystalline/amorphous interface

Bulk metallic glasses (BMG) present great potential for high-tech applications considering the excellent mechanical and corrosion properties. The on-going development of powder additive manufacturing techniques offers the opportunity to produce rather large parts composed of BMG. Relative to the sinter based additive manufacturing techniques, the sintering of a Zr-based BMG (AMZ4, Zr59,3Cu28,8Al10,4Nb1,5) using Zn-based additives was identified as promising: Zn alloys have indeed a melting point (Tm,Zn = 419, 5∘C) lower than the crystallization temperature of the BMG (Tx ≃ 470∘C). Here, the study focuses on the understanding of the reactivity between AMZ4 and Zn as a function of temperature and time. A powder blend and a model interface AMZ4/Zn were studied combining post-mortem characterizations (SEM, EDX, XRD, micro-hardness…) with in situ characterization (DSC). Experimental construction of time-temperature-transformation diagram shows that there is a temperature/time window where sintering is permitted without crystallization. Beyond, an intermetallic phase is formed at the interface between the BMG and Zn, this phase was identified in terms of shape, composition and crystallography. A growth mechanism was proposed combining thermodynamic and kinetic aspects.

Low-speed orthogonal cutting of large Zr-based metallic glasses: A shear angle model considering internal friction and serrated chip formation

Metallic glasses have high hardness, low cutting force, and serrated chip formation, which pose significant challenges for cutting. The chip formation mechanism of metallic glasses under low-speed cutting has been studied, but the effects of compression and internal friction have been neglected. In this study, a shear angle model that considers internal friction was proposed and compared with classical shear angle models. Low-speed orthogonal cutting experiments on Zr-based metallic glasses were conducted and the cutting forces, chip morphology, shear angle, external and internal friction angle under different cutting parameters were measured and calculated. The results show that the internal friction angle ranges from 21.3° to 36.0° and the shear angle ranges from 29.9° to 38.0°. The improved model can better characterize the cutting properties of metallic glasses. This study presents a new method and model for low-speed cutting of metallic glasses and provides insights into their deformation and fracture behaviors.

Development of Zr-based metallic glasses to utilize thermoplastic forming processes of engineering plastics

Metallic glasses (MGs) have garnered significant attention for the possibility to use as advanced structural materials in recent decades. However, their high processing costs remain a major obstacle to their commercialization. This research offers a practical guideline to significantly reduce production costs through tailored alloy design and precise control of thermoplastic forming (TPF) process parameters. Specifically, we discovered commercially available MGs with a low glass transition temperature (Tg) can be developed in the Zr-rich alloy systems. Moreover, we addressed the challenge of maintaining a wide TPF window in Be-free Zr-based MGs while keeping Tg low. Our research has yielded the development of Be-free Zr-rich multicomponent MGs with a low Tg below 350 °C (623 K) and a wide TPF window of over 70 K, resulting in excellent thermoplastic formability (TPFA). Notably, the MGs we developed exhibit a lower Tg than advanced engineering plastics like Polyimide and Polybenzimidazole, which suggests that the TPF process of plastics could be extended to MGs. In addition, we employed Flash-DSC to accurately identify the TPF window and TPFA according to the heating rate in a wide range from 10-1 to 104 K/s, and proposed novel TPFA parameters that are based on continuous heating transformation diagram with iso-viscosity contours. Our findings demonstrate that even marginal MGs have a significant advantage in manufacturing micro-to-nano scale products that can be molded at ultra-fast heating rates, similar to advanced engineering plastics. Indeed, this work will undoubtedly inspire us to further explore the potential of MGs as a practical material for industrial applications.

Rejuvenation-deformation relationship of a well-aged metallic glass during Newtonian to non-Newtonian flow

Stress overshoot is a sign of structural rejuvenation of metallic glass, which usually occurs in non-Newtonian flow with large strain rate. Here we show a heavily-aged Zr-based metallic glass that rejuvenates by low-strain-rate Newtonian flow without showing any stress overshoot. Its rejuvenation does not increase the energy level of its basin of potential energy landscape, but reduces the basin's mechanical stability. Synchrotron X-ray total scattering gives direct evidence that under Newtonian flow, the rejuvenation is contributed by complex structural rearrangements over short- and medium-range order scales. We further find that due to the structurally inhomogeneous response, there is an optimal strain rate for rejuvenation, above which the energy level decreases, but the characteristic size of the medium-range order continues to increase. Thus, the mechanical stability and structural disorder do not decrease synchronously. Our findings refresh the understanding of the relationship between mechanical deformation and structural rejuvenation in metallic glasses.

Self-supporting electrodes obtained by electrochemical dealloying of Zr-based metallic glass alloys for energy storage applications

Self-supporting electrodes obtained by electrochemical dealloying of Zr-based metallic glass alloys for energy storage applications

Mechanical properties and thermal stability of thin film metallic glass compared to bulk metallic glass from ambient to elevated temperatures

Metallic glasses can exhibit a wide range of local atomic arrangements which are determined by their processing history, and which control their mechanical properties. While recent studies show that thermally stable thin film metallic glasses with high strength and plasticity can be synthesized using physical vapor deposition, they often differ in terms of their structure and mechanical performance from bulk metallic glasses. In that aspect, two different fabrication methods – physical vapor deposition and arc melting – were utilized to fabricate compositionally similar Zr-based glasses in thin-film and bulk form. The as-fabricated samples were characterized in terms of oxygen concentration, element composition, and atomic structure. The mechanical response of the thin film metallic glass (TFMG) and the bulk metallic glass (BMG) was examined using in situ micropillar compression in a scanning electron microscope over a temperature range of room temperature to 500 °C. While the two glasses show overall similar failure characteristics, the TFMG exhibits higher strength together than the BMG without sacrificing plasticity at all testing temperatures. At elevated temperatures, the deformation mechanism changes to homogenous deformation above glass transition temperature (Tg). The higher strength and thermal stability of the TFMG is associated with a much higher oxygen concentration in the thin film compared to the BMG. The enhanced mechanical performance of the TFMG compared to the BMG highlights the potential of oxygen in the thermal stability characteristics and deformation capacity of Zr-based thin film metallic glasses.

High-temperature wear behavior of a Zr-based metallic glass

Due to the fascinating application prospects of Zr-based bulk metallic glass (BMG), it is of practical engineering interest to study its wear behavior and mechanism under various temperature conditions. In this work, the wear behavior and mechanism of a commercially available Zr35Ti30Be26.75Cu8.25 BMG at room temperature (RT) to 500 °C were investigated. The results demonstrated that the wear rate increased from ∼24.7 × 10−5 mm3 N−1 m−1 to ∼196.8 × 10−5 mm3 N−1 m−1 as the temperature increased from RT to 500 °C. Accordingly, the coefficient of friction (COF) is reduced from an average of 0.45–0.18 due to the lubricating effect of the oxide layer. At low temperatures of RT and 200 °C, the predominant wear mechanisms are abrasive wear and adhesive wear. However, in the supercooled liquid region (SCLR) of at 350 °C, the dominant wear mechanism is a combination of superplasticity-dominated abrasive wear, severe fatigue wear, and slight oxidative wear. Above the crystallization temperature (Tx) at 500 °C, the primary wear mechanisms are severe abrasive wear and oxidative wear. Our results can provide important guidance for determining the applicable temperature, service life and failure mode of BMG components.

Exploiting Zirconium-Based Metallic Glass Thin Films for Anode-Free Lithium-Ion Batteries and Lithium Metal Batteries With Ultra-Long Cycling Life.

Coating Zr-based metallic glass, Zr53 Cu31 Ni11 Al5 (Zr-MG), on a Cu current collector (CC) and Li metal anode (LMA) significantly improves the cycle performance of both types of Li-ion batteries, namely, anode-free Li-ion batteries (AFLBs) and Li metal batteries (LMB). The inherent isotropy and homogeneity of the Zr-MG significantly improve the surface uniformity of the CC and LMA. A 12nm-thick Zr-MG thin film coating on the CC reduces the overpotential in the AFLB, leading to a more uniform Li plating morphology. The Li film covers almost the entire surface of the Zr-CC, whereas it only covers ≈75% of the bare CC during charging. An LFP||Zr-CC full-cell exhibits a capacity retention of 63.6% after the 100th cycle, with an average CE of 99.55% at a 0.2 C rate. In the case of the LMB, a 12nm-thick Zr-MG thin film-coated LMA (Zr-LMA) exhibits a stable capacity of up to 1500 cycles. An LFP||Zr-LMA full-cell exhibits capacity retention and CE after 1500 cycles of 66.6% and 99.97%, respectively, at a 1 C rate. Zirconium-MG thin films with atomic-level uniformity, outstanding corrosion resistance, lithiophilic characteristics, and high diffusivity result in superior AFLB and LMB performances.

Interface characteristic of Zr-based metallic glass and copper by laser pulse welding

The crystallization behavior of amorphous alloys during welding is more complex than that of traditional metals. In this paper, the Zr-based amorphous alloy and copper crystals were welded by pulsed laser butt welding method, the crystallization behavior of the amorphous alloy/crystalline metal welding interface is deeply studied. The results show that Zr2Cu and Zr2Ni crystal phases appear at the interface between Zr based amorphous alloy and copper, and a Cu rich region is formed at the amorphous side of the interface. A small amount of Zr, Ni, Ti diffuses to the Cu side, forming ZrO2, TiO2, CuO and other oxides on the surface of the sample. These oxides will cause changes in the voltage potential at the interface.

Nanoscale Clustering in an Additively Manufactured Zr-Based Metallic Glass Evaluated by Atom Probe Tomography.

Composition analysis at the nm-scale, marking the onset of clustering in bulk metallic glasses, can aid the understanding and further optimization of additive manufacturing processes. By atom probe tomography, it is challenging to differentiate nm-scale segregations from random fluctuations. This ambiguity is due to the limited spatial resolution and detection efficiency. Cu and Zr were selected as model systems since the spatial distributions of the isotopes therein constitute ideal solid solutions, as the mixing enthalpy is, by definition, zero. Close agreement is observed between the simulated and measured spatial distributions of the isotopes. Having established the signature of a random distribution of atoms, the elemental distribution in amorphous Zr59.3Cu28.8Al10.4Nb1.5 samples fabricated by laser powder bed fusion is analyzed. By comparison with the length scales of spatial isotope distributions, the probed volume of the bulk metallic glass shows a random distribution of all constitutional elements, and no evidence for clustering is observed. However, heat-treated metallic glass samples clearly exhibit elemental segregation which increases in size with annealing time. Segregations in Zr59.3Cu28.8Al10.4Nb1.5 > 1 nm can be observed and separated from random fluctuations, while accurate determination of segregations < 1 nm in size are limited by spatial resolution and detection efficiency.

On the elastic microstructure of bulk metallic glasses

Metallic glasses (MGs) are known to be structurally heterogeneous at the nanometer (nm) scale. In addition, elastic property mapping has indicated the presence of at least an order-of-magnitude larger length scales, of which the origin continues to remain unknown. Here we demonstrate the existence of an elastic decorrelation length of the order of 100 nm in a Zr-based bulk MG using spatially resolved elastic property mapping via nanoindentation. Since compositional modulations, sufficiently large to account for this elastic microstructure, were not resolved by analytical scanning-transmission electron microscopy, chemical phase separation such as spinodal decomposition cannot explain their presence. Instead, we argue that the revealed long-range elastic modulations stem from structural variations affecting the local density. These emerge during solidification and are strongly influenced by the cooling constraints imposed on bulk MGs during the casting process.

Application and Fundamental Researches on Metallic Glasses; Development of Engineering Products and Challenge to Improve Brittleness

Metallic glasses exhibit a high mechanical strength at room temperature and superior formability in a supercooled liquid region, which make them to become promising materials for engineering applications. However, two major drawbacks, one is difficulty in fabricating bulk samples and the other is their intrinsic brittle properties during fracture, highly limited their practical applications. With respect to the former, we focused on fabricating micrometer size products and a Fe-based metallic glassy micro gear was successfully developed through our newly proposed microparts fabrication process. For the latter, a concept of amorphous/glassy state gradient is introduced, intending to improve a brittleness by controlling the crack propagation path depending on a created gradient state. The temperature/thermal history gradient is thermally introduced within a single monolithic Zr-based metallic glass, and it was found that a brittleness presumably improved by thermally created amorphous/glassy state gradient.

Effect of cryogenic cycling and above-Tg annealing on the corrosion behavior of Zr-Cu-Ti-Be metallic glass

This work investigates the electrochemical properties of Zr-based Zr35Ti30Cu8.25Be26.75 metallic glass after cryogenic treatment and isothermal annealing above glass transition temperature. Potentiodynamic polarization and electrochemical impedance spectroscopy experiments are used to understand the effect of structural state on the corrosion behavior of Zr-based metallic glass. The metallic glass samples are cycled between liquid nitrogen to room temperature and isothermally held at liquid nitrogen to unravel the effect of cryogenic treatments on the electrochemical properties. The corrosion of cryogenically treated and high temperature annealed samples is compared with the as-cast samples. The results show that holding at liquid nitrogen temperature improves the corrosion resistance of metallic glass compared to cryogenic cycling and the high temperature annealing. These findings are explained based on the changes in structural state of metallic glass.

Crack-free and high-strength AA2024 alloy obtained by additive manufacturing with controlled columnar-equiaxed-transition

Laser powder bed fusion (LPBF) of high-strength Al alloys is challenging due to the formation of both hot and cold cracks. In the present work, highly dense and crack-free AA2024 samples could be additively manufactured via inoculation treatment of Zr-based metallic glass (MG) powders. The columnar grains in the LPBF-fabricated AA2024 alloy were significantly refined and almost completely transformed to the equiaxed grains with a bimodal grain size distribution consisting of ultrafine grains with a size smaller than 1 μm and relatively coarser grains. The grain refinement can be associated with the formation of Al3Zr particles, serving as the heterogeneous nucleation sites for the α-Al matrix. Complete routes for columnar-equiaxed-transition (CET) have been revealed by tailoring the concentration of nucleation particles and solidification conditions. CET occurs both at the melt pool boundary due to the sufficiently high concentration of Al3Zr particles and at the topmost of the melt pool due to the heterogeneous nucleation driven by constitutional undercooling. Between these two regions, columnar grains epitaxially grow with orientations determined by the thermal gradient. The as-built Zr-based MG inoculated AA2024 specimens are robust in healing hot cracks due to a more tortuous propagation path of cracks for equiaxed grains. The as-fabricated AA2024/5% MG specimens exhibit a high ultimate tensile strength of 531 MPa due to crack elimination and grain refinement, surpassing most of the reported values for the LPBF-fabricated AA2024 alloy inoculated with other inoculated powders. The present work could provide a novel inoculation agent to fabricate high-strength Al alloys and the CET can be used to precisely control the grain morphology.

Synthesis and mechanical properties of highly structure-controlled Zr-based metallic glasses by thermal rejuvenation technique

A novel thermal rejuvenation treatment facility for Zr-based bulk metallic glass (BMG) was developed, consisting of a rapid heating and indirect liquid nitrogen quenching process. The re-introduction of free volume into thermally rejuvenated BMG results in more disordered state. The rejuvenation improves ductility, implying that the re-introduced free volume aids in the recovery of the shear transformation zone (STZ) site and volume. Actually, it is confirmed that relaxation significantly reduces STZ volume; however, it is recovered by thermal rejuvenation. Molecular dynamics simulations also indicate that rejuvenation enhances homogeneous deformation. The current findings indicate that the thermal rejuvenation method is extremely effective for recovering or improving the ductility of metallic glass that has been lost due to relaxation.

Electronic structure and nanoindentation properties of electrochemical hydrogen-charged Zr-based metallic glasses

Zr55Cu30Ni5Al10 metallic glasses were treated by an electrochemical hydrogen- (H-)charging method. Samples with different H content were obtained by changing the H-charging current density and charging time. X-ray diffraction, nanoindentation, X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy, and positron annihilation experiments were used to investigate amorphous structure, nanomechanical properties, electronic structure, and positron annihilation behavior of Zr55Cu30Ni5Al10 metallic glasses after electrochemical hydrogenation treatment. The results showed that the diffraction angle corresponding to the diffuse scattering peak gradually moved to a low angle with increased H content. At the same time, the hardness and elastic modulus of the MG were significantly increased with increased H-charging content. When the H content was high, the sawtooth rheological phenomenon disappeared in the load displacement curve of the MG during nanoindentation. XPS narrow spectrum analysis showed that the Zr-3d peak in samples shifted to higher binding energies, while the other elements shifted toward lower binding energy, indicating that H addition led to the transfer of valence electrons from Zr-3d to the Zr–H bond state, resulting in hardening. Three lifetime components are observed in the uncharged and charged sample, indicating the presence of three size ranges of open volume sites. After electrochemical hydrogen charging it causes a significant decrease in the size (lifetime) of the three open volume defects, indicating that the hydrogen occupies those sites. With the increase of hydrogen content, the concentration (intensity) of the first two open volume defects gradually decreases, while the third open volume defect gradually enhances, indicating that hydrogen atom mainly occupies the first two open volume defects. Positron annihilation experiments showed that H addition reduced the average annihilation lifetime of positron vacancies in these MGs, but no new defects were produced.

Mechanical properties and biocompatibility of a novel miniscrew made of Zr70Ni16Cu6Al8 bulk metallic glass for orthodontic anchorage

The purpose of the present study was to fabricate a miniscrew possible for clinical application using Zr70Ni16Cu6Al8 bulk metallic glass (BMG), which has high mechanical strength, low elastic modulus, and high biocompatibility. First, the elastic moduli of Zr-based metallic glass rods made of Zr55Ni5Cu30Al10, Zr60Ni10Cu20Al10, Zr65Ni10Cu17.5Al7.5, Zr68Ni12Cu12Al8, and Zr70Ni16Cu6Al8 were measured. Zr70Ni16Cu6Al8 had the lowest elastic modulus among them. Then, we fabricated Zr70Ni16Cu6Al8 BMG miniscrews with diameters from 0.9 to 1.3 mm, conducted a torsion test, and implanted them into the alveolar bone of beagle dogs to compare insertion torque, removal torque, Periotest, new bone formation around the miniscrew, and failure rate compared with 1.3 mm diameter Ti-6Al-4 V miniscrew. The Zr70Ni16Cu6Al8 BMG miniscrew exhibited a high torsion torque even if the miniscrew had a small diameter. Zr70Ni16Cu6Al8 BMG miniscrews with a diameter of 1.1 mm or less had higher stability and lower failure rate than 1.3 mm diameter Ti-6Al-4 V miniscrews. Furthermore, the smaller diameter Zr70Ni16Cu6Al8 BMG miniscrew was shown, for the first time, to have a higher success rate and to form more new bone around the miniscrew. These findings suggested the usefulness of our novel small miniscrew made of Zr70Ni16Cu6Al8 BMG for orthodontic anchorage.

Strain rate sensitivity in Zr-based metallic glass: Experiments and molecular dynamics study

This study presents results on the strain rate sensitivity (SRS) of Zr-based metallic glass over a wide range of specimen size (macro and micro) and strain rates (quasi-static and dynamic), and provides information on the correlation among shear band initiate, stress concentration and strain rate in metallic glass. Shear bands readily initiate from stress concentration sites, and metallic glasses are more sensitive to stress concentration at high strain rate. The inevitable stress concentration in bulk metallic glass could result in negative SRS. While its SRS could be enhanced by reducing the stress concentration extent. Even positive SRS could be obtained in micro-pillar metallic glass with little stress concentration. Molecular dynamics simulations show that metallic glass without defects (i.e. stress concentration) exhibits positive SRS, because the atomic mobility is not sufficient for the shear transformation zone operation to initiate a shear band at higher strain rate.