Zr-based Metallic Glass Research Articles

Effect of nanocrystalline process on microstructure of Zr-based metallic glass

This article focused on the microstructure changes of the Zirconium-based alloy with isothermal annealing close to the glass transition temperature. The differential scanning calorimetry (DSC) was used to measure the temperatures of crystallization and glass transition. The Small-angle neutron scattering (SANS) results revealed a peak associated with the interference in isothermal annealing. Under supercooling, crystallization was decomposed, in addition to transmission electron microscopy (TEM) results exhibited that a part of inhomogeneities formed at the early annealing of amorphous alloy had been crystallized later. TEM and x-ray diffraction (XRD) results illustrated that nanocrystalline phase formed after long time annealing, with decomposition of the initial phase. Nanoindentation experiments showed that the hardness descended on the increase of indentation loaded, while the excessive free-volume increased with the increasing indentation load.

The microfabrication of mold for polymer microfluidic devices with Zr-based metallic glass.

Polymer microfluidic devices are used for many purposes such as microarrays and biochips. The key tool for manufacturing these chips in bulk is an appropriate mold. However, the popular material for making molds is nickel or nickel alloys, which have low stiffness and wear out easily. Zr-based metallic glass is a promising material for micro- or nanomolds because it has good mechanical properties and can be easily formed with high precision. In this paper, Zr-based metallic glass is proposed for use as micromold insert to make poly-(methyl methacrylate) (PMMA) microfluidic devices. Our experiments show that they have good feature integrity and replication quality. Microchannels we fabricated using these replicas did not leak and had good flow performance. Zr-based metallic glass can greatly ease the manufacture of plastic microfluidic devices for research and commercial applications.

Investigation into nanoscratching mechanical performance of metallic glass multilayers with improved nano-tribological properties

Friction and wear are the two most important properties that determine the long-term performances of metallic glasses as much as strength and ductility. With this in mind, a multilayered strategy was proposed to improve the nano-scratching properties of metallic glass thin films and the well-characterized Zr-based metallic glasses were chosen to be the representative model materials in current work. It was found that the metallic glass could exhibit improved wear resistance and reduced friction coefficient if it is made in the form of multilayers. The complexity in the temporal scale of the lateral force signal is investigated, elucidating the inhomogeneous (and homogeneous) shear-banding processes during the nanoscratching process. The statistical and dynamic analyses of the stick-slip behaviors showed a transition from a chaotic to a self-organized critical state in the multilayers, indicating that the hetero-interfaces promote extensive shear band-interface interactions and induce the scratch hardening effect, both of which are responsible to the excellent tribological properties. The current work not only highlights the significant roles of hetero-interfaces in improving the nano-tribological properties but also make the multilayered metallic glass thin films a promising candidate towards structural and functional applications for metallic glasses.

Enhanced Thermochromic Properties of Vanadium Dioxide (VO2)/Glass Heterostructure by Inserting a Zr-Based Thin Film Metallic Glasses (Cu50Zr50) Buffer Layer

Vanadium dioxide (VO2) with reversible metal–insulator transition (MIT) is one of the most promising energy-efficient materials. Especially for VO2-based smart windows, the visible transmittance and solar modulation ability are the most critical parameters. However, VO2 thin films that are directly deposited onto glass substrates are of poor crystallinity and MIT performance, limiting the practical applications of VO2/glass heterostructures. In this paper, a buffer layer of Cu50Zr50 was introduced to build a novel Zr-based thin film metallic glass (VO2/Cu50Zr50/glass) with multilayer structures for thermochromic applications. It is observed that the insertion of a Cu50Zr50 buffer layer with appropriate thickness results in a clear enhancement of crystalline quality and MIT performance in the VO2/Cu50Zr50/glass thin films, compared with the single-layer VO2/glass thin films. Moreover, the VO2/Cu50Zr50/glass bi-layer films exhibit better optical performance with enhanced solar modulation ability (ΔTsol = 14.3%) and a high visible transmittance (Tvis = 52.3%), which represents a good balance between ΔTsol and Tvis for smart window applications.

Microdomain atomic structure of Zr50Pd40Al10 metallic glasses and its formation mechanism

Zr-based Zr50Pd40Al10 metallic glasses has not only crystalline phases of about 5 nm in diameter but also amorphous phases. In this work, the radial distribution functions (RDFs) of amorphous structure of Zr50Pd40Al10 metallic glasses were firstly measured by electron diffraction, and then Reverse Monte Carlo (RMC) optimization accompanied by density functional theory (DFT) calculations. The amorphous structure has not only short-range order but also good medium-range order. In the RDFs of its amorphous structure, the first and the second peaks are located at 2.96 Å and 4.79 Å, respectively. Partial radical distribution functions (PRDFs) show that the contributions of the first and the second nearest-neighbor distances of various atom pairs to the G(r) peak values, and the first nearest-neighbor distances of Pd–Zr and Zr–Zr atom pairs are the sources of main G(r) peak values between 2 Å and 6 Å. The competition mechanism for generating the Pd25Zr55Al20 amorphous phase and the intermetallic crystalline phase Pd11Zr9 is associated with the differences of atomic radius, the proportion, and the melting point of different atoms, as well as the heat of mixing between atoms, leading to an equilibrium state of the two phases. Accordingly, a composite system with intertwined nanocrystals and amorphous phases is in turn formed, and improves the stability of the material.

The coupling effects of laser thermal shock and surface nitridation on mechanical properties of Zr-based metallic glass

Laser processing is a versatile tool for applications in the field of metallic glasses (MGs). Previous studies reported that surface nitridation, i.e. the formation of ZrN phase, occurred when laser irradiation of Zr-based MG was performed in nitrogen gas. Additionally, it was reported that laser thermal shock usually softened the irradiated surface. Therefore, the coupling effects of laser thermal shock and surface nitridation on mechanical characteristics of Zr-based MG should be further clarified. For this purpose, in this study, laser irradiation of Zr-based MG was conducted under various experimental conditions, followed by evaluating the surface characteristics by X-ray diffraction (XRD), nanoindentation, and energy-dispersive X-ray (EDX) spectroscopy. Experimental results indicated that the nanoindentation hardness, serrated flow, and surface shear bands were significantly affected by laser irradiation in nitrogen gas. Both surface softening and hardening were observed which depended on the experimental conditions. A competition mechanism between laser thermal shock and the introduction of ZrN phase was employed to rationalize these results. Furthermore, the affecting layer of ZrN phase along the depth direction was measured by EDX. The obtained results suggest a new method to introduce secondary phase into Zr-based MG surface and further to tune the mechanical characteristics of MGs.

A new understanding of the sub-[formula omitted] enthalpy relaxation in metallic glasses

We performed a study of the sub-Tg enthalpy relaxation effect in a bulk Zr-based metallic glass by means of calorimetric and shear modulus measurements. It is found that the increase of the heat absorption in the supercooled liquid state due to sub-Tg preannealing can be well described by a kinetic equation derived within the framework of the Interstitialcy theory. This equation assumes that the heat effects are controlled by the relaxation of the shear modulus occurring upon heating. It is revealed that the heat absorbed during temperature rise up to the supercooled liquid region linearly increases with the shear modulus measured near the room temperature. It is argued that this relationship is determined by a change of glass internal energy, which is controlled by the shear moduli of glass and maternal crystal.On the other hand, it is suggested that sub-Tg enthalpy relaxation as well as relaxation of the shear modulus are governed by concentration changes of interstitialcy-type defects inherited from the melt. This approach, in particular, allows explanation of a new dependence of the heat absorbed during sub-Tg enthalpy relaxation experiment as a function of the preannealing time at temperatures well below Tg.Overall, the obtained results give further clear confirmation of a major role of the shear elasticity in relaxation phenomena in metallic glasses.

Excellent near-infrared transmission of Zr-based thin film metallic glasses

Abstract Zr50Cu50, Zr47Cu44Al9, Zr46.3Cu43.4Al8.3Nb2 and Zr41.2Ti13.8Cu17.5Ni5Be22.5 thin film metallic glasses (TFMGs) were prepared by pulsed laser deposition (PLD) on glass substrates at room temperature. The effect of thickness on the electrical and optical properties of the Zr-based TFMGs was investigated. It was found that the resistivity of the Zr-based TFMGs basically decreased as the thickness varied from 10 nm to 40 nm. Interestingly, while the transmittance in the visible region decreased significantly with the increase of thickness, the transmittance in the near-infrared range still remained at a high level of larger than 80%. Through the characterization of electrical properties, the high transmittance of the Zr-based TFMGs in the near-infrared range was attributed to their rather low carrier concentration. Our findings provided the possibility for TFMGs to be used as transparent electrodes in the field of near infrared sensors and solar cells.

Effect of structural heterogeneity on serrated flow behavior of Zr-based metallic glass

Physical correlation between structural heterogeneity and plastic flow of metallic glasses (MGs) is crucial for the understanding of MGs' deformation mechanism. In this work, different degrees of structural heterogeneity are introduced into Zr-based MGs through different cooling rates casting. The effect of structural heterogeneity on serrated flow behavior was studied. The findings demonstrate that there exists a tendency that serration flow dynamics of the MGs transforms from a chaotic state to a self-organized critical state with increased inhomogeneity. The established correlation between structural heterogeneity and serrated flow behavior shows that the higher degree of structural heterogeneity facilitates a higher frequency of interaction and multiplication of shear bands by increasing nucleation sites, and then promotes serrated flow behavior to be more homogeneous in time and space, thereby induces transformation of dynamics behavior and improves the plasticity. The obtained results shed light on deformation mechanism of plastic flow and provide a new insight into the plasticity of MGs.

A Ni-, Al-, Be-free Zr-based metallic glass for biomedical applications

Biomaterials are attracting an ever-increasing research interest. As part of this overall effort, we report herein the fabrication and characteristics of Zr-based ribbon samples with three different compositions: Zr56Co28Ga16, Zr56Co28Ga14Si2, and Zr56Co28Ga14Sn2. The supercooled-liquid region ΔT = Tx − Tg of these materials is 16, 18, and 29 K, respectively, where Tx is the temperature of the onset of crystallization and Tg is the glass-transition temperature. The samples are thermally characterized by using differential scanning calorimetry and by determining the activation energy. The corrosion resistance is determined by immersing the materials for up to 20 days in a simulated body fluid, and the cytotoxicity is measured from the proliferation of osteoblast-like cells on the samples. Finally, the mechanical properties are investigated by nanoindentation. The Young's modulus is 112 GPa. These results all highlight the suitability of this metallic glass for biomedical applications.

Temperature rise from fracture in a Zr-based metallic glass

Inhomogeneous serrated plastic flow and the subsequent fracture of a Zr-based metallic glass are probed by high-speed in-situ pyrometry and in-situ acoustic emission. Whilst the temperature rise during serrated flow remains below the detection threshold of 300 °C, fracture is accompanied by ΔT of up to approximately 600 °C within less than 100 μs. Heating rates during fracture are up to 107 K/s, for which a dynamic glass transition temperature can be determined. A continuous wavelet analysis of the acoustic-emission pulse from fracture reveals an intermittent crack propagation with phases of intense activity of ca. 5–15 μs. These findings quantify the final stage of a shear-band-to-crack transition in terms of time scales and temperature excursions, the latter of which remains well below the melting temperature of the material in this study.

Correlation between the atomic configurations and the amorphous-to-icosahedral phase transition in metallic glasses

Abstract

Tensile Creep Characterization and Prediction of Zr-Based Metallic Glass at High Temperatures

The high temperature creep behaviors of a Zr-based bulk metallic glass (BMG) are studied by uniaxial tensile creep experiments under applied stresses of 50–180 MPa at temperatures of 660–700 K. The microstructural observations of the BMG samples after creep tests show that crystalline phases can be detected under high temperature or high applied stress. Constitutive models for predicting the high temperature creep behaviors of the studied Zr-based BMG are established based on the θ projection method. The creep activation energy and stress exponent are also calculated to establish the creep model. The parameters of the established models are found to be closely associated with the applied stress and temperature. The results show an excellent agreement between the measured and predicted results, confirming the validity of the established model to accurately estimate the high temperature creep curves for the Zr-based BMG. Moreover, based on the classical diffusion creep theory, a schematic model is proposed to describe the creep behaviors of BMGs from the framework of free volume theory.

Effects of Ti addition on corrosion behavior of Zr-based metallic glass in chloride medium

The effects of Ti element on the corrosion resistance of the metallic glass Zr51.3Al10Ni6Cu31.8Ag0.1Y0.8 in aqueous solution with various chloride concentrations were investigated, and the effect mechanism was discussed. X-ray diffraction confirmed that Ti-added Zr51.3Al10Ni6Cu31.8Ag0.1Y0.8 metallic glasses with diameter of 3 mm were all metallic glasses. Weight loss and electrochemical method were introduced to characterize their corrosion resistance, and X-ray photoelectron spectroscopy study was used to characterize the passive film composition. The results show that the corrosion resistance of metallic glass is significantly improved with Ti addition, and Zr dioxides dominate in passive film during corrosion when Ti content is low. High Ti addition can lead to an obvious accumulation of Ti dioxides, which results in a thicker, Ti-enriched protective passive film.

Additive manufacturing of Zr-based metallic glass structures on 304 stainless steel substrates via V/Ti/Zr intermediate layers

Welding of dissimilar metals is challenging, particularly between crystalline metals and metallic glasses (MGs). In this study, Zr65.7Cu15.6Ni11.7Al3.7Ti3.3 (wt%) MG structures were built on 304 stainless steel (SS) substrates by laser-foil-printing (LFP) additive manufacturing technology in which MG foils were laser welded layer-by-layer onto the SS substrate with a transition route, i.e., SS → V → Ti → Zr → MG. The direct welding of MG on SS would lead to the formation of various brittle intermetallics and the consequent peeling off of the welded MG foils from the SS substrate, which could be resolved via the use of V/Ti/Zr intermediate layers. The chemical composition, formed phases, and micro-hardness were characterized in the dissimilar joints by energy dispersive spectroscopy, X-ray diffraction, and micro-indentation. Since the intermediate materials were highly compatible with the base metals or the adjacent intermediate metals, undesirable intermetallics were not detected in the dissimilar joint. The bonding tensile strength between the SS substrate and the MG part with intermediate layers was measured about 477 MPa.

Measuring Elastic Properties of the Constituent Multilayer Coatings for Different Modulation Periods

This paper is developed to characterize mechanical properties of multilayer coatings for different modulation periods. To that end, Dimensional Analysis Method (DAM) and Finite Element Method (FEM) are applied. Based on these methodologies, two dimensionless forms for the new model are expressed. Numerical nanoindentation tests are carried out for different set properties of multilayer coatings in order to validate the proposed model. Therefore, the mechanical properties of multilayer thin films are identified according to the reverse analysis algorithm. Hence, the input and the identified properties are consistent which ensure the effectiveness and the reliability of the proposed model. Moreover, a case study of Ti-TiN multilayer coating deposited on Zr-based metallic glasses was considered. As a result, the new model is useful for multilayer coatings for different modulation periods and can be used for technological applications.

Softening of Zr-based metallic glass induced by nanosecond pulsed laser irradiation

Laser irradiation has been recently used to tune the mechanical properties of metallic glasses (MGs). However, the mechanism for plasticity improvement by laser irradiation is still not completely clear and requires further investigation. In this study, nanosecond pulsed laser irradiation is applied on a Zr-based MG surface under various laser powers, scanning speeds, and numbers of irradiation cycles. Then, the mechanical properties of the as-cast and laser-irradiated MG surfaces are characterized by nanoindentation tests. In particular, the indentation hardness, load-depth curve, serrated flow, and residual indent morphology of the surfaces are compared. The results show that the nanosecond pulsed laser irradiation softens the irradiated regions; the effect of the irradiation is slightly dependent on the laser irradiation parameters, and especially the laser scanning speed. Furthermore, laser irradiation considerably affects serrated flows in the load-depth curve and shear bands on the top surface, denoting different plastic deformation characteristics compared with the non-irradiated sample. These differences could be rationalized in terms of laser irradiation-induced formation of pre-existing shear bands in the subsurface layer, as well as thermal effects. The present results are expected to enhance the general understanding of the effects of laser irradiation on the mechanical properties of MGs.

Ultrastable metallic glasses formed on cold substrates

Vitrification from physical vapor deposition is known to be an efficient way for tuning the kinetic and thermodynamic stability of glasses and significantly improve their properties. There is a general consensus that preparing stable glasses requires the use of high substrate temperatures close to the glass transition one, Tg. Here, we challenge this empirical rule by showing the formation of Zr-based ultrastable metallic glasses (MGs) at room temperature, i.e., with a substrate temperature of only 0.43Tg. By carefully controlling the deposition rate, we can improve the stability of the obtained glasses to higher values. In contrast to conventional quenched glasses, the ultrastable MGs exhibit a large increase of Tg of ∼60 K, stronger resistance against crystallization, and more homogeneous structure with less order at longer distances. Our study circumvents the limitation of substrate temperature for developing ultrastable glasses, and provides deeper insight into glasses stability and their surface dynamics.

Metallic glass hardening after thermoplastic forming

Thermoplastic forming is an important manufacturing technique for the shaping of metallic glass (MG) components. However, property changes of MGs after such forming are unclear. This paper systematically studied the effect of thermoplastic forming on the structure and mechanical properties of a Zr-based MG. It was found that the MG after forming is of higher hardness; yet this effect increases with the forming temperature rise. Localized shear deformation as commonly observed around a Vickers indentation mark in MGs was not found around the indentation mark of the thermoplastically formed MG. The study concluded that the primary mechanism of such property change of the MG is due to the free volume annihilation induced by the structural relaxation during the thermoplastic forming.

Effects of iron addition on the dynamic mechanical relaxation of Zr55Cu30Ni5Al10 bulk metallic glasses

Dynamic mechanical relaxation behavior of (Zr55Cu30Ni5Al10)100-xFex (x = 0, 1 and 2) bulk metallic glasses was investigated by mechanical spectroscopy. It is found that the main α relaxation of the Zr-based metallic glasses can be well described by the Kohlrausch-Williams-Watts (KWW) function. With the increasing of micro-alloying element content, i.e. iron, the value of Kohlrausch exponent βKWW diminishes for the (Zr55Cu30Ni5Al10)100-xFex (x = 0, 1 and 2) metallic glass, whereas the characteristic relaxation time increases. In the framework of the quasi-point defects theory, the physical correlation factor χ increases with higher iron content below the glass transition temperature Tg. In addition, the parameter a of the quasi-point defect theory can describe the degree of deviations from the Arrhenius law. Based on the theoretical and experimental analysis, it is implied that structural heterogeneity of the Zr55Cu30Ni5Al10 bulk metallic glass could be tailored through minor addition of the iron element.