Zr-based Metallic Glass Research Articles

Buckling of metallic glass bars

Uniaxial compression tests of slender metallic glass bars of composition Zr52.5Cu17.9Ni14.6Al10Ti5 (at.%) have been conducted. It was found that the Zr-based metallic glass bars have a tendency to buckle elastically or plastically rather than to yield or fracture if its slenderness ratio is over a critical value. The elastic buckling undermines the intrinsic strength of the metallic glass, but the plastic buckling imparts the metallic glass a benign failure mode and avoids the catastrophic brittle fracture. The phenomena are understood by the unique stress state across the bar. The result has implication for the measurement of mechanical properties of bulk metallic glasses and is of significance in the application of metallic glass members in engineering structures.

Diffusion bonding of a Zr-based metallic glass in its supercooled liquid region

Based on the analyses of the influences of temperature and pressure on diffusion behavior with time, a Zr-based bulk metallic glass is successfully bonded in its supercooled liquid region. The temperature is found to be a key factor for the success of the bonding process if sufficient pressure and time are adopted. Three-point bending tests show that the flexural performance of the samples bonded with various parameters is significantly different. The parameters in favor of diffusion bonding do not automatically benefit the performance of the bonded materials. Diffusion makes the nano-voids shrink to form metallurgical bonding at the interface and it causes structural relaxation leading to the embrittlement inside bulk. Balance between the two aspects is the key to the bonding success and the utility of the bonded materials.

Forming-Free Resistive Switching Characteristics of 15nm Thick Zr-Based Metallic Glass Oxide

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Resistance to He2+ induced irradiation damage in metallic glass Zr64Cu17.8Ni10.7Al7.5

This paper used He2+ ion-irradiated metallic glass Zr64Cu17.8Ni10.7Al7.5 and metallic W with an energy of 500keV at fluences of 2×1017, 5×1017, 1×1018 and 2×1018ions/cm2. Zr-based metallic glass remained mainly amorphous at different fluences. At the irradiation fluence of 2×1018ions/cm2, there was a channel-like damage layer appeared within the range of the surface ions. Cracking and peeling along the grain boundary occurred on the surface of metallic W at the fluence of 1×1018ions/cm2; or even multi-layer peeling occurred at the fluence of 2×1018ions/cm2. TEM analysis revealed that there were a lot of helium bubbles at the end of the range of helium ion. The connection and coalescence growth process of a helium bubble was observed. The surface rms roughness ρrms of Zr-based metallic glass increased first and then decreased with the increase in fluence. The resistance to He2+ irradiation in Zr-based metallic glass was superior to the one in metallic tungsten.

The microstructure and mechanical properties of nitrogen and boron contained ZrCuAlNi thin film metallic glass composites

In this work, nitrogen contained and B doped ZrCuAlNi thin film metallic glass composites (TFMGCs) were grown by magnetron co-sputtering process. Boron element was doped to evaluate its influence on the microstructure and mechanical properties of nitrogen contained TFMGCs. The supercooled liquid region of TFMG was determined by the differential scanning calorimetry (DSC) analysis. The microstructure was analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The phase structure was confirmed by using X-ray diffraction (XRD). The mechanical properties were measured by nanoindentation. The scratch tester and tests were employed to evaluate the adhesion and tribological properties. The surface roughness was determined by atomic force microscopy (AFM). It was concluded that the surface roughness, microstructure, glass-forming ability and mechanical behaviors of TFMGCs were strongly influenced by the nitrogen and boron doping. The ZrN nanocrystallites were embedded in the amorphous matrix. The hardness, H/E ratio, and indentation toughness increased with increasing boron concentration. Excellent adhesion quality was also confirmed for all coatings. The Zr-based thin film metallic glass composite containing 6.4 B–32.6 N (in at.%) with optima hardness, 16.2GPa, adequate indentation toughness and excellent adhesion quality was achieved in this work.

Serrated flow model for metallic glasses under compressive loading

A rheological model is proposed that incorporates the serrated flow nature of metallic glasses. It involves the process of the nucleation, propagation and the arrest of a shear bands in the samples subjected to compressive deformation at room temperature. Numerical resolution of the constitutive equations resulting from the model is compared with the stress-strain curve obtained from in-situ nano-compression test in SEM of Zrbased metallic glass. Parametric identification method was applied and enabled us to release the physical parameters of the model. The obtained results showed that the model is adequately valid to describe the experimental data and the almost adjustable model parameters are physically meaningful and comparable to literature.

Fabrication and characterizations of thin film metallic glasses: Antibacterial property and durability study for medical application

Metallic glasses with the disordered atomic structure have unique properties of high strength, high toughness, good corrosion and abrasion resistances. These materials are thus potentially useful for medical application. In this work, we evaluate the antibacterial property and durability of materials sputter-coated with Zr-based (Zr53Cu33Al9Ta5) and Cu-based (Cu48Zr42Ti4Al6) thin film metallic glasses (TFMGs). Good adhesive coating of Zr-based TFMG on the dermatome gives rise to blade sharpness improvement of ~27%, substantial surface roughness reduction of ~66% and smoother incised wound on the pig skin. As compared to 48.8° on the bare Si wafer, the water contact angles of 119.5° and 106.6° for Zr- and Cu-based TFMGs, respectively, reveal the hydrophobic characteristic of the coated surfaces. The bacterial adhesion of Escherichia coli and Staphylococcus aureus to both Zr- and Cu-based TFMGs is hindered to different extents.

Influence of free volume and medium-range order on the deformation response of rapidly solidified and bulk Zr-based (Zr52Ti6Al10Cu18Ni14) metallic glass

Free volume and medium-range order (MRO) present in rapidly solidified ribbons (RSRs) and bulk metallic glasses (BMGs) of Zr52Ti6Al10Cu18Ni14 have been probed by high resolution electron microscopy, fluctuation microscopy, positron annihilation and differential scanning calorimetry. In the as-solidified condition, RSRs showed higher free volume and lower MRO in comparison to BMGs. Within BMGs, the central regions showed higher MRO and lower free volume than the peripheral regions. Uniform deformation of BMGs and RSRs modified their structures, where in, free volume increased in the former and reduced in the latter. These changes in structures led to work hardening in RSRs and work softening in BMGs. Such behaviour could be explained by invoking a concept of critical free volume in the glass phase. For samples (in as-solidified condition) having free volume higher than the critical value, free volume decreased with deformation and showed work-hardening behaviour. In contrast, the work softening behaviour was noticed in samples having free volume lower than the critical free volume.

On the nature of the shear viscosity and shear modulus relaxation in metallic glasses

Analysis of independent isothermal and linear heating creep and shear modulus measurements performed on bulk Pd- and Zr-based metallic glasses provides evidence that the relaxation of their viscoelastic and elastic properties is controlled by ‘defects’, which respond to stress and temperature similarly to dumbbell interstitials in simple crystalline metals.

Behavior of high resistance to He2+ induced irradiation damage in metallic glass

This study details the irradiation of various metallic glasses ((Cu47Zr45Al8)98.5Y1.5, Zr64Cu17.8Ni10.7Al7.5, Co61.2B26.2Si7.8Ta4.8) and metallic W using He2+ ions with an energy of 500keV at irradiation fluences of 2×1017, 1×1018 and 2×1018ions/cm2 to investigate the radiation-resistant properties of these metallic glasses compared to the conventional irradiation-resistant material W. These three metallic glasses were able to maintain an amorphous state during these irradiation fluences. There was no significant irradiation damage at the low irradiation fluence. When the irradiation fluence was increased to 2×1018ions/cm2, a damage layer appeared up to a distance corresponding to the range of the ions away from the surfaces of the Cu- and Zr-based metallic glasses without any visible damage on the surface. Significant surface stripping damage appeared in the Co-based metallic glass. Relatively speaking, surface layer peeling appeared in metallic W along the crystal boundary at a fluence of 1×1018ions/cm2. When the fluence was increased to 2×1018ions/cm2, multilayer peeling, stripping, etc. appeared. The roughness of the Cu- and Zr-based metallic glass showed further smoothing with increasing fluence, while the opposite occurred in the Co-based metallic glass. Within the wavelength range of 400–1700nm, after irradiation of He2+ at a fluence of 1×1018ions/cm2, the reflectance of the Cu-based and Co-based metallic glasses were decreased by only 17% and 13%, respectively.

Temperature dependent dynamics transition of intermittent plastic flow in a metallic glass. I. Experimental investigations

Cooling shrinkage can increase the atomic packing density of metallic glasses, which can influence their elastic and plastic behaviour. In the present study, the compressive deformation behaviour of a Zr-based metallic glass at temperatures well below the glassy transition temperature, say 123 K to room temperature, is experimentally revealed. The elastic modulus and the shear modulus at different temperatures are measured to elucidate the yield strength changes with temperature according to the model of shear transformation zones. In the plastic regime, based on the SEM observation and the digital scattering correlation method, an enhanced interaction between the elastic shear strain fields initiated by neighbouring shear bands is discussed, which explains the amplitude of serration events decreasing with the temperature decreasing.

Temperature dependent dynamics transition of intermittent plastic flow in a metallic glass. II. Dynamics analysis

By reducing the testing temperatures down to the temperature well below the glassy transition temperature, the serrated flow behaviour during plastic deformation of a Zr-based metallic glass was experimentally investigated and the results were presented in Part I of the present paper. It shows that the yield strength, the plastic deformation ability, the density of shear bands of the metallic glass increase with decreasing temperature. In order to understand the mechanisms for the changes of the mechanical behaviour at low temperatures, in Part II of this study, the stress-time sequence in the plastic strain regime is characterized by a comprehensive dynamical and statistical analysis. The stress-time sequence is found to exhibit a chaotic state at high temperatures (>203 K), whereas a self-organized critical state is obtained at low temperatures (≤203 K) due to the freezing effect. The reasons for the transition between these two distinct spatio-temporal dynamical states are elucidated by investigating the effect of temperature on the deformation units (shear transformation zones) and the elastic interactions between neighbouring shear bands. The results demonstrate that the low temperatures results in an enhancement of the interactions between the elastic strain fields initiated by neighbouring shear bands, which is primarily responsible for the enhanced plasticity of the metallic glass and a dynamics transition.

Modification of structure and property in Zr-based thin film metallic glass via processing temperature control

The aims of this study are to fabricate the Zr–Cu–Ni–Al thin film metallic glass (TFMG) on silicon substrates by DC magnetron sputtering with single target and to investigate the characteristics of coatings with various substrate temperatures. All the coatings exhibit similar structural and thermal properties, yet the hardness increases with processing temperature. It is demonstrated that amorphous matrix and cluster structure are slightly affected by the processing temperatures due to high cooling rate during deposition and superior glass-forming ability. Besides, atoms and clusters can acquire extra energy via heating substrate to stabilize each cluster, and the amount of free volume is reduced. Thus, the hardness increases with substrate temperature owing to the resistance to the shear band propagation. In summary, this study integrates the correlations among microstructure, thermal and mechanical properties, providing a convenient approach to tune TFMG coating performance.

Superhydrophobic Zr-based metallic glass surface with high adhesive force

Micro/nano hierarchical structures were constructed on Zr35Ti30Be26.75Cu8.25 metallic glass surface by silicon moulding and subsequently chemical etching. The as-formed surface exhibited both superhydrophobicity and high adhesive force towards water. The superhydrophobicity is rationalized based on the modified Cassie-Baxter model [A. B. D. Cassie and S. Baxter, Trans. Faraday Soc. 40, 546 (1944)]. The origin of the robust adhesion is described in terms of intermolecular capillary forces. The present results not only provide a method to fabricate superhydrophobic metallic glasses surface but also explore an important industrial application as dry adhesives and transport of liquid microdroplets.

Simulated body fluid electrochemical response of Zr-based metallic glasses with different degrees of crystallization

The bio-electrochemical response in simulated body fluid of the Zr53Cu30Ni9Al8 metallic glasses with different degrees of partial crystallization was systematically examined and discussed. Through thermal annealing, the volume fractions of the crystalline phases are determined to be 0, 34, 63, and near 100%. Based on the bio-corrosion voltage and current, as well as the polarization resistance, it is concluded that the fully amorphous alloy exhibits the highest bio-electrochemical resistance. With an increasing degree of partial crystallization, the corrosion resistance becomes progressively degraded. The passive current reveals that the fully amorphous metallic glasses can form a more protective and denser passive film on the metallic glass surface. The formation of reactive nanocrystalline phases in the amorphous matrix would reduce the bio-corrosion resistance.

Effect of Ti/TiN multilayer protective nanocoatings on Zr-based metallic glasses mechanical performance

Ti/TiN multilayer and monolithic TiN nanocoatings have been deposited on Zr-based metallic glass substrates by means of RF sputtering technique at room temperature. Nanoindentation and nanoscratch tests are used to characterise the mechanical and tribological properties of coated samples. In addition, a Vickers indentation tests and scanning electron microscopy observation have been carried out to explore the deformation mechanism. When coated with the TiN and Ti/TiN multilayers, Zr60Ni10Cu20Al10 bulk metallic glass shows a significant enhancement of both apparent hardness and elastic modulus with a decrease of the friction coefficient. The Vickers indentation shows a fragile behaviour of TiN coatings compared to the Ti/TiN multilayer one. Based on Bhowmick model description, experimental nanoindentation approach is taken to determine the variation of shear stress as function of the penetration depth. It is found that the shear stress developed in the TiN coatings is higher than that observed in the Ti/TiN multilayer. A correlation between finite-element analysis results and experimental data has been proposed. The monolithic or multilayer type of coatings is found to have an influence on the stress and plastic deformation distributions.

Correlation between flow characteristics and interfacial friction behaviour of a Zr-based metallic glass during micro-extrusion

The interfacial friction behaviour of Zr35Ti30Be26.75Cu8.25 metallic glass during micro-extrusion was investigated at various strain rates and temperatures in the supercooled liquid region. A friction mechanism map that distributes adhesion regime, furrow regime and mechanical engagement regime was constructed. These regimes respectively correspond to Newtonian flow, non-Newtonian flow and inhomogeneous flow by comparing with the typical deformation map. The correlation between flow characteristics and interfacial friction behaviour is well analysed by combining the viscosity theory with the finite-element simulations.

Nanoscale creep deformation in Zr-based metallic glass

Nanoscale creep deformation in Zr61Al7.5Cu17.5Ni10Si4 thin films was investigated via instrumented nanoindentation testing. Over three decades of indentation strain rate with varying penetration depth were used to evaluate the effects of applied strain rate and initial creep depth on the creep deformation within small volumes of the metallic glass. A critical penetration depth was identified, below which the creep deformation was dependent upon the applied strain rate, and above which the strain rate sensitivity of the creep deformation reached a plateau value. It was proposed that an interface diffusion mechanism dominated the creep deformation within the shallow depth regime, whilst a transition from the interface diffusion dominant mechanism to the intrinsic creep behavior of the Zr-based metallic glass occurred within the deep depth regime.

Characteristic Studies on the Zr-Based Metallic Glass Thin Film on Antibacterial Capability Fabricated by Magnetron Sputtering Process

Abastract- Silver and copper are commonly used as antibacterial elements in most of biomedical apparatus. Because silver (Ag) is relatively expensive and has some tissue-toxicity as the concentration of ionized silver reaches a critical value, it is necessary to find an alternative element for treating some kinds of bacterial or fungal infection. Copper-based antibacterial material can be a good candidate because of its lower cost, better antifungal ability, and higher chemical stability than those of silver. A series of ZrCuNiAl thin films are coated on 304 stainless steel by a DC sputtering method with different sputtering power. The amorphous feature of these ZrCuNiAl thin films is confirmed by glancing incident X-ray diffraction (GIXRD). The porosity and surface roughness are observed by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM), respectively. The adhesion capability and hardness of these amorphous thin films are conducted by scratch test and nano indentation, respectively. In addition, the organisms such as Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Acinetobacter baumannii and Candida albicans are used in this study to evaluate the antimicrobial effects for ZrCuNiAl thin films which coating on 304 stainless steel substrate.

Influence of the molten quenching temperature on the thermal physical behavior of quenched Zr-based metallic glasses

Thermo-physical behavior of some Zr-based metallic glasses prepared by different molten quenching temperatures was studied by Differential scanning calorimetry (DSC) measurements. The characteristic thermo-physical properties are normally used for evaluating the glass-forming ability (GFA) of metallic glasses. Our results show that the glass transition temperature, crystallization temperature and supercooled liquid region of these metallic glasses increased with increasing the molten quenching temperature. Their glass-forming abilities were discussed in terms of the GFA criterion γ and the reduced glass transition temperature, Trg, using these thermo-physical properties.