Properties Of Bulk Metallic Glasses Research Articles

Effect of cast temperature, size and annealing condition on the serrated flow during nano-indentation of Zr-based bulk metallic glasses

The present work deals with mechanical properties of five multicomponent Zr-based bulk metallic glasses: Zr58Cu22Fe2Ag6Al12, Zr58Cu22Fe4Ag4Al12, Zr58Cu22Fe4Co4Al12, Zr58Cu22Fe8Al12, and Zr58Cu22Ag8Al12, using nano-indentation technique at very low loading rate (80 μN/s). Zr-based glasses exhibit serrated flow during nano-indentation, manifested as a stepped load-displacement curve. Systematic study on the influence of free volume and nanocrystallization on shear band formation by varying the casting temperature and cross-section of the Zr58Cu22Fe2Ag6Al12, and annealing above and below glass transition temperature of the Zr58Cu22Co4Fe4Al12 alloy is carried out. Analysis of the experimental data has revealed that higher casting temperature and larger casting cross-section cause partial crystallization, which decreases the hardness by promoting multiple shear band formation. However, hardness of the annealed glasses with similar fraction of nanocrystalline phases increases due to the reduction of free volumes as confirmed through electron diffraction studies in transmission electron microscope. Moreover, both free volume and nanocrystalline phase are found to have significant influence on the mechanical properties of bulk metallic glasses investigated in the present study.

Mechanical behavior of bulk metallic glass prepared by copper mold casting with reversed pressure

The effect of applied reversed pressure on mechanical properties of bulk metallic glass (BMG) prepared by copper mold casting was investigated by quasi-static compression experiment and Weibull statistics. The BMG samples prepared by negative pressure casting exhibit higher strength and larger plasticity compared with those prepared by positive pressure casting. The applied reversed pressure plays a key role not only in the formation of cast defect at macro-scale but also for the distribution of free volume at micro-scale, which is responsible for the variable values of strength and plasticity, respectively. In copper mold casting process, negative pressure is also beneficial for reducing porosity content and homogeneous distribution of free volume, which in turn leads to the improvement of the reliability of BMGs.

Enhanced wear resistivity of a Zr-based bulk metallic glass processed by high-pressure torsion under reciprocating dry conditions

Wear properties of bulk metallic glasses (BMGs) are important for industrial applications as much as strength and ductility. Free volume of BMGs is a significant factor which decides wear mechanism and resistance. Increased free volume of a Zr55Al10Ni5Cu30 BMG processed by high-pressure torsion (HPT) affected wear resistance under dry reciprocating conditions. Two- and three-body abrasive wear as well as the delamination of oxide layers simultaneously operated during the wear tests of both as-cast and HPT-processed BMG (HPT-BMG). However, the HPT- BMG had a larger area of the oxide layers on a worn surface compared to the as-cast BMG at the early stage of the wear tests. The increased free volume by the HPT process resulted in ductile plastic deformation, prohibited crack propagation, and delayed delamination of the oxide layers. Therefore, the HPT-BMG had thicker oxide layers, which acted as an adequate protection and increased wear properties of the Zr-based BMG.

Phase separation and significant plastic strain in a Zr–Cu–Ni–Al–Fe bulk metallic glass

In this study, we reported a phase-separated Zr62Cu18Ni10.4Al8Fe1.6 bulk metallic glass exhibiting a significant plastic strain at room-temperature. The engineering plastic strain, fracture strength and Young's modulus were determined to be about 32.6%, 2919MPa and 90GPa respectively. The enhanced ductility was explained from the view point of elastic energy dissipation, separation length and shear modulus difference between separated phases. This result provides a promising approach to improve the mechanical properties of bulk metallic glasses through compositional and structural design by microalloying.

PROPERTIES OF BULK METALLIC GLASSES

A relatively small number of revolutionary discoveries were made in the field of metallurgy and metal physics in the last few decades, and bulk metallic glasses are one of them. The strength and hardness of bulk metallic glasses are much higher while moduli of elasticity are lower than those of crystalline alloys which results in high stored elastic strain energy. These alloys also have very good corrosion resistance. This article covers various properties of bulk metallic glasses, in particular thermal, mechanical, magnetic, electrical properties and corrosion resistance as well as applications of these alloys.

The effect of high energy concentration source irradiation on structure and properties of Fe-based bulk metallic glass

Metallic glasses exhibit metastable structure and maintain this relatively stable amorphous state within certain temperature range. High intensity laser beam was used for the surface irradiation of Fe–Co–B–Si–Nb bulk metallic glasses. The variable parameter was laser beam pulse energy.For the analysis of structure and properties of bulk metallic glasses and their surface after laser remelting the X-ray analysis, microscopic observation and test of mechanical properties were carried out. Examination of the nanostructure of amorphous materials obtained by high pressure copper mold casting method and the irradiated with the use of TITAN 80-300 HRTEM was carried out. Nanohardness and reduced Young‘s modulus of particular amorphous and amorphous-crystalline material zone of the laser beam were examined with the use of Hysitron TI950 Triboindenter nanoindenter and with the use of Berkovich‘s indenter.The XRD and microscopic analysis showed that the test material is amorphous in its structure before irradiation. Microstructure observation with electron transmission microscopy gave information about alloy crystallization in the irradiated process. Identification of given crystal phases allows to determine the kind of crystal phases created in the first place and also further changes of phase composition of alloy.The main value of the nanohardness of the surface prepared by laser beam has the order of magnitude similar to bulk metallic glasses formed by casting process irrespective of the laser beam energy used.Research results analysis showed that the area between parent material and fusion zone is characterized by extraordinarily interesting structure which is and will be the subject of further analysis in the scope of bulk metallic glasses amorphous structure and high energy concentration source.The main goal of this work is the results’ presentation of structure and chosen properties of the selected bulk metallic glasses after casting process and after irradiation process employing the high energy concentration sources.

Role of minor additions on metallic glasses and composites

Abstract

Impact of micro-alloying on the plasticity of Pd-based bulk metallic glasses

Micro-alloying was performed using additions of Co and Fe to monolithic Pd40Ni40P20 bulk metallic glass. Compression tests showed a plastic strain of 13% for the Co addition (1at.%), whereas the Fe addition (0.6at.%) led to immediate failure after reaching the elastic limit. Plasticity is not reflected by the high Poisson’s ratio of 0.4 since it remained unaffected by minor alloying. Applying the fictive temperature concept to analyze the impact of minor alloying suggests that the total amount of free volume frozen-in during vitrification is less important for the mechanical properties of bulk metallic glasses than its local distribution.

Study on Cu<sub>48</sub>Zr<sub>43</sub>Al<sub>9</sub> and Cu<sub>54</sub>Zr<sub>40</sub>Al<sub>6</sub> Amorphous Matrix Alloys by Mechanical Spectroscopy

Anelastic properties of Bulk Metallic Glasses (BMG) were studied by mechanical spectroscopy using a flexural vibration apparatus. BMG’s samples, with nominal composition Cu48Zr43Al9and Cu54Zr40Al6, were produced by skull push-pull casting technique in rectangular cavity cooper mold. In both samples, the differential scanning calorimeter patterns have evidenced the presence of amorphous structure, although the X-ray diffraction for Cu48Zr43Al9composition has shown a heterogeneous microstructure embedded in the amorphous matrix. Anelastic relaxation spectra were obtained using an acoustic elastometer system with vibration frequency in the kilohertz bandwidth, a heating rate of 1 K/min, vacuum greater than 10-5mBar in the temperature range of 300 K to 620 K. In the flexural apparatus, an acoustic elastometer system, the internal friction (energy loss) and the elastic modulus were obtained by free decay of vibrations and by the squared of the oscilation frequency, respectively. Internal friction spectra were not reproducible among the measurements, which may imply atomic rearrangement in the samples due to consecutive heating. Normalized elastic modulus data showed distinct behavior from the first to the other measurements evidencing irreversible microstructural alterations in the samples possibly associated with mechanical relaxation due to the motion of atoms or clusters in the glassy state.

Linking structure to fragility in bulk metallic glass-forming liquids

Using in-situ synchrotron X-ray scattering, we show that the structural evolution of various bulk metallic glass-forming liquids can be quantitatively connected to their viscosity behavior in the supercooled liquid near Tg. The structural signature of fragility is identified as the temperature dependence of local dilatation on distinct key atomic length scales. A more fragile behavior results from a more pronounced thermally induced dilatation of the structure on a length scale of about 3 to 4 atomic diameters, coupled with shallower temperature dependence of structural changes in the nearest neighbor environment. These findings shed light on the structural origin of viscous slowdown during undercooling of bulk metallic glass-forming liquids and demonstrate the promise of predicting the properties of bulk metallic glasses from the atomic scale structure.

INVESTIGATION AND MODELING OF ZR-BASED BULK METALLIC GLASS CRYSTALLIZATION PROCESSES

The article describes the investigation and simulation of Zr-based bulk metallic glass crystallization kinetics using DSC and DIC techniques. The investigation of the kinetics of crystallization processes may eventually provide deeper understanding of the bulk metallic glass crystallization mechanism and promote the evidence-based selection of heat treatment to form desired structure and properties of bulk metallic glasses based composites.

The detrimental effect of flux-induced boron alloying in Pd–Si–Cu bulk metallic glasses

We report on advanced insights into the fluxing of Pd–Si–Cu bulk metallic glasses. Flux-induced boron alloying and trapping of oxides are found to be associated with the employed boron oxide fluxing agent, and both influence the attainable glass-forming ability (GFA) in opposite ways. Incorporated boron strongly deteriorates the GFA due to a rising liquidus temperature, while the oxygen reduction improves it. Thus, proper fine-tuning of the fluxing time and overheating characteristics leads to an enhancement of GFA. In the current case, the critical diameter of Pd77.5Si16.5Cu6 bulk metallic glasses can be increased to 15 mm, as compared to 3 mm in the unfluxed case. Based on these results, we illustrate that the development of further fluxing agents is crucial for enhancement of the key properties of bulk metallic glasses.

High quality factor metallic glass cantilevers with tunable mechanical properties

The resonant properties of bulk metallic glass (BMG) microcantilevers were studied. Pt57.5Cu14.7Ni5.3P22.5 BMG was used to fabricate the cantilevers, on the wafer scale, using a thermoplastic forming technique. The resonant behaviors of the cantilevers were then measured in air and various vacuum levels and annealing conditions. The quality factors increase predictably after annealing at temperatures below the glass transition temperature (Tg) for different times. The increase of quality factor of annealed cantilevers is attributable to the decrease in internal friction of the BMG due to thermally activated structural relaxation. Annealing above Tg resets the quality factor to values comparable to that of the as-formed cantilever. Therefore, the quality factor and mechanical properties of a cantilever could be tuned by the selection of suitable annealing temperatures and times. The measured quality factors are in excess of 2000 in air and 8100 in vacuum.

Materials by design: An experimental and computational investigation on the microanatomy arrangement of porous metallic glasses

The correlation of a material’s structure with its properties is one of the important unresolved issues in materials science research. This paper discusses a novel experimental and computational approach by which the influence of the pores on the mechanical properties of bulk metallic glasses (BMGs) can be systematically and quantitatively analyzed. The experimental stage involves the fabrication of a template whose pore configurations are pre-determined by computer-aided design tools, and replication of the designed patterns with BMGs. Quasi-static mechanical characterization of these complex microstructures is conducted under uniaxial tension and in-plane compression. For the numerical simulations, a non-local gradient-enhanced continuum mechanical model is established, using thermodynamic principles and periodic boundary conditions. The combination of the experimental and numerical results has identified the importance of the pore configuration, overall porosity and diameter to the spacing ratio of the pores to attain optimized material properties.

Fluxing of Pd–Si–Cu bulk metallic glass and the role of cooling rate and purification

Boron oxide fluxing represents an interesting processing technique for attaining a simultaneous improvement in many properties of bulk metallic glasses (BMGs). This concerns glass-forming ability (i.e. a more than three times larger critical casting thickness), in combination with a significant improvement of thermal and mechanical characteristics. In particular, a better understanding of the flux treatment can result in further enhancement of toughness and ductility, which is crucially needed for structural applications. This study investigates the effects of fluxing of Pd–Si–Cu BMGs. By studying four differently processed materials (i.e. cast, water-quenched, fluxed-cast and fluxed alloys), the influences of applied cooling rate and purification associated with flux treatment can be decoupled. The better glass-forming ability is linked to the reduction of heterogeneities, whereas the thermal characteristics depend on both parameters. The interplay of slower quenching rates and the suppression of heterogeneous nucleation is reflected in an extended supercooled liquid range, improving the formability of the BMG. Better ductility is also obtained and can be explained in terms of purification, which is correlated with a decrease in oxygen concentration. In summary, the properties of fluxed specimens are improved not only by the reduction of heterogeneous nucleation, but also via modified cooling rates during fluxing. This study illustrates the importance of adequate processing of BMG-forming liquids to achieve improved properties and casting thicknesses.

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.

Effects of B2 precipitate size on transformation-induced plasticity of Cu–Zr–Al glassy alloys

To demonstrate the effect of processing on the microstructure and subsequent mechanical property of bulk metallic glasses, we prepared two alloys, Cu47.5Zr47.5Al5 and Cu47.5Zr48Al4Co0.5, using two different designs of suction mold – one with a sharp inlet and one with a blunt inlet. The two alloys have been demonstrated previously to be ductile via phase transformation of the B2 phase and twin formation during plastic deformation. Microstructures of the as-cast as well plastically deformed samples, in particular, the size and distribution of the B2 phase, were examined using X-ray diffraction, scanning and transmission electron microscopy. Compressive tests were conducted on samples cast by different molds and their properties were found to closely correlate with the B2 morphology. Fluid dynamics during suction casting was also analyzed. Effects of Vena contracta, flow velocity, and Reynolds number were discussed and compared favorably with experimental observations.

Linking high- and low-temperature plasticity in bulk metallic glasses: thermal activation, extreme value statistics and kinetic freezing

At temperatures well below their glass transition, the deformation properties of bulk metallic glasses are characterized by a sharp transition from elasticity to plasticity, a reproducible yield stress and an approximately linear decrease of this stress with increasing temperature. In the present work, it is shown that when the well-known properties of the undercooled liquid regime, in terms of the underlying potential energy landscape, are assumed to be also valid at low temperature, a thermal activation model is able to reproduce the observed onset of macroscopic yield. At these temperatures, the thermal accessibility of the complex potential energy landscape is drastically reduced, and the statistics of extreme value and the phenomenon of kinetic freezing become important, affecting the spatial heterogeneity of the irreversible structural transitions mediating the elastic-to-plastic transition. As the temperature increases and approaches the glass transition temperature, the theory is able to smoothly transit to the high-temperature deformation regime where plasticity is known to be well described by thermally activated viscoplastic models.

Determination of accurate theoretical values for thermodynamic properties in bulk metallic glasses

Deviation values of specific heat difference \( \Updelta C_{\rm p},\) the Gibbs free energy difference \( \Updelta G , \) enthalpy difference \( \Updelta H , \) and entropy difference \( \Updelta S \) between the supercooled liquid and corresponding crystalline phase produced by the linear, hyperbolic, and Dubey’s expressions of \( \Updelta C_{\rm p}\) and the corresponding experimental values are determined for sixteen bulk metallic glasses (BMGs) from the glass transition temperature \( T_{\text{g}} \) to the melting temperature \( T_{\text{m}}. \) The calculated values produced by the hyperbolic expression for \(\Updelta C_{\rm p}\) most closely approximate experimental values, indicating that the hyperbolic \(\Updelta C_{\rm p}\) expression can be considered universally applicable, compared to linear and Dubey’s expressions for \( \Updelta C_{\rm p},\) which are accurate only within a limited range of conditions. For instance, Dubey’s \(\Updelta C_{\rm p}\) expression provides a good approximation of actual experimental values within certain conditions (i.e., \( \xi = \Updelta C_{\rm p}^{\rm g}/\Updelta C_{\rm p}^{\rm m}< 2 , \) where \(\Updelta C_{\rm p}^{\rm g}\) and \(\Updelta C_{\rm p}^{\rm m}\) represent the specific heat difference at temperatures \( T_{\text{g}} \) and \( T_{\text{m}} , \) respectively).

Structure and corrosion resistance properties of Ni–Fe–B–Si–Nb amorphous composite coatings fabricated by laser processing

Ni-based amorphous composite coatings with a composition of Ni40.8Fe27.2B18Si10Nb4 have been prepared on a mild steel substrate by high power diode laser cladding plus laser remelting processes. The microstructure of the coating was studied by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Polarization tests and electrochemical impedance spectroscopy (EIS) measurements were employed to study corrosion behavior of the coatings in 3.5% NaCl solution. The corrosion resistance properties of bulk metallic glasses (BMGs) ribbon with same nominal composition and 316L stainless steel were also measured for comparison. It was found that the laser remelted coatings exhibit dense amorphous structure matrix embedded by some crystal phases. Due to the existence of grain boundaries, the Ni-based amorphous composite coating exhibits worse corrosion resistance than BMGs ribbon. While the laser remelted coating shows better corrosion resistance properties than 316L stainless steel and laser cladded coating. A capacitive loop and a straight line are shown in the Nyquist plot, indicating that a Warburg element can be drawn in the equivalent electrical circuit representative of the laser remelted coating.