Zr50Cu40Al10 Bulk Metallic Glass Research Articles

Comparative analysis of nanoindentation-induced incipient deformation of zirconium-based bulk metallic glass in various structural states

The incipient plastic deformation behaviour of as-cast and annealed samples of Zr50Cu40Al10 (atom %) bulk metallic glass was investigated by nanoindentation. A validated load-over-displacement versus displacement plot showed the existence of a precursor event to incipient plasticity in both samples. The activation stress remained consistent in both samples, indicating that the event corresponds to local behaviour in regions with the same energy state, and it is not influenced by the overall microstructure. Conversely, the first serration detected in the as-relaxed sample exhibited a greater magnitude, potentially arising from a distinct energy-dissipation rate related to larger-scale microstructural characteristics.

Influence of Mo micro-particles on crack formation, microstructure, and mechanical behaviour of laser powder bed fusion fabricated CuZrAl bulk metallic glass composites

ABSTRACT In this work, a new design principle, i.e. doping with refractory metal particles with a low diffusion rate to prevent the formation of cracks and to improve the mechanical properties of bulk metallic glass (BMG) composites, was put forward. It was proven that crack-free and dense Mo(p)/Cu47Zr47Al6 BMG composites with enhanced mechanical properties can be produced via LPBF. The dislocations generated in the Mo particles can release thermal stress, thereby inhibiting the formation of thermal-cracks. The fracture patterns of Mo particles show that they can delay rapid of crack expansion, thereby improving the inherent strength and toughness of the material.

Effect of pre-straining on the structure and nano-mechanical properties of a CuZrAl bulk metallic glass

Pre-straining was carried out on a CuZrAl bulk metallic glass (BMG), in order to understand the physical correlation between its structural heterogeneity and nano-mechanical performance. As the pre-strain increases, the studied glass remains its amorphous structure whereas the degree of local order firstly decreases and then increases, yielding a minimum value at 10 % pre-strain, and the Helmholtz activation energy (ΔF*), shear transformation zone (STZ) volume, number of atoms in the STZ (N), and the nanohardness value exhibits a similar trend. The variation in the structure and thus mechanical performance induced by pre-straining has been interpreted from the viewpoint of free volume concept. The results obtained here can be beneficial for tailoring the structure and the corresponding mechanical properties of BMGs.

Combustion behavior and mechanism of Cu46Zr46Al8 bulk metallic glass in oxygen-enriched environments

The present work used a specially designed experimental apparatus with an in situ measurement system to study the combustion of a Cu46Zr46Al8 bulk metallic glass (BMG). This material exhibited more violent and much more rapid combustion compared with its crystalline counterpart. The combustion mechanism was explored by evaluating the associated thermodynamics and kinetics and the effects of various crucial factors on the combustion behavior. The present findings improve our understanding of the combustion mechanisms of metastable metallic materials and also provide guidelines for the development of novel BMGs as advanced energetic materials.

Composition origin of Cu-Zr bulk metallic glasses understood via a “dual-cluster” model of binary eutectics

Cu-Zr is an essential binary bulk glass-forming system with the three best bulk metallic glasses at Cu64Zr36, Cu56Zr44, and Cu50Zr50, which are eutectic or near-eutectic compositions. The current study reveals their composition origin by interpreting these eutectics via a “dual-cluster” model, where a eutectic is composed of two single-cluster-based chemical units derived from the corresponding eutectic phases in simple integer proportions. Each chemical unit represents a stable liquid formulated by the cluster-plus-glue-atom model. For example, eutectic Cu61.8Zr38.2 is deciphered as [Cu-Cu7Zr5]Cu1+4{[Zr-Cu10Zr6]Cu1} = Cu61.6Zr38.4, where the former is from eutectic phase Cu8Zr3 and the latter from another eutectic phase Cu10Zr7. The excellent glass forming composition Cu64Zr36 within this eutectic zone originates from the chemical unit of the Cu8Zr3 phase, [Cu-Cu7Zr5]Cu1 = Cu64.3Zr35.7. Two other eutectics, Cu56.0Zr44.0 and Cu45.7Zr54.3, are also interpreted using this dual-cluster model, leading to suitable glass formers Cu56Zr44 and Cu50Zr50.

Unraveling the microstructural heterogeneity and plasticity of Zr50Cu40Al10 bulk metallic glass by nanoindentation

Unraveling the microstructural heterogeneity is an important issue to understand the physical and mechanical properties of metallic glasses. Structural relaxation below the glass transition temperature Tg and cold rolling at ambient temperature are effective ways to tune the state within the potential energy landscape of metallic glasses, modifying the microstructural heterogeneity. With the help of nanoindentation technique, by scrutinizing the local reduced modulus and hardness of a typical Zr50Cu40Al10 metallic glasses in different energy states (from structural relaxed state to rejuvenated state), we demonstrate that the enhancement of microstructural heterogeneity plays an important role in tailoring the mechanical behavior. The internal friction coefficient is obtained by fitting the experimental load-displacement curves with finite element simulation. It is found that internal friction coefficient decreases with the increase of concentration of flow defects. The stress exponent obtained from the creep stage shows a strong dependence on the structural state of metallic glasses. Effects of structural relaxation and rejuvenation on the structural state are rationalized in terms of the relative flow defects concentration. Finally, the statistics of discrete displacement bursts during the deformation process were probed. We find that the displacement bursts behavior is sensitive to the structural energy state (microstructural heterogeneity). The displacement bursts phenomenon changes from obvious (relaxed state) to unapparent behaviors (rejuvenated state). By given a physical schematic, the correlation between the displacement bursts size and the shear band size in the local plastic zones is well established, which will lead to a deeper understanding of the rejuvenation-induced plasticity of metallic glasses.

A detailed investigation on highly dense CuZr bulk metallic glasses for shielding purposes

Abstract Gamma-ray shielding properties of eight different metallic glasses based on CuxZr100-x: x = 35 (Cu35Zr65) − 70 (Cu70Zr30) were determined using Monte Carlo simulations and Phy-X/PSD software. A typical gamma-ray transmission setup has been modeled in MCNPX Monte Carlo code. The general trend of the linear attenuation coefficients (μ) was reported as (μ)Cu35Zr65 < (μ)Cu40Zr60 < (μ)Cu45Zr55 < (μ)Cu50Zr50 < (μ)Cu55Zr45 < (μ)Cu60Zr40 < (μ)Cu65Zr35 < (μ)Cu70Zr30. In terms of half value layer (HVL) values, the Cu35Zr65 sample has the highest value (2.984 cm) and the Cu70Zr30 sample has the lowest value (2.769 cm) at 8 MeV photon energy. The mean free path (MFP) values were 4.305 and 3.995 cm for Cu35Zr65 and Cu70Zr30 samples, respectively. Generally, MFP and HVL values of the studied glasses were reported as (MFP,HVL)Cu35Zr65 > (MFP,HVL)Cu40Zr60 > (MFP,HVL)Cu45Zr55 > (MFP,HVL)Cu50Zr50 > (MFP,HVL)Cu55Zr45 > (MFP,HVL)Cu60Zr40 > (MFP,HVL)Cu65Zr35 > (MFP,HVL)Cu70Zr30 for all photon energy range. The Cu70Zr30 sample showed maximum values of both the effective conductivity (C eff) and effective electron density (N eff). In addition, the Cu70Zr30 sample has minimum exposure and energy absorption buildup factor (EBF and EABF) values at all studied gamma-ray energies. The results revealed that the Cu70Zr30 sample has superior attenuation properties among all studied samples.

Combustion Behavior and Mechanism of Cu46zr46al8 Bulk Metallic Glass in Oxygen-Enriched Environments

Combustion Behavior and Mechanism of Cu46zr46al8 Bulk Metallic Glass in Oxygen-Enriched Environments

Influence of combinatorial annealing and plastic deformation treatments on the intrinsic properties of Cu46Zr46Al8 bulk metallic glass

In this paper, the effect of severe plastic deformation (SPD) induced by high-pressure torsion (HPT) and isothermal heat treatment (HT) below the glass transition on the structure-property relationships of Cu46Zr46Al8 bulk metallic glass (BMG) is assessed separately and alternately in reference to the as-cast state. Pronounced modifications are confirmed by X-ray diffraction, differential scanning calorimetry, dynamic mechanical analysis (DMA), dilatometry analysis, and scanning electron microscopy. Diffusion-controlled crystallization is achieved via HT with optimized parameters, and HPT is used afterwards to disperse crystalline phases relatively homogenous throughout the matrix. The dispersion of the second phase improves the thermomechanical stability around the glass transition temperature, as confirmed by DMA. Compared to a single HT process, a sequential combination of HT + HPT leads to a glass showing a linear hardness profile with values higher than the as-cast state. This study provides insights into possible processing routes for enhancing the mechanical and/or thermal properties of CuZr-based BMGs, which can also be used to tailor new design routes for other BMG systems.

Generality of abnormal viscosity drop on cooling of CuZr alloy melts and its structural origin

It has been widely accepted that the viscosity of alloy melts increases monotonically with temperature decreasing after exceeding the liquidus temperature. However, a distinct viscosity-drop has been observed in several alloy melts in our previous works. To further understand this dynamic anomaly, we investigated the viscosity of CuZrAl and CuZrTiNi melts by gradually changing the compositions of alloy systems. The results suggest that when the amounts of doping elements (Al, Ti, Ni) become large enough, this abnormal viscosity-drop disappears. For CuZr binary alloys, the anomaly exists when the composition of Zr ranges between 27.3–66.7%, which nearly corresponds to the available content of Zr in CuZr bulk metallic glasses. By conducting molecular dynamics simulation, the mechanism that four icosahedron-like clusters with high fragility evolves with temperature in Cu62Zr38 melts has been recognized. In contrast to general aggregation or growth of clusters during cooling process, an unexpected tendency that more segregations are formed among these clusters and the clusters become further dispersed in liquids has been discovered around 1400 K; meanwhile, the viscosity-drop in our experiments begins simultaneously at this temperature. Below 1300 K, these icosahedron-like clusters aggregate abruptly again. Experimental results from differential scanning calorimeter (DSC) and high-resolution transmission electron microscope (HRTEM) further approve the influence of these fragile icosahedron-like clusters on crystallization processes. This finding uncovers the same structural origin that underlies both the formation of bulk metallic glasses and the dynamic anomaly in melts, and demonstrates the dominant role of fragile icosahedron-like clusters in the feature of liquid dynamics.

Investigation of relaxation behavior in highly rejuvenated bulk metallic glasses by in-situ synchrotron X-ray scattering

Relaxation behaviors of highly rejuvenated Zr50Cu40Al10 bulk metallic glass was investigated using synchrotron X-ray scattering coupled with differential scanning calorimetry. The relaxation of rejuvenated volume is found to correspond to a marked exothermic event prior to the glass transition. High-energy synchrotron X-ray measurements of the structure factor show that annihilation of rejuvenated volume correspond to a sharpening of the scattering peaks. The calculated reduced pair distribution function suggests that the atomic re-arrangement in the second shell are largely responsible for the reduction in the free volume and decrease in full-width at half-maximum of the Total Structure Factor observed during structural relaxation. Mechanical properties in the highly rejuvenated metallic glass were evaluated as a function of annealing temperature.

Centimeter-sized CuZrAl bulk metallic glass with good plasticity and chemical heterogeneity

In this study, a new CuZrAl ternary bulk metallic glass (BMG) with glass forming ability (GFA) of 10 mm in diameter was fabricated. The GFA of the BMG was discussed based on the suppression of the competing crystal phase and the efficient dense packing of the constituting atoms. Compression testing showed that the CuZrAl ternary BMG has good true plastic deformation of 11.7%, whereas its adjacent composition has a plastic deformation of 16.1%. Mapping by energy-dispersive X-ray spectroscopy in scanning transmission mode revealed that chemical heterogeneity exists in the CuZrAl BMGs. Chemical heterogeneity revealed to be a possible reason for the observed mechanical behavior of the CuZrAl ternary BMGs.

Reduction of shear localization through structural rejuvenation in Zr–Cu–Al bulk metallic glass

The effect of high-pressure torsion (HPT) on the structure and mechanical behavior of Zr50Cu40Al10 bulk metallic glass was investigated using calorimetry, density measurement, high-energy X-ray scattering and nanoindentation. Increase in rotation number, and thus plastic deformation, lowers the hardness and elastic modulus, as well as the critical strain rate for suppressing the shear localization. Strain-softening induced by plastic deformation is attributed to the structural rejuvenation. Wide-angle X-ray scattering (WAXS) measurements suggest that HPT deformation reduces and broadens the peaks in the pair distribution function indicative of pronounced structural disordering and enabling structural rejuvenation. Measured excess free volume of 0.8% for samples deformed by HPT with a maximum structural relaxation enthalpy of 29.5 J/g in the sample with 20 and 50 revolutions.

Four Dimensional Scanning Transmission Electron Microscopy during the in situ Annealing of a CuZrAl Bulk Metallic Glass

Journal Article Four Dimensional Scanning Transmission Electron Microscopy during the in situ Annealing of a CuZrAl Bulk Metallic Glass Get access Thomas C Pekin, Thomas C Pekin Department of Physics, Humboldt-Universität zu Berlin, Newtonstraße 15, 12489 Berlin, GermanyDepartment of Materials Science & Engineering, University of California, Berkeley, CA 94720, USANational Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA Corresponding author: tcpekin@physik.hu-berlin.de Search for other works by this author on: Oxford Academic Google Scholar Christoph Gammer, Christoph Gammer Erich Schmid Institute of Materials Science, Jahnstraße 12, Leoben, Austria, 8700 Search for other works by this author on: Oxford Academic Google Scholar Colin Ophus, Colin Ophus National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA Search for other works by this author on: Oxford Academic Google Scholar Robert O Ritchie, Robert O Ritchie Department of Materials Science & Engineering, University of California, Berkeley, CA 94720, USAMaterials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA Search for other works by this author on: Oxford Academic Google Scholar Andrew M Minor Andrew M Minor Department of Materials Science & Engineering, University of California, Berkeley, CA 94720, USANational Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 25, Issue S2, 1 August 2019, Pages 1470–1471, https://doi.org/10.1017/S1431927619008080 Published: 01 August 2019

Enhanced compressive plasticity in a Cu-Zr-Al – Based metallic glass composite

One possible key to improve plasticity in a CuZrAl bulk metallic glass is to introduce soft metallic crystalline particles. Tantalum particles with two different geometries were chosen in the present work: (i) irregularly shaped particles of equivalent average diameter of 45 μm (Ta1) and (ii) spherical particles of average size 25 microns (Ta2). When the volume fraction of tantalum goes from 0% to 50%, the modulus increases (from 95 GPa to 140 GPa), the Poisson's ratio decreases only slightly (from 0.37 to 0.35) and the hardness decreases regularly (from 485 HV30 to about 300 HV30), whatever the particles size. All these results are in agreement with simple laws of mixtures, involving only the volume fraction of the second phase. The results obtained during the compression tests are more complicated. The yield strength decreases when the Ta content exceeds 20% in volume. This evolution is identical for both types of particles. Similarly, an increase in plasticity is always observed when the tantalum content exceeds about 10% in volume. For the highest values of this content, a significant damage of the sample follows this plastic deformation before rupture. But a large dispersion of the values is observed, more particularly for small particles of tantalum. This is due to a problem of heterogeneity of the particles dispersion and the presence of clusters; this difficulty in dispersing the particles is more marked for small spherical particles. An image analysis was performed to characterize this clustering effect. Clusters have a negative effect because they facilitate the propagation of cracks through Ta-Ta weak interface instead of deflecting it. An optimal content to combine a high elastic limit, a good hardness and a high plasticity seems to exist near 30% vol. of crystalline particles.

Localized atomic segregation in the spalled area of a Zr50Cu40Al10 bulk metallic glasses induced by laser-shock experiment

Laser-shock experiments were performed on a ternary bulk metallic glass. A spalling process was studied through post-mortem analyses conducted on a recovered sample and spall. Scanning electron microscopy magnification of fracture surfaces revealed the presence of a peculiar feature known as cup-cone. Cups are found on sample fracture surface while cones are observed on spall. Two distinct regions can be observed on cups and cones: a smooth viscous-like region in the center and a flat one with large vein-pattern in the periphery. Energy dispersive spectroscopy measurements conducted on these features emphasized atomic distribution discrepancies both on the sample and spall. We propose a mechanism for the initiation and the growth of these features but also a process for atomic segregation during spallation. Cup and cones would originate from cracks arising from shear bands formation (softened paths). These shear bands result from a quadrupolar-shaped atomic disorder engendered around an initiation site by shock wave propagation. This disorder turns into a shear band when tensile front reaches spallation plane. During the separation process, temperature gain induced by shock waves and shear bands generation decreases material viscosity leading to higher atomic mobility. Once in a liquid-like form, atomic clusters migrate and segregate due to inertial effects originating from particle velocity variation (interaction of release waves). As a result, a high rate of copper is found in sample cups and high zirconium concentration is found on spall cones.

Dynamic characterization of Cu–Zr binary bulk metallic glasses: A molecular dynamics study

In the present study, a molecular dynamics simulation employing embedded atom method potential is performed to investigate the formation and characterization of CuZr bulk metallic glasses (BMGs). To elucidate the effect of component concentration of three samples of BMGs including Cu25Zr75, Cu50Zr50, and Cu75Zr25 that are formed by melt quenching. The local structure of BMGs is analyzed by means of radial distribution function and local atomic number density, ρ. The mechanical behavior of three compositions is investigated using uniaxial compressive loading at a constant strain rate. It is revealed from the results that yield strength increases with increasing Cu concentration. Thermal expansion of CuZr BMGs is examined and variation in length and volume is measured. The analysis revealed that Cu25Zr75, and Cu50Zr50 exhibited the typical expansion behavior while Cu75Zr25 showed an anomalous behavior.

The Effect of Ag Addition on the Enhancement of the Thermal and Mechanical Properties of CuZrAl Bulk Metallic Glasses

In this study, the thermal and mechanical properties of Cu50−xZr43Al7Agx (x = 0, 3, 4, 5, 6) bulk metallic glasses (BMGs) are investigated by using an X-ray diffractometer (XRD), a differential scanning calorimeter (DSC), differential thermal analysis (DTA), a Vickers hardness tester, a material test system (MTS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Cu50−xZr43Al7Agx (x = 0, 3, 4, 5, 6) BMGs were made by arc-melting and an injection casting process. The results revealed that the glass transition temperature (Tg) and the crystallization temperature (Tx) of CuZrAl alloy decreased with the Ag addition. Hence, the supercooled liquid region and γ of Cu45Zr43Al7Ag5 alloy increased to 76 K and 0.42, respectively. The thermal stability and glass forming ability of CuZrAlAg BMG alloys were enhanced by the microalloyed Ag content. The room temperature compressive fracture strength and strain measured of Cu47Zr43Al7Ag3 were about 2200 MPa and 2.1%, respectively. The distribution of vein patterns and the formation of nanocrystalline phases on the fracture surface of Cu47Zr43Al7Ag3 alloy can be observed by SEM and TEM to be significant, indicating a typical ductile fracture behavior and an improved plasticity of alloys with the addition of microalloyed Ag from 0 to 6 atom %.

Abnormal change of electrical resistivity in the Cu46Zr46Al8 bulk metallic glass during crystallization

The crystallization of bulk metallic glass occurs with heat release, volume shrinkage, and electrical resistivity decrease because of the differences in properties between the glass and crystalline phases. A standard four-probe electrical resistivity measurement during the crystallization of the Cu46Zr46Al8 bulk metallic glass shows an abnormal increase of resistivity at the initial stage before the normal declining stage. High-density nanocrystals emerged in the matrix, which enhanced electron scattering and resulted in increasing of resistivity. The subsequent normal declining of resistivity was dominated by the growth of the nanocrystals. This high-density site-saturated nucleation followed by slow growth crystallization kinetics was supported by microstructure analysis with SEM and TEM.

Investigation of Elastic Deformation Mechanism in As-Cast and Annealed Eutectic and Hypoeutectic Zr–Cu–Al Metallic Glasses by Multiscale Strain Analysis

Elastic deformation behaviors of as-cast and annealed eutectic and hypoeutectic Zr–Cu–Al bulk metallic glasses (BMG) were investigated on a basis of different strain-scales, determined by X-ray scattering and the strain gauge. The microscopic strains determined by Direct-space method and Reciprocal-space method were compared with the macroscopic strain measured by the strain gauge, and the difference in the deformation mechanism between eutectic and hypoeutectic Zr–Cu–Al BMGs was investigated by their correlation. The eutectic Zr50Cu40Al10 BMG obtains more homogeneous microstructure by free-volume annihilation after annealing, improving a resistance to deformation but degrading ductility because of a decrease in the volume fraction of weakly-bonded regions with relatively high mobility. On the other hand, the as-cast hypoeutectic Zr60Cu30Al10 BMG originally has homogeneous microstructure but loses its structural and elastic homogeneities because of nanocluster formation after annealing. Such structural changes by annealing might develop unique mechanical properties showing no degradations of ductility and toughness for the structural-relaxed hypoeutectic Zr60Cu30Al10 BMGs.