Bulk Metallic Glass Materials Research Articles

Prediction of glass forming ability of bulk metallic glasses based on convolutional neural network

Bulk metallic glasses (BMGs) have been widely used in different fields owing to their unique and excellent properties. In order to accelerate the development of BMGs, different feasible parameters or criteria of their glass forming ability (GFA) have been proposed. With the advent of the era of big data, machine learning (ML) methods provide novel insights into the study of BMGs. In this paper, we trained a convolutional neural network (CNN) model to investigate GFA of BMGs. A hundred alloying elements and their possible combinations were taken into account by mapping an alloying composition into a 10 × 10 feature graph. Compared with the other prediction methods of GFA in BMGs, the alloy composition is the only variable input without the requirement for various physical and chemical properties obtained through pre-experiments. The predictive ability of our proposed model is quantified by a training R2 of 0.9745 and a test R2 of 0.8137. This work suggests that ML approaches has great potential in guiding the design of new BMG materials.

Designing bulk metallic glasses materials with higher reduced glass transition temperature via machine learning

Bulk metallic glasses (BMGs) are considered as one of the most promising candidates in the field of alloy materials due to their outstandingly high yield strengths and large elastic limits at ambient conditions compared to their crystalline counterparts. The formation of BMGs is determined by reduced glass transition temperature (Trg) that represents the glass forming ability (GFA). Experimental search for BMGs with higher Trg is a challenging task due to the vast chemical space and lack of predictive guidelines. Here, we demonstrate a machine learning approach to guide experimental synthesis in search of BMGs with higher Trg. The relationships between the Trg and chemical compositions of BMGs were investigated by using three different machine learning algorithms including support vector regression (SVR), back propagation artificial neural network (BPANN) and gradient boosting regression (GBR). The best predictions from SVR, BPANN, and GBR models were recommended for experimental tests. Based on the leave-one-out cross-validation (LOOCV), the correlation coefficient (R) and root mean squared error (RMSE) between predicted and experimental Trg were 0.894 and 0.0116, respectively. Furthermore, virtual screening based on machine learning results was adopted to design BMGs with higher Trg. The average relative error of Trg from newly synthesized BMGs is 1.00%, which is satisfactory compared to that of the known experimental samples (3.91%). Among the newly synthesized BMGs, Mg0.65Ag0.19Cu0.06Gd0.1 owns the highest Trg of 0.6658, exceeding the highest Trg (0.6576) in the reported experiments before.

Combining Mg-Zn-Ca Bulk Metallic Glass with a Mesoporous Silica Nanocomposite for Bone Tissue Engineering.

Mg–Zn–Ca bulk metallic glass (BMG) is a promising orthopedic fixation implant because of its biodegradable and biocompatible properties. Structural supporting bone implants with osteoinduction properties for effective bone regeneration have been highly desired in recent years. Osteogenic growth peptide (OGP) can increase the proliferation and differentiation of mesenchymal stem cells and enhance the mineralization of osteoblast cells. However, the short half-life and non-specificity to target areas limit applications of OGP. Mesoporous silica nanoparticles (MSNs) as nanocarriers possess excellent properties, such as easy surface modification, superior targeting efficiency, and high loading capacity of drugs or proteins. Accordingly, we propose a system of combining the OGP-containing MSNs with Mg–Zn–Ca BMG materials to promote bone regeneration. In this work, we conjugated cysteine-containing OGP (cgOGP, 16 a.a.) to interior walls of channels in MSNs and maintained the dispersity of MSNs via PEGylation. An in vitro study showed that metal ions released from Mg–Zn–Ca BMG promoted cell proliferation and migration and elevated alkaline phosphatase (ALP) activity and mineralization. On treating cells with both BMG ion-containing Minimum Essential Medium Eagle-alpha modification (α-MEM) and OGP-conjugated MSNs, enhanced focal adhesion turnover and promoted differentiation were observed. Hematological analyses showed the biocompatible nature of this BMG/nanocomposite system. In addition, in vivo micro-computed tomographic and histological observations revealed that our system stimulated osteogenesis and new bone formation around the implant site.

Dynamic mechanical relaxation and thermal creep of high-entropy La30Ce30Ni10Al20Co10 bulk metallic glass

Dynamic mechanical relaxation is a fundamental tool to understand the mechanical and physical properties of viscoelastic materials like glasses. Mechanical spectroscopy shows that the high-entropy bulk metallic glass (La30Ce30Ni10Al20Co10) exhibits a distinct β-relaxation feature. In the present research, dynamic mechanical analysis and thermal creep were performed using this bulk metallic glass material at a temperature domain around the β relaxation. The components of total strain, including ideal elastic strain, anelastic strain, and viscous-plastic strain, were analyzed based on the model of shear transformation zones (STZs). The stochastic activation of STZ contributes to the anelastic strain. When the temperature or external stress is high enough or the timescale is long enough, the interaction between STZs induces viscous-plastic strain. When all the spectrum of STZs is activated, the quasi-steady-state creep is achieved.

Pop-In Phenomenon as a Fundamental Plasticity Probed by Nanoindentation Technique.

The attractive strain burst phenomenon, so-called “pop-in”, during indentation-induced deformation at a very small scale is discussed as a fundamental deformation behavior in various materials. The nanoindentation technique can probe a mechanical response to a very low applied load, and the behavior can be mechanically and physically analyzed. The pop-in phenomenon can be understood as incipient plasticity under an indentation load, and dislocation nucleation at a small volume is a major mechanism for the event. Experimental and computational studies of the pop-in phenomenon are reviewed in terms of pioneering discovery, experimental clarification, physical modeling in the thermally activated process, crystal plasticity, effects of pre-existing lattice defects including dislocations, in-solution alloying elements, and grain boundaries, as well as atomistic modeling in computational simulation. The related non-dislocation behaviors are also discussed in a shear transformation zone in bulk metallic glass materials and phase transformation in semiconductors and metals. A future perspective from both engineering and scientific views is finally provided for further interpretation of the mechanical behaviors of materials.

Experimental investigations on flank contour accuracy of milling groove for Zr-based bulk metallic glass using mesoscale milling

The milling groove experiments of Zr-based bulk metallic glass (Zr-based BMG) (Zr52Cu17.5Ti16Ni12Nb2.5) are conducted by using an ultra-precision lathe. In order to study the milling groove flank contour accuracy in mesoscale groove milling for Zr-based bulk metallic glass component, the milling force and the flank contour shape were investigated by single-factor experiment. The effect of milling process parameters of Zr-based bulk metallic glass materials on the milling force and the flank contour profile of milling groove were obtained, and the relationship between flank contour profile of milling groove and milling force was also obtained. The flank contour profile of milling groove for Zr-based bulk metallic glass is analyzed theoretically. The effect of milling experimental parameters on the deviation between the actual flank contour profile of milling groove and the theoretical flank contour profile of milling groove is analyzed and summarized through the experiment.

Relationship between the Surface Roughness of Biodegradable Mg-Based Bulk Metallic Glass and the Osteogenetic Ability of MG63 Osteoblast-Like Cells.

Mg-based bulk metallic glass materials have been investigated for their large potential for application in orthopedic implants due to their biocompatibility, low degradation rate, and osteogenetic ability. As an orthopedic implant, initial cell adhesion has been a critical issue for subsequent osteogenesis and bone formation because the first contact between cells and the implant occurs upon the implants surface. Here, we aimed to create Mg-based bulk metallic glass samples with three different surface roughness attributes in order to understand the degradation behavior of Mg-based bulk metallic glass and the adhesion ability and osteogenetic ability of the contact cells. It was found that the degradation behavior of Mg66Zn29Ca5 bulk metallic glass was not affected by surface roughness. The surface of the Mg66Zn29Ca5 bulk metallic glass samples polished via #800 grade sandpaper was found to offer a well-attached surface and to provide a good cell viability environment for Human MG63 osteoblast-like cell line. In parallel, more calcium and mineral deposition was investigated on extracellular matrix with higher surface roughness that verify the relationship between surface roughness and cell performance.

Production of Bulk Metallic Glasses by Ultrasonic Welding of Nickel Based Amorphous Ribbons

With the evolution of society new materials or classes of materials must be developed. The metallic alloys with amorphous structure have exceptional physical properties due to the spatial order of the atoms in structure and the absence of crystalline defects such as dislocations, grain boundaries, etc. Due to the metastable states in which these alloys are located, obtaining bulk materials from amorphous metal alloys is difficult, being limited to simple geometries and high production cost. This problem can be solved by using the ultrasonic welding of amorphous ribbons for the production of bulk metallic glasses.In this paper, we aimed to produce bulk metallic glasses materials by welding the ribbon packages in ultrasonic field. In order to prove the preservation of the amorphous structure of both the primary welding alloys as well as after the welding of the amorphous ribbons, Differential thermal analysis (DTA), X-ray diffraction (XRD), Scanning electron microscopy (SEM) analysis were carried out. Vickers micro-hardness test was also performed in order to reveal the mechanical properties in the welded joint.

Size-dependent failure of the strongest bulk metallic glass

Upon reducing the sample size into micrometer scale, an obvious brittle-to-ductile transition accompanied by a drastic change of failure mode from shattering to shear-banding was observed when compressing the brittle but strong Co55Ta10B35 bulk metallic glass (BMG). The shattering failure under macroscopic compression is dominated by splitting cracking, which completely differs from shear-banding and originates from extrinsic defects like inclusions. To reveal the critical conditions for shear-banding and splitting cracking, various micropillar specimens with intentionally introduced holes as extrinsic defects were tested, and the stress distributions at the failure moment were analyzed with finite element simulation. The shear plane criterion was found to be quite effective to estimate the nominal stress required for the failure dominated by shear-banding. However, brittle splitting cracking does not occur although the maximum tensile stress reaches the critical value, which is different from traditional brittle solids. To initiate splitting cracking, a high-tensile-stress region over a critical distance, which depends on defect size and fracture toughness of the BMG, is required. The critical conditions for shear failure and splitting cracking demonstrated in this approach can be used to estimate the failure conditions of various BMG components with complex geometries in a wide range of length scales, and to design tough composites based on brittle BMGs. As an example, a design criterion to avoid brittle splitting fracture of porous BMG materials is proposed.

Size-Dependent Failure of the Strongest Bulk Metallic Glass

Upon reducing the sample size into micrometer scale, an obvious brittle-to-ductile transition accompanied by a drastic change of failure mode from shattering to shear-banding was observed when compressing the brittle but strong Co55Ta10B35 bulk metallic glass (BMG). The shattering failure under macroscopic compression is dominated by splitting cracking, which completely differs from shear-banding and originates from extrinsic defects like inclusions. To reveal the critical conditions for shear-banding and splitting cracking, various micropillar specimens with intentionally introduced holes as extrinsic defects were tested, and the stress distributions at the failure moment were analyzed with finite element simulation. The shear plane criterion was found to be quite effective to estimate the nominal stress required for the failure dominated by shear-banding. However, brittle splitting cracking does not occur although the maximum tensile stress reaches the critical value, which is different from traditional brittle solids. To initiate splitting cracking, a high-tensile-stress region over a critical distance, which depends on defect size and fracture toughness of the BMG, is required. The critical conditions for shear failure and splitting cracking demonstrated in this approach can be used to estimate the failure conditions of various BMG components with complex geometries in a wide range of length scales, and to design tough composites based on brittle BMGs. As an example, a design criterion to avoid brittle splitting fracture of porous BMG materials is proposed.

Investigations in nanosecond laser micromachining on the Zr52.8Cu17.6Ni14.8Al9.9Ti4.9 bulk metallic glass: experimental and theoretical study

In addition to their attractive mechanical properties, the lack of grain boundaries and crystal defects of Bulk Metallic Glasses (BMGs) make them suitable materials for integration in micro-systems fabrication chains, either as final components or mould inserts. The application of short or ultra-short pulsed lasers has recently been demonstrated for the processing of BMGs in this context, particularly as a possible solution for machining micro-scale features on the surface of BMG workpieces. Therefore, complementary studies that consider both experimental and thermal simulation data at the same time in the context of multiple and moving pulses irradiating a BMG specimen are desirable to gain insight into micromachining phenomena. Although such models have been reported in the context of single pulse processing of BMG substrates, their extension to multiple pulse scenarios for micromachining is lacking. Thus, the overall objective of this paper is to combine both theoretical and experimental laser micromachining investigations using multiple pulses when irradiating a BMG workpiece. The specific focus is on conducting such laser operations in the nanosecond regime on a Zr-based BMG, with composition Zr52.5Cu17.9Ni14.6Al10Ti5, also known as Vitreloy 105. This combined experimental and theoretical approach enabled the identification of a suitable set of laser parameters with respect to the process efficiency over a range of pulse duration, fluence values, scanning speed and track distance between machined grooves. In addition, it was highlighted that laser micro-machining operations can lead to BMG materials experiencing thermal cycles, which are quite different from that taking place during the conventional synthesis of glassy alloys, thus complicating the further characterisation and understanding of crystallisation phenomena at play.

Glass forming ability and bending plasticity evolutions in Zr-Co-Al bulk metallic glasses and their structural origin

The effect of composition tuning on glass forming ability (GFA), mechanical properties and atomic structure in ZrxCo84−xAl16 bulk metallic glasses (BMGs) with x = 51–58 has been investigated by using copper-mold suction casting, nanoindentation, high-energy X-ray diffraction, extended X-ray absorption fine structure experiments and ab initio molecular dynamics simulations, respectively. It is found that GFA firstly increases then decreases with increasing Zr content, exhibiting a maximum diameter of 7 mm with the Zr content of 55 and 56, while an abrupt reduction of bending plasticity occurs as the Zr content drops below 55. Both experimental and theoretical results find that GFA is remarkably enhanced, due to the abnormal reduction in the fractions of the Co-centered ⟨0, 2, 8, 1⟩, ⟨0, 3, 6, 2⟩ and ⟨0, 3, 6, 3⟩ polyhedra, and the denser atomic packing of Zr atoms around center Co atom, as the Zr content increases from 51 to 56. Meanwhile, the simultaneously improved plasticity is associated with the increased Co-centered ⟨0, 3, 6, 0⟩, and Al-centered ⟨0, 2, 8, 1⟩ and ⟨0, 3, 6, 2⟩ polyhedra, which provide more fertile sites for the nucleation of shear transformations. Further Zr addition to 58 increases remarkably the fractions of Zr- and Al-centered ⟨0, 1, 10, 2⟩ and ⟨0, 3, 6, 4⟩ polyhedra, and causes looser atomic packing of Co atoms around center Zr atom, leading to the reduction in GFA. However, the plasticity is not enhanced further but remains nearly constant, which may be related to the deteriorated effect on plasticity of the decreased fractions of Zr-centered ⟨0, 1, 10, 5⟩ and Co-centered ⟨0, 3, 6, 0⟩ polyhedra, and the increased fractions of Zr-centered ⟨0, 1, 10, 3⟩ and ⟨0, 2, 8, 4⟩ and Co-centered ⟨0, 2, 8, 0⟩ polyhedra. Compositional tuning, with internal structure tuned to favor both GFA and plastic flow, offers new possibilities in developing ductile BMG materials.

Anharmonic model for the elastic constants of bulk metallic glass across the glass transition

Here we examine the role of anharmonicity in the elastic constants of bulk metallic glasses and develop an anharmonic model to consider the effects of both pressure and temperature across the glass transition. By comparing against reported experimental data and elastic constants obtained from molecular dynamics simulations, we show that the model is able to capture reported elastic constants from cryogenic temperatures through the glass transition and under hydrostatic pressures up to 18 GPa. Microstructural indicators based on short-range order analysis also display strong correlations with the bulk and shear moduli across the range of pressures and temperatures studied. These results not only greatly expand our understanding in the physical origins of elastic properties of bulk metallic glasses but are also of practical interest for application to processing routes for bulk metallic glass materials.

A comparative study of the friction and wear performance of Fe-based bulk metallic glass under different conditions

PurposeThis study aims to compare the friction and wear behaviors of Fe68.3C6.9Si2.5 B6.7P8.8Cr2.2Al2.1Mo2.5 bulk metallic glass (BMG) under sliding using dry, deionized water-lubricated and oil-lubricated conditions. The comparison was performed using a unidirectional ball-on-flat tribometer under different applied loads, and the results were compared to the properties of a conventional material, SUJ2. Fe-based BMG materials have recently been attracting a great deal of attention for prospective engineering applications.Design/methodology/approachAs a part of the development of Fe-based BMGs that can be cost-effectively produced in large quantities, an Fe-based BMG Fe68.8C7.0Si3.5B5.0P9.6 Cr2.1Mo2.0Al2.0 with high glass forming ability was fabricated. In the present study, the friction and wear properties of Fe-based BMG has been comparatively evaluated under dry sliding, deionized water- and oil-lubricated conditions using a unidirectional ball-on-flat tribometer under different applied loads, and the results were compared to the properties of conventional material SUJ2.FindingsThe results show that the Fe-based BMG had better friction performance than the conventional material. Both the friction coefficient and wear mass loss increased with increasing load. The sliding wear mechanism of the BMG changed with the sliding conditions. Under dry sliding conditions, the wear scar of the Fe-based BMG was characterized by abrasive wear, plastic deformation, micro-cracks and peeling-off wear. Under water- and oil-lubricated conditions, the wear scar was mainly characterized by abrasive wear and micro-cutting.Originality/valueIn this investigation, the authors developed a new BMG alloy Fe68.8C7.0Si3.5B5.0P9.6Cr2.1Mo2.0Al2.0 to improve the friction and wear performance under dry sliding, deionized water- and oil- lubricated conditions.

Role of copper addition on properties of bulk metallic glass materials

In this paper the role of copper addition has been studied to examine thermal, mechanical, magnetic and corrosion properties of the Fe43Co22Ni7B19Si5Nb4 bulk metallic glass alloy material. It is found that the copper addition in alloys exhibited low supercooled liquid region as compared to copper-free alloy. It is observed that microhardness was reduced in Cu-containing alloy with generation of shear bands along faces of micro indent impression while in Cu-free alloy straight and long microcracks appeared at the indent corners indicating its brittle behavior. The magnetic properties slightly decrease with Cu addition however the corrosion resistance of Cu-containing alloy showed superior properties indicating commercial benefits in aggressive environment.

Bio-inspired multifunctional metallic glass

As a novel class of metallic materials, bulk metallic glasses (BMGs) have attracted a great deal of attention owing to their technological promise for practical engineering applications. In nature, biological materials exhibit inherent multifunctional integration, which provides some inspiration for scientists and engineers to construct multifunctional artificial materials. In this contribution, inspired by superhydrophobic self-cleaning lotus leaves, multifunctional bulk metallic glasses (BMG) materials have been fabricated through the thermoplastic forming-based process followed by the SiO2/soot deposition. To mimic the microscale papillae of the lotus leaf, the BMG micropillar with a hemispherical top was first fabricated using micro-patterned silicon templates based on thermoplastic forming. The deposited randomly distributed SiO2/soot nanostructures covered on BMG micropillars are similar to the branch-like nanostructures on papillae of the lotus leaf. Micro-nanoscale hierarchical structures endow BMG replica with superhydrophobicity, a low adhesion towards water, and self-cleaning, similar to the natural lotus leaf. Furthermore, on the basis of the observation of the morphology of BMG replica in the Si mould, the formation mechanism of BMG replica was proposed in this work. The BMG materials with multifunction integration would extend their practical engineering applications and we expect this method could be widely adopted for the fabrication of other multifunctional BMG surfaces.

An experimental study on grinding of Zr-based bulk metallic glass

There are limited studies in the literature about machinability of bulk metallic glass (BMG). As a novel and promising structural material, BMG material machining characteristics need to be verified before its utilization. In this paper, the effects of cutting speed, feed rate, depth of cut, abrasive particle size/type on the BMG grinding in dry conditions were experimentally investigated. The experimental evaluations were carried out using cubic boron nitride (CBN) and Al2O3 cup wheel grinding tools. The parameters were evaluated along with the results of cutting force, temperature and surface roughness measurements, X-ray, scanning electron microscope (SEM) and surface roughness analyse. The results demonstrated that the grinding forces reduced with the increasing cutting speed as specific grinding energy increased. The effect of feed rate was opposite to the cutting speed effect, and increasing feed rate caused higher grinding forces and substantially lower specific energy. Some voids like cracks parallel to the grinding direction were observed at the edge of the grinding tracks. The present investigations on ground surface and grinding chips morphologies showed that material removal and surface formation of the BMG were mainly due to the ductile chip formation and ploughing as well as brittle fracture of some particles from the edge of the tracks. The roughness values obtained with the CBN wheels were found to be acceptable for the grinding operation of the structural materials and were in the range of 0.34–0.58 μm. This study also demonstrates that conventional Al2O3 wheel is not suitable for grinding of the BMG in dry conditions.

Martensitic transformation induced plasticity in ZrCuAl metallic glass composites: Precipitate size and volume effects

The effects of Co alloying on mechanical properties of ternary Cu–Zr–Al bulk metallic glass (BMG) are systematically examined. Room temperature compression tests reveal enhanced fracture strain in ZrCuAlCo BMG materials upon appropriate amount of Co alloying. The microstructures of the composite materials investigated by X-ray diffraction and transmission electron microscopy reveal that the enhancement of fracture strain depends on the size and volume fraction of the B2 phase. The stress induced martensite transformation can only occur when the size of B2 grains is larger than a critical value, which enhances crack resistance within the vicinity of crack tip.

Influence of Poisson’s ratio and stress triaxiality on fracture behavior based on elastic strain energy density

The present study highlighted a new homenergic ellipse criterion to describe the fracture behavior of bulk metallic glass materials (BMGs) as well as a variety of other materials due to the inappropriate classical failure criteria of depicting the fracture behavior of BMGs, such as the maximum normal stress criterion, Tresca criterion, Mohr–Coulomb criterion, and von Mises criterion. Specifically, the fracture angles, revealing the fracture property, were discussed through studying the critical fracture stresses of uniaxial tension. In addition, based on elastic strain energy density, the fracture angles in uniaxial tension were uniquely depended on Poisson’s ratio. Further study found that fracture angles in complex stress-states not only depended on Poisson’s ratio, but also on stress triaxiality.

Weldability of Cu54Zr22Ti18Ni6 bulk metallic glass by ultrasonic welding processing

Cu54Zr22Ti18Ni6 (numbers indicate at%) bulk metallic glass with glass forming ability of 6mm was joined using ultrasonic welding. After welding fully amorphous materials, crystallization was investigated using micro area x-ray diffraction, scanning electron microscopy, and differential scanning calorimetry. However, there was no crystallization through the joint and the weld interface could not be ascertained. In view of joint morphology and phase stability, ultrasonic welding processing shows a potent capability for joining bulk metallic glass materials.