Properties Of Bulk Metallic Glasses Research Articles

Partial crystallization in Pd-BMG systems: From understanding structure towards influencing functionality through temperature-time series

Small quantities of crystalline domains created in an amorphous matrix are seen as an active driver for enhanced properties in bulk metallic glasses (BMGs). We investigated partial crystallization and phase transformations through a series of isotherms at 370° performed on amorphous Pd-based BMG samples with the nominal composition of Pd43Cu27Ni10P20 (Pd-BMG) and a density of 9.425g/cm3. X-ray based methods such as X-ray diffraction (XRD) and phase enhanced micro-computed tomography (μ-CT) have been pushed to their limits for studying atomic structure and morphology, while time available before crystallization has additionally been investigated via differential scanning calorimetry (DSC), and are combined with optical microscopy (OM), scanning electron microscopy (SEM), and hardness measurements for their mechanical properties. We reveal that Pd-based BMG samples isothermally treated at 370°C start to crystallize after 20 minutes and still undergo phase transformations and recrystallization even after being fully crystalline after 60 minutes of the isothermal treatment. Interestingly, 3D phase enhanced micro-computed tomography shows a clear separation of two domains of slightly different densities. We highlight X-ray tomographic scans, allowing the 3D spatial visualization of extremely low-density contrast in different material domains, thus providing a multi-scale physical description of the Pd-BMG system. Interesting is the fact, that the re-crystallization is not homogenous and the crystalline domains can reach large size of (100-200 μm) in an amorphous matrix.

Surface Modification of Zr48Cu36Al8Ag8 Bulk Metallic Glass through Glow Discharge Plasma Nitriding

Bulk metallic glasses are modern engineering materials with unique functional properties. Zr-based alloys are particularly attractive as they exhibit high glass forming ability as well as good mechanical properties. Due to their relatively high thermal stability, reaching as much as 400 °C, they can be surface-treated in low-temperature plasma to further improve their mechanical properties. The subject of this study was to determine the influence of the technological parameters of nitriding in low-temperature plasma on the structure and mechanical properties of Zr48Cu36Al8Ag8 bulk metallic glass. In the course of this study, the influence of the ion accelerating voltage on the structure and micromechanical properties of the bulk metallic glass was analyzed. The produced samples were characterized in terms of nanohardness, layer adhesion by using the scratch test, and wear resistance by using the ball-on-disc method. As a result of low-temperature plasma nitriding, a significant increase in the surface nanohardness of the Zr48Cu36Al8Ag8 bulk metallic glass was obtained. The produced layers exhibited high adhesion to the substrate and they improved the wear resistance of the glass. The present study indicates the possibility of modifying the surface properties of bulk metallic glasses by using diffusion processes in low-temperature plasma without substrate crystallization.

Preparation of Zr-based metallic glasses gradient composites with designable amorphous fraction by laser powder bed fusion

Introducing ductile crystals in situ into the matrix is an efficient approach for enhancing the mechanical properties of bulk metallic glasses (BMGs). However, controlling the volume of the crystalline phase is challenging, and the introduction of crystals may be detrimental to its strength and ductility trade-off. In addition, BMGs prepared by conventional casting process suffers from the disadvantages of size limitation, inhomogeneous crystallization, and uncontrollable crystallization fraction. In this study, Zr48Cu47.5Al4Co0.5 amorphous powder with better forming ability was utilized as raw material and printed by selective laser melting (SLM) technique with high cooling rate. Through parameter adjustments and proactive design of amorphous fractions, gradient metallic glasses (GMGs) based on Zr has been successfully prepared. Micro-morphology, DSC tests, micro-area XRD, optical calculations and nanoindentation experiments all indicate the presence of gradient structures. The microstructure reveals that the crystalline phases in the heat affected zone (HAZ) are mainly B2 phase. In addition, the results of room temperature compression show that the yield strength (1.2 GPa) and plastic deformation (0.8 %) of the gradient structure are better than those of the samples prepared with a single parameter. The theme of amorphous fraction gradient structure design, realized by SLM technology, opens a new window for the large-scale development of high-performance BMGs.

Equation of State and Thermal Properties of Bulk Metallic Glass under High Compressions

Equation of State and Thermal Properties of Bulk Metallic Glass under High Compressions

An end-to-end explainable graph neural networks-based composition to mechanical properties prediction framework for bulk metallic glasses

Accurate prediction of the properties of bulk metallic glasses (BMGs) can provide an important guideline for the design of novel BMGs. While various machine learning (ML) models have been employed to predict the properties of BMGs, feature engineering is typically necessary to choose suitable descriptors based on domain knowledge or experience. In this work, an end-to-end generic framework has been proposed based on graph neural networks (GNNs) for composition-to-property prediction of BMGs. Firstly, an innovative graph representation of alloy compositions is designed. Then, two classes of GNNs have been developed to predict the fracture strength and plastic strain of BMGs. The R2 values for the optimal model on the test set were 0.963 and 0.801, respectively. Additionally, the optimal model has been fine-tuned using transfer learning for the problem of skewed distributions in the plastic strain dataset. As a result, the R2 scores on the test set improved significantly by 23.8% and 6.24%, respectively. Finally, a Hybrid Explainer has been developed to explain the entire prediction process of the model. The results of this study indicate that the proposed GNNs models may be informative for the rational design of BMGs.

Size-dependent vitrification in metallic glasses

Reducing the sample size can profoundly impact properties of bulk metallic glasses. Here, we systematically reduce the length scale of Au and Pt-based metallic glasses and study their vitrification behavior and atomic mobility. For this purpose, we exploit fast scanning calorimetry (FSC) allowing to study glassy dynamics in an exceptionally wide range of cooling rates and frequencies. We show that the main α relaxation process remains size independent and bulk-like. In contrast, we observe pronounced size dependent vitrification kinetics in micrometer-sized glasses, which is more evident for the smallest samples and at low cooling rates, resulting in more than 40 K decrease in fictive temperature, Tf, with respect to the bulk. We discuss the deep implications on how this outcome can be used to convey glasses to low energy states.

Effects of adding niobium on microstructures and mechanical properties of ((Zr40Ti40Ni20)72Be28)100-xNbx bulk metallic glasses

Effects of adding niobium (Nb) on the glass-forming ability and mechanical properties of bulk metallic glasses (BMGs) ((Zr40Ti40Ni20)72Be28)100-xNbx (at.%, x = 0, 3, 6, 9, 12) were studied by taking the (Zr40Ti40Ni20)72Be28 BMGs alloy system as a research object. Through X-ray diffraction (XRD) and differential scanning calorimeter (DSC) tests, addition of appropriate amounts of Nb first weakens, then enhances the glass-forming ability (GFA) of the alloy system and it improves the thermal stability of the alloys. Mechanical tests show that addition of Nb enhances the room-temperature plasticity of the alloys. When the Nb content is 3 at.%, the compression deformation reaches 29.7%, indicating an increase of 258% compared with that of the initial system. The new Zr-Ti-Ni-Be-Nb system exhibits great potential for applications in engineering structural materials.

Artificial Neural Network Supported Prediction of Magnetic Properties of Bulk Metallic Glasses

Artificial Neural Network Supported Prediction of Magnetic Properties of Bulk Metallic Glasses

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.

Tailoring the mechanical properties of bulk metallic glasses via cooling from the supercooled liquid region

Tailoring the mechanical properties of bulk metallic glasses via cooling from the supercooled liquid region

Applicability of Pre-Plastic Deformation Method for Improving Mechanical Properties of Bulk Metallic Glasses.

Pre-plastic deformation (PPD) treatments on bulk metallic glasses (BMGs) have previously been shown to be helpful in producing multiple shear bands. In this work, the applicability of the PPD approach on BMGs with different Poisson's ratios was validated based on experimental and simulation observations. It was found that for BMGs with high Poisson's ratios (HBMGs, e.g., Zr56Co28Al16 and Zr46Cu46Al8), the PPD treatment can easily trigger a pair of large plastic deformation zones consisting of multiple shear bands. These PPD-treated HBMGs clearly display improved strength and compressive plasticity. On the other hand, the mechanical properties of BMGs with low Poisson's ratios (LBMG, e.g., Fe48Cr15Mo14Y2C15B6) become worse due to a few shear bands and micro-cracks in extremely small plastic deformation zones. Additionally, for the PPD-treated HBMGs with similar high Poisson's ratios, the Zr56Co28Al16 BMG exhibits much larger plasticity than the Zr46Cu46Al8 BMG. This phenomenon is mainly due to more defective icosahedral clusters in the Zr56Co28Al16 BMG, which can serve as nucleation sites for shear transformation zones (STZs) during subsequent deformation. The present study may provide a basis for understanding the plastic deformation mechanism of BMGs.

The effect of impurities in zirconium on the formation and mechanical properties of Zr55Cu30Al10Ni5 metallic glass

Minor alloying has been developed as an effective method to modify and optimize various properties of bulk metallic glasses (BMG). In this work, as inevitable minor alloying elements, two major impurities, hafnium (Hf) and oxygen (O) were quantitatively confirmed to co-exist in two zirconium (Zr) raw materials with different grades of impurities. The effects of these two impurities on the thermal properties, crystallization behavior, glass-forming ability (GFA), and mechanical properties of the nominal Zr55Cu30Al10Ni5 BMG were systematically studied. The O impurity was found to promote the formation of the Al5Ni3Zr2 intermetallic compound phase, which could account for the poor GFA, thermal stability, and plasticity associated with BMGs with higher O content in the Zr raw material. In contrast, although the impurity of Hf has a much higher content than O, a negligible effect of Hf on the Zr55Cu30Al10Ni5 BMG was revealed. These findings were further confirmed by deliberately adding extra O and Hf with designed contents into the Zr55Cu30Al10Ni5 BMG. Our results clarify the effects of different impurities in Zr raw materials on the Zr-based BMG and will help guide industrial production and applications of Zr-based BMGs.

Effects of Various Processing Parameters on Mechanical Properties and Biocompatibility of Fe-based Bulk Metallic Glass Processed via Selective Laser Melting at Constant Energy Density

The unique properties of bulk metallic glass (BMG) render it an excellent material for bone-implant applications. BMG samples are difficult to produce directly because of the critical cooling rate of molding. Advancements in additive manufacturing technologies, such as selective laser melting (SLM), have enabled the development of BMG. The successful production of materials via SLM relies significantly on the processing parameters; meanwhile, the overall energy density affects the crystallization and, thus, the final properties. Therefore, to further determine the effects of the processing parameters, SLM is performed in this study to print Fe-based BMG with different properties three dimensionally using selected processing parameters but a constant energy density. The printed amorphous Fe-based BMG outperforms the typical 316 L stainless steel (316 L SS) in terms of mechanical properties and corrosion resistance. Moreover, observations from nanoindentation tests indicate that the hardness and elastic modulus of the Fe-based BMG can be customized explicitly by adjusting the SLM processing parameters. Indirect cytotoxicity results show that the Fe-based BMG can enhance the viability of SAOS2 cells, as compared with 316 L SS. These intriguing results show that Fe-based BMG should be investigated further for orthopedic implant applications.

Thermodynamically-guided machine learning modelling for predicting the glass-forming ability of bulk metallic glasses

Glass-forming ability (GFA) of bulk metallic glasses (BMGs) is a determinant parameter which has been significantly studied. GFA improvements could be achieved through trial-and-error experiments, as a tedious work, or by using developed predicting tools. Machine-Learning (ML) has been used as a promising method to predict the properties of BMGs by removing the barriers in the way of its alloy design. This article aims to develop a ML-based method for predicting the maximum critical diameter (Dmax) of BMGs as a factor of their glass-forming ability. The main result is that the random forest method can be used as a sustainable model (R2 = 92%) for predicting glass-forming ability. Also, adding characteristic temperatures to the model will increase the accuracy and efficiency of the developed model. Comparing the measured and predicted values of Dmax for a set of newly developed BMGs indicated that the model is reliable and can be truly used for predicting the GFA of BMGs.

Force constant disorder in the Ni44Nb56 bulk metallic glass as observed by deep inelastic neutron scattering augmented by isotopic substitution

In this work, the force-constant disorder in nickel-niobium metallic glass, Ni44Nb56, was studied using the deep inelastic neutron scattering (DINS) technique augmented by isotopic substitution. The distributions of DINS observables (the nuclear kinetic energies, the width of the nuclear momentum distributions, and the effective force constants) were measured in Ni44Nb56 and compared with their counterparts obtained from ab initio harmonic lattice (HLD) simulations for the crystalline forms of nickel, niobium, and the NiNb crystal and from the reverse Monte Carlo (RMC) simulations augmented by effective force fields performed for Ni44Nb56. The force-constant distribution of nickel, obtained from the analysis of the results of the DINS experiments, was found to be two times broader than its counterparts estimated based on the HLD and RMC simulations. In the case of niobium, the force-constant distribution inferred from the DINS experiments is estimated to be an order of magnitude broader than the ab initio HLD prediction in the NiNb crystal. Moreover, no disorder-induced softening (with respect to its crystalline counterparts) of the effective force constants of Ni and Nb in Ni44Nb56 was observed. The lack of disorder-induced softening in Ni44Nb56 is consistent with the correlation between the short-range order, defined by the average coordination number and the interatomic distances, and the magnitudes of the effective force constants. The obtained results are consistent with a picture, whereby disorder induces symmetrical broadening of phonon dispersion curves, and phonon softening is limited to low-energy modes carrying negligible amounts of nuclear kinetic energy. The obtained results have important ramifications for engineering the properties of bulk metallic glasses.

Bulk metallic glass cantilever beams: Outstanding at large-deflection deformation and their application in complaint mechanisms

Excellent combination of mechanical properties of bulk metallic glasses (BMGs) are a class of relatively young and promising candidate materials for compliant mechanisms (CMs), which are usually associated with the nonlinear large-deflection deformation. In this study, an effective design strategy was proposed to enhance the flexibility of BMG cantilever beam quantitatively, which by means of increasing the ratio of loading distance to beam thickness. Moreover, the accuracy of modulus of elasticity in bending, Eb, which measured by cantilever bending test was affected seriously by the support compliance of the fixed end, and the accurate Eb value of BMG beam can be attained after eliminating this influencing factor. The critical boundary condition of cantilever beams within the scope of small-deflection deformation was identified, which situates at non-dimensional deflection parameter, δy/L, is 0.2. Correspondingly, the critical loading distance-to-thickness ratios, (L/t)c, of cantilever beams within small-deflection deformation were derived for BMGs and conventional crystalline metals, which provide a criterion to predict the potential to achieving large-deflection deformation. It is noticed that by plotting the flexural stress-δy/L relations for BMG and several conventional crystalline metals used in CMs, the unique advantages of BMG cantilever beam in the aspect of achieving large-deflection deformation and enduring higher flexural stress can be reflected more intuitively. These advantages of BMG cantilever beam are well suitable for CMs which designed to have a small footprint and requirement of large-deflection motions, such as in the fields of microelectromechanical systems (MEMS) and biomedicines.

Determination of material properties of bulk metallic glass using nanoindentation and artificial neural network

An artificial neural network (ANN) model is combined with finite element (FE) nanoindentation to evaluate free volume model (FVM) parameters for bulk metallic glass (BMG). FVM is numerically implemented with the user material subroutine (UMAT). A material database is generated based on FE analysis, in which indentation parameters are obtained from FVM parameters. An ANN is generated in order to correlate FVM and indentation parameters and trained/tested from the generated database after the application of removal of multicollinearity, sampling, and normalization for computational efficiency. The fully trained ANN inversely evaluates the FVM parameters from the indentation parameters. The ANN approach is experimentally validated by sphero-conical/Berkovich indentation load-depth curves of Zr55Cu30Ag15 and Zr65Cu15Al10Ni10.

Распределение микротвердости по поверхности металлического стекла на основе циркония, подвергнутого интенсивной пластической деформации кручением

Identifying the peculiarities of the transformation of the structure and properties of bulk metallic glass (BMG) under high-pressure torsion (HPT) is of great interest. It is known that under HPT, the degree of deformation differs from the center to the edge of a disk which leads to the non-uniformity of the structure of obtained specimens. The change in microhardness value indicates the direction of change in BMG structure under the HPT, and the microhardness distribution indicates the HPT-specimen non-uniformity. The aim of the study is to identify the HPT influence on the microhardness value and microhardness distribution over the surface of specimens of amorphous alloys using an example of Vit105Zr-based BMG (Zr52.5Cu17.9Ni14.6Al10Ti5). The authors studied the distribution of microhardness over the surface of Vit105 Zr-based bulk metallic glass (BMG) in the initial state, in the state after HPT at n=1 and n=5 rotations, and after relaxing annealing. The study shows that the initial Vit105 BMG is characterized by a small spread in microhardness values, which indicates the material's high homogeneity. By reducing the excessive free volume, relaxing annealing increases microhardness without a significant increase in the spread of its values. HPT leads to a decrease in the zirconium BMG microhardness, which indicates an increase in the excessive free volume, but, at the same time, increases the uneven microhardness distribution over the specimen, while the microhardness values in one half of the HPT sample (n=1) are higher than in the other one. It demonstrates that BMG specimen deformation during HPT is related to the specific loading mechanisms.

Structural rejuvenation in a Zr-based bulk metallic glass via electropulsing treatment

Structural rejuvenation is a fascinating issue of bulk metallic glasses (BMGs). In this paper, we use the electropulsing treatment (EPT) to rejuvenate the atomic packing in a Zr45(Cu4.5/5.5Ag1/5.5)48Al7 BMG, which remains amorphous after undergoing fast heating and cooling. It is found that the voltages less than 110 V have little rejuvenation effect on BMGs. However, the discharging at 130 V greatly reduces the density, modulus, and hardness while generating more excess free volume and enhancing the β-relaxation. The changes in properties of EPT samples are almost consistent with the variations of total content and average size of free volume. Our work provides an efficient way to alter the structure and properties of BMGs.

Acoustic properties of metallic glasses at low temperatures: Tunneling systems and their dephasing

The low temperature acoustic properties of bulk metallic glasses measured over a broad range of frequencies rigorously test the predictions of the standard tunneling model. The strength of these experiments and their analyses is mainly based on the interaction of the tunneling states with conduction electrons or quasiparticles in the superconducting state. A new series of experiments at kHz and GHz frequencies on the same sample material essentially confirms previous measurements and their discrepancies with theoretical predictions. These discrepancies can be lifted by considering more correctly the line widths of the dominating two-level atomic-tunneling systems. In fact, dephasing caused or mediated by interaction with conduction electrons may lead to particularly large line widths and destroy the tunneling sytems' two-level character in the normal conducting state.