Behavior Of Bulk Metallic Glass Research Articles

Modeling and simulation of dynamic compression of Bulk Metallic Glasses at room and elevated temperatures using split Hopkinson pressure bar setup

This paper presents a modeling and simulation study of dynamic compression behavior of Bulk Metallic Glasses (BMGs) at room and elevated temperatures using the split Hopkinson pressure bar (SHPB) setup. The primary objective of this study is to develop and validate a constitutive model and simulation methodology capable of predicting the high strain rate response of BMGs at different temperatures. We propose a constitutive model for BMGs that accounts for the effects of high strain rates and elevated temperatures. We numerically implemented this model in ABAQUS/Explicit Finite Element Analysis software by writing a Vectorized User Material (VUMAT) subroutine. The methodology for modeling and simulation of dynamic compression of BMG specimens using the SHPB setup is developed. The present simulations are able to correctly predict the rate-independent response of Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vitreloy-1) BMG under dynamic compression at room and elevated temperatures. Furthermore, the present simulations are also able to correctly predict the negative strain rate sensitivity (SRS) of Zr52.5Cu17.9Ni14.6Al10Ti5 (Vitreloy-105) BMG at room temperature. Finally, the present simulations correctly predict that the failure stress of Zr64.13Cu15.75Ni10.12Al10 BMG decreases with increasing temperature and exhibits a minimal positive SRS. The present study is the first successful attempt to model the mechanical response of various BMGs under dynamic compression and at room and elevated temperatures. In particular, the experimentally observed negative SRS in some BMGs has been successfully simulated. The present work has important implications for the design of next generation spacecraft shields that are based on BMGs for mitigating the effects of hypervelocity impacts from debris in space.

A micromechanical nested machine learning model for characterizing materials behaviors of bulk metallic glasses

In the present work, a novel micromechanical data-driven Machine Learning (ML) framework was proposed to characterize material parameters in bulk metallic glasses (BMGs) using nanoindentation simulations with Berkovich and spherical tips. A vast collection of data on material behavior in BMGs during nanoindentation was compiled, utilizing a series of Drucker-Prager model coefficients. The predictive model was constructed using a nested machine learning algorithm, which incorporated hyper-parameters tuning and a principal model. This nested configuration optimized the architecture of a deep neural network, acting as the key estimator for BMG material properties. The outcomes indicated that the ML model proficiently predicted critical material properties, including compressive yield strength, elastic modulus, flow stress ratio, and Poisson ratio. Notably, the ML model exhibited superior accuracy in predicting elastic modulus and compressive strength, suggesting a robust correlation with flexural elasticity and compressive strength. Furthermore, the study highlighted the significance of input feature weight functions, as they strongly influenced the ML model's performance. Each output target's dependence on the individual proportion of input features contributed to the model's adaptability in handling variations in material properties. Finally, the findings of this work contribute to a deeper understanding of the relationships between input features and material properties, facilitating improved predictions of BMG behavior.

Enhanced corrosion resistance of a ZrCuNiAl bulk metallic glass in simulated groundwater by minor crystallization

Understanding the corrosion behaviors of bulk metallic glasses (BMGs) in practical working environment is essential for the applications of BMGs as corrosion resistance materials. The present work investigated the corrosion behaviors of Zr50.7Cu28Ni9Al12.3 (at. %) BMG and also its heat treated alloys with different volume fraction of crystalline phase in a solution simulating groundwater. It was shown that the corrosion of the present ZrCuNiAl alloy is induced by pit etching and Cu would be aggregated at the corrosion positions in a form of Cu2+ ions. Zr, Ni and Al would inversely be dissolved by the simulated groundwater and so were lack at the corrosion positions, and they are probed as form of Zr4+, Ni2+ and Al3+ ions on the corrosion surface, which supports the formation of metal oxides ZrO2, CuO, NiO and Al2O3. The experimental results discover a corrosion resistance trend first enhancing and then reducing with increasing crystalline phase volume fraction, proving that minor crystallization in fact also improve corrosion resistance in this BMG system, but large volume fraction of crystalline phases would deteriorate the anti-corrosion performance of BMGs. Thus the amorphous state itself improves corrosion resistance of the studied alloy.

Temperature rise in shear bands and its effect on crystallization behavior in bulk metallic glasses

Since the operation of shear band in bulk metallic glasses (BMGs) is accompanied by severe localization in both size and time scales, the measurement of heating and temperature of shear band is extremely difficult. In this paper, temperature rise in the shear bands and its effect on crystallization behavior are investigated in experimental and analytical ways. The released elastic energy, the thickness of shear band and the elapsed time for the energy transfer into the shear band are the key parameters in determining the temperature profile inside and around shear bands. By using the glass transition temperature (Tg) and liquidus temperature (Tliq) in the analytical model, it is possible to determine the shape and the size of hot and liquid zones. It is found that, the size of hot zone is equal to the stable crack growth region and also the size of liquid zone is equal to the vein pattern size on the fracture surface. Since the heating and cooling rates in a hot shear band are extremely high, crystallization cannot appear within the shear band, but is likely to occur around it. In a cold shear band, the heating and cooling in the supercooled liquid region occurs slowly, which is suitable for nucleation and growth of the crystalline phase inside the shear band. However, the crystalline phase appears only on the compressive side of the specimen. These findings provide a new insight for better understanding the deformation behavior of bulk metallic glasses through an analytical method.

Investigating the fracture behaviors of bulk metallic glasses under different dynamic loading rates using phase-field model

Bulk metallic glasses (BMGs) attract significant attention because of their superior mechanical properties. They are potential dynamic structural materials that may be applied in military and aerospace fields as energy penetrators. Unfortunately, the structural reliability under dynamic loading cannot be guaranteed at room temperature because of the catastrophic crack initiation and propagation. Thus, it is vital to ascertain the dynamic fracture behaviors of BMGs and their corresponding mechanisms. In this work, the dynamic fracture behaviors of Zr-based BMGs are investigated through the analysis of the mode-I fracture evolution under different high strain rates using the phase-field method. The crack initiation was observed to change from several branches at the notch tip to one branch with the rate increase, while the evolution in metallic glass changed from one stable crack to fragmentation with multiple branches as the rate increased. To investigate crack evolution features, the relationship between crack extension displacement xs and time t was obtained from the simulation results, and the crack velocity was derived through fitting. The changes in fracture behavior with strain rate are attributed to the effects of the strain rate on the crack dynamics and energy dissipation for the crack initiation. Comparison of crack velocities in different fracture modes allowed to determine the critical velocity for the bifurcation. These results can help design new materials for dynamic structures.

Effect of sample size and cooling rate on the plastic deformation behavior of bulk metallic glasses: A comparative study

Understanding the differences between the cooling-rate and size effects on the plastic deformation behavior of bulk metallic glasses (BMGs) is important not only for uncovering the plastic deformation mechanisms but also for achieving better plasticity of BMGs. In the present work, both the cooling-rate and size effects of a Zr-based BMG were investigated by quasi-static compressive experiments. The findings show that the macroscopic plasticity of BMGs can be remarkably enhanced by increasing the casting cooling rate, but moderately improved by decreasing the sample size. The intrinsic atomic arrangement stemming from cooling rate is the primary factor which affects the plastic deformation behavior rather than the extrinsic size effect, and the size effect is also dependent on the intrinsic cooling rate. The findings provide more explanations for the different size effects of BMG communities at different conditions, and are also of significance for achieving better plasticity in BMGs and BMG structures.

Investigation on the serrated flow behavior of bulk metallic glasses based on machine learning

This study proposed a long short-term memory (LSTM) model for predicting the serrated flow behaviors of bulk metallic glasses (BMGs) under nanoindentation. A series of load-controlled nanoindentation tests were conducted on a Pd40Cu30Ni10P20 BMG. The LSTM model was introduced to establish a neural network for predicting the serrated flow at different loading rates, and was verified by the comparisons of experimental data with predictive results. Further investigation based on the predictive serrated flows under different loading rates showed that the serrations exhibit a significant self-organized critical (SOC) phenomenon at different loading rates. The SOC phenomena of the serrations under a lower loading rate were more obvious than that under a higher loading rate.

Atomic-scale homogeneous plastic flow beyond near-theoretical yield stress in a metallic glass

The onset of yielding and the related atomic-scale plastic flow behavior of bulk metallic glasses at room temperature have not been fully understood due to the difficulty in performing the atomic-scale plastic deformation experiments needed to gain direct insight into the underlying fundamental deformation mechanisms. Here we overcome these limitations by combining a unique sample preparation method with atomic force microscopy-based indentation, which allows study of the yield stress, onset of yielding, and atomic-scale plastic flow of a platinum-based bulk metallic glass in volumes containing as little as approximately 1000 atoms. Yield stresses markedly higher than in conventional nanoindentation testing were observed, surpassing predictions from current models that relate yield stress to tested volumes; subsequent flow was then established to be homogeneous without exhibiting collective shear localization or loading rate dependence. Overall, variations in glass properties due to fluctuations of free volume are found to be much smaller than previously suggested.

Softening and hardening on a Zr-based bulk metallic glass induced by nanosecond laser surface melting

The study reported here confirms that laser surface melting (LSM) can be employed to modify the hardness and the shear banding behaviour of bulk metallic glasses (BMGs). More specifically, by conducting LSM operations on the Zr-based Vitreloy 105 BMG in ambient atmosphere using a nanosecond laser, it was found that surface hardening can be achieved, in addition to the well-known surface softening effect. Besides, it was found that the presence of compressive residual stress and an increased introduction of crystalline precipitates accompanied LSM-induced surface hardening. On the contrary, tensile residual stress and a reduced fraction of crystalline precipitates were observed for a softened surface post-LSM. Finally, differences in shear-banding mechanisms were detected near the surface of the laser irradiated regions. More specifically, overall reduced serrated flow but important surface shear bands events were observed following the LSM-based introduction of compressive residual stress. In contrast, more pronounced serrated flows and the likely distribution of shear banding activity well beneath the irradiated BMG surface was promoted when LSM resulted in the introduction of tensile residual stress.

Tailored hardening of ZrCuAl bulk metallic glass induced by 2D gradient rejuvenation

The work hardening behavior of bulk metallic glasses has not been previously ascribed to their intrinsic structure but rather to the introduction of other components that act as hardening elements. Here, we present clear evidence of a 2D gradient rejuvenation state that can induce tailored hardening of a monolithic bulk metallic glass. We show that the local free volume content related to the rejuvenation state controls the shear band angle and the maximum effective shear stress. Hence, shear band propagation is prohibited, and the formation of a complete shear plane transecting the whole specimen is blocked. The generation of plastic strain is accompanied by an increase in the critical shear stress, resulting in sustainable apparent hardening. In this way, we present a bulk metallic glass that has a tailored hardening mechanism and establish an experimental link between a gradient rejuvenation state and mechanical properties.

Correlation Between Dynamic Compressive Strength and Fracture Behaviors of Bulk Metallic Glasses

The mechanical behaviors of Zr43.5Cu43.5Ni4Al8Nb1, Zr55.4Cu31.6Ni4Al8Nb1, Ti32.8Zr30.2Ni5.3Cu9Be22.7 (at.%) metallic glass at different strain rates were studied. For all the present alloys, the dispersion over 700 MPa was observed on the strength in the repeated dynamic compressions, which was much stronger than that of the quasi-static compressive strength. Such the dispersion of the dynamic compressive strength was well correlated with the corresponding fracture behaviors. The area of fracture surface was calculated and also showed a strong dispersion for all the fractured specimens tested at the strain rate of 500 s−1 and 1000 s−1. All the specimens showed a linear relationship between the square of dynamic compressive strength and the area of fracture surface in the dynamic compression tests. This phenomenon was mainly thought to be related to the difference of mean initial free volume concentration of different samples, stress concentration caused by the split Hopkinson pressure bar experimental setup and high sensitivity of defects under dynamic deformation. These findings were beneficial to deeply understand the effect of strain rate on the mechanical properties of the metallic glass.

Cyclic stress induced surface nanocrystallization adjacent to indentation edge of Zr-based bulk metallic glass at room temperature

Crystallization behaviors of bulk metallic glass (BMG) have been obtaining widespread concern, especially under service conditions including elevated temperature, electrical pulse, mechanical stress and high pressure. In this paper, cyclic stress was considered as typical service condition and applied on a Zr55Cu30Al10Ni5 BMG specimen with prefabricated double V-notches. Through indentation tests on fatigue-fractured specimen along with the connection line between notch tips, diversities in indentation serrated flow behaviors and morphological anisotropies were directly observed. Through transmissionelectronmicroscopy (TEM) characterization and selected area electron diffraction (SAED) analysis of thinned BMG specimen adjacent to indentation edge, direct experimental evidence of local crystallization at room temperature (RT) was verified. Meanwhile, the distance-dependent crystallization behavior was investigated in terms of gradually increased quantity of diffraction spots and precipitated nanocrystalline adjacent to indentation edge. Furthermore, high resolution transmission electron microscopy (HRTEM) images and SAED patterns at identical indentation microregion of tensile-fractured BMG specimen did not exhibit obvious nanocrystalline and diffraction spots, which indicated that the cyclic stress rather than static stress induced surface crystallization adjacent to indentation edge at RT.

Deformation Behavior of Bulk Metallic Glasses and High Entropy Alloys under Complex Stress Fields: A Review.

The plastic deformation of bulk metallic glasses (BMGs) depends significantly on applied stress states, and more importantly, in practical applications of BMGs as structural materials, they always deform under complex stress fields. The understanding of deformation behavior of BMGs under complex stress fields is important not only for uncovering the plastic deformation mechanisms of BMGs, but also for developing BMG components with excellent mechanical performance. In this article, we briefly summarize the recent research progress on the deformation behavior of BMGs under complex stress fields, including the formation and propagation of shear bands, tunable macroscopic plasticity, and serrated plastic flows. The effect of complex stress fields on the plastic deformation mechanisms of BMGs is discussed from simple stress gradient to tailored complex stress fields. The deformation behavior of high entropy alloys (HEAs) under complex stress states has also been discussed. Challenges, potential implications and some unresolved issues are proposed.

Intrinsic correlation of the plasticity with liquid behavior of bulk metallic glass forming alloys

Nowadays, plasticizing has become a critical issue for the engineering application of bulk metallic glasses (BMGs). What is the origin of plastic flow and how to evaluate the plasticity of BMGs with a unified standard are still open questions. Here we report a universal fragility criterion to scale the plasticity of BMGs from the equilibrium liquids and supercooled liquids. Based on our experimentally measured and previously reported viscosities at superheated and supercooled region for 51 glasses, the plasticity (ε) of BMGs has been found to positively correlate to the supercooling liquid fragility (m) with the equation of ε = 92exp[− 73/(m−15)], where ε is the plastic strain and m the fragility near glass transition temperature, but negatively correlate to the fragile-to-strong (F-S) transition tendency characterized by F-S transition factor and temperature. The intrinsic mechanism of the plasticity can be well interpreted in the frame of structural relaxation theory. This work provides a new insight into the microscopic essence of the plasticity of glassy solids and a universal approach to scale the fluidity of metallic glasses.

Effect of atomic mobility on the electrochemical properties of a Zr58Nb3Cu16Ni13Al10 bulk metallic glass

The corrosion behaviour of bulk metallic glasses is greatly related to their microstructures. The microstructures in bulk metallic glasses of the same chemical composition are represented to a certain extent by their atomic mobility. Evolution of the microstructure and mechanical properties of Zr58Nb3Cu16Ni13Al10 bulk metallic glass after annealing were studied with X-ray diffraction, dynamic mechanical analysis and Vickers hardness tests. Polarization curve, open circuit potential, electrochemical impedance spectroscopy and Mott-Schottky analysis were performed to investigate the effect of atomic mobility on the corrosion behaviour in 1 mol/L de-aerated H2SO4 at 333 K. Dynamic mechanical analysis indicated that the atomic mobility of Zr58Nb3Cu16Ni13Al10 bulk metallic glass was reduced by structural relaxation and crystallization. All electrochemical measurements showed that the passivation ability decreased and the corrosion resistance of Zr58Nb3Cu16Ni13Al10 bulk metallic glass deteriorated as the annealing temperature increased. Mott-Schottky analysis revealed that the defect concentration in the passive films increased and the flat-band potential shifted to a negative potential with a decrease in the atomic mobility. X-ray photoelectron spectroscopy results proved that the main chemical compositions of the passive films were ZrO2, Al2O3 and Nb2O5. The formation of a passive film was suppressed because the atomic mobility of strong passivating elements (Zr, Al and Nb) decreased. In addition, the precipitation of crystals (Zr2Cu and Cu10Zr7) accelerated the corrosion of the bulk metallic glass in H2SO4.

Deformation behavior of bulk metallic glasses under a mixed-mode (I/II) loading condition

Bulk metallic glasses (BMGs) demonstrate different deformation behavior under varying loading conditions. In the present work, a Zr57Cu20Al10Ni8Ti5 (atomic percent, at.%) BMG was subjected to a mixed-mode (I/II) loading condition by tailoring double-side notches. The findings show stable plastic-flow plateau stages in the loading-displacement curves, and this phenomenon is different from other notched BMG specimens with predominant-mode-I failure. More importantly, due to the stress concentrations between two notches, most of the slip events with large load drops occur on the fracture plane, resulting in a wide smooth region consisting of several shear steps on the fracture surface. We show that despite different deformation behavior, the specimens still display slip-size statistics of the plastic flow, which are similar to those seen in compression tests. The present findings give more insight into the deformation behavior/mechanisms of BMGs under varying loading conditions for practical structural applications.

Optimization of Cr/Mo molar ratio in FeCoCrMoCBY alloys for high corrosion resistance

Abstract The corrosion behavior of bulk metallic glasses (BMGs) (Fe41Co7Cr15Mo14C15B6Y2)100–xCrx (x=0, 4, 8, 12, molar fraction, %) was investigated in 1 mol/L HCl aqueous solution with electrochemical tests. The electrochemical measurements demonstrate that the passive current density of Fe-based amorphous alloy is reduced by about one order of magnitude, and meanwhile, the stability of passive film can be guaranteed by the Cr/Mo molar ratio. The Mott–Schottky (M–S) curves show that the passive film is the densest when the molar ratio of Cr/Mo is between 1.37 and 1.69. X-ray photoelectron spectroscopy (XPS) analysis was performed to clarify chemical states of elements in the passive films. The results show that the corrosion resistance of the alloy is related to the molar ratio of Cr/Mo. The stability of passive film is determined by the synergistic action of Cr and Mo elements. The main component of the passive film is Cr3+ oxide. When the potential is greater than 0.5 V (vs SCE), Mo6+ ions play an important role in keeping the stability of the passive film. The appropriate molar ratio of Cr/Mo can reduce the dissolution rate of the passive film.

Fracture Behaviors of Bulk Metallic Glasses Under Complex Tensile Loading

Up to now the theoretical analysis for fracture behaviors of bulk metallic glasses (BMGs) are limited to uniaxial loading. However, materials usually suffer complex stress conditions in engineering applications. Thus, to establish an analysis method that could describe fracture behaviors of BMGs under complex loading is rather important. In this paper, a universal formula for the fracture angle is proposed toward solving this problem. The ellipse criterion is used as an example to show how to predict fracture behaviors of BMGs subjected to complex loading according to this formula. In this case, both the fracture strength and fracture angle are found to be well consistent with experimental data.

Size matters in mechanical behavior of bulk metallic glasses

Size matters in mechanical behavior of bulk metallic glasses

Influence of thin-film metallic glass coating on fatigue behavior of bulk metallic glass: Experiments and finite element modeling

A coating of the Zr-based thin-film metallic glass (TFMG) was deposited on the Zr50Cu30Al10Ni10 bulk metallic glass (BMG) to investigate shear-band evolution under four-point-bend fatigue testing. The fatigue endurance-limit of the TFMG-coated samples is ~ 33% higher than that of the BMG. The results of finite-element modeling (FEM) revealed a delay in the shear-band nucleation and propagation in TFMG-coated samples under applied cyclic-loading. The FEM study of spherical indentation showed that the redistribution of stress by the TFMG coating prevents localized shear-banding in the BMG substrate. The enhanced fatigue characteristics of the BMG substrates can be attributed to the TFMG coatings retarding shear-band initiation at defects on the surface of the BMG.