Bulk Metallic Glass Specimens Research Articles

On the dynamic failure mechanism of Vit-1 bulk metallic glass: Coupling effects of pre-made damage and strain rate

To clarify the two distinct effects and the underlying physical mechanisms of pre-made damage on the failure strength of bulk metallic glass (BMG), i.e. strengthening or weakening, the influence of axial pre-compression on the dynamic failure of Vit-1 BMG are investigated experimentally. Quasi-static and dynamic compression tests were conducted on pre-compressed BMG specimens for a wide range of nominal strain rates between 0.001 s−1 to 6000 s−1. The focus is on the coupled effects of pre-compression and strain rate on the dynamic failure stress. Two contrasting mechanisms were identified that influence how the pre-made shear bands affect the propagation of cracks under different strain rates. It will be shown that the dynamic failure stress exhibits a transition from strengthening to knockdown with increasing strain rate; and, that the extent of these strengthening and knockdown effects depends on the pre-compression strain level. Finally, a failure model that captures the effects of both strain rate and pre-made damage is proposed.

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.

Tribocorrosion behaviors of Ti-based bulk metallic glass via laser shock peening in 3.5 wt % NaCl solutions

A Ti40Zr25Ni3Cu12Be20 bulk metallic glass (BMG) is treated by laser shock peening (LSP) with 1, 2 and 30 times, and then the phase structure, thermal, mechanical and tribocorrosion behaviors of the Ti-based BMG after LSP processing were studied in detail. The results demonstrate that although LSP did not significantly alter the phase structure of the Ti-based BMG, it facilitated rejuvenation and induced residual compressive stress within the BMG, thereby introducing internal structural heterogeneity. This heterogeneity promoted the generation of a substantial amount of free volume in the LSP-processed BMG specimens, leading to a marked improvement in plasticity and resistance to crack propagation. Consequently, the LSP-1 specimen exhibited higher surface microhardness (7.1 GPa) and plasticity, making it both plastic and tough and mitigating fatigue peeling wear caused by brittleness during reciprocating sliding wear. The average tribocorrosion volume loss rate of the LSP-1 specimen decreased by approximately 11 % to 5.73 × 10−4 mm3 N−1 m−1 (400 mV). However, excessive LSP resulted in elevated surface roughness (552.9 nm) and rejuvenation (ΔHrelax = 3.68 J g−1), rendering the surface of LSP-2 specimens more susceptible to pitting and significantly reducing their tribocorrosion resistance.

Strain rate response and rheological characteristics of ZrCuNiAl bulk metallic glass in supercooled liquid region

In this study, the plastic deformation behavior of Zr55.7Cu22.4Ni7.2Al14.7 bulk metallic glass (BMG) in the supercooled liquid region (SLR) was studied by high temperature compression experiments at various strain rates. The results show that the high temperature plastic deformation behavior of the BMG in SLR is highly sensitive to the strain rate. With the decrease in strain rate, the steady-state flow stress and peak stress decreases, and the viscosity increases. Meanwhile the stress overshoot gradually disappears, the deformation of the BMG specimen changes from non-Newtonian flow to near-Newtonian flow, and there is a critical strain rate of 5 × 10−4 s−1. The surface deformation profile changes from an "S" shaped truncated cone to a true truncated cone. The plastic deformation of BMGs at room temperature is completed by the initiation and expansion of the shear bands, while the high temperature plastic deformation is caused by the generation and annihilation of free volume.

The size-dependence of compressive mechanical properties and serrated-flow behavior of Ti-based bulk metallic glass

In this work, the size-dependence on the compressive mechanical and serrated-flow behaviors of Ti-based bulk metallic glass (BMG) was systematically investigated. The results demonstrated that the compressive plasticity of the BMGs was greatly improved from 1.0 ± 0.6% to 2.4 ± 0.5% with the specimen diameter reducing from 4 to 2 mm, while the fracture strength decreased from 2070 ± 40 to 1870 ± 31 MPa, indicating a trend of smaller and softer characteristics. Meanwhile, the Weibull distribution analysis of the strength and plasticity indicated that when the specimen diameter was increased from 2 to 4 mm, the Weibull strength modulus (mσ) decreased from 83.5 to 46.6 and the Weibull plasticity modulus (mε) decreased from 0.70 to 0.36, revealing a more discrete distribution of both the strength and the plasticity with the increase in diameter. The average shear-band velocity (ASBV), which was calculated based on the stick–slip dynamics, indicated an increasing trend with the increase in specimen diameter, while the shear-band instability index (SBI) presented a similar increasing trend. Meanwhile, the serrated-flow analysis revealed that the BMG specimen with smaller size possessed a lower average stress drop and a larger Weibull modulus of stress drop, which is the substantial cause for the considerable malleability in smaller specimen. Moreover, the fitting result for the cumulative probability distributions of the stress drop indicated that the stress drops in smaller specimens exhibit better coincidence.

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.

Dynamic mechanical performance and constitutive model for Zr58Cu12Ni12Al15Nb3 metallic glass

Abstract In this study, compression tests under quasi-static and dynamic states and plate impact experiments were performed on Zr58Cu12Ni12Al15Nb3 bulk metallic glass (BMG). The experimental results demonstrated that the BMG specimen fractured catastrophically without noticeable plastic deformation. Therefore, the Johnson-Holmquist II (JH-2) constitutive model was used to describe the mechanical response of the presented alloy. The constitutive parameters of the Zr-based BMG were determined from the experimental results based on the JH-2 constitutive equations. Subsequently, the constitutive model with the presented material parameters was programmed in the commercial finite element analysis software LS-DYNA to simulate the dynamic compression and penetration process. The good agreement between the numerical simulations and experimental results indicates that the obtained JH-2 constitutive parameters are accurate and effective.

Study of micro indentation assisted deformation on HPT processed Zr62Cu22Al10Fe5Dy1 bulk metallic glass

In the present work, investigation on high pressure torsion (HPT) and accumulative HPT (ACC HPT) processed Zr62Cu22Al10Fe5Dy1 bulk metallic glass (BMG) is performed. BMG plate was cut into four pieces (disc) for HPT and ACC HPT processing. BMG specimens obtained after n=2, 10 and 11 revolutions of the HPT and ACC HPT are termed as BMG 2, BMG 10 and BMG 11, respectively. Alloys are found to retain the glassy phase before and after HPT process. Homogeneous amorphous structure of BMG initial is obtained with slight decrease in microhardness at different locations on the plate. Besides, significant reduction in hardness for BMG 2, BMG 10, and BMG 11 specimens is observed due to HPT processing from central to peripheral region of the disc. Present study shows that ACC HPT more intensively transform the structure of BMG in comparison to that of conventional HPT.

Synthesis of Bulk Zr48Cu36Al8Ag8 Metallic Glass by Hot Pressing of Amorphous Powders

The critical cooling rate necessary for glass formation via melt solidification poses inherent constraints on sample size using conventional casting techniques. This drawback can be overcome by pressure-assisted sintering of metallic glass powders at temperatures above the glass transition, where the material shows viscous-flow behavior. Partial crystallization during sintering usually exacerbates the inherent brittleness of metallic glasses and thus needs to be avoided. In order to achieve high density of the bulk specimens while avoiding (or minimizing) crystallization, the optimal combination between low viscosity and long incubation time for crystallization must be identified. Here, by carefully selecting the time–temperature window for powder consolidation, we synthesized highly dense Zr48Cu36Ag8Al8 bulk metallic glass (BMG) with mechanical properties comparable with its cast counterpart. The larger ZrCu-based BMG specimens fabricated in this work could then be post-processed by flash-annealing, offering the possibility to fabricate monolithic metallic glasses and glass–matrix composites with enhanced room-temperature plastic deformation.

Deformation behaviours of TiZrCuNiBe bulk metallic glass in supercooled liquid region

In this work, the deformation behaviours of the Ti33Zr30Cu9Ni5.5Be22.5 bulk metallic glass (BMG) in the supercooled liquid region (SLR) were explored through a series of uniaxial compression experiments with a Gleeble 3500 thermal simulator at different strain rates. Results showed two main deformation modes in the SLR: plastic flow and brittle fracture. With increasing temperature and decreasing strain rate during the plastic flow process, the stress overshoot gradually disappeared, and the steady flow stress decreased. At 648 K, a transition from Newtonian flow to non-Newtonian flow was observed while the strain rate exceeded 1 × 10−3 s−1. The morphologies of the deformed BMG specimens changed with increasing temperature and consequently exhibited three profiles: asymmetric deformation, upright drum shape and uniformly flattened column shape. Studies of fracture behaviours showed that as the temperature increased from 618 K to 638 K, the critical strain rate of the fracture increased from 3 × 10−3 s−1 to 6 × 10−3 s−1. Moreover, the fracture angles increased from 46° to 57° due to the change in cohesive strength according to the Mohr–Coulomb criterion. Unlike the condition at room temperature, unique fracture morphologies, including fishbone-like characteristics and a large area of viscous flow layers, were formed under the high-temperature condition.

Electro-Discharge Machining of Zr67Cu11Ni10Ti9Be3: An Investigation on Hydroxyapatite Deposition and Surface Roughness

This study attempts to simultaneously machine and synthesize a biomimetic nanoporous hydroxyapatite coating on the Zr67Cu11Ni10Ti9Be3 bulk metallic glass (BMG) surface. The aim is to investigate and optimize the hydroxyapatite deposition rate and the surface roughness during the electro-discharge coating of Zr67Cu11Ni10Ti9Be3 BMG. Scanning Electron Microscopy (SEM), X-ray powder Diffraction (XRD) and Energy-dispersive X-ray Spectroscopy (EDS) were employed to characterize and analyze the results. Response Surface Methodology using D-optimum custom design approach was utilized to generate the models and optimize the input parameters. A globule nanostructured and nanoporous coating of about 25.2 µm thick, containing mainly Ca, O, and K were ascertained. Further XRD analysis confirmed the deposition of biocompatible oxides (HA, CaZrO3, and ZrO2) and hard ZrC coating on the Zr67Cu11Ni10Ti9Be3 BMG surface. A significant improvement in cell viability was observed in the HA electro-discharge coated BMG specimens. The numerical models for the Hydroxyapatite Deposition Rate (HDR) and Surface Roughness (SR) were developed and experimentally validated using the optimized parameters setting suggested by the software. The achieved average predicted error of 4.94 and 5.09% for the HDR and SR respectively confirmed the excellent reproducibility of the developed models.

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.

Achieving stable plastic flows in a Zr-based bulk metallic glass under tailored mixed-mode (I/II) loading conditions

The achievement of stable plastic flows plays a key role for practical structural applications of bulk metallic glasses (BMGs). In this work, by designing complex stress fields through tailored double-side notches, stable plastic flows in a Zr-based BMG were achieved under mixed-mode (I/II) loading conditions. The deformation behavior of the notched BMG specimens, including the shear-banding and fracture behaviors, was examined and correlated to the designed complex stress fields. The findings have shown that the stable plastic flows were mainly caused by the introducing of mode-II component under the mixed-mode (I/II) loading conditions. Increase of the mode-II component can result in not only more stable plastic flows, but also larger bearing loads. The present findings are of significance in uncovering the plastic deformation mechanisms of BMGs under mixed-mode loading conditions and in designing BMG structures with better mechanical performance.

Characterization, adhesion strength and in-vitro cytotoxicity investigation of hydroxyapatite coating synthesized on Zr-based BMG by electro discharge process

In this study, biocompatible hydroxyapatite (HA) coatings by HA mixed electro discharge coating (HA-EDC) process was synthesized on the Zr-based bulk metallic glass (BMG) surface. The aim is to promote the cells proliferation by synthesizing a strongly adhered oxide and carbide coating on the Zr-based BMG and blocking the release of Ni and Be in the BMG alloy. Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), X-ray Photoelectron Spectroscopy (XPS) and X-ray Diffraction (XRD) were employed to characterize the surface morphology, elemental compositions and the phases present in the electro-discharge coated Zr-based BMG. SEM analysis presented the formation of various micro and nano-sized craters, porosities and cracks on the coated and uncoated BMG surface. The EDX and XPS results depicted the migration of HA elements (Ca, P, O and K) to the workpiece surface, which replaced the Ni and Be in the Zr-based BMG alloy. The SEM cross-section revealed the formation of the nanoporous coating of about 27.2 μm thick and a reduced recast layer thickness. The XRD characterization identified the phases like CaZrO3, ZrO2, Ca5(PO4)3OH, ZrC and TiC formed on the coated BMG surface. A strongly adhered HA coating with adhesive failure of about 132 N load was achieved during the scratch test. A cytotoxicity study using an in-vitro 3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) Assay revealed a significant rise in cells viability on the coated Zr-based BMG specimen.

Effect of dynamic fragmentation on the reaction characteristics of a Zr-based metallic glass

The reaction behavior and dynamic fragmentation of ZrCuNiAl bulk metallic glass (BMG) subjected to high velocity impact was investigated. ZrCuNiAl BMG specimens were launched into a quasi-sealed chamber filled with air or argon (Ar) under various velocities. The results demonstrated that the ZrCuNiAl metallic glass generated debris after impact, the debris reacted with oxygen in the air atmosphere. The combustion of Zr and Cu and the combination reaction of aluminum and nickel released heat, which caused significant over-pressure inside the chamber. This reaction was related to the fragmentation and the critical fragment size for reaction was determined by scanning electron microscope (SEM) images; In Ar atmosphere, the cumulative mass of debris of ZrCuNiAl BMG was following a near power function distribution. A model was established by combining the dynamic fracture distribution with chemical reaction of ZrCuNiAl BMG, which can predict the quasi-pressure inside the chamber under a certain range of velocities with acceptable accuracy.

Effect of complex stress fields on the plastic energy accumulation in a Zr-based bulk metallic glass

In the practical applications of bulk metallic glasses (BMGs) as structural materials, they always deform under complex stress states. In this work, some single-side-notched BMG specimens with varying notch radii and geometries were fabricated, and tested under tensile loadings. The effect of complex stress fields on the accumulation of plastic energy in the notched BMG specimens was examined and discussed. The results show that the notched BMGs can dissipate more plastic energy before fracture than conventional tensile specimens which have a relatively-uniform stress distribution. To accumulate more plastic energy, it necessitates high orders of stress concentration to initiate more shear bands and appropriate distribution of complex stress fields to confine their propagations. The present findings are of significance for practical structural-applications of BMGs, where complex stress fields are usually presented.

Rate-dependent shear banding and fracture behavior in a ductile bulk metallic glass

The rate-dependent shear banding and fracture behavior of a ductile bulk metallic glass (BMG) under compressive loading are investigated in this paper. The continuous deformation process of the BMG specimens is captured by using the high-speed camera under both quasi-static and dynamic compression. Their characteristic shear banding and fracture behavior are synchronized with corresponding mechanical responses. The rate effect on initiation of shear bands is attributed to an increase in the coalescence rate of free volume. Rate-dependent shear banding behavior, i.e., the transition from multiple shear banding at lower strain rate to single shear banding at higher strain rate, are resulted from an increase in free-volume concentration level with increasing loading rate. The transition of fracture behavior from shear-dominated progressive sliding along slip planes under quasi-static compression to crack-dominated failure under dynamic compression is controlled by the patterns and time-scale of shear banding at various strain rates.

Additive manufacturing of an iron-based bulk metallic glass larger than the critical casting thickness

Fe-based bulk metallic glasses (BMG) are of increasing research interest, driven in part by a unique combination of mechanical, magnetic and chemical properties. However, the maximum thickness and geometry of BMGs achievable in traditional manufacturing processes is limited. This work examines the capabilities of laser based powder bed additive manufacturing (AM) to produce relatively large Fe-based bulk metallic glass specimens. AM fabricated specimens exceed the critical casting thickness of the material by a factor of 15 or more in all dimensions. Resulting microstructural and mechanical properties are reported. Despite decreasing quench effect with increasing build thickness, X-ray diffraction analysis suggests that a fully amorphous structure was maintained throughout the build. However, a low concentration of sparsely distributed nano-grain clusters was discovered using a high-resolution electron backscatter diffraction scan. The results pave the way for novel applications of metallic glasses achievable through appropriate material design and optimization of existing additive manufacturing processes.

Anisotropy in a bulk metallic glass induced by uni-directional heat flow

In this work, a controlled uni-directional heat flow was realized during the bulk metallic glasses preparation by using a vertical Bridgman solidification apparatus. Fully amorphous Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass specimens were prepared. The obvious difference in hardness between the cross and longitudinal sections of the as-prepared Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass specimens was identified, indicating strong mechanical anisotropy. The observed anisotropy can be ascribed to the uni-directional heat flow during the process of Bridgman solidification. The mechanical anisotropy may be explained by the free volume theory.

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.