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Heterogeneous gradient nanostructured metals have been shown to achieve the strength-ductility synergy, thus potentially possessing the enhanced tribological performance in comparison with their homogeneous nanograined counterparts. In this work, a facile laser surface remelting-based surface treatment technique is developed to fabricate a gradient nanostructured layer on a TiZrHfTaNb refractory high-entropy alloy. The characterization of the microstructural evolution along the depth direction from the matrix to the topmost surface layer shows that the average grain size in the ∼100 μm-thick gradient nanostructured layer is dramatically refined from the original ∼200 μm to only ∼8 nm in the top surface layer. The microhardness is therefore gradually increased from ∼240 HV in matrix to ∼650 HV in the topmost surface layer, approximately 2.7 times. Noticeably, the original coarse-grained single-phase body-centered-cubic TiZrHfTaNb refractory high-entropy alloy is gradually decomposed into TiNb-rich body-centered-cubic phase, TaNb-rich body-centered-cubic phase, ZrHf-rich hexagonal-close-packed phase and TiZrHf-rich face-centered-cubic phase with gradient distribution in grain size along the depth direction during the gradient refinement process. As a result, the novel laser surface treatment-introduced gradient nanostructured TiZrHfTaNb refractory high-entropy alloy demonstrates the significantly improved wear resistance, with the wear rate reducing markedly by an order of magnitude, as compared with the as-cast one. The decomposed multi-phases and gradient nanostructures should account for the enhanced wear resistance. Our findings provide new insights into the refinement mechanisms of the laser-treated refractory high-entropy alloys and broaden their potential applications via heterogeneous gradient nanostructure engineering.

Kirigami, the ancient Japanese paper cutting technique, has been applied to achieve high stretchability and low energy loss of designed metallic glass. Despite the exploration of the underlying deformation mechanism of kirigami-inspired structures from the energy point of view, the morphable responses of the kirigami patterns and the origin of the kirigami response are yet to be fully understood. This study reveals the mechanical driven-forms of the kirigami structure with the corresponding deformation stages. Based on the beam deflection theory, the elastic buckling behavior of kirigami metallic glass is manifested and a critical force prediction model is developed. Moreover, a force concentration parameter is introduced in the rigid-plastic deformation stage, predicting the nominal ultimate force. The kirigami-inspired facture force is firstly proposed. The findings of these models are in good agreement with the experimental size-dependent kirigami responses, and expected to provide significant insights into the understanding of the deformation behavior and the design of kirigami metallic glasses.

In this study, we additively manufactured a CrMnFeCoNi/AlCoCrFeNiTi0.5 laminated high-entropy alloy (HEA), with alternating layers of both constituent materials, that exhibits enhanced strength-plasticity synergy during compression (yield strength up to 990 MPa and no complete fracture until 80% strain), surpassing those of monolithic bulk HEAs. The enhanced strength-plasticity synergy originates from heterogenous microstructures of ultra-hard body-centered-cubic equiaxed grains and soft face-centered-cubic columnar grains periodically arranged in the AlCoCrFeNiTi0.5 and CrMnFeCoNi lamellae, respectively. This study demonstrates a feasible and flexible way to design HEAs with heterogenous microstructures and superior mechanical properties.

The deformation behavior in Zr36Cu64 metallic glasses with pre-introduced indent-notches has been studied by molecular dynamics simulation at the atomic scale. The indent-notches can trigger the formation of densely-packed clusters composed of solid-like atoms in the indent-notch affected zone. These densely-packed clusters are highly resistant to the nucleation of shear bands. Hence, there is more tendency for the shear bands to nucleate outside the indent-notch affected zone, which enlarges the deformation region and enhances both the strengthening effect and the plastic deformation ability. For indent-notched MGs, when determining the initial yielding level, there is a competition process occurring between the densely-packed clusters leading to the shear band formation outside the indent-notch affected zone and the stress-concentration localizing deformation around the notch roots. When the indent-notch depth is small, the stress-concentration around the notch root plays a dominant role, leading to the shear bands initiating from the notch root, reminiscence of the cut-notches. As the indent-notch depth increases, there are many densely-packed clusters with high resistance to deformation in the indent-notch affected zone, leading to the shear band formation from the interface between the indent-notch affected zone and the matrix. Current research findings provide a feasible means for improving the strength and the plasticity of metallic glasses at room temperature.

Compared to crystalline metals, metallic glasses (MGs) show an exceptional feature of improved ductility after being mechanically processed by wire drawing. However, its underlying mechanisms have not yet been fully elucidated. In this study, with the aid of atomistic simulations, wire drawing and subsequent tensile loading were performed on MG nanowires to systematically investigate the deformation mechanisms of MGs in wire drawing, the deformation-induced heterogeneities and their influences on the tensile ductility. The results revealed that the deformation mechanisms of MGs in wire drawing are closely associated with the area reduction ratio (R): at a small R of 4.7%, the area reduction is realized via shear transformations of atoms near the surface, leaving the core intact; while at a large R of 9.3%, it relies on the formation of multiple spatially distributed shear bands that redistributes the plasticity throughout the sample. The deformation-induced heterogeneities were understood through the detailed analysis of the resultant residual strain and stresses, the gradient rejuvenated amorphous structures, the unique free volume distribution and spatially distributed shear bands. Moreover, the tensile simulations revealed improved ductility synchronized with decreased yield strength of the drawn samples. The improved ductility is attributed to the synergistic effects of three beneficial factors: 1) The surface compressive residual axial stress leads to a shift of the yield sites from the surface to the core, suppressing the rapid formation of shear bands; 2) The rejuvenated structures near the surface constrain and accommodate the plastic deformation in the core; 3) The spatially distributed shear bands, generated at large R, serve as heterogeneous nucleation sites for highly dispersed plastic shearing. The findings provide a comprehensive elucidation of the deformation-induced heterogeneities of MGs in wire drawing and establish a physical relationship between these heterogeneities and mechanical properties, which can serve to interpret the experimental results.

We report that the tensile ductility of metallic glass (MGs) is tunable by introducing gradient rejuvenated amorphous structures (GRASs) using large-scale atomistic simulations. The results reveal that the ductile GRASs promote the formation and propagation of new shear bands in the interior unrejuvenated region by suppressing the catastrophic propagation of individual shear bands across the GRASs, thus resulting in a more dispersed plastic shearing throughout the sample. It is also demonstrated that increasing both the volume fraction and degree of structural disordering of GRASs can improve the tensile ductility of MGs and lead to a brittle-to-ductile transition of the deformation mode, although at the expense of some strength. Moreover, the critical volume fraction of GRASs required for switching the transition is found to depend on the specific degree of structural disordering. The observed structural state-dependent transition of the deformation mode is further understood from a mechanical perspective by considering the competition between the macroscopic yield strength and the critical stress of the material required for shear delocalization, based on which a criterion is developed to predict the critical transition boundary in MGs with GRASs across a wide range of structural states. The findings provide a detailed atomistic understanding of the relationship between the structural state and mechanical properties in MGs with partially rejuvenated amorphous structures, which may offer useful insights for designing and processing MGs with a sought-after combination of ductility and strength.

Increasing demands for electrochemical glucose sensors with high overall performance have recently attracted intensive attention. Herein, we report a novel sandwich-like nanoarchitecture composed of uniform CuO nanowire array layers grown on the nanoporous Cu2O film, which was synthesized via annealing the nanoporous copper thin film obtained by dealloying Cu-based metallic glass precursors. The glucose sensor based on the newly developed CuO/Cu2O nanocomposite exhibits prominent overall electrocatalytic performance towards the oxidation of glucose with a wide linear dynamic detection range from 0.1 to 6 mM, high sensitivity up to 1.95 mA/cm2·mM, fast response time of less than 1.5 s, low detection limit of 1 μM (S/N = 3) as well as excellent selectivity. The enhanced electrocatalytic property of the nanocomposite is attributed to the high surface area originating from the in-situ grown CuO nanowire array structure and synergetic bi-continuous nanoporous Cu2O substrate. This finding not only provides promising candidates for blood glucose sensing, but also opens a new avenue to designing nanostructured catalysts for engineering applications in general.

Bulk metallic glasses (BMGs) have serrated flows to accommodate plastic deformation at room temperature, where the mechanical energy is accumulated in a stress arising process and then released by a following stress drop. In this study, the variation of the mechanical energy accumulation rate of a Zr-based BMG under varying external disturbances, including the geometric confinement, sample sizes and stress gradients, has been investigated at varying strain rates. In all groups of specimens, the accumulation rates for the elastic strain energy during the plastic-flow serrations are different from the values at the initial elastic stages under compression tests, and have large variations. The variations of the accumulation rates are affected by the applied strain rates, and smaller variations are observed at relatively-lower strain rates (5 × 10−4 s−1 and 5 × 10−5 s−1). Such variations in the change of the applied strain rates are independent of the presence of the geometric confinement, size effect and stress gradients, and may be attributed to the intrinsic deformation mechanisms of BMGs. The findings give further insights into the mechanisms on the evolution of flow serrations in BMGs.

The effects of interfaces in crystalline Cu/amorphous Cu50Zr50 on shear banding dynamics are investigated using molecular dynamics simulations. The results show that the introduction of amorphous-crystalline interfaces can effectively promote the homogeneous distribution of shear transformation zones (STZs). We found that the high potential energy combined with the defects of the interfaces promote the nucleation of STZs. Further, the amorphous-crystalline interfaces are transition regions that mediate the transmission of dislocations in the crystallites into STZs in the metallic glasses. The accumulation of STZs and dislocations at the interfaces provide the sources for the enhanced plastic deformation in nanocomposites. These results allow us to determine the fundamental atomic structure of amorphous-crystalline interfaces in nanocomposites.

Degradation of organic contaminants in industrial wastewaters has become a worldwide conundrum and attracted extensive attention. In this paper, we report a flexible grid structure with uniform mesh fabricated by plain weaving melt-extracted Fe80B20 glassy micro-wires, and the produced wire grid with a dosage of 0.3 g/L can completely degrade 0.2 g/L DB 15 azo dyes for

In this work, micro/nano size pits were introduced to the surface of Fe80B20 amorphous ribbons by electrochemical etching treatment. The results show that the size of the pits is more sensitive to the applied etching potential, while the pit homogeneity is time dependent. The etching treatment at −0.30 V (vs saturated calomel electrode) for three hours in 1 M HCl solution saturated by KCl leads to the formation of numerous pits with an average diameter of 222 nm. The large amount of pits results in higher degradation efficiency on Direct Blue 15 when compared with the as-spun amorphous alloy.

The magnetic properties and magnetostriction of a binary Dy50Co50 glassy alloy were studied in the present work. The Dy50Co50 glassy ribbon shows spin glass like characteristics with a spin freezing temperature of about 80 K. The magnetostriction of the glassy ribbon is reversible at temperatures above 60 K, where the glassy ribbon is soft magnetic; but is irreversible at temperatures well below 60 K, where the ribbon is hard magnetic. The effect of the magnetic structure on the magnetic and magneto-strictive behavior, as well as the mechanism of large magnetostriction for the glassy alloy, were examined.

A series of multilayer amorphous Cu50Zr50/Cu nanolaminates with consideration of grain boundary characteristics in the Cu layers were constructed and compressed to investigate the atomistic mechanisms of yielding and plastic deformation behavior using large-scale atomistic simulations. The results revealed that yielding occurs initially in the Cu layers through lattice dislocations, while plastic deformation in the amorphous layers is induced by the transfer of dislocation plasticity from the Cu layers, mainly at the intersections of the crystalline-amorphous interfaces and grain boundaries. Similar to the roles of defects-like secondary phases, the Cu layers serve as sites for heterogeneous nucleation of embryonic shear bands, as well as barriers to their propagation into mature ones. The coupled interplay between the crystal plasticity and the glassy plasticity in the nanolaminates promotes a more homogeneous redistribution of plastic deformation, providing a kind of hardening mechanism. In addition, our simulations also demonstrate a transition of the deformation mode from localized to homogeneous-like deformation by tailoring the relative volume fraction of the Cu layers. The findings provide more detailed atomistic information for understanding the underlying deformation mechanisms that are difficult to obtain by post-mortem observations and are useful for optimizing the structure of amorphous/crystalline metallic nanolaminates.

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.

For room-temperature magnetic refrigerators, magnetocaloric materials are critical for their performance and reliability. Among various magnetocaloric materials, Fe-based metallic glasses, especially in the FeZrB system, have been intensively studied recently due to their promising properties such as low fabrication cost and broad magnetic entropy change peak. In order to further improve the magnetocaloric effect (MCE), the influence of minor additions of Co, Er, Sm and Mn on the MCE of FeZrB-based metallic glasses was systematically investigated in this work. The composition-dependent Curie temperatures ( T C ) were studied and the magnetic field-dependent MCE was investigated. In two compositions, Fe 88 Zr 7 B 3 Co 2 and Fe 86 Zr 8 B 4 Sm 2 , it was found that their Curie temperatures were close to room temperature and the values of the refrigerant capacity and peak magnetic entropy change were larger than those reported for Fe-based metallic glass at room temperature.

Some highly stretchable kirigami metallic glass (MG) structures with ultra-small strain energy loss during cyclic loading are developed. Less than 3% of strain energy loss is achieved after 1000 loading/unloading cycles, which is much smaller than the Kapton or nanocomposites-based kirigami structures. By optimizing the kirigami pattern design and smoothing the kirigami cuts may further reduce the stress energy loss, and one kirigami MG structure even shows no obvious strain energy loss. They are potentially useful for developing reversible mechanical metamaterials/devices or substrates of functional optoelectronic devices.

The microstructural inhomogeneity of Zr 46 Cu 46 Al 8 metallic glasses is investigated quantitatively by molecular dynamics simulation. A parameter, the change ratio of polyhedral volume, is used to characterize the microstructural inhomogeneity in metallic glasses. Based on identifying the polyhedral volume expansion and contraction around each atom, the microstructural heterogeneity of metallic glasses can be revealed and quantified. The relation between the redistribution of the free volume and production or annihilation of defects has been established. By molecular dynamics simulations of dynamic mechanical tests, the distribution of the change ratio of polyhedral volume is correlated to dynamic heterogeneities in metallic glasses at the atomic level. Our work opens a new technologically avenue towards the characterization of microstructural inhomogeneity that affects the thermodynamics, dynamics and deformation in metallic glasses.

The atomic movements for completing the fcc-γ → hcp-e → bct-α Plastic Deformation-Induced Martensitic Transformation (PDIMT) has been revealed to be confined purely on one specific { 111 } γ plane. However, so far nothing has been known for the possible intersection of two fcc-γ → hcp-e → bct-α PDIMTs pre-developed from two individual { 111 } γ slip systems. For the first time, here we capture the nucleation of bcc-α′ in the intersection of two bct-α phases in 304 stainless steel, following a novel polymorphic fcc-γ → hcp-e → bct-α → bcc-α′ PDIMT. High-resolution transmission electron microscopy observations were mainly performed to unveil the underlying atomic process in the final-step bct-α → bcc-α′ transition, which is executed by the cooperation of partial dislocation dipoles gliding on every second { 110 } α planes of two bct-α phases (equivalent to { 110 } α ′ and { 011 } α ′ planes), and atom shuffling along the [ 1 1 ¯ 0 ] α 1 / [ 1 ¯ 12 ] α ′ and [ 1 1 ¯ 0 ] α 2 / [ 21 1 ¯ ] α ′ directions.

The formability and magnetic properties of a low cost Nd50Co50 binary metallic glass were studied in the present work. The Nd50Co50 binary alloy was successfully vitrified into amorphous state with a poor but sufficient formability for glassy ribbon. The Nd50Co50 glassy sample exhibits a spin-glass-like behavior with a Curie temperature of ~ 78 K and a spin freezing temperature of ~ 61 K. The magnetocaloric properties of the Nd50Co50 glassy sample were poor and the mechanism involved was studied. The magnetostriction of the Nd50Co50 glassy sample under 5 T reached to 170 ppm at 30 K, which is not as high as those of Tb(Dy)-based amorphous alloys but much higher than those of TM-based metallic glasses. The binary Nd50Co50 alloy is expected to play a role as basic alloy for developing low-cost multicomponent metallic glasses with outstanding glass formability and magnetostriction.

Near-fully dense CoCrFeMnNi high-entropy alloy (HEA) matrix composites reinforced with 5 wt% TiB2 nanoparticles were successfully additively manufactured via the laser-engineered net shaping technique. Compared to the monolithic CoCrFeMnNi printing process, a higher energy density input is shown to produce a synergic combination of Marangoni flow and capillary force in the laser-generated melt pool. It facilitates the enhancement of wettability, and hence a more uniform distribution of the reinforcement material and a high degree of densification of 99.72%, which are able to delay the early fracture of the material. The as-deposited composites exhibit improved yield strength, surpassing that of the monolithic HEA by 42%. The enhanced strength is mainly ascribed to dispersion strengthening. Besides, the refined grain size, the increased dislocation density, and the additional load transfer effect also contribute to the strength enhancement. Furthermore, the wear resistance properties of the CoCrFeMnNi/TiB2 composite are also shown to be superior to those of the CoCrFeMnNi, indicating a decrease in friction coefficient by 22.4%. The enhanced tribological properties are attributed to the synergic effect of high-hardness and self-lubrication of TiB2 nanoparticles. The findings provide guidelines for achieving high-performance HEA-matrix composites.

In the present work, we report the outstanding magneto-elastic and magneto-caloric properties of a Tb-Co binary amorphous alloy. The glass forming ability (GFA) of Tb-Co binary alloys was studied and the best glass former was obtained near the eutectic point of the binary alloys. The magnetic properties of the eutectic Tb 62.5 Co 37.5 amorphous alloy were measured, and it was found that the Tb 62.5 Co 37.5 amorphous ribbons exhibited excellent magneto-elastic properties (the magnetostriction of nearly 470 ppm at 50 K under 5 T) and magneto-caloric properties (the peak magnetic entropy change of 9.3 Jkg −1 K −1 at 92.5 K under 5 T). The mechanism for the improved GFA, magneto-caloric effect (MCE) and magneto-elastic properties of the Tb 62.5 Co 37.5 amorphous ribbons was analyzed.

Alloys exhibiting table-like magnetic entropy change (−Δ S m ) profiles are regarded as ideal magnetic refrigerants for the Ericsson magnetic refrigeration cycle. In this work, we fabricated two Gd-Co-based amorphous hybrids using various combinations of Gd 50 Co 50 , Gd 50 Co 48 Fe 2 , Gd 50 Co 48 Mn 2 and Gd 50 Co 45 Mn 5 amorphous ribbons with Curie temperatures ranging from 245 K to 278 K, and obtained table-like −Δ S m profiles across the ice point of water within different temperature ranges. The maximum −Δ S m and refrigeration capacity of the amorphous hybrids were higher than those of other amorphous alloys or composites with flattened −Δ S m values near room temperature, indicating that amorphous hybrids are good candidates for magnetic refrigerants in house-hold magnetic refrigerators.

Stick-slip dynamics during nanoscratching is investigated for the Ni 62 Nb 38 metallic glass. Detrended fluctuation analysis is introduced to explore the influence of loading force on the temporal scaling and stick-slip behavior. The self-similar characteristics and complexity in the temporal scale of the lateral force signal are investigated. A modified Cauchy class model is used for the stochastic stick-slip process, which connects the fractal dimension and the Hurst exponent and features the positive correlation process. The confidence intervals of the differential friction coefficient at different loading forces elucidate the inhomogeneous (and homogeneous) shear-branching processes during the nanoscratching process.

Among various amorphous magnetic materials, even though Fe-based materials do not have high magnetocaloric effect (MCE), their advantages of tunable Curie temperature (TC) and low cost have attracted considerable attention in regard to room temperature magnetic refrigeration applications. With the aim of enhancing the MCE, the influence of boron addition on Fe-based amorphous materials was investigated in this study. Fe94−xZr6Bx (x=5, 6, 8 and 10), Fe91−yZr9By (y=3, 4, 5, 6, 8 and 10) and Fe89−zZr11Bz (z=3, 4, 5, 6, 8 and 10) specimens were made in ribbon form and their magnetocaloric effect was investigated. The Curie temperature (TC) of all three series of ribbons underwent an almost linear increase, and the peak magnetic entropy change, | Δ S M p e a k | (obtained in a magnetic field of 1.5 T), generally increases with increasing boron content. The results further show that the Fe86Zr9B5 ribbon exhibits a relatively large | Δ S M p e a k | value of 1.13 J/kgK at 330 K and a large refrigerant capacity value of 135.6 J/kg under 1.5 T. On the basis of these results, although there is still much scope for improvement before totally replacing the conventional cooling method, the Fe-based amorphous ribbon can be seen as a promising magnetocaloric material for room temperature magnetic refrigeration applications.

In this work, a small-scale resistance spot welding method was utilized to join two dissimilar Zr-based bulk metallic glasses and to fabricate the sandwich-laminated metallic glass plates. The laminates exhibit an almost fully amorphous structure without undesirable crystallization. Elemental line scanning across the joint interface shows a uniform distribution of the main elements, demonstrating favorable metallurgical bond in the laminate. The resultant tensile strength of the welded laminate is comparable to that of the parent metallic glasses. The fractured surface of the laminate exhibits extensive multiple failure planes, suggesting that the fracture instability was mediated by a crack branching mechanism over across the joint interface. Such a crack branching mechanism results in a stepwise fracture behavior which is contrastingly different from the conventional single primary shear band dominated catastrophic fracture in monolithic metallic glasses under tension. The unique stepwise fracture behavior endows the sandwiched metallic glass laminates with an excessive strain energy absorption through the joint interface than monolithic metallic glasses. Our results demonstrate that small-scale resistance spot welding is a promising approach to scaling up metallic glasses and to fabricating metallic glass laminates with desirable mechanical performance for structural applications.

In this work, the effect of external disturbances on the strain-rate dependent plastic deformation behavior of a Zr 57 Cu 20 Al 10 Ni 8 Ti 5 bulk metallic glass (BMG) has been examined by tailoring the geometric confinement, stress gradient, and sample size. With the external disturbances, the fracture strains of the BMG specimens become less dependence on the strain rates, and it is found that the confinement of the propagation of shear bands is the dominant deformation mechanism. This is different from previous findings in that multiplication of the shear bands also plays a critical role in accommodating the plastic deformation of BMGs with external disturbances. The present findings not only shed more light on the deformation mechanisms of BMGs under external disturbances, but also suggest that the use of external disturbances can reduce the dependence of the plastic deformation behavior of BMGs on the strain rates.

It is important to interpret the scattering of the plastic deformation behavior data for the structural-applications of bulk metallic glasses (BMGs), however, few studies have focused on statistical analysis of the variation and reliability of the plastic deformation behavior of BMGs. In this work, statistical analyses show unavoidable large variations in the maximum nominal strains of as-cast BMGs, although they exhibited greatly-enhanced average values of the maximum nominal strains with reduced sample sizes and in the presence of stress gradients. The large variations are attributed to the intrinsic variability of the atomic arrangements stemming from the solidification processes. Nevertheless, the investigations show enhanced cut-off nominal strains (safety threshold) in the specimens with stress gradients. The findings suggest that, despite large variations in the plastic deformation behavior, BMGs are still reliable in practical structural-applications where the materials always deform under more complex stress states.

The origin of the deformation in metallic glasses is attributed to rearrangements of atoms in some structurally weak spots behaving as flow units, which are associated with free volumes. In the present study, Xe-ion beam is used to manipulate the free-volume fraction, and influence on the mechanical behavior of a Zr-based metallic glass. The irradiation at low dosages can change the structure by increasing the free volume, and by homogenising the distribution of free volume. The increase in the free-volume fraction is equivalent to the increase in the deformation temperature, thus resulting in the decrease in the yield strength. The analysis of stochastic strain burst size in the metallic glass irradiated at different dosages indicates that the strain burst depends on the yield strength and homogeneity of the glassy phase. The results of this study highlight the fact that the quantitative manipulation of the homogeneity and the amount of free volumes can be achieved through low-dose ion irradiation, which can modify the mechanical behavior of metallic glasses.

In this work, saw-tooth-like bulk metallic glass (BMG) structures were developed, exhibiting greatly enhanced energy-absorption performance as compared with existing cellular metals, such as conventional metal foams and BMG foams/honeycombs. The excellent energy absorption capacity is attributed to the change of the deformation modes from bending, buckling and collapse of the structural units in conventional cellular solids to large plastic deformation in the present BMG structures. Additionally, the energy absorption capacity of designed saw-tooth-like BMG structures can also be tuned by tailoring the periodic distribution of the structural units.

Inducing residual stress in metallic glasses (MGs) is recognized to be beneficial for plasticity but the mechanisms on how it affects shear band nucleation, propagation and multiplication remain poorly understood. With the aid of experimental and computational approaches, we address this issue by comparatively studying the deformation behavior of two types of MG samples, which were individually prepared by surface imprinting and photo-chemical etching but having similar surface patterns. Results showed that the imprinted MGs exhibit simultaneously enhanced plasticity and compressive strength, while the etched ones show limited plasticity improvement and reduced strength. The enhanced mechanical properties of the imprinted MGs are attributed to the compressive residual stresses generated near the surfaces, rather than the resultant geometrical pits. Finite element analysis revealed that the residual stress induces obvious stress gradient and inhomogeneous plastic deformation, which facilitate heterogeneous nucleation of multiple shear bands near the surfaces. Complementary atomistic simulations further revealed that the stress gradient resulting from the residual stress slows down the shear banding dynamics and causes deflection and branching, which consequently promotes shear band multiplication during propagation. This work uncovers the interactions between the residual stresses and shear bands, which are useful for processing MGs with desirable mechanical properties.

Recently, interfacial solar-driven evaporation has received tremendous attention due to its potential for enhancing solar thermal conversation ability via heat localization at the evaporation interface. Diverse materials and configurations have been explored to boost the evaporation using plastic foam as the thermal insulator at the cost of complex assembly and environmental threats. Herein, we demonstrate a biodegradable, cost-effective, and scalable three-dimensional (3D) cotton paper-based solar steam generator prepared by one-step laser-induced forward transfer in the ambient atmosphere. The as-prepared evaporator has excellent solar absorption ability. The defining advantages of this method are that it can easily form a 3D structure and it is free from hazardous raw material involvement and waste generation. With further novel design by using a natural air gap instead of artificial plastic material to insulate the steam generation area and the underlying bulk water, the as-prepared evaporation system can achieve a high evaporation rate of 1711 g m−2 h−1 with a corresponding efficiency of 83% under one sun illumination. Such solar vaporization functions offer new insights into the future development of high-performance solar steam generators through an environmentally friendly and cost-effective pathway.

Due to the localization in space and the transience in time, investigations on the shear bands in metallic glasses are extremely difficult. The liquid-like layer frozen on fracture surfaces suggests a decreased viscosity in the shear band. Whether it is resulted from locally heating remains controversial. In this paper, the temperature rise in shear bands is profiled as a function of the duration of shear banding event, the distance from the shear band center and the thickness of shear band. The elastic energies released from the specimen and the testing machine are estimated regarding the serrations with different load drops in the compressive load–displacement curve of a Zr-based metallic glass. The duration of shear event and the released energy by serration are the two main factors determining the temperature rise in shear bands. It is found that both “cold” and “hot” shear bands are attainable. Then the sliding speed, the viscosity and the crystallization probability of shear band are studied. These results can help to better understand and describe the operation of shear band in a quantified and analytical way.

In this study, self-detached nanoporous titanium-based metal oxide was synthesized for the first time by ultrafast anodization in a fluoride-free electrolyte containing 10% HNO3. The nanoporous oxide has through-holes with diameters ranging from 10 to 60 nm. The as-formed oxides are amorphous, and were transformed to crystalline structures by annealing. The performance of a dye sensitized solar cell using nanoporpous Ti–10Zr oxide (TZ10) was further studied. It was found that the TZ10 film could increase both the short-circuit current and the open-circuit photovoltage of the solar cell. The overall efficiency of the solar cell was 6.99%, an increase of 20.7% as compared to that using a pure TiO2 (P25) film.

A large tensile plastic deformation was achieved in ZrCu-based metallic glass composites with a metastable B2 phase. It was found that the B2 phase can effectively promote the density of the stress concentration sites and enhance the formation and interaction of multiple shear bands, which significantly stabilize the tensile plastic deformation of metallic glass composites. Based on the concept of the normalized strain-hardening rate, the critical volume fraction for the stable tensile plastic deformation of metallic glass composites was determined.

Cutting behavior exerts a considerable influence on the fabrication of bulk metallic glass (BMG) components. In this study, the influences of machining parameters (i.e., depth of cutting, feed rate, and spindle rate) on the turned surface of a Zr-based BMG after observing the 3D morphologies of this surface were characterized. The results showed that the influence of the spindle rate on the surface morphologies is more substantial as compared to the depth of cutting and the feed rate. Nanoscratch tests were conducted to further characterize the separation mechanism of the chips, which revealed that the chips are torn off the surface of a BMG because of inhomogeneous localized maximum shear stress.

Macroscopic bulk metallic glass (BMG) structures have been investigated as potential structural materials in recent decades, due to their superior energy absorption ability and excellent mechanical properties. However, lack of understanding the deformation mechanisms of BMG structures significantly hindered their potential structural applications. In the present study, through macroscopic geometrical control, five BMG structural elements (struts) have been designed and investigated under both tensile and compressive loadings. Under tension, the particular BMG structural elements show tunable large macroscopic axial elongations, which are mainly attributed to the controllable plastic deformation in localized regions and the straightening of the curved segments in the BMG structural elements. Under compression, three different deformation modes are observed in the BMG structural elements. This work is of significance in understanding the deformation behavior of macroscopic BMG structures.

Uniaxial compression tests of slender metallic glass bars of composition Zr-52 5Cu17.9Ni14.6Al10Ti5 (at.%) have been conducted. It was found that the Zr-based metallic glass bars have a tendency to buckle elastically or plastically rather than to yield or fracture if its slenderness ratio is over a critical value. The elastic buckling undermines the intrinsic strength of the metallic glass, but the plastic buckling imparts the metallic glass a benign failure mode and avoids the catastrophic brittle fracture. The phenomena are understood by the unique stress state across the bar. The result has implication for the measurement of mechanical properties of bulk metallic glasses and is of significance in the application of metallic glass members in engineering structures. (C) 2013 Elsevier B.V. All rights reserved.

Based on the analyses of the influences of temperature and pressure on diffusion behavior with time, a Zr-based bulk metallic glass is successfully bonded in its supercooled liquid region. The temperature is found to be a key factor for the success of the bonding process if sufficient pressure and time are adopted. Three-point bending tests show that the flexural performance of the samples bonded with various parameters is significantly different. The parameters in favor of diffusion bonding do not automatically benefit the performance of the bonded materials. Diffusion makes the nano-voids shrink to form metallurgical bonding at the interface and it causes structural relaxation leading to the embrittlement inside bulk. Balance between the two aspects is the key to the bonding success and the utility of the bonded materials. (C) 2013 Elsevier Ltd. All rights reserved.

In this work, the non-equiatomic high entropy alloy AlCoCrFeNiTi0.5 was additively manufactured via the laser engineered net shaping (LENS™) process. Contrary to the columnar grain microstructure commonly observed in previously reported alloys, the as-deposited AlCoCrFeNiTi0.5 specimens exhibit a fully equiaxed grain microstructure in a wide range of temperature gradients G (85 to 1005 K/mm) and solidification velocities V (5 to 20 mm/s). The main microstructural characteristics were found to be B2-structured proeutectic dendrites delineated by lamellar or rod-like B2/A2 eutectic structures. The formation of this microstructural feature can be discussed with the aid of Scheil's solidification model. The proeutectic B2-structured dendrites were frequently found to be fragmented, which may provide profuse effective nucleation sites, and hence promote equiaxed grain formation. Furthermore, we estimated the volume fraction ϕ values of equiaxed crystals at solidification front for various G - V combinations established in this paper, which can provide a theoretical basis for our experimental findings. The current work provides guidelines for producing fully equiaxed alloys by the additive manufacturing (AM) process. © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The deformation behaviors of body-centered cubic Cu 0.5 CoNiCrAl high-entropy alloys processed by the cooling rate gradient are investigated by the molecular dynamics simulations. The plastic deformation ability of the high-entropy alloy is significantly improved by triggering multiple-type dislocation slips along different deformation paths. The cooling rate gradient introduces abundant atomic vacancies, proliferating the nucleation sites of dislocations. Additionally, the nucleation barriers of dislocations are reduced by the resultant structural disorder, high potential energy and chemical segregation. Consequently, the cooling rate gradient enhances the structural heterogeneity, promoting the formation of multiple deformation paths and preventing strain localization.

The equiatomic CrMnFeCoNi high entropy alloy is additively manufactured by the laser engineered net shaping (LENSTM) process, and the solidification conditions, phase formation, as-deposited microstructures, and tensile behavior are investigated. The LENSTM-deposited CrMnFeCoNi alloy exhibits a single-phase disordered face centered cubic (FCC) structure, as evidenced by X-ray diffraction (XRD), and rationalized by Scheil's solidification simulation. Furthermore, microstructures at multiple length scales, i.e. columnar grains, solidification substructures, and dislocation substructures, are formed. The tensile deformation process is mainly accommodated by dislocation activities with the assistance of deformation twinning. The tensile yield strength of the LENSTM-deposited CrMnFeCoNi alloy is comparable to that of finer-grained wrought-annealed counterparts, due to the additional initial-dislocation strengthening. However, the uniform tensile elongation, by contrast, is lowered, which is attributed to the increased dynamic dislocation recovery rate and hence the weakened work hardening capability of the LENSTM-deposited CrMnFeCoNi. This study demonstrates the capability of the LENSTM process for manufacturing the CrMnFeCoNi alloy, with high performance, for engineering applications.

A transparent nanocrystalline Cu2O thin film has been synthesized by electrodeposition using a reverse potential waveform with a cathodic peak potential of − 1200 mV, an anodic dissolution peak potential of + 800 mV and a cycle time of 80 s. For each cycle, Cu2O particles are firstly deposited on the substrate, followed by the deposition of Cu particles. When the current changes from cathodic to anodic, the deposited Cu particles will be dissolved. With repeated cyclic deposition and dissolution, a Cu2O thin film with nanocrystallized structure is obtained, and it exhibits a blueshift of optical bandgap to 2.87 eV.

In this work, the deformation behavior of a Zr-based bulk metallic glass specimen under a tailored complex stress state was investigated. When the specially designed specimen was subjected to a uniaxial tensile loading, the in-plane stress distribution along the symmetrical plane was hyperbolic, with the presence of both compressive and tensile stresses. The evolution of deformation in the specimen was found to consist of three stages: the shear band initiation stage (stage I), the shear band multiplication stage (stage II) and the final rapid fracture stage (stage III). In a conventional tensile specimen with uniformly distributed stresses, the specimen fractures (stage III) catastrophically after stage I. However, in the specially designed specimen, the complex stress distributions result in not only more stable shearing processes in stage I, but also the evolution of stage II before stage III, which causes the formation of a large number of shear bands. The findings shed more light on the deformation mechanisms of bulk metallic glasses under complex stress states.

We have demonstrated, for the first time, the enhanced plasticity of multi-layer Pd-based bulk metallic glasses (BMGs) synthesized by thermoplastic bonding (TB). The structural relaxation was minimized by using a low bonding temperature and a very short holding time. As compared to the as-cast and the two-layer BMG samples, the three-layer samples achieve larger plasticity. The fracture morphology of the multi-layer samples exhibit radiating-ridge patterns as compared to the river-like cell patterns observed in as-cast BMGs. The enhanced plasticity is due to the blocking effect of the bonding interface for the propagation of shear bands. Our research opens a promising way to synthesize BMGs with larger size and enhanced plasticity for potential structural applications.

In this work, a rare earth (RE) free Mg69Zn27Ca4 bulk metallic glass (BMG) of diameter 1.5 mm was successfully fabricated by the injection casting method using recycled materials in atmospheric air. Without using high vacuum conditions, high purity starting materials and expensive rare earth materials, the findings of the work are of significance in reducing the cost and improving the manufacturability of BMGs. The results of the uniaxial compression tests further showed that there were no obvious differences between BMGs prepared under high vacuum or in atmospheric environment. The electrochemical polarization measurements in simulated physiological media revealed that the atmospheric Mg69Zn27Ca4 BMG manifested much lower passive current densities, higher pitting potential and a wider passive region than those of ZK60 and pure Mg alloys. The findings not only present Mg69Zn27Ca4 BMG as low cost material for potential biomedical applications, but also provide new insights into understanding of the effects of oxygen on glass formation.

The effect of shear bands on pitting corrosion of a pre-deformed Zr-based bulk metallic glass was studied through immersion test in 1 M HCl solution. It was found that pitting always preferentially occurred at the offsets of the shear bands, but this selective corrosion behavior disappeared when the shear offsets were polished, although shear bands did exist at the same locations. This demonstrates that the shear offsets, rather than the structural changes in the shear bands, is the dominant factor for the pitting initiation.

In the present study, the stress gradient is shown to significantly affect the deformation behavior of a monolithic bulk metallic glass (BMG) at room temperature under tensile loading. It is demonstrated that the stress concentration areas of the BMG specimens facilitate the formation of shear bands, and the presence of “soft” and “hard” regions due to the stress gradient confines the propagation. With these stress gradients, brittle monolithic BMGs exhibit plastic deformation at the stress concentration areas under tensile loading, and higher orders of stress gradient result in larger confinement for the propagation of shear bands. The findings are significant in controlling the plastic deformation behavior of BMGs and in understanding the deformation mechanisms of monolithic BMGs under complex stress states, which is important for potential engineering applications.

In the present work, a novel Fe 43 Co 4.5 Cr 16.5 Mo 16.5 C 14 B 4 Y 1.5 (at.%) bulk metallic glass rod with 10 mm in diameter has been developed by Cu-mold suction casting using commercial grade raw materials. The thermal stability and corrosion behaviors of the centimeter-sized Fe-based alloys have been studied by differential scanning calorimeter and electrochemical measurements, respectively. The as-cast Fe-based alloy exhibits a high glass transition temperature of 820 K and a large super-cooled liquid region of 60 K, demonstrating an excellent thermal stability. Moreover, the Fe-based alloy developed appears to have corrosion resistance comparable to (or better than) that of 316L stainless steel, based on the measurements of breakdown potential and corrosion weight loss in simulated acid rain and seawater solution. The affluent of chromium and molybdenum elements included is conceived to be highly responsible for the high corrosion resistance in the current Fe-based bulk metallic glass, which may be good candidates to be used as low-cost, high-strength, and corrosion-resistant amorphous alloy.

Viscous flow has rarely been observed in solid-state sintering of metal, while operates the dominant mass transport mechanisms in vitreous materials. In the present study, Ti-based bulk metallic glasses (BMGs) with nearly 100% relative density were fabricated by spark plasma sintering of a gas-atomized Ti48Ni32Cu8Si8Sn4 glassy alloy powder. Two main shrinkage stages of densification occurred at a constant heating rate. Based on the analysis of experimental data and microstructure observations of samples sintered at various temperatures, sintering mechanisms are proposed for the sintering of Ti-based metallic glassy powders in light of the viscous flow model.

The rapid in situ formation of a Ti alloy/TiC porous composite was achieved using the powder metallurgy approach. Ti6Al4V powders were mixed with 14.5 vol.% of multiwalled carbon nanotubes (MWCNTs) and the particle size of Ti6Al4V was reduced to ∼5 μm by ball milling. The MWCNTs acted as microwave susceptors as well as reactants for the rapid sintering of Ti alloys. The green compact of the Ti6Al4V/MWCNTs powder was sintered in a 1.4 kW, 2.45 GHz bi-directional microwave emission furnace without using any protective gas environment. The microwave sintering was completed within 2 min. The surface temperature of the sample reached 1620 °C during sintering, as measured by a pyrometer. Titanium carbide was formed after the sintering as confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The composite has a porosity of approximately 25%, compressive strength of 270.41 ± 24.97 MPa, compressive yield stress of 145.48 ± 27.28 MPa, compressive Young’s modulus of 10.87 ± 2.46 GPa and compressive strain of 3.75 ± 1.11%. The Vickers hardness value in the TiC region (545.4 ± 13.9 HV) is significant higher than that in the Ti alloy region (435.9 ± 12.9 HV). An overall Rockwell hardness of 47 HRA was measured.