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As a semimetal with a zero band gap and single-atom-scale thickness, single layer graphene (SLG) has excellent electron conductivity on its basal plane. If the band gap could be opened and regulated controllably, SLG would behave as a semiconductor. That means electronic elements or even electronic circuits with single-atom thickness could be expected to be printed on a wafer-scale SLG substrate, which would bring about a revolution in Moore's law of integrated circuits, not by decreasing the feature size of line width, but by piling up the atomic-scale-thickness of an SLG circuit board layer by layer. Employing scanning electrochemical microscopy (SECM), we have demonstrated that the electrochemically induced brominating addition reaction can open and regulate the band gap of SLG by forming SLG bromide (SLGBr). The SLG/SLGBr/SLG Schottky junction shows excellent performance in current rectification, and the rectification potential region can be regulated by tuning the degree of bromination of SLG. This work provides a feasible and effective way to regulate the band gap of SLG, which would open new applications for SLG in micro–nano electronics and ultra-large-scale integrated circuits (ULSI).

The structural and mechanical properties of low-dimensional nanostructured metals have been attracting tremendous interest in the fast-growing fields of nanosciences and nanotechnologies. However, it still remains a challenge today to develop strong yet ductile low-dimensional metals that can support the further development of nanodevices. Here, through the polymer-assisted assembly of gold nanocrystals, we successfully fabricated the freestanding, ultrathin gold nanomaterial. Unlike conventional bulk gold or other low-dimensional gold nanostructures (i.e., nanowires and nanosheets), these gold nanosheets are composed of highly distorted gold nanocrystals that are 3-5 nm in size, which are joined together through nanosized amorphous carbon interphases. As a result, the gold nanosheets exhibit superb strength (up to 1.2 GPa), excellent ductility (50%), and superior fracture toughness (100 J/m

Understanding the structure and dynamic process of water at the solid–liquid interface is an extremely important topic in surface science, energy science and catalysis1–3. As model catalysts, atomically flat single-crystal electrodes exhibit well-defined surface and electric field properties, and therefore may be used to elucidate the relationship between structure and electrocatalytic activity at the atomic level4,5. Hence, studying interfacial water behaviour on single-crystal surfaces provides a framework for understanding electrocatalysis6,7. However, interfacial water is notoriously difficult to probe owing to interference from bulk water and the complexity of interfacial environments8. Here, we use electrochemical, in situ Raman spectroscopic and computational techniques to investigate the interfacial water on atomically flat Pd single-crystal surfaces. Direct spectral evidence reveals that interfacial water consists of hydrogen-bonded and hydrated Na+ ion water. At hydrogen evolution reaction (HER) potentials, dynamic changes in the structure of interfacial water were observed from a random distribution to an ordered structure due to bias potential and Na+ ion cooperation. Structurally ordered interfacial water facilitated high-efficiency electron transfer across the interface, resulting in higher HER rates. The electrolytes and electrode surface effects on interfacial water were also probed and found to affect water structure. Therefore, through local cation tuning strategies, we anticipate that these results may be generalized to enable ordered interfacial water to improve electrocatalytic reaction rates. Interfacial water consists of hydrogen-bonded water and Na·H2O, its structure changes at hydrogen evolution reaction (HER) potentials, and when structurally ordered it aids interfacial electron transfer, resulting in higher HER rates.

If hydrogen can be stored and carried safely at a high density, hydrogen-fuel cells offer effective solutions for vehicles. The stable chemisorption of atomic hydrogen on single layer graphene (SLG) seems a perfect solution in this regard, with a theoretical maximum storage capacity of 7.7 wt %. However, generating hydrogenated graphene from H2 requires extreme temperatures and pressures. Alternatively, hydrogen adatoms can easily be produced under mild conditions by the electroreduction of protons in solid/liquid systems. Graphene is electrochemically inert for this reaction, but H-chemisorption on SLG can be carried out under mild conditions via a novel Pt-electrocatalyzed "spillover-surface diffusion-chemisorption" mechanism, as we demonstrate using dynamic electrochemistry and isotopic Raman spectroscopy. The apparent surface diffusion coefficient (∼10-5 cm2 s-1), capacity (∼6.6 wt %, ∼85.7% surface coverage), and stability of hydrogen adatoms on SLG at room temperature and atmospheric pressure are significant, and they are perfectly suited for applications involving stored hydrogen atoms on graphene.

As a promising hydrogen-storage material, graphene is expected to have a theoretical capacity of 7.7 wt%, which means a carbon-hydrogen atomic ratio of 1:1. However, it hasn’t been demonstrated yet by experiment, and the aim of the U.S. Department of Energy is to achieve 5.5 wt% in 2025. We designed a spatially-confined electrochemical system and found the storage capacity of hydrogen adatoms on single layer graphene (SLG) is as high as 7.3 wt%, which indicates a carbon-hydrogen atomic ratio of 1:1 by considering the sp3 defects of SLG. First, SLG was deposited on a large-area polycrystalline platinum (Pt) foil by chemical vapor deposition (CVD); then, a micropipette with reference electrode, counter electrode and electrolyte solution inside was impacted on the SLG/Pt foil (the working electrode) to construct spatially-confined electrochemical system. The SLG-uncovered Pt atoms act as the catalytic sites to convert protons (H+) to hydrogen adatoms (Had), which then spill over and are chemically adsorbed on SLG through surface diffusion during the cathodic scan. Because the electrode processes are reversible, the Had amount can be measured by the anodic stripping charge. This is the first experimental evidence for the theoretically expected hydrogen-storage capacity on graphene at ambient environment, especially by using H+ rather than hydrogen gas (H2) as hydrogen source, which is of significance for the practical utilization of hydrogen energy.

Multi–principal element alloys (MPEAs) exhibit outstanding mechanical properties because the core effect of severe atomic lattice distortion is distinctly different from that of traditional alloys. However, at the mesoscopic scale the underlying physics for the abundant dislocation activities responsible for strength-ductility synergy has not been uncovered. While the Eshelby mean-field approaches become insufficient to tackle yielding and plasticity in severely distorted crystalline solids, here we develop a three-dimensional discrete dislocation dynamics simulation approach by taking into account the experimentally measured lattice strain field from a model FeCoCrNiMn MPEA to explore the heterogeneous strain-induced strengthening mechanisms. Our results reveal that the heterogeneous lattice strain causes unusual dislocation behaviors (i.e., multiple kinks/jogs and bidirectional cross slips), resulting in the strengthening mechanisms that underpin the strength-ductility synergy. The outcome of our research sheds important insights into the design of strong yet ductile distorted crystalline solids, such as high-entropy alloys and high-entropy ceramics.

Ir-Ni-Ta metallic glasses (MGs) exhibit an array of superior high-temperature properties, making them attractive for applications at high temperatures or in harsh environments. However, Ir-Ni-Ta bulk MGs are quite brittle and often fracture catastrophically even before plastic yielding, significantly undercutting their high-strength advantage. Here, we show that the Ir-Ni-Ta MGs are not intrinsically brittle, but rather malleable when the feature size is reduced to micro/nano-scales. All tested Ir-Ni-Ta MG micropillars with a diameter ranging from ~500 nm to ~5 µm display a large plastic strain above 25% (the maximum up to 35%), together with a yield strength up to 7 GPa, well exceeding the strength recorded in most metallic materials. The intrinsic shear stability of Ir-Ni-Ta MGs, as characterized by the normalized shear displacement during a shear event, is much larger than those malleable Zr- and Cu-based MGs. Our results suggest that Ir-Ni-Ta MGs are excellent candidates for micro/nanoscale structural applications used at high-temperature or extreme conditions.

Metallic glasses (MGs) have attracted considerable academic attention owing to their unique properties and great application prospects. Unlike other glassy materials, such as oxide glasses, MGs have limited glass forming-ability (GFA) that often leads to failure during new MG development. Although intensive studies have proposed various parameters and criteria enabling the evaluation of the GFA of MG samples, achieving accurate predictions of glass formation before the actual MG sample synthesis remains a great challenge and an open topic. In this study, we investigated the glass formation through the data-driven machine learning technique and trained a backpropagation neural network model based on a dataset assembled from thousands of ternary alloys. Applying the well-trained model, we accurately identified the MG and non-MG classes. More importantly, our model can effectively predict glass-formation likelihood of multicomponent alloys and locate the probable MG compositions without any prior experiment, thereby directing the MG design. From the model's predictions, we discovered several new MGs in the ribbon form. Glass-formation likelihood reveals the correlation with the thermodynamic and topological parameters, which provides insights into the GFA of MGs.

Conventional Laves phase is extremely brittle at room temperature. However, through a systematic study, we showed that the quinary Co-Cr-Fe-Ni-Nb Laves phase in a eutectic high entropy alloy (EHEA) can be plastically deformed at room temperature when its size is refined below 200 nm. Based on our current results, we propose a general micromechanical model that not only explains the suppression of cracks in the high entropy Laves phase but also enables the extraction of its fracture toughness even when the high entropy Laves phase deforms and cracks in a dual-phase microstructure.

Unusual secondary relaxations were revealed in metallic glasses (MGs) recently. In this paper, we explore the structural origins of secondary relaxations in La-based MGs alloyed with different species of elements. With the combination of synchrotron X-ray diffraction and ab initio molecular dynamics simulations, solute-atom-centered clusters with a string-like type of medium-range order are found in the MGs, the formation of which leaves dispersed low-electron-density regions. It is found the activation energy of fast secondary relaxation increases with the reduction of low-electron-density regions, while slow secondary relaxation relates to the distance of La in next nearest La-La atomic pairs and the size of the string-like solute-atom-centered clusters. The phenomena are interpreted within the framework of the generalized Maxell model and free volume model. Our results demonstrate fast secondary relaxation as the activation of a small concentration of liquid-like regions with extremely low viscosities preceding slow secondary relaxation, and provide evidence for the correlation of secondary relaxations with short- to medium-range electronic and atomic structure in MGs.

The compositional design of metallic glasses (MGs) is a long-standing issue in materials science and engineering. However, traditional experimental approaches based on empirical rules are time consuming with a low efficiency. In this work, we successfully developed a hybrid machine learning (ML) model to address this fundamental issue based on a database containing ~5000 different compositions of metallic glasses (either bulk or ribbon) reported since 1960s. Unlike the prior works relying on empirical parameters for featurization of data, we designed modeling guided data descriptors in line with the recent theoretical models on amorphization in chemically complex alloys for the development of the hybrid classification-regression ML algorithms. Our hybrid ML modeling was validated both numerically and experimentally. Most importantly, it enabled the discovery of MGs (either bulk or ribbon) through the ML-aided deep search of a multitude of quaternary to scenery alloy compositions. The computational framework herein established is expected to accelerate the design of MG compositions and expand their applications by probing the complex and multi-dimensional compositional space that has never been explored before.

Pyridinium has been shown to be a cocatalyst for the electrochemical reduction of CO2 on metal and semiconductor electrodes, but its exact role has been difficult to elucidate. In this work, we create cooperative cobalt-protoporphyrin (CoPP) and pyridine/pyridinium (py/pyH+) catalytic sites on metal-organic layers (MOLs) for an electrocatalytic CO2 reduction reaction (CO2RR). Constructed from [Hf6(μ3-O)4(μ3-OH)4(HCO2)6] secondary building units (SBUs) and terpyridine-based tricarboxylate ligands, the MOL was postsynthetically functionalized with CoPP via carboxylate exchange with formate capping groups. The CoPP group and the pyridinium (pyH+) moiety on the MOL coactivate CO2 by forming the [pyH+--O2C-CoPP] adduct, which enhances the CO2RR and suppresses hydrogen evolution to afford a high CO/H2 selectivity of 11.8. Cooperative stabilization of the [pyH+--O2C-CoPP] intermediate led to a catalytic current density of 1314 mA/mgCo for CO production at -0.86 VRHE, which corresponds to a turnover frequency of 0.4 s-1.

Ion current rectification (ICR) phenomena in conical nanopores have been extensively investigated since their early discovery. Several theoretical explanations were proposed to quantitatively descr...

Fe-based alloys are an important soft magnetic material that plays a pivotal role in a variety of energy-related industrial applications, such as electric transformers, motors and converters. However, the trade-off between magnetic softness and saturation magnetization (Bs) has been hindering the development of next-generation Fe-based soft magnetic materials. In this work, we demonstrate a facile route to obtain nanostructured Fe-based alloy out of a marginal glass former, which exhibits a core-shell like nanostructure and a synergetic increase of Bs, magnetic permeability (μe) and hardness upon thermal annealing, giving rise to a unique combination of Bs > 1.83 T, μe ∼25000 and ultrahigh hardness of ∼15 GPa. In terms of the combined magnetic/mechanical properties, the nanostructured Fe-based alloy outperforms the variety of Fe-based soft magnetic alloys hitherto reported. Furthermore, compared to the existing high performance soft magnetic Fe-based nanocrystalline alloys, the core-shell like nanostructure in our Fe-based nanocrystalline alloy displays an excellent thermal stability, which offers a large time window which would facilitate materials processing for future large-scale industrial production.

Ceramics are easy to break, and very few generic mechanisms are available for improving their mechanical properties, e.g., the 1975-discovered anti-fracture mechanism is strictly limited to zirconia and hafnia. Here we report a general mechanism for achieving high plasticity through liquefaction of ceramics. We further disclose the general material design strategies to achieve this difficult task through entropy-boosted amorphous ceramics (EBACs), enabling fracture-resistant properties that can withstand severe plastic deformation (e.g., over 95%, deformed to a thickness of a few nanometers) while maintaining high hardness and reduced modulus. The findings reported here open a new route to ductile ceramics and many applications., Comment: 16 pages,4 figures

High entropy alloys (HEAs) exhibit an unusual combination of high fracture strength and ductility. However, atomic mechanisms responsible for crack propagation in HEAs are still not clear, which limits further improving the damage tolerance. Here we investigate effect of crystal orientation on the crack-tip behaviors in single-crystal HEA CrMnFeCoNi using atomic simulations to explore fracture micromechanism. The formation of deformation twinning and activation of multislip systems are observed during the propagation crack with the $(001)\ensuremath{\langle}110\ensuremath{\rangle}$ orientation, consistent with the previous experiments. Under the $(\overline{1}10)\ensuremath{\langle}110\ensuremath{\rangle}$ orientation, the amorphous region takes place throughout the crack growth, and is difficult to occur in traditional metal materials. Dissimilarly, for the $(1\overline{1}\overline{1})\ensuremath{\langle}110\ensuremath{\rangle}$ orientation, the blunting and slip bands occur at the front of the crack tip by switching the slip mode from the planar to wavy slip, observed in recent transmission electron microscopy experiments. The chemical disorder leads to the obvious fluctuation of flow stress, but hardly affects the deformation mechanism at the crack tip. Compared to traditional metals and alloys, the high local stress concentration induced by coupling effect of severe lattice distortion and tension strain leads to the structure transformation from crystallization to amorphization at the crack tip in HEA. While the presented atomic simulations and the associated conclusions are based on CrMnFeCoNi HEA, it is believed that the current deformation mechanism at crack tip could also be applied to other face-centered-cubic HEA.

Through detailed experimental and theoretical analyses, here we uncover the mechanism of plasticity initiation in the Ni-P nano-grained metallic glass (NGMG) which contains nano-sized hard amorphous inclusions and soft amorphous inter-granular regions. In this dual nano-phase amorphous structure, plasticity is mainly initiated through the elongation and coalescence of the amorphous nano-grains, resulting in a shear band much wider than in its monolithic counterpart. Consequently, the NGMG turns out to be softer at the microscopic scale. At the fundamental level, our finding provides a universal mechanism which explains the unusual strength weakening observed in a variety of dual nano-phase amorphous systems.

We report density fluctuations spanning from nano-to micrometer scale in the three-dimensional (3D) space in metallic glasses (MGs) detected with synchrotron X-ray nano-computed tomography, which decouple with the chemical homogeneity. The MG quenched from fragile supercooled liquid exhibits a more heterogeneous microstructure with a gradient density fluctuation. Severe inhomogeneous deformation rejuvenates the microstructure of the MG with the creation of a large amount of low-density regions, which percolate into shear-band-like layers. Ramified 2.5-dimensional fractal low-density regions exist in all the MGs with the correlation length increasing with microstructural heterogeneity. The formation of the density fluctuations with fractal order in the MGs is discussed based on the percolation of low-density regions and shear transformation zones during the glass transition and deformation processes. Our results directly demonstrate the existence of fractal low-density entropic droplets in MGs affected by fragilities and thermomechanical histories, which could be significant for understanding and controlling the disordered structure of amorphous solids.

Laves phase and laves-phase based conventional composites usually show extreme brittleness at room temperature due to poor fracture toughness. However, in this work, we design a FeCoNiNb0.5 medium-entropy-alloy nanocomposite which possesses a high volume fraction (>50%) of a cubic laves phase but shows superb strength and excellent malleability at room temperature. This high mechanical performance results from the formation of an in-situ nano-scale lamellar structure that joins the hard cubic laves phase and soft medium entropy face-centered cubic (FCC) phase through a semi-coherent interface. When the size of the lamellar structures is tuned below a critical value, this nanocomposite exhibits strong and sustainable strain hardening, leading to a fracture strain over 20% and fracture strength over 3.5 GPa in conventional compression. The mechanism for the unusual strain hardening in the laves-phase rich nanocomposite is explored afterwards with micromechanical experiments and theoretical modeling, which unveils a size-controlled transition in the plasticity mechanism from dislocation slip to twinning in the nano-scale laves phase. Our current work demonstrates that, through mixing a set of carefully selected elements, one can obtain high performance dual-phase eutectic nanostructures which are promising for structural applications.

It is a longstanding notion that alloying different sized elements can cause lattice distortion and phase transition in chemically complex alloys. However, a quantitative understanding of it remains difficult for traditional alloys, and becomes even more challenging for equimolar multicomponent alloys, also known as “high entropy alloys”, which recently emerged as a promising structural/functional material and have been attracting tremendous research interest due to their unique properties. In this work, we carried out extensive first-principles calculations on a series of equimolar complex alloys with a chemically disordered crystalline structure, and characterized their atomic-scale lattice distortions in terms of the local residual strains. Albeit the confounding chemical/geometric complexities, we are able to show that the average attributes of such an atomic-scale distorted lattice, such as the lattice constant and the overall magnitude of the distortion induced residual strains, can be predicted very well by a simple physical model taking into account the efficient packing of different sized atoms interacting in an effective elastic medium. The findings of our current research unveils the details of locally distorted atomic packing in chemically disordered complex alloys, which sheds quantitative insights into the unusual strengthening mechanism as recently discovered in high entropy alloys.

Chemical short-range ordering (CSRO) or demixing in solid solution high entropy alloys (HEAs) is a fundamental issue yet to be fully understood. In this work, we first developed a generalized quasi-chemical solid solution model that enables quantitative computation of the local chemical ordering or demixing in solid solution HEAs. After that, we performed synchrotron diffraction experiments, extensive Reverse Monte Carlo (RMC) simulations, and first principles calculations on the CoCrFeNi model alloy to study the development of local chemical environments after long time thermal annealing. The outcome of the combined research demonstrates that the development of local chemical ordering or demixing in CoCrFeNi is not only affected by the heat of mixing between dislike atoms but also coupled with local lattice distortion.

It has been an enduring and heated debate whether the yield strength of metallic glasses (MGs) is size dependent or size independent. In this work, we first develop a micromechanical model by taking into account the stochasticity for shear band initiation in microcompression. Our modeling is subsequently verified through the extensive in-situ and ex-situ microcompression experiments. Through the efforts of combined experiments and modeling, we show a size-controlled stochastic transition from the size dependent to the size independent yield strength in the MG micropillars. Such a stochastic transition is featured with a strong fluctuation in the measured yield strengths when the micropillar size is near an intrinsic length scale which varies with the chemical composition of MGs. In contrast, such a size-controlled transition appear deterministic with little data scattering in tension. At the fundamental level, our results unfold a size dependent shear band initiation process in MGs, which may be applicable to other amorphous materials of technological importance.

Spherical nanoindentation was performed at room temperature to characterize the time-dependent plasticity behavior of the single-phase CoCrFeMnNi high-entropy alloy (HEA). It was observed that incipient plasticity occurred after a period of waiting time in the apparent elastic regime. Through the experimental data, an activation energy ∼0.74 eV and an activation volume ∼1.54b3 (b = Burgers vector) were extracted for the delayed plasticity. Our results indicate that heterogeneous dislocation nucleation governs the delayed plasticity in the single-phase CoCrFeMnNi, and also provide quantitative insights into viscoplastic behavior and creep mechanisms in HEAs.

Since the advent in 2004, high-entropy alloys (HEAs) have been attracting a great deal of research interest worldwide. Being deemed as a major paradigmatic shift, the design of HEAs without base elements poses challenges to the existing thermodynamic models and theories that were long established for traditional alloys, one of which is related to the thermodynamic mechanisms for the formation of random solid solution in a concentrated multicomponent alloy. In this article, we discuss the design of HEAs from the perspective of correlated mixing (nonideal mixing of atoms with interatomic correlations). In a quantitative manner, we can show that the formation of a random solid solution in HEAs depends not only on the number of constituent elements but also on the alloy’s melting/processing temperature and on various interatomic correlations. Through the correlated mixing rule, we further demonstrate a strategy to screen out equiatomic alloys with the thermodynamic characteristics close to those of random solid solutions from an expanded library of 20 candidate elements.

Eutectic and near-eutectic high entropy alloys (HEAs) have recently attracted a great deal of interest because of their promising properties, such as an excellent castability and unique combination of good ductility and high strength. However, in the absence of a phase diagram, it remains a non-trivial task to find a eutectic or near-eutectic composition for a HEA system, which usually demands a tremendous amount of efforts if a trial-and-error approach is followed. In this paper, we briefly review the thermodynamics that governs the eutectic solidification in regular binary and ternary alloys, and proceed to the discussion for the design of eutectic HEAs. Based on the data reported, we then propose an improved strategy which may enable an efficient search for the eutectic or near eutectic HEA compositions.

Compared with mechanical machining, ECM has several advantages, such as avoiding tool wear, none thermal or mechanical stress on machining surfaces, as well as high removal rate. Moreover, ECM is capable of making complex three-dimensional structures and is appropriate for flexible, fragile, or fissile materials even materials harder than the machining tool. Thus, ECM has been widely used for various industrial applications in the fields of aerospace, automobiles, electronics, etc. ECM methods can be classified usually as electrolytic machining based on anodic dissolution and electroforming based on cathodic deposition of metallic materials. Recently, high technology industry, such as ultralarge scale integration (ULSI) circuits, microelectromechanical systems (MEMS), miniaturized total analysis systems (μ-TAS) and precision optics, has developed more and more rapidly, where miniaturization and integration of functional components are becoming significant. Nowadays, the feature size of interconnectors in ULSI circuits has been down to 20 nanometers, predicted by Moore’s law. Confined etchant layer technique (CELT) was proposed in 1992 to fabricate three-dimensional micro- and nanostructures (3D-MNS) on different metals and semiconductors, which has been developed an effective machining method with independent intellectual property rights. Generally, there are three procedures in CELT: (1) generating the etchant on the surface of the tool electrode by electrochemical or photoelectrochemical reactions; (2) confining the etchant in a depleted layer with a thickness of micro- or nanometer scale; (3) etching process when the tool electrode is fed to the workpiece, which applicable for 1D milling, 2D polishing, and 3D microfabrication with an accuracy at micro or nanometer scale. External physical-field modulations have recently been introduced into CELT to improve its machining precision. In this review, the advances of CELT in principles, instruments and applications will be addressed as well as the prospects.

In this letter we explore the magnetization effect on mechanical properties of a ductile Fe83C1B11Si2P3 metallic glass (MG). We firstly demonstrate that magnetic anisotropy can be systematically created by plastic deformation using high-load Berkovich indentation, and then provide compelling evidence by subsequent spherical nanoindentation which reveals tunable magnetization-induced submicron elastic heterogeneity. A new mechanism of magnetomechanical interaction, different from the alteration of “flow defect”, is proposed for explaining the apparent softening in the region without plastic deformation. Our studies have significance for modification and controlling of the microstructure and mechanical properties of MGs with respect to magnetic effect.

High entropy alloys (HEAs) and compositionally complex alloys (CCAs) have recently attracted great research interest because of their remarkable mechanical and physical properties. Although many useful HEAs or CCAs were reported, the rules of phase design, if there are any, which could guide alloy screening are still an open issue. In this work, we made a critical appraisal of the existing design rules commonly used by the academic community with different machine learning (ML) algorithms. Based on the artificial neural network algorithm, we were able to derive and extract a sensitivity matrix from the ML modeling, which enabled the quantitative assessment of how to tune a design parameter for the formation of a certain phase, such as solid solution, intermetallic, or amorphous phase. Furthermore, we explored the use of an extended set of new design parameters, which had not been considered before, for phase design in HEAs or CCAs with the ML modeling. To verify our ML-guided design rule, we performed various experiments and designed a series of alloys out of the Fe-Cr-Ni-Zr-Cu system. The outcomes of our experiments agree reasonably well with our predictions, which suggests that the ML-based techniques could be a useful tool in the future design of HEAs or CCAs.

The rise of nanotechnology has been propelled by low dimensional metals. Albeit the long perceived importance, synthesis of freestanding metallic nanomembranes, or the so-called 2D metals, however has been restricted to simple metals with a very limited in-plane size (< 10��m). In this work, we developed a low-cost method to synthesize 2D metals through polymer surface buckling enabled exfoliation. The 2D metals so obtained could be as chemically complex as high entropy alloys while possessing in-plane dimensions at the scale of bulk metals (> 1 cm). With our approach, we successfully synthesized a variety of 2D metals, such as 2D high entropy alloy and 2D metallic glass, with controllable geometries and morphologies. Moreover, our approach can be readily extended to non-metals and composites, thereby opening a large window to the fabrication of a wide range of 2D materials of technologic importance which have never been reported before.

We developed a facile ultrasonic vibration route is developed to synthesize BMGs and metallic glass-glass composites., Design of bulk metallic glasses (BMGs) with excellent properties has been a long-sought goal in materials science and engineering. The grand challenge has been scaling up the size and improving the properties of metallic glasses of technological importance. In this work, we demonstrate a facile, flexible route to synthesize BMGs and metallic glass-glass composites out of metallic-glass ribbons. By fully activating atomic-scale stress relaxation within an ultrathin surface layer under ultrasonic vibrations, we accelerate the formation of atomic bonding between ribbons at a temperature far below the glass transition point. In principle, our approach overcomes the size and compositional limitations facing traditional methods, leading to the rapid bonding of metallic glasses of distinct physical properties without causing crystallization. The outcome of our current research opens up a window not only to synthesize BMGs of extended compositions, but also toward the discovery of multifunctional glass-glass composites, which have never been reported before.

Pyridinium has been shown to be a cocatalyst for the electrochemical reduction of CO

In this paper, we studied the high entropy alloy (HEA) of SnBiInZn as a low temperature solder with a melting point about 80 oC. The microstructure of the HEA solder is very complicated. There are three phases at least in the solder, including Bi-rich phase, Sn-rich phase and InBi phase. The wetting reaction between the solder and Cu substrate was conducted at 100 oC and 120 oC. The wetting angle ranges from 30 to 40 degrees, indicating that the solder has a good wetting ability even at such low soldering temperature. The scallop and finger shape intermetallic compounds were determined to be Cu6Sn5. The thickness measurement of the IMC layer shows that the interfacial reaction rate is very slow. The shear stress ranges from 19 MPa to 28 MPa, which indicates that the solder joint is strong enough for electronic packaging technology.

Owing to its unique functionalities, micro-origami has been attracting tremendous research interest recently as a novel method for micro- and nano-fabrication of 3D structures. Here, we develop a facile method to fabricate micro-origami through self-folding or -rolling of 2D metallic nanosheets (also termed as “2D metals” in the literature). Unlike in the previous works, the 2D metals used in this work are mass-produced via polymer surface buckling enabled exfoliation and have an in-plane size on the scale of 1 cm and thickness ranging from ~10 nm to ~100 nm, which enables a discovery of an intriguing geometric effect on the mechanism for the self-construction of the micro-origami that has never been reported before in the origami literature. More interestingly, we demonstrate a passive but rapid method to unfold and re-fold the micro-origami of 2D metals by surface tension. The outcome of our combined research, including experiments, modeling and simulations, indicates that the large sized 2D metals provide a unique way for the mass fabrication of 3D micro-origami structures with a great potential for novel applications.

In this study, we develop a non-equiatomic Co2CrNi1.5Al0.25Ti0.25 quinary medium-entropy alloy (MEA). The heterogeneous grain structure (HGS) (comprising residual deformed grains, micro-sized recrystallized grains and nano-sized recrystallized grains) and heterogeneous precipitation (HP) of the L12 phase corresponding to different kinds of grain structures are simultaneously introduced into the alloy by the well-designed thermomechanical processing. The alloy exhibits an ultra-high yield stress ( σ y ) of 1.73 GPa, ultimate tensile stress ( σ u ) of 1.89 GPa and remarkable total elongation ( e te ) up to 16.0% at 293 K, as well as ultra-high σ y up to 2.02 GPa, σ u up to 2.31 GPa and excellent e te up to 21.2% at 77 K. The synergy of multiple hardening mechanisms, mainly including back-stress hardening, precipitation hardening and pre-existed dislocation hardening contributes to the ultra-high σ y at 293 K and 77 K. The HGS promotes the continuously increased geometrically necessary dislocations (GNDs) density, which, combined with the nano-spaced stacking fault (SF) networks, leads to the outstanding three-stage work-hardening behaviors during tensile tests at 293 K and 77 K. The simultaneous introduction of HGS and HP into this newly-developed MEA without brittle intermetallic phase, is a new effective method in designing high-performance alloys applied at both ambient and cryogenic temperatures.

Recent experiments showed that elemental segregation occurs in some high entropy alloys (HEAs) although their X-ray diffraction patterns exhibit a nominal single-phase solid solution structure. Based on the 3-D atom probe tomography (APT) results obtained from the FeNiCoCrCu HEA, here we propose a simple thermodynamics model based on the notion that elemental segregation facilitates stabilizing the solid solution phase with a minimized Gibbs free energy. Our model enables distinguishing nominal single-phased solid-solution HEAs with and without elemental segregation. The predictions of our model are found in good agreement with the experimental data reported hitherto in the literature.

Bulk metallic glasses (BMGs) are well-known for their superb strength (1–4 GPa) (Ashby and Greer, 2006) [1] but poor/localized plasticity when deformed at low temperatures or high strain rates (Inoue and Takeuchi, 2011; Kumar et al., 2009) [ 2 , 3 ]. Therefore, processing of BMGs, such as forming and shaping for various important applications, is usually performed above their glass transition temperatures (Tg) – also known as “thermo-plastic” forming (Geer, 1995) – for which the selection of alloy composition and the protocol for thermal treatment is demanding in order to promote extensive homogeneous plastic flows while avoiding crystallization (Geer, 1995). In stark contrast, here we demonstrate that homogeneous super-plasticity can occur rapidly in different BMGs below their Tg when subjected to ultrasonic agitations. Through atomistic simulations and nanomechanical characterization, we provide the compelling evidence to show that this super-plasticity is attributed to dynamic heterogeneity and cyclic induced atomic-scale dilations in BMGs, which leads to significant rejuvenation and final collapse of the solid-like amorphous structure, thereby leading to an overall fluid-like behavior. Our finding uncovers that BMGs can undergo substantial plastic flows through unusual liquefaction near room temperature and, more importantly, it leads to the development of a facile and cost-effective “ultrasonic-plastic” forming method to process a wide range of BMGs at low temperatures.

Summary Scalable production of two-dimensional (2D) materials is pivotal to their widespread engineering applications. However, unlike for graphene, h-BN, and MoS2, we still lack a scalable production method for 2D metals, which are newcomers to the family of 2D materials but have shown great potential for various important applications. Here, we develop a low-cost, high-yield scalable production method for 2D metals through polymer surface buckling enabled exfoliation (PSBEE). Compared to the traditional synthesis methods for 2D metals, PSBEE is desirable in terms of its high yield (30%–100%), superior production rate (101–103 mg/h), and low energy consumption rate (107–109 J/g). Most important, PSBEE enables the fabrication of freestanding 2D metallic nanosheets with a thermodynamically stable or metastable atomic structure, a large in-plane size, and unrestricted chemical makeup (from elemental metals to chemically complex alloys), which is incredibly rare in the field of 2D materials.

SnBiInZn-based high-entropy alloy (HEA) was studied as a low reflow temperature solder with melting point around 80 °C. The wetting angle is about 52° after reflow at 100 °C for 10 min. The intermetallic compound (IMC) growth kinetics was measured to be ripening-control with a low activation energy about 18.0 kJ/mol; however, the interfacial reaction rate is very slow, leading to the formation of a very thin IMC layer. The low melting point HEA solder has potential applications in advanced electronic packaging technology, especially for biomedical devices.

Wetting reactions of the medium entropy alloy of SnBiIn and SnBiInAg on Cu substrate have been investigated. The melting points of both SnBiIn and SnBiInAg are about 80 °C. The reactions were performed at 120 °C, 140 °C, and 160 °C. The kinetics of interfacial intermetallic compound (IMC) growth of Cu6Sn5 was studied to be ripening-controlled with activation energy about 11.1 kJ/mol for SnBiIn and 10.4 kJ/mol for SnBiInAg. However, the addition of Ag has effectively reduced the IMC growth by 20–30%. We propose that it is because Ag has reduced the pre-factor of diffusivity by increasing the entropy of the alloy.

Although metallic glasses (MGs) with unique disordered atomic structure have increasingly attracted great research interest as one of the most innovative heterogeneous catalysts in water remediation, few works focused on the synergistic role of different elemental constituents to well understand their superb catalytic performance. Herein, Co atoms were selected to partially substitute for the Fe elements in Fe-based MGs to study the corresponding synergistic catalytic function in dye degradation. Experimental results demonstrated that the Fe36Co36Si4.8B19.2Nb4 MG with a kinetic rate constant of k = 0.06 min−1 degrades rhodamine B (RhB) dye 20 times faster than the Fe73.5Si13.5B9Cu1Nb3 MGs with k = 0.003 min−1. Three types of dye including RhB, methylene blue (MB) and malachite green were investigated to draw attention to the broad, practical applications. Various chemical parameters, such as catalyst dosage, persulfate concentration, and dye concentration, were also studied. Quenching experiments indicated that the highly active hydroxyl (⋅OH) and sulfate (SO4⋅−) radicals are largely produced from persulfate by the activation of the Fe36Co36Si4.8B19.2Nb4 MG catalyst. This critical work uncovers a new paradigm to establish an effective approach for alloy design in widespread catalytic applications.