High-efficiency transformation of amorphous carbon into graphite nanoflakes for stable aluminum-ion battery cathodes.

Highly efficient strategies for the transformation of amorphous carbon into graphite with high graphitization and crystallinity features have been significantly pursued in recent years; however, critical issues, including high processing temperature, insufficient graphitization, introduction of catalyst impurities, complicated post-purification procedures, and generation of greenhouse gas, still remain in traditional approaches. For significantly addressing these challenges, herein, a highly efficient catalyst-free, eco-friendly and low-temperature electrochemical transformation strategy was proposed for the preparation of highly graphitized porous graphite nanoflakes. Using inert SnO as an anode in CaCl-LiCl molten salts, the graphitization transformation of amorphous carbon materials could be realized at 700 °C, approaching the record in high-efficiency converting amorphous carbon to graphite; moreover, systematical analysis was performed to understand the electrochemical transformation of amorphous carbon into highly graphitized graphite nanoflakes.

3D Printing of Auxetic Metamaterials with Digitally Reprogrammable Shape.

Two-dimensional lattice structures with specific geometric features have been reported to have a negative Poisson's ratio, termed as auxetic metamaterials, that is, stretching-induced expansion in the transversal direction. In this paper, we designed a novel auxetic metamaterial; by utilizing the shape memory effect of the constituent materials, the in-plane moduli and Poisson's ratios can be continuously tailored. During deformation, the curved meshes ensure the rotation of the mesh joints to achieve auxetics.

Metal-organic framework derived hollow porous CuO-CuCoO dodecahedrons as a cathode catalyst for Li-O batteries.

Herein, hollow porous CuO-CuCoO dodecahedrons are synthesized by using a simple self-sacrificial metal-organic framework (MOF) template, which resulted in dodecahedron morphology with hierarchically porous architecture. When evaluated as a cathodic electrocatalyst in lithium-oxygen batteries, the CuO-CuCoO composite exhibits a significantly enhanced electrochemical performance, delivering an initial capacity of 6844 mA h g with a remarkably decreased discharge/charge overpotential to 1.15 V ( Li/Li) at a current density of 100 mA g and showing excellent cyclic stability up to 111 charge/discharge cycles under a cut-off capacity of 1000 mA h g at 400 mA g.

Grayscale digital light processing 3D printing for highly functionally graded materials.

Three-dimensional (3D) printing or additive manufacturing, as a revolutionary technology for future advanced manufacturing, usually prints parts with poor control of complex gradients for functional applications. We present a single-vat grayscale digital light processing (g-DLP) 3D printing method using grayscale light patterns and a two-stage curing ink to obtain functionally graded materials with the mechanical gradient up to three orders of magnitude and high resolution. To demonstrate the g-DLP, we show the direct fabrication of complex 2D/3D lattices with controlled buckling and deformation sequence, negative Poisson's ratio metamaterial, presurgical models with stiffness variations, composites for 4D printing, and anti-counterfeiting 3D printing.

TEM diffraction contrast images simulation of dislocations.

For end-on screw dislocations and inclined dislocations within thin transmission electron microscopy (TEM) foil, TEM diffraction contrast image is largely modified around piercing point due to free surface relaxation. Based on many-beam Schaeublin-Stadelmann equations, TEM diffraction contrast images simulation of inclined dislocations within thin pure Fe TEM foil are performed and the difference between isotropic and anisotropic dislocation models are studied. Image force are superposed onto bulk elastic field of dislocation in thin foil, the elastic distortions nearby the two emerging points of a straight inclined dislocation located in an elastically isotropic/anisotropic thin foil are expressed as semianalytical solution in Fourier space, and the semianalytical image stress solutions in Fourier space are implemented into CUFOUR for studying free surface relaxation effect on TEM diffraction contrast of dislocation.

Temperature Rise Associated with Adiabatic Shear Band: Causality Clarified.

One of the most important issues related to adiabatic shear failure is the correlation among temperature elevation, adiabatic shear band (ASB) formation and the loss of load capacity of the material. Our experimental results show direct evidence that ASB forms several microseconds after stress collapse and temperature rise reaches its maximum about 30  μs after ASB formation. This observation indicates that temperature rise cannot be the cause of ASB.

Step-freeze-drying method for carbon aerogels: a study of the effects on microstructure and mechanical property.

In this paper, a novel step-freeze-drying method was used to prepare carbon aerogels. The effects of step-freeze-drying on the density, linear shrinkage, specific surface area, pore size distribution, microstructure and compressive strength of carbon aerogels were investigated, and compared to traditional freeze-drying methods. It was found that the step-freeze-drying method reduced the density, linear shrinkage and pore size of carbon aerogels compared to traditional freeze-drying.

Effect of Hatch Spacing on Melt Pool and As-built Quality During Selective Laser Melting of Stainless Steel: Modeling and Experimental Approaches.

In this study, a combined simulation and experimental approach is utilized to investigate the influence of hatch spacing on the microstructure and as-built quality of 316L stainless steel (SS) samples fabricated by selective laser melting (SLM). A three-dimensional finite element model (FEM) is employed to investigate heat transfer and melt pool during the SLM of 316L SS. The phase transformation and variation of the thermo-physical properties of the materials are considered in this model.

Study of Size Effect on Microstructure and Mechanical Properties of AlSi10Mg Samples Made by Selective Laser Melting.

The macroscopic mechanical performance of additive manufactured structures is essential for the design and application of multiscale microlattice structure. Performance is affected by microstructure and geometrical imperfection, which are strongly influenced by the size of the struts in selective laser melting (SLM) lattice structures. In this paper, the effect of size on microstructure, geometrical imperfection, and mechanical properties was systemically studied by conducting experimental tests.

Ultrathin Flexible Carbon Fiber Reinforced Hierarchical Metastructure for Broadband Microwave Absorption with Nano Lossy Composite and Multiscale Optimization.

The implementation of thin structure for broadband microwave absorption is challenging due to the requirement of impedance match across several frequency bands and poor mechanical properties. Herein, we demonstrate a carbon fiber (CF) reinforced flexible thin hierarchical metastructure (HM) composed of lossy materials including carbonyl iron (CI), multiwall carbon nanotube (MWCNT), and silicone rubber (SR) with thickness of 5 mm and optimal concentration selected from 12 formulas. Optimization for the periodical unit size is applied, and impacts of structural sizes on absorption performance are also investigated.

Ultrabroadband Three-Dimensional Printed Radial Perfectly Symmetric Gradient Honeycomb All-Dielectric Dual-Directional Lightweight Planar Luneburg Lens.

An ultrabroadband all-dielectric planar Luneburg lens has been designed and fabricated in this study, which is in the form of a radial gradient lightweight honeycomb column. Because of the novel design of a radial symmetric honeycomb-like microstructure in the subwavelength dimension and the radial gradient configuration according to the refractive index distribution of Luneburg lens, the present lens can focus incident plane waves on the opposite side with high convergence, and its operating frequency range is rather broadband, spanning from 6 to 16 GHz. Besides, the all-dielectric honeycomb-like lens is lightweight with a mass density of 0.

Deformation mechanism of innovative 3D chiral metamaterials.

Rational design of artificial microstructured metamaterials with advanced mechanical and physical properties that are not accessible in nature materials is very important. Making use of node rotation and ligament bending deformation features of chiral materials, two types of innovative 3D chiral metamaterials are proposed, namely chiral- chiral- antichiral and chiral- antichiral- antichiral metamaterials. In-situ compression and uniaxial tensile tests are performed for studying the mechanical properties and deformation mechanisms of these two types of 3D chiral metamaterials.

Research on Mechanisms and Controlling Methods of Macro Defects in TC4 Alloy Fabricated by Wire Additive Manufacturing.

Wire feeding additive manufacturing (WFAM) has broad application prospects because of its advantages of low cost and high efficiency. However, with the mode of lateral wire feeding, including wire and laser additive manufacturing, gas tungsten arc additive manufacturing etc., it is easy to generate macro defects on the surface of the components because of the anisotropy of melted wire, which limits the promotion and application of WFAM.

A new technique for nanoparticle transport and its application in a novel nano-sieve.

A new technique is proposed to transport and further classify nanoparticles of different sizes. A graphene sheet is used as the substrate; a nanoparticle is placed on the substrate and a sliding block is located below the substrate. As the sliding block moves under the graphene substrate, a driving force is yielded from the van der Waals interaction between the sliding block and the nanoparticle.

Soft mechanical metamaterials with unusual swelling behavior and tunable stress-strain curves.

Soft adaptable materials that change their shapes, volumes, and properties in response to changes under ambient conditions have important applications in tissue engineering, soft robotics, biosensing, and flexible displays. Upon water absorption, most existing soft materials, such as hydrogels, show a positive volume change, corresponding to a positive swelling. By contrast, the negative swelling represents a relatively unusual phenomenon that does not exist in most natural materials.

Hydrophilic/Hydrophobic Composite Shape-Shifting Structures.

Swelling-induced shape transformation has been widely investigated and applied to the design and fabrication of smart polymer devices, such as soft robotics, biomedical devices, and origami patterns. Previous shape-shifting designs using soft hydrogels have several limitations, including relatively small actuation force, slow responsive speed, and relatively complicated fabrication process. In this paper, we develop a novel hydrophilic/hydrophobic composite structure by using photopolymers.

Layered Halide Double Perovskites CsM(II)SbX (M = Sn, Ge) for Photovoltaic Applications.

Over the past few years, the development of lead-free and stable perovskite absorbers with excellent performance has attracted extensive attention. Much effort has been devoted to screening and synthesizing this type of solar cell absorbers. Here, we present a general design strategy for designing the layered halide double perovskites CsM(II)SbX (M = Sn, Ge) with desired photovoltaic-relevant properties by inserting [MX] octahedral layers, based on the principles of increased electronic dimensionality.

Revealing the role of thiocyanate anion in layered hybrid halide perovskite (CHNH)Pb(SCN)I.

The effect of the SCN ion on the structural, electronic, optical, and mechanical properties of the layered (MA)Pb(SCN)I (MA=CHNH) perovskite is investigated by using first-principles calculations. Our results suggest that the introduction of SCN ions at the apical positions gives rise to shorter Pb-S bond lengths, more distorted octahedra, and more hydrogen bonds, which have important effects on the electronic, optical, mechanical, and piezoelectric properties in (MA)Pb(SCN)I. Furthermore, a strong relativistic Rashba splitting is induced due to the breaking of the inversion symmetry, which helps to suppress the carrier recombination and enhance the carrier lifetime.

Constructing Repairable Meta-Structures of Ultra-Broad-Band Electromagnetic Absorption from Three-Dimensional Printed Patterned Shells.

Ultra-broad-band electromagnetic absorption materials and structures are increasingly attractive for their critical role in competing with the advanced broad-band electromagnetic detection systems. Mechanically soft and weak wax-based materials composites are known to be insufficient to serve in practical electromagnetic absorption applications. To break through such barriers, here we developed an innovative strategy to enable the wax-based composites to be robust and repairable meta-structures by employing a three-dimensional (3D) printed polymeric patterned shell.

Graphene-Based Sandwich Structures for Frequency Selectable Electromagnetic Shielding.

Due to substantial development of electronics and telecommunication techniques, materials with electromagnetic interference (EMI) shielding performance are significant in alleviating the interference impacts induced from a remarkable variety of devices. In the work, we propose novel sandwich structures for manipulating the EM wave transport, which holds unique EMI shielding features of frequency selectivity. By employing electrical and magnetic loss spacers, the resultant sandwich structures are endowed with tunable EMI shielding performance, showing substantial improvements in overall shielding effectiveness along with pronounced shielding peak shift.

Origami by frontal photopolymerization.

Origami structures are of great interest in microelectronics, soft actuators, mechanical metamaterials, and biomedical devices. Current methods of fabricating origami structures still have several limitations, such as complex material systems or tedious processing steps. We present a simple approach for creating three-dimensional (3D) origami structures by the frontal photopolymerization method, which can be easily implemented by using a commercial projector.

An elevated-temperature depth-sensing instrumented indentation apparatus for investigating thermo-mechanical behaviour of thermal barrier coatings.

In our study, an elevated-temperature depth-sensing instrumented indentation apparatus was designed and developed to investigate thermo-mechanical response of thermal barrier coatings (TBCs). A furnace was used to heat the test region up to 1600 °C and a heat protection design was proposed to protect electronic devices from high temperature environment. Load was applied by a precise loading motor and a piezoelectric actuator in high (0-440 N) and low (0-40 N) load ranges, respectively.

A Novel Ultrafast Rechargeable Multi-Ions Battery.

An ultrafast rechargeable multi-ions battery is presented, in which multi-ions can electrochemically intercalate into graphite layers, exhibiting a high reversible discharge capacity of ≈100 mAh g and a Coulombic efficiency of ≈99% over hundreds of cycles at a high current density. The results may open up a new paradigm for multi-ions-based electrochemical battery technologies and applications.