Mechanical reliability is a critical issue in all forms of energy conversion, storage, and harvesting. In Li-ion batteries, mechanical degradation caused by the repetitive swelling and shrinking of electrodes upon lithiation cycles is now well recognized; however, the impact of mechanical stresses on Li transport and hence the capacity of batteries is less obvious and underestimated. In particular, the stress field within the heterogeneous electrodes is complex, making the characterization of the chemomechanical behaviors of electrodes a challenging task. We develop a finite element program that computes the coupled Li diffusion and stresses in three-dimensional composite electrodes. We employ the reconstructed models of both cathode and anode materials to investigate the mechanical interactions of the constituents and their influence on the accessible capacity. The state of charge in the percolated particles is highly inhomogeneous regulated by the stress field. An ample space of design is open for the optimization of the capacity and mechanical performance of electrodes by tuning the size, shape, and pattern of active particles, as well as the properties of the inactive matrix.

Among the different energy storage technologies under study, lithium–oxygen batteries are one of the most promising due to their great gravimetric energies and capacities 6–10 times greater than other technologies such as conventional lithium-ion cells. The current study provides a comprehensive understanding of how the anodic (e.g., dendrites) and cathodic designs (e.g., porosity of the carbon cathode and mass fraction of oxygen) affect the discharge characteristics of lithium–oxygen cells. When comparing all changes in dendrite surface, porosity and oxygen restriction, it is concluded that although the changes in porosity and oxygen decrease the performance of the cells, the dendrites led to the greatest decrease in performance of the battery when examining the capacity of the cell. This comprehensive understanding will aid in the design of a cyclable and commercially viable lithium–oxygen battery that could be used for a wide range of energy storage applications.

Boron cluster chemistry roared to life in the 20th century with seminal discoveries outlining the incredibly versatile chemistry of boron, producing a range of neutral and ionic boron compounds that paved the way for a robust suite of hybrid materials that incorporate these electronically delocalized inorganic clusters with the additional organic flexibility. Looking toward further materials research in the 21st century, these stable, inorganic polyhedral borane clusters discovered during previous century will provide a particularly fertile ground for exploration. These stable clusters have already seen significant exploration, but their utility has been obscured by classical synthetic routes using highly toxic neutral borane compounds. This incongruity is quite ironic given the current variety of medical explorations conducted with the essentially nontoxic dodecahedral borane dianion. This article will lay out some essential context and outline key synthetic studies that may dramatically simplify access to these unique compounds to a broader community of materials scientists and engineers.

The slip systems in ZrB2 flexural tested at 1000 °C and 1500 °C have been quantified. The dislocations in both samples were long and straight with a dislocation density of approximately 1013 m−2. The structure of the dislocations as well as the low density is in agreement with a ceramic that is hard and brittle and dislocation nucleation and motion is restricted. The low temperature slip systems were found to include c-prismatic slip— ${1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-\nulldelimiterspace} 3}\left[ {0001} \right]\left( {\bar 1010} \right)$ —and a-pyramidal slip— ${1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-\nulldelimiterspace} 3}\left[ {11\bar 20} \right]\left( {\bar 1101} \right)$ whereas the elevated temperature sample revealed a-basal slip— ${1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-\nulldelimiterspace} 3}\left[ {11\bar 20} \right]\left( {0001} \right)$ . Density functional theory Generalized Stacking Fault Energy curves for perfect slip were calculated and agreed well with geometric considerations for slip, including interplanar spacing and planar packing. Though basal slip has the lowest fault energy, the presence of the other dislocation types is suggestive that the activation barrier is not a hindrance for the temperatures studied and is likely activated to increase the number of plastic degrees of freedom.

This paper critically evaluates methods used to synthesize boride compounds with emphasis on diborides of the early transition metals. The earliest reports of the synthesis of boride ceramics used impure elemental powders to produce multiphase reaction products; phase-pure borides were only synthesized after processes were established to purify elemental boron. Carbothermal reduction of the corresponding transition metal oxides emerged as a viable production route and continues to be the primary method for the synthesis of commercial transition metal diboride powders. Even though reaction-based processes and chemical synthesis methods are mainly used for research studies, they are powerful tools for producing diborides because they provide the ability to tailor purity and particle size. The choice of synthesis method requires balancing factors that include cost, purity, and particle size with the performance needed in expected applications.

Recently, a new boron allotrope B52 with orthorhombic structure was theoretically predicted to be more stable than α-tetragonal boron B50. In experiments however, only tetragonal boron phases have been obtained so far. Here, we report for the first time on the preparation of orthorhombic boron phase of B52-type, space group Pnnn, a = 8.894 Å, b = 8.784 Å, c = 5.019 Å, by normal-pressure annealing of α-tetragonal boron, synthesized at high pressures by pyrolysis of decaborane, B10H14. We have investigated temperature-induced structure evolution and thermal desorption of boron samples, which allowed us to regard the structure of mother “α-tetragonal boron” as a boron-rich hydride with composition close to B51.5H7.7. In accordance with density-functional theory calculations, the most preferable sites of hydrogen placement in tetragonal unit cell are 8j and 4g; the tetragonal-to-orthorhombic transition takes place spontaneously upon complete dehydrogenation.

Near-infrared (NIR) absorption in solar-control LaB6 nanoparticles (NPs) is derived from the localized surface plasmon resonance (LSPR) at 1.3 eV, and accompanies an unclarified subpeak at 1.8 eV. As an origin of this subpeak, a disk-like particle shape of LaB6 NP has recently been proposed, besides the previously-proposed, milling-derived LaO phase. A series of heating experiments at 200–850 °C in air for LaB6 NPs pulverized with different media beads have been made, followed by x-ray diffraction and transmission electron microscopy observations, to clarify that LaB6 NPs oxidizes to amorphous phases B2O3 and La–B–O at 450–600 °C, and crystallize to LaB3O6 at 650–750 °C, without forming LaO or La2O3. Dielectric functions of LaO have been derived by first-principles calculations using sX-LDA, and Mie scattering calculations have been made for various sizes, shapes, and the ensembles, showing that LaO NPs, if existed, should exhibit an excessively-broadened absorption band with a blunt LSPR peak at 2.1 eV buried in several interband-transition absorptions at 1.2–4.0 eV. These analyses confirm that the observed 1.8 eV subpeak could not originate from LaO and support the nonspherical shape of NPs as the origin of the subpeak.

A continuous process was developed to synthesize submicron boron carbide particles from boric acid and sucrose-based precursor solutions using a home-made spray pyrolysis system. A control set of samples was also prepared for comparison purposes of the microstructure and morphology of the ones synthesized via the spray pyrolysis method. Moreover, nickel nitrate was used in a precursor solution to investigate its catalyst effects on the reaction kinetics of boron carbide formation. The boron carbide phase was observed in the particles synthesized with spray pyrolysis at a reactor temperature of 1550 °C. The average particle size was approximately 0.46 μm. No effect of nickel additions was observed as a catalyst in boron carbide formation. Computational fluid dynamics software was used to model and simulate the experimental system. Simulation results provided information about the residence time and the temperature distribution along the tube reactor.

The effect of boron on the room-temperature dynamic properties of Ti-6Al-4V alloy with and without boron addition in as-cast and β-forged conditions is studied by varying number of loading cycles, frequency of loading, and strain amplitude. Boron addition seems to lower the complex modulus and increases the damping of the base Ti-6Al-4V alloy. TiB precipitates in boron modified alloys play a key role in improving the damping through dislocation pinning (at all frequencies) and grain boundary pinning (at high frequencies). These effects are more prominent after β-forging wherein arrangement of TiB particles is found to be a deciding factor. Strain amplitude variation of damping shows trend reversal between 10 and 87 Hz frequencies; damping increases with strain amplitude at 10 Hz but reduces with strain amplitude at 87 Hz. A damping peak occurs near the 50 Hz frequency, and cycling through this range results in a significant improvement in damping (21% for as-cast and 93% for β-forged alloys).

The object of this paper is to propose a novel method to evaluate the maximum inclusion size in medium strength steel by ultrasonic fatigue testing. The inclusion sizes in the medium strength steel were evaluated by ultrasonic fatigue testing using the fatigue specimen with a large risk volume under water-cooling condition. To ensure fatigue specimens of medium strength steel fracture from the internal inclusion, heat treatment and oxynitrocarburization were conducted to increase the strength of the specimen and to protect the specimen from surface corrosion induced by cooling water. The results show that evaluation of the inclusion size by the proposed method is more accurate than traditional approaches, which are based on inclusion size characterization from arbitrary two dimensional cross sections. Additionally, as the method is based on fatigue testing in the ultrasonic frequency regime, it can be conducted in a reasonable amount of time.

A series of characterization tests were performed to elucidate the high-cycle fatigue (HCF) behavior in SAE 1050 steel subjected to tensile elastic pre-deformation at different strain rates. In the pre-strained stage, the deformation was maintained constant at 0.16%, which was close to the low yield point at strain rates ranging from 10−5 s−1 to 10−2 s−1. Although pre-deformation occurred entirely in the elastic regime, using different pre-straining rates resulted in the occurrence of heterogeneous microscopic strain at different sites and locations during subsequent fatigue tests. It was found that the effect of pre-straining rate on crack initiation and crack propagation was not monotonous and was influenced by the homogeneity of deformation within grain boundaries, the integrity of the boundary structure, and the fracture toughness. In addition, the rough set theory model was introduced for the attribute reduction of characteristic parameters and provided a scientific basis to establish the fatigue model. The model was able to effectively predict the lifetime of the process of HCF in pre-strained steel. Hence, the pre-straining rate should be an important boundary condition in further studies.

Hot-rolled Nb-stabilized ferritic stainless steel samples were produced with and without annealing. The samples were then cold rolled and isothermally annealed at 650–1000 °C for 10–14,400 s. The recrystallized volume fraction was quantified using the Johnson–Mehl–Avrami–Kolmogorov model and by measuring the microhardness of samples annealed for various duration. The texture evolution was analyzed using electron backscatter diffraction. The calculated Avrami exponents were between 0.8 and 1.2. The intensity of the {111}〈121〉 and {111}〈011〉 components of the γ-fiber increased and the deformation texture seen in the α-fiber decreased with increasing annealing time. The intensity of the rotated-cube component decreased with increasing annealing time. The intensity distributions of the early nucleation and full recrystallization textures were noticeably different. The {554}〈225〉 texture component, which was associated with the largest grains, appeared during the late stages of recrystallization. The final annealing led to a grain refinement with a final average grain diameter of 8 µm.

A new technology for preparing and forming ceramic particle-reinforced metal matrix composites, powder thixoforming, has been proposed. The effect of the SiCp volume fraction on the microstructure and tensile properties of thixoforged SiCp/2024 Al-based composites was studied. The results indicated that the volume fraction affected the effective liquid fraction, primary particle size and shape, and microstructure compactness. A composite with 10 vol% SiCp had the best comprehensive tensile properties, an ultimate tensile strength of 388 MPa, a yield strength of 295 MPa, and an elongation of 3.8%, representing increases of 29.3 and 33.5%, and a decrease of 63.5%, respectively, compared with the values for the thixoforged 2024 Al matrix alloy. During tensile testing, cracks were initiated in the secondary solidified structures, the debonded SiC/Al interface, and the cracked SiCp. For composites containing over 10 vol% SiCp, agglomerated SiCp acted as additional zones of crack initiation.

The high-temperature flow behavior and flow stress sensitivity of BT25y alloy were investigated. Results show that hot deformation is accompanied by the dynamic competition between work hardening and flow softening. The strain rate sensitivity exponent m tends to decrease with the strain rate after a first rise, and reaches the maximum at strain rate of 0.1 s−1. There is a large temperature range exhibiting m values above 0.2 at strain rates of 0.01–0.1 s−1. The temperature sensitivity exponent s shows an overall dropping trend with elevated temperature. The strain hardening exponent n first decreases and then increases with the strain at strain rate of 0.01 s−1. Large positive n values lie in areas with high strain rate, and small negative n values are located in areas with lower temperature and small strain rate. Secondary lamellar α appears near the phase transition temperature. The microstructure presents elongated characteristics at high strain rate.

Recently, cold metal transfer (CMT) process has been successfully applied to weld dissimilar metals. In this paper, two different aluminum alloy AA6061-T6 and pure copper T2 lapped joints were performed by CMT with AA4043 aluminum alloy wire as the filler metal. Results indicated that sound lapped joints between aluminum alloy AA6061-T6 and pure copper T2 could be performed by CMT technology. The joint was composed of Al–Al welding joint and Al–Cu brazing joint. The Al–Al welding joint was formed between the Al weld metal and the Al base metal, and the weld metal in Al–Al welding joint was composed of α-Al solid solution, α-Al, and CuAl eutectic phase. Al–Cu brazing joint was formed between the Al weld metal and the local molten Cu base metal, and composed of three copper-weld metal interfaces with a large amount of intermetallic compounds (IMCs), i.e., CuAl2, CuAl. The optimum strength of two joints could reach up to 1.23 kN and 1.56 kN, respectively, which was mainly due to the differences of the size of Cu/Al IMCs and stress condition. In addition, the distribution of microhardness and fracture surface of two joints were observed and analyzed in detail.

Electrocatalysts for oxygen evolution reaction (OER) has been at the center of attention for water splitting reactions. In this article we have presented a methodology to significantly improve the OER catalytic efficiency of electrodeposited Ni3Se2 films. Specifically, the pristine Ni3Se2 on surface nanostructuring induced through electrochemical etching shows a remarkable decrease of overpotential (@10 mA cm−2) to 190 mV, making it as one of the best OER elecrocatalyst known till date. Through detailed structural and morphological characterization of the catalyst film, we have learnt that such enhancement is possibly caused by the increased surface roughness factor and electrochemically active surface area of the etched film. The morphology of the film also changed from smooth to rough on etching further supporting the enhanced catalytic activity. Detailed characterization also revealed that the composition of the film was unaltered on etching. Ni3Se2 film was also active for HER in alkaline medium making this a bifunctional catalyst capable of full water splitting in alkaline electrolyte with a cell voltage of 1.65 V.

Herein, we present a method for decorating multi-walled carbon nanotubes (MWCNTs) with gold nanoparticles (AuNPs) using ethylenediamine (en) as a linker between MWCNTs and AuNPs. The amine group in en is as growth points for synthesis of AuNPs through electrostatic attraction between the amine groups and ${\rm{AuCl}}_4^ -$ anion while sodium citrate act as reducing agent. The influence of HAuCl4 concentration on the size and distribution of AuNPs in the structure of the Au-decorated nanotubes were investigated. Morphology of the decorated nanotubes was characterized by field emission scanning electron microscopy and transmission electron microscopy while the elemental composition of the decorated tubes and crystallography were investigated by energy dispersive x-ray, x-ray diffraction, Raman spectroscopy, and Fourier transform infrared techniques. Cyclic voltammetric and electrochemical impedance spectroscopic analysis revealed that the Au-decorated nanotubes have increased the electro-active surface area and conductivity of electrochemical substrate.

A diamond film was deposited on YT14 cemented carbide cutting tools with a chemical vapor deposition, the surface-interface morphologies, compositions of chemical elements, phases, atomic bonding energies, and structures of the films were analyzed with a scanning electron microscopy, energy dispersive spectrometer, x-ray diffraction, x-ray photoelectron spectroscopy, and Raman, respectively, and the mechanical properties of the film were characterized with a nanoindentation and scratch test, respectively. The results show that the surface of diamond film is continuous and dense, the surface roughness of the film is 79.2 nm, and the average grain size is 478.2 nm. The atomic binding energies of C1s are composed of sp 2 at the Raman shift of 1363.01 cm−1 and sp 3 at the Raman shift of 1556.26 cm−1. The hardness and equivalent elastic modulus of the film is 16.27397 GPa and 166.1791 GPa, respectively, and the binding strength of the film-substrate is 26.2 N, showing a high anti-scratch ability.