This report summarizes a recent study demonstrating simple and rapid synthesis of a new Al–Mg alloy system and ultimately synthesizing a metal matrix nanocomposite, which was achieved by processing stacked disks of the two dissimilar metals by conventional high-pressure torsion (HPT) processing. The synthesized Al–Mg alloy system exhibits exceptionally high hardness through rapid diffusion bonding and simultaneous nucleation of intermetallic phases with increased numbers of HPT turns through 20, and improved plasticity was demonstrated by increasing strain rate sensitivity in the alloy system after post-deformation annealing. An additional experiment demonstrated that the alternate stacking of high numbers of dissimilar metal disks may produce a faster metal mixture during HPT. Metal combinations of Al–Cu, Al–Fe, and Al–Ti were processed by the same HPT procedure from separate pure metals to examine the feasibility of the processing technique. The microstructural analysis confirmed the capability of HPT for the formation of heterostructures across the disk diameters in these processed alloy systems. The HPT processing demonstrates a considerable potential for the joining and bonding of dissimilar metals at room temperature and the expeditious fabrication of a wide range of new metal systems.

The crack initiation and early growth behaviors of a TC4 titanium alloy under high cycle fatigue and very high cycle fatigue were experimentally investigated. The results show that it exhibits the duplex S–N curve characteristics associated with surface and interior failures at a stress ratio of 0.1, while it represents the similar S–N curve characteristics only related to surface failure at a stress ratio of −1. The interior failure is accompanied with the occurrence of facets, granular bright facets (GBFs), and fisheye. Slip-like patterns are observable on the facets easily formed under positive stress ratio. The interior failure process is characterized as (i) occurrence of slip lines on partial α grains under cyclic loading, (ii) initiation and growth of microcracks within some α grains, (iii) coalescence of microcracks and formation of GBF, (iv) stable long crack growth within fisheye, (v) unstable crack growth outside fisheye, and (vi) final momentary fracture.

Li[Lix/3Mn2x/3M1−x]O2 (M = Ni, Mn, Co) (HE-NMC) materials, which can be expressed as a combination of trigonal LiTMO2 (TM = transition metal) and monoclinic Li2MnO3 phases, are of great interest as high capacity cathodes for lithium-ion batteries. However, structural stability prevents their commercial adoption. To address this, Si doping was applied, resulting in improved stability. Raman and differential capacity analyses suggest that silicon doping improves the structural stability during electrochemical cycling. Furthermore, the doped material exhibits a 10% higher capacity relative to the control. The superior capacity likely results from the increased lattice parameters as determined by X-ray diffraction (XRD) and the lower resistance during the first cycle found by impedance and direct current resistance (DCR) measurements. Density functional theory (DFT) predictions suggest that the observed lattice expansion is an indication of increased oxygen vacancy concentration and may be due to the Si doping.

Ni2P/ZnS and Ni2P/CdS core/shell composites were synthesized using a simple two-step route at a low temperature. We used X-ray powder diffraction, scanning electron microscopy, energy dispersive spectroscopy, and so on to characterize their composition, structure, and morphology. The characterized results show that Ni2P/ZnS and Ni2P/CdS core/shell composites consist of Ni2P microsphere core and ZnS (or CdS) nanostructure shell, and CdS nanorods and ZnS nanoparticles are deposited on the surface of Ni2P microspheres, respectively. Then choosing methylene blue (MB) as a typical organic dye, the photocatalytic degradation activities of Ni2P/ZnS and Ni2P/CdS are investigated, which exhibit a good photocatalytic activity. When the concentration of MB solution is 1 × 10−5 mol/L and the mass of the added photocatalyst is 0.05 g, it is found that two composites have enhanced photocatalytic degradation ratios (89 and 78%) compared to that of Ni2P microsphere (65%), which might be due to the effective separation of photogenerated electron-hole pairs.

6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) and pentacene-based high-voltage organic thin film transistors (HVOTFTs) have been fabricated on solid and flexible substrates via a low-temperature (<100 °C) solution-processed and vacuum-deposited fabrication method. A high-k dielectric Bi1.5Zn1Nb1.5O7 and an organic dielectric parylene-C have been incorporated into the transistor design. The reliability of the HVOTFTs was analyzed under flexure, where a nonsaturating I–V characteristic behavior was observed. Here, the HVOTFT exhibited a mobility μ of 0.018 cm2/(V s) and a large breakdown voltage of |VDS| > 120 V and >550 V for TIPS-pentacene and pentacene devices, respectively. The large breakdown voltages are attributed to an organic semiconductor channel region which is partially gated, allowing for a large potential drop. Thiolphenol-based SAMs were used to help improve charge injection. Electrical measurements were also performed with samples designed with a top metal field plate to improve control of the charge carrier within the channel.

PMMA/β-TCP composites were evaluated to be suitable for laser sintering earlier, but the possible after effects are not known yet. Effects of sintering on the biological nature and the influences of critical compositions and process parameters have not been investigated so far. The current research attempts this, first identifying experimentally the most suitable laser process conditions for the specific grades of PMMA and β-TCP and then subjecting single layer sintered samples to FTIR analysis and in vitro studies involving MTT and ALP assays, alizarin red S tests, and real-time PCR analyses. While the laser interactions are not detrimental, the biological responses are generally positive proving the selective laser sintering of PMMA/β-TCP composites to be a potential approach for specific medical applications.

Microstructural patterns resulting from self-organization are responsible for phase transitions and property changes in many materials maintained far from the thermodynamic equilibrium. Understanding the origin and the selection of possible spatiotemporal patterns for dissipative systems, i.e., systems for which the energy is not conserved, is a major theme of research opening doors to many technological applications ranging from plasmonics to metamaterials. Almost forty years after Turing’s seminal paper on patterning, progress on modeling instabilities leading to pattern formation has been achieved. The first part of this work demonstrates that main field approaches succeeded in capturing the underlying physics responsible for the formation of radiation-induced spatiotemporal patterns experimentally observed. The second part of the text highlights the interest of the phase field method, a self-consistent mean field approach, to discuss the evolution of these patterns in a universal picture neglecting specific aspects of radiation-induced dynamics.

A thorough investigation of nanoindentation response of fiber/matrix composites by using a Berkovich indenter and its equivalent conical counterpart was carried out. Three-dimensional finite element models were developed to study how fiber orientations and the axial distance between the fiber and nanoindenter affect the nanoindentation response of fiber/matrix composites. This demonstrates that the indenter geometry and its orientation have little effect on the nanoindentation response when the fiber is horizontally aligned to the surface. However, when the fiber is vertically embedded in the matrix, the apparent modulus measured by using the Berkovich indenter (depending on the indenter orientation) can be significantly different from its conical counterpart. The results demonstrate that when the ratio of fiber-to-indenter distance over fiber diameter is relatively small, nanoindentation response strongly depends on fiber orientation and distance between fiber and indenter as well as indenter geometry.

In this work, a N-doped CsTi2NbO7@g-C3N4 (NTCN) heterojunction nanocomposite was synthesized by a simple one-step calcination method. The as-prepared samples were characterized by means of X-ray diffraction patterns, scanning electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, and Fourier transformed infrared spectroscopy. The results showed that g-C3N4 was formed both on the surface and within the interlayers of CsTi2NbO7, in which CsTi2NbO7 was in situ doped by nitrogen atoms to form N–CsTi2NbO7. The NTCN composite displayed higher electrocatalytic activity toward the detection of nitrite than pure CsTi2NbO7 and g-C3N4. The main reasons could be attributed to the synergistic effects of morphology engineering, N-doping, and layered heterojunction. The NTCN-based electrochemical sensor expressed a good linear relationship range from 0.0999 to 3.15 mmol/L with a detection limit of 2.63 × 10−5 mol/L. The good recovery, stability, and reproducibility of this biosensor showed the potential application in environmental monitoring.

Recently, highly active, easy-to-make, and efficient bifunctional electrocatalysts have attracted tremendous attention because of their potential applications in clean energy. Herein, we report a simple, one-step approach for fabricating three-dimensional (3D) Ni–P nanorod arrays by direct phosphorization of commercial nickel foam (Ni foam) with different times. When used as a 3D electrode for oxygen evolution reaction, the obtained Ni–P nanorods with two hours of phosphatization treatment display high activity with an overpotential of 270 mV required to generate a current density of 30 mA/cm2 and excellent stability in 1.0 M KOH. Additionally, the Ni–P nanorod arrays are also highly active for electrocatalyzing the hydrogen evolution reaction in the alkaline media. As a result, the bifunctional Ni–P catalysts enabled a highly performed overall water splitting, in which a low applied external potential of 1.6 V led to a stabilized catalytic current density of 10 mA/cm2 over 12 h.

We report the synthesis and photovoltaic characterization of four novel polymers based on poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7) incorporating various numbers of photocrosslinkable n-octyl chloride sidechains (PTB-Cl). These polymers showed similar optoelectronic properties to PTB7 and readily cross-linked in the form of thin films after deep-UV exposure. Photolithography with micrometer-scale patterning is demonstrated. PTB-Cls exhibit similar PV performances to PTB7 and lightly cross-linked PTB-Cls showed stable high photoconversion efficiencies after prolonged thermal treatment. However, it is found that a high-degree cross-linking is needed to prevent the formation of PCBM crystallites at high annealing temperatures even though the PV performance is stabilized with a much lower degree of cross-linking. This implies that the complete prevention of PCBM crystallite formation is not necessary to affect the stabilization of PV devices against excessive heat.

Mesoscale heterogeneous material systems are efficient and adaptive to real world environments, owing to the non-uniform stress fields that result from the convolution of component geometries, loading conditions, and environmental changes. With the advent of multi-material additive manufacturing, the production of heterogeneous material systems with a pre-defined mesoscale material distribution becomes feasible. This unlocks the design freedom at a characteristic length scale between the macroscale geometry and microstructures, but also calls for a new design framework to optimize the mesoscale material distribution in multi-material additive manufacturing. Here, we propose and demonstrate such a design framework by incorporating digital image correlation-based deformation mapping with 3D finite element modeling-based computational optimization. The constitutive behavior of each constituent material or their mixtures is calibrated by matching the local deformation data. The optimal mesoscale material distribution can then be determined using global optimization algorithms and validated experimentally.

We present classical potential molecular dynamics simulations of nanoporous gold (np-Au) impacted by a spherical indenter. The atomic structure was generated using a phase field model as a template. In agreement with previous experiments, we observe densification in the region under the indenter. The hardness values obtained from our simulations exhibit a transition from an initially perfect-plastic plateau to hardening behavior in the later stages of indentation. This transition occurs when the relative density beneath the indenter exceeds ∼0.9. Hardness values obtained from the nanoindentation simulations reach 0.6 GPa, due to the densification of the material under the indenter. Elevated dislocation densities are observed in the densified region. The mechanism of pore collapse in the densified layer under the indenter is seen to switch from uniaxial to triaxial, consistent with a change in deformation mechanism from one based on shearing of individual ligaments in np-Au to one involving dislocation-mediated plasticity around voids in a Au single crystal undergoing uniaxial compression.

Classical alloy design strategies often aim to benefit from metastability. Examples are numerous: metastable transformation- and twinning-induced plasticity steels, cobalt or titanium based alloys, age hardenable aluminum alloys, and severe plastic deformed nanostructured copper. In each of these cases, superior engineering property combinations are achieved by exploring limits of stability. For the case of high-entropy alloys (HEAs), on the other hand, majority of present research efforts focus on exploring compositions that would yield stable single-phase structures. HEA metastability and its effects on microstructure and property development constitute only a relatively small fraction of ongoing work. To help motivate and guide a corresponding shift in HEA research efforts, here in this paper, we provide an overview of the research activities on metastability in HEAs. To this end, we categorize the past research on the topic into two groups based on their focus, namely, compositional and structural stability, and discuss the most relevant and exciting findings.

In this study, we report on the mechanical cleavage of conductive metal-based aluminum diboride (AlB2) flakes. The cleavage resulted in a highly single crystalline 2D material and had an atomically flat and smooth surface as shown by atomic force microscopy (AFM) and secondary ion mass spectrometry. Nanoindentation and AFM imaging of freshly cleaved specimens revealed sub-nm roughness and 30% improvement in the nanomechanical properties as compared to the as-grown AlB2 flakes. Once exposed to ambient air, the cleaved AlB2 flakes formed a superficial oxidation layer of less than 1 nm thickness within 5 min. Owing to the smooth surface, ultra-thin and stable oxide layer, and the excellent mechanical and electrical characteristics of AlB2, the cleaved flakes present an ideal 2D material for emerging applications in microfabrication such as the growth of epitaxial thin films. To prove the sub-nm surface characteristics of cleaved AlB2, a 10-nm thick TiO2 film was deposited on a freshly cleaved AlB2 using atomic layer deposition. Surface roughness and compositional consistency of this film were compared with a control sample deposited on Si. The TiO2 film on AlB2 showed a distinct thin interface layer with fewer defects than TiO2 on Si and superior flatness.

The soft magnetic alloy Fe–Co–2V, also known as Permendur-2V or Hiperco® 50A, was subjected to equal channel angular extrusion (ECAE) at 750–850 °C using two processing routes. Hiperco is a trade name of Carpenter Technology Corporation. ECAE, which is a severe plastic deformation process, refined the grain size to about 1.5–3 μm, compared to 25–70 μm for the conventional Hiperco® bar. The fine-grain microstructure is homogenous throughout the ECAE material, from center to edge, due to the simple-shear ECAE process. Fine-grained Hiperco® has previously only been obtainable in the sheet form. ECAE resulted in yield and tensile strengths of 650–700 MPa and 900–1400 MPa, respectively, representing a 2–3-fold strength increase compared to the conventional bar. The yield strength was demonstrated to fit well to the Hall–Petch relationship established using previous reports on the strength of conventional bar and sheet materials. High ductility, up to 18%, was obtained in the ECAE processed billets and attributed primarily to the partially disordered bcc crystal structure upon quenching from ECAE.

In the recent past, two-dimensional (2D) nanocrystalline (NC) transition metal dichalcogenides such as MoS2 received a great deal of attention due to their extraordinary physical properties. There has been a great interest to study the defects present in MoS2 NCs, which alter the material’s catalytic, electrical, and magnetic properties. This work reports paramagnetic point defects present in the hydrothermally grown 2H–MoS2 NCs. X-band electron spin resonance (ESR) spectroscopy has been used to identify the defects which contain unpaired electron spins in the as-prepared and Ar-annealed MoS2 NCs. At least seven ESR signals were detected originating from four inequivalent paramagnetic defect sites such as adsorbed oxygen species, sulfur vacancies, thio-, and oxo-Mo5+. Upon Ar-annealing, most of these defects did not survive, instead conduction ESR signal was observed. This work signifies the importance of employing ESR spectroscopy and broadens the knowledge in identifying the atomic defects in MoS2 NCs.

N-doped ordered mesoporous carbon (N-OMC) has been one of the most promising choices as the electrode for supercapacitors due to its large surface area and uniform mesoporous structure. However, there is still a big challenge to prepare N-OMC using a relatively simple method. Here, a straightforward preparation of N-OMC was reported in which the precursor zeoliticimidazolate framework was in situ grown in the SBA-15 template by a fast, solvent-free, and atom economic solid–solid grinding strategy. After pyrolysis and removing of the template, the N-OMC was obtained with ordered mesoporous structure, rich oxygen and nitrogen, and a large specific surface area of 1004 m2/g. As the electrode material for supercapacitors, N-OMC displayed an excellent specific capacitance of 228 F/g at 0.2 A/g and superb charge/discharge cycling stability, which is promising for high-performance energy storage. This solid–solid grinding strategy may offer a low-cost and scalable method to produce high-performance N-OMC for the electrode from the zeoliticimidazolate framework.

Carbon nanofibers are prepared via the electrospinning method accompanied by the phase-separation process using polyacrylonitrile as a carbon precursor. Effects of preoxidation and carbonation temperatures on electrochemical performance are studied and optimized in detail. The morphology and porous structure are characterized by scanning electron microscope, transmission electron microscope, and nitrogen adsorption and desorption measurements, respectively; the electrochemical performances are measured by the CHI660E workstation. The results show that the diameter of carbon nanofibers is about 150–200 nm with a uniform and smooth surface. The optimized preoxidation temperature is 280 °C with a carbonation temperature of 700 °C. The highest capacitance is up to 155 F/g, and the symmetric supercapacitor delivers a maximum energy density of 7.78 W h/kg with a power density of 400 W/kg and a maximum power density of 4000 W/kg with an energy density of 2.0 W h/kg. The symmetric supercapacitor also exhibits good cycle stability 91.0% of initial specific capacitance after 5000 cycles.

Strain path changes during clock rolling cause more serious interaction between adjacent grains, resulting in the occurrence of interactive regions (IRs) with random orientations. Furthermore, plenty of new grains with relatively random orientations are introduced by the subsequent annealing of these IRs. The morphology of the IR and the origin of random orientations were therefore investigated in this study, and the electron backscatter diffraction technique was used to characterize crystallographic orientations of nuclei and deformed matrices. A short-time annealing was imposed on a specimen to catch the transient nucleation behaviors. The results indicate that the orientations of nuclei are similar to their surrounding deformed matrices, especially the points with larger local-misorientation. Additionally, the shape of new grains depends on where it forms, and it is suggested that this fact mainly results from the great difference in stored energies between deformed matrices with {111} and {100} orientations.