Effects of traveling magnetic field (TMF) on freckle formation of directionally solidified Pb–Sn alloys were investigated experimentally and numerically. The experimental results demonstrated that freckles could form without any magnetic field and with the upward TMF. In the former case, the formation location is the center. In the latter case, it diverted from the center to the surface with the increasing intensity of TMF. However, freckle could not form under the downward TMF. Numerical results indicated that the change of the formation location under upward TMF should be attributed to the different solid/liquid interface shape, and no formation under downward TMF should be attributed to the convection intensity driven by TMF. These magnetic fields are used to modulate melt flow, which is similar to the effects of the gravity. For eliminating freckle, a microgravity environment can be established under the suitable downward TMF.

Aluminum laminates of high and technical purity layers were produced by accumulative roll bonding (ARB) at room temperature. To study the thermal stability, the laminates after 2 to 9 ARB cycles were annealed between 100 and 400 °C for one hour. Changes of the microstructure were analyzed by electron backscatter diffraction. For low ARB cycle numbers (4 or below) and 300 °C annealing temperature, the deformed technical pure layers start to recrystallize while the high-purity coarse recrystallized layers experience intralayer grain growth. For higher ARB cycle numbers (6 and 8) and an annealing temperature of 300 °C or above, the ultra-fine grained layers of technical purity are consumed by the layer overlapping growth of high-purity grains producing a banded grain structure. For 9 ARB cycles and at an annealing temperature of 400 °C, a globular grain structure develops with grain sizes larger than twice the layer thickness. The effect of impurities on recrystallization and grain growth of ARB laminates is discussed with regard to tailoring its microstructure by heat treatment. For further analyses, the results are compared with Potts model simulations finding a rather good qualitative agreement with the experimental data albeit some simplified model assumptions.

In this research, Ce3+ and Tb3+ doped alkaline-earth silicate Sr2MgSi2O7 phosphors have been synthesized by solid-state reaction. The results show that the Sr2−x MgSi2O7:xCe3+ phosphors exhibit a violet–blue emission with excitation at 348 nm, whereas the Sr2−y MgSi2O7:yTb3+ phosphor show a green emission with excitation at 243 nm. In addition, the structure of Sr2MgSi2O7 host has been analyzed by Crystalmaker program. Staggered arrangements of [SiO4] and [MgO4] units in the Sr2MgSi2O7 system underlie possible chemical tuning and phase segregation, providing a potential candidate of tunable luminescence. A red shift of wave length is clarified by crystal field theory and Van Uitert expression. The FESEM image of Sr1.99MgSi2O7:0.01Ce3+ phosphors reveal that it has a proper particle size for application in WLEDs. With different Tb3+ doping concentration, the CIE chromaticity coordinates Sr2MgSi2O7:Tb3+ phosphors still remain a steady position. These results indicate that Sr2−x MgSi2O7:xCe3+, Sr2−y MgSi2O7:yTb3+ phosphors are promising phosphors for WLEDs.

The push–pull fatigue characteristics of the peak-aged Mg–0.2Zn–0.5Zr alloys with different addition levels of neodymium (Nd) have been investigated. The fatigue strength (σf) of the Mg–xNd–0.2Zn–0.5Zr (NZx0K) alloy increases proportionally with the increase of the Nd content (C Nd) as follows: σf (T6) ≈ (13.8–14.0) C Nd + 46 (for x between 0 and 3.0 wt%). The cyclic stress amplitude also increases but the plastic strain value decreases with the increase of the Nd content. The studied alloys exhibit the strain hardening followed by cyclic softening during fatigue test. During the low-cycle fatigue (LCF) test, the cracks originate from the cyclic deformation and cumulative damage. In high-cycle fatigue (HCF), the failure is due to the cyclic deformation and damage irreversibly caused by environment-assisted cyclic slip. The LCF lives of the alloys fitted well with the Coffin–Manson relation and Basquin laws, the three-parameter equation, and the energy-based concepts. The developed multi-scale fatigue (MSF) life models can be used to predict the LCF and HCF lives of the alloys. Among these models, the MSF life can well capture the influence of Nd addition on fatigue.

We report the development of hybrids consisting of supercapacitive graphene oxide (GO), reduced GO (rGO), electrochemically reduced GO (ErGO), multilayer graphene (MLG) decorated with pseudocapacitive nanostructured cobalt oxides (CoO, Co3O4) and nanoparticles (CoNP) via electrodeposition and hydrothermal synthesis facilitating chemically bridged (covalently and electrostatically anchored) interfaces with tunable properties. These hybrid samples showed heterogeneous transport behavior determining diffusion coefficient (4 × 10−8–6 × 10−6 m2/s) following CoO/MLG < Co3O4/MLG < Co3O4/rGOHT < CoO/ErGO, CoNP/MLG and delivering the maximum specific capacitance >550 F/g for Co3O4/ErGO and Co3O4/MLG. We found an ultrahigh sensitivity of 4.57 mA/(mM cm2) and excellent limit of glucose detection <50 nM following Co3O4/rGOHT < CoO/ErGO < CoNP/MLG < Co3O4/MLG. These findings are due to open pore network and topologically multiplexed conductive pathways provided by graphene nanoscaffolds to ensure rapid charge transfer and ion conduction. Density functional theory determined density of states in the vicinity of Fermi level in-turn providing contribution toward electroactivity due to orbital re-hybridization.

Carbon aerogels (CAs) are a unique class of high surface area materials derived by sol–gel chemistry. Their high mass-specific surface area and electrical conductivity, environmental compatibility, and chemical inertness make them very promising materials for many applications, such as energy storage, catalysis, sorbents, and desalination. Since the first CAs were made via pyrolysis of resorcinol–formaldehyde (RF)-based organic aerogels in the late 1980s, the field has really grown. Recently, in addition to RF-derived amorphous CAs, several other carbon allotropes have been realized in aerogel form: carbon nanotubes (CNTs), graphene, graphite, and diamond. Furthermore, the popularity of graphene aerogels has inspired research into aerogels made of a host of graphene analog materials (e.g., boron nitride, transition metal dichalcogenides, etc.), with potential for an even wider array of applications. Finally, the development of three-dimensional-printed aerogels provides the potential for CAs to have an even broader impact on energy-related technologies. Here, we will present recent work covering the novel synthesis of RF-derived, CNT, graphene, graphite, diamond, and graphene analog aerogels.

In this study, the influence of an externally applied elastic strain on the electrochemical activity of metal film catalysts during the oxygen reduction reaction (ORR) was examined. A novel three-layer specimen, composed of a 10 nm-thick Pt or Pd surface film on a 20 nm-thick Pd70Zr30 metallic glass film that was first deposited on a polymer substrate was used. The intermediate metallic glass layer is instrumental in allowing the top-layer catalytic film to be elastically deformed to a large elastic strain, (up to 2%), enabling a strain effect to be clearly observed. The results consistently show that an applied compressive strain improves the ORR catalytic activity of the Pd and Pt surface layer, while a tensile strain degrades it. These experimental findings are consistent with the prediction of the d-band model, and provide an opportunity to improve the catalytic response during ORR.

Structural instabilities of nanocrystalline and ultrafine-grained (UFG) materials have been recognized as a major challenge during cyclic loading, especially in the low cycle fatigue regime. Although a severe deterioration of the mechanical properties has been reported during cyclic deformation, quantification of the softening portion solely due to grain coarsening was not possible. It will be demonstrated that cyclic high pressure torsion (CHPT) is a versatile method to enable direct measurement of the impact of grain coarsening on cyclic softening, as failure of the sample is prevented. Here, CHPT experiments have been performed on 99.99% UFG nickel. Grain coarsening similar to conventional uniaxial fatigue experiments was observed and could be studied up to large cyclic accumulated macro strains of 50. The correlation of electron back scatter diffraction images with microhardness measurements facilitated quantification of the cyclic softening as a consequence of grain growth for the very first time. Further, structural investigations revealed distinctly enhanced grain coarsening within shear bands. Thus, the cyclic strain seems to be the most important parameter controlling mechanically driven boundary migration during cyclic loading at low homologous temperatures.

The kinetic relaxation pathways for strained heteroepitaxial films are mapped using a process simulator that integrates experimental and model descriptions of the energetic and kinetic parameters that define the nucleation, propagation, and interaction of strain relieving dislocations. This paper focuses on Ge x Si1−x /Si(100), but the methodologies described should be extendible to other systems. The kinetic pathways for strain evolution are plotted for film growth as functions of the primary kinetic parameters: growth temperature, growth rate, and initial lattice mismatch, generating relaxation surfaces for parameter pairs. Sensitivity analyses are presented of how deviations from mean parameters disperse the resultant relaxation surfaces. Finally, multi-parameter “fingerprinting” of the dislocation array is shown to illustrate how fundamental kinetic mechanisms—particularly dislocation nucleation mechanisms—define the final dislocation array. The overarching goal is to establish a robust framework for predicting, interrogating, and optimizing strain relaxation pathways and underlying mechanisms, for misfit dislocations in strained heteroepitaxial films.

In this work, a three-dimensional (3D) porous hybrid nickel/aluminum layered double hydroxide (Ni/Al-LDH)-carbon cloth (CC), the working electrode without binders or conductive additions for supercapacitor, was successfully synthesized via facile one-step hydrothermal method. The as-obtained Ni/Al-LDH/CC sample exhibited good charge storage performance (the specific capacitance was up to 359 F/g at a current density of 0.3 A/g), as well as superior cycling stability (5.9% capacitance increase after 3000 cycles at 1.0 A/g). Furthermore, an asymmetric supercapacitor, Ni/Al-LDH/CC as positive electrode and activated carbon (AC) as negative electrode (Ni/Al-LDH/CC//AC), achieved a high energy density (20.9 Wh/kg vs. the power density 262.5 W/kg) and good cycle lifetime (83.9% retention of the initial value after 3000 cycle tests at a current density of 0.5 A/g). The unique 3D porous structure and binder-free electrode display great potential in supercapacitors.

TiO2 nanotubes have been demonstrated with promising future in photoelectrocatalytic (PEC)_ applications and deposition of Pt nanoparticles on TiO2 has been widely used to enhance their PEC activities. However, those Pt nanoparticles are normally randomly deposited on the surface of TiO2 nanotubes. Selective deposition of Pt nanoparticles is important to achieve better charge separation. In this study, we reported an electrochemical activation step to prepare TiO2 nanotubes deposited with Pt nanoparticles on their open ends. The “activation step” played a key role in achieving a clean surface of the TiO2 nanotubes, thus ensuring the uniform growth of Pt nanoparticles and efficient photogenerated electrons transportation. The Pt-A-TiO2 films have photocatalytic activities in hydrogen generation and methyl orange degradation with a high hydrogen generation rate of 0.74 mL/h/cm2, three times that of the pure TiO2 nanotubes (0.24 mL/h/cm2). Thus, this study demonstrated an effective method for improving the performance of Pt/TiO2 photocatalyst.

The present study addressed the weldability of Hastelloy C-276 and Type 321 austenitic stainless steel (ASS) dissimilar combination used for manufacturing of high-temperature equipments in nuclear power plants. Investigation of the microstructural evolutions across the different welding passes and their subsequent effect on the mechanical properties and corrosion resistance would be helpful in better understanding and pave way for the frequent application of such dissimilar joints in the industrial applications. The problem of segregation associated with the multi-pass gas tungsten arc welding process was also investigated systematically. The fusion zone microstructures exhibited a transition from columnar to an equiaxed dendritic structure with varying passes. The topologically closed packed (TCP) phases (such as P and μ) were observed in the fusion zone as well as at the weld interface of Hastelloy C-276. Polarization test was performed to evaluate the corrosion resistance and results indicated that the Cr and Mo depleted zones formed around the TCP phases might be responsible for decreased Epit value for fusion zone. The novelty of this work is to explore the possibilities of substitution of an expensive Hastelloy C-276 with a cost-effective Ti-stabilized Type 321 ASS.

A novel hybrid processing has been developed to achieve dense and crack-free mullite films with large critical thicknesses. The amorphous solid nanoparticles obtained from the mullite sol–gel precursor were mixed with the same liquid precursor to form stable suspensions, which were subsequently used to form mullite coatings with the dip-coating method, followed by drying and firing. The hybrid precursor suspensions resulted in highly close-packed nanoparticles, which reduced shrinkage during sintering. Selecting the solvent with a low evaporation rate and high surface tension can effectively eliminate the surface instability caused by the lateral flow during solvent evaporation. The mullite film density was significantly improved at low sintering temperatures, because of the high packing density and viscous flow at above the glass transition temperature of the amorphous gel nanoparticles before crystallization. Dense and crack-free mullite films with 500–600 nm thickness can be obtained from the novel hybrid approach.

Effects of crystal tilt on the determination of the relative positions of different ion columns in compounds such as ferroelectric PbTiO3 are of critical importance, because the displacements of Ti and O relative to Pb correlate directly to the spontaneous polarization and ferroelectric properties. Here a study about the effects of small-angle crystal tilt on the relative image spots positions of different ions in PbTiO3 was carried out under high angle angular dark-field (HAADF) and bright-field imaging for aberration corrected Scanning Transmission Electron Microscope. The results indicate that crystal tilt affects the relative positions of Pb, Ti, and O greatly, and the effects are proved to depend highly on crystal tilt angle and PTO thickness. HAADF image simulations on PbTiO3, SrTiO3, and SrRuO3 indicate that the difference in atomic number is a main contributor to the relative image spot position change of different ion columns when crystal tilts.

Ceramic scaffolds are being developed to control both proliferation and differentiation of hematopoietic stem cells into desired cell products in bioreactors. These scaffolds mimic important aspects of the microenvironment or “niche” inside bone marrow. In particular, hematopoietic stem cell fate is thought to be effected by the architecture of trabecular bone and the presence of calcium. Here we report the effects of ceramics processing on the phase distribution and microstructure of biphasic ceramics used to culture hematopoietic stem cells. Processing of biphasic ceramics by powder mixing resulted in tetracalcium phosphate on the sintered surface. This correlated with observed surface deposits, weight gain, and the release of calcium ions in saline over 28 days. In contrast, impregnation of partially sintered hydroxyapatite with calcium nitrate resulted in calcium carbonate on the sintered surface. Impregnation correlated with the release of calcium ions into the saline, surface pitting, and weight loss.

Graphene due to its unique physicochemical properties mainly its large surface to volume ratio, excellent thermal and electrical conductivity, biocompatibility, as well as broad electrochemical potential, has received considerable attention for biosensing applications. In this review paper, we provide a comprehensive overview of the recent advances in the field of electrochemical biosensors developed using the graphene nanomaterial including graphene oxide, reduced graphene oxide, CVD graphene, and various graphene based nanostructures including nanomesh, nanowalls, etc. in healthcare related applications. The review focusses on material synthesis, device fabrication, and biofunctionalization of graphene electrodes in biosensing such as those based on electrochemical impedance, amperometry/voltammetry, potentiometry, conductometry, and field effect transistor. Additionally, several ingenious biosensing strategies of graphene biosensor in clinical diagnosis for detection of proteins (disease biomarkers), nucleic acids (mutation analysis in genetic diseases), small molecules (disease metabolites like glucose, lactic acid etc.), and pathogens (bacterial and viral infections) have also been discussed.

The strain-rate sensitivity of the flow stress represents a crucial parameter for characterizing the deformation kinetics of a material. In this work a new method was developed and validated for determining the local strain-rate sensitivity of the flow stress at different plastic strains. The approach is based on spherical nanoindentation strain-rate jump tests during one deformation experiment. In the case of ultrafine-grained Al and ultrafine-grained Cu good agreement between this technique and macroscopic compression tests has been achieved. In contrast to this, individual spherical nanoindentation experiments at constant strain-rates resulted in unrealistically high strain-rate sensitivities for both materials because of drift influences. Microstructural investigations of the residual spherical imprints on ultrafine-grained Al and ultrafine-grained Cu revealed significant differences regarding the deformation structure. For ultrafine-grained Cu considerably less activity of grain boundary sliding has been observed compared to ultrafine-grained Al.

A chemomechanical coupling model is presented in the temperature range of 1200–1800 °C based on the microstructure during oxidation of ZrB2–SiC. The model includes the interaction of the oxidation rate and the mechanical stress. The stress is generated due to the constraint from the substrate to the lateral growth. The generated stress results in the shrink of the pores in the oxide. At the outer glassy layer surface, the boundary layer evaporation is adopted to describe the evaporation rate. Using the coupling model, the evolutions of the oxide layer thickness, weight gain, pore radius, and stress in both the oxide and substrate are provided, and the theoretical calculated results agree well with the reported experimental results. The results reveal large stress in the oxide layer during the oxidation process. By comparing the results of ZrB2 with different volume fractions of SiC, it is found that ZrB2 with higher volume fraction of SiC has more excellent oxidation resistance and smaller stress.

In this study, the buckling behaviors of single-walled carbon nanocones (SWCNCs) under bending at finite temperatures are predicted using a proposed multiscale quasi-continuum approach based on the temperature-dependent higher order Cauchy–Born (THCB) rule. The hyper-elastic constitutive model is derived exactly in the context of the higher order gradient theory that incorporates the details of the interatomic interaction. The numerical simulations for the deformation of SWCNCs are implemented using the developed meshless computational framework based on moving least-squares interpolation, which can precisely reproduce the deformation process and buckling patterns of SWCNCs under bending. The underlying correlations of the critical bending angle with respect to the geometry of SWCNCs and temperature are revealed by the numerical results. Furthermore, our simulation captures the transformation from the local to the global buckling process of SWCNCs, accompanied with an average strain energy jump. Our results correspond with previous studies.

Photovoltaics made from organic–inorganic hybrid perovskite semiconductors are attracting significant interest due to their ability to harvest sunlight with remarkable efficiency. The presence of lead in the best performing devices raises concerns regarding their toxicity, a problem that may create barriers to commercialization. Hybrid perovskites with reduced lead content are being investigated to overcome this issue and here we evaluate bismuth as a possible lead substitute. For a series of hybrid perovskite films with the general composition CH3NH3(Pb y Bi1−y )I3−x Cl x , we characterize their optical and structural properties using UV–Vis spectroscopy, scanning electron microscopy and grazing incidence wide angle X-ray scattering. We show that they form crystalline structures with an optical band gap, around 2 eV for CH3NH3BiI3. However, preliminary solar cell tests show low power conversion efficiencies (<0.01%) due to both incomplete precursor conversion and material de-wetting from the substrate. The overall outcome is severely limited photocurrent. With current processing methods the general applicability of hybrid bismuth perovskites in photovoltaics may be limited.