Nearly dense and almost single-phase bulk (Cr1–xVx)2AlC (x = 0, 0.25, 0.5, 0.75, and 1.0) ceramics were successfully fabricated by in situ hot-pressing method using Cr, V, Al, and C powders as raw materials. A possible synthesis mechanism was proposed to explain the formation of (Cr1–xVx)2AlC solid solutions. The lattice parameters, microstructure, and mechanical properties of the (Cr1–xVx)2AlC ceramics were investigated in detail. The results indicated that the lattice parameters increased with the substitution of Cr by V and the aspect ratio of the grain changed from 1.4 to 3.2. The dependence of the mechanical properties on the V content was a single-peak type. The (Cr0.5V0.5)2AlC ceramic possessed the optimal mechanical performance and its Vickers hardness, flexural strength, and fracture toughness reached the maximum values of 5.18 GPa, 402 MPa, 5.91 MPa m1/2, respectively, due to the solid solution effect. The energy-consuming mechanisms of the material were also discussed.

Yttrium aluminum garnet (YAG)-based ceramics represent a valuable alternative to single crystals as active media in laser devices for specific applications. In this connection, the 1.5–1.65 µm emission channel of Er3+-doped YAG is of particular importance for the realization of diode pumped solid state lasers operating in the so-called ‘eye-safe’ region. A well-known drawback of this material is related to its small absorption cross section in correspondence to the diode pumping radiation at 940–980 nm. However, its emission performance can be significantly improved through sensitization with Yb3+ ions that can efficiently absorb the excitation radiation and transfer it to the Er3+ ions. This work deals with the fabrication of polycrystalline YAG co-doped with Er3+ and Yb3+ ions from oxide powders via solid state sintering in high vacuum conditions and its microstructural analysis by transmission electron microscopy–energy-dispersive x-ray spectroscopy to determine the dopants distribution and to assess their influence on the sintering process and on the spectroscopic properties. For this purpose, the absorption and emission spectra of the prepared material have been measured and compared with those of a single crystal having the same composition, appositely prepared by the micro-pulling down method. Suitable calculations have been finally carried out to verify the effective perspectives of application of the investigated ceramics as active lasing medium.

Morphological evolution and phase transformation of metastable intermediate precipitates are critical to their mechanical properties for the non-isothermal processing. During the non-isothermal precipitation, the formation of the new phases usually couples with structural evolution. Traditional structural characterization has limitation to resolve comprehensive changes simultaneously. In this study, we report direct observation, precipitation sequence, and the details of concurrent morphological and structural changes of various intermediate precipitates during non-isothermal heating in the Al–Cu systems with different pretreatments. The structural heterogeneity during the non-isothermal precipitation processes is resolved into coexistence of two different precipitate phases and quantitatively studied in terms of the phase transition and the morphological evolution. This paper presents the in situ small- and wide-angle synchrotron x-ray scattering (SAXS and WAXS) to refine and to identify the mixed structural information during multiple precipitation stages. The WAXS results show that the precipitation sequence is θ″ → (θ″ + θ′) → θ′ → (θ′ + θ) → θ upon heating. Due to the fact of the specifically oriented SAXS intensity, the evolution of the aforementioned phase transformation is resolved by the refinement of the SAXS intensity integrated over the selected area. These methods reveal multiscale information that is not trivial comparing to the traditional characterization methods.

For years, substituted iron nitrides have been studied by various types of approaches: physical, chemical, and materials engineering, both experimental and theoretical. More recently, substituted iron nitrides have been studied by theoretical models for calculation of electronic structure, presenting the advantage of being economically viable. The properties of these compounds have potential application not only as a recording material but also in other areas: as resistance to corrosion and wear. The changes occurred in the alloys when transformed into nitrides still require further studies. Thus, the electronic and magnetic structure of IrFe3 and Ir3Fe alloys and the changes caused in their ground state properties when the nitrogen atoms were included in their stoichiometry, turning them into substituted iron nitrides type Ir3FeN and IrFe3N, will be investigated in this study. The electronic structure of these compounds was modeled using the linearized augmented plane waves (LAPW), an augmented plane wave (APW – method of Slater) modification. The following methodology was used in this study: the cohesive energy for steady state was calculated and then the ground state properties, such as charge transfer, magnetic moment, hyperfine properties, and the density of states, were obtained. The ground state properties are also assessed from the pressure variation experienced by these compounds, that way, the induced changes in the alloys caused by introducing the nitrogen atom are obtained. This study may assist in obtaining new and better nitrides.

Multiferroic CoFe2O4–BiFeO3 (CFO–BFO) core–shell nanofibers were synthesized by coaxial electrospinning. The spinel structure of CFO and perovskite structure of BFO were confirmed by x-ray diffraction and high-resolution transmission electron microscopy. The core–shell configuration of nanofibers was verified by scanning electron microscopy and transmission electron microscopy images. The macroscopic ferromagnetic property of core–shell nanofibers was demonstrated by magnetic hysteresis loop. The local magnetoelectric (ME) coupling was confirmed by using dual frequency piezoresponse force microscopy (PFM) under an external magnetic field, showing magnetically induced evolution of piezoresponse and domain structure. The ferroelectric characteristics are demonstrated by the switching spectroscopy PFM. From PFM hysteresis and butterfly loops, it is observed that the piezoresponse amplitude is reduced while coercive voltage increased under external in-plane magnetic field, induced through the mechanical interactions between magnetostrictive CFO and piezoelectric BFO, from which the lateral ME coupling can be estimated quantitatively. The nanofibers thus can find a variety of applications as a one-dimensional multiferroic material.

The demands for highly transparent thin films for many integrated optical systems increase rapidly. The aim of the present work is to address these important needs. We show a novel approach for the nanocolloidal processing of barium titanate with enhanced optical transparency. The results showed that the stability of the prepared solution and optical transparency of the resulted thin film improved significantly. The study of the structure and properties of the prepared solutions indicated that the enhanced and homogenous transparency is due to the size-effect of the particles embedded in the solution, which are nanostructured. It seems to us that the proposed method has the capability of being a general strategy for obtaining highly transparent solutions and thin films. Moreover, the enhanced transparency of the prepared thin films can improve the energy efficiency of the solar power systems significantly.

Gold–silver (Au–Ag) bimetal dispersed SiO2 composite films were fabricated via a chemical solution approach combining sol–gel with a spin-coating process, and they were investigated by transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), and ultraviolet-visible absorption spectra. TEM image indicated that Ag and/or Au nanoparticles (NPs) had a spherical structure with large size distributions. The XPS results demonstrated that the presence of both Ag and Au NPs in the composite film is in each metal state. The optical absorption spectra of the composite film further confirmed the formation of nanosized Au and Ag particles, given by the two surface plasmon resonance (SPR) peaks. Unlike other Au–Ag composite films, these two SPR peaks had almost the same intensity, which is rarely obtained by a chemical approach. Compared to optical absorption spectra calculated by the modified Mie theory, the location and intensity of SPR peaks had a little difference, which could be attributed to large size distributions of Ag and Au bimetal NPs in the composite film along with the experimental process. In addition, the intensity of both SPR peaks was content-related.

An investigation was carried out to characterize the tensile behavior of multiwalled carbon nanotube (MWCNT) modified epoxy nanocomposites in the glassy, viscoelastic, and rubbery regimes. 1 and 2 wt% MWCNT predispersed epoxy was used in this study. The cured samples were characterized using dynamic mechanical analysis for selection of different temperatures. The stress–strain behavior and toughness were determined in the temperature band of 25–140 °C. Addition of 1% CNT resulted in 16% improvement in the storage modulus at glassy state but 6% reduction in storage modulus was seen for 2% CNT-epoxy system. Tensile results showed that the strength and modulus have improved for 1% CNT-epoxy system. This study also revealed that for all the three systems, failure strain was maximum near the glass transition temperature (Tg) and significantly reduced above Tg. Also the CNT-modified epoxies showed improved toughness.

Using phase separation, alumina-based porous ceramics with three-dimensional frameworks were prepared, with fine structural roughness created by subsequent hot-water treatment. The pore volume of the porous alumina and its specific surface area increased concomitantly with increasing hot-water treatment time. Porous alumina/fluorinated oil bulk composites were prepared by coating hydrophobic silane onto the porous ceramic surface and subsequently impregnating fluorinated oil. A wetting ridge formed at the bottom of the water droplets on the composites. Partial contact between the water and solid surface was inferred from a comparison of interface energies in the system. The composites provided a smaller sliding angle (SA) than that of the sample without impregnating fluorinated oil. The composite with fine roughness exhibited longer sustainability of a small SA than that without fine roughness. Particle image velocimetry revealed that the dominant sliding mode for water droplets on this composite was slipping. The droplets moved on the surface under an external electric field. Coulombic force contributes to this motion.

Laser sintering allows producing end-use parts directly from computer files with no tooling required. For these parts to be used in industrial applications, their mechanical properties throughout in-service applications must be examined. The aim of this article is to provide an understanding of the dynamic performance of laser-sintered Nylon 12 parts. To investigate the viscoelastic properties of the material, dynamic thermal mechanical analysis has been performed in different frequencies and temperatures. Tension–tension cyclic behavior of samples has been studied and creep is shown to have a great impact in such behavior in addition to fatigue. Stress relaxation plots are provided and compared with the cyclic loading plots validating the fact that samples experience a combination of creep and fatigue in tension–tension loading. Hysteresis loops indicate brittle crack propagation in the samples experiencing fatigue.

Al-induced crystallization (AIC) of amorphous SixGe1–x (a-SixGe1–x) alloys with compositions over the entire range of the isomorphous Si–Ge system has been investigated. The crystallization progress was monitored by dedicated in situ x-ray diffraction analysis while gradually increasing the annealing temperature. Auger sputter-depth profiling was applied to investigate the occurrence of Al-induced layer exchange of the Al and a-SixGe1–x sublayers after complete crystallization. A-SixGe1–x alloys with x < 0.13 and x > 0.41 show largely different AIC behaviors with respect to crystallization rate and possible layer exchange of the Al and a-SixGe1–x sublayers upon crystallization. A thermodynamic model for AIC of a-SixGe1–x alloys is presented, which well explains these experimental observations and thereby demonstrates the dominant role of interface thermodynamics in the AIC process of amorphous semiconductors. The model can be used to predict the AIC behaviors of a-SixGe1–x alloys over the entire composition range at specified annealing temperatures.

The paradox of strength and ductility is now well established and denotes the difficulty of simultaneously achieving both high strength and high ductility. This paradox was critically examined using a cast Al–7%Si alloy processed by high-pressure torsion (HPT) for up to 10 turns at a temperature of either 298 or 445 K. This processing reduces the grain size to a minimum of ∼0.4 μm and also decreases the average size of the Si particles. The results show that samples processed to high numbers of HPT turns exhibit both high strength and high ductility when tested at relatively low strain rates and the strain rate sensitivity under these conditions is ∼0.14 which suggests that flow occurs by some limited grain boundary sliding and crystallographic slip. The results are also displayed on the traditional diagram for strength and ductility and they demonstrate the potential for achieving high strength and high ductility by increasing the number of turns in HPT.

The variant selection from the parent α phase to the product β phase during the enhanced phase transformation induced by the electric current pulses (ECPs) was investigated in a Cu–Zn alloy. The electron backscatter diffraction results showed that the crystallographic variant selection was not only across those prior α/α grain boundaries, but also within the α grain interior, and it implied that the nucleation of the β phase on the up-transformation obeyed a preferred orientation selection. Further analysis revealed that the orientation relationship between the α phase and the β phase variants nucleated from the α phase was close to 44.3° about <114>, which clearly described the rotation axes and the misorientation angles in terms of an axis/angle description when the high temperature phase nucleated from the matrix. Therefore, the ECP treatment would provide a new promising and convenient method to investigate the variant evolution on the up-transformation.

The commercially abundant low purity calcium fluoride powder was directly loaded for spark plasma sintering (SPS). In a vacuum atmosphere with a constant pressure held at 70 MPa the sintering temperature was systematically varied in the range of 500–850 °C. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) techniques were used to characterize the raw powder; and for studying the microstructural properties and in-line transmittance of the finalized ceramics, SEM and Fourier transform infrared spectroscopy (FTIR) were used. Digital images of the 700 °C sintered translucent CaF2 ceramic were taken along with transmittance recordings. The grain growth mechanisms and activation energy values were determined; and the influences of temperature on the relative density, grain size, and optical transmittance were demonstrated. Furthermore, for the first time, a plausible predominant mechanism was proposed for describing the different sintering stages of calcium fluoride ceramics.

Oxide-dispersion-strengthened (ODS) ferritic alloys are fascinating materials for future high temperature energy production technologies. MgAl2O4 ODS alloy incorporating nanoscale oxide particles were produced by mechanical milling (MM) followed by hot isostatic pressing (HIP). The MgAl2O4 nanoscale oxide particles were formed during the HIP process by the addition of MgO and Al2O3 to the Fe–Cr matrix. Microstructural evolution of ODS alloys was structurally characterized at each step of the elaboration processes by means of scanning electron microscope (SEM), transmission electron microscope (TEM), and x-ray diffraction (XRD). The observations of structure of the mixed powders in ODS alloys after MM indicated that the initial powders, coupled with the original MgO and Al2O3 powders, got fractured by severe plastic deformation and ultrafine bcc grains (∼17 nm) of the matrix and amorphous phase composed of Mg, Al, and O were formed during MM. The main driving force for the formation of amorphous phase comes from the increase of volume fraction of bcc Fe grain boundary and the increase of interfacial energy due to the decrease in the size of MgO and Al2O3 powders. The MgAl2O4 nanoscale oxide particles formed at 1173 K which was far below the traditional sintering temperature of the raw material. And the structures of MgAl2O4 nanoscale oxide particles were observed by TEM.

Amorphous polymers are among the most common materials used in adhesives, and a clear understanding of the effects of molecular scale features on macroscopic responses is necessary to design new, better performing adhesives. While many features have been investigated, including effects of molecular weight, inclusion of filler materials, and some effects of crosslinking, much of the understanding of the adhesive response remains empirical. Specifically, choosing the appropriate combination of polymer properties that optimize the work required to debond is still a challenge and the interplay between mechanical and chemical properties of polymers at interfaces is largely unknown. Here, we perform molecular dynamics simulations on a simple coarse-grained polymer model to directly investigate the role of crosslinking in determining the adhesive response of amorphous polymers at the molecular level. We find that crosslinking has a dramatic effect on the mechanical properties even at relatively low crosslink densities, and that crosslinking alone can be effective for optimizing the adhesive response of amorphous polymer adhesives. We observe a clear transition from cohesive to adhesive failure as the crosslink density is increased which coincides with the optimal toughening in the films. Furthermore, we find that our model captures the key molecular scale deformation mechanisms that control the adhesive response. For low crosslink densities, increased crosslinking improves the adhesive response by inhibiting chain sliding and allowing the structures to achieve large deformations, but as the crosslink density is increased further, the adhesive response is diminished due to reduced overall deformability. Our results provide simple but important insights into how crosslinking in amorphous polymer adhesives can be used to tune the mechanical response and ultimately to optimize adhesive performance for various applications.

In this study, impurity segregation and solute drag effects on grain boundary (GB) motion were investigated in a binary Al–Ni model system with an inclined Σ5 GB by direct molecular dynamics simulations. By extending the interface random walk method to impure systems, it was found that the GB mobility was significantly influenced by the segregated impurities, which generally decreased as the impurity concentration increased. Moreover, based on simulations at different temperatures and impurity concentrations, we validated that the solute drag effects can be well modeled by the theory proposed by Cahn, Lücke, and Stüwe (CLS model) more than 50 years ago, provided that proper adaptations were made. In particular, we found that in strongly segregated GB system, the boundary mobility was deeply correlated to the impurity diffusivity in the direction perpendicular to the boundary plane in the frame of the moving boundary, instead of the impurity bulk diffusivity assumed in the original CLS model and many past studies.

The thickness dependence of the electrical stability under monotonic and cyclic tensile loading is investigated for Cu films on polymer substrates. As for monotonic tensile deformation, thicker films show better stability than thinner films due to their higher ductility and the larger capability of strain accommodation. For the fatigue resistance, however, a more complex behavior was observed depending on the amount of the applied strain. For low strain amplitude in the high cycle fatigue (HCF) regime, thinner films exhibit longer fatigue life because the larger strength of thinner films suppresses dislocation movement and damage nucleation. However, for high strain amplitudes in the low cycle fatigue (LCF) regime, the fatigue life for thinner films is drastically reduced compared to thicker films. It is shown that fatigue coefficients in the LCF regime can be obtained when applying the Coffin–Manson relationship.

Cobalt was doped into the Ce-doped SrMnO3 system to enhance the low ionic conductivity of Ce-doped SrMnO3 (SCM) for solid oxide fuel cell cathode application. Structural and conductivity changes as a function of the Co content were investigated. Sr0.9Ce0.1Mn1–xCoxO3−δ (SCMCo, x = 0.1, 0.2, 0.3) cathode materials were synthesized by an EDTA citrate complexing process, which yielded a single perovskite structure, and the lattice volume was expanded by substituting Ce and Co ions. The increased lattice volume was attributed to a decrease in the valence state of the manganese and cobalt and an increase in the oxygen vacancy concentration. An increase in the concentration of oxygen vacancies with increasing Co content was identified by thermogravimetric analysis. The electrical conductivity decreased with increasing Co content, which was attributed to an increase in the activation energy for polaron hopping. Although the electrical conductivity was decreased by cobalt-doping, the polarization resistance of SCMCo also decreased significantly (from 5.611 to 1.171 Ω cm2 at 800 °C). The decreased polarization resistance is attributed to enhanced oxygen-ion transfer kinetics with cobalt-doping. We conclude that cobalt substitution leads to enhancement in the electrochemical properties of the cathode due to an increase in oxygen vacancy concentration.

SnZn(OH)6 (ZHS) hollow cubes were synthesized by a facile self-templated method at room temperature, and Ag/AgCl/ZHS particles were prepared by a photodepositing method. The crystalline structure and morphology of the prepared particles were characterized by x-ray diffraction, UV-vis diffuse reflectance spectroscopy, scanning electron microscopy, and N2 adsorption. The results indicated that the particles had almost uniform monoclinic geometry and size. The photocatalytic oxidation of Rhodamine B was used to evaluate the photocatalytic activity of the synthesized photocatalysts. It is found that the hollow Ag/AgCl/ZHS showed the highest catalytic performance under visible or UV light, which can be attributed to the synergetic effect of Ag, AgCl, and ZHS.