High-entropy alloys (HEAs) consisting of multiprincipal elements have demonstrated many interesting structural, physical, and chemical properties for a wide range of applications. This article is a review of the current theoretical research on the elastic parameters of HEAs. The performance of various ab initio-based computational models (effective medium and supercell approaches) is carefully analyzed. Representative theoretical elastic parameters of different HEAs, including single-crystal elastic constants, polycrystalline elastic moduli, elastic anisotropy, and Debye temperature, are presented and discussed. For comparison, simple mixtures of the elastic moduli of pure elements are calculated and contrasted with the ab initio results. The present work provides a reference for future theoretical investigation of the micromechanical properties of systems based on HEAs.

Dynamic-mode cantilever sensors are used in many different applications but especially in materials research to study properties of novel (nano)materials. Decreasing sample sizes require an increase in sensitivity of the analysis tools. For cantilever-based methods that is achieved through a reduction in cantilever dimensions. However, the increase in sensitivity has to be balanced with the detectability as also for a small cantilever a reliable detection of its oscillatory state has to be ensured. A recently introduced co-resonant measurement principle for cantilever sensors addresses this challenge by coupling and eigenfrequency matching of a micro- and a nanocantilever. Here, the sensor concept is reviewed with focus on the application in materials research by the instructive example of an iron-filled carbon nanotube, giving insight into the features and benefits of the sensor concept and demonstrating the reliable derivation of magnetic sample properties.

Sterilization is one of the last stages prior to the implantation of a biomaterial. Therefore, the method should be chosen carefully as this is determinant not to compromise the properties of the material. In this context, three sterilization processes were evaluated as to their effect on the properties of a silane hybrid coating: steam autoclave, ethylene oxide, and hydrogen peroxide plasma. The coating was obtained from a sol consisting of alkoxysilane Tetraethoxysilane and organoalcoxysilane Methyltriethoxysilane (MTES), applied to the Ti6Al4V substrate, to increase its corrosion resistance and biocompatibility. After sterilization, the samples were characterized by scanning electron microscopy, atomic force microscopy, profilometry, wetabillity, and Fourier transform infrared spectroscopy. The electrochemical behavior was monitored by open circuit potential and potentiodynamic polarization curves. The cytocompatibility was evaluated by adhesion, viability, and morphological alterations in the MG-63 cells. The results showed that the protective behavior of the hybrid coating was compromised regardless of the sterilization method. However, the steam autoclave caused more morphological changes on the silane hybrid coating as well as on the Ti6Al4V substrate than the other two sterilization methods. Although the sterilized hybrid coating did not show cytotoxicity, the hybrid coating sterilized by hydrogen peroxide plasma showed a higher percentage of viable cells. The ethylene oxide presented the lowest percentage of viability and the highest cell death rate.

Carbon nanotubes (CNTs) and silicon carbide nanoparticle (nano-SiCp)-reinforced magnesium (Mg) matrix hybrid composites were prepared through a three-step melt spinning process (ball milling, mechanical stirring, and ultrasonic vibration processing). The hybrid nanoreinforcements showed high strengthening efficiency by which the yield and tensile strength of the hybrid composites experienced 46.7 and 15.2% increment, respectively, compared with the matrix alloy. Obviously, the mixed ball-milling process of SiC nanoparticles and CNTs promoted the dispersion of each other, and both the uniformly distributed SiC nanoparticles and CNTs contributed to the enhanced mechanical performance of the hybrid composites. Besides, the addition of the hybrid nanoreinforcements induced the precipitation of nanosized rod-like MgZn2 phases in the as-extruded composites which also made a contribution to the enhanced performance of the composites. Investigations on the strengthening mechanisms of the hybrid composites show that it originates from grain refinement, load transfer, precipitation enhancement, and Orowan reinforcing. More importantly, the contribution made by each part was analyzed in detail.

Coupling oxidation type semiconductors is a feasible strategy to improve the photocatalytic activity of reduction type g-C3N4 photocatalysts. In this work, Bi2O3 was used as an oxidation type semiconductor to construct direct Z-scheme Bi2O3/g-C3N4 photocatalysts by a one-step calcination method. The obtained Bi2O3/g-C3N4 composites exhibited excellent photocatalytic activity and stability toward methylene blue degradation under visible light irradiation. The composite with 1% weight content of Bi2O3 to g-C3N4 exhibited the highest photocatalytic activity with an apparent rate constant of 0.063 min−1, which was 3.0 and 3.7 times higher than that of pure Bi2O3 and g-C3N4, respectively. The enhanced photocatalytic activity of the Bi2O3/g-C3N4 composite was mainly attributed to the improved charge separation efficiency and stronger redox ability. This work gave a new insight in developing g-C3N4-based Z-scheme heterojunction photocatalysts with enhanced photocatalytic activity.

Electrocatalytic water splitting for the production of H2 is increasingly becoming a significant method to mitigate the current energy crisis and environmental pollution. However, oxygen evolution reaction (OER), a slow four-electron progress, is the bottle neck of water splitting. Thus, developing new, low cost, and effective catalysts for OER is a research hotspot in material and energy resource fields. Therefore, the research of nonprecious, metal-based OER catalysts has been popular. In this work, it is validated that 3D hollow Co(OH)2 nanoflowers synthesized by a facile template-based strategy at room temperature are effective electrocatalysts for OER. The catalysts display high activity with a current density of 10 mA/cm2 at an overpotential of 310 mV and a small Tafel slope of 68.9 mV/dec in alkaline condition. It’s noteworthy that this material is stable for over 20 h of chronopotentiometry. This work offers a simple and promising way to prepare efficient and durable electrocatalysts.

In the present work, the effect of cooling rate on the evolution of the microstructure and mechanical properties of an α + β titanium alloy has been systematically investigated. Titanium alloy samples were heated to 1066 °C (above the β transus), 930 °C (just below the β transus), and 850 °C (well below the β transus) followed by oil quenching, air cooling, and furnace cooling, respectively. Primary alpha (αp), lamellar alpha (αL), and martensite (α′) were the dominant features of the microstructures for all the samples heated below the β transus. Furnace-cooled samples showed variation in the size and shape of the αp and fraction of αL according to the heating temperature. At slower cooling rates, the thickness of the αL increased with the increase in temperature. Transmission electron microscopy and X-ray diffraction confirmed the presence of α′ in all the quenched samples. The volume fraction and size of the αp decreased with the increase in temperature but was independent of the cooling rate. The microhardness was relatively unaffected by the cooling rate for heating just below the β transus, i.e., 930 °C. The modulus of elasticity was found to be extremely sensitive to the microstructure.

Microstructure and phase evolution in magnetron sputtered nanocrystalline tungsten and tungsten alloy thin films are explored through in situ TEM annealing experiments at temperatures up to 1000 °C. Grain growth in unalloyed nanocrystalline tungsten transpires through a discontinuous process at temperatures up to 550 °C, which is coupled to an allotropic phase transformation of metastable β-tungsten with the A-15 cubic structure to stable body centered cubic (BCC) α-tungsten. Complete transformation to the BCC α-phase is accompanied by the convergence to a unimodal nanocrystalline structure at 650 °C, signaling a transition to continuous grain growth. Alloy films synthesized with compositions of W–20 at.% Ti and W–15 at.% Cr exhibit only the BCC α-phase in the as-deposited state, which indicate the addition of solute stabilizes the films against the formation of metastable β-tungsten. Thermal stability of the alloy films is significantly improved over their unalloyed counterpart up to 1000 °C, and grain coarsening occurs solely through a continuous growth process. The contrasting thermal stability between W–Ti and W–Cr is attributed to different grain boundary segregation states, thus demonstrating the critical role of grain boundary chemistry in the design of solute-stabilized nanocrystalline alloys.

One of the founding concepts of the high-entropy alloy (HEA) field was that the lattice structures of multicomponent solid solution phases are highly distorted. The displacement of the constituent atoms, away from their ideal locations (local lattice strain), has been widely cited as the reason for a number of the observed physical and mechanical properties. However, very little data directly characterizing these lattice distortions exist and, thus, the validity of this hypothesis remains an open question. Here, the concept is reviewed by considering the underlying principles of the lattice distortions, the suitability of different assessment methods, and the direct experimental data currently available. It is found that, at present, there is no clear evidence that the lattice distortions in HEAs are significantly greater than those of conventional alloys. However, so few alloys have been appropriately characterized that this conclusion cannot be considered overarching and further research is required.

This review aims to consolidate scarce literature on the use of modern nanomechanical testing technique like instrumented nanoindentation in the field of archaeometry materials research. The review showcase on how can the nanoindentation tests provide valuable data about mechanical properties which, in turn, relate to the evolution of ancient biomaterials as well as human history and production methods. This is particularly useful when the testing is limited by confined volumes and small material samples (since the contact size is in the order of few microns). As an emerging novel application, some special considerations are warranted for characterization of archaeometry materials. In this review, potential research areas relating to how nanoindentation is expected to benefit and help improve existing practices in archaeometry are identified. It is expected that these insights will raise awareness for use of nanoindentation at various world heritage sites as well as various museums.

The ZnO/g-C3N4 binary heterostructures were formed by two steps, then the firm connection between ZnO NRs and lamellar g-C3N4 was characterized through powder XRD, FESEM with EDS, TEM, XPS, and Thermogravimetric analysis. Then the gas sensing performances of ZnO/g-C3N4 nanoheterostructures were analyzed systematically by using ethanol as a molecular probe. The results revealed that the fabricated compositive sensor not only exhibited quick response/recovery characteristics in the whole operating temperature (OT) range of 200–300 °C but also got a maximum response of 14.29 toward 100 ppm of ethanol at the optimal OT of only 260 °C. Moreover, such heterostructures also demonstrated good selectivity and superb reproducibility to acetone among all the tested toxic gases, especially higher response and faster response–recovery speeds than the pristine ZnO sensor. The above ZnO/g-C3N4 heterostructures may also supply other novel applications in the aspects of lithium-ion batteries, photocatalysis, optical devices, and so on.

Herein, we report the synthesis of Cu(OH)2 nanobelts with high yield at low cost by a simple aqueous solution reaction. The Cu(OH)2-FTO electrode was then fabricated by a facile electrophoresis deposition method with the as-prepared Cu(OH)2 nanobelts, which require no binding agents. By subsequent heat treatment at 300 °C for 2 h, the Cu(OH)2-FTO electrode was converted to the CuO-FTO electrode. The investigation of electrocatalysis of the Cu(OH)2-FTO and CuO-FTO electrodes for water oxidation was conducted in a 0.2 M phosphate buffer solution at pH 12. The CuO-FTO electrode can catalyze water oxidation with an impressive onset overpotential of 370 mV and an overpotential of 500 mV for a current density of 1 mA/cm2 with a low Tafel slope of 57 mV/dec. This facile fabrication strategy is appealing for realizing the practical application of Cu-based electrocatalysts for water oxidation and is expected to be extended to prepare other heterocatalyst electrodes.

The valence states, the distribution of Co ions, and defect structures in the Co-doped ITO films with Co concentrations of 5–13 at.% were examined by X-ray absorption spectroscopy (XAS) at Co, K, and L-edges. The structural analyses and ab initio calculations reveal that the Co atoms are substantially incorporated into the ITO lattice and form cobalt–vacancy complexes, while partial formation of Co0 species is observed for all the films. The analyses of Co–K edge XAS reveal that the Co–O bond length RCo–O is shortened and the corresponding Debye–Waller factor (σ2) obviously increases with Co doping, implying the relaxation of oxygen environment around the substitutional Co ions. The qualitative fitting of Co L3-edge XAS further confirms the coexistence of Co0 and Co2+ in the films. The Co atoms mainly occupy the substitutional sites of In2O3 lattices with the metallic Co clusters being about 20–43 at.% for the 5, 7, and 8.5 at.% Co-doped ITO films. However, a significant fraction (∼57 at.%) of metallic Co clusters is found in the 13 at.% Co-doped ITO film.

The use of the advanced manufacturing technique of strain annealing for nanocomposite magnetic ribbons enables control of relative permeabilities and spatially dependent permeability profiles. Tuned permeability profiles enable enhanced control of the magnetic flux throughout magnetic cores, including the concentration or dispersion of the magnetic flux over specific regions. Due to the correlation between local core losses and temperature rises with the local magnetic flux, these profiles can be tuned at the component level for improved losses and reduced steady-state temperatures. We present analytical models for a number of assumed permeability profiles. This work shows significant reductions in the peak temperature rise with overall core losses impacted to a lesser extent. Controlled strain annealing profiles can also adjust the location of hotspots within a component for optimal cooling schemes. As a result, magnetic designs can have improved performance for a range of potential operating conditions.

Eutectic Al–13% Si alloys are widely used in automotive components, such as pistons and cylinder heads. Recently, the demand on the performance of piston alloys at high temperature is greatly increased to enhance the engine efficiency and to reduce exhaust emission. In the present work, Mn was added to strengthen the aluminum matrix via the formation of thermally stable dispersoids. The evolution of dispersoids during heat treatment and their influence on elevated-temperature properties were studied. The results showed that the as-cast microstructures in the experimental alloys without/with Mn addition were similar, which were composed of eutectic Si, primary Mg2Si, Al–Fe–Ni, Al–Cu–Ni, and π-Al–Mg–Fe–Si intermetallic phases. In the alloy with Mn addition, a number of α-Al(Mn,Fe)Si dispersoids started to form after a heat treatment at 425 °C for 24 h and reached the peak condition at 500 °C for 6 h, resulting in a remarkable increase of the microhardness at room temperature and the improvement in the yield strength and creep resistance at 300 °C. As a complementary strengthening mechanism, the dispersoid strengthening in the aluminum matrix provides a novel approach to improve the elevated-temperature properties of Al–Si piston alloys.

Two α-alumina + YSZ samples were prepared by sintering for 3 h one at 1500 °C and the other at 1700 °C. The samples were then converted to Na-β″-alumina + YSZ by vapor phase conversion. Characterization techniques such as X-ray diffraction, scanning electron microscopy, and electrochemical impedance spectroscopy in addition to dimensional geometrical changes reveal the evolution of slight anisotropy in these samples during conversion. This results in an electrical conductivity anisotropy factor of about 5.5 and 1.8 for samples sintered at 1500 °C and 1700 °C, respectively. In all samples, the higher ionic conductivity was measured across the sample thickness as opposed to parallel to the disc faces. The ionic conductivity measurements show the conductivity of about 0.15 S/cm and 0.07 S/cm at 300 °C for samples sintered at 1500 °C and 1700 °C, respectively. The larger anisotropy in samples sintered at 1500 °C is explained by the higher aspect ratio of grains in this sample and by different Na concentrations.

Ti–47Al samples with a diameter of 18 mm are obtained by electromagnetic confinement and directional solidification at different growth velocities. Controlled by a Ti–43Al–3Si seed, the α grains are aligned well and the parallel lamellar microstructure is obtained at the growth velocity of 10 μm/s. With the growth velocity increases to 25 and 50 μm/s, although the lamellar microstructures are still aligned well in the initial transition stage, the lamellar alignment fails due to the nucleation and growth of new β and α grains and then the inclined and perpendicular lamellar microstructures form eventually. The room temperature tensile properties of the different lamellar microstructures are measured and the results show that the desired lamellar microstructure has a tensile strength of 693 MPa and an elongation of 10.0% simultaneously. They are the maximum values that have been reported in binary γ-TiAl alloys so far and are far higher than those of the other two types of lamellar microstructures. The fracture behaviors of the lamellar microstructures are checked by scanning electron microscopy and transmission electron microscopy. Two models are used to illustrate the fracture mechanism of the different lamellar structures.

TiB2 particulates were formed in situ in an aluminum matrix via chemical reactions between an aluminum melt and the mixture of K2TiF6 and KBF4 salts. Different effects of Sc addition on the formation of the TiB2 particulates were revealed depending on the participation of Sc at different stages of the formation of the particulates. The metal–salt reactions resulted in boride layers along the α-Al grain boundaries in the presence of Sc, while the addition of Sc after the metal–salt reactions broke up the boride layers improving the dispersion of the TiB2 particulates to a limited degree. Sc promoted the growth of the TiB2 particulates, resulting in the coarsening of TiB2 particulates. The participation of Sc in the formation of TiB2 particulates altered the coarsening of the TiB2 particulates, resulting in different morphologies of the TiB2 particulates depending on the participation of Sc in the formation of the TiB2 particulates at different stages.

To investigate the effects of adding Au nanoparticles (AuNPs) to TiO2 films on the crystallization, phase transformation, and photocatalysis, films of both TiO2 and TiO2 embedded with AuNPs (Au–TiO2) with various characteristics were prepared by using the dip-coating method with preheating and post-heating treatments. The AuNPs acted as anatase nucleation agents and crystallized a lot of small anatase crystals with sizes of tens of nanometers, which suppressed the growth of anatase crystals that are large enough for them to transform into rutile crystals, resulting in repression of the transformation from anatase into rutile. The AuNPs affected the progress of the photocatalytic and adsorption reactions, resulting in improved photocatalytic activity. Of all the films we tested, the Au–TiO2 film preheated at 400 °C and post-heated at 400 °C (AT400-400), which consisted of small anatase crystals with high covalent character and high crystallinity, contained dispersed AuNPs with the smallest average crystallite size and showed the highest photocatalytic activity. This high activity resulted from the high reaction rate constants for adsorption and photocatalysis.

We present a side-by-side comparison of the stability of three different types of benchmark solution-processed organic solar cells (OSCs), subject to thermal cycling stress conditions. We study the in situ performance during 5 complete thermal cycles between −100 and 80 °C and find that all the device types investigated exhibit superior stability, albeit with a distinct temperature dependence of device efficiency. After applying a much harsher condition of 50 thermal cycles, we further affirm the robustness of the OSC against thermal cycling stress. Our results suggest that OSCs could be a promising candidate for applications with large variations and rapid change in the operating temperature such as outer space applications. Also, a substantial difference in the efficiency drops from high to low temperature for different systems is observed. It suggests that maintaining optimum performance with minimal variations with operating temperature is a key challenge to be addressed for such photovoltaic applications.