Advanced alloys with both high strength and ductility are highly desirable for a wide range of engineering applications. Conventional alloy design strategies based on the single-principle element are approaching their limits in further optimization of their performances. Precipitation-hardened high-entropy alloys (HEAs), especially those strengthened by coherent L12-nanoparticles, have received considerable interest in recent years, enabling a new space for the development of advanced structural materials with superior mechanical properties. In this review, we highlight recent important advances of the newly developed L12-strengthened HEAs, including the aspects of computation-aided alloy design, unique properties, atomic-level characterization, phase evolution, and stability. In particular, we focus our attention on elucidating fundamental scientific issues involving the alloying effects, precipitation behaviors, mechanical performances, and the corresponding deformation mechanisms, all of which provide a comprehensive metallurgical understanding and guidance for the design of this new class of HEAs. Finally, future research directions and prospects are also critically assessed.

Nanosize SiCp (n-SiCp) reinforced Mg–9Al matrix composites (Mg–9Al–xSiC, x = 2.5, 5, 7.5, 10 wt%) with nearly full densification are fabricated by the semisolid powder hot pressing technique assisted with ultrasonic. The effect of SiC nanoparticle contents on microstructures and mechanical properties of the composites is systematically investigated. Grain size and density of Mg–9Al–xSiC composites and morphology of bonding interfacial between the n-SiCp and matrix are found to be greatly dependent on the n-SiCp contents, resulting in the strength and ductility of the composites increase first and then decrease as the increase of n-SiCp contents. As the SiCp content increasing to 7.5 wt%, superior mechanical properties with the yield strength of 191 MPa, ultimate tensile strength of 248 MPa, and elongation to failure of 5.3% are achieved. The improved mechanical properties could be attributed to grain boundary strengthening, Orowan strengthening, and load transfer strengthening.

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.

Photovoltaic organic semiconductors are emerging in many therapeutic applications, including drug delivery and optical control of cell function. However, for their safe use the possible concomitant elicitation of undesired responses in target cells need to be carefully evaluated. Here we describe molecular responses activated by semiconducting polymer nanoparticles based on poly(3-hexyl)thiophene (P3HT) in the model Hydra vulgaris, previously shown to respond to P3HT-NP photostimulation and showed a decrease in the total antioxidant capacity and an increase in the DNA and protein oxidation levels, paving the way to a novel use of photovoltaic devices to control intracellular redox equilibrium.

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.

This work is part of the interlaboratory collaboration to study the stability of organic solar cells containing PCDTBT polymer as a donor material. The varieties of the OPV devices with different device architectures, electrode materials, encapsulation, and device dimensions were prepared by seven research laboratories. Sets of identical devices were aged according to four different protocols: shelf lifetime, laboratory weathering under simulated illumination at ambient temperature, laboratory weathering under simulated illumination, and elevated temperature (65 °C) and daylight outdoor weathering under sunlight. The results generated in this study allow us to outline several general conclusions related to PCDTBT-based bulk heterojunction (BHJ) solar cells. The results herein reported can be considered as practical guidance for the realization of stabilization approaches in BHJ solar cells containing PCDTBT.

Monosized spherical Cu–20% Sn (wt%) alloy particles with diameter ranging from 70.6 to 334.0 μm were prepared by the pulsated orifice ejection method (termed “POEM”). Fully dense without pores and bulk inclusions, the cross-sectional micrographs of the spherical alloy particles indicate an even distribution of Cu and Sn. These spherical Cu–Sn alloy particles exhibit a good spherical shape and a narrow size distribution, suggesting that the liquid Cu–Sn alloy can completely break the balance between the surface tension and the liquid static pressure in the crucible micropores and accurately control the volume of the droplets. Furthermore, the cooling rate of spherical Cu–20% Sn alloy particles is estimated by a Newton’s cooling model. The cooling rate of the Cu–20% Sn alloy particle decreases gradually with the particle diameter increasing. Smaller particles have higher cooling rates and when the particle diameter is less than 70 μm, the cooling rate of particles can reach more than 3.3 × 104 K/s. The secondary dendrite arm spacing has strong dependence on particle diameter which increases gradually with the increase of particle diameter. The results demonstrate that POEM is an effective route for fabrication of high-quality monosized Cu–20% Sn alloy particles.

The elastic properties and solid-solution strengthening (SSS) of the binary Ni–Co and Ni–Cr, and ternary Ni–Co–Cr alloys were investigated by the first-principles method. The results show that both Co and Cr increase lattice parameters of the binary alloys linearly. However, nonlinearity is found in compositional dependence of lattice parameters in the ternary Ni–Co–Cr alloys, that is, Co increases but decreases the lattice parameter at low and high Cr concentrations, respectively. Co increases the bulk, shear, and Young’s moduli (B, G, and E), while Cr increases B but decreases G and E in the binary alloys. In the ternary Ni–Co–Cr alloys, G and E have a similar compositional dependence to those in the binary alloys, except for B. Based on the Labusch model, the SSS parameter of Ni–Cr is larger than that of Ni–Co. The SSS effect increases significantly with Cr addition, especially at low Co concentrations in the ternary Ni–Co–Cr alloys. Meanwhile, it increases mildly with Co addition at low Cr concentrations but decreases with Co addition at high Cr concentrations.

In this investigation, an electron beam melting-processed γ-TiAl alloy (Ti–48Al–2Cr–2Nb, at.%) was oxidized in air to improve its in vitro tribological, electrochemical, and biocompatibility properties. The γ-TiAl alloy samples were oxidized at 400, 600, and 800 °C for 1 and 4 h. The oxidized layer thickness, composition, and surface morphology found to change with oxidation temperature. The oxidation thickness varied between 1.29 ± 0.2 and 2.18 ± 0.2 μm. The primary oxides on the surface were Al2O3 and TiO2 with minor concentrations of Cr2O3, Nb2O5, and nitrides of Ti. The surface hardness of the alloy increased by 1.7-fold with increasing temperature from 400 to 800 °C with 1 h soaking, and at 4 h, the maximum hardness was 12.26 GPa. The high hardness of the oxidized γ-TiAl alloy resulted in two orders of magnitude lower wear rate than the bare γ-TiAl alloy. Oxidation at 800 °C for 4 h resulted in significant reduction in corrosion current and no passivity breakdown was observed. In vitro cell culture experiments, using mouse preosteoblast cells, revealed high cell density on the oxidized γ-TiAl alloy, suggesting its enhanced cell proliferation compared to the bare γ-TiAl alloy and CP-Ti.

Recent advances in the additive manufacturing technology now enable fused filament fabrication of polyetheretherketone (PEEK). A standardized lumbar fusion cage design was 3D printed with different speeds of the printhead nozzle to investigate whether 3D-printed PEEK cages exhibit sufficient material properties for lumbar fusion applications. It was observed that the compressive and shear strength of the 3D-printed cages were 63–71% of the machined cages, whereas the torsion strength was 92%. The printing speed is an important printing parameter for 3D-printed PEEK, which resulted in up to 20% porosity at the highest speed of 3000 mm/min, leading to reduced cage strength. Printing speeds below 1500 mm/min can be chosen as the optimal printing speed for this printer to reduce the printing time while maintaining strength. The crystallinity of printed PEEK did not differ significantly from the as-machined PEEK cages from extruded rods, indicating that the processing provides similar microstructure.

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.

High entropy alloys are multicomponent alloys, which consist of five or more elements in equiatomic or nearly equiatomic concentrations. These materials are hypothesized to show significantly decreased self-diffusivities. For the first time, diffusion of all constituent elements in equiatomic CoCrFeNi and CoCrFeMnNi single crystals and additionally solute diffusion of Mn in the quaternary alloy is investigated using the radiotracer technique, thereby the tracer diffusion coefficients of 57Co, 51Cr, 59Fe, 54Mn, and 63Ni are determined at a temperature of 1373 K. The components are characterized by significantly different diffusion rates, with Mn being the fastest element and Ni and Co being the slowest ones. Furthermore, solute diffusion of Cu in the CoCrFeNi single crystal is investigated in the temperature range of 973–1173 K using the 64Cu isotope. In the quaternary alloy, Cu is found to be a fast diffuser at the moderate temperatures below 1273 K and its diffusion rate follows the Arrhenius law with an activation enthalpy of about 149 kJ/mol.

TiO2 nanomaterials with platelet or nanosheet morphologies can offer improved properties for photocatalytic applications, but established methods to produce them typically require structure-directing agents since anatase-phase TiO2 does not have a layered structure. In the present work, the preparation of TiO2 nanosheets by the chemical oxidation of TiS2 nanosheets is demonstrated. Electrochemical exfoliation of bulk TiS2 into TiS2 nanosheets, followed by the hydrothermal treatment at 180 °C for 14 h is performed. The results show that polycrystalline TiO2 nanosheets with the anatase structure are formed, and that the nanosheet morphology can still be maintained after the hydrothermal treatment. The TiO2 nanosheets show good photocatalytic activity for the degradation of methylene blue, but the performance is negatively affected by the residual carbon black that was needed in the TiS2 electrode to enable electrochemical exfoliation. These results show that conversion of TiS2 nanosheets to TiO2 nanosheets is a promising synthetic strategy but highlights how the interfacial properties of the obtained materials could be affected by ancillary components in the preparation method.

One of the key aims of the OSCAR project (Optical Sensors based on CARbon-materials)—in the framework of the REXUS/BEXUS program—was to explore the use of organic-based solar cells for (aero)space applications through the in-flight investigation of devices’ performance during a stratospheric balloon flight. Next to the in-flight experiments, complementary lab stability assessment tests were performed. In this contribution, both the in-flight and lab experimental methodology and the corresponding technical aspects will be discussed in detail. Furthermore, attention will be paid to the issues of packaging and radiation. The importance of the OSCAR-balloon experiment is not only that it has demonstrated for the first time the use of organic-based solar cells in (aero)space conditions but also that it can be considered as the pioneering start of specific stability assessment methodologies for organic-based solar cells for (aero)space applications.

We report on a novel processing route to prepare La0.8Ce0.2(Fe0.95Co0.05)11.8Si1.2/Cu bulk composites by low-temperature hot pressing. With increasing copper content, the compressive strength of the composites first decrease and then increase owing to the buffering effect of copper, but the magnetocaloric effect reduces to some extent. Copper addition improves the thermal conductivity of the composites, which compensates for the decrease in thermal conductivity due to porosity. A relatively large entropy change of 5.75–7.19 J/(kg K) at 2 T near the Curie temperature (249 K), good thermal conductivity of 7.51–15.55 W/(m·K), and improved compressive strength of 151.1–248.0 MPa make these composites attractive magnetic refrigeration materials.

Bismuth vanadate (BiVO4) is regarded as a viable material for water oxidation due to various benefits such as visible light absorption, low production cost, and resistance to photocorrosion. Recently, numerous attempts have been adopted to improve the performance of BiVO4. In this work, we highlight the important strategies that have been made for improving the performance of the photoanode material, such as fabricating nanostructured electrode, controlling reacting facet, stacking with other materials, utilizing plasmonics, loading co-catalyst, and controlling the interfacial band bending with ferroelectrics. Taking advantage of the strategies, highly efficient BiVO4 photoelectrodes could be demonstrated. Finally, we discuss the perspective of BiVO4-based photoanodes.

In in vitro separate compartment model of neuronal cells and extracellular iron oxide nanoparticles (IONs)–amyloid complexes, a traversing proton-induced Coulomb nanoradiator effect (CNR) was found to break up the ION–amyloid fibrils and to induce redox changes in the IONs. We found that the CNR effect caused the conversion of redox-active iron (II) into redox-inactive iron (III) as well as the disruption of the ION–amyloid fibrils without significantly damaging normal neuronal cells. Our observations suggest a non-invasive redox inactivation and β-amyloidolyis-based therapy of neurotoxic Aβ plaque involving a traversing proton Coulomb nanochelator that would not substantially impact normal neuronal cells.