Cerium oxide nanoparticles (CNPs) are of significant interest to the scientific community due to their widespread applications in a variety of fields. It is proposed that size-dependent variations in the extent of Ce3+ and Ce4+ oxidation states of cerium in CNPs determine the performance of CNPs in application environments. To obtain greater molecular and structural understanding of chemical state transformations previously reported for ceria of ≈3 nm nanoparticles (CNPs) in response to changing ambient conditions, micro-XRD and Raman measurements were carried out for various solution conditions. The particles were observed to undergo a reversible transformation from a defective ceria structure to a non-ceria amorphous oxyhydroxide/peroxide phase in response to the addition of 30% hydrogen peroxide. For CNPs made up of ∼8 nm crystallites, a partial transformation was observed, and no transformation was observed for CNPs made up of ∼40 nm crystallites. This observation of differences in size-dependent transition behavior may help explain the benefits of using smaller CNPs in applications requiring regenerative property.

Constant strain rate nanoindentation is a popular technique for probing the local mechanical properties of materials but is usually restricted to strain rates ≤0.1 s−1. Faster indentation potentially results in an overestimation of the hardness because of the plasticity error associated with the continuous stiffness measurement (CSM) method. This can have significant consequences in some applications, such as the measurement of strain rate sensitivity. The experimental strain rate range can be extended by increasing the harmonic frequency of the CSM oscillation. However, with commercial instruments, this is achievable only by identifying higher CSM frequencies at which the testing system is dynamically well behaved. Using these principles, a commercial system operated at the unusually high harmonic frequency of 1570 Hz was successfully used to characterize of the strain rate sensitivity of a Zn22Al superplastic alloy at strain rates up to 1 s−1, i.e., an order of magnitude higher than with standard methods.

A novel microtensile setup was developed to overcome typical issues encountered in small-scale testing, particularly sample fabrication, sample handling, and misalignment. The system features a silicon (Si) gripper, which is able to self-align with the specimen main axis. Finite element simulations were employed to optimize the microtensile specimen geometry and to mechanically characterize the system. Specimens were prepared using focused ion beam milling, while reactive ion etching was employed to produce the grippers. The system was calibrated using single-crystal (100) Si specimens. The strength asymmetry of brittle crystals was investigated on the example of gallium arsenide (GaAs). Microtensile GaAs specimens and square micropillars sharing lowest dimensions of 1.70 ± 0.19 µm were tested along the [001] crystallographic orientation. Micropillars underwent plastic deformation via twinning in {111} planes and exhibited yield stress of 2.60 ± 0.14 GPa. The tensile experiment showed brittle failure at 1.86 ± 0.17 GPa associated with complex fracture surfaces and no measurable dislocation activity.

Iron sulfides have attracted much interests for their potential as anode materials in energy storage devices in view of their low costs, and environmentally benign and high theoretical capacities. Among them, Fe1−xS is relatively rarely investigated. In this work, Fe1−xS@rGO has been synthesized using a facile in situ hydrothermal method. After wrapped by rGO, the morphology of Fe1−xS particles changes from hexagonal flakes to irregular particles with much smaller sizes. As the anode material for lithium ion batteries, Fe1−xS@rGO exhibits excellent lithium storage ability. It can deliver an initial discharge capacity of 1575.5 mA h/g in the potential window of 0.005–3 V, and a reversible capacity of 907.8 mA h/g can be maintained after 200 cycles at 100 mA/g. Its improved electrochemical performance can be attributed to the effect of enhanced contact area and shortened Li+ ion transport distance because of rGO’s contribution.

Pressureless sintering is a simple and traditional processing method for producing dense ceramics by heating at a high temperature. The introduction of water vapor into this atmosphere can decrease the sintering temperature and accelerate grain growth. In this work, we report water vapor-assisted sintering of submicrometer titania (TiO2) powder. Dense TiO2 pellets with a relative density over 99% were obtained in 0.1 MPa of water vapor at a lower temperature than in air. The submicrometer particles (∼0.5 µm) grew to an average size of 181 µm after sintering at 1400 °C in water vapor, whereas the particle size obtained by sintering in air was 51 µm. Furthermore, we verified the incorporation of oxygen from water vapor into TiO2 by using isotopically labeled water (H218O). Water vapor-assisted sintering can potentially lead to the production of single crystal-like ceramics by a pressureless route and without any additives.

This study reports the fabrication of high mass loading (32 mg/cm2) electrodes of niobium pentoxide (Nb2O5) nanoparticles and carbon nanotubes (CNTs) using a facile procedure. The as-obtained Nb2O5 nanoparticles by microwave-assisted hydrothermal synthesis presented pseudohexagonal (TT) phase, and when exposed to the thermal treatment, the Nb2O5 nanoparticles changed to orthorhombic (T) phase. Distinct morphologies were obtained, which exhibited a specific surface area of 216 m2/g and 47 m2/g to pseudohexagonal and orthorhombic phases, respectively. Cyclic voltammetry and electrochemical impedance spectroscopy techniques were performed in a three-electrode system using 1 M Li2SO4 as electrolyte with a potential window of 0–0.9 V (versus standard calomel electrode). Both materials showed capacitive behavior with a specific capacitance of 0.11 F/cm2 and 0.09 F/cm2 to nanocomposites CNT + TT-Nb2O5 and CNT + T-Nb2O5 at 2 mV/s, respectively. Thus, an efficient, simple, and promising process to produce electrodes for supercapacitors was demonstrated.

Laves phase plays a positive role in improving the strength of high-entropy alloys (HEAs); Nb and Ti elements have potential to promote Laves phase formation in some HEAs. For improving the strength of the face-centered cubic (FCC) CoCrFeMnNi HEA, a series of (CoCrFeMnNi)100−xNbx (atomic ratio: x = 0, 4, 8, 12, 16) and (CoCrFeMnNi)100−xTix (atomic ratio: x = 0, 2, 4, 6, 8, 12) HEAs were prepared by melting. The effects of Nb and Ti on the microstructure evolution and compressive properties of the CoCrFeMnNi HEAs were investigated. For (CoCrFeMnNi)100−xNbx HEAs, the second-phase (Laves and σ phase) volume fraction increased from 0 to 42%. The yield strength also increased gradually from 202 to 1010 MPa. However, the fracture strain decreased from 60% (no fracture) to 12% with increasing Nb content. For (CoCrFeMnNi)100−xTix HEAs, the yield strength increased from 202 to 1322 MPa. The Laves phase volume fraction also increased from 0 to 27%. However, the fracture strain decreased from 60% (no fracture) to 7.5% with increasing Ti content. Addition of Nb and Ti has a good effect on improving the strength of FCC CoCrFeMnNi HEA.

GH3536 alloy is one of the high-temperature nickel-based alloys and widely applied in aviation and aerospace industries. In this study, a combination of experiment and simulation is proposed to study the effect of processing parameters on the selective laser melting (SLM) of GH3536 powder. It is concluded that the relationship between density and laser input energy during SLM complies with a quadratic function and presents an inverted U-shaped distribution. By fitting density and input power to a quadratic polynomial, the optimal laser input energy during SLM of GH3536 alloy can be obtained. The result shows that using 275 W laser power and 960 mm/s scanning speed, the SLM GH3536 specimens can reach the maximum density. This experimental result is consistent with the simulation result obtained by analyzing molten pool dimension. Furthermore, a full process energy prediction diagram for SLM GH3536 alloy based on the simulated molten pool depth and width is proposed. The result shows that it provides an innovative and efficient method for the selection of processing parameters during SLM of GH3536 powder.

Diffusion barrier materials play an important role in both structure reliability and performance stability of thermoelectric (TE) modules. Preferred barrier materials are screened out from various candidates by comparing the interdiffusion at the barrier material/TE substrate interfaces. Traditionally, for each barrier material candidate, complicated fabrication processing of TE elements (electrode/barrier material/TE material) must be finished to obtain relative interfaces, which makes the screening costly and time consuming. In this article, using a high-throughput strategy, we developed a high-efficiency screening method of barrier materials. By cosintering the mixture of TE substrate material and various barrier material candidates simply following the TE material’s sintering parameters, various microinterfaces were integrated to one single sample. This enables parallel aging and microstructure characterization of different interfaces, and preferred barrier materials can be swiftly screened out. As a result, it makes the design and optimization of TE modules much more efficient and economical.

A major limitation in nanoindentation analysis techniques is the inability to accurately quantify pile-up/sink-in around indentations. In this work, the contact area during indentation is determined simultaneously using both contact mechanical models and direct in situ observation in the scanning electron microscope. The pile-up around indentations in materials with low H/E ratios (nanocrystalline nickel and ultrafine-grained aluminum) and the sink-in around a material with a high H/E ratio (fused silica) were quantified and compared to existing indentation analyses. The in situ projected contact area measured by Scanning Electron Microscopy using a cube-corner tip differs significantly from the classical models for materials with low H/E modulus ratio. Using a Berkovich tip, the in situ contact area is in good agreement with the contact model suggested by Loubet et al. for materials with low H/E ratio and in good agreement with the Oliver and Pharr model for materials with high H/E ratio.

AlMgB14–TiB2 ceramic was successfully brazed to TC4 alloy with inactive AgCu filler alloy. X-ray diffractometer, SEM, and energy-dispersive spectrometer were used to study interfacial microstructure and shear strength of the joints under different brazing temperatures. The results indicated that the typical microstructure of the TC4/AlMgB14–TiB2 joint was TC4/Ti(s.s) + Ti2Cu/Ti2Cu/TiCu/TiCu2Al/Ag(s.s) + Cu(s.s)/TiB whiskers/TiB2 reaction layer/AMBT. By increasing the brazing temperature, the thickness of the TC4 diffusion layer was improved, whereas that of the brazing seam decreased remarkably. When the brazing temperature was increased to 880 °C, the brazing seam was composed of Ti–Cu intermetallic Ag(s.s) with a few Cu(s.s), TiCu2Al distributed. Meanwhile, the formation of a continuous TiB2 reaction layer at the interface of the AMBT and brazing filler facilitated the improvement of joint shear strength. The joint with the maximum shear strength of 46.7 MPa was obtained while brazing at 880 °C for 10 min.

Composites of 0–20 vol% Ti-coated cBN (cBN@Ti) particles dispersed in WC–Ni were densified by spark plasma sintering under 50 MPa at 1300 °C. The cBN particles were distributed homogeneously with a Ti-rich interfacial layer between the cBN particles and WC–Ni matrix. Increasing cBN@Ti to 20 vol% decreased the sample densification, but all the composites were still >97.5% dense. The Vickers hardness and flexural strength initially increased and then decreased, reaching the maximum values of 1820 HV10 with 15 vol% cBN@Ti and 1500 MPa with 5 vol% cBN@Ti, respectively, whereas the fracture toughness KIC gradually increased from 8 to 13 MPa m1/2. For cutting rocks, the wear significantly decreased with 5–15 vol% cBN@Ti but increased with 20 vol% cBN@Ti because of cBN particles pull-out.

High-entropy alloys (HEAs) have been proven to exhibit superior structural properties from cryogenic to high temperatures, demonstrating their structural stability against the formation of complex intermetallic phases or compounds as major fractions. These characteristics can find applications in nuclear and aerospace sectors as structural materials. As the dissimilar joint design is necessary for such applications, an attempt is made to fabricate the dissimilar transition joint between Al0.1CoCrFeNi-HEA and AISI304 austenitic stainless steel by conventional tungsten inert gas welding. Microstructural characterization by SEM and EBSD clearly revealed the evolution of columnar dendritic structures from the interfaces and their transformation to equiaxed dendritic grains as they reach the weld center. Also, considerable grain coarsening was observed in the heat-affected zone of the HEA. The tensile test results depict that the dissimilar weld joint showed significantly higher tensile strength (590 MPa) than the HEA (327 MPa), making it suitable for structural applications.

Twenty one years ago, the discovery of the giant magnetocaloric effect (GMCE) at room temperature completely revolutionized the magnetocaloric materials field demonstrating the potential of magnetic refrigeration at room temperature and setting the beginning of a race for the best magnetocaloric material. Since then, hundreds of different bulk magnetic materials were studied in detail; however, only a small set of these exhibit GMCE. In the last ten years, the broad interest on these materials leads to the extension of their study to the micro- and nanoscale. In this review, we highlight the main motivations for exploring the size-reduction both from the technological and the purely scientific point of view and stress the general consequences on the magnetic and magnetocaloric properties. The emergence of different underlying mechanisms driving these effects will be identified with particular emphasis for the set of materials presenting GMCE.

Cast tungsten carbide is widely used to reinforce iron or steel substrate surface composites to meet the demands of harsh wear environments due to its extremely high hardness and excellent wettability with molten steel. Cast tungsten carbide particle/steel matrix surface composites have demonstrated great potential development in applications under the abrasive working condition. The thermal shock test was used to investigate the fatigue behavior of the composites fabricated by vacuum evaporative pattern casting technique at different temperatures. At elevated temperatures, the fatigue behavior of the composites was influenced by the oxidation of tungsten carbide, producing WO3. Thermodynamic calculations showed that the W2C in the tungsten carbide particle was oxidized at an initial temperature of approximately 570 °C. The relationship between oxidation and thermal fatigue crack growth was investigated, and the results suggested that oxidation would become more significant with increasing thermal shock temperature. These findings provide a valuable guide for understanding and designing particle/steel substrate surface composites.

In this investigation, we have reported the alloying behavior, phase evolution, and thermal stability of equiatomic AlCoCrFeNiTi high-entropy alloy (HEA). The 40 h milled powder shows good chemical homogeneity with agglomerated particles varying in the range of ∼3–18 μm. The formation of a nanostructured single-phase BCC (a = 2.85 ± 0.01 Å) was observed along with the minor tungsten carbide (WC) phase that formed due to contamination during milling. Thermal stability of the alloy has been studied using dynamic differential scanning calorimetry (DSC) thermogram and in situ X-ray diffraction. It has been found that this HEA is stable up to 600 °C (873 K). Consolidated samples at 1000 °C (1273 K) showed the transformation of body centered cubic (BCC) phase into the B2 (a = 2.87 ± 0.03 Å) phase co-existing with minor hexagonal WC (a = 2.90 Å, c = 2.83 Å) phase.

ZL104 alloy foam and ZL104 alloy/aluminum fiber composite foams with a porosity of 71–90% were prepared by an infiltration casting method. The pore structure and the sound absorption properties of these two kinds of foams were studied. The results show that fibers partially embedded in the porous pore walls and partially extending out of the pore in the composite foams. The sound absorption coefficient of the foams has a sound absorption peak and a sound absorption trough with increasing frequency. The fiber composite foam possesses better sound absorption properties compared with the alloy foam. As porosity, fiber diameter, and fiber content increases, the average sound absorption coefficient of the composite foam first increases and then decreases. The average sound absorption coefficient (0.88) of the composite foam with a fiber content of 5 vol%, a fiber diameter of 0.1 mm, and a porosity of 82% increased 10% compared with that of the alloy foam. The surface roughness and specific surface area of the foam increase after fiber compounding, and the sound wave drives the fibers to vibrate to enlarge the consumption of sound energy.