The classical dynamic recrystallization (DRX) kinetics models, such as Avrami equation, are often used to describe the DRX behaviors of alloys. However, it is found that the classical DRX kinetics models cannot be directly applied to evaluate DRX volume fractions under inconstant deformation conditions, such as at fluctuant deformation temperature and strain rate. It obviously limits their application in the practical industrial production. Therefore, an improved DRX kinetics model is proposed based on the hypothesis that the derivatives of DRX volume fraction with respect to strain only depends on the current deformation temperature, strain rate, and DRX volume fraction. To verify the improved DRX kinetics model, the hot compressive tests in which the strain rate is inconstant are carried out on a solution-treated Ni-based superalloy. Experimental results indicate that the improved DRX kinetics model can well predict the DRX behavior under inconstant deformation conditions.

Glasses doped with rare earth elements (lanthanide series) are the most popular materials used in upconversion devices. The main aspect to develop these devices is to find suitable host materials for rare earth ions. The host material should have a high transmission of the upconverted photons, high thermal stability, good mechanical properties, low price, and easy to manufacture and shaping. Present work is concerned with studying the mechanical and structural properties for the oxide glass system doped with rare earth metal (erbium oxide, Er2O3). Ultrasonic pulse-echo technique is used to measure the sound velocities in the glass system (30%B2O3·30%Bi2O3·20%Li2O·10%BaO·10%Pb3O4·xEr2O3), (x = 0, 0.5, 1, 2, 3, 4) mol%. Ultrasound velocities (longitudinal and shear) are measured as a function of the Er2O3 content at a frequency of 4 MHz for longitudinal wave and 2 MHz for the shear wave at a temperature of 300 K. The elastic moduli and some physical parameters, such as Debye temperature, coordination number, and compressibility, were evaluated. Furthermore, the dimensionality of the glass network has been calculated in terms of the d ratio which equals G/B ratio. These parameters beside the x-ray diffraction, differential scanning calorimetry, and Fourier Transform Infrared (FTIR) measurements throw more light on the structure of the glass system. The measurements in this study exhibit remarkable anomalous changes in the network structure of the investigated glass doped with Er2O3.

In this article, we have explored the interface states that form between the channel of a monolayer MoS2 transistor and a high-κ gate dielectric. These interface states lead to large hysteresis in the drain current versus gate voltage characteristic or the so-called transfer characteristic of the transistor. By applying carefully designed pulses to the gate of the transistor, we show that it is possible to both understand the nature of the interface states and minimize the hysteresis, so that the transfer characteristic can be reliably used for subsequent extraction of material parameters such as mobility.

A novel and efficient photocatalyst of three dimensional (3D) Ba5Ta4O15 flower-like microsphere was synthesized via an alkaline etch under hydrothermal condition. The influence of reaction temperature, reaction time, and alkaline concentration on the morphology were investigated for the 3D Ba5Ta4O15 flower-like microsphere photocatalyst. The morphology and structure of the 3D Ba5Ta4O15 were characterized using x-ray diffraction, scanning electron microscope, transmission electron microscope, and high-resolution transmission electron microscopy. The results show that the elegant flower-like structure was composed of Ba5Ta4O15 nanosheets. The 3D Ba5Ta4O15 flower-like microspheres show a higher photocatalytic activity in the degradation of methylene blue under ultraviolet light than the bulk Ba5Ta4O15 microcrystal by the solid-state-reacted synthesized. The UV–vis diffuse reflectance spectra, photoluminescence spectra, volumetric adsorption method, and photocurrent response of the Ba5Ta4O15 photocatalyst were characterized indicated that the higher photocatalytic activity of flower-like Ba5Ta4O15 microspheres was due to the high crystallinity, large surface area and the effective charge separation.

Microalloying refers to the addition of a small concentration of an alloying element to tune the properties of the parent alloy. Microalloying technology enables to control the glass formation and the mechanical properties of bulk metallic glasses (BMGs). This manuscript presents a comprehensive review on recent developments and breakthroughs in the field of microalloying for tuning the properties of BMGs and composites with focus on the results. The ability of multiple element co-addition to optimize the glass formation and the importance of future alloy developments have been highlighted. Proper microalloying can be used to tailor not only the mechanical properties of the amorphous phase but also those of the crystalline phase, which opens up the possibility for tuning the mechanical performance at different length scales. The effectiveness in controlling the mechanical performance through microalloying was shown to greatly depend on the alloy composition and closeness to the critical amorphous diameter. A tentative outlook commenting the potential and challenges of this exciting field of research is also presented.

Red-emitting (La,Eu)2O2SO4 phosphors have been successfully prepared using the layered hydroxide of (La,Eu)2(OH)4SO4·2H2O as the precursor. The precursor compound was firstly crystallized via hydrothermal reaction (100 °C and pH = 9.0) as well-dispersed nanoplates, followed by dehydration and dehydroxylation in the 400–1200 °C temperature range in ambient air to yield (La,Eu)2O2SO4. The phosphors show intense red emissions originated from the f–f transitions of Eu3+, dominantly peaking at 617 nm, under O–Eu charge transfer excitation at 284 nm. The optimal Eu3+ content was experimentally determined to be 5 at.%, agreeing well with theoretical analysis, and the concentration quenching of luminescence was suggested to be due to exchange interactions. Fluorescence decay analysis indicates that a higher calcination temperature or Eu3+ content would decrease the lifetime of the 617 nm emission.

Gold nanoparticles have been deposited on the surface of hematite nanorod array photoanode to improve the photoelectrochemical water splitting performance. The Au nanoparticles induce the Fermi level equilibration, the surface catalysis, and the plasmonic enhancement effects in the Au/hematite photoanode. The Fermi level equilibration effect promotes the extraction of photo-generated charge carriers, suppressing the charge recombination. Surface catalysis effect reduces the overpotential for photoelectrochemical water oxidation. In the Au/hematite sample, the Fermi level equilibration and the surface catalysis effect make major contribution to photocurrent enhancement while the plasmonic effect makes a little contribution. In addition, the Au@SiO2 particle has been immobilized on hematite nanorod array surface that has been passivated. In the Au@SiO2/hematite sample, the photocurrent enhancement originating from plasmonic effects is negligible. Both the Femi level equilibration and the surface catalysis effects were excluded due to the isolated Au and hematite while surface passivation is mainly responsible for the photocurrent enhancement.

To improve photocatalytic activity of TiO2, 3-hexylthiophene monomers were in situ polymerized on porous TiO2 nanocrystalline thin film. Poly-3-hexylthiophene (P3HT) was homogenously modified on the thin film. The surface modification amounts of P3HT were controlled using different concentrations of 3-hexylthiophene monomer ether solutions and detected by the absorption spectra. The photocatalytic performance tested in methyl orange solution under ultraviolet light irradiation was significantly enhanced due to the modification of P3HT. Within 210 min, approximately 80% of methyl orange was degraded for the modified film with the optimized modification amount, it is twice higher than that of the film without modification. Photoluminescence spectra and open-circuit voltage decay processes of the samples were measured to demonstrate the photocatalytic activity enhancement mechanism due to the in-situ polymerization of P3HT. The homogenous modification of P3HT can promote separation of photogenerated electron–hole pairs on the TiO2 nanocrystalline thin film, which suppresses the recombination of photogenerated charge carriers, thus improving its photocatalytic activity.

Potassium dihydrogen phosphate (KDP) is an important nonlinear optical crystal material for light frequency converters and Pockels photoelectric switches in laser systems. However, KDP is apt to fracture, is deliquescent, and can suffer from microstructural changes under a temperature variation. As such, KDP has been one of the most difficult-to-handle materials, but its properties have not been well understood. This paper aims to explore the mechanical properties of KDP crystals in detail with the aid of the nanoindentation technique using a Berkovich diamond indenter. It was found that the mechanical properties of KDP can be easily altered by machining-induced subsurface damage. It was also discovered that a KDP crystal is a visco-elasto-plastic material during micro/nanoscale deformation, although it is very brittle macroscopically.

Graphite flakes (Gf)/Si/Al composites have been fabricated with different volume fraction of graphite by vacuum gas pressure infiltration. In the composites, the addition of Si played a role of spacing apart graphite layers, which can produce voids between layers for the infiltration of molten aluminum. Microstructural characterization indicated that the reinforcements were fairly distributed in the Al and a clean interface lacking of Al3C4 phase was formed between Al and Gf. With the increase of Gf from 39 to 81 vol%, the longitudinal thermal conductivity (TC) of composites increased from 294 to 390 W/m K, but the open porosity increased from 1.85 to 6.03%. Besides, a joint M1–M2 prediction model was established, which considered that the microstructure of composites lies in between two models: (M1) a layered structure in binary metal-particle composites and (M2) ternary composites that oriented flakes randomly distributed in metal-particle confirmed a better theoretical prediction of TC.

Tungsten foams with directional, controlled porosity were created by directional freeze-casting of aqueous WO3 powder slurries, subsequent freeze-drying by ice sublimation, followed by reduction and sintering under flowing hydrogen gas to form metallic tungsten. Addition of 0.51 wt% NiO to the WO3 slurry improved the densification of tungsten cell walls significantly at sintering temperatures above 1250 °C, yielding densely sintered W–0.5 wt% Ni walls with a small fraction of closed porosity (<5%). Slurries with powder volume fractions of 15–35 vol% were solidified and upon reduction and sintering the open porosity ranges from 27–66% following a linear relation with slurry solid volume fraction. By varying casting temperature and powder volume fraction, the wall thickness of the tungsten foams was controlled in the range of 10–50 µm. Uniaxial compressive testing at 25 and 400 °C, below and above the brittle-to-ductile-transition temperature of W, yields compressive strength values of 70–96 MPa (25 °C) and 92–130 MPa (400 °C).

A new ultrahigh strength hot rolled Ti–Mo-bearing ferritic steel was developed through chemical composition design and rolling processing optimization. To maximize the potential of nanometer-sized (Ti, Mo)C carbide in terms of strengthening ferrite matrix, the optimal chemical composition of 0.1C–0.2Ti–0.4Mo (wt%) was determined through considering the atomic ratio of elements, the solubility temperature of (Ti, Mo)C in austenite, and the excessive growth critical temperature of austenite grain during reheating. The rolling condition in the region through austenite recrystallization region to austenite nonrecrystallization region was adopted to realize a homogenous and fine ferrite grain structure. Results showed that the simulated coiling at 600 °C was found to provide an attractive combination of ferrite grain refinement hardening (360 MPa) and precipitation hardening (324 MPa). An optimal combination of strength and ductility was achieved after coiling at 600 °C (yield strength: 912 MPa; ultimate tensile strength: 971 MPa; total elongation: 16.0%). In addition, the nanometer-sized (Ti, Mo)C carbide was characterized by transmission electron microscopy (TEM) and physical–chemical phase analysis, and its role was discussed in details.

Phosphorene is a new-emerging two-dimensional material with many fascinating electronic and thermal properties. Using nonequilibrium Green's function technique, we investigate the thermoelectric transport properties of phosphorene in the ballistic transport regime. We find that while the electronic conductance and thermal conductance of phosphorene are highly anisotropic, the Seebeck coefficient is isotropic. The maximum predicted thermopower reaches 2500 μV/K. We also find that the Wiedemann–Franz law is valid only when the chemical potential is inside valence band or conduction band. When the chemical potential is near the valence band maximum or conduction band minimum; however, the Wiedemann–Franz law becomes invalid, and interestingly, the figure of merit ZT reaches its maximum value. We also find that figure of merit ZT increases with the increase of temperature, and ZT in the armchair direction is much higher than that in the zigzag direction. By analyzing the various effects on ZT, we discuss the possible routines to enhance figure of merit ZT.

The effect of boron on the room-temperature dynamic properties of Ti-6Al-4V alloy with and without boron addition in as-cast and β-forged conditions is studied by varying number of loading cycles, frequency of loading, and strain amplitude. Boron addition seems to lower the complex modulus and increases the damping of the base Ti-6Al-4V alloy. TiB precipitates in boron modified alloys play a key role in improving the damping through dislocation pinning (at all frequencies) and grain boundary pinning (at high frequencies). These effects are more prominent after β-forging wherein arrangement of TiB particles is found to be a deciding factor. Strain amplitude variation of damping shows trend reversal between 10 and 87 Hz frequencies; damping increases with strain amplitude at 10 Hz but reduces with strain amplitude at 87 Hz. A damping peak occurs near the 50 Hz frequency, and cycling through this range results in a significant improvement in damping (21% for as-cast and 93% for β-forged alloys).

Tribology is a phenomenon concerning the relative motion between at least two amalgamating surfaces. In the machining process, surface roughness is the most important element for studying this occurrence, which contributes to the evaluation of part quality. This paper will provide detailed analysis for better understanding of tribological during the machining process of Inconel 718 alloy using a multi-layer TiAlN/AlCrN-coated carbide ball end inserted in dry cutting condition. The analysis focused on the relationship of tool wear with cutting temperature, cutting force, and surface integrity. Results found that the cutting temperature increased around 7.5% and surface roughness of machined surface improved about 10.3% when the cutting speed increased. Flaking at the rake face and notching at the flank face were determined as the main tool failures during milling Inconel 718. Furthermore, high friction between the tool–workpiece interfaces during machining was due to the build-up edge (BUE) formation that causes an alteration in microstructure at machine surface.

From recent nanoindentation experiments, two types of pop-in modes have been identified: a single pop-in with a large displacement excursion and a number of pop-ins with comparable and small displacement excursions. Theoretical analyses are developed here to study the roles played by indenter tip radius, pre-existing defect density, heterogeneous nucleation source type, and lattice resistance on the pop-in modes. The evolution of dislocation structures in earlier pop-ins provides input to modeling a stochastic, heterogeneous mechanism that may be responsible for the subsequent pop-ins. It is found that when the first pop-in occurs near theoretical shear stress, the pop-in mode is determined by the lattice resistance and tip radius. When the first pop-in occurs at low shear stress, whether the successive pop-in mode occurs depends on how the heterogeneous dislocation nucleation source density increases as compared to the increase of the total dislocation density. The above transitions are found to correlate well with the ratio of indenter tip radius to the mean spacing of dislocation nucleation sources.

Carbon fiber reinforced plastic (CFRP) is an expensive composite which has become valuable material as the demand for this composite increased in the industries. It is suitable to be used in automotive, aerospace, and aircraft because of its properties which is stronger than steel and also stiffer than titanium while retaining its lighter weight. However machining of CFRP is a mess to machinist due to its nature which is abrasive. The paper presents the wear mechanism on solid carbide cutting tool during milling CFRP. The wear mechanism is observed under dry and chilled air machining. The machining parameters tested were at cutting speed of 200 m/min with constant feed rate and depth of cut. For both dry and chilled air machining, it is observed that carbide cutting tool experienced abrasive wear which has been influenced by abrasive powdering chips and fibers during milling CFRP. Under microscope and scanning electron microscope, the abrasive wear is represented by shiny and polish area on the cutting tool respectively. This abrasive wear is observed higher under dry machining compared to the chilled air machining which was due to the heat generated during machining. Thus, chilled air has a potential of improving machinability of CFRP by using solid carbide cutting tool.

Pb2+-doped (Sr1−xPbx)3Ti2O7 (SPT) ceramics were fabricated by a solid state reaction. The stability and lattice structure of Sr3Ti2O7 and Sr4Ti3O10 Ruddlesden–Popper (RP) phases were studied as a function of Pb2+ content and sintering atmosphere. X-ray diffraction indicates that SrO(SrTiO3)n RP phase formation is sensitive to the Sr:Ti ratio of the raw materials and is a complex circularly iterative process. When the PbO concentration is less than x = 0.03, pure Sr3Ti2O7 can be obtained. Sr4Ti3O10 was found to be the main phase in the SPT samples for x ≥ 0.075. Pb2+ stabilizes SrO(SrTiO3)n RP phases by substitution for Sr2+ which reduces the lattice stress of the RP phase. It was observed that SrO vaporization losses at high temperature can be compensated by the decomposition of the intermediate SrPbO3 phase at lower temperature.

A novel CuWO4/Cu1−x Zn x WO4/ZnWO4 hybrid photocatalyst with sandwiched heterojunction structure was prepared by a one-port synthesis with Zn doping into CuWO4. The crystalline structure, optical, and morphological properties as well as photocatalytic performance of the as-prepared hybrid photocatalyst were studied. By adjusting the amount of Zn doped, the optimal doping level was determined to be 0.1 wt% Zn2+. More than 80% photocataytic degradation of rhodamine B was achieved within 20 min over 0.1 wt% Zn2+ doped CuWO4, while only 20% was achieved for the pure CuWO4. The enhancement was proposed to be due to the formation of a CuWO4/Cu1−x Zn x WO4/ZnWO4 sandwiched heterojunction. Such tandem type heterojunction was found to be efficient for charge separation compared to traditional single heterojunction, which, in turn, resulted in a significantly enhanced photocatalytic activity. Our finding is also expected to be valuable for the exploration of CuWO4-material as a new group of efficient photocatalysts.

Tungsten oxide (WO3−x) nanomaterials with controlled morphology and composition were fabricated by thermal evaporation of WO3 and S powders at different temperatures in a vacuum tube furnace. At 850 °C the obtained green particle is still of the same monoclinic WO3 phase as that of the starting powder. At a temperature between 900 and 1100 °C, the resultant dark-blue products are particle-like clusters composed of numerous monoclinic WO2.90 short nanorods, but the clusters became looser and the nanorods grew somewhat longer as the temperature increased. At a temperature between 1150 and 1250 °C, elongated and thoroughly separate purple-red monoclinic W18O49 nanorods were obtained. The growth of the prepared WO3−x nanomaterials was controlled by a gas–solid mechanism. Their photocatalytic degradation on organic contaminants was evaluated by decomposing methylene blue (MB) in aqueous phase under sunlight, in which WO3 particles presented higher photocatalytic activity than its oxygen-deficient counterparts, WO2.90 and W18O49. But the W18O49 nanorods had higher adsorption ability to MB in all the samples.