Soft robots are being developed to mimic the movement of biological organisms and as wearable garments to assist human movement in rehabilitation, training, and tasks encountered in functional daily living. Stretchable artificial muscles are well suited as the active mechanical element in soft wearable robotics, and here the performance of highly stretchable and compliant polymer coil muscles are described and analyzed. The force and displacements generated by a given stimulus are shown to be determined by the external loading conditions and the main material properties of free stroke and stiffness. Spring mechanics and a model based on a single helix are used to evaluate both the coil stiffness and the mechanism of coil actuation. The latter is directly coupled to a torsional actuation in the twisted fiber that forms the coil. The single helix model illustrates how fiber volume changes generate a partial fiber untwist, and spring mechanics shows how this fiber untwist generates large tensile strokes and high gravimetric work outputs in the polymer coil muscles. These analyses highlight possible as yet unexplored means for further enhancing the performance of these systems.

Silicon carbide (SiC) is the main semiconductor alternative for low loss high voltage devices. The wide energy band gap also makes it suitable for extreme environment electronics, including very high temperatures. Operating integrated electronics at 500–600 °C poses several materials challenges. However, once electronics is available for these high temperatures, the added challenge is designing integrated circuits capable of operating in the entire range from room temperature to 500 °C. Circuit designers have to take into account parameter variations of resistors and transistors, and models are needed for several temperatures. A common circuit design technique to manage parameter variations between different transistors, without wide temperature variations, is to use negative feedback in amplifier circuits. In this paper we show that this design technique is also useful for adapting to temperature changes during operation. Two different amplifier designs in SiC are measured and simulated from room temperature up to 500 °C.

The structure and origin of twin defects have been studied over the past half-century. Recently, there has been renewed interest in investigating the mechanisms by which twin defects facilitate the growth of bulk and nanoscale systems. This article reviews our understanding and experimental advances to unravel the complex role that twin defects play during crystal growth. The following topics are addressed: growth promotion at single and multiple, parallel and antiparallel twin boundaries; the role of {100} and {111} solid–liquid interfaces during crystallization; the application of realtime imaging to the study of crystal growth in the presence of twin defects; and suggested future research needed to shed light on the driving forces for twin-related phenomena. By providing a broad survey of the existing literature on twin-assisted crystal growth, we anticipate that our review will aid researchers in deciphering various growth forms that arise in materials processing applications.

The Al–50Si alloy, as a kind of potential electronic packaging material, is manufactured by different methods, such as casting and spray deposition. The possible influences of the P refiner on the microstructure of the Al–50Si alloy are investigated at different cooling rates. The refinement mechanism of primary Si phase is discussed in view of the P refiner addition, and the variation of the cooling rates. The thermal conductivity (TC), as a key parameter for electronic materials, is measured. The coupled effects of the cooling rate and the addition of the P refiner during the solidification of the Al–50Si alloy on the TC are elucidated based on structural observations. Furthermore, the porosity in the Al–50Si alloy is treated as a second phase influencing the TC.

Pt based alloys are one of the most important intermetallic materials with widespread applications. In this article, we have investigated the structural stability, elastic modulus, and electronic structure of Pt3M alloys by applying first-principles density functional theory, where M atom covers alkali metals, alkali earth metals, main group metals, and transition metals. The calculated elastic constants and elastic modulus demonstrated that all Pt3M alloys studied in this article are mechanically stable, possess good stability against shear and behavior in a ductile manner. The equilibrium lattice constant and the binding energy are also calculated to reveal the law with the change of elements. In addition, the LDOS and deformation charge density is presented to reveal the structural stability and the extent of charge transfer between Pt and M atoms. These results help us to better understand the physical properties of Pt3M alloys and also indicate that Pt3M alloys provide an extensive selection of intermetallic materials.

Hot deformation is an effective way to tackle major problems in powder metallurgy, i.e., inferior mechanical properties and low relative density. To characterize the hot deformation behavior of NiAl-based alloy manufactured by hot pressing sintering, the isothermal compression tests were performed in the deformation temperature range of 1100–1300 °C with strain rate of 0.001–1 s−1. The result indicates that calculated hot activation energy Q is 326.31 kJ/mol. The processing efficiency maps and instability maps of NiAl-based alloy were established to optimize deformation parameters on the basis of dynamic material model. They were validated through microstructure evolution. The microstructure observation revealed that fine grains, dislocation pile-up, cracks appear in high efficiency, low efficiency, and instability domains, respectively. According to effective processing window revealed by processing maps, hot forging of sintered billets was performed. The elevated temperature elongation increases from 17.86% to 74.87% after forging. The stripping feature is found on fracture surface after forging.

Heavy tungsten alloys with the following compositions 98W2Fe, 93W7Fe, and 95W2Fe3Ni were successfully prepared through gaseous reduction of metal oxide mixtures in the temperature range of 850–1000 °C. Reduced samples were subjected to sintering processes in reducing atmosphere (Ar/4% H2) at different temperatures (1200–1300 °C) and dwell times (30, 90 min). The prepared alloys together with the sintered samples were characterized by x-ray diffraction (XRD), field emission scanning electron microscope (FESEM), and optical microscope. The microhardness of the sintered samples was measured and correlated to sintering temperature and dwell time. The presence of iron oxide decreases the reducibility of WO3 whereas the presence of NiO increases the reducibility of both iron oxide and tungsten oxide. With the increase of sintering temperature and dwell time, porosity of samples decreases forming dense structure which is coupled with the increase of hardness particularly for 95W2Fe3Ni alloy.

The microstructure formation and wear resistance of a superduplex stainless steel modified with the addition of 3 wt% boron produced by spray forming were investigated. Thermodynamic simulations were used as comparison basis and to explain the experimentally observed microstructure, which was composed by primary M2B-type borides, an austenitic-ferritic matrix, and eutectic M3B2-type borides. The predicted solidification sequence started with the precipitation of primary M2B boride, followed by ferrite/austenite formation and a final eutectic reaction resulting in M3B2 borides. A good correlation with the simulations and final microstructure was found. The abrasive wear resistance was investigated with the dry sand/rubber wheel test and the results indicated an outstanding performance, similar to the cobalt-based Stellite 1016 alloy. The excellent wear resistance resulted from the presence of a significant amount (about 35 vol%) of hard borides homogeneously dispersed in the microstructure, which was effective at increasing hardness and protecting the duplex matrix against abrasion.

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.

Ordered phases and ductility of Fe–6.5 wt% Si magnetic material were investigated under different rolling temperatures, and the constitutive equation of the warm deformation was established. The results show that at high rolling temperature, accompanying with the appearance of some shallow dimples, the intergranular fracture can be transformed into the quasicleavage fracture, which makes the ductility of warm-rolled sheets greatly improved. In the 450–650 °C rolling temperature range, the antiphase domains (APDs) of warm-rolled sheets are cut, the superdislocation density increases greatly with decreasing warm rolling temperatures, resulting in a decrease in APD sizes during warm deformation. Meanwhile, more B2 and DO3 ordered phases occurring in the matrix improve the long range order parameters, thereby significantly reducing ductility of the alloy. The work softening of Fe–6.5 wt% Si alloy is attributed to a contribution combining the sizes of APDs with ordered phases.

Highly oriented Ni–Mn–Ga thin film with multiple variants and room temperature orthorhombic martensite structure were prepared on a single crystalline Al2O3 $\left( {11\bar 20} \right)$ substrate by DC magnetron sputtering. X-ray diffraction and rocking curve measurements reveal the film as (202)7M oriented with an excellent crystal quality (Δω = 1.8°). Spot-like pole figures indicate that the Ni–Mn–Ga film grows with a strong in-plane preferred orientation. An in-depth analysis of the measured pole figure reveals the presence of a retained austenite phase in the film. Two phase transformations, M S ∼345 K and T C ∼385 K, are observed and are attributed to first order structural transformation from cubic to orthorhombic, and second order phase transformation from ferromagnetic to paramagnetic, respectively. In situ high temperature x-ray diffraction measurements provide a clear indication of a thermally-induced martensite ↔ austenite reversible structural phase transformation in the film. The presence of martensite plates with seven modulated orthorhombic structure and adaptive nano-twins are some of the important microscopic features observed in the film with transmission electron microscopy investigations.

The effect of magnesium nitrate on the thermo-foaming of powder dispersions in molten sucrose for the preparation of alumina foams has been studied. The magnesium nitrate decreases the melting point of sucrose from 180 to 160 °C and acts as a blowing and setting agent. The foaming time and setting time decreases with an increase in foaming temperature as well as an increase in magnesium nitrate concentration. The rapid foaming followed by foam collapse is observed beyond 140 °C. The accelerated foaming and setting is due to an increase in the rate of –OH condensation because of the catalytic effect of H+ generated by the hydrolysis of magnesium nitrate. The porosity of alumina foam increases while cell size and grain size decrease with an increase in magnesium nitrate concentration. A change in foam structure, from partially interconnected cellular to completely interconnected reticulate-like, occurs when the magnesium nitrate concentration increase from 4 to 8 wt%.

TiO2 nanofibers (TNFs) with different anatase/rutile phase ratios were fabricated using electrospinning technique followed by the annealing at different temperatures. The effect of annealing temperatures on their morphology, structural, and optical properties and photocatalytic activity was investigated. The photocatalytic performance of TNFs was evaluated by degradation of methyl orange (MO) in aqueous solution under the irradiation of simulated solar light. Annealing temperature significantly influenced photocatalytic degradation of MO due to the incorporation of rutile phase which suppresses recombination of photoactivated electron and hole pairs. Turnover frequency (TOF) of MO degradation was introduced to describe the intrinsic activity of TNFs. TNFs acquired best anatase/rutile phase ratio (A/R = 83/17) when annealed at 650 °C, resulting in highest TOF value 2394 h−1, two times higher as compared to P25 with similar anatase/rutile phase ratio (A/R = 85/15). Appropriate crystalline structure could be the reason for good photocatalytic activity as well as intrinsic activity of TNFs.

The pure and Er3+-modified binary Pb(Zn1/3Nb2/3)O3–9PbTiO3 (PZN–9PT) single crystals were grown by using the flux method. The phase structure of the as-grown single crystals at room temperature was confirmed by the x-ray diffraction analysis. The effect of Er3+ addition on the electrical properties and upconversion luminescence of PZN–9PT was investigated. The rhombohedral to tetragonal phase transition temperature and the Curie temperature of the Er3+-modified PZN–9PT single crystals were 370 and 451 K, respectively. The coercive field E C at room temperature was evidently higher by 11.6 kV/cm than that of the PZN–9PT single crystals (E C, ∼3.5 kV/cm). Furthermore, the green and red upconversion emission bands were obtained under the 980 nm excitation, which are related to (2H11/2, 4S3/2) → 4I15/2 and 4F9/2 → 4I15/2 transitions.

Refractory carbides possess metal-like electronic and catalytic properties, which make them interesting candidates for anodes in solid oxide fuel cells. However, significant challenges include phase instability due to electrochemical potential gradient driven oxidation. This requires an understanding of both the chemical thermodynamics in operating environments along with direct measurement of the catalytic activity in fuel mixtures. Here, we present an experimental study on nanostructured WC as an anode for solid oxide fuel cells operating at 300–500 °C. This is enabled by combining calculated thermochemical equilibria validated against experiments at the material level and in fuel cell devices combined with flow reactor studies on fuel-selective catalytic activity directly at working anode interfaces. With an optimized anode microstructure and hydrogen–methane fuel mixtures, WC anode-based solid oxide fuel cells are shown to achieve a near-ideal open circuit voltage of 1.1 V at 500 °C.

H3PW12O40/polymethylmethacrylate (PMMA)/polycaprolactam (PA6) nanofibrous membrane with a sandwich structure was prepared by electrospinning. Characterization with Fourier transformation infrared spectroscopy (FT-IR), energy-dispersive x-ray spectroscopy (EDX), and x-ray photoelectron spectroscopy (XPS) indicated that H3PW12O40 has been successfully loaded into the upper and bottom layers of the sandwich membrane and its Keggin structure was not destroyed. The photocatalytic efficiency of the sandwich membranes were much higher (≥87.2%) than that of H3PW12O40 only (15.6%) and H3PW12O40/PMMA composite nanofibrous membrane (11.6%) in the degradation of methyl orange (MO) under ultraviolet irradiation. It may be caused by two factors: one was the photoreduction mechanism induced by the electron donating from PA6 to H3PW12O40, the other was the double contact area between H3PW12O40 and MO due to the sandwich structure of the laminated membrane. What is noteworthy is that the sandwich membranes were stable in water, so that they could be easily separated from the aqueous MO solution and reused without appreciable losses in photocatalytic activity after three photocatalytic cycles. In view of this, H3PW12O40/PMMA/PA6 sandwich nanofibrous membrane is promising as a photocatalyst to remove organic pollutants from practical wastewater.

There has been a continuous call for active, durable, and low-cost catalysts for a range of catalysis reactions. In this paper, porous Co@C composed of uniformly dispersed Co metal nanoparticles in hexagonal-shaped prisms carbon matrix were fabricated by in situ pyrolysis of hexagonal-shaped prismatic Co-MOF-74 crystals. The obtained nanoporous carbons have a high surface area of 195.2 m2/g and a strong magnetic response, thereby realizing fast molecular diffusion of reactant and easy magnetic separation. The resulting Co@C catalyst show a superior and durable catalytic activity for reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). Moreover, Co@C can be recycled and still retains more than 75% of its original catalytic activity after 6 cycles. Therefore, it is reasonable to believe that such Co@C nanocomposites have great potential as a highly efficient and low-cost heterogeneous catalyst. It is believed that MOFs can be used to produce other catalysts with high porosity and uniformly dispersed active sites.

Novel porous Yb3Al5O12 ceramics are successfully fabricated via a green and simple foam-gelcasting approach. Using a nontoxic water-soluble copolymer of isobutylene and maleic anhydride (Isobam), together with a surfactant EMAL TD (Surf-E), 50 vol% solid loading Yb3Al5O12 aqueous ceramic slurries are prepared. Thanks to the small contents of organic additives (0.4 wt% Isobam and 1 vol% Surf-E) added, low linear shrinkage (∼13.9%), and mass loss (∼2.21 wt%) are obtained after pressureless sintering of gelcasted green body at 1600 °C for 4 h under an air atmosphere. Furthermore, porous Yb3Al5O12 ceramics with controlled porosity and spherical-like cells possess excellent structural and shape stability. The flexural strength and compressive strength of the as-prepared porous Yb3Al5O12 ceramics with a relative density of 20% remain as high as 6.3 and 19.7 MPa, respectively, and the gas permeability can be tuned between 4.3 × 10−13 and 7.8 × 10−11 m2 with exponentially increasing porosity from 58% to 84%.