With the emergence of flexible/stretchable electronics, flexible solar cells (SCs) are able to attract much academic and industrial attention due to its advantages of lightweight, foldability, low cost, and extensive applications. Wearable technology has become a hot topic in the tech industry in this few years, shirts that read wearer's biological and physiological information are just beginning to make their way into society and will change the way that we interact with technology. The high strength and good electronic properties of graphene fiber make it a good candidate for some specific applications, such as wearable SCs, since it can be obtained at relatively low cost and it is amongst the strongest commercial yarns in existence. In this review, a summarized state of the art regarding wearable SCs is presented including several applications of graphene and its derivatives with their remarkable unconventional applications.

With the advent of flexible, wearable and portable electronic products, flexible lithium-ion batteries (LIBs) and electrochemical capacitors (ECs), which are able to withstand repeated deformation or bending, have attracted considerable attention as one type of energy-storage device. However, the fabrication of these flexible electrodes is the main bottleneck in the practical utilization and application of these energy-storage devices. Up to now, enormous efforts have been made in addressing the shortcomings and remarkable improvements have also been achieved. So a systematic review of the status and progresses is highly required. In this review, we first make a short introduction about the challenges faced in the conventional batteries and capacitors. Then, we summarize the recent improvements in flexible and wearable LIBs and ECs with a focus on the flexible active materials and substrates. Finally, we discuss the prospects and challenges towards the practical applications of the flexible electrodes in the future.

We have reported the chemical blending carbonization method to obtain microporous carbon with high surface area for application as electrode materials in supercapacitors. Aliphatic dicarboxylic acids with different methylene numbers (n = 2, 4, 6, and 8) react with phenolic resin (PF) during curing process. Abundant micropores are created in the carbon matrix after the decomposition of grafted or blocked diacids at temperature higher than 400 °C. The specific surface area (SSA) of the carbonized blending system increases with the diacid chain length, but decreases after n > 4 of the chain length. The maximum SSA of the blending system is up to 605.9 m2/g, which increased approximately 68% compared to that of the neat carbonized PF. Electrochemical investigation indicates that the highest specific capacitances of the blending system reaches 175 F/g at a specific current of 0.1 A/g in 30 wt% KOH aqueous electrolyte. Furthermore, the capacitance maintenance achieves 82.8% as the current density enlarged 55 times.

In this study, the ternary Ge–Sb–Se chalcogenide glass was fabricated by a standard melt-quenching technique for flexible infrared lenses. Chalcogenide glass should have unique thermal and mechanical properties to be applied to precision glass molding (PGM) process. Therefore, the relations between thermal properties and the moldability were investigated for (35–20)Ge–(5–20)Sb–60Se glass systems. The thermal and thermos-mechanical properties were characterized by the differential scanning calorimeter and thermos-mechanical analysis, respectively. Preceding experiments using a pressing tester were conducted before PGM process to evaluate the moldability. The surface condition of both chalcogenide glass disks and Tungsten Carbide (WC) molds were characterized by using an optical microscopy and an interferometer. The preferential compositions in (35–20)Ge–(5–20)Sb–60Se glass systems were selected to produce molded lenses. Finally, the molded chalcogenide lens was successfully fabricated using the preferential compositions and the processing conditions from the preceding experiments using a pressing tester.

The effects of annealing temperatures on the structure and photocurrent response of nanoporous iron oxide film prepared by anodization of iron foil in an ethylene glycol, NH4F, and H2O electrolyte were studied. The as-anodized anodic film was found to be rather amorphous and crystallized to predominantly α-Fe2O3 upon annealing in nitrogen. Nitrogen was used as to reduce the thickening of the barrier layer which affects the photocurrent response of the oxide. However, annealing must be done above 300 °C to produce crystalline oxide but must be kept lower than 500 °C since high temperature promotes grain growth, destroying the nanoporous structure and also thickens the barrier layer, which significantly reduce the photocurrent of the film. Sample annealed at 450 °C in nitrogen has the highest photocurrent of 1.04 mA/cm2 (0.5 V versus Ag/AgCl in 1 M NaOH) compared to 0.13 mA/cm2 at 0.5 V for air-annealed sample.

Microstructure evolution and tensile properties of large dimensional bulk 304 stainless steel after being rolled with different thickness reductions were characterized in detail. The results showed that the steel consisted of nano-submicro-microcrystalline austenite and nanocrystalline ferrite. Submicrocrystalline austenite was broken down with the thickness reduction, when thickness reduction was 70%, all submicrocrystalline were broken down to nanocrocrystalline, and dispersed more uniformly in the microcrystalline austenite phase in the steel, but the grain size of the nanocrystalline austenite increased to 70 nm. Tensile strength increased from 850 MPa to 965 MPa, yield strength increased from 652 MPa to 837 MPa, elongation decreased from 33% to 19%, intergranular corrosion rate decreased from 1.36 g/(m2 h) to 0.46 g/(m2 h). Strength and intergranular corrosion properties increased much. When the thickness reduction was 70%, the tensile strength, yield strength, elongation, and intergranular corrosion properties were the best in the reported value of the steel.

The effects of rare earth oxide Y2O3 additive on microstructure and mechanical properties of proeutectoid ferrite/granular bainitic coating by flux-cored arc welding were investigated. The results show that the primary austenite in the bainitic coating can be refined by Y2O3. The grain size of primary austenite is decreased from 51.2 µm to 40.1 µm with the increased Y2O3. The size of proeutectoid ferrite is decreased significantly and the fraction of the bainite is increased, which in turn facilitates the uniform distribution of the M/A island. Large number of the dislocation martensite is transformed into M/A. With the increased Y2O3 additive, the hardness and the tensile strength of the coating increases from HV 272 ± 13 to HV 312 ± 8 and from 764 ± 10 MPa to 885 ± 12 MPa, respectively. Moreover, the wear resistance of the coating with Y2O3 additive is increased simultaneously.

The microstructures and mechanical properties of ternary (Ni75Al9V16) and multicomponent (Ni69Al9V9.5Nb3Ti1.5Co4Cr4) dual two-phase intermetallic alloys charged with C were investigated by scanning electron microscope, electron probe microscopic analyzer, x-ray diffraction, Vickers hardness, and tensile tests. Solid solubility limits of C in the dual two-phase microstructures were small, mostly less than 0.1 at.%. When C was charged exceeding the solid solubility limit, large-sized carbides were solidified with no structural coherency with the dual two-phase microstructure. Major transition metals constituting the carbides changed from Nb and Ti to V with increasing charged C content. This transition was correlated with the capability of the carbide formation. C dissolving in the dual two-phase microstructure enhanced hardness and flow strength through solid solution hardening without sacrificing tensile ductility. The formed carbides little contributed to strengthening, rather, contributed to softening through depleting constituent element V as well as alloying metals Nb, Ti, and Cr from the dual two-phase microstructures.

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.

Microstructures and austenite grain growth behavior of the alumina-forming austenitic (AFA) steel subjected to normalizing and annealing at various temperatures were investigated. A modified kinetic model of austenite grain growth was constructed based on consideration of the heating history. Abnormal growth of austenite grain occurs when the temperature is increased to 1473 K, and some special large particles of the precipitates located at grain boundaries form when the sample is normalized at the temperature of 1523 K. Both NbC and NiAl precipitates are identified using routine x-ray diffraction. The fitted data based on the kinetic model used and the consideration of the heating history is in agreement with the changes in the austenite grain growth in the AFA steel even when there is abnormal grain growth. The grain growth exponents are shown to be 2.85 and 2.42 for normalizing and annealing, respectively.

Nanocomposites of 2024 aluminum–MoSi2 were prepared using mechanical alloying method followed by cold and hot pressing. Influences of volume fraction and distribution of nanosized MoSi2 reinforcement on mechanical properties of the composites were investigated. Microstructural characterization was carried out by scanning electron microscopy and energy dispersive spectroscopy. Mechanical properties of the nanocomposites were evaluated via hardness, wear, and also room and high temperature compression tests. The results showed that although the distribution of low content of MoSi2 nanoparticles in the matrix is homogeneous, with increasing the reinforcement fraction, the tendency of agglomeration is gradually intensified. The addition of reinforcing particles continuously brings a considerable enhancement in the mechanical properties of the matrix alloy but by exceeding a certain amount of the reinforcement fraction, this improvement reduces mainly because of the microstructure inhomogeneity. In addition, the nanocomposite with 3 vol% MoSi2 exhibits the optimum mechanical properties at ambient temperature.

Very high cycle bending fatigue behaviors of FV520B steel under fretting wear were studied by the ultrasonic fatigue technique. The specimen system for ultrasonic bending testing was designed and the stress distribution of fatigue specimen was obtained by finite element method. The microstructure of FV520B steel was characterized by means of optical microscope, transmission electron microscope, and energy-dispersive spectroscope. The P–S–N curve was drawn based on fatigue data. The micromorphology characteristics of fretting wear surface and fracture surface for fatigue specimen were observed. The results indicate that the microstructure of FV520B steel is mainly composed of lath martensite, ferrite, and precipitation particles, with some randomly distributed internal inclusions. The P–S–N curve shows that there exists no “conventional fatigue limit” and the fatigue life decreases continuously with the increase of applied stress Smax. Most of fatigue cracks are observed on fractography and initiate from the overlap region of fretting wear zone and stress concentration zone. The fracture failure for tested specimen is ascribed to fretting wear and bending vibration fatigue.

The pitting corrosion resistance of AL-6XN PLUS™ superaustenitic stainless steel, 304L, 316L, and 317L austenitic stainless steels was investigated using the cyclic polarization technique. These materials were evaluated in the as received condition and heat-treated at temperatures between 500 °C and 900 °C for 72 h. A thermodynamic simulation was performed using the software Thermocalc® to predict possible deleterious phases in selected temperatures. The simulations have predicted the sigma phase in the selected temperature range. An aqueous solution of sulfuric acid and sodium chloride was used as electrolyte in the corrosion tests. The results showed that pitting corrosion was not observed on the samples of AL-6XN PLUS™ steel. The 304L steel suffered pitting corrosion. All the polarization curves of this steel showed hysteresis characteristics of pitting corrosion. The 316L and 317L steels were resistant to pitting corrosion, but susceptible to crevice corrosion.

To study the hot deformation behavior of the Ti–22Al–25Nb alloy, isothermal compression tests were conducted at the temperature range of 930–1080 °C with strain rates of 0.001–1.0 s−1. Both the strain rate and the deformation temperature have a significant influence on the stress–strain behavior of the Ti–22Al–25Nb alloy. A hyperbolic–sine constitutive equation is established to quantitatively demonstrate the relationship between the parameters involved, and the hot deformation activation energy Q is determined as 621 kJ/mol. To optimize the processing window, a hot processing map is established, which is related to the microstructure evolution in hot working. The lamellar globularization as well as the dynamic recrystallization (DRX) would contribute to the stable regions with high power dissipation, while the adiabatic shear bands would lead to unstable regions. Moreover, an Avrami-type kinetics model is applied to examine the evolution of DRX during isothermal deformation process.

As the core materials with excellent soft magnetic properties, Fe–6.5 wt% Si steel was fabricated by using the warm rolling process due to its extremely limited ductility and formability at room temperature. In this work, the effects of warm rolling reduction varying from 50% to 85% on the microstructure, texture, and magnetic properties of sheets were explored. The microstructure and texture evolution at the various processing steps were investigated in detail using optical microscopy, electron backscatter diffraction, and transmission electron microscopy. The results demonstrate that the finer recrystallization grains are accompanied with an increasing warm rolling reduction, and the final annealed sheets are characterized by strong α-fiber and γ-fiber textures. Accordingly, on the whole, as the increase of warm rolling reductions, the values of magnetic induction (B8, B50) in the final annealed sheets increase sharply up to a maximum value and then decrease to a certain value, and the values of iron loss (P15/50, P10/400) increase monotonically.

The fluctuation of material parameters and coupling effects of them have significant effects on cross-sectional deformation of rectangular tube in rotary draw bending process. So, in this research, a global sensitivity analysis (GSA) system was established based on the combination of Morris' GSA method and 3-D finite element method, and the reliability of the system is validated. Based on the system built, the sensitivity values of different material parameters combinations were analyzed. The results show that (i) the maximum cross-sectional deformation ratio decreases with the increase of Young's module E and strain hardening exponent n, while the effects of strength coefficient K, initial yield stress σS, and thickness anisotropy exponent γ on cross-sectional deformation are opposite to those of E and n, (ii) the groups which contain E and γ simultaneously show greater sensitivity and the effect of group only including E and γ on cross-sectional deformation is the most remarkable, while the most insensitive group in different combinations contains K, and (iii) mostly, the sensitivity values of coupling groups to cross-sectional deformation are larger than those of one-parameter groups.

Thermomigration (TM) and electromigration (EM) are two persistent reliability issues and they generally appear concurrently in solder joints. Many previous studies have attempted to understand the fundamental principles behind these phenomena with the majority of which focusing their interest into the faster migration elements in solders like Bi, Ni, or Cu. However, Sn as the slower migration element has not received that much attention. In the present study, a special linearly symmetrical structure was used. An unusual TM phenomenon of Sn atoms in the Sn58Bi solder joint was observed. The unusual TM of Sn atoms along the vertical edges was attributed to the coupled effect of the EM in the horizontal direction and the TM in vertical direction. The relationships between the microstructural characteristics and the temperature distribution were established. The results also indicated that elevated temperature and sufficient thermal gradient were the two major factors that caused TM.

The machining of shape memory alloys (SMAs) is fairly essential and integral part in the manufacture of components for utilizing in engineering applications. An effort has been made in the present work to study the effect of wire electro discharge machining process parameters such as pulse on time (Ton), pulse off time (Toff) and servo voltage (SV) have been analyzed on material removal rate and surface roughness. The investigation clearly reveals that an increased pulse on time with decrease in pulse off time as well as SV increases the amount of material removed in machining of SMAs. On the other hand, the surface roughness increases with increased pulse on time and decreases with increased pulse off time as well as SV. The surface topography of the machined surface was analyzed using scanning electron microscope (SEM) and confocal micrographs. Phase changes on the machined surface with respect to pulse on time and SV were evaluated from X-ray diffractometer (XRD) analysis.