A facile method that allows chemical functionalization of graphene sheets is described. These result in a solution processable graphene-based material, namely F-graphene, which can be integrated in organic photoelectronic devices, due to its unique structural and photophysical properties. The resultant poly(3-hexylthiophene)(P3HT):F-graphene are soluble in common organic solvents, facilitating the structure/property characterization and the device fabrication by solution processing. The synthesized F-graphene is blended with the conjugated polymer in optimized concentration. The high and sensitive photoresponse of P3HT:F-graphene was demonstrated by the photodetector. A heterojunction photovoltaic device based on the solution-cast P3HT:F-graphene (with a BHJ structure of ITO/ZnO/P3HT:F-graphene/MoO3/Ag) showed a power conversion efficiency of 1.9% under AM1.5 illumination (100 mW/cm2). It provides a new method for graphene application in organic photoelectronics. It can easily enhance the performance of devices by optimizing the structure and bulk heterojunction blend in the near future.

The 1 nm tin oxides–tin (SnO x –Sn) compound films were thermally evaporated onto the chemical vapor deposition (CVD)-grown graphene films for the improved nitrogen dioxide (NO2) gas sensitivity, and the effects of the fabrication temperature and oxygen (O2) flux on the properties of the SnO x –Sn/graphene hybrid sensors including their composition, morphology, and microstructure as well as NO2 sensitivity were investigated. The composition of the SnO x –Sn compound films exhibited strong dependence on the fabrication temperature and O2 flux which could be ascribed to the hybrid effect of the desorption of the oxygen functional groups on the graphene and oxidation of the graphene and Sn. Such combining effects also demonstrated tremendous influence on the SnO x –Sn film morphology, in which the enhanced desorption of the oxygen functional groups on the graphene together with the oxidation of Sn with increasing fabrication temperature would facilitate the formation of large grain-sized and discontinuous films while the increasing O2 flux showed the opposite effects. Meanwhile, the crystallization of the SnO x –Sn compound films was promoted and deteriorated with the increasing temperature and O2 flux, respectively. The SnO x –Sn film morphology played vital role in NO2 gas sensitivity at room temperature, and the mechanism responsible for that was also discussed.

Using the peeling-induced splitting method, the effect of the irradiation of ultraviolet (UV) light on the formation of surface gratings on the surface of PMMA(Poly(Methyl Methacrylate))-based films is investigated at room temperature. The thickness of the PMMA-based films is in range of 236–534 nm, and the irradiation dose is in range of 0–5 J/cm2. Surface gratings are formed on the surface of the irradiated PMMA-based films. The spatial wave length is a linear function of the film thickness, independent of the UV doses used. The peeling-induced splitting process introduces compressive stress on the surface of the PMMA-based films, much larger than the corresponding surface energy. The magnitude of the apparent surface force increases with the increase of the film thickness. All the surface gratings formed have amplitudes approximately in the same range.

Density modulated tungsten (W) thin films with nanoscale porosity contents of 7% to 40% by volume were grown on Si substrates through magnetron sputter deposition. Process parameters were selected according to the structure zone model, which resulted in film thicknesses between 105 nm and 520 nm. Nanomechanical properties of samples were investigated by means of instrumented nanoindentation. Reduced-χ2 analysis was carried out to assess four models formulated through differential effective medium approach. The model that factored in both the crowding effect and the maximum random packing of pores successfully captured the experimental trends. Attempts to breach the auxetic barrier resulted in large-scale pulverization or spontaneous conversion into WO3. Porosity corrected yield strength calculations underlined the possibility of defining a porosity threshold beyond which the compressive yield strength of density modulated nanoporous metallic thin films would drop abruptly due to aggravated geometric slenderness effects in agreement with earlier hypotheses.

In this paper, we determine the electronic transport properties of Au–C20–Au molecular system under finite bias voltage using the non-equilibrium Green function and the density functional theory, along its localized pseudo atomic orbitals. Our aim is to peruse the various nanometer-scale transport properties and eventually predict the overall quantum transport behavior of this organic mesoscopic system. We investigate the density of states, transmission spectrum, molecular orbitals, current–voltage characteristics, rectification ratio, and differential conductance characteristics at discrete bias voltages to get the insight about various transport phenomena. The observed results elucidate that the quantum tunneling causes the electron transport in this molecular bridge and becomes prominent due to strong mechanical interactive coupling between the molecule and the electrodes having low HOMO–LUMO (highest occupied molecular orbital–lowest unoccupied molecular orbital) gap of 0.55 eV. We conclude that Au–C20–Au device exhibited metallic nature forming the current coulomb staircase with transition points at ±1 V and the quantum conductance of order 2G0 at low bias voltages.

Diethyl ether is widely used in the fields of diesel engines, agriculture, food, chemical, biological, pharmaceutical, and medical industries. It is necessary to carry out real-time monitoring of this molecule due to its harmful effects on human health. In this study, a highly sensitive SnO2/rGO gas-sensing material has been prepared by a hydrothermal method. The surface adsorption and reaction processes between the SnO2/rGO gas-sensing film and diethyl ether have been studied by the in situ diffuse-reflectance Fourier-transform infrared spectroscopy at different temperatures. The results show that the SnO2/rGO gas-sensing material has high sensitivity to diethyl ether, and the lowest detection limit can reach 1 ppm, and that ethyl $\left( {{\rm{C}}{{\rm{H}}_{\rm{3}}}\mathop {{\rm{C}}{{\rm{H}}_{\rm{2}}}}\nolimits^ \cdot } \right)$, oxethyl $\left( {{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{C}}{{\rm{H}}_2}{{\rm{O}}^ \cdot }} \right)$, ethanol (CH3CH2OH), formaldehyde (HCHO), acetaldehyde (CH3CHO), ethylene (C2H4), H2O, and CO2 surface species are formed during diethyl ether adsorption at different temperatures. A possible mechanism of the reaction process is discussed.

Novel mixed micelle was successfully fabricated by the synergistic self-assembly of poly(methacrylate isobutyl polyhedral oligomeric silsesquioxane (POSS)-co-N-isopropylacrylamide-co-oligo(ethylene glycol)methyl ether methacrylate-co-acrylic acid) (P(methacrylate isobutyl (MAPOSS)-co-NIPAM-co-OEGMA-co-AA)) and poly(methacrylate isobutyl POSS-co-N-isopropylacrylamide-co-oligo(ethylene glycol) methyl ether methacrylate-co-2-vinylpyridine) (P(MAPOSS-co-NIPAM-co-OEGMA-co-2VP)). Dynamic light scattering (DLS) and transmission electron microscopy characterizations demonstrate that the formation of mixed micelles is driven by electrostatic interaction. The formation of the mixed micelles was further implied by a simple fluorescence resonance energy transfer based technique. The mixed micelle possesses the biggest size at pH = 7.0, which is attributed to the strongest electrostatic interaction between the two kinds of micelles. The zeta potential under different pH was detected to further investigate the surface charges corroborating the discussions. DLS and UV-vis indicate that the lower critical solution temperature (LCST) is pH dependent. The mixed micelles reach the highest LCST at pH 7.0. The LCST of the mixed micelle can be tuned by adjusting the volume ratio of the two kinds of micelles as well. Moreover, the thermo-responsive behavior of the mixed micelle is absolutely reversible.

Monte Carlo (MC) simulations of the magnetization states of disordered self-assembled arrays of particles consisting of Co87Cu13 alloy are investigated. The assemblies of magnetic particles with ellipsoidal shapes and volumes ranging from 5 to 50 µm3 exhibit densities of about 3 × 106 particles per mm2. Magnetization was obtained in the framework of Stoner–Wohlfarth model extended to include phenomenological contributions of second-order magnetic anisotropy and coercivity mechanism with distinct configuration of easy axes of magnetization. MC simulations for assemblies containing no more than 100 particles with negligible magnetic interaction between each other and exhibiting saturation magnetization and magnetic anisotropy constant values close to those found for cobalt in bulk are in good agreement with experimental results. We evaluate and validate our computational modeling using samples having particles with different sizes and different angular distributions of the easy axis of magnetization. A simple numerical approach with minimum of parameters was used to take into account the coercive fields of the samples. Reasonable simulation results are generated based on realistic size distributions and angular distributions of easy axis of magnetization.

PACS numbers: 75.30.Gw,75.60-d,75.70-i

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.

We introduce a method to measure accurately surface residual stresses in the pre-equilibrium state, which were generated in workpieces during the milling process. The method takes into account strain changes and uses the inverse calculation. Material in the stress layer was removed layer by layer, and the strain change on the opposite side of the machined surface was measured. We also consider the change of the bending moment caused by the changed neutral layer. The stress values were calculated from the last layer to the first layer, and the residual stresses generated by milling are measured. We created a finite element model of a real workpiece and the measured stress values were used as inputs for the model. The measuring method was validated using finite element analysis. We find that our measuring method can be successfully used in practice to measure surface residual stresses and it provides reliable indicators for evaluating the surface properties of machined workpieces.

The oxidation behavior of three types of stainless steels, namely AISI 321, AISI 316, and AISI 409, was compared. In all stainless steels, oxide layers were formed and their masses and thicknesses increased with oxidation time. Among them, AISI 409 ferritic stainless steel demonstrated higher oxidation rate. According to the kinetical oxidation behavior of them at elevated temperatures, the oxidation mechanism was determined. Among them, the AISI 409 ferritic stainless steel showed the lowest and AISI 321 austenitic stainless steel demonstrated the highest oxidation resistance. Based on the experimental results, it was suggested that the kinetic of oxide growth in stainless steels was followed by a parabolic relationship. In all cases, a well-known Cr-rich internal oxidation zone (IOZ) was observed. The formation of IOZ was suggested by the Gibbs free energy expression and confirmed by following up the formed oxide layers at different holding times. Furthermore, the formation of thicker oxide layers in ferritic stainless steel was explained by using solid-state diffusion relations and supported by quasi-steady-state approximation of Fick's first law.

Double deformation technique is often used to study static recrystallization (SRX) behavior of materials, and SRX volume fraction can be calculated by the analysis of the stress–strain curve from this technique. The suggested methods to analyze the curve are different, which may lead to different results or even large deviation. In the present research, the methods were discussed based on the stress–strain curves from double deformation compression tests. The results showed that 2% offset method agrees well with 5% total strain method and they can give a better evaluation of SRX volume fraction for the tested steel in the absence of precipitates. While the results from 2% offset or 5% total strain method deviate from the ones from area measurement method when precipitation occurs. Therefore, area measurement method is more suitable when precipitates play a role in SRX process. However, the strain should be large enough to perform this method.

Isothermal homogenization heat treatments for a GCr15 bearing steel cast billet were performed at temperatures of 1000–1250 °C and holding times of 30–180 min. The grain size of austenite was measured with a metallographic microscope through the linear intercept method. Experimental results show that the grain size of austenite increases with the increase in heating temperature and holding time. The relationship between grain size and homogenization cycles was established. The homogeneity of the cast billet has an obvious effect on the austenite grain size distributions. Small and large grains were observed in the high- and low-concentration regions, respectively. The log-normal function can describe the grain size distributions more accurately than other functions after heating at low temperatures for short times. However, the Weibull function fits the grain size data well when the heating temperatures and holding times are improved.

In the present study, the surface properties and the corrosion behavior of a nanocrystalline surface layer fabricated on 45 steel by electropulsing-ultrasonic surface treatment (EUST) were investigated. EUST offered the specimen a smooth (R a < 0.33 µm) surface layer with nanoscale grains and compressive stress by the synergistic effect of high-energy electropulsing processing and ultrasonic impact. Open-circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy studies indicated that EUST-induced surface nanocrystallization decreased the corrosion susceptibility of 45 steel in 3.5 wt% NaCl aqueous solution, leading to a decrease in corrosion current density (i corr) by 55% and an increase in charge transfer resistance (R ct) by 36%. The enhancement in surface comprehensive mechanical properties and corrosion resistance can be explained in terms of the decrease in surface roughness, the extent of grain refinement and the change of stress state, which were closely related to the introduction of high-energy electropulsing processing.

The effect of electropulsing assisted ultrasonic surface modification (EUSM) on microstructure and surface properties of S50C steel welded components is investigated. Compared with conventional ultrasonic surface modification (USM) process, EUSM process achieves significant improvements in microstructure, including deeper strengthened layers and gradient microstructure on the surface. The EUSM-induced microstructure results in higher levels of surface compressive residual stress and greater surface microhardness and its effective depth. Conventional USM process is inevitably accompanied by some plastic damages, such as pit and crack defects. The damages, however, can be eliminated to some extent during the EUSM process. These enhancements may be attributed to the thermal and athermal effects caused by electropulsing treatment, which accelerates the mobility of dislocations in the dynamic recrystallization process.

The present study aims to investigate the effect of strain rate on volume fraction of martensite (VFM) in 304L austenitic stainless steel through dome test. Findings of this study show that martensitic transformation affects the deformation mode and formability of this material. Three strain rates are applied by controlling forming punch speed to conduct the stretching experiments and VFM is measured using magnetic saturation method. Results of the present study reveal that maximum VFM of 56% forms at the pole at low strain rates, whereas VFM of 47% is seen at high strain rates, and transforms in the region close to the flange. It is noted that blanks show good formability under low strain rate and poor formability at high strain rates. The relationship between VFM and strain rate, strain, percentage of shell reduction, equivalent of stress, and triaxiality are discussed. The experimental procedure is simulated and predicted findings show good agreement with the experimental results.

This study investigates the ternary intermetallic phases in the Mg–Zn–Ca system, which is of great interest for metallic biodegradable implant applications. According to published phase diagrams, the key alloy composition studied herein is located within the Ca2Mg5Zn5, Ca2Mg6Zn3, and IM1 phase fields. Through controlled cooling of the melt, a quasibinary ∼Ca2Mg5Zn5–Mg microstructure was obtained. The large polygonal grains had a composition of Ca2Mg5Zn5 as determined by energy-dispersive x-ray spectroscopy (EDX). Differential scanning calorimetry revealed that Ca2Mg5Zn5 begins to form at ∼417 °C, and the eutectic temperature is ∼369 °C. Based on single-crystal x-ray diffraction data, Ca2Mg5Zn5 was determined to be hexagonal (P63/mmc), with lattice parameters of a = 9.5949(3) Å and c = 10.0344(3) Å. This was also verified by transmission electron microscopy. Further refinements, which considered the possibility of mixed Mg/Zn sites, significantly improved the data fit compared to the initial ordered structural model. The final refined structure possesses a composition of Ca16Mg42Zn42, very similar to the chemical analysis results from EDX.

The damage induced by oxidation and stress during the service process of Cr35Ni45Nb alloy and their influences on the microstructure evolution and creep rupture life of this alloy were studied. Continuity, compactness, and high temperature stability of the oxide layers are conductive to the performance of the alloy. A slight but complete layer of oxidation on surface improves the creep rupture life of the specimens. However, being exposed to long-term oxidation is observed to be counter-productive. Temperature stress generated during the air-cooling process creates large carbides near the surface of the specimen's cracks. Moreover, tiny carbides are precipitated from γ matrix and interfacial defects due to creep stress, but strip carbides are dissolved due to creep stress and the Gibbs–Thomson effect.

The deformation behaviors (flow behavior, power dissipation, dynamic recrystallization, and microstructure evolution) of a typical powder metallurgy nickel-based superalloy were investigated in compression tests at temperatures range of 1020–1140 °C and strain rates range of 0.001–1.0 s−1 with the true strains of 0.3, 0.5, and 0.7, respectively. The efficiency of power dissipation can be shown by the power dissipation maps at different true strains. The results showed that true strain had a great effect on the power dissipation. Besides, the deformed microstructures were investigated. The processes of microstructure evolution at different deformation temperatures and strain rates are different. The continuous dynamic recrystallization takes place at the deformation condition of 1080 °C/0.1 s−1. The fine and uniform dynamic recrystallized grains gradually replace the pre-existing grains with the increase of true strain. The discontinuous dynamic recrystallization takes place at the deformation condition of 1110 °C/0.001 s−1. The fine dynamic recrystallized grains grow up and a part of new fine grains appear in the dynamic recrystallized grains because of the periodic dynamic recrystallization.

The present work discusses about the mechanical and metallurgical properties of Incoloy 800 H friction welded joints. The process parameters namely friction pressure, friction time, upsetting pressure, upset time, and rotational speeds were varied from low level to high level to study their effects on the properties of the weldments. The tensile tests were carried out at four different temperatures namely at room temperature, 550, 650, and 750 °C. From the results, it is observed that as the testing temperature increased, there was a reduction in tensile strength of welds. The friction welds had higher hardness than the base metals. This was due to the formation of secondary phases (γ′ and M23C6) in friction welds. The tensile and impact fracture surfaces were further analyzed through SEM and finally the individual effects of the parameters with respect to the microstructures variation in the welds were studied.