Ultrasonic vibration can lead to significant load reduction in metal forming, and this concept has been widely applied in microforming. Recently, we discovered that low-frequency mechanical vibration (less than 100 Hz) with micro-amplitudes also features the same effects. In this study, low-frequency vibration-assisted tensile deformation experiments were conducted on commercially low-carbon steel. Effects of vibration softening and residual softening were obtained during experiments. Both these softening effects became prominent at high vibration amplitudes. Detailed microstructural analyses reveal that a low-frequency vibration treatment altered the interior characteristics of the metal. Electron backscatter diffraction results showed low-angle grain boundaries, and the interior misorientation angle increased greatly with the application of a low-frequency vibration. Changes in the microstructure became more pronounced with the rise of vibration amplitudes. Instantaneous stress reduction results from the additional energy applied in the form of vibration, which lowers the barrier energy for the dislocation motion. The residual softening effect can be interpreted via a dislocation density decrease as a result of vibration markedly improving the opportunity for dislocation annihilation or stacking.

Core–shell silicon–silicon oxide nanowires are synthesized at low temperatures using inorganic and organic compounds of a tin as a catalyst. In situ simultaneous one-dimensional growth of pristine silicon nanowires (SiNWs) using alloy catalyst is reported here. Such a development process generates a high-quality SiNW that is not determined by other atomic species in the plasma. A possible growth model is discussed to understand the synchronized precipitation of a SiNW core and an oxide shell. Nanowires grown here eliminate the additional fabrication steps to deposit anticipated oxide shell that is achieved by precipitation from the same catalyst that precipitates core nanowires.

In this study, TiO2 photoanodes doped with samarium ions via a method of hydrothermal treatment were used to fabricate dye-sensitized solar cells (DSSCs). Different doping concentrations were investigated on the effects of the cell’s performance. Some techniques including XRD, scanning electron microscopy, HRTEM, XPS, UV-Vis, photoluminescence were used to characterize the morphology, structure, and optic properties of the prepared photoanodes. The photovoltaic performance of the fabricated cells was further evaluated by measuring the current density–voltage (J–V) curves. It was found that: (1) The down-conversion luminescence effect derived from samarium doping could enhance the light-harvesting ability. (2) Compared with the undoped sample, the samarium-doped cells exhibited enhanced photovoltaic performance. Among the cells with different doping concentrations, the cell TiO2:0.015 Sm showed the best power conversion efficiency of 6.08% with a high open-circuit voltage (V oc) and a short-circuit current density (J sc).

The catalytic property toward oxygen reduction reaction (ORR) plays a significant role in the power generation of fuel cells (FCs). Here we demonstrate a graphene/activated carbon aerogel (GA/AC) composite to facilitate the ORR process, which is synthesized by a one-step hydrothermal method. The aligned pores and high porosity enable its mass density 20-times lighter than bare AC. Electrochemical studies show that the composite exhibits a remarkably improved electro-catalytic performance. The onset potential shifts positively from 0.68 to 0.83 V, and the number of electrons transferred is increased from 2.85 to 3.52, indicating that a four-electron pathway dominates the ORR process. This composite presents a mesoporous structure containing a large number of multi-scale pores and having a high specific surface area of 758.19 m2/g, which is responsible for its excellent onset potential and charge transfer rate. These aerogel-composites show great potential as ORR catalysts for assembling lightweight FCs and metal-air batteries.

Tin oxide (SnO2) nanoparticles in gram scale quantity were synthesized from inexpensive Sn feedstock by flame oxidation. Selection of optimal feedstock size based on computational fluid dynamics ensures complete conversion of Sn into SnO2 nanoparticles. The rapid melting and oxidation of feedstock in high-temperature oxidative flame endow the crystalline and phase-pure SnO2 nanoparticles, as evident from x-ray diffraction and transmission electron microscopy analysis. Dye-sensitized solar cells fabricated using flame-SnO2 nanoparticles show higher efficiency (ɳ = 2.72%) than that of commercial SnO2 nanoparticles (ɳ = 1.53%). The increased efficiency is attributed to suppression of electron recombination caused by passivation of sub-band-edge surface states.

Pure Cu was made ultrafine-grained by equal channel angular pressing on route BC at ambient temperatures and deformed in situ in a scanning electron microscope at the elevated temperature of 373 K and at a constant total strain rate of 10−4 s−1. Deformation was repetitively stopped to take micrographs of the grain structure on the same area of observation, revealing limited activity of discontinuous dynamic recrystallization. During the stops of deformation, the flow stress was relaxing. The relaxation of stress as function of time was used to determine the rate of inelastic deformation as a function of stress, from which the activation volume ${V^ * }$ of the thermally activated flow was derived. It is found that the normalized values of ${V^ * }$ were lying in the same order generally found for coarse-grained pure materials. This seems to be in conflict with the literature. However, the conflict is resolved by noting that the literature results refer to quasistationary deformation with the concurrent dynamic recovery in contrast to the present results obtained at a virtually constant microstructure. The interpretation of the two kinds of activation volumes for thermally activated flow is discussed.

The plastic deformation mechanisms and the microstructure development during creep deformation of L12-hardened Co-base superalloys show a number of unique features. The preferred orientation of rafting is determined by their positive lattice mismatch. In addition, the regular interfacial dislocation networks often found in rafted specimens of other types of superalloys do not form. While the ordered γ′-L12 precipitates are supposed to harden the material, they are actually found to be frequently cut by partial dislocations generating stacking faults. In this work, specimens from creep tests interrupted at different strains were investigated using transmission and scanning electron microscopy. By this, it is possible to find out which of these processes take place in which stage of creep deformation. For a better understanding of creep deformation, the balance between γ′ cutting and dislocation activity within the matrix channels is of special interest.

Age-hardening of homogenized and cold-rolled invar-based Sn alloys results in the development of continuously-formed (CP) and discontinuously-formed (DP) Ni3Sn2 precipitates. In situ investigation of the DP reaction front (RF) velocity (V) revealed a nonsteady-state behavior upon early aging stages followed by a constant V after prolonged aging. The reason for the initial nonsteady-state behavior was experimentally studied and attributed to the reduction of matrix Sn-supersaturation ahead of the DP RF as a result of the simultaneous CP coarsening (in homogenized specimen) or the CP increased volume fraction (in cold-rolled specimen). A similar trend of V variation in the homogenized specimen was obtained after the modification of the original Hornbogen model for the nonsteady-state DP growth kinetics. In general, variations of the transformed matrix fraction via the DP reaction suggest the faster kinetics of this reaction in cold-rolled specimen as compared to the homogenized one due to the existence of more nucleation sites induced by the cold deformation.

The present work describes the shear creep behavior of the superalloy LEK 94 at temperatures between 980 and 1050 °C and shear stresses between 50 and 140 MPa for loading on the macroscopic crystallographic shear system (MCSS) (011) $\left[ {01\bar 1} \right]$ . The strain rate versus strain curves show short primary and extended secondary creep regimes. We find an apparent activation energy for creep of Q app = 466 kJ/mol and a Norton-law stress exponent of n = 6. With scanning transmission electron microscopy, we characterize three material states that differ in temperature, applied stress, and accumulated strain/time. Rafting develops perpendicular to the maximum principal stress direction, γ channels fill with dislocations, superdislocations cut γ′ particles, and dislocation networks form at γ/γ′ interfaces. Our findings are in agreement with previous results for high-temperature and low-stress [001] and [110] tensile creep testing, and for shear creep testing of the superalloys CMSX-4 and CMSX-6 on the MCSSs (111) $\left[ {01\bar 1} \right]$ and (001)[100]. The parameters that characterize the evolving γ/γ′ microstructure and the evolving dislocation substructures depend on creep temperature, stress, strain, and time.

Cobalt oxide thin films with different thicknesses were synthesized by atomic layer deposition. After a thermal reduction process, under a controlled atmosphere of hydrogen, it was possible to convert cobalt oxide to metallic cobalt. The different thicknesses were obtained considering from 500 to 2000 cycles of CoCp2/O3. The thin films were characterized by x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray microanalysis, and by magneto-optical Kerr effect measurements. The indirect synthesis process allows us to obtain cobalt oxide and cobalt thin films with controlled thicknesses and extraordinary magnetic properties, with coercivities above 500 Oe.

A modification of the metal processing technique known as equal channel angular pressing (ECAP) to incorporate shear plane rotation, called ECAP-R, is presented. The new process was developed to produce hybrid materials with helical architecture of their constituents, which holds promise to enable enhanced mechanical properties. The process was trialled experimentally using a specially designed laboratory-scale rig. It was shown that a positive mean stress (negative hydrostatic pressure) in a part of the multipiece billet leads to separation of the constituents within that region. A way to improving the process design was suggested based on finite element simulations. It was demonstrated that the proposed processing results in excellent bonding between the helical parts of the hybrid in the regions of positive hydrostatic pressure. Subsequent annealing gave rise to further improvement of the quality of bonding. Processing by ECAP-R at elevated temperatures was suggested as a viable method of producing hybrid materials with helical architecture.

To investigate the solute transport and redistribution in the slab continuous casting processes of high sulfur steel, a three-dimensional model coupling turbulent flow, heat and solute transportation was developed. And then a thermodynamic model for MnS precipitation was established to study the MnS precipitation and distribution in strand on a macroscale and its effect on solute macrosegregation was also explored. The results showed that the temperature and solutes concentration were the main factors for the precipitation of MnS. The effect of temperature was significant when the solid fraction was greater than 0.8. Due to the precipitation of MnS, the segregation ratio of solutes Mn and S on the center line declined from 1.05–1.15 to 0.97–1.01 and from 1.2–1.45 to 1.00–1.08, respectively. And the solute concentration of Mn and S declined and distributed more uniformly in the strand, and the macrosegregation of Mn and S was also suppressed greatly.

This article presents innovative work undertaken to evaluate the auxetic composite materials developed using weft-knitted fabrics with negative Poisson’s ratio (NPR) produced from high-tenacity filaments of para-aramid (p-AR) and polyamide. The aim of this study is to develop polymeric composite materials reinforced with auxetic knitted fabrics and to evaluate the degree of transference of the auxetic behavior from the fibrous reinforcement to the composite produced. The results show that the NPR values remained in the composites. Regardless of the type of resin used, either epoxy or polyester, the highest values were obtained for samples produced with p-AR auxetic knitted fabrics. The NPR composites developed within this work present great potential for applications in industrial areas, including personal protection products, such as bulletproof vests, helmets, knee, and elbow protectors, and in all other areas where energy absorption is a key factor to be considered.

Microstructure and pitting corrosion behavior of base metal (BM), heat-affected zone (HAZ), and weld zone (WZ) in the 316L stainless steel weld joint was investigated. The results indicated that WZ, including ferrite and austenite phases, was mainly composed of columnar dendrites, while BM and HAZ exhibited a full-austenite structure with low Σ coincidence site lattice boundaries especially twin boundary primarily. No obvious pitting occurred in WZ, while the millimeter-scale pits were observed in HAZ and BM after immersion test in 6% FeCl3 solution. HAZ had a lower pitting potential than WZ and BM, while not much difference in pitting potential was observed between WZ and BM. Dendrite-selected corrosion occurred in WZ, while grain boundary was the preferable site for pitting corrosion in HAZ and BM. Gain refinement and a decrease in twin boundary volume fraction promoted the pitting corrosion susceptible of HAZ.

Shot-peened CM400 maraging steel was used to study the mechanism of enhanced notch fatigue properties of ultra-high strength materials. After shot peening, the specimen surface became rougher, but the transversal machining traces were reduced. The yield strength was slightly improved while the ultimate tensile strength and hardness maintained constant; as a result, the fatigue limit was promoted by about 1.5 times. The nucleated sites of the fatigue fracture were partly changed from the surface to subsurface/interior of the specimen. To further analyze the influencing factors of fatigue properties, the fatigue damage process may be resolved to two aspects: (a) fatigue damage rate affected by shear deformation and (b) fatigue damage tolerance controlled by the dilatation fracture process. Considering the stress state near the notch tip, the hydrostatic stress and maximum shear stress are considered for better understanding these two aspects. It is observed that the fatigue damage tolerance increased while the fatigue damage rate decreased after shot peening. Therefore, the notch fatigue properties of CM400 maraging steels can effectively be improved.