Microelectromechanical systems (MEMS) are increasingly at our fingertips. To understand and thereby improve their performance, especially given their ever-decreasing sizes, it is crucial to measure their functionality in situ. Atomic force microscopy (AFM) is well suited for such studies, allowing nanoscale lateral and vertical resolution of static displacements, as well as mapping of the dynamic response of these physically actuating microsystems. In this work, the vibration of a tuning fork based viscosity sensor is mapped and compared to model experiments in air, liquid, and a curing collagen gel. The switching response of a MEMS switch with nanosecond time-scale activation is also monitored – including mapping resonances of the driving microcantilever and the displacement of an overhanging contact structure in response to periodic pulsing. Such nanoscale in situ AFM investigations of MEMS can be crucial for enhancing modeling, design, and the ultimate performance of these increasingly important and sophisticated devices.

The alloyed layers were produced on Mg by heating the specimens in contact with pure Al powder or Al + Zn powder mixtures. The powder material acting as the source of diffusion elements was held under pressure during heating, and this led to the formation of thick, continuous layers in a short heating time (1 h). The layer formation process took place through partial melting at the substrate/powder interface. The Al-enriched layer was characterized by a eutectic structure composed of an Mg17Al12 intermetallic phase and a solid solution of Al in Mg. The Al/Zn-enriched layers produced from Al + 20% Zn and Al + 40% Zn powder mixtures consisted of Mg17(Al,Zn)12 and Mg5Al2Zn2 and a solid solution of Al and Zn in Mg. The alloyed layers had higher hardness and better wear resistance than the Mg substrate. The results of the polarization measurements show that the Al- and the Al/Zn-enriched layers provide a certain level of protection to Mg against corrosion.

This paper details an investigation into the effect of martensite–austenite (M–A) constituent on impact toughness of intercritical heat-affected zone (IC HAZ) in Q690 steel, a low carbon bainitic steel. Large samples with uniform microstructure similar to that of the actual IC HAZ were achieved through combinations of heat treatments. The samples were heated to temperature between 750 and 830 °C for 30 min and then quenched in water. After these heat treatments, hard martensite islands distribute along the boundaries of soft matrix, and the size of martensite islands increases with heating temperature. The microstructure is quite similar to that of the IC HAZ. Using these large samples, the impact toughness could be measured conveniently. It was found that the embrittlement of the IC HAZ depends on the deformability and size of the M–A constituent. When the size of the M–A constituent whose deformability is low exceeds a critical value (2.0 μm), the embrittlement of the IC HAZ occurs.

Piezoelectricity and magnetoelectricity are contradictory properties with a rather limited set of natural (often hard) materials that exhibit both. Composite materials – almost always restricted to hard ones – provide a limited recourse with the attendant limitations of small strains, fabrication challenges among others. In this article, using the concept of electrets, we propose a simple scheme to design soft, highly deformable materials that simultaneously exhibit piezoelectricity and magnetoelectricity. We demonstrate that merely by embedding charges and ensuring elastic heterogeneity, the geometrically nonlinear behavior of soft materials leads to an emergent piezoelectric and magnetoelectric behavior. We find that an electret configuration made of sufficiently soft (nonpiezoelectric and nonmagnetic) polymer foams can exhibit simultaneous magnetoelectricity and piezoelectricity with large coupling constants that exceed the best-known ceramic composites. Moreover, we show that these properties can be tuned with the action of an external field.

The kinetic and static friction forces between Al2O3 nanowires (NWs) and a Si substrate were simultaneously determined by the use of bending manipulation, which bent a NW into a “hook” shape, and then let it recover elastically. An analytical model was developed to estimate the kinetic friction force based on the hypothesis that part of the elastic energy stored in the bent NW was consumed by the work of the friction during recovering. The static friction force was also calculated using force equilibrium. Finite element analysis and experimental testing were performed to verify the analytical model. The kinetic and static friction forces per unit area obtained were in the ranges of 1.16–3.4 MPa and 0.68–2.7 MPa, respectively, which agree well with most of the values reported previously for NWs or nanoparticles on flat substrates. It was also found that the NW size had no apparent effect on the interfacial shear stress.

The texture and deformation microstructures of Ta–2.5W alloy were investigated during cold rolling process. The microhardness can reach 280 HV when the reduction was 40%. Meanwhile, the mature body-centered cubic rolling texture was developed. The dislocation configuration appeared in a sequence from long straight dislocations and dislocation loops, followed by dislocation tangles and finally to cells boundaries and long, continuous planar boundaries. Microbands did not appear until the reduction reached 20%. The density of microbands increased with increasing reduction. The dislocations within the boundaries of microbands tended to rearrange themselves with increasing strain in a sequence from tangled dislocations, followed by parallel dislocations and finally into dislocation nets. Meanwhile, the boundaries had at least one primary set of parallel dislocations lying along the longitudinal direction of the boundaries during the whole cold-rolled process. The formation of microbands based on the double cross-slip of long straight screw dislocations was confirmed.

The effect of current direction (CD) on the microstructural evolution and mechanical properties of a Cu–Zn binary phase (α + β) alloy during the primary process of phase transformation induced by electric current pulses (ECP) treatment was investigated. To clarify the effect of CD, the samples were prepared with different angles between the CD and rolling direction (RD) from 0° to 90°. Results showed that not only the microstructural evolution but also the corresponding mechanical properties all had a saddle point in the sample with the angle 45°. Analyzed from the mechanical properties, it could be found that the anisotropic of the materials becomes stronger due to the application of ECP. An important finding is that by changing the angles between the CD and the RD, a novel and effective approach to control the phase transformation process could be provided.

Many solar fuel generator designs involve illumination of a photoabsorber stack coated with a catalyst for the oxygen evolution reaction (OER). In this design, impinging light must pass through the catalyst layer before reaching the photoabsorber(s), and thus optical transmission is an important function of the OER catalyst layer. Many oxide catalysts, such as those containing elements Ni and Co, form oxide or oxyhydroxide phases in alkaline solution at operational potentials that differ from the phases observed in ambient conditions. To characterize the transparency of such catalysts during OER operation, 1031 unique compositions containing the elements Ni, Co, Ce, La, and Fe were prepared by a high throughput inkjet printing technique. The catalytic current of each composition was recorded at an OER overpotential of 0.33 V with simultaneous measurement of the spectral transmission. By combining the optical and catalytic properties, the combined catalyst efficiency was calculated to identify the optimal catalysts for solar fuel applications within the material library. The measurements required development of a new high throughput instrument with integrated electrochemistry and spectroscopy measurements, which enables various spectroelectrochemistry experiments.

A CoCrFeNiMn high-entropy alloy (HEA), in the form of a face-centered cubic (fcc) solid solution, was processed by high-pressure torsion (HPT) to produce a nanocrystalline (nc) HEA. Significant grain refinement was achieved from the very early stage of HPT through 1/4 turn and an nc structure with an average grain size of ∼40 nm was successfully attained after 2 turns. The feasibility of significant microstructural changes was attributed to the occurrence of accelerated atomic diffusivity under the torsional stress during HPT. Nanoindentation experiments showed that the hardness increased significantly in the nc HEA during HPT processing and this was associated with additional grain refinement. The estimated values of the strain-rate sensitivity were maintained reasonably constant from the as-cast condition to the nc alloy after HPT through 2 turns, thereby demonstrating a preservation of plasticity in the HEA. In addition, a calculation of the activation volume suggested that the grain boundaries play an important role in the plastic deformation of the nc HEA where the flow mechanism is consistent with other nc metals. Transmission electron microscopy showed that, unlike conventional fcc nc metals, the nc HEA exhibits excellent microstructural stability under severe stress conditions.

In this work, the electrical characterization of nanocomposites made of epoxy resins with multiwalled carbon nanotubes is presented. As the filler, two different types of multiwalled carbon nanotubes with different aspect ratios (280, 1250) and defectiveness were selected. The production procedure, the morphological characterization, the I–V DC characteristics, and the low frequency complex permittivity (in the range 100 kHz–12 MHz) of these nanocomposites are discussed. To investigate the dispersion of the solution, a study which linked the mixing time to the zeta potential was performed. The experimental results show that with the same matrix and by using the same measurement techniques, the two nanocomposites give different results and can be correlated with the characteristics of nanotubes. The dc conductivity of the nanocomposites was measured by means of a two-point probe technique. The conductivity in the frequency range 100 KHz–12 MHz was evaluated using a circular disk capacitor and measuring the impedance. The measured conductivity follows a percolation scaling law of the form σ ∝ (p − p c)t . A best fit to the measured conductivity data was obtained and the values of the exponent t compared to those in the literature.

Electrochemical micromachining (ECMM) with microtool electrodes is a promising method for microshaping bulk metallic glasses (BMGs) at room temperature. A key challenge is the control of the electrode reactions to impede the disturbing passive layer formation on machined surface regions. In the example case of a Fe-based glassy Fe65.5Cr4Mo4Ga4P12C5B5.5 alloy, it will be demonstrated that by using an aqueous electrolyte based on 0.1 M H2SO4 solution with up to 0.1 M Fe2(SO4)3 addition and by applying ultrashort voltage pulses, complex microstructures can be machined with high precision. Potentiodynamic polarization measurements reveal that the salt addition reduces the charge transfer resistance of the microtool and therefore, the negative bias potential effect. The free corrosion and passive state of the BMG workpiece are affected, but not the transpassive regime. Systematic ECMM studies were conducted to obtain optimum parameters for shaping complex lateral structures with very smooth and well-defined machining areas.

We report a cost-effective, surfactant-free, and scalable synthesis technique for lead telluride (PbTe) nanocubes by a chemical precipitation method. The high-resolution transmission electron microscopy studies indicated the evolution of nucleation centers (spherical) into nanocubes with the addition of the Pb and Te atoms. The spark plasma sintered PbTe nanocubes exhibited an enhanced Seebeck coefficient, S > +400 µV, higher than the reported values of the bulk PbTe over an extended temperature range of 300–425 K, and a moderate electrical conductivity, σ ∼ 8000 S/m at 300 K. A significant reduction in the lattice thermal conductivity was observed due to effective phonon scattering from the presence of numerous interfaces introduced by nanostructuring. The resulting figure-of-merit (ZT) ∼ 0.45 at 300 K is higher than the reported values at this temperature in other PbTe nanostructures. Moreover, a moderate thermoelectric compatibility factor makes the PbTe nanocubes a potential candidate for green energy generation.

Cr is one of common alloying elements that improve the oxidation resistance of Cu. Its content and distribution are the two important factors that influence the oxidation resistance of alloys. In this paper, the cluster structure model of stable solid solutions was used for designing Cu–Cu12–[Crx/(12+x)Ni12/(12+x)]5 (x = 1, 2, 4, 6 or 8) alloys. The insoluble antioxidative Cr was uniformly distributed in the Cu matrix with the help of Ni element. The solid solution and precipitation of alloys were effectively controlled by changing the Cr/Ni ratio, and the effects of the distribution of alloying elements on the oxidation resistance of Cu alloy were discussed. The studies on isothermal oxidation at 850 °C show that element Cr of the Cu–Ni–Cr alloys designed using cluster model can be dispersed in the Cu matrix, and a continuous protective Cr-rich oxide layer can be formed when the Cr content dispersed in the alloys reaches 9.26 at% during isothermal oxidation. 1/2 of Cr in the Cu–Ni–Cr alloys is replaced by Fe, forming Cu–Ni–(Cr + Fe) alloys; oxide precipitates exhibit a columnar structure revealing the orientation of growth perpendicular to the matrix, thereby forming a lot of O diffusion channels and resulting in a sharp decline in its oxidation resistance. Therefore, the growth morphology of the oxide precipitates may significantly affect the oxidation resistance.

Microstructure modification and room temperature tensile properties of Ti–6Al–4V plates fabricated by electron-beam melting (EBM) were investigated. Firstly, Ti–6Al–4V slabs were direct rolled at various preheat temperatures below β transus with various reductions, then the deformed samples were annealed at 800 °C for various soaking times. After rolling, the microstructure modification consists of elongation, bending, kinking, and rotation of α lamellae. Specimens rolled below 900 °C exhibited flow instability (local deformation bands). The mean aspect ratio of α lamellae was further decreased following annealing, and the fraction of α particles showed a relatively strong dependence on preceding rolling reduction. The variations of mean aspect ratio and spheroidization fraction with annealing time were rationalized on the basis of various processes during spheroidization. The mechanical properties of Ti–6Al–4V plates fabricated by EBM were significantly improved after rolling compared with as-cast Ti–6Al–4V plates. The following annealing of 1 h resulted in significant improvements on elongation without obvious loss of ultimate tensile strength (UTS).

An interesting experimental phenomenon was obtained by Mintz that the hot ductility of an austenitic steel decreases with decreasing strain rate whereas that of a ferritic steel increases. However, the mechanism is still unclear. In this study, the critical time and critical cooling rate of nonequilibrium grain-boundary segregation (NGS) are calculated. It is shown that for Mintz's thermal cycle prior to tensile testing, the effective time of the austenitic steel is shorter than the critical time and that of the ferritic steel is longer than the critical time. When the strain rate decreases, the elastic stress aging time increases. As a result, for the austenitic steel, the grain-boundary segregation of impurity increases, thereby reducing the hot ductility, whereas for the ferritic steel, the segregation of impurity decreases, thereby enhancing the hot ductility. Consequently, the hot ductility loss of both austenitic and ferritic stainless steels is induced by NGS of impurity.

Titanium (Ti) thin films were deposited by DC magnetron sputtering at conventional conditions with different substrate temperature, deposition rate, and inert gas pressure. The compositional, structural, morphological, and optical properties of the Ti films were investigated. It is shown that the films were crystalline with α-Ti phase and hcp structure only. The crystallinity increased with increase in substrate and deposition rate. Analysis of the atomic force microscopy images shows that the films were uniform, crack free, and adhered well to the substrate. It is found that, a strong relation existed between the structural and optical properties of the films. The optical properties of the Ti films were most influenced under the deposition conditions. From this dependence, the optimum deposition conditions are obtained to prepare metallic, crystalline, and dense Ti films with smooth surface under conventional conditions.

The laser cladding Co–Cr–W coating has coarse dendritic and network carbides, which can lead to crack and exfoliation easily, limiting the application of Co–Cr–W coating. In this work, friction stir processing (FSP) was carried out on a laser cladding Co–Cr–W alloy coating to modify its microstructure. FSP transforms the laser clad coarse dendritic grains (grain size: 2–4 μm) into nanograins (grain size: 50–200 nm) and crushes the network carbides into nanoparticles dispersed in Co-base solution. The microstructure and thickness of plastic surface layer are controllable by the condition of FSP. Moreover, a WCx reinforced Co–Cr–W thin layer was formed because the WC particles of stir tool were squeezed into the Co–Cr–W coating surface layer. More interestingly, when the FSP rotary speed was 1500 rpm, an interlocking bonding between Co–Cr–W coating and steel substrate was formed, which was favorable for the connection with substrate. The surface nanocrystallization significantly strengthened the laser clad Co–Cr–W alloy after FSP.

In this study, the mechanism of ferrite grain refinement during warm compression deformation in the (γ + α) region of Cu–P–Cr–Ni–Mo weathering steel was analyzed by optical microscopy and electron backscatter diffraction. Results showed that fine equiaxed ferrite grains surrounded by high-angle boundaries (HABs) formed along the initial boundaries as the strain is increased. As the deformation temperature decreased, some low-angle boundaries shifted to HABs in intragranular ferrite, and ferrite grain refinement was promoted by continuous dynamic recrystallization. Microstructural observations also indicated that the fine ferrite grains of approximately 1.4–3 μm in size can be obtained by deformation at 750 °C with a strain over 0.69 because of ferrite dynamic recrystallization. Moreover, both strain and deformation temperature influenced the ferrite grain size and volume fraction. Thus, the predominant mechanism for ferrite grain refinement in the (γ + α) region was continuous dynamic recrystallization.

The axial loading test was performed to investigate the effect of carburizing on crack initiation and growth behaviors of a gear steel under high cycle fatigue (HCF) and very high cycle fatigue (VHCF). As a result, the carburized gear steel exhibits the duplex S–N characteristics associated with different interior failure mechanisms. The failure process in the HCF regime can be described as inclusion → fisheye → final crack growth zone (FCGZ) → momentary fracture zone (MFZ), whereas that in the VHCF regime is described as inclusion → fine granular area (FGA) → fisheye → FCGZ → MFZ. Based on the definition of crack sizes at different transition stages and the evaluation of stress intensity factor, the models for predicting crack initiation and growth lives in the HCF regime and in the VHCF regime were established. The predicted crack initiation life tends to increase with the decrease of stress amplitude. In the VHCF regime, the crack initiation life associated with the FGA size is almost equivalent to the total fatigue life, whereas the crack growth life only occupies a tiny fraction. In view of the good agreement between the predicted and experimental results, the theoretical modeling method based on crack initiation and growth can be well used to predict the fatigue life of carburized steel with the interior inclusion-induced failure in the HCF regime and in the VHCF regime.

The subject of hot ductility in C–Mn steels has been the focus of interest for a long time in materials science and engineering. However, the mechanism of loss in hot ductility continues to be unclear. In the present paper, the experimental hot ductility data in C–Mn steels involve: (i) a ductility trough appears at a certain temperature when the sample is held for a certain time at various temperatures after cooling quickly from a higher temperature; (ii) the ductility healing phenomenon which occurs with the duration of holding time; (iii) the ductility deteriorates with the increase of temperature difference between solution treatment temperature and test temperature during a tensile test; (iv) a minimum ductility appears when samples are cooled from a higher temperature to a lower one at a certain cooling rate; and (v) the formation of cavities at grain boundaries during tests. All of these are analyzed and calculated from the perspective of thermally induced nonequilibrium grain-boundary segregation (TNGS). Based on our detailed analyses, the loss in hot ductility of C–Mn steels is ascribed to TNGS of impurities.