Microwave sintering is a novel and efficient technology for the rapid preparation of metallic materials. In this paper, an investigation has been performed on the distribution of microwave electromagnetic fields in a metallic particle system and its influence on sintering behavior. The results show that the microstructure of the “metallic-void” will induce a nonuniform distribution and focusing effect of electromagnetic fields during microwave processing, which may accelerate the sintering process. However, further study shows that the focusing effect will decline as the neck grows larger, and will also decline from outside to inside within the loosely packed powder system, which will result in the slowdown of the sintering rate. These results were supported by the synchrotron radiation computed tomography experimental observation of the microstructure evolution of metallic powders during an entire uninterrupted microwave sintering process.

The Ag3PO4/C3N4 composites with improved photocatalytic activity were prepared by a facile in situ deposition of Ag3PO4 particles on the surface of C3N4 sheets and characterized by x-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy, UV–vis diffuse reflectance absorption spectra, Fourier transform infrared spectra, and photoluminescence spectra. The photocatalytic degradation of Rhodamine B (RhB) over the Ag3PO4/C3N4 composites was investigated and optimized, indicating that the optimal amount of Ag3PO4 in the composites was 90 wt%. The remarkably improved photocatalytic activity of Ag3PO4/C3N4 composites could be attributed to the effective separation of photogenerated charge carriers. The photoelectrochemical measurements confirmed that the charge separation efficiency was improved for the formation of composites. Moreover, the tests of radical scavengers demonstrated that h+ and ·O2− were the main active species for the degradation of RhB.

A new theoretical model is proposed to describe the mechanical properties of bimodal nanocrystalline (BNC) materials. This composite model is comprised of coarse grains evenly distributed in the nanocrystalline (NC) matrix. In this study, we have studied the effect of grain size distribution on the constitutive behavior of BNC materials. During the plastic deformation, effects of nanocracks and dislocation emission from crack tips on the constitutive behavior of BNC materials are also analyzed. Numerical calculations have been carried out according to the model, and it is found that the nanocracks make a positive effect on the strain hardening, and the results show that this model can describe the enhanced strength and strain hardening of BNC materials successfully. The prediction of the bimodal Cu–Ag material is in good agreement with the experimental results.

The metadynamic recrystallization (MDRX) behaviors in deformed Nimonic 80A superalloy were investigated by isothermal interrupted hot compression tests on a Gleeble-1500 thermo-mechanical simulator. Compression tests were performed using double hit schedules in the deformation temperature range of 1050–1150 °C, the interpass time range of 0.5–10 s, the strain rate range of 0.01–4 s−1, and the prestrain range of 0.30–0.50. To characterize the MDRX behaviors of the alloy, the effects of deformation temperature, strain rate, and prestrain on the metadynamic softening and recrystallized grain size were analyzed. The results reveal that the effects of deformation temperature and strain rate on the metadynamic softening fraction and recrystallized grain size are significant. However, the effects of prestrain on the metadynamic softening fraction and recrystallized grain size are not very marked and can be neglected. Then, by regression analysis of the experimental data, the MDRX kinetic model and recrystallized grain size model were proposed. The predicted results show good agreement with the experimental ones, which indicates that the proposed models can give an accurate prediction of the softening behaviors and microstructural evolution for Nimonic 80A.

Recent efforts have demonstrated enhanced tailoring of material functionality with mixed anion materials, yet exploratory research with mixed anion chemistries is limited by the sensitivity of these materials to synthesis conditions. Synthesis of a particular metal oxynitride compound by traditional reactive annealing requires specific, limited ranges of both oxygen and nitrogen chemical potentials to establish equilibrium between the solid-state material and a reactive atmosphere. Using Ta–O–N as an example system, we describe a combination of reactive sputter deposition and rapid thermal processing (RTP) for synthesis of mixed anion inorganic materials. Heuristic optimization of reactive gas pressures to attain a desired anion stoichiometry is discussed, and the ability of RTP to enable amorphous to crystalline transitions without preferential anion loss is demonstrated through the controlled synthesis of nitride, oxide, and oxynitride phases.

Experimental observations have shown that carbon nanotubes (CNTs)/Al nanocomposites with high level ordered nanolaminates exhibit greatly improved plasticity. The increased plasticity is mainly attributed to enhanced dislocation storage capability and two-dimensional alignment of the reinforcement. Here a theoretical model is proposed with interactions between aligned CNTs and grain boundary dislocations emitted from a crack tip taken into consideration to investigate crack blunting and fracture toughness in nanocrytalline metal matrix composites (MMCs). The critical shear stress for emission of first dislocation from intersections between a long, flat crack and aligned CNTs is quantitatively characterized. The final equilibrium positions and maximum numbers of emitted dislocations for different orientation angles and microstructures of aligned reinforcement are evaluated. In addition, the dependence of enhanced fracture toughness on effective gliding distance of emitted dislocations is also determined. The results show that the existence of aligned CNTs can lead to an increase of critical crack intensity factor by 77% than that in dislocation free case under certain conditions. The model may provide a basis understanding of ductility in aligned CNTs-reinforced nanocrystalline MMCs on respective of emission and motion of dislocations.

In recent years wearable devices have attracted significant attention. Flexibility and stretchability are required for comfortable wear of such devices. In this paper, we report flexible and stretchable touch sensors with two different patterns (interdigitated and diamond-shaped capacitors). The touch sensors were made of screen-printed silver nanowire electrodes embedded in polydimethylsiloxane. For each pattern, the simulation-based design was conducted to choose optimal dimensions for the highest touch sensitivity. The sensor performances were characterized as-fabricated and under deformation (e.g., bending and stretching). While the interdigitated touch sensors were easier to fabricate, the diamond-shaped ones showed higher touch sensitivity under as-fabricated, stretching or even bending conditions. For both types of sensors, the touch sensitivity remained nearly constant under stretching up to 15%, but varied under bending. They also showed robust performances under cyclic loading and against oxidation.

Quantitative characterization of interface adhesion and fracture properties of thin film materials is of fundamental and technological interests in modern technologies. Sandwich beam specimens used in fracture mechanics techniques, such as four-point bending and double-cantilever beam have been widely adopted, including the semiconductor industry. In this work, we highlight some of the challenges that these techniques are facing in characterizing ever thinner films and tough interfaces, and propose a simple strategy to address these challenges by engineering the stack structure of the specimen. We show that crack propagation in a multilayer stack can be controlled using a super-layer (SL) structure, and the dependence of the cracking behavior on the thickness and mechanical properties of the SL is studied. The effectiveness of the SL strategy is demonstrated for a range of technologically important material systems used in the on-chip interconnects of modern microprocessors, which represents one promising path to extend the industry-standard techniques to meet future characterization needs.

Ti was added to Mg–Ni alloy (Mg95Ni5) by a novel hydriding combustion synthesis (HCS) process. The effect of Ti on hydrogen absorption/desorption kinetics of Mg95Ni5 was investigated. The results showed that Ti had superior catalytic effects on hydrogen storage properties of Mg95Ni5, which required only 80 s to reach its saturated hydrogen absorption capacity of 6.29 wt% at 473 K and released 5.49 wt% hydrogen within 900 s at 553 K. Based on an Arrhenius analysis, the activation energy of the hydrogen desorption process was 80.8 kJ mol−1 for the main phase of MgH2 in the Ti-doped Mg95Ni5. The excellent hydriding/dehydriding properties were related to the existence of TiH1.924, which improved the efficiency of mechanical milling and was helpful in the refinement of the crystallite size of MgH2, resulting in more fresh surface area and grain boundary area. Besides, it was thought to restrain the Mg particles from growth during the hydrogenation/dehydrogenation cycles.

Operando energy-dispersive x-ray diffraction (EDXRD) was carried out on a newly formed 8 Ah lithium iron phosphate (LiFePO4) battery with the goal of elucidating the origin of asynchronous phase transformation commonly seen with in situ x-ray diffraction studies. The high-energy photons at the NSLS X17B1 beamline allow for penetration into a fully assembled battery and therefore negate any need for a specially designed in situ cell which often uses modified current collectors to minimize x-ray attenuation. Spatially-and-temporally resolved phase-mapping was conducted with a semiquantitative reference intensity ratio (RIR) analysis to estimate the relative abundance of the delithiated phase. The data show an asynchronous response in the stoichiometry versus the electrochemical profile and suggest limited diffusion in the electrode toward the end of discharge. Our results confirm that the asynchronous electrode response is not just limited to specially designed cells but occurs in fully assembled cells alike. We attribute this behavior to be a consequence of performing a local measurement over a wide-area heterogeneous reaction.

The (3 + 1)-dimensional crystal structure of the Nowotny chimney–ladder compound Rh17Ge22 was revealed using powder x-ray diffraction technique. As in the case of the higher manganese silicide MnSiγ (known as Mn11Si19, etc.), this germanide consists of two tetragonal subsystems of [Rh] and [Ge] with an irrational c-axis ratio γ = cRh/cGe, and hence the structural formula can be represented as RhGeγ. As expected from first-principles calculations of the approximate structure and the valence electron count, n-type (negative Seebeck coefficient) conduction was experimentally confirmed over the whole temperature range of 333–984 K. Although the absolute value of the Seebeck coefficient was limited to |S| ≤ 53 μV/K, a high electrical conductivity (σ = 4.8 × 103 S/cm) yielded a reasonable power factor of S2σ ∼ 1 mW/K2 m above 600 K. A maximum dimensionless figure-of-merit of ∼0.1 at 900 K was expected using thermal conductivity data of a sintered pellet.

We investigated improvements to the mechanical properties of iron matrix composites for the case where the surfaces of the reinforcing particles are coated with copper and a hybrid mixture of different types of reinforcing ceramic particles (hybrid particles mixture) is used. Copper coating on the surfaces of SiC, TiC, and TiN particles can eliminate interfacial defects to significantly improve the composites' mechanical properties. The addition of uncoated hybrid particles mixture has little effect on the tensile strength improvement of composites compared with composites reinforced by monolithic particles, whereas copper-coated hybrid reinforcement has a significant effect. Any composite reinforced with copper-coated hybrid particles mixture will always have higher strength than that reinforced with monolithic particles. Our findings suggest that the load transfer between the matrix and reinforcing particles improved because of different elastic moduli, coefficients of thermal expansion and reaction heats of different types of reinforcing particles.

The mechanical response of materials under repeated impact loading is of primary importance to model different types of surface mechanical treatments, such as shot peening. A reverse identification method of stress–strain curves using repeated impact has been developed by Kermouche et al. [Kermouche et al., Mater. Sci. Eng., A569, 71–77 (2013)] and later improved by Al Baida et al. [Al Baida et al., Mech. Mater.86, 11–20 (2015)]. This study deals with the experimental validation of this method on three materials: a home-made pure iron, a commercially pure copper, and an industrial aluminum alloy. An approximate method derived from cone indentation theory to check the reverse method reliability. Balls of different sizes have been used to cover a wide enough range of strain. The results are also compared with macroscopic compression and traction tests. The effect of the strain rate on the stress–strain curve is discussed. The conclusion section highlights the rapidity and the ease of use of the reverse identification method.

We presented the investigation on the cooling rate dependent undercooling of the microsized and nanosized Bi droplets in the Zn matrix via differential fast scanning calorimetry at scanning rates ranging from 300 to 6000 K/s. The experimental results demonstrated that the embedded nanosized Bi droplets gave more reproducible undercooling measurements than that of microsized Bi droplets at the grain boundaries. In addition, different cooling rate dependences of undercooling of microsized and nanosized Bi droplets were found. When the cooling rate is increased from 300 to 6000 K/s, the undercooling of the embedded nanosized Bi droplets increased gradually from 125 to 130 K. However, for microsized Bi droplets at the grain boundaries, there was an obvious increase of undercooling when the cooling rate was higher than 2000 K/s. In other words, the undercooling evolution displayed a sigmoidal relationship with the increase in cooling rate, indicating the change of the heterogeneous nucleation mechanism from a surface-induced mode to a volume-induced one.

The fracture strength of β-Mg17Al12 and τ-Mg32(Al, Zn)49 intermetallic coatings on AZ91E Mg alloy was investigated using a nanoindentation-based microcantilever bending technique. A set of micrometer-sized cantilevers with varying dimensions were machined using focused ion beam milling. A nanoindenter was then used to apply an increasing bending load until each cantilever fractured. The corresponding linear-elastic finite element models were created to simulate the deflection of the cantilevers and the fracture strength σm was derived from the models. The results showed that the fracture occurred at the root of the cantilever where the tensile stresses were highest; the average fracture strengths of the β-Mg17Al12 and τ-Mg32(Al, Zn)49 phases were 1.76 and 1.05 GPa, respectively. The potential sources of error are also discussed.

The development of high performance Al–Cu based alloys generally depends on the strict control of the Fe content. However, with the increasing use of recycled aluminum alloys, it is necessary to increase the tolerance for the Fe content in Al–Cu cast alloys for the purpose of low cost, energy saving, and environment protection. In this study, the formation of Fe-rich intermetallics and their effect on the tensile properties of squeeze-cast Al–5.0 wt% Cu–0.6 wt% Mn alloys with an Fe content of up to 1.5 wt% have been investigated. The full formation sequence of squeeze-cast Al–5.0 wt% Cu–0.6 wt% Mn alloys with different Fe contents has been established. The results were also compared with the corresponding results obtained for Al–5.0Cu–0.6Mn alloys prepared by gravity die casting. It is found that the Fe-rich intermetallic compounds mainly consist of α-Fe and β-Fe in alloys with a low Fe content, changing into Al6(FeMn) and Al3(FeMn) for alloys with a high Fe content. The applied pressure promotes the formation of the Fe-rich intermetallics α-Fe/Al6(FeMn) and prevents the precipitation of needle-like β-Fe/Al3(FeMn). The elongation of the alloys gradually decreases with the Fe content, and a maximum value for both the ultimate mechanical strength and the yield strength was found for the alloys with 0.5 wt% Fe. The tensile properties of alloys with a different Fe content significantly increased as the applied pressure was increased from 0 to 75 MPa, especially the elongation.

The microstructures, high-temperature mechanical properties, and fracture behavior of Mg–Gd–Y–Zr alloy components produced by low-pressure sand casting with different Gd and Zr contents, have been investigated. The ultimate tensile strength (UTS), tensile yield strength, and total elongation (EL) were measured within the 25–300 °C range. At the same temperatures, the UTS and yield strength (YS) of the T6 treated Mg–xGd–3Y–0.5Zr alloys increased with Gd content increasing from 9 to 11%, which was attributed to the improvement of precipitation strengthening. Increasing the Zr content from 0.3 to 0.5% leads to dramatic decrease in grain size and improved tensile properties of T6 treated Mg–10Gd–3Y–yZr alloys which is considered to be due to grain-boundary strengthening. With the increase of tensile temperature, both UTS and YS of the T6 treated Mg–xGd–3Y–yZr alloys initially increase and then decrease. The β′ precipitates provide important strengthening sources in experimental alloys, especially at elevated temperatures. The Mg–10Gd–3Y–0.5Zr alloy shows good combination of strength and EL within the 25–300 °C range.

The fracture toughness values of nanosized Cu and Ni single crystals with an edge nanocrack were determined under quasi-static loading conditions. Molecular statics (MS) simulations that can essentially capture the discreteness and the nonlinearity of materials were used in the present study. Different crack lengths were used to evaluate the effects of crack size on the fracture toughness. Based on MS simulations, the energy release rate was calculated using the energies obtained from two models with neighboring crack lengths under the same loading conditions. Furthermore, continuum counterparts of the atomistic models were used to calculate the toughness by the finite element method for linear elastic fracture mechanics (LEFM). The reasons behind the discrepancies between the toughness values obtained using different methods were discussed, and the applicable ranges of the toughness and the LEFM were indicated in terms of the lattice constants.

High performance die castings are urgently expected to be used as structural components subjected to dynamic loading. Therefore, tensile properties, fatigue, and corrosion-fatigue behavior of automotive die cast AlMg5Si2Mn alloy are studied in the current work. The results indicate that the tensile strength and yield strength of the as-cast specimens are obviously lower than those of the age-treated specimens, while the elongation decreases with increasing aging time. Neutral corrosive environment (3.5% NaCl solution) dramatically decreases the fatigue limits from 75 to 50 MPa. Fatigue lives of the directly corroded and precorroded specimens are close to each other. The values of material constants m and C are in the range of 5.756–5.874 and 2.421 × 10−10 to 4.285 × 10−9, respectively. Obscure fatigue striations and featureless facets are observed in crack propagation regions. Anodic dissolution is dominantly responsible for the premature crack initiation and stress corrosion cracking leading to the formation of fractured α-Al matrix.