The dynamic response of structured materials, such as regular lattices, is nontrivial partly due to the interaction of mechanical waves throughout the structure and free surfaces as the material is dynamically compressed. The existence of an elastic precursor wave in additively manufactured lattices was recently shown to match theoretical predictions and simulation results. Following up on this work, we have investigated the behavior of the elastic precursor with propagation distance, impact speed, and impact material. Through a series of gas gun experiments coupled to X-ray phase contrast imaging measurements and complementary simulations, the elastic precursor wavespeed appears to be nearly independent of impact speed and impact material. We observed evidence for the sustained elastic wave propagation through many unit cells at four significantly different impact conditions. We compared these results with direct numerical simulations of the experiments and found good agreement.

In certain alloy systems, a liquid of a fixed composition freezes to form a mixture of two solid phases, one of which may be faceted and the other nonfaceted (i.e., a ‘degenerate’ or irregular eutectic). The role of trace metallic additions on the microstructure of the eutectic has received significant research interest over the last half-century, culminating in advances in theoretical, computational, and experimental fronts. The drastic morphological, topological, and crystallographic changes that accompany metallic additions strongly influence the mechanical properties of the as-synthesized eutectic microstructure. In this review, we survey the mechanistic origins leading to a modified eutectic microstructure and describe the current status in the field of eutectic solidification in the presence of metallic modifying agents. We will also discuss the remaining challenges and future opportunities that would help move the field forward and enable bottom–up tuning of the complex degenerate microstructures to technological demands.

The grain boundary network of nanocrystalline Cu foils was modified by the application of cyclic loadings and elevated temperatures. Broadly, the changes to the boundary network were directly correlated with the applied temperature and accumulated strain, including a 300% increase in the twin length fraction. By independently varying each treatment variable, a matrix of grain boundary statistics was built to check the plausibility of hypothesized mechanisms against their expected temperature and stress/strain dependences. These comparisons allow the field of candidate mechanisms to be significantly narrowed. Most importantly, the effects of temperature and strain on twin length fraction were found to be strongly synergistic, with the combined effect being ∼150% that of the summed individual contributions. Looking beyond scalar metrics, an analysis of the grain boundary network showed that twin related domain formation favored larger sizes and repeated twin variant selection over the creation of many small domains with diverse variants.

The oxidation behavior of nanograined and coarse-grained alloys may differ significantly. This empirical observation has been justified on the basis of accelerated grain boundary diffusion. However, thermal destabilization of nanograined microstructures studied in model sputter deposited NiCrAl alloys progresses concurrently with the onset of oxidation. This phenomenon makes it challenging to pinpoint the specific contribution of the original grain boundary network. In this study, dilute additions of Y are used to delay the onset of microstructural evolution at elevated temperatures through nanocluster formation and grain boundary pinning. The enhanced microstructural stability resulted in measurably different oxide morphologies during the transient stages of oxidation and slower oxidation rates overall. This coupling between the earliest stages of oxidation and microstructural evolution are directly manipulated to study fundamental oxidation processes in sputtered NiCrAl. Insights gained from this study may ultimately be used to develop novel strategies for improved oxidation resistance in structural alloys.

A supersaturated single-phase Cu–26 at.% Co alloy was produced by high-pressure torsion deformation, leading to a nanocrystalline microstructure with a grain size smaller than 100 nm. The nonequilibrium solid solution decomposed during subsequent isothermal annealing. In situ high-energy X-ray diffraction was used to map changes linked to the separating phases, and the development of a nanoscale Cu–Co composite structure was observed. To gain further information about the relationship of the microstructure and the mechanical properties after phase separation, uniaxial tensile tests were conducted on as-deformed and isothermally annealed samples. Based on the in situ diffraction data, different isothermal annealing temperatures were chosen. Miniaturized tensile specimens with a round cross section were tested, and an image-based data evaluation method enabled the evaluation of true stress–strain curves and strain hardening behavior. The main results are as follows: all microstructural states showed high strength and ductility, which was achieved by a combination of strain-hardening and strain-rate hardening.

The creep behavior of 200-nm thick gold films was investigated by plane-strain bulge testing between 23 and 100 °C. The polycrystalline gold films were produced by thermal evaporation and their columnar microstructure was stabilized by a preliminary heat treatment at 120 °C. The creep tests were performed at constant stress values between 80 and 300 MPa over 12 h, using a custom-built bulge tester. The stress exponent calculated from the creep data decreased from 4.3 to 2.8 between 23 and 100 °C, suggesting a possible transition in deformation mechanisms. The stress exponent and activation energy measured around room temperature point toward the climb of dislocations at grain boundaries being the rate-limiting deformation mechanism. Above 75 °C, scanning electron microscope inspections of tested membranes suggest an increased contribution of diffusion and of grain-boundary mediated deformation, as evidenced by the formation of grooves along grain boundaries. This is presumably the reason for the decrease of the apparent stress exponent and sudden increase of the apparent activation energy.

This article showcases details on enumerative information of dissimilar aluminum (Al) to steel welds manufactured using different friction-based welding processes with an emphasis on the description of the manufacturing process, influence of parameters, microstructural variations, formation of intermetallic compounds (IMCs), and variations in mechanical properties. Friction-based welding processes such as friction welding, friction stir welding, hybrid friction stir welding, friction stir spot welding, friction stir spot fusion welding, friction stir scribe welding, friction stir brazing, friction melt bonding, friction stir dovetailing, friction bit joining, friction stir extrusion, and friction stir assisted diffusion welding are analyzed for the formation of dissimilar Al–steel joints. It can be summarized that friction-based joining processes have great potential to obtain sound Al–steel joints. The amount of frictional heat applied decides the type and volume fraction of IMCs that subsequently affects mechanical joint properties. Process variations and novel process parameters can enhance joint properties.

Lithium-ion batteries featuring electrodes of silicon nanoparticles, conductive carbon, and polymer binders were constructed with electrolyte containing 1.2 M LiPF6 in ethylene carbonate and diethyl carbonate (1:1, w/w). Material binders used include polyvinylidene difluoride (PVdF), polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), and a mixture of equal masses of CMC and PAA (CMCPAA). Hard X-ray photoelectron spectroscopy (HAXPES) was performed on the electrodes when fresh, cycled at reduced potential, and cycled one full time to study how substrate material binders affect the early formation of the solid electrolyte interphase (SEI) layer. Electrodes cycled 5, 10, and 20 times were also analyzed to discern what changes to the SEI occur after initial formation. We also present estimates of the SEI thickness by cycle count, indicating that PAA develops the thinnest SEI, followed by CMCPAA, CMC, and PVdF in order of increasing layer thickness.

Recently, double perovskite-based oxide materials have been proposed for thermoelectric (TE) applications due to their environment-friendly nature, high-temperature stability, better oxidation resistance, and lower processing cost compared to conventional chalcogenides and intermetallics. In this review article, we have comprehensively summarized our recent research studies on Sr2B′B″O6-based double perovskites for high-temperature TE power generation. We have shown that decoupling of phonon-glass and electron-crystal behavior is possible in oxides by reducing thermal conductivity due to induced dipolar glassy state as a result of relaxor ferroelectricity. We have also introduced metal-like electrical conductivity (∼105 S/m) in these ceramics that are inherently insulator in nature. Moreover, we have observed interesting behavior of temperature-driven p–n type conduction switching assisted colossal change in thermopower in some of these oxides, hitherto, obtained only in chalcogenides. The charge transport mechanism in these complex oxides has been analyzed by small polaron hopping conduction model in conjugation with defect chemistry.

Kevlar (polyparaphenylene terephthalamide) and PBDT (poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide))-derivatives have very similar chemical structures with aromatic rings. In this study, thermal conductivities of their single chains were calculated using molecular dynamics simulations. Chain rotation was found to be the key to reducing the thermal conductivity. By introducing a new chain rotation factor (CRF), we can easily quantify chain rotation level of single-chain polymers. We demonstrated that thermal conductivity decreases as the CRF increases. We performed further calculations on phonon properties and unveiled that the small thermal conductivity led by large chain rotation can be attributed to reduced phonon group velocities and shortened phonon mean free paths. Insights obtained in this study can be used for tuning thermal conductivity of various polymers and facilitating their various applications including thermal energy conversion and management.

Twenty one years ago, the discovery of the giant magnetocaloric effect (GMCE) at room temperature completely revolutionized the magnetocaloric materials field demonstrating the potential of magnetic refrigeration at room temperature and setting the beginning of a race for the best magnetocaloric material. Since then, hundreds of different bulk magnetic materials were studied in detail; however, only a small set of these exhibit GMCE. In the last ten years, the broad interest on these materials leads to the extension of their study to the micro- and nanoscale. In this review, we highlight the main motivations for exploring the size-reduction both from the technological and the purely scientific point of view and stress the general consequences on the magnetic and magnetocaloric properties. The emergence of different underlying mechanisms driving these effects will be identified with particular emphasis for the set of materials presenting GMCE.

Energy-savvy auto-combustion synthesis was used to form the porous BaLi2Ti6O14 titanate anode. It registered the lowest calcination temperature (800 °C) along with the shortest calcination duration (2 h). Rietveld analysis confirmed the purity of the orthorhombic (s.g. Cmca) product phase. The bond valence site energy analysis indicated a 1D ionic conduction along c axis with low activation energy and 2D pathways along (010) with high activation energy. AC conductivity analysis revealed a bulk conductivity of 2.41 × 10−4 S/cm (at 300 °C) with a moderate activation energy barrier (0.68 eV). From cyclic voltammetry, the Li+ diffusion coefficient was calculated to be 10−11–10−12 cm2/s. The as-synthesized BaLi2Ti6O14 reversibly intercalated ∼1.3 Li+ involving a 1.42 V Ti4+/Ti3+ redox activity delivering capacity ∼100 mA h/g with good cyclability over 100 cycles. Furthermore, BaLi2Ti6O14 was found to reversibly intercalate ∼0.89 Na+. With suitable diffusional and electrochemical performance, BaLi2Ti6O14 form a safe titanate anode for secondary batteries.

Despite lower hardness, stiffness, and resistance to harsh environments, heavy metallic parts and soft polymer-based composites are often preferred to ceramics because they offer higher resilience. By contrast, highly mineralized biomaterials combine these properties through hierarchical and heterogeneous architecture. Reproducing these internal designs into synthetic highly mineralized materials would therefore widen their range of application. To this aim, external fields have been used to control the orientation and position of microparticles and build complex architectures. This approach is compatible with most manufacturing processes and provides large flexibility in design. Here, I present an overview of these processes and describe how they can augment the properties of the materials produced. Theoretical and experimental descriptions are detailed to determine the strengths and limitations of each technique. With this knowledge, potential areas of improvement and future research directions will lead to the creation of highly mineralized materials with unprecedented functionalities.

The application of microwave radiation (MWR) during materials synthesis can generate a wide range of interesting phenomena, such as rapid, low-temperature phase transitions and the formation of nonequilibrium phases. However, the underlying mechanisms by which MWR can influence processes like nucleation, crystallization, sintering, and grain growth remain unknown. A critical need for studying these mechanisms is the ability to quantitatively characterize the effects of MWR exposure on atomic structure. In this regard, synchrotron X-ray sources provide an opportunity to shed new light on electromagnetic (EM) field–assisted synthesis due to the availability of high-energy X-rays that enable a wide range of experimental characterization techniques. Here, we review the use of synchrotron X-ray sources for both ex situ and in situ studies of MWR-assisted synthesis. While many synchrotron-based tools are available to characterize the structural effects of MWR from the micron down to the atomic scale, work in this field is ongoing, and no clear consensus exists regarding the underlying mechanisms of EM field–mediated phase transitions. We discuss the instrumentation available to study field–matter interaction mechanisms and identify future needs in synchrotron characterization to better understand how EM fields can engineer advanced materials.

Conventional pNIPAAm microgel synthesis utilizes surfactants to suspend pre-gel droplets in the immiscible continuous phase due to the slow polymerization required for synthesizing pNIPAAm in aqueous solvent. To improve the fabrication process and to eliminate the effects of surfactant on microgel quality, a surfactant-free and water-free method was developed. Rapid polymerization of high-quality microgels was achieved in a single-channel microfluidic device to help maintain the integrity of gel particles without the addition of surfactants. The droplet generation mechanism and the effect of flow rate of the two in-going immiscible fluid on the geometry of the produced microgels were studied. The produced microgels have low polydispersity with a dispersity index of 6.4%. The pNIPAAm hydrogels fabricated in the DMSO solvent has smaller pore size and more uniform microstructure compared to that synthesized in water. The fabricated pNIPAAm microgels show a sharp volume phase transition at ∼32 °C and high deswelling/swelling rate.

This article reviews the state of the art in the gas-phase synthesis of graphene in atmospheric plasmas. The substrate-free process involves the delivery of a carbon-containing precursor into a microwave-generated Ar plasma. Factors that influence the synthesis of graphene include precursor composition, reactor design, and the flow rates of gases. These factors have elucidated the mechanisms of graphene formation in atmospheric plasmas. Gas phase–synthesized graphene is pure and highly ordered and possesses unique features that make the material useful in applications such as catalysis, energy storage, lubrication, and the transmission electron microscopy imaging of nanomaterials. However, the main challenge in the synthesis process is the low rate of graphene production. This article anticipates future research aimed at overcoming this challenge and compares the atmospheric plasma method with contemporary graphene production techniques.