Epitaxial graphene of uniform thickness prepared on SiC is of great interest for various applications. On the Si-face, large area uniformity has been achieved, and there is a general consensus about the graphene properties. A similar uniformity has yet not been demonstrated on the C-face where the graphene has been claimed to be fundamentally different. A rotational disorder between adjacent graphene layers has been reported and suggested to explain why multilayer C-face graphene show the π-band characteristic of monolayer graphene. Utilizing low energy electron microscopy, x-ray photoelectron electron microscopy, low energy electron diffraction, and photoelectron spectroscopy, we investigated the properties of C-face graphene prepared by sublimation growth. We observe the formation of micrometer-sized crystallographic grains of multilayer graphene and no rotational disorder between adjacent layers within a grain. Adjacent grains are in general found to have different azimuthal orientations. Effects on C-face graphene by hydrogen treatment and Na exposure were also investigated and are reported. Why multilayer C-face graphene exhibits single layer electronic properties is still a puzzle, however.

The current work provides an overview of the state-of-the-art in polymer and metal additive manufacturing and provides a progress report on the science and technology behind gradient metal alloys produced through laser deposition. The research discusses a road map for creating gradient metals using additive manufacturing, demonstrates basic science results obtainable through the methodology, shows examples of prototype gradient hardware, and suggests that Compositionally Graded Metals is an emerging field of metallurgy research.

Knowledge of the plasticity associated with the incipient stage of chip formation is useful toward developing an understanding of the deformation field underlying severe plastic deformation processes. The transition from a transient state of straining to a steady state was investigated in plane strain machining of a model material system—copper. Characterization of the evolution to a steady-state deformation field was made by image correlation, hardness mapping, load analysis, and microstructure characterization. Empirical relationships relating the deformation heterogeneity and the process parameters were found and explained by the corresponding effects on shear plane geometry. The results are potentially useful to facilitate a framework for process design of large strain deformation configurations, wherein transient deformation fields prevail. These implications are considered in the present study to quantify the efficiency of processing methods for bulk ultrafine-grained metals by large strain extrusion machining and equal channel angular pressing.

The bulge test was used to investigate the fatigue properties of gold thin films with a thickness between 100 and 300 nm. The membranes were pressurized at a rate of 0.2 Hz up to 105 times, during which their stress and strain states were continuously recorded. Gold films on a silicon nitride substrate were cyclically loaded into tension and compression. Due to the presence of the substrate, no membrane failure was observed, but the residual stress shifted from an initially tensile state to an increasingly compressive one. Typical fatigue damage mechanisms consisting of extrusions were found in some large grains. Freestanding films were cyclically loaded in pure tension until failure occurred. The data acquired during the fatigue tests show a strong ratcheting of the films, which is indicative of cyclic plastic creep. Microstructural investigations clearly show grain boundary sliding in very thin films with columnar grains extending through the thickness.

New-type Ni-based superalloys with and without Nb were designed in this study. Their hot corrosion behaviors were investigated at 800 °C with the deposition of a mixture of Na2SO4 and NaCl. The corrosion kinetics was studied by thermogravimetry. Microstructure of the corrosion scales was studied by SEM and the phase constituent was analyzed by XRD. Results showed that the corrosion kinetics followed approximately parabolic law. The corrosion scales on the two Ni-based alloys were comprised of Cr2O3, Al2O3, TiO2, and NiCr2O4. NiO was only detected in the scale on alloy without Nb. Nb2O5 appeared with the addition of 2.0 wt% Nb. No sulfide emerged in the scales. The corrosion scales both exhibited a layered structure. With Nb addition, the hot corrosion resistance of the alloy was notably improved. The action mechanism of Nb was investigated extensively in this study.

The effects of the different shot peening parameters on the 6061 alloy specimens' surface have been investigated. It is found that the compressive residual stresses and the surface roughness of the surface layer for all shot-peened specimens are improved greatly. The maximum stress value and the maximum roughness are obtained by the shot flow rate of 5.5 lbs/min and air pressure of 20 psi. The microstructure observation results indicate that a nanostructured layer with an average grain size below 100 nm has been created on the top surface layer of each specimen. In the top surface nanostructured layer, the microhardness is enhanced. It is resulted from the grain refinement and the strain hardening. The results of electrochemical measurements, surface corrosion morphology observation, and EDS analysis indicate that the corrosion susceptibility of the 6061 alloy could be significantly enhanced by means of the shot-peening-induced surface nanocrystallization.

Nanoporous carbon membranes (NCMs) were fabricated by the blends of resorcinol–formaldehyde (RF) resin and Pluronic F-127 through the processes of assembly, membrane-casting, solidification, and pyrolysis. The effect of the catalyst type (i.e., NaOH and Na2CO3) on the structure and property of precursors and their derived NCMs was investigated. The as-obtained precursors and NCMs were characterized by thermogravimetry, differential scanning calorimetry, x-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, elemental analysis, nitrogen adsorption, and gas permeation techniques. The results have shown that defect-free NCMs can be easily procured by the NaOH and Na2CO3 catalysts. In contrast, the precursor made from the Na2CO3 catalyst exhibits higher char yield than that from NaOH after pyrolysis. NaOH-based NCMs are beneficial for the separation of H2/N2 and CO2/N2 gas pairs. Na2CO3-based NCMs are more favorable for the separation of O2/N2 with an ideal selectivity of 6.29 and an O2 permeability of 3.27 Barrer.

This article explores the growth of graphene under low-pressure Ar conditions. Carbon- and silicon-face 4H–SiC samples are subjected to epitaxial graphene growth at 1600 °C in vacuum, in 1 mbar argon, or in 10 mbar of argon. High-resolution x-ray scattering is used to characterize all graphene films. On the C-face, specular scans reveal a bimodal distribution of thicknesses that decrease with increasing Ar pressure. Thin and thick regions are approximately 15 and 46 monolayers in C-face graphene grown at high vacuum, 14 and 42 monolayers thick in graphene grown at 1 mbar, and 12 and 32 monolayers thick in graphene grown at 10 mbar. Azimuthal scans confirm in all cases that graphene layers are epitaxial and display expected crystallographic relationships with the underlying SiC substrate. In-plane azimuthal scans show the rotational disorder increases as pressure increases. Peaks in radial scans are asymmetric, suggesting the grain structure has a bimodal distribution of large and small domains. The sample displaying the lowest average Hall mobility (grown at 1 mbar) has the largest population of small crystallites (coherence length on the order of ∼30 nm). Variations in structure and mobility of C-face graphene are attributed to inadequate control of Si sublimation during growth.

A theoretical model of nanovoid nucleation at triple junctions in nanocrystalline materials is developed in this article. The sliding of grain boundaries (GBs) meeting at triple junctions, which can be attributed to the gliding of GB dislocations (GBDs), provides the driving force for nanovoid nucleation. The GB sliding is accommodated by the emission of partial dislocations from GBs as well as GB diffusion. The corresponding energy characteristics of the pile-ups of GBDs, the emission of partial dislocations from the GBs, and GB diffusion are calculated, respectively. Furthermore, an energy balance method to calculate the nucleation of nanovoid at triple junctions is studied. The analysis demonstrates that the nucleation of the triple junction nanovoid depends mainly on the applied stress, the GB length (length of the pile-up), the GB structures, and the GB sliding accommodations.

The effects of electropulsing treatment (EPT) on the recrystallization and texture of Ni9W alloy were investigated using micro-hardness and electron backscattered diffraction patterns. It is found that compared with conventional annealing, EPT tremendously accelerates the recrystallization process of Ni9W alloy. Moreover, the full recrystallization temperature of EPT is decreased by ∼180 °C. The rapid recrystallization process is attributed to the substantial increase in the atomic flux resulting from the athermal effect. EPT also significantly reduces the intensity of cube texture after full recrystallization. The evolution of recrystallization microstructure and texture reveals that EPT greatly increases the proportion of noncube oriented nuclei but has little effect on the size advantage of cube grains. It is suggested that the change of recrystallization texture results from the different effects of EPT on cube band nucleation and shear band nucleation.

Nanostructured Al1−x Mnx /Al1−y Mny multilayers were deposited from room temperature ionic liquid using galvanostatic control at various current densities and electrolyte compositions. By tuning the deposition parameters, multilayers with both micrometer and nanometer layer thicknesses were synthesized, with modulation of the elastic modulus and hardness between Mn-lean and Mn-rich layers. Surface morphology, composition, and microstructure of the films were characterized using x-ray diffraction and electron microanalysis tools. Nanoindentation and nanoscratch tests were performed to evaluate the mechanical and tribological properties of selected multilayers. Finally, the effects of deposition parameters on the microstructure evolution and mechanical properties of the multilayers were discussed.

The selective-laser-melting (SLM) technique is an outstanding new production technology that allows for time-efficient fabrication of highly complex components from various metals. SLM processing leads to the evolution of numerous microstructural features strongly affecting the mechanical properties. For enabling application in envisaged fields the development of a robust production process for components subjected to different loadings is crucially needed. With regard to the behavior of SLM components subjected to cyclic loadings, the damage evolution can be significantly different depending on the raw material that is used, which is, in this case, highly ductile austenitic stainless steel 316L and high-strength titanium alloy TiAl6V4. By means of a thorough set of experiments, including postprocessing, mechanical testing focusing on high-cycle fatigue and microstructure analyses, it could be shown that the behavior of TiAl6V4 under cyclic loading is dominated by the process-induced pores. The fatigue behavior of 316L, in contrast, is strongly affected by its monotonic strength.

Yttrium–aluminum garnet doped with Ce was plasma sprayed using two different processes – gas-stabilized plasma torch and water-stabilized plasma torch. Coatings on various substrate materials (stainless steel, ceramics, YAG undoped crystals), as well as self-standing plates, were obtained. The coatings adhered on materials with relatively large variety of thermal expansion coefficient. Besides microstructural, crystallographic, and thermal-stability investigations, numerous optical tests were performed. They included cathodoluminescence (CL), UV-VIS-NIR reflectance, and response of the Ce:YAG on light with various wave lengths. After spraying, the desired YAG crystalline phase sustained without any decomposition, but an amorphous fraction was present in both types of coatings. Selected coatings were heat-treated to crystallize fully and change their optical properties. Minor amorphous fraction crystallized at 930 °C. The heat-treated coatings exhibited higher CL and also larger visible emission when illuminated with a 366 nm lamp. Microhardness of the coatings was tested as well and proved the mechanical similarity of both coating types and difference from the single crystal. The optical responses of the coatings were influenced by imperfections like splat boundaries, pores, and thin cracks, which were healed only partly by heat treatment. However, the Ce:YAG was first plasma sprayed and moreover produced by both spray techniques without an irreversible loss of the desired garnet phase.

Homogenous strontium titanate (SrTiO3) nanofibers were prepared via the electrospinning of precursor solutions containing both strontium and titanium salts. Photocatalytic activities of these SrTiO3 nanofibers for hydrogen generation from water were examined and compared to that of SrTiO3 nanoparticles. The nanofibers calcined at 700 °C showed the highest photocatalytic activity of 167 μmol/h/g among the SrTiO3 samples tested. The high activity was attributed to the ideal stoichiometric ratio of Ti/Sr, small crystallite size, high crystallinity, mesoporous structure, large surface area, and appropriate energy gap. These were confirmed through field emission scanning electron microscopic with energy dispersive spectroscopic observations, x-ray diffraction patterns, N2 gas absorption–desorption isotherm measurements, photoelectron yield spectroscopy in air, and UV-visible spectrophotometry.

Creep and electromigration (EM) have been two reliability concerns in microelectronic devices for a long time. The related failure mechanisms have been widely investigated and comprehended individually. However, there is a lack of attention with regard to the interaction(s) between current density and creep, the coupling effect of which is more analogous to the real service conditions of lead-free solder joint. In this study, a series of experiments were carried out on the simple shear lap joint to investigate the effects of current density magnitude on the creep behavior of solder joints. The results indicated that dislocation creep was the main failure mechanism for low current density sample. For high current density sample, the failure mechanism was mainly dominated by copper atom migrating process which led the joint experience a higher risk of brittle fracture failure.