The present investigation addressed the weldability of Super Ni 718 alloy and AISI 316L using gas tungsten arc (GTA) welding process using three different filler wires, such as ER2594, ERNiCrMo-4 and ERNiCrCoMo-1. Interface microstructures showed the formation of secondary phases at the heat-affected zone (HAZ) of Super Ni 718 alloy and delta ferrite colonies at the HAZ of AISI 316L. It was witnessed from the weld microstructures that the deleterious phases were suppressed or controlled while using these filler wires for joining the bimetals. Tensile results corroborated that the failure occurred at the parent metal of AISI 316L in all the cases. The presence of microvoids and dimples characterized for the ductile mode of fracture in these weldments. Charpy V-notch test results showed that the weldments using ERNiCrMo-4 filler exhibited higher impact energy. A detailed study has been made to investigate the structure–property relationships of these weldments using optical and scanning electron microscopic techniques.

Practical implementation of oxide thermoelectrics on an industrial or commercial scale for waste heat energy conversion requires the development of chemically stable interfaces between metal interconnects and oxide thermoelements that exhibit low electrical contact resistances. A commercially available high-chrome iron alloy (i.e., Crofer® 22 APU) serving as the interconnect metal was spray coated with LaNi0.6Fe0.4O3 (LNFO) or (Mn,Co)3O4 spinel and then interfaced with a p-type thermoelectric material—calcium cobaltate (Ca3Co4O9)—using spark plasma sintering. The interfaces have been characterized in terms of their thermal and electronic transport properties and chemical stability. With long-term exposure of the interfaced samples to 800 °C in air, the cobalt–manganese spinel acted as a diffusion barrier between the Ca3Co4O9 and the Crofer® 22 APU alloy resulting in improved interfacial stability compared to that of samples containing LNFO as a barrier layer, and especially those without any barrier. The initial area specific interfacial resistance of the Ca3Co4O9/(Mn,Co)3O4/Crofer® 22 APU interface at 800 °C was found to be ∼1 mΩ·cm2.

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.

By combining two types of ligands, phenylpyridine and quinoline, a new type of organometallic IrQ(ppy)2 compound has been synthesized, which exhibits two phosphorescences: green and red. Using an appropriate catalyst, the final IrQ(ppy)2 compound has a good chemical yield up to 60% and becomes a stable dual emitter at room temperature. This compound is important because it exhibits stable red emission which is limited by the quantum yield due to the low energy band gap. As a result, an overlap between the ground state and the excited state occurs due to the vibrations that increase the nonradiative transitions, destroying the red emissions. Structural characteristics of the IrQ(ppy)2 powder reveal a triclinic structure confirmed by x-ray diffraction and scanning electron microscopy images. Thermal analysis of the final compound confirms a good stability against decomposition and structural changes up to 350 °C. X-ray photoelectron spectroscopy reveals Ir–O chemical bonds and several differences between the intermediate and final compounds, such as Ir–Cl bonds. Cathodoluminescence patterns show a phosphorescent triclinic structure with a higher efficiency for the red color. Backscattering electron images prove that there is a uniform distribution of iridium ions in the IrQ(ppy)2 nanocrystals.

The feasibility of an accelerated test method on revealing the high cycle fatigue (HCF) limit stresses of a near alpha titanium alloy was successfully verified firstly during the rotary bending tests. The stress-controlled low cycle fatigue (LCF) tests at room temperature were then carried out over a range of maximum stresses and stress ratios to reveal the basic LCF strength. Finally, the core emphasis was focused on the influences of the predamage from LCF loadings on the subsequent HCF limit stresses corresponding to the life of 106 cycles. A total of eight levels of predamage from LCF with different stress levels, stress ratios, and proportions of LCF life were introduced, which resulted in obvious deterioration of the HCF stress limits (even under only 2% of expected LCF life). The fracture analysis exhibited that there were typical LCF failure characteristics in crack initiation regions of specimens under prior LCF loadings.

The oxidant peroxo method (OPM) exhibits several advantage and unique characteristics not found in the traditional methods for the synthesis of lead- and bismuth-based oxides. First of all, it is a clean method based on hydrogen peroxide that matches perfectly with the green chemistry approach. Second, the oxidizing local atmosphere provided by the precursor during its crystallization is unique among all the wet chemical techniques of synthesis, which usually result in reducing environment. Besides these advantages, only a few studies have focused on the use of the OPM to obtain better materials, which makes this field of study an excellent opportunity for the development of materials with higher purity and controlled morphologies.

Barium strontium titanate (BST) glass-ceramics were fabricated via controlled crystallization with different crystallization routes. Effects of the microwave crystallization and microwave treatment on the microstructure and energy storage properties of the glass-ceramics were systematically investigated. Results showed that microwave crystallization can increase the dielectric constant. In addition, it was found that the microwave process had little impact on the crystallinity (about 90 wt%), but preferred the crystallization of SrAl4O7. Most importantly, the dielectric breakdown strength (BDS) of the glass ceramics was significantly improved from 561.3 to 791.4 kV/cm by the microwave crystallization. And it can be further enhanced to 900.0 kV/cm by conventional crystallization combined with microwave treatment. The corresponding energy densities of samples derived from the microwave processes were increased to 1.05 and 1.13 J/cm3, respectively, compared with the sample fabricated by the conventional crystallization route (0.47 J/cm3).

Periodic, highly uniform arrays of dome-like Ge quantum dots (QDs) with 50 nm interdot pitch have been achieved on Si (001). The Si surface was patterned using ultra-low-dose focused ion beam and defect-selective etching, resulting in a continuously height-modulated, “egg-carton” morphology. The directed self-assembly process is robust, occurring across a range of ion doses, growth temperatures, and deposition rates. By selectively etching off the Ge dots to reveal the underlying Si surface just prior to Ge growth, we showed that Ge QDs preferentially formed on crowns (regions of negative curvature) rather than pits (regions of positive curvature) as is mostly seen in the literature. The width of the QD size distribution mimics that of the underlying substrate pattern, indicative of a complete lack of coarsening during the Ge growth, despite the small length scales, and extensive mass transport leading to QD formation.

Hot-rolled Mg–Zn–Ca alloy, followed by annealing, shows high formability at room temperature because of the reduced intensity of the basal texture. [Y. Chino et al., Mater. Trans. 51, 818 (2010).] In the present work, microstructures of the as-rolled Mg–Zn–Ca alloy were investigated using electron backscattered secondary diffraction and transmission electron microscopy. In addition, first-principles calculations were performed to investigate the twinnability of the Mg–Zn–Ca alloy. The microstructural investigations revealed that fine $\left\{ {10\bar 12} \right\}$ twins and local fine-grained microstructures were formed. It is therefore suggested that the fine twins induce this local fine-grained microstructure, which become the nuclei for recrystallization during annealing. As a result, the intensity of the basal texture is reduced. Calculations revealed that the $\left\{ {10\bar 12} \right\}$ twinnability is enhanced by the addition of Ca because of the increased unstable stacking fault energy (γus) and decreased unstable twin fault energy (γut).

Graphene, a single atomic sheet of sp2-bonded carbon atoms arranged in a honeycomb lattice, exhibits extraordinary electrical and mechanical properties, attracting much attention in both academia and industry. The preparation of high quality large-area graphene and the tuning of graphene electronic properties are important topics in this field. In this feature paper, we review our recent work on epitaxial graphene (EG) on SiC(0001). First, we introduce the bottom-up growth mechanism of the first few EG layers on SiC(0001), and the modification of graphene electronic properties by means of surface transfer doping with electron withdrawing materials (F4-TCNQ and MoO3). Next, we summarize the adsorption behaviors of organic (PTCDA, ClAlPc, and C60F48) and inorganic (bismuth) materials on EG/SiC(0001). Finally, as an example of tuning the electronic properties of graphene by reducing its dimensionality, we demonstrate the molecular self-assembly of atomically precise armchair graphene nanoribbons with varying widths and electronic structures.

Additive manufacturing technologies, also known as 3D printing, have demonstrated the potential to fabricate complex geometrical components, but the resulting microstructures and mechanical properties of these materials are not well understood due to unique and complex thermal cycles observed during processing. The electron beam melting (EBM) process is unique because the powder bed temperature can be elevated and maintained at temperatures over 1000 °C for the duration of the process. This results in three specific stages of microstructural phase evolution: (a) rapid cool down from the melting temperature to the process temperature, (b) extended hold at the process temperature, and (c) slow cool down to the room temperature. In this work, the mechanisms for reported microstructural differences in EBM are rationalized for Inconel 718 based on measured thermal cycles, preliminary thermal modeling, and computational thermodynamics models. The relationship between processing parameters, solidification microstructure, interdendritic segregation, and phase precipitation (δ, γ′, and γ″) are discussed.