The effect of the intercritical temperature on the microstructure and mechanical properties of a newly developed quenching and partitioning steel using martensitic microstructure prior to the heat treatment process was studied. Such a quenching and partitioning process possessed a unique microstructure evolution, especially during intercritical annealing after prequenching. Excellent mechanical properties were obtained due to this unique multiphase microstructure. Significant amount of interlath-retained austenite was acquired and the relationship between the microstructure and work-hardening behaviors was proposed. The martensite/austenite islands increased at elevated annealing temperature, which deteriorated the total elongation and increased the tensile strength as hard constituents when it was excessive. The result indicated that the present full martensitic microstructure before the intercritical annealing is probably more suitable to an industrial application and is a better way to produce high strength steels with suitable ductility.

Considerable interest in understanding interfacial phenomena occurring across nanostructured solid oxide fuel cell (SOFC) membrane electrode assemblies has increased demand for in situ characterization techniques with higher resolution. We briefly outline recent advancements in atomic force microscopy (AFM) instrumentation and subsystems in realizing real time imaging at high temperatures and ambient pressures, and the use of these in situ, multi-stimuli probes in collecting local information related to physical and fundamental processes. Here we demonstrate direct probing of local surface potential gradients related to the ionic conductivity of yttria-stabilized zirconia (YSZ) within symmetric SOFCs under intermediate operating temperatures (500–600 °C) via variable temperature scanning surface potential microscopy (VT-SSPM). The conductivity values obtained at different temperatures are then used to estimate the activation energy. These locally collected conductivity and activation energy values are subsequently compared to macroscopic electrochemical impedance results and bulk literature values, thus supporting the validity of the approach.

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.

Three-dimensional (3D) morphological evolution and growth mechanisms of primary I-phase particles have been investigated in directionally solidified Al–6Mn–2.5Be (wt%) alloy at a wide range of growth rates (100–1500 μm/s). At relatively low growth rates (100–600 μm/s), the I-phase particles exhibit faceted growth with strong anisotropy, forming a hierarchical flower-like aggregate with icosahedral morphological symmetry composed of several attached irregular polyhedrons or pentagonal dodecahedrons. At higher growth rates (e.g., 1000 μm/s), the interface of the I-phases becomes unstable along the edges and corners of the pentagonal dodecahedron, thereby arousing growth perturbations. Correspondingly, a transition from faceted to nonfaceted growth occurs with increasing growth rate. Further increase of the growth rate leads to the formation of I-phase columnar dendrites' preferential growth along the 3-fold axis. The configurations of the flower-like aggregates can be adequately illustrated by a geometrical model in terms of the perfect and elongated pentagonal dodecahedrons. A growth mechanism for the flower-like aggregates has been proposed based on the clear understanding of the 3D morphological evolution of the I-phase particles.

The effects of surface modifications of multiwalled carbon nanotubes (MWCNTs) on their dispersibility in different solvents and poly(ether ether ketone) (PEEK) have been studied. MWCNTs were treated by mixed acids to obtain acid-functionalized MWCNTs. The acid-functionalized MWCNTs were modified with five different chemical agents separately, 1,6-diaminohexane, hexadecyltrimethyl ammonium bromide, silane coupling agent 3-aminopropyltriethoxysilane, anhydrous sulfanilic acid, and ethanolamine. Multiwalled carbon nanotube and PEEK (MWCNT/PEEK) composite films were fabricated to explore systematically the dispersibility of differently modified MWCNTs in PEEK as well as in different solvents. The morphology and structures of MWCNTs and the compatibility between MWCNTs and PEEK have been investigated. It was observed that the MWCNTs modified with anhydrous sulfanilic acid have an excellent dispersion in the PEEK grafted by sulfonic acid groups and that the MWCNTs modified with ethanolamine are also dispersed well in pure PEEK. The results herein provide useful insights into the development of MWCNT/PEEK composites for a wide variety of applications.

Since the advent of the transmission electron microscope (TEM), continuing efforts have been made to image material under native and reaction environments that typically involve liquids, gases, and external stimuli. With the advances of aberration-corrected TEM for improving the imaging resolution, steady progress has been made on developing methodologies that allow imaging under dynamic operating conditions, or in situ TEM imaging. The success of in situ TEM imaging is closely associated with advances in microfabrication techniques that enable manipulation of nanoscale objects around the objective lens of the TEM. This study summarizes and highlights recent progress involving in situ TEM studies of energy storage materials, especially rechargeable batteries. The study is organized to cover both the in situ TEM techniques and the scientific discoveries made possible by in situ TEM imaging.

This study was to analyze the microstructure, microhardness, tensile and fatigue performance of the welded joints performed by a fiber laser on 22MnB5 and dual-phase steels (DP590, DP980) in similar and dissimilar combinations. The result shows that the weld zone (WZ) basically consisted of lath martensite. The HAZ in these steels can be divided into 3 parts: quenched, incomplete quenched, and tempered region. The WZ had the highest hardness, and a soft zone existed in the HAZ of all steels. Inside the WZ of the dissimilar welded joints, two hardness subregions were observed due to the difference in the alloying elements of these steels. Tensile specimens of the 22MnB5–22MnB5 and 22MnB5–DP980 welded joints were all broken in HAZ, while the 22MnB5–DP590 welded joints failed in the DP590 base metal (BM). The BM had a higher fatigue life than the welded joints, and the fatigue failure of the 22MnB5 similar and 22MnB5–DP980 dissimilar welded joints respectively occurred in the HAZ and DP980 BM. The fatigue fracture contained 3 parts: crack initiation, crack propagation, and the final fast fracture region.

First-principles shear tests were performed on pure Mg, Mg–Li, Mg–Ca, Mg–Al, Mg–Sn, Mg–Ag, and Mg–Zn models to investigate the mechanical and chemical effects of the solute elements on the generalized stacking fault energy (GSFE) of Mg. The mechanical effect increased the unstable stacking fault energy (USFE), independent of the kind of solute element tested. The intensity of the mechanical effect was explained by the average distance between a solute atom and the surrounding Mg atoms, not by a difference in atomic radius between a solute atom and a Mg atom. In contrast, the chemical effect on the USFE was complicated, and the chemical effects of Ag and Zn were lower than expected from their electronegativity. Also, the chemical effect increased the USFE for the Li addition, but it decreased the USFE for the Ca addition although the electronegativity of Li is almost the same as that of Ca.

The paradox of strength and ductility is now well established and denotes the difficulty of simultaneously achieving both high strength and high ductility. This paradox was critically examined using a cast Al–7%Si alloy processed by high-pressure torsion (HPT) for up to 10 turns at a temperature of either 298 or 445 K. This processing reduces the grain size to a minimum of ∼0.4 μm and also decreases the average size of the Si particles. The results show that samples processed to high numbers of HPT turns exhibit both high strength and high ductility when tested at relatively low strain rates and the strain rate sensitivity under these conditions is ∼0.14 which suggests that flow occurs by some limited grain boundary sliding and crystallographic slip. The results are also displayed on the traditional diagram for strength and ductility and they demonstrate the potential for achieving high strength and high ductility by increasing the number of turns in HPT.

To fabricate practical light-emitting devices, identification and minimization of nonradiative processes are necessary. In this study, an electrical measurement technique for time-resolved analyses of nonradiative processes was proposed. From the comparison between a commercial light-emitting diode (LED) and rare-earth-doped semiconductors, the technique, called electrical frequency-response analysis (FRA), revealed differences in the charge behaviors in the pn junction of bulk semiconductors and impurities. Although the charge response time constant on the order of a nanosecond realized effective recombination of the electron–hole pairs in a LED, the time constant larger than a microsecond still limited the emission intensity of the rare-earth-doped semiconductors such as Er-doped Si nanocrystals and GaAs with Er and O codopants. The energy-loss processes of the Er-doped semiconductors were investigated, and countermeasures to enhance the emission intensity were proposed.

We derive the dispersion relation of SiC substrate phonon-induced surface plasmon polariton (SPP) in epitaxial graphene (EG) grown on 4H–SiC, in SiC's restrahlen band (8–10 μm) by solving Maxwell equation in transverse magnetic mode. We also fabricated EG waveguide using photolithography and RIE etching for experimental study. Both theory and experimental data correlate in good agreement. Finally, we explain the viability of plasmonic device in EG both in theoretical and experimental point of view to explain electron–hole pair recombination. SPP formation finds application in nanophotonic devices for optical computing because of graphene's unique plasmonic properties. This can be applicable for high speed data switching in microprocessor and random access memory as well as optical interconnect in modern VLSI technology.