Self-energy correction density functional theory local density approximation–1/2 (LDA-1/2) method was successfully applied to predict the electronic structure and optical properties of the N-doped, Ti-vacant Ti3−δO4N oxynitride [G. Hyett et al., J. Am. Chem. Soc.129, 15541–15548 (2007)], which was shown experimentally to be more photocatalytic than titania. The procedure takes into consideration of the two possible types of Ti vacancies (with different numbers of nitrogen and oxygen neighbors) and their formation energies, according to the experimental data on fractional occupancies, with potential effects on the electronic structure and photocatalyst mechanisms analyzed. Different defective model structures were calculated for optimal final configuration, whose optical calculations revealed massive damping in infrared spectrum, while transparency in green region. The band gap determined by our methodology is 2.5 eV, in close agreement to the experimental value of 2.6(1) eV. Results presented in this work represent the first report of an electronic structure modeling of Ti3−δO4N, which is a starting point to help provide an understanding of its photocatalytic activity.

For understanding the atomic processes involved, in situ observation at near-atomic spatial resolution is needed in the studies of lithium ion battery materials. We show that the Li transport and the lithiation of carbon atoms may be triggered by the electron beam in an electron microscope, together with simultaneous real-time monitoring of electron energy-loss spectroscopy to reveal the chemical state of the species. The local electric field induced in an electrolyte particle by an electron beam acts on Li ions, resulting in Li transport and reaction with carbons. This process closely mimics the charging process of an electrochemical battery charge cycle, without an external power supply. We find that the lithium transport occurs in the form of Li+.

In this study, the effects of Sm on the microstructure and corrosion resistance of hot-extruded AZ61 magnesium alloys were investigated by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results showed that uniformly dispersed Al2Sm particles with size of ∼2 μm were discovered in the hot-extruded AZ61 magnesium alloy sample modified with 1.0 wt% Sm, which promoted dynamic recrystallization grain growth during the hot-extruded process, gradually increasing the grain of the alloy as Sm content increased. The morphology of the corroded surface and the corrosion rate of the hot-extruded AZ61 magnesium alloy both were significantly improved after Sm addition. The alloy sample modified with 2.0 wt% Sm after immersion in 3.5 wt% NaCl solution for 12 h showed minimum corrosion rate value, 3.1 mg/cm2 day, which is only 3.7% of the corrosion rate of unmodified alloy (82 mg/cm2 day).

By combining the techniques of directional solidification and coating Y2O3, a Cr–20Nb–40Ti alloy was manufactured successfully with various growth rates. The revolution of microstructures and corresponding mechanical properties was discussed to develop the Cr2Nb based alloys with good combination of mechanical properties. The results show that the favorable growth dynamics of plane (220) of Laves phase Cr2Nb was observed with the increase of growth rate. Phase selection took place in microstructures evolved from the primary Cr2Nb, via the dendrite-like eutectic Cr2Nb/β-Ti, and finally to the primary β-Ti, with increasing the growth rate from 5 to 200 μm/s. Based on the coupled zone of eutectic, the competitive growth of solidified phases in the directionally solidified Cr–20Nb–40Ti alloy was elucidated. In addition, the mechanical properties of alloy depended on the growth rate, and the fracture toughness of the alloy reached 16.50 MPa m1/2 at 200 μm/s, much larger than 1.40 MPa m1/2 for single-phase Cr2Nb.

The mechanical behavior of a Zircaloy-4 sheet as induced by a pulsed laser was studied with an accurately developed computational process that was validated with experiments. A modified Gaussian model of the heat source and the use of experimentally obtained thermal and mechanical properties of Zircaloy-4 in the computational process provided reliable simulation results of the phase transition and mechanical deformation of Zircaloy-4. A parametric study of the pulsed laser welding conditions of Zircaloy-4 was undertaken using the developed computational process. The analyzed parameters were the laser power, pulse duration, and pulse frequency. The simulation results revealed that the deformation was significantly dependent on the geometry of the molten zone and the heat-affected zone, which can be designed by the analyzed laser parameters.

The effects of Fe2B-grain orientation on microstructure and properties of bulk Fe2B intermetallic fabricated by directional and ordinary solidification techniques have been investigated. The results show that unidirectional solidified Fe2B intermetallic possesses a strong (002) texture in the transverse direction owing to the opposite unidirectional heat-squeeze effect while random Fe2B grains can be produced under ordinary solidification conditions. The nonoriented Fe2B intermetallic has the highest linear expansion coefficient of 13.04 × 10−6 °C−1 while the microhardness and fracture toughness of transverse Fe2B intermetallic in the (002) plane are larger than those of Fe2B with other grain orientations and their values are ∼18.72 GPa and 6.42 MPa·m1/2, respectively. Liquid zinc corrosion results indicate that unidirectional Fe2B intermetallic with long axis perpendicular to the direction of liquid zinc corrosion displays the best corrosion resistance to liquid zinc owing to its beneficial barrier effect. The FeB transition phase can naturally form and grow parabolically during liquid zinc corrosion.

The fracture behavior of precracked nanocrystals with grain size gradients is simulated using the molecular dynamics method. A large grain size gradient is found to elevate resistance to crack propagation and transform the fracture mode from intergranular to intragranular when the crack is obstructed by a coarse grain. But the intragranular crack is nipped in its bud due to the difficulty of intragranular fracture. However, intergranular fractures can be always kept in nanocrystals with a small grain size gradient. Both the Schmid factors for the slip systems of grains near the crack tip and the critical stress intensity factors are calculated, and energy partitioning is conducted to analyze the mechanisms behind this phenomenon. The research exhibits the key role of grain size gradient in improving the antifracture ability of nanocrystals.

Recent studies have shown that chemical immiscibility is important to achieve enhanced radiation tolerance in metallic multilayers as immiscible layer interfaces are more stable against radiation induced mixing than miscible interfaces. However, as most of these immiscible systems have incoherent interfaces, the influence of coherency on radiation resistance of immiscible systems remains poorly understood. Here, we report on radiation response of immiscible Cu/Fe multilayers, with individual layer thickness h varying from 0.75 to 100 nm, subjected to He ion irradiation. When interface is incoherent, the peak bubble density decreases with decreasing h and reaches a minimum when h is 5 nm. At even smaller h when interface is increasingly coherent, the peak bubble density increases again. However, void swelling in coherent multilayers with smaller h remains less than those in incoherent multilayers. Our study suggests that the coherent immiscible interface is also effective to alleviate radiation induced damage.

The mechanisms of densification and creep were examined during spark plasma sintering (SPS) of alumina doped with a low and high level of zirconia or yttria, over a temperature range of 1173–1573 K and stresses between 25 and 100 MPa. Large additions of yttria led clearly to in situ reactions during SPS and the formation of a yttrium-aluminum garnet phase. Dopants generally lead to a reduction in the densification rate, with substantial reductions noted in samples with ∼5.5 vol% second phase. In contrast to a stress exponent of n ∼ 1 for pure alumina, the doped aluminas displayed n ∼ 2 corresponding to an interface-controlled diffusion process. The higher activation energies in the composites are consistent with previous data on creep and changes in the interfacial energies. The results reveal a compensation effect, such that an increase in the activation energy is accompanied by a corresponding increase in the pre-exponential term for diffusion.

Lithium thio-phosphorus oxynitride glasses, LiPOSN, have been prepared by mechanical milling process from the mixture of Li2S and LiPON glass. The anionic substitution of oxygen by sulphur and nitrogen in the phosphate glass structure has been confirmed by 1D 31P solid state nuclear magnetic resonance and x-ray photoelectron spectroscopy. The study of thermal and electrical properties reveals a decrease in the glass transition temperature, likely due to the depolymerization of glass network by the decrease of bridging oxygens and sulphurs, along with a sharp increase in the ionic conductivity when lithium sulphide is incorporated into the oxynitride glasses. The improvement of chemical durability by the introduction of nitrogen, together with the increase in ionic conductivity up to values closed to the value of commercial LiPON thin film electrolyte, suggests that these LiPOSN glasses could be good candidates as solid electrolytes for lithium microbatteries.

This article addresses the metallurgical and mechanical properties of Nd:YAG laser welded Inconel 625 and duplex stainless steel SAF 2205. Keyhole plasma mode laser welding was adopted to obtain the joints. Microstructure studies showed slight grain coarsening at the heat affected zone of Inconel 625. Line mapping and elemental mapping analysis were carried out at the weld interface and in the fusion zone to examine the elemental migration as well as the composition of the phases present in these regions. The fusion zone microstructure showed the presence of Nb, Mo rich Laves phase segregated at the interdendritic arms. Tensile studies corroborated that an average joint strength of 820 MPa has been displayed by these weldments, which was almost equal to one of the parent metals, SAF 2205. It is evident from the charpy v-notch studies that the impact toughness of these laser weldments was found to be 10 J and this low toughness could be reasoned out to the formation of Mo rich phases. The structure–property relationships of these weldments have been addressed in detail and the outcomes of the study will be highly useful for marine and geothermal applications.

This study modified the surfaces of three kinds of TiNi-based shape memory alloys (SMAs) by dry electrical discharge machining (EDM) in nitrogen (N2) and acetylene (C2H2) gas mixture. The effects of composition of the dielectric medium and work-piece on the machining performance and surface characteristics were investigated. Increasing the ratio of acetylene gas in gas mixture was beneficial for improving the material removal rate (MRR). However, adding a large amount of acetylene gas resulted in unstable discharge. A recast layer, comprising nitrides and carbides, which well adhered on the EDMed surface exhibited high hardness. Among Ti50Ni50, Ti50Ni49.5Cr0.5, and Ti40.5Ni49.5Zr10 SMA as a work-piece, Ti40.5Ni49.5Zr10 SMA has the lowest MRR owing to it possessed the highest melting temperature and thermal conductivity. The recast layer on Ti40.5Ni49.5Zr10 SMA, comprising zirconium nitride, exhibited the highest hardness and adhesion among all the SMAs. However, the high-hardness recast layer deteriorated the shape recovery of the SMA.

The effect of erosion speed on the interaction between erosion and corrosion of the Fe–3.5 wt% B alloy in a flowing zinc bath has been investigated using a rotating-disk technique. The total erosion–corrosion rate increases rapidly, whereas the pure erosion rate tends to increase linearly with an increase in erosion speed and with low damage. The increase in total erosion–corrosion rate is strongly dependent on erosion–corrosion interaction. During the erosion–corrosion process, the severe corrosion reaction roughens the surface by forming a loose corrosion layer and cracks in the anticaustic Fe2B skeleton, which eventually facilitates erosion. The micromechanical scouring effect of liquid zinc worsens corrosion by accelerating the removal of corrosion products and causing spallation of anticaustic Fe2B. An increase in erosion speed intensifies the micromechanical scouring effect of flowing zinc significantly. A strong erosion–corrosion interaction occurs at high erosion speed, which leads to a greater material loss rate.

An alloy with the composition of Mg–3.7Zn–0.3Y–0.3Gd (in at.%) which contains quasicrystal phase was studied by multiple means. The as-cast alloy has dendritic structure and consists of α-Mg, I-phase, W-phase, and Mg–Zn precipitations. The alloy was forged one pass and annealed at 440 °C for 4 h, then followed by two passes of compressions. Eutectics were crushed and partially dissolved after deformation and annealing. The tensile strength increased after each forge pass. Submicron scale particles precipitated all around the grains during the deformations, and the amount of precipitations was proportional to the amount of deformations. These precipitated particles were observed by high resolution transmission electron microscopy (TEM). The existence of rhomboid W'-phase with face center cubic (FCC) structure and globular I-phase was confirmed. A quasi-periodicity lamellar phase combined with I-phase was founded, which was considered to be the transient phase between I-phase and W'-phase. This phase had orientation relationship with $\left( {1\bar 101} \right)$ of α-Mg basis and one of the 5-fold planar of the I-phase.

The mechanical properties of ultrafine-grained aluminum produced by equal-channel angular pressing (ECAP) are strongly influenced by strain rate. In this work, an experimental investigation of local strain rate sensitivity as it relates to microstructure was performed using a combination of scanning electron microscopy and digital image correlation. Uniaxial tension tests were carried out at 200 °C and strain rates alternating between 2.5 × 10−5 s−1 and 3.0 × 10−3 s−1. The results demonstrate that the heterogeneous microstructure generated by ECAP has a strong effect on the microstructure scale strain rate sensitivity. Deformation centered at grain boundaries separating regions of banded microstructure exhibits the greatest strain rate sensitivity. Strain rate sensitivity is limited in deformation occurring in regions of microstructure composed of ultrafine grains separated by low-angle grain boundaries. The tensile specimens all failed by shear bands at 200 °C and at room temperature they failed by necking with little plastic deformation apparent outside of the neck.

Over the last decade, the inclusion of nanofeatures has been demonstrated extensively for improving the performance of thermoelectric materials. The continued approach is to nanofeaturing these materials in a smart manner tailoring their electronic and thermal response. This research provides a computational tool for predicting all parameters in the thermoelectric figure of merit for a Si/Ge superlattice structure as a function of doping and layer thickness. The approach involves coupling a nonequilibrium Green's function electronic and thermal transport model. The phonon description is communicated between the two models to facilitate spatially resolved multiphonon frequency electron–phonon scattering. Findings support the consideration of multiple phonon frequency scattering to accurately predict ZT values. An extrema in ZT as function of both doping and geometry were predicted. Furthermore, the optimal superlattice design was determined to be a Si(2 nm)/Ge(7 nm) with a donor concentration on the order of 1019 cm−3 for operation at 300 K.

Microelectromechanical systems (MEMS) are increasingly at our fingertips. To understand and thereby improve their performance, especially given their ever-decreasing sizes, it is crucial to measure their functionality in situ. Atomic force microscopy (AFM) is well suited for such studies, allowing nanoscale lateral and vertical resolution of static displacements, as well as mapping of the dynamic response of these physically actuating microsystems. In this work, the vibration of a tuning fork based viscosity sensor is mapped and compared to model experiments in air, liquid, and a curing collagen gel. The switching response of a MEMS switch with nanosecond time-scale activation is also monitored – including mapping resonances of the driving microcantilever and the displacement of an overhanging contact structure in response to periodic pulsing. Such nanoscale in situ AFM investigations of MEMS can be crucial for enhancing modeling, design, and the ultimate performance of these increasingly important and sophisticated devices.

The alloyed layers were produced on Mg by heating the specimens in contact with pure Al powder or Al + Zn powder mixtures. The powder material acting as the source of diffusion elements was held under pressure during heating, and this led to the formation of thick, continuous layers in a short heating time (1 h). The layer formation process took place through partial melting at the substrate/powder interface. The Al-enriched layer was characterized by a eutectic structure composed of an Mg17Al12 intermetallic phase and a solid solution of Al in Mg. The Al/Zn-enriched layers produced from Al + 20% Zn and Al + 40% Zn powder mixtures consisted of Mg17(Al,Zn)12 and Mg5Al2Zn2 and a solid solution of Al and Zn in Mg. The alloyed layers had higher hardness and better wear resistance than the Mg substrate. The results of the polarization measurements show that the Al- and the Al/Zn-enriched layers provide a certain level of protection to Mg against corrosion.

Aluminum matrix composite with 10 wt% of MoO3 particulate reinforcement was synthesized through powder metallurgy technique. The cold upsetting studies of the composites were investigated based on Taguchi L9 orthogonal array experimental design to evaluate the significance of compaction pressure, sintering temperature, and sintering time on strength coefficient. The combination of 350 MPa pressure, 600 °C temperature, and 90 minutes sintering time was identified as the optimum blend for maximum strength coefficient using the main effect plot. From the analysis of variance, compaction pressure and sintering temperature were identified as highly contributing parameters on strength coefficient. Further, a confirmation test was also conducted with the optimum parameter for validation of the Taguchi results. X-ray diffraction and scanning electron microscopy were used to confirm the presence of MoO3 and its uniform distribution over the aluminum matrix.

The effect of surface preparation—grinding, polishing, and electrochemical etching—on the duplex stainless steel passive film conductivity was investigated by in situ current sensing atomic force microscopy. The current maps show that the current in the passive film on three prepared surfaces is different, especially for the ferrite and austenite phase surface. The current on the austenite and ferrite is similar on either mechanical ground or polished surfaces, but the current on the austenite surface is much higher than current on the ferrite surface after electrochemical etching. The difference in the passive film conductivity originates from the changes in the chemical composition and thickness of the passive film and the change in topographical properties induced by the preparation procedures. This is confirmed by AFM, x-ray photoelectron spectroscopy, and auger electron spectroscopy measurements.