The structure and origin of twin defects have been studied over the past half-century. Recently, there has been renewed interest in investigating the mechanisms by which twin defects facilitate the growth of bulk and nanoscale systems. This article reviews our understanding and experimental advances to unravel the complex role that twin defects play during crystal growth. The following topics are addressed: growth promotion at single and multiple, parallel and antiparallel twin boundaries; the role of {100} and {111} solid–liquid interfaces during crystallization; the application of realtime imaging to the study of crystal growth in the presence of twin defects; and suggested future research needed to shed light on the driving forces for twin-related phenomena. By providing a broad survey of the existing literature on twin-assisted crystal growth, we anticipate that our review will aid researchers in deciphering various growth forms that arise in materials processing applications.

A kind of nickel–aluminum bronze (Cu–10Al–4Fe–4Ni) prepared by centrifugal casting (CC) and gravity casting (GC), respectively, were investigated. The results indicate that CC alloy, which is totally different from GC alloy, consists of α, κI, κII, κIII, κIV, and β′ phases and the microstructures of CC alloy shows nonuniformities from external to internal layer mainly because the distribution of iron and nickel are influenced by centrifugal force. Besides, it is noted that comprehensive mechanical properties of CC alloy are superior to those of GC alloy. Additionally, heat treatments were performed on CC alloy. The results demonstrate the optimal heat treatment is aging at 450 °C/1 h by air cooling after solution treated at 890 °C/1 h by water quench. The ultimate tensile strength and hardness are increased by about 10% and 56%, respectively, and wear resistance is also greatly improved. However, the elongation is decreased by 53%.

The photocathodic current density of ZnO/hematite hetero nanoarchitectures electrode has been reported in the current investigation. The electrode was obtained with a cheap and two-step hydrothermal functionalization of pristine silicon doped hematite film. The optical, structural, and morphological properties of the electrodes have been studied in detail and it is found that the ZnO functionalization of hematite changes its crystallographic properties by decreasing the Bragg peak intensity ratio for (104) planes. The morphology obtained in this case is unique in the sense that it does not cover the original hematite film and is formed in an isolated manner. Finally, employing a qualitative energy band gap model for mixed metal oxides energy levels has identified the photocathodic properties of the electrode. Here it is found that the photocathodic properties of the electrode are much higher when an electron transfer takes place from the conduction band of ZnO into the electrolyte while hole generated in ZnO is transferred back to hematite but it also degrades the structures after running photoanodic current density sweep. That points to the decrease of water oxidation behavior of hematite in conjunction with ZnO.

A hot wire chemical vapor deposition technique is described for synthesis of 1D nanostructures of a controlled morphology, stoichiometry, and composition. The synthesis involves the evaporation and condensation of metal oxide vapor through the reaction of oxygen with the hot filaments of respective transition metals. The stoichiometry and morphology of MoO3 and WO3 were modulated by varying the filament temperature and partial pressure of oxygen in the growth chamber. Based on the results under different conditions, a morphological phase diagram, and a growth model based on the extent of gas phase supersaturation were developed to understand the growth mechanism. Further, ternary transition metal oxide, NiMoO4, was synthesized as a proof-of-concept for tuning the composition of deposition through simultaneous evaporation of two metal oxides.

The dislocation movements under the action of electric pulses (athermal effect) at cryogenic conditions were studied by ex situ transmission electron microscopy (TEM) observations and slip trace analysis innovatively. By applying electric pulses directly through aluminum TEM samples in a liquid nitrogen bath, plenty of non-octahedral-like dislocation glides generally forming at high temperatures (e.g., >453 K for aluminum) were observed at cryogenic temperatures (<130 K). Occurrence of the non-octahedral-like dislocation glides indicates a substantial increase in the degrees of freedom for dislocation glides, offering a new/complementary explanation for the acceleration effect of electric pulses on dislocation movements, especially in the sole athermal effect. In comparison, previous theories relied on extra driving force and/or increased dislocation mobility on the octahedral planes in a face-centered cubic metal. The athermal effects of electric pulse were discussed and the selective heating at the dislocation cores was proposed to account for non-octahedral-like dislocation glides.

A novel core–shell particle that consists of epoxide-terminated hyperbranched polymer (HBP) and silica nanoparticles was incorporated into an epoxy/hydroxyl-terminated HBP blend to fabricate a high-performance epoxy thermoset. The effect of the core–shell particle content on the mechanical properties of the epoxy thermosets was investigated in detail. Results from tensile, flexural, and impact tests are provided. The impact fracture surface was studied by field emission-scanning electron microscopy. The incorporation of 2 wt% core–shell particles improved the tensile strength, percent elongation at break, flexural strength, and impact resistance of epoxy/hydroxyl-terminated HBP thermosets. Field emission-scanning electron micrographs showed that core–shell particle addition resulted in large-scale shear deformation and debonding from the epoxy matrix, and improved the epoxy resin toughness.

Inconel 617 alloy (IN 617) is an important candidate material of advanced ultrasupercritical power unit above 700 °C. However, there are some issues in welding of IN 617 such as constitutional liquation and hot cracking. Tungsten inert gas (TIG) is considered as an effective welding method to join IN 617 because of low heat input and high quality. Investigation of the microstructure variation of TIG welded joint and its correlation with properties is helpful in deep understanding the stability and reliability of IN 617 welded joint. In this paper, the microstructure evolution and element segregation of IN 617 welded joint were investigated systematically. It is found that the base metal (BM) with significant banded structure is characterized by austenitic grains and some secondary phases distribute along the grain boundaries and inside the grains. The fine secondary phases are determined as M23C6 enriched with Cr and Mo elements. A few large polygon phases are identified as Ti(C, N) with a size of about 10 μm. The coarsened secondary phases are observed in the heat affected zone (HAZ) close to BM whilst the lamellar structure enriched with Cr and Mo is present along grain boundaries in the HAZ near the fusion line. The weld metal (WM) is fully austenitic with a dendritic structure and contains particles dispersing in the matrix. The element segregation on grain boundaries of IN 617 welded joint was analyzed by energy dispersive spectrometer. No obvious element segregation was observed in HAZ. In WM, the area in the vicinity of solidification grain boundaries and solidification subgrain boundaries (SSGBs) has a local depletion of Ni and Co while the Cr and Mo have no obvious segregation. Microhardness and high temperature tensile test of BM and WM were conducted. The WM has a little bit larger hardness value than BM and HAZ because of the strengthening effect of SSGBs. The fracture position is determined in the middle of WM, which is attributed to the grain boundary failure in the center of WM. The high temperature tensile properties of the welded joint are close to BM. In this investigation, the constitutional liquation in HAZ and solidification in WM have little effect on the high temperature tensile properties. TIG welding method is proved to be a suitable welding method to join IN 617.

A new lab-based aerosol jet fog (ajFOG) deposition system with an atomizer consisting of two opposing jets located within the deposition chamber is introduced and its capabilities are examined. The unique opposing configuration of the atomizer enables the formation of a highly uniform fog even from low volatility precursors. Aluminum oxide phosphate (AlPO) thin films were deposited onto Si wafers at room temperature and sub-atmospheric pressure by using an aqueous precursor. Films were characterized by spectroscopic ellipsometry, x-ray diffraction and reflectivity, scanning electron microscopy, and metal/oxide/semiconductor (MOS) capacitor electrical measurements. Film thickness uniformity, density, surface roughness, and charge transport mechanisms were found to be comparable to spin-coated thin films deposited using the same precursor, demonstrating the effectiveness of this aerosol technique. A process model was developed to predict film thickness as a function of precursor concentration, exposure time, fog settling time, and number of exposures.

(KxNa1−x)NbO3 films were deposited on Nb-doped (100)SrTiO3 substrates at 240 °C for times between 1 and 6 h by a hydrothermal method. Over this time series, the measured (K + Na)/Nb ratio of the films was found to remain constant, but the bulk K/(K + Na) ratio, x, decreased from an initial value of 0.75–0.56. It was determined that film growth initially proceeded through crystallization of the K-rich phase (K0.75Na0.25)NbO3. For film growth times greater than 3 h, a second perovskite phase with a smaller unit cell volume was detected, with an estimated composition of (K0.36Na0.64)NbO3. As such, the measured bulk composition value x = 0.56 was determined to be the result of a combination of these two phases, as opposed to originating from a single phase. Cross-sectional transmission electron microscopy analyses of films prepared for 6 h revealed that they consist of two layers in the direction normal to the substrate; this bilayer-type structure, only observed for hydrothermal growth of this material, is considered to arise from the large solubility mismatch between the Nb precursor and KOH and NaOH in the growth solution.

A scale formed by heat treatment of Ti in a nitrogen atmosphere containing oxygen at an extremely low partial pressure exhibited an exceptional degree of hydroxyapatite (HAp) formation in a simulated body fluid. Scanning transmission electron microscopy and electron energy loss spectroscopy indicated that the subsurface of this scale was composed of nitrogen doped rutile-type TiO2. The N-K edge energy-loss near edge structure spectrum of this layer in conjunction with the theoretical spectra of possible compounds obtained using the augmented plane wave plus local orbital band method suggested that oxygen sites were replaced by two nitrogens, resulting in an effective charge of +2. The enhanced HAp forming ability of this scale is likely related to the positively charged surface induced by the presence of N. Conversely, the subsurface scale formed by heat treatment in air, in which N is not found, leads to much slower HAp coverage, believed to be related to the lack of surface charge.

Understanding magnetosome magnetite biomineralization is of fundamental interest to devising the strategies for bioinspired synthesis of magnetic materials at the nanoscale. Thus, we investigated the early stages of magnetosome formation in this work and correlated the size and emergent crystallinity of magnetosome nanoparticles with the changes in chemical environment of iron and oxygen by utilizing advanced analytical electron microscopy techniques. We observed that magnetosomes in the early stages of biomineralization with the sizes of 5–10 nm were amorphous, with a majority of iron present as Fe3+, indicative of ferric hydroxide. The magnetosomes with intermediate sizes showed partially crystalline structure with a majority of iron present as Fe3+ and trace amounts of Fe2+. The fully maturated magnetosomes were indexed to magnetite. Our approach provides spatially resolved structural and chemical information of individual magnetosomes with different particle sizes, attributed to magnetosomes at different stages of biomineralization.

The objective of this investigation was to utilize the first-principles molecular dynamics computational approach to investigate the lithiation characteristics of empty silicon clathrates (Si46) for applications as potential anode materials in lithium-ion batteries. The energy of formation, volume expansion, and theoretical capacity were computed for empty silicon clathrates as a function of Li. The theoretical results were compared against experimental data of long-term cyclic tests performed on half-cells using electrodes fabricated from Si46 prepared using a Hofmann-type elimination–oxidation reaction. The comparison revealed that the theoretically predicted capacity (of 791.6 mAh/g) agreed with experimental data (809 mAh/g) that occurred after insertion of 48 Li atoms. The calculations showed that overlithiation beyond 66 Li atoms can cause large volume expansion with a volume strain as high as 120%, which may correlate to experimental observations of decreasing capacities from the maximum at 1030 mAh/g to 553 mA h/g during long-term cycling tests. The finding suggests that overlithiation beyond 66 Li atoms may have caused damage to the cage structure and led to lower reversible capacities.

In this study, the ternary Ge–Sb–Se chalcogenide glass was fabricated by a standard melt-quenching technique for flexible infrared lenses. Chalcogenide glass should have unique thermal and mechanical properties to be applied to precision glass molding (PGM) process. Therefore, the relations between thermal properties and the moldability were investigated for (35–20)Ge–(5–20)Sb–60Se glass systems. The thermal and thermos-mechanical properties were characterized by the differential scanning calorimeter and thermos-mechanical analysis, respectively. Preceding experiments using a pressing tester were conducted before PGM process to evaluate the moldability. The surface condition of both chalcogenide glass disks and Tungsten Carbide (WC) molds were characterized by using an optical microscopy and an interferometer. The preferential compositions in (35–20)Ge–(5–20)Sb–60Se glass systems were selected to produce molded lenses. Finally, the molded chalcogenide lens was successfully fabricated using the preferential compositions and the processing conditions from the preceding experiments using a pressing tester.

In this work, the selective removal of ions from multicomponent mixtures using functionalized magnetic nanoparticles (FMNPs) was demonstrated. As, Sb, and Se ions were efficiently removed from complex mixtures, such as Rhodiola rosea extracts and influent water from the sewage treatment unit of a beer brewery. As, Sb, and Se ions could be selectively adsorbed by FMNP, as demonstrated by the inductively coupled plasma mass spectrometer analyses. We also demonstrated that Pb ions are weakly adsorbed, whereas Cu, Cd, and Zn ions cannot be adsorbed by FMNP. The complexity of the mixture did not affect the selective removal of As, Sb, and Se ions. FMNP could be recycled and used repeatedly. Magnetic separation could then be applied for the selective separation of complex mixtures, such as plant extracts, industrial wastewater, and tap water.

In this paper many studies have been carried out to ascertain the phenomenon of strain-induced precipitation and coarsening of carbides in AISI H13 hot-work die steel during the tests at 700 °C. The microstructure of H13 with various loadings was studied to identify the effects of mechanical strain on the evolutionary behavior of carbides. SEM and TEM were used to observe the size and distribution of the carbides of each sample. It was found that the coagulation of carbides is more obvious in mechanical strained samples than that in mechanical strain-free sample which means mechanical strain promotes the precipitation and coarsening of carbides, and these processes are affected by the mechanical strain amplitude. Precipitation is increased by the strain enhanced because of more nucleation sites produced and accelerate the diffusion of solute atoms. Moreover, the results are shown that lower strain rates are more beneficial for precipitation and coarsening of carbides under the same strain because they provide a longer time to nucleate and grow into nuclei.

We have recently reported the repair of carious enamel using a full-length amelogenin–chitosan hydrogel through guided stabilization and growth of mineral clusters. The objective of this study was to further evaluate the enamel repair potential of smaller amelogenin peptides like LRAP (leucine-rich amelogenin peptide) and compare their efficiency with their full-length counterpart. The demineralized tooth slices treated with a single application of LRAP–chitosan hydrogel for 3 days showed a dense mineralized layer consisting of highly organized enamel-like apatite crystals. Focus-ion beam technique showed a seamless growth at the interface between the repaired layer and native enamel. There was a marked improvement in the surface hardness after treatment of the demineralized sample with almost 87% recovery of the hardness value to that of sound enamel sections. This current approach can inspire the design of smaller peptide analogues based on naturally occurring amelogenin as a competent, low-cost, and safe strategy for enamel biomimetics to curb the high prevalence of incipient dental caries.

The potency of many biomedical applications of gold nanoparticles (AuNPs); i.e., (i) bioimaging, (ii) diagnostic, (iii) therapeutic, (iv) drug carriers, and (v) immunochemical properties; are limited due its sensitivity toward salt and pH allowing variation in nanogeometry during practical applications. Such limitations directed the synthesis of AuNPs having extreme salt and pH resistant ability which has been undertaken in current research program. It has been found that the pH and salt tolerance ability of AuNPs are dependent on the nature of reducing and stabilizing agents. The use of organic amine containing reagents, i.e., polyethylenimine, 3-aminopropyltrimethoxysilane, in the presence of formaldehyde is examined that allows controlled and rapid synthesis of AuNPs having salt and pH tolerance ability. The mechanism justifying these properties of as-made AuNPs are presented herein. These reagents not only allow the synthesis of monometallic nanoparticles (NPs) but also enable the synthesis of bimetallic and trimetallic NPs. The synthesis of Au–Ag/Ag–Au, Pd-Au/Ag@(PdAu) NPs are examined involving the contribution of organic amine.

Bulk nanocrystalline (NC) silvers were fabricated by spark plasma sintering process. The effects of sintering temperature on physical and mechanical properties of the NC silvers were investigated. The results indicate that no impurities were introduced into the bulk compacts during the preparation procedure. Both the density and the electrical conductivity of the NC Ag increase with an increase in sintering temperature. However, the micro-hardness and ultimate tensile strength (UTS) of the bulk compacts increase initially and then decrease with increasing sintering temperature. The NC Ag sintered at 500 °C exhibits the highest micro-hardness of 85.3 HV along with the best compression yield strength of 379 MPa and the highest UTS of 534 MPa. The deterioration of the mechanical properties of the NC Ag sintered at 550 °C should be attributed to the rapid grain growth.

Powder metallurgy processing of aluminum alloy based metal matrix composites (MMC) is realized to be a promising alternative as expected to advance rapidly compared to other conventional methods. This paper reviews the extensive development in metal–matrix composite research works with particular focus on aluminum alloys 2xxx series as metal–matrix particulates processed by powder metallurgy route. Effect of reinforcement materials such as SiC and Al2O3 on the mechanical properties of the composites manufactured through conventional methods and powder metallurgy route are compared and presented. The influence of percentage of reinforcement material on the overall properties of the MMC's as reported by the researchers are presented. Summary on fundamental aspects of manufacturing MMC's via powder metallurgy route, the effect of mechanical properties, tribological properties, and microstructural properties are presented. Eventually, some advantages of powder metallurgy method are mentioned which may substantiate the claim to consider this as a novel method for near net shape manufacturing.

Wear and corrosion exist as one of the main important factor of energy and material losses in mechanical and chemical process. Coating is classified as one of the ways to enhance energy, chemical, and mechanical durability. Several previous investigations reported that addition of nanoparticle as an additive will enhance the characteristic of surface roughness and wear properties. The objective of this study is to investigate the wear, surface roughness, and corrosion resistance of Co–Ni–Fe nanoparticles electrodeposited on mild steel. The effect of deposition time toward physical properties (composition, surface morphology, and surface roughness), hardness, corrosion, and slurry wear erosion properties of coated mild steel were investigated. The finding showed that the increase of the deposition time led to an increment of hardness and coating thickness. The optimum Co–Ni–Fe nanoparticles deposited at 30 min produced a uniform coating and microhardness of 277.42 HV. Besides, the cumulative coating mass loss obtained from 30 min deposited coating sample was the lowest at both rotational speeds of 300 and 1200 rpm. It was observed that the optimum deposition time improved the surface roughness, coating morphology, hardness and resistance toward slurry erosion and corrosion.