A large depth of 800 μm gradient microstructure was produced in pure titanium (Ti) by means of surface rolling treatment (SRT). The microstructural characteristics with different depths from the top surface were analyzed by optical microscopy, transmission electron microscopy, and electron backscattered diffraction. The results showed that, on the outmost surface, nanograins with an average grain size of ∼100 nm were achieved. In the subsurface, i.e., the deformation twinning region, a large volume fraction of {10$\overline 1$2} deformation twins together with a low fraction of {11$\overline 2$2} and {11$\overline 2$4} twins were identified. Based on the microstructural analysis, the grain refinement mechanisms with increasing strain are summarized as: (i) prior division by deformation twinning, (ii) refinement effect of subgrain boundaries resulting from the accumulation of high density of dislocation, and (iii) transformation effect from low angle grain boundaries to high angle grain boundaries. The results of tension tests also show that the titanium sample after SRT shows higher strength than the as-received titanium sample.

A reduction of iron (III) oxides deposited on expanded graphite (EG) matrixes of three types in hydrogen flow was studied in dynamic and static regimes. In the dynamic regime, the EG matrix was shown not to influence the temperature range of the iron (III) oxide reduction. However, the C/O atomic ratios, varying depending on the type of EG matrixes, affect the completeness of reduction of these oxides to metallic iron. The reduction kinetics of iron (III) oxides deposited on EG and of bulk oxides were found to be similar and could be described by the combination of expanded Prout–Tompkins autocatalysis and n-dimensional growth of nuclei models. The prolonged hydrogen treatment at 600 °C of the samples in the static regime results in quantitative reduction of iron (III) oxide to α-Fe independent of the type of EG matrix used. The obtained samples demonstrate the relatively high values of saturation magnetization of 35 emu/g together with a high sorption capacity for crude oil of 93 g/g.

Fe3O4@TiO2 magnetic photocatalysts containing sub-10-nm TiO2 nanocrystals with two different morphologies (nanoparticles and nanorods) were prepared via a facile straight dipping process. A series of comparative experiments on organic pollutant degradation demonstrated that Fe3O4@TiO2 nanorods show superior activity and faster degradation rates than Fe3O4@TiO2 nanoparticles. Combined with the study of high resolution transmission electron microscopy, crystal models are given to analyze the morphology effect of TiO2 nanocrystals on their photocatalytic activities for organic degradation. TiO2 nanorods with more (100) crystal planes, which have relatively higher surface energy and relative higher density of Ti atoms, showed a higher activity than that of TiO2 nanoparticles. Furthermore, both Fe3O4@TiO2 nanorods and Fe3O4@TiO2 nanoparticles show better photocatalytic activities than several comparison Fe3O4@TiO2 samples due to the strong size effect arising from the tiny size of TiO2 nanorods and nanoparticles. These magnetic photocatalysts also show advantages in separation and recycling utilization.

Titanium carbide (TiC) twins are believed to be extremely unstable because of their high twin boundary energy. Here, we report that TiC twins are always presented in platelets with dimensions of 2–3 μm in length and less than 300 nm in width. In-depth microstructural characterizations by high-resolution transmission electron microscopy demonstrate that Al atoms at the twin boundary play a decisive role in stabilizing TiC twins. With different amounts of Al, perfect and defective TiC twins are formed. For perfect twins, three types of twin boundaries can be formed depending on the amount of remaining Al at the twin boundary. With inadequate Al, the TiC twins become defective with certain degrees of deviation from the perfect twin orientation. Based on a detailed analysis of the microstructure of the twin boundaries, a mechanism for the formation and stabilization of TiC twins is proposed.

Materials and processes used for medical applications should have specific attributes. For bone repair and reconstruction, controlled open porosity and osteoconductivity are essential apart from mechanical strength and biocompatibility. Several forms of calcium phosphates are often used for these applications, considering properties similar to bone minerals, but often in combinations with other biopolymers. Polymethyl methacrylate (PMMA) and β-tricalcium phosphate (β-TCP) are identified as a suitable combination for the current research, considering specific properties both individually and in combinations, when processed by different means for specific medical applications. Specific responses of the biocomposite material formed by mechanically mixing the two materials in the powder form to selective laser sintering (SLS) under varying conditions are investigated. The results indicate the suitability of the material system for SLS, while controlled porosity and mechanical property combinations are possible by optimizing material composition and process parameters.

It is widely accepted that oxygen will severely deteriorate the glass-forming ability (GFA) of an alloy. In this work, we report that the GFA of a Fe76Si9B10P5 glassy alloy can be significantly improved (the critical diameter for fully glass formation is increased from 1 to 3 mm) under oxygen casting atmosphere. Furthermore, the pressure of oxygen atmosphere gives an obvious enhancement in the critical diameter of Fe76Si9B10P5 glassy alloy. A dependence of GFA on casting atmosphere species (argon, nitrogen, air, and oxygen) is also observed for this glassy alloy, and its critical diameter is 1, 1.5, 2.5, and 3 mm, respectively. In addition, the Fe-based glassy alloy exhibits excellent soft magnetic properties regardless of the applied casting atmosphere. The mechanism for such an unusual oxygen effect on the GFA of Fe76Si9B10P5 glassy alloy is attributed to the reduced nucleation rate caused by the enhancement of surface tension of the alloy melt.

The fracture property estimation of ductile materials with small volumes at room temperature was performed experimentally and analytically in this study. A modified energy method of the small punch test (SPT) was applied to estimate fracture toughness based on the membrane stretch analysis. The effective strain was assumed to be the average value of center strain and contact boundary strain. To overcome the problem involved in strain calculation by microscopic observation, one relatively simple correlation which related effective fracture strain to displacement was proposed. The results obtained by the modified energy model and conventional experiment were in good agreement. Furthermore, a three-dimensional finite element model was established successfully. The influence of ball diameter and center hole diameter in the lower die on the SPT was analyzed by detailed discussion. Finally, the applicability and accuracy of the modified energy model based on the SPT were proved. An economic, effective energy method can be obtained from the present study to assess the properties of in-service components and micrometer scale materials.

Two-dimensional crystals are an important class of materials for novel physics, chemistry, and engineering. Germanane (GeH), the germanium-based analogue of graphane (CH), is of particular interest due to its direct band gap and spin–orbit coupling. Here, we report the successful co-deposition growth of CaGe2 films on Ge(111) substrates by molecular beam epitaxy and their subsequent conversion to germanane by immersion in hydrochloric acid. We find that the growth of CaGe2 occurs within an adsorption-limited growth regime, which ensures stoichiometry of the film. We utilize in situ reflection high energy electron diffraction (RHEED) to explore the growth temperature window and find the best RHEED patterns at 750 °C. Finally, the CaGe2 films are immersed in hydrochloric acid to convert the films to germanane. Auger electron spectroscopy of the resulting film indicates the removal of Ca, and RHEED patterns indicate a single-crystal film with an in-plane orientation dictated by the underlying Ge(111) substrate. X-ray diffraction and Raman spectroscopy indicate that the resulting films are indeed germanane. Ex situ atomic force microscopy shows that the grain size of the germanane is on the order of a few micrometers, being primarily limited by terraces induced by the miscut of the Ge substrate. Thus, optimization of the substrate could lead to the long-term goal of large area germanane films.

TiO2 has attracted tremendous research interest for photocatalytic water splitting, solar hydrogen generation, environmental pollution removal, dye-sensitized solar cells, lithium-ion batteries, supercapacitors, and field emission. Microwave absorption materials (MAMs) play important roles in many military (e.g., the stealth coating on the B-2 bomber) and civil (e.g., telecommunications, noise reduction, information security, signal, and data protection) applications. However, TiO2 is not a good MAM due to its poor absorption in the microwave region. Here, we report that via hydrogenation excellent and tunable microwave absorption is achieved with hydrogenated TiO2 nanocrystals. After hydrogenation, 4.3x and 103x improvements have been obtained in storing and dissipating the electric energy of the microwave electromagnetic field. Their permittivity values are higher than those of the current carbonaceous MAMs. Instead of relying on the dipole rotation or ferromagnetic resonance mechanisms for traditional MAMs, the hydrogenated TiO2 nanocrystals work as good MAMs based on a newly proposed collective-movement-of-interfacial-dipole (CMID) mechanism. Although there is still no direct physical evidence of the interface effects of the CMID mechanism, the CMID as a hypothesis at this point successfully explained the origin of the enhanced microwave absorption of the hydrogenated TiO2 nanoparticles. This study thus may open new applications for TiO2 nanocrystals and also stimulate new approaches for new MAM development.

To evaluate the influence of strain rate on mechanical behavior of nanocrystalline (NC) materials, a phase mixture constitutive model composed of ordered grain interior phase and plastically softer grain boundary dislocation pile up zone phase was built. Because of dissimilar properties and mismatch between the two phases, dislocation density evolution controlling mechanism based on statistically stored dislocations and geometrically necessary dislocations was analyzed and extended to NC regime to consider their disparate effects. Based on the composite model, a new stress–strain constitutive relation for strain rate-dependent behaviors was firstly established based on dislocation density evolution and strain gradient theory. The calculated data were then compared with corresponding experimental curves and strong strain rate-dependent behaviors were exhibited, which indicated that the predictions kept in good agreement with experiments. Further discussions were presented for calculations of strain rate sensitivity and activation volume for NC Ni through the proposed model.

Solution-processed CuInGaS2 (CIGS) thin-film solar cells are promising for large-scale commercialization due to their economic process although the efficiency still needs to be improved to compete with vacuum-based materials. Systematic studies were performed to optimize the series and shunt resistance of hydrazine-based CIGS solar cells. Optimization was achieved through compositional adjustment of copper (Cu) near the p–n junction and gallium (Ga) near the back contact. Cu adjustments optimized the shunt resistance between 4000 and 5000 Ω cm2. Ga adjustments optimized the series resistance to 2 Ω cm2. Shunt and series resistance play vital roles in the fill factor. Fill factor was hence improved upward of 0.80 with the optimization of Cu and Ga. Chemical etching was also conducted to investigate the durability of the materials and to remove small crystals near the interface. Device conversion efficiencies were improved up to 12.4%. This study provides the implications for improving the device performance of chalcogenide solar cell materials.

In this study, we obtain true stress–strain (SS) curves for a sheet specimen under consideration of local necking and material anisotropy. We first extract the SS curve up to the diffuse necking point from the tensile test load–displacement data. The curve's part after the onset of diffuse necking is extrapolated by the weighted-average method proposed by Ling [Y. Ling, AMP J. Technol. 5, 37–48 (1996)]. Initiation of local necking is predicted by means of the minor-to-major strain ratio in the specimen's center. We propose a criterion to determine the strain ratio at the onset of local necking and the major strain corresponding to the strain ratio at local necking. We complete the true SS curve by cutting off the SS curve at the major strains corresponding to the local necking or apparent fracture point. Finally, the effects of material anisotropy on SS curves are discussed.

In this study, nickel acetate tetrahydrate (NACTH)/poly(styrene-co-acrylonitrile) (SAN) sol was used for the fabrication of nanocrystalline NiO nanofibers. An indigenous setup was developed to use these nanofibers for the oxidation of carbon monoxide (CO) and unburnt hydrocarbons (HC) from diesel engine exhaust. The morphological, compositional, and crystalline properties of the NiO nanofibers obtained after calcination were studied by scanning electron microscopy, Fourier transform infrared (FTIR) spectroscopy, and x-ray diffraction (XRD). Clear evidence of defects in the fibers was observed in ultraviolet–visible–near infrared (UV-Vis-NIR) spectra, Raman spectra, and magnetic property measurements. The NiO nanofiber mats supported by glass fiber mats were efficient in oxidizing CO and HC from diesel engine exhaust, and the maximum efficiency was achieved by using NiO nanofibers with the maximum amount of defects.

Our research aims at exploring a new oxygen reduction reaction (ORR) catalyst with effective catalytic capability, which can be used in the metal-air batteries. ORR electrocatalysts of carbon black and carbon aerogel supported Pt-based nanoparticles were synthesized by a chemical impregnation reduction method. The electrochemical measurement consisted of cyclic voltammetry (CV) and line scan of scanning electrochemical microscopy (SECM) conducted in alkaline medium as well as the single-cell tests. All the tests indicate that the Pt–Zn/carbon aerogel (Pt–Zn/CA) catalyst, with the specific discharge capacity reaching 1349.5 mA h g−1, exhibits the best catalytic performance among all the tested catalysts. The doping of Zn forms Pt-rich surface, creates more d-band vacancies, and reduces the leaching problem; the use of carbon aerogels brings larger specific surface area. These aspects have all improved the catalytic activity per unit mass.

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.

Aluminum metal matrix hybrid composites were synthesized through powder metallurgy route from ball milled powders to yield the compositions: Al + 0% TiO2, Al + 2.5% TiO2, Al + 2.5% TiO2 + 2% Gr, and Al + 2.5% TiO2 + 4% Gr. The densification and deformation properties of sintered Al–TiO2–Gr composites during cold upsetting were investigated experimentally. The powder preforms are compacted using suitable punch and die in 40 kN hydraulic press and the initial percentage theoretical density was maintained as 85%. Sintering was done in an electric muffle furnace at the temperature of 590 °C for a period of 3 h. The sintered preforms were subjected to incremental compressive loading of 10 kN until cracks were found at the free surface. The true axial stress (σz), true hoop stress (σθ), true hydrostatic stress (σm), and true effective stress (σeff) were calculated for all the preforms and all these stresses are correlated with the true axial strain (εz). The densification behaviors of the composites were studied against true axial strain (εz) and lateral strain. Better densification and deformation property were obtained for pure aluminum preforms compared with other composite preforms. Addition of TiO2 to the pure Al and Gr reinforcements increases the strength coefficient of the Al–TiO2 composite.