The effect of layer thickness on the hardness of nanometallic material composites with both coherent and incoherent interfaces was investigated using nanoindentation. Then, atomistic simulations were performed to identify the critical deformation mechanisms and explain the macroscopic behavior of the materials under investigation. Nanocomposites of different individual layer thicknesses, ranging from 1–30 nm, were manufactured and tested in nanoindentation. The findings were compared to the stress–strain curves obtained by atomistic simulations. The results reveal the role of the individual layer thickness as the thicker structures exhibit somehow different behavior than the thinner ones. This difference is attributed to the motion of the dislocations inside the layers. However, in all cases the hybrid structure was the strongest, implying that a particular improvement to the mechanical properties of the coherent nanocomposites can be achieved by adding a body-centered cubic layer on top of a face-centered cubic bilayer.

La4LiAuO8 is a stable Au3+ oxide that was recently examined as a possible model compound for the role of Au3+ in heterogeneous catalysis. Due to the paucity of thermodynamic data, the energetics of La4LiAuO8 and its likely decomposition product, LiLaO2, were investigated. The ΔHf−ox, of La4LiAuO8 and LaLiO2 are both exothermic at −187.7 ± 5.8 and −41.4 ± 9.6 kJ/mol, respectively. From the thermodynamic data, the decomposition temperature of La4LiAuO8 was calculated as either 979 ± 95 or 1331 ± 43 °C for the formation of LiLaO2 or Li2O, respectively. Thus, LiLaO2 is the expected decomposition product.

The structural features of wood were replicated in silica on all levels of hierarchy from the macroscopic to the nanoscopic level of the cellulose elementary fibrils. This was achieved by a series of processing steps on spruce wood templates. Sodium chlorite was used to partially remove the lignin matrix from the wood cell walls, exposing the cellulose fibrils. These were optionally functionalized with maleic acid anhydride to stabilize the fibrillar structure and reduce the shrinkage of the template. Repeated infiltration with tetraethyl orthosilicate in ethanol deposited silica on the fibrils. Calcination at 500 °C removed the rest of the organic template by oxidation and resulted in the fusion of the deposited material into a positive silica replica. Small-angle x-ray scattering evidenced fibrillar structures parallel to the original cellulose fibrils at length scales in the order of 10 nm, suggesting the successful nanoscopic replication of the cellulose fibrils and their orientation.

Nacre from mollusk shell is a high-performance natural composite composed of microscopic mineral tablets bonded by a tough biopolymer. Under tensile stress, the tablets slide on one another in a highly controlled fashion, which makes nacre 3000 times tougher than the mineral it is made of. Significant efforts have led to nacre-like materials, but none can yet match this amount of toughness amplification. This article presents the first synthetic material that successfully duplicates the mechanism of tablet sliding observed in nacre. Made of millimeter-size wavy poly-methyl-methacrylate tablets held by fasteners, this “model material” undergoes massive tablet sliding under tensile loading, accompanied by strain hardening. Analytical and finite element models successfully captured the salient deformation mechanisms in this material, enabling further design refinements and optimization. In addition, two new mechanisms were identified: the effect of free surfaces and “unzipping.” Both mechanisms may be relevant to natural materials such as nacre or bone.

The thermal conductivity of nacre from red abalone (Haliotis fulgens) has been determined as a function of temperature (2–300 K), direction, and treatment to partially demineralize or to remove a portion of the organic matrix. The room-temperature thermal conductivity and specific heat of nacre are ∼1 W m−1 K−1 and 0.9 J K−1 g−1, respectively. The thermal conductivity of nacre is rather low and glass-like. It is not as anisotropic as one might expect on the basis of brick-and-mortar structure, in support of recent findings that the aragonite tablets are not monolithic. Partial removal of the mineral component reduces the thermal conductivity in both principal directions, whereas partial removal of the proteins (as observed by 13C NMR) only reduces the thermal conductivity across the aragonite layers.

A single step gas phase method was developed to synthesize silica-coated iron oxide nanocomposite materials in a furnace aerosol reactor (FuAR) using premixed precursors. Synthesis of single component silica and magnetic iron oxide was studied to understand the decomposition mechanism of the precursors, identify the product crystal phase, and optimize the viable operating conditions for the controlled synthesis of nanocomposite material with desirable crystal phase, size, and morphology. The single component decomposition results are further extended to synthesize silica-coated magnetic iron oxide nanocomposite material using premixed precursor. A mechanism was proposed to explain the formation of SiO2-coated γ-Fe2O3 nanocomposite in a single step in a FuAR based on chemical kinetics and was verified by supporting characterization results. The synthesized magnetic γ-Fe2O3/SiO2 nanocomposite material was further tested for suspension stability, magnetic properties, and surface reactivity and was compared with uncoated γ-Fe2O3 nanoparticles to demonstrate improved surface properties.

Nickel-titanium (NiTi) alloys combine several remarkable characteristics, among them are shape-memory, superelasticity, great strain recovery, good biocompatibility, and corrosion resistance. These render them well suited to a wide range of medical applications, such as cardiovascular stents, laparoscopy, and dental applications such as NiTi endodontic files (EFs) used for root canal treatment, which are the focus of this work. Unfortunately, fatigue-induced and incidental failure of NiTi EFs is not uncommon, which may lead to severe medical consequences. Here we examine the effects of cobalt coatings with impregnated fullerene-like WS2 nanoparticles on file fatigue and failure. Dynamic x-ray diffraction, nanoindentation and torque measurements all indicate a significant improvement in the fatigue resistance and time to breakage of the coated files, stemming from reduced friction between the file and the surrounding tissue. These methods are possibly applicable to a variety of NiTi-based medical devices where fatigue and consequent failure are of relevance.

This study investigated a fundamental aspect of thermoelastic martensitic transformations in different shape memory alloys by means of interrupted thermal analysis technique using differential scanning calorimetry (DSC). The objective of this study was to determine the true transformation temperature interval. It also provides the opportunity to further the discussion of time dependence of the transformations. The study applied a technique of thermal arrest amidst phase transformations. The transformation temperature intervals were found to be 8.4 and 12.9 K for the forward and reverse B2↔B19′ martensitic transformation in a near-equiatomic Ti-50.2 at.% Ni alloy and 14.7 and 12.8 K in a Ni-rich Ti-50.8 at.% Ni alloy and 7.3 and 9.1 K for the L21↔orthorhombic transformation in a Ni43Co7Mn39In11 alloy. These values were significantly smaller than those commonly reported in the literature. The experimental evidences also demonstrated that the apparent time dependences of the martensitic transformations manifested in DSC analysis were artifacts caused by instrumental thermal inertia.

In this work, we have systematically explored the influence of thermo-mechanical treatment on the precipitation behavior and its strengthening in Inconel 740, a relatively new Ni-based superalloy, using specimens on which different levels of stresses were applied at 700 °C. With increasing applied stress, fraction of gamma prime precipitates increased (without significant size change) and nanoindentation hardness was enhanced. The stress effects were discussed in terms of the free energy barrier for heterogeneous nucleation and the prevailing mechanisms of precipitation strengthening.

In this study, compact Charpy impact testing was used to investigate the effect of processing history and dendrite morphology of bulk metallic glass matrix composites (BMGMCs) on impact toughness. Composite samples were fabricated via suction casting and semisolid forging, and the results were compared with crystalline alloys in the same geometry. A strong dependence on processing was observed, with samples exhibiting up to a 30-fold increase in impact toughness depending on processing and microstructure. Provided that attention is paid to processing techniques, BMGMCs are shown to have properties that equal or surpass some conventionally used crystalline alloys. These properties invite further exploration of these materials in structural applications.

The interaction between a dislocation and hydrogen is considered to play an important role in hydrogen-related fractures for metals; it has been experimentally reported that hydrogen affects the dislocation mobility. These studies, however, show different macroscopic softening and/or hardening effects in iron, and the interaction between the dislocation and hydrogen remains unclear. In this study, we investigated the occurrence of interactions between a {112}<111> edge dislocation and a hydrogen atom via the estimation of the stress-dependent energy barriers for the dislocation motion and hydrogen diffusion in alpha iron using atomistic calculations. Our results show the existence of boundary stress conditions: dislocation mobility increment (softening) occurs at a lower applied stress, dislocation mobility decrement (hardening) occurs at an intermediate stress, and no effects occur for the steady motion of a dislocation at a higher stress in this analysis condition.

Microcantilevers fabricated by microelectromechanical system processes were used to study the residual stresses in the film/substrate systems. Aluminum films were deposited on silicon nitride substrates by thermal evaporation at room and elevated temperatures, and residual stresses were characterized from the deflection profiles of the Al/SiNx microcantilevers. The Al/SiNx microcantilever beam made of room-temperature-deposited Al film was found to deflect toward the substrate side, which in turn resulted in compressive residual stress in the film. In contrary, the microcantilever of Al film deposited at 105 °C was found to deflect toward the side of Al film when the thickness ratio of film to substrate was greater than 0.31 and the residual film stresses were tensile. The axes with zero bending strain component and zero stresses, i.e., the bending and the neutral axes in the film/substrate system were also investigated. The results can be applied to the arm of the atomic force microscope to characterize its deflection and stresses.

Here, we describe the synthesis of novel titania nanosheets controllably doped with binary transition metal ions and their layer-by-layer self-assembly. The tailored Mn and Fe doping in exfoliated Ti0.6Mnx/2Fe(0.8-x)/2O2 (x = 0.0–0.4) nanosheets is achieved by systematically changing the molar ratio of Mn/Fe in K0.8Ti1.2MnxFe0.8-xO4 using a codoping strategy. The protonated layered crystals exhibit a delaminated behavior in the tetrabutylammonium hydroxide solution and are exfoliated into colloidal single sheets, which are characterized by a large lateral size and a thickness in molecular dimension. The resulted nanosheets are able to be layer-by-layer deposited with oppositely charged polymers into a composite organic/inorganic system.

In this study, we synthesized ZnO nanowires using Au catalytic particles formed on a ZnO seed layer. We modulated the microstructure of the ZnO seed layer by changing the sputtering power to investigate how the underlying ZnO film microstructure affects the distribution of ZnO nanowires. Examining the samples after each of the three key steps of the growth process (ZnO seed layer deposition, Au catalytic particle formation, and nanowire growth) using various characterization methods such as scanning electron microscopy, transmission electron microscopy, and x-ray diffraction helped us illuminate the profound impacts of the grain size of the seed layer on the nanowire density.

We report a detailed study of the structural, chemical, electrical, and magnetic properties of undoped ZnO thin films grown under different conditions and the films that were annealed in various environments and irradiated with an ultraviolet laser. Samples prepared in low oxygen pressure or subsequently annealed in vacuum have always been strongly magnetic. Oxygen-annealed films displayed a sequential transition from the ferromagnetic to the diamagnetic state as a function of the annealing temperature. Reversible switching of room temperature ferromagnetism and n-type conductivity have been demonstrated either by annealing in different environments or by a novel laser irradiation treatment. Enhancements in both the electrical conductivity and magnetic moment have been controlled precisely with laser pulses, without altering the crystal structure. Electron paramagnetic resonance data were found to be in good agreement with the magnetization and conductivity measurements. Our secondary ion mass spectrometer and electron energy loss spectrometer studies conclusively rule out the presence of any external ferromagnetic impurities.

Gallium-doped zinc oxide spin-coated thin films have been prepared by the sol–gel method. The influence of two solvents, isopropanol and 2-methoxyethanol (2-ME), and two chelating agents, monoethanolamine (MEA) and diethanolamine (DEA), was investigated. X-ray diffraction shows preferential (002) c-axis orientation of the crystallites influenced by the doping content and starting solution composition. Better orientation was obtained with 2-ME as a solvent because of a slower evaporation rate during the spin coating. Better orientation was also obtained using MEA as a stabilizer due to the weaker bonds formed with the Zn2+ ions. Typical film thickness was 550 nm. The transparency of the films was greater than 85% in the entire visible range. A sheet resistance of 68 Ω/□ was obtained for the ZnO film doped with 2 at.% of Ga using 2-ME and MEA as a solvent and stabilizer, respectively. The results show that the denser packing created using a high boiling temperature solvent and a low organic content stabilizer improved the layer’s electrical and optical properties.

We have measured at room temperature polarized visible and near-infrared and unpolarized mid-infrared (2.7 μm) emission spectra of Er3+ in LiNbO3 (LN) crystals grown from congruent melts doped with 0.0/0.5, 0.5/0.5, and 1.0/0.5 mol%/mol% In2O3/Er2O3. From the measured emission spectra, the emission and absorption cross section spectral distributions were analyzed based on McCumber theory and discussed in comparison with those spectra of only Er-doped LN bulk material and/or Ti: Er: LN waveguide structure and with the results from the unpolarized absorption measurements. For the 530 and 1530 nm transitions, the cross section value, polarization dependence, and spectral shape all change from the only Er-doped material to the In–Er-codoped crystal and show definite In2O3 doping level effect. The 559, 673, 996, and 1530 nm emission lifetimes were also measured and used to evaluate nonradiative multiphonon relaxation rate. The calculated radiative, measured lifetimes, and multiphonon relaxation rate also show In-codoping effects.

Recent studies by a number of research groups have shown that the structure of epitaxial BiFeO3 (BFO) films changes drastically as a function of substrate-induced biaxial compression, with the crystal structure changing from one being nearly rhombohedral (R-like) to one being nearly tetragonal (T-like), where the “T-like” structure is characterized by a highly enhanced c/a ratio of out-of-plane c to in-plane a lattice parameters. In this work, we show that the critical compressive strain σc necessary to induce this transition can be reduced significantly by substituting 10% Ba for Bi [Bi0.9Ba0.1FeO3−δ (BBFO)] and that the “T-like” phase in both BBFO and BFO is stable up to the decomposition temperatures of the films in air. Furthermore, our results show that the BBFO solid solution shows clear ferromagnetic properties in contrast to its undoped BFO counterpart.

A composite of boron nitride nanotubes (BNNTs) and iron (Fe) has been synthesized using a novel one-step process and characterized by optical, electron microscope, and mechanical measurement techniques. The BNNT–Fe composite, the first of this type produced to the best of our knowledge, is shown to have up to 24% higher specific yield strengths from stress–strain measurements and Rockwell Hardness C Scale (HRC), depth of penetration into sample of 120° diamond cone, 50% higher relative to a control sample of pure Fe. Scanning and transmission electron microscope imaging shows that the composite is comprised of a uniform nanoscale mixture of BNNTs bridging the metal particles.