The mechanical properties of ultrafine-grained and nanograined materials have received a great deal of recent attention because of their unusual and promising values. However, some of the most important mechanisms of deformation remain unclear. In this work, the deformation behavior of ultrafine-grained Al films and ultrafine-grained Fe is studied through in situ nanoindentation in a transmission electron microscope. Deformation-induced coarsening by grain boundary migration was observed in the ultrafine-grained Al films during deformation at room temperature, whereas no grain boundary motion was found in ultrafine-grained Fe. The lack of grain boundary motion in Fe was attributed to the pinning effect of nano-sized particles at the Fe grain boundaries.

In the relationship between unloading contact stiffness, elastic modulus, and contact area, which is the fundamental basic equation for nanoindentation analysis, a multiplicative correction factor is generally needed. Sometimes this correction factor is called γ to take into account the elastic radial inward displacements, and sometimes it is called β to correct for the fact that the indenter shape is not a perfect cone. In reality, these two effects simultaneously coexist and thus it is proposed that this correction factor is α = βγ. From nanoindentation data measured on three materials of different elastic moduli with a sharp Berkovich indenter and a worn one, the tip of which was blunt, it is demonstrated that the correction factor α does not have a constant value for a given material and indenter type but depends on the indenter tip rounding and also on the deformation of the indenter during indentation. It seems that α increases with the tip radius and also with the elastic modulus of the measured materials.

A facile solvothermal approach was successfully developed for the large-scale synthesis of amorphous phosphorus nitride imide (H3xP3N5+x) nanotubes with high luminescent properties by the reaction of 1,3,5-hexachlorotriphosphazene (P3N3Cl6) with sodium amide (NaNH2) at low temperatures. Transmission electron microscope images showed that the inner diameter of nanotubes is 120 ± 20 nm, wall thickness is 40 ± 10 nm, and length ranges from several to ten micrometers. Scanning electron microscope images revealed that the proportion of the nanotubes exceeds 90%. X-ray photoelectron spectroscopy spectra indicated that the binding energies of P2p and N1s are 133.30 and 398.40 eV, respectively, and the atomic ratio of P:N is 3:5.13. The infrared spectra of the sample are comparable to those of the reported HPN2 and HP4N7. Thermogravimetric analysis revealed that the product is very robust in a nonoxidizing atmosphere. The structure and the optical properties of the product and the annealed samples were investigated by x-ray diffraction and photoluminescence measurements, respectively.

The cationic surfactant cetyltrimetylammonium bromide was used to synthesize mesostructured γ–Al2O3. The effects of the surfactant concentration and of the sol aging (at 95 °C for 24 h) were studied by x-ray powder diffraction, nuclear magnetic resonance, transmission electron microscopy, and analysis of the low-temperature nitrogen adsorption-desorption isotherms. Mesostructured alumina with wormhole morphology and amorphous walls was obtained through the precipitation by ammonium hydroxide of a 0.1 M aluminum nitrate aqueous solution in presence of 0.1 M surfactant. The pore size was smaller than 5 nm. After digesting the milky suspension under atmospheric pressure at 95 °C, a crystallized boehmite-surfactant phase, with fiber morphology, is formed which at 550 and 700 °C is transformed into a highly porous γ−Al2O3. A similar evolution was observed using 0.01 M CTAB solution and aging. Pore volume up to 1.1 cm3/g and pore size up to 16 nm were obtained. Without surfactant, the same aging treatment led to aggregated fibers: the pore size is less than 8 nm and the pore volume is smaller than 0.6 cm3/g. The γ-alumina surface area is determined mainly by the organization generated by the surfactant and to a lesser extent by the boehmite precursor particle size. From the point of view of catalyst preparation, the surfactant at the concentration of 0.01 M in 0.1 M aluminum nitrate and the aging treatment in solution play a beneficial role.

Titanium targets with a bias voltage ranging from −500 to +500 V were submitted to multipulse high repetition rate Nd:yttrium aluminum garnet (YAG; λ = 1.064 μm, τ ∼ 300 ns, ν = 30 kHz) laser irradiations in nitrogen at intensity values below the single-pulse melting threshold. The morphology of the TiN structures formed under the cumulative action of the laser pulses on the surface of the unbiased and biased targets was investigated by profilometry and scanning electron microscopy. Under these irradiation conditions, a specific columnar surface microrelief developed. The height of the microcolumns reached about 10–15 μm, and their diameter about 1–2 μm. The development of TiN microcolumns was enhanced by the applied bias voltage. The enhancement in the negative biased samples was stronger than that in the positive biased ones.

We examined the influence of the boundary plane on grain-boundary diffusion in Ni through a series of molecular dynamics simulations. A series of 〈010〉 ∑5 tilt boundaries, including several high symmetry and low symmetry boundary planes, were considered. The self-diffusion coefficient is a strong function of boundary inclination at low temperature but is almost independent of inclination at high temperature. At all temperatures, the self-diffusion coefficients are low when at least one of the two grains has a normal with low Miller indices. The grain boundary self-diffusion coefficient is an Arrhenius function of temperature. The logarithm of the pre-exponential factor in the Arrhenius expression was shown to be nearly proportional to the activation energy for diffusion. The activation energy for self-diffusion in a (103) symmetric tilt boundary is much higher than in boundaries with other inclinations. We discuss the origin of the boundary plane density–diffusion coefficient correlation.

Compositional and microstructural differences from bottom to top along a water-quenched Zr41Ti14Cu12.5Ni10Be22.5 alloy rod, 90 mm in length and 22 mm in diameter, were investigated experimentally by x-ray diffraction measurement, differential scanning calorimetry, and composition analysis. The results show that the upper part of the rod contains more beryllium atoms and is amorphous. The lower part with less beryllium atoms contains crystalline phases. The composition gradient is possibly due to the gravity-driven transport of Be-rich clusters and un-melted tiny solid pieces in the alloy melt.

Nanostructured titanium carbonitride (TiC0.5N0.5) powders were synthesized by a Mg-thermal reduction process. The evaporated liquid solution made from TiCl4 + ¼C2Cl4 reacted with liquid magnesium protected with nitrogen gas. The extremely fine titanium carbonitride particles of about 50 nm were successfully produced by the reaction of Ti and C atoms released from chloride reduction with liquid magnesium and nitrogen gas. After the reduction process, the residual phases of MgCl2 and the excess Mg were removed by mechanical vacuum conditions. To obtain the maximized stoichiometry of product, the process optimization with thermodynamic study was performed with various experimental parameters such as reaction temperatures and solution feeding rates.

It has been generally accepted that YBa2Cu3O7−x (YBCO) films deposited on deformation textured polycrystalline metal tapes result in YBCO grain boundary (GB) networks that essentially replicate the GBs of the underlying substrate. Here we report that for thicker YBCO films produced by a BaF2 ex situ process, this is not true. Using electron backscatter diffraction combined with ion milling, we have been able to map the evolution of the YBCO grain structure and compare it to the underlying template in several coated conductors. For thin (≤0.5 μm) YBCO films deposited on rolling-assisted biaxially textured substrates (RABiTS), the YBCO GBs nearly directly overlap the substrate GBs. For 0.7–1.4 μm YBCO films, the GBs were found to meander along the substrate GBs and along the sample normal, with displacements several times the film thickness. In very thick films (2.5–2.9 μm), the YBCO grains can completely overgrow substrate grains and GBs, resulting in a substantial disconnection of the YBCO and substrate GB networks. Similar behavior is found for BaF2 ex situ YBCO films on ion-beam-assisted deposition-type templates. The ability of the YBCO to overgrow substrate grains and GBs is believed to be due to liquid-phase mediated laminar grain growth. Although the behavior of the YBCO GB networks changes with YBCO film thickness, the samples maintained high critical current density (Jc) values of >2 MA/cm2 for films up to 1.4 μm thick, and up to0.9 MA/cm2 for 2.5–2.9-μm-thick films.

Numerous studies have examined arsenic adsorption on varying adsorbents including iron oxides, aluminum hydroxides, alumina, and carbon as a means of arsenic removal in drinking water treatments. The objectives of this study were to evaluate the effect of magnetite particle size on the adsorption and desorption behavior of arsenite and arsenate, and to investigate the competitive adsorption between natural organic matter (NOM) and arsenic. Increases in adsorption maximum capacities for arsenite and arsenate were observed with decreasing magnetite particle size. Arsenic desorption is hysteretic, more so with the smaller nanoparticles. Such desorption hysteresis might result from a higher arsenic affinity for magnetite nanoparticles. In the presence of NOM, substantial decrease in arsenic sorption to magnetite nanoparticles was observed. It would be beneficial to thoroughly investigate adsorption and desorption of arsenic on magnetite nanoparticles for further practical purposes.

In this work, the effect of Fe2O3 addition on the microstructure and piezoelectric properties of Pb(Zn1/3Nb2/3)0.2Ti0.4Zr0.4O3 (0.2PZN–0.8PZT) ceramics were investigated. The studies indicated that the solution limit of Fe2O3 in the lattice of perovskite structure was about 0.1 wt%. Phase analysis shows that small addition of doping Fe2O3 results in the phase evolution from rhombohedral to tetragonal, sharp decrease of the Curie temperature, and remarkable increase of the grain size. Meanwhile, Fe2O3 addition within the solution limit led to the increase of the εr, kp, and d33. It is believed that the variation in the dielectric and piezoelectric properties are closely related to the microstructure change, phase evolution, and tetragonal distortion as Fe2O3 added.

The leaching of Cs from well-characterized Cs-bearing hollandite powders with ideal formula Cs0.8Ba0.4Ti8O16 was studied at 200 °C under static oxidizing conditions achieved using dilute nitric acid solutions. A variety of techniques were used to elucidate the leaching mechanism including x-ray powder diffraction, magnetic susceptibility, x-ray absorption near edge structure, and electron microscopy. Under the conditions of the study, Cs is leached from Cs-hollandite according to a deceleratory rate law with contracting geometries. The principal reaction products are rutile and brookite. The leaching mechanism involves the formation of a quasi-continuous, and hence relatively impermeable, secondary titanium oxide phase (rutile and/or brookite) on the surfaces of the hollandite crystallites. The driving force for the leaching reaction appears to be the oxidation of Ti3+ in the structure by the oxidizing acid, which then promotes extraction of Cs and Ba from the hollandite tunnels followed by tunnel destabilization and transformation to rutile and brookite.

Characteristics of the dynamic strain aging (DSA) in the Portevin-Le Chatelier effect are experimentally investigated by dynamic indentation tests and numerically analyzed by using literature models. Experimental results obtained on Al–Mg alloys show that the occurrence and development of the plastic instabilities—serrated indentation—depend strongly on the solute content. During dynamic microindentation tests the amplitude of microhardness drops—similarly to the global hardness—and is changing as a power law function of Mg solute content with an exponent of 2/3. It has been shown that the term describing the effect of DSA in serrated flow is not proportional but rather a power expression of the local solute concentration, Cs, on the dislocation line with the exponent of 1/2. Together with this, the kinetics of solute segregation during DSA is controlled by the pipe diffusion.

The superplastic behavior of the Zr65Al10Ni10Cu15 glass metallic alloy produced by the powder metallurgy method was examined in the supercooled liquid region. A tensile elongation as large as 750% was obtained at 6.3 × 10−3 s−1 at 697 K. Large strain hardening took place during the course of deformation and systematic trend was observed in the hardening behavior. Plots of stress versus strain and strain rate versus stress at 697 K showed that Newtonian viscous flow governed the plastic flow until the onset of strain hardening. Microstructure and differential scanning calorimetry analyses as well as flow stress versus testing time curves provided consistent evidence that the strain hardening was induced by crystallization. Crystallization was enhanced in the gauge region (deformed region) as compared to the grip region (undeformed region). Crystallization is expected to decrease tensile ductility by decreasing the strain-rate-sensitivity value and increasing the degree of brittleness. Hardening by crystallization, however, can contribute to neck stability if crystallization is enhanced in the neck region. The strain hardening and plastic stability parameters were measured as a function of strain for different strain rates at 696 K. The strain hardening parameter remained highly positive until failure. Because of this, the neck stability parameter (I) could be I < 0 in the entire hardening region. The contribution of hardening by crystallization to neck stability was found to be much more significant than that by grain growth in the superplastic metallic alloys. Reducing the specimen heating-and-holding time was suggested to promote superplasticity deformation without delaying initiation of crystallization. The largest tensile strain in the hardening region where crystallization may be obtained at the strain rates and temperatures where crystallization rate is controlled to be the lowest while maintaining I ≤ 0 throughout deformation.

Interest in finding binary alloys that can form bulk metallic glasses has stimulated recent work on the Cu–Zr system, which is known to show glass formation over a wide composition range. This work focuses on copper mold casting of Cu50Zr50 (at.%), and it is shown that fully amorphous rods up to 2-mm diameter can be obtained. The primary intermetallic phase competing with glass formation on cooling is identified, and the glass-forming ability is interpreted in terms of a metastable eutectic involving this phase. Minor additions of aluminum increase the glass-forming ability: with addition of 4 at.% Al to Cu50Zr50, rods of at least 5-mm diameter can be cast fully amorphous. The improvement of glass-forming ability is related to suppression of the primary intermetallic phase.

The influence of the microstructure of strontium-titanate-oxide (SrTiO3 or STO) thin films on their optical properties was investigated through an extensive characterization. The STO films have been deposited on silicon substrates by reactive pulsed laser deposition. The effect of the oxygen deposition pressure on the crystalline quality of the films was systematically studied by x-ray diffraction and scanning electron microscopy. Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, and secondary ion mass spectrometry were used to determine the atomic density and depth concentration profiles of the various species forming the film. The refractive index and extinction coefficient were obtained using variable angle spectroscopic ellipsometry. Based on this full characterization, it is demonstrated that the optical characteristics of the films are directly correlated to their microstructural properties. In particular, the refractive index increases with film density, while losses decrease. In addition, the interface between STO and Si is characterized by an interdiffusion layer. As the deposition pressure is enhanced, the width of this layer significantly increases, inducing localized inhomogeneity of the refractive index.

The competition between fracture modes in monolithic brittle materials loaded in cyclic contact in aqueous environments with curved indenters is examined. Three main modes are identified: conventional outer cone cracks, which form outside the maximum contact; inner cone cracks, which form within the contact; and median–radial cracking, which form below the contact. Relations describing short-crack initiation and long-crack propagation stages as a function of number of cycles, based on slow crack growth within the Hertzian field, are presented. Superposed mechanical driving forces—hydraulic pumping in the case of inner cone cracks and quasiplasticity in the case of median–radials—are recognized as critically important modifying elements in the initial and intermediate crack growth. Ultimately, at large numbers of cycles, the cracks enter the far field and tend asymptotically to a simple, common relation for center-loaded pennylike configurations driven by slow crack growth. Crack growth data illustrating each mode are obtained for thick soda-lime glass plates indented with tungsten carbide spheres in cyclic loading in water, for a range of maximum contact loads and sphere radii. Generally in the glass, outer cone cracks form first but are subsequently outgrown in depth as cycling proceeds by inner cones and, especially, radial cracks. The latter two crack types are considered especially dangerous in biomechanical applications (dental crowns, hip replacements) where ceramic layers of finite thickness are used as load-bearing components. The roles of test variables (contact load, sphere radius) and material properties (hardness, modulus, toughness) in determining the relative importance of each fracture mode are discussed.

A family of microporous phases with compositions Na2Nb2−xTixO6−x(OH)x⋅H2O (0 ≤ x ≤ 0.4) transform to Na2Nb2−xTixO6−0.5x perovskites upon heating. In this study, we have measured the enthalpies of formation of the microporous phases and their corresponding perovskites from the constituent oxides and from the elements by drop solution calorimetry in 3Na2O·4MoO3 solvent at 974 K. As Ti/Nb increases, the enthalpies of formation for the microporous phases become less exothermic up to x = ∼0.2 but then more exothermic thereafter. In contrast, the formation enthalpies for the corresponding perovskites become less exothermic across the series. The energetic disparity between the two series can be attributed to their different mechanisms of ionic substitutions: Nb5+ + O2− → Ti4+ + OH− for the microporous phases and Nb5+ → Ti4+ + 0.5VO.. for the perovskites. From the calorimetric data for the two series, the enthalpies of the dehydration reaction, Na2Nb2−xTixO6−x(OH)x⋅H2O → Na2Nb2−xTixO6−0.5x + H2O, have been derived, and their implications for phase stability at the synthesis conditions are discussed.

Electron paramagnetic resonance (EPR) spectra were obtained for samples of Ti-doped NaAlH4 subjected to different numbers of cycles of dehydrogenation/re-hydrogenation. Ti is observed to evolve from its initial Ti(III) state through a series of Ti(0) species during the first 5 cycles. Although the conversion of Ti(III) to Ti(0) occurs much more readily for TiCl3-doped samples than those prepared with TiF3, in both cases the evolution of Ti follows the same sequence that involves 3 distinguishable Ti(0) species and ends in the predominance of the same single Ti(0) species. The spectrum of a sample of NaAlH4 containing 2 mol% of cubic Al3Ti is distinctly different than any of those observed for the Ti(0) species that arise during the hydrogen cycling of the hydride. The major changes in the nature of the predominant Ti species have little if any effect on the dehydrogenation kinetics, which strongly suggests that the profoundly enhanced hydrogen cycling kinetics of Ti-doped NaAlH4 are due to a Ti species present in only a relatively minor amount.

Nanoindentation technique was used to measure the strain rate sensitivity (m) of a nanocrystalline Cu-Ni-P alloy prepared by means of electrodeposition. The m value decreases from 0.034 to 0.018 when the nominal grain size increases from 7 nm to 33 nm. Both m values of the alloy are obviously lower than those of the pure Cu with similar grain size, implying that P segregation at grain boundaries might play a key role in retarding grain boundary activities as compared to pure Cu samples.