Nanoindentation experiments and microstructural analysis were performed on advanced 12% Cr ferritic steel having extremely fine and complex martensitic microstructures, to answer unsolved questions on the contributions of grain boundaries to strengthening and aging degradation mechanisms in both as-tempered and thermally aged steels. Interesting features of the experimental results led us to suggest that among several high angle boundaries, block boundary is most effective in enhancing the macroscopic strength in as-tempered virgin sample, and that a decrease in matrix strength rather than reduction in grain-boundary strengthening effect is primarily responsible for the macroscopic softening behavior observed during thermal exposure.

Nanoindentation tests and finite element analysis that considers elastic-mesoplastic deformation for single crystals were used to investigate the mechanical properties of CaF2 under spherical indentation. The goal was to gain a better understanding of microfractures and crystalline anisotropy and their effect on the surface quality of CaF2 during manufacturing. In this analysis, indentations of the three main crystallographic planes (100), (110), and (111) were studied and compared to examine the effects of crystalline anisotropy on the load–displacement curves, surface profiles, contact radius, spherical hardness, stress distributions, and cleavage at two stages, namely at the maximum indentation load and after the load had been removed. Our model results were compared with experimental observation of surface microroughness, subsurface damage, and material removal rate in grinding of CaF2.

Creation of mirror dots, localized areas of smooth surface with a shape of laser beam on a glass material, using a XeCl laser irradiation is reported. Laser irradiation of a 40BaO–40TiO2–20B2O3 sample heated to 300 °C induced a smooth and flat surface, where no scratches caused by a mechanical polishing were observed. The present finding indicates that the melting of the surface occurred by the combined effect of the heat-assistance and the increased absorption coefficient of TiO2. In the present system, the absorption coefficient in the ultraviolet region, which originates from TiO2, was found to increase with increasing temperature. The presented technique will open new possibilities in integrated optics; the surface of a small protruded or hollow area can be made smooth, which cannot be achieved by conventional mechanical polishing.

The electrical behavior of modified soft lead zirconate titanate (PZT) ceramics has been studied as a function of temperature at different direct current (dc) electric fields and grain sizes. As ferroelectrics, such as PZT, are highly polarizable materials, poling, depolarization, and electric conduction contribute to the total electrical current, which leads to anomalous electrical behavior as a function of temperature. The PZT appeared to have a high pyroelectric coefficient, and it was found that the displacement current hides the conduction current near room temperature. The (long-time) steady-state electrical resistivity of the soft PZT used has a typical, relatively high value of 3.6 × 1012 Ω·cm near room temperature. The resistivity above the Curie temperature was two orders of magnitude lower than the room temperature. The resistivity decreases with increasing grain size probably due to the increased Pb vacancy concentration resulting as a consequence of a higher sintering temperature. The values of activation energies suggest that the charge carriers at high temperature are mainly oxygen vacancies. At intermediate temperature, the electrical behavior is controlled by the counteracting effect of depolarization and conduction. Considering the pyroelectric effect and the conduction, it was thus possible to explain the electrical behavior of this soft PZT ceramic over the temperature range considered.

Recently, we reported the discovery of new high-aspect ratio titania nanotubes. These nanotubes were synthesized by means of anodization in an oxalic acid electrolyte containing chlorine ions and were found to have significant carbon content. In this article, the synthesis of similar titania nanotubes in oxalic, formic, trichloroacetic, gluconic, hydrochloric, and sulfuric acid is reported. Differences in carbon content and morphology are analyzed, which in turn provides information on the chemistry of the formation of these nanotubes. Our results suggest that the carbon content in the nanotubes can be controlled by the use of an appropriate organic acid.

We investigated the acoustic properties in the sub-GHz frequency regime of a multilayer system comprising alternating 100-nm scale TiO2/poly(methyl methacrylate) (PMMA) layers through a laser photoacoustic method, impulsive stimulated thermal scattering (ISTS). The acoustic dispersion curves were determined, and the mechanical properties were extracted from the experimental results.

A floating catalyst chemical vapor deposition method was developed for the synthesis of quasi-one-dimensional (1D) boron nitride (BN) nanostructures. By carefully tuning the experimental parameters such as growth temperature, floating catalyst concentration, and boron precursor, high quality 1D BN nanostructures including nanotubes, nanobamboos, and nanowires were selectively produced. The microstructures of the obtained 1D BN nanomaterials were characterized, and it was found that the nanostructures are composed of hexagonal BN phase with (002) planes stacking in different manners. A growth mechanism of the BN nanostructures was proposed based on the analysis of their structural characteristics and growth conditions.

We investigated the photovoltaic response of nanocomposites made of colloidal, infrared-sensitive, PbSe nanocrystals (NCs) of various sizes and conjugated polymers of either regioregular poly (3-hexylthiophene) (RR-P3HT) or poly- (2-methoxy-5-(2-ethylhexoxy)-1,4-phenylene vinylene) (MEH-PPV). The conduction and valence energy levels of PbSe NCs were determined by cyclic voltammetry and revealed type II heterojunction alignment with respect to energy levels in RR-P3HT for smaller NC sizes. Devices composed of NCs and RR-P3HT show good diode characteristics and sizable photovoltaic response in a spectral range from the ultraviolet to the infrared. Using these materials, we have observed photovoltaic response at wavelengths as far to the infrared as 2 μm (0.6 eV), which is desirable due to potential benefits of carrier multiplication (or multi-exciton generation) from a single junction photovoltaic. Under reverse bias, the devices also exhibit good photodiode responses over the same spectral region.

Continuous, small-diameter polymer fibers may be fabricated by a method that involves injecting a solvated polymer into a highly viscous moving medium through a microaperture. The extruded fiber moves in a predictable spiral path and is collected around a spinning mandrel that also serves to pull the extruded fiber away from the aperture. In this study, fibers as small as 400 nm diameter were observed, but there was no indication that the experiments reported here have achieved the smallest structures possible by this technique. Video microscopy experiments revealed significant fiber diameter reduction in close proximity to the point of precursor injection via hydrodynamic focusing. This occurred due to flow mismatch between the precursor and surrounding media. This effect may be the dominant draw-down mechanism in a process that can produce truly continuous nanofiber. This method is capable of generating fibers from precursors with viscosities that would render them unspinnable by any other known method.

A nanocrystalline surface layer of a Cu–Zn alloy was developed by electropulsing (ECP) surface treatment. The average grain size was about 20 nm on the top surface layer and was gradually augmented with the increase in depth from the top surface. Nanoindentation measurements showed that the hardness was significantly enhanced on the top surface layer compared with the as-annealed Cu–Zn sample. The mechanism for the evolution of this structure and property was related not only to a solid-state phase transformation, but also to the effect of the enhancement of the nucleation rate and the skin effect during the ECP treatment. Therefore, the ECP surface treatment provides a promising method for obtaining surface self-nanocrystallization materials.

We have studied the heteroepitaxial growth of 3C–SiC film on an Si(100) substrate by plasma chemical vapor deposition using monomethylsilane, a single-molecule gas containing both Si and C atoms. We have tried to introduce an interval process, in which we decrease the substrate temperature for a few minutes at a suitable stage of film growth. It was expected that, during the interval process, stabilization such as desorption of nonreacted precursors and lateral diffusion of species produced at the initial stage of film growth would occur. From the results, it appears that the interval process using a substrate temperature of 800 °C effectively suppresses polycrystallization of 3C–SiC growth on the Si(100) surface

The enthalpies of the monoclinic to orthorhombic transition for a series of A2M3O12 (A = Al, Cr, Fe, In, and Sc; M = Mo or W) compounds were measured by differential scanning calorimetry, and entropies of transition were estimated. The enthalpies of formation from the binary oxides at 25 °C for several A2M3O12 samples were obtained from drop solution calorimetry in molten 3Na2O·4MoO3 at 702 °C. The monoclinic and orthorhombic phases of Sc2Mo3O12 and Sc2W3O12 are the only phases that are enthalpically stable under ambient conditions. The enthalpies of formation from the oxides (ΔHf,ox) for orthorhombic Sc2Mo3O12 and Sc2W3O12 are −47.2 ± 2.1 kJ/mol and −8.5 ± 2.7 kJ/mol, respectively. For Fe2Mo3O12, In2Mo3O12, and In2W3O12, ΔHf,ox values are 51.5 ± 4.5, 7.4 ± 2.9, and 44.5 ± 2.3 kJ/mol, respectively. These phases are entropically stabilized and/or metastable. Enthalpies of formation for phases that could not be measured by calorimetry have been estimated from the enthalpies of transition or trends in the enthalpies of formation. In general, the monoclinic phase is slightly enthalpically stabilized over the orthorhombic phase, while transition to the orthorhombic phase is entropically favored. This confirms that the orthorhombic phase is stable at high temperatures, the monoclinic is stable at low temperatures, and the monoclinic to orthorhombic transition is reversible.

The finite element method (FEM) was used to study the flat cylindrical indentation fatigue behavior using a kinematic hardening model (A-F model). This study was motivated by the experimental work of the preceding paper [B.X. Xu and Z.F. Yue, J. Mater. Res.21, 1793 (2006)], in which there were obvious similarities in the behavior of conventional fatigue specimens and indentation fatigue specimens. It is proposed that the A-F model can predict the indentation fatigue behavior. Generally, the experimental behavior of the indentation fatigue testing can be explained by the FEM analysis. In addition, the effect of residual stress on the indentation depth per cycle was studied. The effect of friction between the indenter and the specimen and evolution of von Mises stress beneath the indenter was also investigated. Numerical results showed that the effect of friction on the indentation depth propagation can be neglected. Further analysis showed that the steady-state indentation depth per cycle increases with increasing compressive residual stress and decreasing tensile residual stress.

The Cu–Sn binary system is important for various applications, especially for recent developments in the electronics packaging industry. The ϵ-Cu3Sn and η-Cu6Sn5 (η′ phases) phases are frequently encountered in electronics products. However, the two phases have been described as line compounds in previous thermodynamic modeling, and their compositional homogeneities were not considered. In this study, the thermodynamic properties of the Cu–Sn binary system are modeled and the phase diagram is calculated by the CALPHAD method, using experimental information reported in the literature. The ϵ and η (η′) phases are described using compound energy models with two and three sublattices, respectively, so that their compositional homogeneities could be calculated. Good agreement was observed between the calculated result and the existing experimental data.

The electron beam welding technique was used to join Zr41Ti14Cu12Ni10Be23 bulk metallic glass (BMG) to crystalline pure Zr. Compositional, microstructural, and mechanical property variations across the welded interface were evaluated. It is shown that a crystalline layer develops close to the welding interface. Transmission electron microscopy of this layer indicates the crystalline phase to be tetragonal with lattice parameters close to that reported for Zr2Ni. However, the composition of this phase is different as it contains other alloying additions. The interface layer close to the bulk metallic glass side contains nanocrystalline Zr2Cu phase embedded in the glassy matrix. Nanoindentation experiments indicate that the hardness of the crystalline layer, although less than the bulk metallic glass, is more than the Zr itself. Commensurately, tensile tests indicate that the failure of the welded samples occurs at the Zr side rather than at the weld joint.

Tetrakis-diethylamino hafnium (TDEAH), tris-diethylamino aluminum (TDEAA), and ozone were used for the atomic layer deposition (ALD) of HfO2, Al2O3, and HfAlOx films. The ALD rates were measured to be 1.1 Å/cycle for HfO2 and 1.3 Å/cycle for Al2O3. The ALD temperature windows were found to be between 200 and 325 °C for TDEAA, and between 200 and 275 °C for TDEAH. The overlap of these ALD windows between 200 and 275 °C is critical for ALD of the composite film, HfAlOx. In addition to the overlapping ALD temperature windows, the two metal precursors have similar thermal characteristics, as shown by TGA and differential scanning calorimetry. As-deposited films and films postannealed at 600 and 800 °C films were analyzed using Fourier transformed infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy, and x-ray diffraction (XRD) techniques. FTIR spectra revealed interfacial oxide growth during deposition of both HfO2 and Al2O3 whose thickness increased with annealing temperature. The FTIR data also indicated hydroxyl and nitrate groups in the films; these species were removed after annealing in Ar at a temperature of ⩾600 °C. Both FTIR and XRD results indicated the crystallization of pure HfO2 after annealing at temperatures as low as 600 °C. On the other hand, pure Al2O3 remained amorphous after annealing at temperatures up to 800 °C. XRD data of the composite HfAlOx film show that films deposited by alternating five cycles of HfO2 and one cycle of Al2O3 remained amorphous after annealing at 600 °C. Rutherford backscattering analysis of HfAlOx deposited with a varied number of alternating HfO2 and Al2O3 cycles demonstrated a strong correlation between the cyclic dosage of TDEAA and TDEAH and the film composition.

In the present study, we solidified magnesium-based AZ31 alloys by an electromagnetic vibration technique in a superconducting magnetic field at a vibration frequency of 500 Hz. Two groups of processing variables were used to carry out experiments; one is that the electric current is set as 60 A so as to testify to the influence of magnetic flux density on microstructure development from 1 up to 10 T. The other is that the electric current increases from 10 up to 120 A in the static magnetic field of 10 T, from which the dependence of structure formation on electric current is revealed. It is found that with the increase of both magnetic flux density and the level of electric current, solidified structures experience a transition from coarse dendrites to equiaxed grains. The melt fluid induced by the vibration force during solidification may promote the dendrite to a fragment. Meanwhile, the solids can be driven to move out of the operating region of the solute redistribution boundary. These effects make it difficult to form a complete dendrite but a refined structure. Furthermore, the vibration force can result in the formation of deformation twins in the alloy that has a low critical stress for basal slip. Regarding the effect of the electric current on microstructure, heat (measured in joules) can be produced when a large electric current is imposed, which can ripen the microstructure and induce a nonuniform structure. The slow cooling rate also makes the number fraction of deformation twinning decrease due to a rapid migration rate of atoms at high temperatures.

This study elucidates the tunability of the magnetic properties of cobalt spinel ferrites embedded in a polyvinyl alcohol (PVA) hydrogel by changing the structure of the polymer network. We report on the preparation and characterization of sPS-CoFe2O4 ferrofluid and PVA/sulfonated polystyrene (sPS)-CoFe2O4 ferrogels obtained by submitting the samples to a different number of freezing–thawing (F–T) cycles. The magnetic properties were evaluated and interpreted as a function of the PVA/sPS-CoFe2O4 composition and final structure of the ferrogels.

Ba2CuWO6 (BCW) was first synthesized in the mid 1960s, and it was predicted to be a ferroelectric material with a very high Curie temperature of 1200 °C [N. Venevtsev and A.G. Kapyshev: New ferroelectrics. Proc. Int. Meet. Ferroelectr.1, 261 (1966)]. Since then, crystallographic studies were performed on the compound with the result that its crystal structure is centrosymmetric. Thus for principal reason, BCW cannot be ferroelectric. That obvious contradiction was examined in this study. Disk-shaped ceramic samples of BCW and Ba2Cu0.5Zn0.5WO6 (BCZW) were prepared. Because of the low electrical resistivity of the ceramics, it was not possible to perform a typical polariszation hysteresis loop for characterization of ferroelectric properties. Scanning electron microscopy investigations strongly suggest that the reason for the conductivity is found in the impurities/precipitations within the microstructure of the samples. With atomic force microscopy (AFM) in piezoresponse force microscopy (PFM) mode, it is possible to characterize local piezoelectricity by imaging the ferroelectric domains. Neither BCW nor BCZW showed any domain structure. Nevertheless, when local electric fields were applied to the surfaces of the ceramics topographic displacements, imaged with AFM, and surface charges, imaged with Kelvin probe force microscopy (KFM) and PFM, were measured and remained stable on the surface for the time of the experiment. Therefore BCW and BCZW are considered to be electrets and possibly relaxor ferroelectrics.

Fe-sheathed MgB2 tapes were fabricated using powder chemically treated through an ex situ process employing a powder-in-tube (PIT) technique. The treatment of MgB2 powder in a benzene solution of benzoic acid caused the pulverization and disappearance of large grains. Compared with the pristine powder without treatment, the tape made from this powder showed a fivefold increase in critical current density (Jc) in 10 T. This was due to the pulverization of grains by the chemical treatment and the removal of surface MgO layers from MgB2 grains by dissolution in the acid solution. The removal of MgO layers was effective in promoting substitution of carbon from the solvent for boron.