This article presents a comparative study of the deformation-induced structural changes observed within a glassy phase in two different Zr- and Ni-based alloys. Ductile Zr65Al7.5Ni10Pd17.5 bulk glassy alloy, which exhibits dynamic nanocrystallization forming a crystalline cubic phase within shear bands on plastic deformation, is presumed to contain pre-existing nuclei. On the contrary, no obvious dynamic nanocrystallization is observed within the shear bands in the glassy phase of the Ni50Pd30P20 bulk alloy, which, however, contains clear medium-range order zones on the order of 1 nm in size in an as-solidified state. This alloy exhibits nucleation and growth-transformation behavior on heating. At the same time, clear nucleation and growth of the cubic Ni-based phase are observed near the microcrack area in the deformed sample. High energy released at the time of the microcrack propagation caused nanocrystallization and blockage of the crack-tip propagation.

“In situ x-ray study of the γ- to α-Al2O3 phase transformation during atmospheric pressure oxidation of NiAl(110)” [J. Mater. Res. 21, 3047 (2006)]

Highly dense and crack-free Pb(Zr,Ti)O3 (PZT) thick films with a controlled microstructure and orientation were deposited on a platinized silicon substrate by the radio frequency magnetron sputtering method using a single oxide target. The microstructure and orientation of the films were adjusted by applying a thin (100) PZT seed layer by the sol-gel method and subsequent repeated sputtering. When a thin layer was deposited on the seed layer, the film had small grains with a columnar structure. However, as the film became thicker, it developed a large and non-columnar grain structure. Therefore, reducing the thickness of the film per deposition allowed the columnar microstructure to be maintained. The (100) orientation of the film was able to be maintained by depositing it on a (100) oriented seed layer. PZT thick films with controlled orientations and microstructures were successfully deposited up to a thickness of about 5 μm, and their ferroelectric and piezoelectric properties were characterized.

Four-point-bend fatigue experiments were conducted on the Fe48Cr15Mo14Er2C15B6 bulk metallic glass (BMG), amorphous steel, under load control, employing an electrohydraulic machine, at a frequency of 10 Hz (using a sinusoidal waveform) with an R ratio of 0.1, where R = σmin./σmax. (σmin. and σmax. are the applied minimum and maximum stresses, respectively). The test environment was laboratory air. Fe48Cr15Mo14Er2C15B6 exhibited a high fatigue-endurance limit (682 MPa), which is found to be greater than those of the Zr-based BMG, Al-alloy, and high-nitrogen steel. However, the stress versus number of fatigue cycles curve of Fe48Cr15Mo14Er2C15B6 has a significantly brittle fracture mode. Some fatigue cracks initiated from the inclusions or porosities, and the fatigue-crack propagation region was large. However, other cracks initiated from the outer tensile surface of the specimen, and the fatigue-crack propagation region was very small. The mechanisms of fatigue-crack initiation are suggested.

We show that the thickness of yttrium–barium–copper–oxide (YBCO) superconducting films grown from trifluoroacetate precursors can be strongly modified using polymeric additives, while deposition conditions by spin or dip coating remain unchanged. A screening of different families of organic additives has been performed, and the best results have been achieved using polymers having an oxygen functionalized backbone. Two different polymeric additives, polyvinyl pyrrolidone (PVP) and poly(ethylene glycol) (PEG), have been more thoroughly investigated, and thermal analysis suggests that PEG is the most promising alternative because the pyrolysis step of the new complex precursors remains sharp and narrow and hence the final homogeneity of the film is preserved. The combination of anhydrous trifluoroacetic acid (TFA) solutions and poly(ethylene-glycol) (PEG8000) as additive can produce an increase of the YBCO film thickness up to 300%, while keeping a fast pyrolysis process and high critical current densities.

Iron-molybdenum powders ground in a planetary ball mill under different operating conditions were studied by x-ray diffraction line profile analysis using a recently developed whole powder pattern modeling approach. The evolution of the microstructure, expressed in terms of size distribution of coherent scattering domains, average dislocation density, and edge/screw character, shows the importance of the main process parameters: the ratio between jar and main disk rotation speeds, and ball milling time. A characteristic three-stage process is observed, with work hardening followed by particle flattening/bending before nanocrystalline grains form by a fragmentation process triggered by localized deformation. The relationship between lattice defect density and domain size suggests a progressive transition between statistically stored to geometrically necessary dislocations, with the latter mostly present as excess dislocations at the nanodomain boundary.

High-quality doped GaN layers were grown on silicon substrates by radio frequency nitrogen plasma-assisted molecular-beam epitaxy. High-temperature-grown AlN (about 200 nm) was used as a buffer layer. In-growth doping was done using high-purity Si and Mg as n- and p-type dopants, respectively. X-ray diffraction revealed that monocrystalline GaN was obtained. This is in good agreement with the results of morphological study by atomic force microscopy. Micro-photoluminescence (PL) and micro-Raman spectroscopy were used to study the room-temperature optical properties of the doping films. No yellow-band emission was observed in the PL spectroscopy. From the Hall measurements, the resulting n-type doping concentration was measured to be (1–2) × 1019 cm−3. Fairly uniform hole concentration as high as (4–5) × 1020 cm−3 throughout the GaN crystal was achieved. In terms of the carrier concentration, it was found that the results determined from the Fourier transform infrared analysis are in good agreement with the results determined from the Hall measurements.

The addition of Ti, Nb, or Ta altered the crystallization behavior of the Zr65Al7.5Cu27.5 glass, and a metastable nanoscaled I-phase was obtained on primary crystallization of these quaternary glasses. The complete substitution of Al by Nb also led to the precipitation of I-phase upon crystallization. Negative heats of mixing between the addition metals and the transition metals of the mother alloy were demonstrated to be not a necessary condition for I-phase formation in the present alloy system.

“Structural characterization of a new layered-ternary Ta4AlC3 ceramic” [J. Mater. Res. 21, 2587 (2006)]

This paper examines the strain rate sensitivity of the hardness νH in relation to the strain rate sensitivity of the flow stress (νσ) in hard solids when there is friction between the indenter and specimen. Finite element analysis is used to simulate indentation creep of von Mises solids with a range of hardness/modulus ratios (H/E*) and coefficients of friction, μ, for indenter–specimen contact. We find that, although the level of H is affected by friction, the ratio νH/νσ as a function of H/E* remains nearly unchanged. Measurements indicate that νH = 0.015 ± 0.02 for fused silica, from which, based on the present analysis, νσ ≈ 0.022 and from which an activation volume of 0.13 nm3 can be estimated for plastic deformation.

Epitaxial ZnO thin films doped uniformly with nitrogen at 1020 atoms/cm3 were fabricated by pulsed laser ablation of a Zn-rich Zn3N2 target. The films grown at 300 °C and annealed at 600 °C in O2 showed p-type conductivity. Two acceptor levels at 105 and 224 meV were determined by temperature-dependent Hall and photoluminescence measurements of the p-type samples. Transmission electron microscopy studies revealed that the p-type ZnO films consist of 10–20 nm columnar grains with a high density of defects and grain boundaries that may facilitate the annihilation of native donors and the activation of acceptors during postdeposition annealing.

A Zr-based metallic glass matrix composite with 40 vol% tungsten fiber reinforcement was loaded step by step. After each loading step, shear-band patterns and fracture surface were observed. The results show that shear bands, cracks, and voids form during plastic deformation, and they exhibit different feature characteristics at various loading stages. As reinforcement, the tungsten fiber substantially affects the deformation and fracture processes of the composite.

If a metal contracts upon solidification, the specific volume of a metallic liquid phase must not be smaller than that of the corresponding crystal. As molten metals have higher thermal expansion coefficients compared with those of the corresponding crystals, the intersection point of two specific-volume–temperature plots of the liquid and the corresponding solid crystalline phase by analogy with Kauzmann’s paradox for entropy could be treated as an ideal glass-transition temperature. This paper describes this phenomenon observed for a number of pure metals and gives a semiempirical criterion for the achievement of a good glass-forming ability.

BaTiO3 particles were prepared by heating a suspension of titania derived from the hydrolysis of titanium isopropoxide in a barium hydroxide [Ba(OH)2] aqueous solution. Well-crystallized cubic phase BaTiO3 fine particles were obtained by heating at a temperature >328 K for 24 h. The morphology and size of the obtained particles were affected by the reaction temperature and the Ba(OH)2/titanium alkoxide molar ratio. The secondary particles with a larger size were obtained at a lower reaction temperature. The nucleation process of BaTiO3 depended on the reaction temperature. The formation mechanism of BaTiO3 and the formation kinetics were investigated by measuring the concentrations of Ba2+ ions in the solution during the heating process. The BaTiO3 particle formation occurred on the surface of the titania particles after strong adsorption of the Ba2+ ions from the solution. The experimental results showed that the heterogeneous nucleation of BaTiO3 occurred on the titania surface.

We report the preparation and thermoelectric properties of oriented higher manganese silicide (HMS) with a composition of MnSi1.73 bulk. The grain alignment and densification were achieved by rotating high magnetic field and spark plasma sintering (SPS) techniques, respectively. The easy magnetization axis of MnSi1.73 was found to be c-axis, and the applied magnetic field of 2 T was strong enough to rotate the powder with a mean grain size of 1 μm. The c-axis of grains was oriented when applying the magnetic field, and the degree of orientation was further increased after heat treatment. However, a secondary phase that was mono manganese silicide (MnSi) was observed as a result of oxidation on the surface of synthesized powder. The electrical conductivity of the c-axis oriented specimen along the ab-plane was about 40% larger than that for sample processed only by SPS, while the Seebeck coefficient of oriented and nonoriented specimens showed similar values regardless of existence of the second phase. Consequently, the power factor of the c-axis oriented specimen along the ab-plane was enhanced by about 35% compared to the nonoriented one. The proposed approach is found to be very effective not only in obtaining the oriented materials with nonductility but also in enhancing the thermoelectricity.

The chemical stability and toxicity of Te–As–Se (TAS) infrared fibers are investigated. These fibers are used for biosensing applications that involve direct contact with live cultivated human cells. It is shown that TAS fibers exhibit a small oxidation layer after extended exposure to air. This layer is highly soluble in water and easily removed. However, the TAS glass itself is stable in water over several days. While oxidized fibers release arsenate ions, which result in toxic effects to the cells, fresh or washed fibers show no toxic effects. A good correlation is shown between surface etching and the disappearance of toxicity.

We present a simple method for preparing nanometer-sized, Ti-based amorphous powders from the Y28Ti28Al24Co20and Y36Ti20Al24Co20two-phase amorphous alloys. The initial microstructure of these rapidly quenched alloys is composed of Ti-based, amorphous, spherical, nanometer-sized particles embedded in a Y-based amorphous matrix, with particle size dependent on the alloy composition. The Ti-based powders were extracted from the two-phase amorphous alloys through selective dissolution of the Y-rich matrix in a 0.1 M HNO3solution. The powders of size ranging between 20 and 200 nm have smooth and spherical morphology, and exhibit different magnetic behavior than the bulk alloy of identical composition.