The microstructure of a bearing-grade silicon nitride, prepared by pressureless sintering with Y2O3, AlN, and TiO2 additives and then hot-isostatically pressed, is examined with high-resolution transmission electron microscopy, scanning electron microscopy, and x-ray diffraction. The material consists of large acicular β–Si3N4 grains and small equiaxial α–Si3N4 grains. An amorphous phase containing the sintering aids is observed at the two-grain boundaries and at the grain pockets. No crystalline boundary phase is identified. The α-to-β and β-to-β grain boundaries appear straight and well defined. The dominant crystalline planes observed at the β-grain boundaries are (1010) and (1120). The intergranular spacing of the two-grain boundaries (α-to-β and β-to-β) is 1.0 nm when a high-contrast boundary phase is present, and it is 0.8 nm when a low-contrast boundary phase is present, confirming that the film thickness is strongly dependent on the boundary-phase composition. The α-to-α boundaries are often curved, and the thickness of the amorphous film at these boundaries varies from 0.7 to 1.1 nm. Evidence of near-intimate contact between β-grains is also observed.

We demonstrated in “Phase separation in undercooled molten Pd80Si20: Part I” that when a molten Pd80Si20 ingot is undercooled into its undercooling regimen with ΔT ≥ 220 K (ΔT = T1 – T, where T1 is the liquidus and T is the temperature of the undercooled melt), liquid-state phase separation by spinodal decomposition occurs. On crystallization, one of the metastable liquid spinodals becomes Pd3Si, whereas the other one turns into Pd9Si2. In both cases, Pd particles precipitate out. Microstructural analysis indicates the Pd3Si subnetwork forms first. It then acts as a seed for the subsequent crystallization of the remaining undercooled melt, which finally forms the Pd9Si2 dendrites. As crystallization proceeds, latent heat and volume contraction bring about morphological changes.

This article discusses the mechanical properties of vapor-grown carbon fiber (VGCF)/nylon and VGCF/polypropylene composites. Fibers in the as-produced condition yielded composites with marginally improved mechanical properties. Microscopic examination of these composites clearly showed regions of uninfiltrated fibers, which could account for the unsatisfactory mechanical properties. The infiltration of the fibers by both polymers was improved by carefully ball milling the raw fiber so as to reduce the diameter of the fiber clumps to less than 300 μm. Properties of composites made with ball-milled material were improved in every respect. VGCF reinforcement in nylon slightly improved the tensile strength and doubled the modulus, while VGCF in polypropylene doubled the tensile strength and quadrupled the modulus compared to unreinforced material. Moreover, the composites were sufficiently improved that differences in fiber surface preparation became important. For example, air-etched fibers and fibers covered with low concentrations of aromatics produced polypropylene composites with significantly better mechanical properties than did fibers whose surfaces were heavily coated with aromatics. Both the tensile strength and the modulus of the composites fabricated with clean fibers exceeded theoretical values for composites made with fibers randomly oriented in three dimensions, indicating that the injection-molding process oriented the fibers to some extent.

This paper reports the formation of a solid solution in the system Bi2O3–TiO2–CuO. This solid solution seems to be isostructural with Bi4Ti3O12, according with the x-ray powder diffraction patterns. Microstructural studies done using scanning electron microscopy show the typical elongated Bi4Ti3O12 grain morphology only in samples with 2 : 2 : y molar ratios of the Bi2O3 : TiO2 : CuO oxides (y = 1, 2, or 3).

Highly oriented calcium metaphosphate glass-ceramics were obtained directly from the corresponding melt. On the interface between the Ca(PO3)2 melt and an Al2O3 rod, the nucleation could easily be induced. The dependence of the crystal growth rate on the crystallization temperature was determined. The crystal growth rates observed were up to 71 μm/s. The c axes of most crystals were oriented in the direction perpendicular to the surface of the Al2O3 rod as illustrated by scanning electron microscope and pole figures. The degree of crystal orientation increased with increasing crystallization temperature. At higher temperatures (e.g., at 892 °C), even single-crystal-like dendrites were formed.

The mechanochemical synthesis of NbC-based cermets is described. Nanocrystalline NbC is synthesized by room-temperature milling of Nb and graphite (or hexane) mixtures. While some structural coarsening occurs during powder consolidation to full density, a nanoscale structure is maintained. Grinding media wear occurs during milling, and milled powders contain Fe from this abrasion. This phase, homogeneously distributed in milled powders, segregates during consolidation and heat treatment, and a cermetlike microstructure results. Copper added to the powder charge yields NbC–Cu or NbC–Cu-Fe cermets. Copper-containing materials have different phase morphologies. In particular, relatively large NbC particles are dispersed in a matrix containing finer NbC and metal particles. Higher Cu-content materials also develop a pure Cu constituent on heat treatment. A companion paper, “Mechanochemically synthesized NbC cermets: Part II. Mechanical properties,” addresses aspects of the mechanical behavior of these materials.

The synthesis of barium titanate (BaTiO3) was investigated in water at 90 °C in the presence of polymeric additives. Homopolymers (polyacrylic acid) and block copolymers (polyethylene oxide-block-polymethacrylic acid) were added during synthesis to influence particle morphology and size distribution. The polymers affected the morphological evolution of the forming powder by adsorbing preferentially on specific planes. The polymeric species additionally slowed the formation of barium titanate. The barium concentration also changed the morphology, particle size, and other powder characteristics.

The sintering behavior of cBN powder with various particle sizes from 0.5 to 12 µm was investigated when sintered at temperatures from 1500 to 2500 °C and pressure of 7.7 GPa without additives. Above 2000 °C, translucent sintered bodies were obtained. Microstructure observation indicated that the optimum sintering temperature was near 2350 °C for fine powders of 0.5 to 1.2 µm and 2 to 4 µm, and slightly higher than 2350 °C for powders from 8 to 12 µm. The fracture toughness of the well-sintered bodies decreased with grain growth above the optimum sintering temperature.

Ba1−xSrxTiO3-based positive temperature coefficient resistance (PTCR) ceramics were prepared by use of a vapor-doping method. When doped with Bi, the PTCR effect is improved; when doped with lead, however, the effect is weakened. The different influences of Bi and Pb doping on the ceramic properties are discussed in terms of the defect chemistry.

Films of nominal composition Pb(Zr0.53Ti0.47)O3 (PZT) in the thickness range 0.25−10 μm have been fabricated on Pt/Ti/SiO2/Si substrates using a propanediol-based sol-gel route. The spun-on coatings were prefired at 350 and 600 °C between successive depositions before firing the multilayer stack at 700 °C for 15 min. The variations in crystallite orientation, microstructure, and dielectric and ferroelectric properties were determined as a function of film thickness. For a constant applied field of 150 kV cm−1, remanent polarization decreased progressively from 35 to 17 μC cm−2 as film thickness decreased in the range 10–0.25 μm; values of coercive field were reasonably constant, 18–19 kV cm−1, for films between 2 and 10 μm, but increased sharply below 2 μm, reaching 46 kV cm−1 for a 0.25 μm film. Relative permittivity (εr) decreased from approximately 1400 to approximately 940 with most of the reduction occurring in films less than 2 μm in thickness. These trends are discussed in terms of the presumed influence of interfacial phenomena on the measured electrical response.

Thin films of cubic boron nitride (c-BN) were synthesized using an organometallic precursor trimethylborazine (TMB) which contains both boron and nitrogen in 1 : 1 stoichiometric ratio. The films were deposited at different temperatures ranging from 300 to 500 °C at a pressure of 2 Torr and at 360 W microwave power, using N2 as carrier gas. The deposited films were characterized by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), and scanning electron microscopy (SEM), which reveal the presence of amorphous BN and crystalline c-BN in varying proportions. The x-ray diffraction pattern of the deposited films showed a strongest peak at 2θ = 57.1° where the interplanar distance value, d = 2.06 Å, agreed well with the (111) crystallographic orientation of c-BN phase.

The mechanical behavior of mechanochemically synthesized NbC cermets was investigated. Material hardnesses range from a high of 19.6 GPa for as-synthesized cermets containing about 4 vol% of Fe to a low of about 4 GPa for heat-treated cermets containing about 34 vol% Cu. Higher hardness generally correlates with lower fracture toughness (about 2 MPa m1/2 for cermets containing the highest percentage of NbC) and vice versa. Highest fracture toughness (about 7.5 MPa m1/2) is found in NbC–18 vol% Fe cermets heat treated extensively following consolidation. Abnormally low fracture toughnesses are found in high-Cu-content cermets in which Cu segregation takes place during heat treatment. Current models of ceramic toughening can be applied to describe the fracture behavior of NbC–Fe cermets.

The effect of the additive KCl, on the structural, microstructural, and polar properties of bismuth vanadate (BiV) ceramics is investigated. The scanning electron microscopic (SEM) studies reveal a remarkable modification in the microstructure and the occurrence of high grain-orientation (75%) on KCl addition. The energy dispersive x-ray (EDX) analyses indicate the presence of chemically inhomogeneous distribution of KCl, with core-shell-like grain structure. The KCl-modified BiV samples exhibit a broad and depressed phase transition, with no frequency dispersion, as a result of the increased internal stress and the formation of core-shell-like grain structure. Significant anisotropies are observed in the dielectric, piezoelectric, and pyroelectric responses of these grain-oriented ceramic samples. These samples are characterized by near rectangular ferroelectric hysteresis loops, with a significant anisotropy in the Pr (Pr┴/Pr∥ = 2.43, at 300 K) and Ec (Ec∥/Ec┴= 2.22, at 300 K) values between the directions parallel and perpendicular to the cold-pressing axis.

Enthalpies of formation were determined for β-sialon phases (Si6–zAlzOzN8–z, z = 0.46 to 3.6) by high-temperature oxidative drop solution calorimetry using an alkali-metal borate (52 wt% LiBo2; 48 wt% NaBO2) solvent. Oxygen gas was bubbled through the melt to accelerate oxidation of the oxynitride samples during dissolution. Sialons near z = 2 appear less stable energetically than ones with higher or lower nitrogen content. A large configurational entropy contribution for sialons with z > 2 may further stabilize these materials. This larger free energy driving form may be the reason for success in pulse-activated processing of these materials. The enthalpies of formation further suggest that a greater driving form for oxynitride formation exists in batch synthesis using SiO2 rather than Al2O3.

In hydroxylated poly(styrene-b-butadiene-b-styrene) (HO–SBS) micelle, ZnS/CdS composite nanocrystals were prepared by adding Cd2+ ions and Zn2+ ions to the system sequentially. The resulting composites were identified with elemental analysis, transmission electron microscopy, x-ray diffraction, surface photovoltage spectroscopy, and electric field induced surface photovoltage spectroscopy.

Scanning acoustic microscopy (SAM) was used to obtain the critical fragmentation length of a 7-μm-diameter carbon fiber embedded in an optically transparent epoxy matrix and was subjected to a standard fiber fragmentation test. The SAM-assessed critical fragmentation length of 356 ± 59.5 μm compared favorably with the value 341 ± 52.3 μm obtained independently from commonly used photoelastic techniques. Additionally, the SAM images allowed an assessment of regions of fiber-matrix debond, including the measurement of an average debond of 61.0 ± 11.8 μm along the fiber from the fragment ends, which could not be obtained with photoelastic methods. The application of SAM to the assessment of optically opaque composite materials is explained in this paper.

An attempt was made to develop an engineering ceramic plastically deformable at high temperatures with low flow stress at high strain rates, and without strain hardening. Dense ceramic preforms were fabricated by pressureless sintering Si3N4 + SiO2 mixed powders with an addition of MgAl2O4 at 1500 °C. A transient liquid, which occurs during the reaction sintering of Si2N2O, was utilized for subsequent net-shape forming. The ceramic (6Φ × 6 mm column) was deformed without any cracks and cavities in compression tests at high strain rates (10−2−10−3:s−1) at 1500 °C, but this was not achieved in a test at lower strain rates for a long time, because of the growth of elongated Si2N2O grains during the test. Potassium fluoride (KF) was used as a dopant for retardation of nucleation of Si2N2O during sintering and hot-working. The KF-doped preforms were successfully plastically deformed even in the test for a long time.

The metastable liquid miscibility gap of Pd–Si is determined structurally. The glass-forming ability of Pd–Si is then discussed in the light of the metastable liquid miscibility gap. Analysis indicates that it does not favor the formation of glass.

Deposition characteristics of (Ba,Sr)TiO3 (BST) thin films by metalorganic chemical vapor deposition with a mixture solution were investigated. Ba(methd)2 (methd = methoxyethoxytetramethylheptanedionate), Sr(methd)2, and Ti(MPD)2(tmhd)2 (MPD = methylpentanedioxy, tmhd = tetramethylheptanedionate) were dissolved together in methanol solvent. Mass spectrometry showed that Ba(methd)2 was less aggregated than Ba(tmhd)2-tetraglyme adduct (tetraglyme = tetraethylene glycol dimethyl ether) in the gas phase. Similar results were obtained from Sr precursors. Step coverage and electrical properties of the BST films were investigated as a function of deposition temperature from 350 to 600 °C. With the increase of the deposition temperature up to 500 °C, Ti composition in the films was increased, but Ba and Sr remained almost constant, and the step coverage became poor. Also, leakage current density and SiO2 equivalent oxide thickness was reduced as the deposition temperature increased. Poor incorporation of Ti below the deposition temperature of 500 °C was observed.

A simple bridging model is proposed for the toughening of a discontinuous fiber-reinforced brittle matrix composite, in which the frictional bridging of fibers during, as well as after, the interfacial debonding is considered. The R-curve behavior and the work-of-fracture of the composite can be theoretically predicted by the computation of the bridging model applying material parameters, such as fiber volume fraction, size and shape of fibers, fiber tensile strength, elastic moduli of fibers and matrix, fracture toughness and work-of-fracture of matrix, and frictional shear stress at interface. The experimental result obtained from a SiC-whisker-reinforced Al2O3 composite confirms the theoretical predictions of the present bridging model. Through the model calculation, the R-curve, crack profile, and bridging stresses of the composite can be estimated correspondingly to the bridging processes.