A novel technique has been developed for simultaneous combustion synthesis and consolidation of intermetallics in a single step from elemental powders. The method has been applied for the synthesis and consolidation of MoSi2. A temperature profile of the combusted compact provides the temperature-time regime for consolidation. The products were characterized for density, phase formation, and microstructure.

The molten salt method has in the past been employed to synthesize a large number of compounds at low temperatures. In this work we report the formation of solid solutions of BaTiO3–SrTiO3 and BaZrO3–SrZrO3 using a molten salt eutectic of NaOH–KOH as a solvent. Alkaline earth carbonates and titanium oxide were used as precursors for the titanate system, and alkaline earth carbonates and zirconium oxide were used as precursors for the zirconate system. It was found that both systems form solid solutions throughout the composition range. The implications of these results with regards to the applicability of the molten salt method as a tool to investigate low temperature phase equilibria are discussed.

We have compared the microwave-hydrothermal (M-H) processing with conventional hydrothermal (C-H) processing in the preparation of two layered anion exchangers, i.e., Mg3Al(OH)8NO3 · nH2O and Ni1-xZn2x(OH)2(CH3COO)2x · nH2O. Both these phases can be crystallized more rapidly (an order of magnitude) under M-H processing compared to C-H processing. The above layered mixed basic salt of Ni and Zn was found to exhibit very high selectivity for PO4= (Kd = 15,000). Its order of selectivity for various anions in the presence of 0.1 N̲ NaC1 (ratio of C1- to anion in question is 100) increases as follows: PO4= ≫ SO4= > NO3-.

Borosilicate glass films were made by the sol-gel method from tetraethoxysilane and trimethylborate precursors. The precursor or glass composition at each stage of processing was analyzed to determine the sources of boron loss. The films were heated in a furnace and with a laser to compare boron volatilization by the two heating methods. The films were characterized by infrared spectroscopy, ellipsometry, induction-charged plasma spectroscopy, and Auger microscopy. The highest losses of boron occurred during coating and low temperature (<500 °C) furnace firing. Films with the highest boron concentrations were made by dip coating and rapid firing, either with a laser or by placing them into a hot furnace. Infrared spectroscopy revealed Si–O–B bonds, indicating incorporation of boron into the borosilicate glass structure for laser- and furnace-fired films.

The formation of Pb-doped 80 K phase from nitrate precursors was studied in the Bi1.84Pb0.34Sr1.91Ca2.00Cu3.04O10.05 system. Sr(Pb, Bi)O3, Ca5Bi14O26, CuO, and CaO were found to be the intermediate compounds reacting to produce 80 K phase between 600 and 820 °C. Synthesis was complete at 800 °C for 24 h. 110 K phase formed at the expense of 80 K phase at temperatures above 820 °C. Partial melting was detected and 80 K and 110 K phases were unstable in the presence of liquid phase. They decomposed to 2201, Cu2O, and (Ca, Sr, Cu) complex oxides. The melting and decomposition were accompanied by oxygen loss.

High-resolution electron microscopy was used to examine the structural features of grain boundaries in Al–1.5% Mg and Al–3% Mg solid solution alloys produced with submicrometer grain sizes using an intense plastic straining technique. The grain boundaries were mostly curved or wavy along their length, and some portions were corrugated with regular or irregular arrangements of facets and steps. During exposure to high-energy electrons, grain boundary migration occurred to reduce the number of facets and thus to reduce the total boundary energy. The observed features demonstrate conclusively that the grain boundaries in these submicrometer-grained materials are in a high-energy nonequilibrium configuration.

A two-dimensional quasicrystal with fivefold symmetry and two large-unit-cell crystalline approximants in an Al–Co–Ni–Tb alloy, which were observed in previous studies, are suggested to be composed of the same kind of atom cluster. Some characteristics of the atom cluster can be deduced from a high-resolution electron microscopy image of the Al–Co–Ni–Tb quasicrystal when the image is associated with a fivefold aperiodic tiling. By using the cut-and-projection method, a quasiperiodic tiling generated by an irrational projection is proposed as an ideal quasilattice of the Al–Co–Ni–Tb quasicrystal; in the meantime, periodic tilings generated by a rational projection present the lattices of the crystalline approximants.

Dynamic hot-stage microscopy and sessile drop experiments have identified three stages in the spreading of Ag–28 wt. % Cu liquid on the surface of high-purity Ni foil: (I) nonreactive flow, (II) secondary spreading, and (III) breakout flow. The first stage is deGennes-type spreading driven by capillary forces and resisted by viscous drag. A (Cu, Ni) reaction layer forms quickly at temperature along the liquid-solid interface. Stage I ends when the liquid braze attains a quasistatic contact angle on the reacted surface. Stage II spreading involves a complex advance of a thin liquid sheet outward from the triple line as a result of differences in wetting between Ni grain surfaces and grain boundaries. The advancing liquid meniscus is distorted as the liquid moves ahead along the better wetted grain boundary regions and is held back (pinned) on those surfaces that are poorly wet, resulting in a stick-slip motion of the triple line. The change in contact area with time is linear during this stage, and the rate of spreading is independent of temperature in the range of 780–870 °C. Although the diffusion of Cu into Ni grain boundaries likely drives the capillary flow, it is not the controlling process since an activation energy is not observed. The final stage of spreading, breakout flow, involves the flooding of the liquid braze over previously wetted surfaces due to a change in the balance of interfacial energies. Spreading ends during stage II or III either by isothermal solidification which stems from interdiffusion between the braze filler and the substrate or by curtailment of the liquid supply when it pulls back on the (Cu, Ni) reaction layer. Hold time, peak temperature, and heating rate all have an effect on both the terminal area of spread and the spreading kinetics of braze flow on polycrystalline Ni. The heating rate effect has not been emphasized in previously published literature for soldering and brazing and, if overlooked could easily impair one's ability to apply test results to other studies or practical situations. Roughness-enhanced spreading was not observed with the Ni foil surfaces used in this study. There was, however, a localized effect on the shape of the triple line that did not affect spreading kinetics or terminal area of spread in a systematic fashion.

The present paper describes the effect of Hf and Ti additions on the microstructures and mechanical properties of two-phase composites based on the Cr2Nb–Nb eutectic. The microstructures of directionally solidified in situ composites containing 50–70% by volume of the Laves phase Cr2Nb which was modified with Hf (7.5–9.2%) and Ti (16.5–26%) are described. Partitioning of Hf and Ti between the two phases is discussed using microprobe and EDS results. The tensile properties at 1100 and 1200 °C are described and compared with those of an analogous niobium silicide-based composite. The Cr2(Nb)–(Nb) composite tensile yield strengths at 1200 °C were increased over that of monolithic Cr2Nb to ∼130 MPa. However, at 1200 °C the yield strengths of the silicide-based composites were approximately twice those of the Cr2(Nb)–(Nb) composites.

This paper describes the application of dynamic secondary ion mass spectrometry (SIMS) to the study of the chemistry of welds in V–Cr–Ti alloys and presents preliminary data on the distribution of minor and trace elements (H, C, N, O, P, S, and C1) in welds produced by gas tungsten arc (GTA) and electron beam techniques. The motivation for this research is to develop techniques that determine correlations between the concentration and distribution of trace elements in alloy metal welds and the physical properties of the weld. To this end, quantitative SIMS techniques were developed for N, O, and S analysis in vanadium alloy welds using an ion implantation/relative sensitivity factor methodology. The data presented in this paper demonstrate that trace compositions and distributions of selected welds correlate, at least qualitatively, with such properties as microhardness and tensile elongation. These data support continuing these investigations to develop microanalysis methods that quantitatively correlate weld composition with mechanical properties.

We investigate the mechanical and microstructural properties of a diamond-like carbon coating (DLC) which is deposited by plasma enhanced chemical vapor deposition (PECVD) onto an alumina/aluminosilicate glass composite used for biomedical applications. Ball-on-ring tests yield a fracture strength that is essentially influenced by the surface topology/roughness. The surface topology of the coating is investigated by atomic force microscopy (AFM). Tribology tests and nanoindentation represent the wear resistance and hardness; these are properties that are mainly influenced by the microstructural properties of the DLC coating. This microstructure is investigated by transmission electron microscopy (TEM) and analyzed by parallel electron energy loss spectroscopy (PEELS). For the general applicability of the coated composite, the interfacial adhesion of the DLC coating on the comparably rough substrate (roughness amplitudes and wavelengths are in the micrometer range) is important. Therefore, we focus on TEM investigations that show the interface to be free of gaps and pores that we, together with a characteristic microstructure adjacent to the interface, relate to the excellent adhesion. The interlayer consists of a high density of SiC grains, part of them directly bound to the substrate, and part of them bound to other SiC grains. This interlayer is followed by an essentially different region of the coating as concerns the microstructure; this region consists of nanocrystalline diamond particles embedded in an amorphous carbon matrix. It is this heterogeneous microstructure to which we attribute (i) the good adhesion based upon the interface stabilizing SiC grains, and (ii) the high hardness and wear resistance based upon the diamond nanocrystals in the coating.

This paper develops a mathematical model using mosaic patterns to characterize structural features of complex, multiphase, and multidimensional microstructures, such as those for cement paste. A multiphase microstructure can be characterized by m independent parameters; the first m– 1 parameters are equivalent to the volume fractions of the phases, while the final parameter describes the grain size, and thus, the spatial arrangement of the microstructure. An evaluation procedure for the parameters is given; they can be evaluated based on a 2D image, and then the 3D microstructure can be simulated by the present model. The relationship among the model parameters and material parameters, such as water-to-cement ratio and particle size distribution, are also established.

Barium titanate has been prepared at room temperature from a well-characterized crystalline barium titanium oxo alkoxide by reaction with acetone. An aldol condensation apparently supplies oxygen to condensing oxo alkoxide clusters. Transmission electron microscopy confirms that the crystallites so formed are dense and perfect with an average size of approximately 85 Å. Characterization of reactants and products provides a tentative understanding of structural evolution and the intermediates of the transformation. Crystalline SrTiO3 and BaZrO3 were also formed at room temperature by this same method.

One composition of Pr–Ce mixed oxide and a range of compositions of Pr–Zr mixed oxide were prepared by coprecipitation methods and characterized by x-ray powder diffraction, thermogravimetric analysis, and x-ray photoelectron spectroscopy. Based on phases formed, the PrOy—ZrO2 system in an oxygen-containing atmosphere at moderate temperatures (up to 800–1000 °C) is analogous to that of CeO2–ZrO2. Addition of either Ce or Zr to pure Pr oxide affects both the total amount of oxygen that can be reversibly exchanged between oxide and gas phase and the kinetics of the redox processes. Ce dramatically increases the amount (per Pr atom) and lowers the temperature of exchange, Zr slightly decreases the amount and also lowers the temperature of exchange, and both modifiers speed up the rate. These observations are rationalized in terms of bulk and surface structural features of the mixed oxides.

Ferroelasticity of the tetragonal displacive (t′) phase was studied on 4.7 mol% Y2O3 partially stabilized zirconia single crystals. Samples were deformed at 1400 °C at constant strain rate to induce the ferroelastic behavior. Domain reorientation due to the applied stress has been studied as a function of the compression axis and aging time at 1600 °C. Domain switching was found in the as-received and 2-h-aged crystals deformed along the 〈100〉 direction, in which an exceptional high flow stress was reached (>700 MPa). Transmission electron microscopy observations were performed on deformed and undeformed crystals to study the microstructural changes associated with the domain switching. Incremental strain steps on the stress-strain curves and surface texture on the lateral faces of the deformed samples were correlated with the microstructural evidence.

The influence of nitrogen on amorphous silicon carbide films deposited at room temperature using pulsed laser ablation has been investigated. Depositions were carried out either in ultrahigh vacuum or in a nitrogen ambient ranging from 10 to 100 mT. The mechanical and optical properties, as well as composition and structure of the resulting films, were evaluated using a variety of analytical techniques. Vacuum-deposited films exhibited high hardness but suffered from high compressive stresses (>1 GPa). At low nitrogen background pressures (<30 mT), films with an optimum balance among hardness (∼16 GPa), adhesion, and intrinsic stress (<220 MPa) were found, making them ideal candidates for protective coating applications. As nitrogen pressure was increased, mechanical performance degraded due to the increasing amount of SiO2 found in the films as evidenced by spectroscopic ellipsometry, infrared spectroscopy, and Auger electron spectroscopy measurements. The source of oxygen is attributed to residual water vapor present in our vacuum system. Optical emission spectroscopy was used to confirm the presence of Si–O species in the laser-induced plasma plume.

Nanoindentation load-displacement curves provide a “mechanical fingerprint” of a materials response to contact deformation. Over the last few years, much attention has been focused on understanding the factors controlling the detailed shape of unloading curves so that parameters such as true contact area, Young's modulus, and an indentation hardness number can be derived. When the unloading curve is well behaved (by which we mean approximating to linear behavior, or alternatively, fitting a power-law relationship), then this approach can be very successful. However, when the test volume displays considerable elastic recovery as the load is removed [e.g., for many stiff hard materials and many inhomogeneous systems (e.g., those employing thin hard coatings)], then the unloading curve fits no existing model particularly well. This results in considerable difficulty in obtaining valid mechanical property data for these types of materials. An alternative approach, described here, is to attempt to understand the shapes of nanoindentation loading curve and thus quantitatively model the relationship between Young's modulus, indentation hardness, indenter geometry, and the resultant maximum displacement for a given load. This paper describes the development and refinement of a previous approach by Loubet et al1 originally suggested for a Vickers indenter, but applied here to understand the factors that control the shape of the loading curve during nanoindentation experiments with a pointed, trigonal (Berkovich) indenter. For a range of materials, the relationship P = Kmδ2 was found to describe the indenter displacement, δ, in terms of the applied load P. For each material, Km can be predicted from the Young's modulus (E) and the hardness (H). The result is that if either E or H is known, then the other may be calculated from the experimental loading curve. This approach provides an attractive alternative to finite element modeling and is a tractable approach for those cases where analysis of unloading curves is infeasible.

The effect of BaSnO3 on the phase formation and the dielectric properties of Ba2Ti9O20 was investigated as a function of the amount of BaSnO3 in the temperature range of 20 °C to 80 °C at 7 GHz. In the reaction of 2BaCO3 + 9TiO2 → Ba2Ti9O20 + 2CO2↑, the batch with the addition of BaSnO3 enhanced the reactivity compared to the batch with the addition of SnO2. The enhancement of reactivity caused single phase Ba2Ti9O20 to form effectively with less amounts of BaSnO3. As the amount of BaSnO3 increased up to 0.03 mol, the unloaded Q increased due to an increase of the Ba2Ti9O20 phase; for further addition of BaSnO3 over 0.3 mol, the unloaded Q decreased due to the increase of rutile and BaTi4O9 phases. The dielectric constant increased with increasing BaSnO3. As single phase Ba2Ti9O20 was present in the specimen, the Q·ƒ0 value, the dielectric constant, and the TCF were approximately 37,900, 38.7, and 1.7 ppm/°C, respectively.

Positive temperature coefficient of resistivity barium titanate ceramic is a semiconductor at room temperature, so it is self-heated under certain applied voltage, and then changes into an insulator. The electrical breakdown has been investigated with the resistance-temperature characteristics of the three samples which have different compositions. The grain size effect on the breakdown voltage also is discussed. As the applied voltage increased, the electrical breakdown was initiated when the specimen interior was heated above the temperature corresponding to the maximum resistance on the resistance-temperature curves by joule heat.

Inversion domain boundaries (IDB's) in ZnO ceramics, associated with Sb2O3 doping, have been characterized using a range of electron microscopy techniques. The IDB's lie primarily on basal planes, but frequently are stepped along prismatic planes. The basal IDB can be characterized as (i) an inversion that causes an antisite exchange of cations and anions across the boundary, (ii) an effective displacement of the sixfold screw axis in the wurtzite structure vectors by a translation of 1/3 and (iii) a displacement normal to the boundary. Significant Sb segregation is detected in the basal IDB segments in agreement with previous work, and in ceramics doped with Sb2O3 and Bi2O3. These IDB's contained both Sb and Bi, suggesting that while Bi does not participate in IDB nucleation, it resides in the boundary. Comparison of experimental and calculated HREM images suggests that the IDB is composed of a monolayer of Type I (111) zinc antimonate spinel, consisting of a single layer of octahedrally coordinated zinc and antimony cations.