The surface morphology (001)-oriented single-crystal magnesium oxide (MgO) implanted with xenon ions has been examined using atomic force microscopy. It was found that at the lowest fluence used in this study (1.0 × 1014/cm2), a slight roughening of the (001) surface occurred. The magnitude of this roughening remained fairly constant with increases in fluence in the range 1.0 × 1014/cm2 to 3.0 × 1016/cm2. Implantation at fluences of ≥ 1.0 × 1017/cm2 caused significant surface roughening with the concomitant formation of micron-sized blisters. The appearance of some of these blisters resembles the rosette pattern that is also observed when the cleaved surfaces of MgO crystals are etched following indentation using a spherical indenter. This observation suggests that these blisters are formed by the growth of xenon inclusions, during implantation, by a dislocation loop punching mechanism.

Sintered AlN ceramics were implanted by 1 × 1017 Ti/cm2 at an energy of 70 keV in order to investigate the role of the chemical properties of the implanted species on the phase formed during the implantation process. The implanted ions were found in a depth profile corresponding to the calculated distribution of the vacancies produced during the implantation process instead of the predicted ion profile. Identification of the local environment of Ti and of the resulting phase led us to conclude that Ti is surrounded by N after the collision cascade and forms TiN after post-implantation annealing. The TiN nucleus if formed by substitution of Al by Ti. Therefore, the heat of formation, which is more negative for TiN than for AlN, is found to be a key parameter to predict the final system.

The nature of amorphous carbon has been explored by molecular mechanics by examining the structures of species such as C84Hx and C150Hx, wherein the percentage of sp3 carbons is progressively increased in a graphitic network. The nature of diamond-like carbon has been similarly investigated by examining the structures of C84Hx and C102Hx where the percentage of sp2 carbons is varied in an sp3 network. The dependence of the average coordination number as well as the sp3/sp2 atom ratio on the atom fraction of hydrogen has been investigated in light of the random covalent network model.

A mathematical model of micropyretic synthesis, including the consideration of pressure rise (due to gas evolution) in a porous compact, is developed for a multistep reaction. D'Arcy's law of gas flow, continuity equation, and gas law are combined to obtain a relationship between the pressure and temperature of gas. This equation for the gas pressure is solved along with the energy equations of gas and solid phase. The numerical analysis shows that the magnitude of pressure increase depends on the initial gas pressure, temperature, and permeability. When gas evolution is considered, the pressure increase depends on the variables that determine the kinetics of the gas evolution reaction, such as the activation energy and the pre-exponential factor. The pressure increase is maximum when the gas evolution takes place in the combustion reaction zone. The gas evolution is noted not to influence the combustion wave propagation.

A phase transformation study was carried out with barium aluminosilicate (BAS) forming powders (BaCO3, Al2O3, and SiO2) in a BAS-Si3N4 system. Powders were heat-treated in air at 1 atm pressure at different temperatures from 600 to 1150 °C at an interval of 50 °C to study the phase transformations during the formation of BAS. The phase transformations of α to β-Si3N4 is studied by heat-treating the powders at 1600 °C for different sintering times in a nitrogen environment at 1 atm pressure. Formation of different phases was identified by using powder x-ray diffraction. Formation of different forms of barium silicates occurs as an intermediate step between 650 and 950 °C and hexagonal BAS forms between 900 and 950 °C. The hexagonal form of BAS always forms first and persists as a metastable phase in the composites with no evidence of the monoclinic phase. An attempt made to fully transform hexagonal BAS to monoclinic BAS by using LiF as a mineralizer proved to be successful. The hexagonal form of BAS forms first when heat-treated at 1000 °C and is fully transformed to monoclinic BAS when heat-treated at 1100 °C.

Formation of nanocrystalline composites γ-TiAl + Ti2AlN by mechanically alloying (MA) Ti50Al50 in a N2 atmosphere and subsequent annealing treatment are investigated. The development of the microstructure was monitored by x-ray diffraction, and differential thermal analysis and transmission electron microscopy. The amorphous phase could be obtained after milling for 30 h in a nitrogen atmosphere. The TEM results show that some nanocrystalline solid solution of Al in Ti also existed in the amorphous matrix. The results of annealing treatments at different temperatures for 0.5 h on the amorphous phase obtained by MA in N2 gas for 30 h show the formation of γ-phase (TiAl) and a nitride of titanium and aluminum (Ti2AlN). Available annealing treatments could produced nanocrystalline composites of γ-TiAl and Ti2AlN with a grain size less than 20 nm. With increasing annealing temperature, the crystalline sizes of γ-TiAl and Ti2AlN increase, but the values of microhardness increase slightly.

Thin films (4-1000 Å) of Pt were deposited via UHV electron beam evaporation at room temperature on monocrystalline, n-type α (6H)-SiC(0001) substrates and examined in terms of chemistry, microstructure, and electrical properties. The as-deposited contacts were polycrystalline and showed excellent rectifying behavior with low ideality factors (n < 1.1) and leakage currents of 5 × 10−8 A/cm2 at −10 V. The Schottky barrier height increased from 1.06 eV before annealing to 1.26 eV after successive 20 min anneals at 450, 550, 650, and 750 °C. In addition, the leakage currents decreased to 2 × 10−8 A/cm2 at −10 V. Interfacial reactions were not observed at annealing temperatures below 750 °C; above this temperature, Pt2Si and C precipitates were identified in the reaction zone.

The influence of the key nucleation and grain growth parameters on (i) the evolution of the microstructure of the product phase (on a microscopic level) and (ii) the combustion synthesis process (on a macroscopic level) were investigated for the combustion synthesis process in the Nb-C system. This work is an integral part of the continuing effort1–3 to develop a more complete theoretical model for combustion synthesis processes in general. In particular, the nucleation and growth of the NbC(s) product phase from the supersaturated liquid Nb/C mixture that appears briefly during the combustion synthesis process was treated in a greater detail by using a decidedly more sophisticated treatment of the nucleation and growth process (as developed in the field of rapid solidification and welding). It was shown that the microstructure of the NbC(s) product phase, including the evolution of the grain size and the size distribution, and the development of the grain's morphology, as well as the combustion wave velocity, are significantly influenced by the total number density of the nucleation sites, nmax, that are present in the system. The grain size distribution was shown to possess a monosize distribution, since during the combustion synthesis process the rate of increase of the degree of local undercooling was very high so that the nucleation process took place (locally) during a very brief period of time. This work provides a sound basis for developing a better control of the microstructure, and for a better understanding and interpretation of the results of related experimental studies.

Paste development and evolution of microstructure, microchemistry, and mechanical properties of macro-defect-free composites were investigated. Mixing torque plots from a Banbury mixer showed a “window of processibility” within which an optimum polymer-particle network structure formed. This processing window can be controlled by mixing rate and temperature. Network development during paste formation governed the flexural strength and microstructure of the cured material. Electron microscopy studies of the composites corresponding to various points along the mixing torque curve revealed a matrix formation-destruction process that was linked to the mixing activity and the mechano-chemistry of the system. Microchemical evolution in the composite was studied by EDS. These studies suggested that a combined convection and diffusion mechanism was responsible for the migration of Al3+ and Ca2+ ions into the different regions of the microstructure. Increasing concentrations of these elements in the polymer regions stiffened the matrix, leading to complete degradation on further mixing.

A self-constraint strengthening mechanism for multilayered brittle materials is proposed. The strengthening is a result of the self-constraint of the individual layers on each other, and no additional reinforcements are needed. The proposed model predicts that when individual brittle layers are stacked and properly “glued” together with a weak interphase, each layer will be ensured a minimum tensile strength, regardless of the flaw size in the individual layers. Estimation of the minimum strength using this model yields an apparently close agreement with the measured values for one type of nacreous structure reported in the literature. It is also predicted that low-strength ceramic sheets, which might be produced by some low-cost fabrication techniques, can be used to construct high strength man-made nacreous ceramics.

The efficacy of various non-diamond carbon films as precursors for diamond nucleation on unscratched silicon substrates was investigated with a conventional microwave plasma-enhanced chemical vapor deposition system. Silicon substrates were partially coated with various carbonaceous substances such as clusters consisting of a mixture of C60 and C70, evaporated films of carbon and pure C70, and hard carbon produced by a vacuum are deposition technique. For comparison, diamond nucleation on silicon substrates coated with submicrometer-sized diamond particles and uncoated smooth silicon surfaces was also examined under similar conditions. Except for evaporated carbon films, significantly higher diamond nucleation densities were obtained by subjecting the carbon-coated substrates to a low-temperature high-methane concentration hydrogen plasma treatment prior to diamond nucleation. The highest nucleation density (∼3 × 108 cm−2) was obtained with hard carbon films. Scanning electron microscopy and Raman spectroscopy demonstrated that the diamond nucleation density increased with the film thickness and etching resistance. The higher diamond nucleation density obtained with the vacuum are-deposited carbon films may be attributed to the inherent high etching resistance, presumably resulting from the high content of sp3 atomic bonds. Microscopy observations suggested that diamond nucleation in the presence of non-diamond carbon deposits resulted from carbon layers generated under the pretreatment conditions.

The possibility of an autostoichiometric vapor deposition is explored. Heterometal-organic complexes such as double alkoxides are potential candidate precursors for such deposition. Two reaction schemes, the hydrolysis-assisted pyrolysis and the hydrolysis-polycondensation of double alkoxides, are identified to be autostoichiometric reactions. A simple low-pressure apparatus is suggested for autostoichiometric vapor deposition. Mass-flow analysis allows for the identification of a nonstoichiometry factor K which can be used as a quantitative measure of the precursor's autostoichiometric capability.

Stoichiometric β-SiC powders have been successfully prepared by solid state reaction of elemental silicon and carbon powders via the mechanical alloying process. The mechanical alloying process was performed in a high-energy ball mill under argon gas flow at room temperature. The solid-state reacted alloy powders have been characterized as a function of the milling time by means of x-ray diffraction, infrared absorption, scanning and transmission electron microscopy, and chemical analysis. Complete fcc-SiC (β-phase) alloy powders were obtained after 1080 ks of continuous milling. The lattice parameter (a0) of the formed β-SiC was calculated to be 0.4357 nm. No free silicon and/or carbon crystals were observed. The existence of transverse optical (TO) and longitudinal optical (LO)-like phonon modes is observed for the end-product alloy powders. Mechanically alloyed β-SiC powders are stable at elevated temperatures (1773 K) and did not transform to any other phases. The end-product β-SiC alloy powders possess excellent morphological properties, such as homogeneous shape (spherical morphology) with fine and smooth surface relief and uniform size (less than 0.5 μm in diameter). The fabricated β-SiC alloy powders have fine cell-like structure with nanoscale dimensions of about 7 nm.

The mechanism and kinetics of the chemical reaction between Nb(s) and C(s) under self-propagating high-temperature synthesis (SHS)-like (or combustion synthesis-like) conditions have been studied. Experiments were designed and conducted in order to produce a transport-resistance-free reaction between Nb and C under time-temperature conditions that are characteristic of the combustion synthesis process. To do so, a reaction couple, consisting of carbon and either a thin niobium foil or a fine niobium wire, was used. The effects of the temperature history and the formation of a liquid phase on the reaction were studied. In addition, theoretical experiments of the reaction were also conducted. The results showed that at high temperatures, layered niobium carbide phases formed in a direction that was parallel to the original carbon-niobium interface. As might be expected, local melting played a very significant role in the reactions. The mechanism and kinetics of these reactions provide a fundamental understanding of the manner and rate by which a powder-based Nb/C SHS process takes place, and, by extension, to a large, general class of solid-solid material synthesis processes that are based on the SHS (or combustion synthesis) process.

Ultralow load indentation techniques can be used to obtain time-dependent mechanical properties, termed indentation creep, of materials. However, the comparison of indentation creep data to that obtained during conventional creep testing is difficult, mainly due to the determination of the strain rate experienced by the material during indentation. Using the power-law creep equation and the equation for Newtonian viscosity as a function of stress and strain rate, a relationship between indentation strain rate, , and the effective strain rate occurring during the indentation creep process is obtained. Indentation creep measurements on amorphous selenium in the Newtonian viscous flow regime above the glass transition temperature were obtained. The data were then used to determine that the coefficient relating indentation strain rate to the effective strain rate is equal to 0.09, or .

A rapid self-sustaining solid-state precursor route to transition-metal borides, boride solid solutions, and boride composites has been developed. Solid-state metathesis (SSM) reactions between transition-metal chlorides and magnesium boride (MgB2) produce crystalline borides and magnesium chloride. Boride solid solutions are formed using mixed chloride precursors. By using a third precursor, such as NaN3, boride-nitride composites are synthesized. The reaction products are characterized by powder x-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and inductively coupled plasma atomic absorption spectroscopy. These boride reactions become self-propagating when the adiabatic temperature is greater than the melting point of the by-product salt, MgCl2 (mp 987 K).

In the determination of mechanical properties by ultra-microindentation, various errors can appear. This paper analyzes various sources of errors in estimation of elastic modulus and hardness. These errors arise from uncertainties of the indenter geometry and properties, as well as measuring instrument limitations and errors, such as the minimum detectable load, compliance, and noise of the system. Other sources of errors are thermal drift, shape of the impression, and scatter of properties of the tested material. Characteristic features and the magnitude of individual kinds of errors are discussed, together with formulas and recommended methods for their reduction.

Microtexture dependence of diamond transition in starting graphite materials under shock compression was examined, taking account of two critical points. (i) As the starting materials, several different graphite materials, each of which possesses homogeneous microtexture throughout the material, were used. (ii) In order to distinguish the effect of the microtexture from that of other external conditions, an advanced technique that made the pressure-temperature condition common for the individual materials was developed. Four graphite materials, a glassy carbon, two types of carbon black, and artificial graphite foil, were selected and characterized in detail by x-ray diffractometry, Raman spectroscopy, transmission electron microscopy (TEM), and electron energy-loss spectroscopy (EELS) prior to the shock loading. Shock compressions were performed for the materials, changes in the microtexture and transformed products of the recovered samples were characterized by TEM and EELS, and the effect of the microtexture on the transition to diamond was also discussed.

The amount of Si3N4 in a Si3N4-BaO · Al2O3 · 2SiO2 (BAS) composite and the time of sintering was examined in the context of the low temperature hexagonal to orthorhombic transformation in BAS. It was found that with increasing amounts of Si3N4 in the composite, the temperature of the hexagonal to orthorhombic transformation was decreased. As the sintering time was increased for a given composite composition, a drop in the temperature of the hexagonal to orthorhombic transformation was observed. which was linked to an increase in the β-Si3N4 content in the composite. In addition, as the Si3N4 content in the composite was increased, a resultant drop in the coefficient of thermal expansion of the composite occurred. The extent of the linear dimensional change of the composite during the BAS hexagonal to orthorhombic transformation is reported.

The crystallization kinetics of the pyrochlore to perovskite phase transformation in lead zirconate titanate (PZT) thin films have been analyzed using rapid thermal processing (RTP). Sol-gel PZT thin films, fabricated on platinum electrodes, were annealed at 550 °C to 650 °C with hold times ranging from 1 s to 5 min. Glancing angle x-ray diffraction (XRD) was used for depth profiling to identify the location of phases in the films. Transmission electron microscopy (TEM) provided information on grain structure, nucleation, and growth. The phase information was correlated to the ferroelectric and dielectric properties. The perovskite phase nucleated in the pyrochlore phase throughout the film thickness, and at 650 °C the transformation was complete in 15 s. Fast growing (100) PZT nucleated at the platinum and consumed a small-grained matrix until a columnar structure was obtained. A ramp rate of 100 °C/s was sufficiently fast to prevent transformation during heating and allowed the direct application of an Avrami model for transformation kinetics. An activation energy of 610 kJ/mol was determined.