Raman microprobe spectroscopy was employed to measure stresses in ceria partially stabilized zirconia/alumina (Ce-TZP/Al2O3) composites toughened by transformation zone shielding. The near crack-tip stresses in in situ loaded compact specimens were measured by measuring stress-induced shifts in the frequency of a Raman peak corresponding to the tetragonal zirconia phase. The peak shift as a function of the applied stress was separately calibrated using a ball-on-ring flexure test. Both analytical function-fitting methods and numerical methods that determine centroids were evaluated for measuring the shift in the frequency with applied stress. A method based on locating the centroid of the intensity peak with a moving range of frequencies was selected because it gave the best correlation between the frequency shift and the applied stress. The stresses measured within an inner core of the transformation zone (∼30 μm), where the volume fraction of the transformed monoclinic phase was essentially constant, were used to estimate a local crack-tip stress intensity (Kl). The amount of total crack shielding (ΔKs) was then estimated from the applied stress intensity (Ka) and the estimated local crack-tip stress intensity. Comparisons with the predictions of two different theories of zone shielding indicated that transformation toughening models can account for 80 to 89% of the measured crack shielding, depending upon the value of the crack-tip stress intensity assumed in the models.

The high-temperature oxidation of CrN films which were deposited onto stainless steel substrates using an arc ion plating apparatus was studied at temperatures ranging from 1023 to 1173 K for 0.6 to 480 ks in air. The oxidation rate obtained from mass gain as a function of time was found to fit well to a parabolic time dependence. Formed oxide layers were analyzed by XRD, SEM, and SAM. An activation energy of the oxidation of CrN was slightly lower than that of the self-diffusion coefficient of Cr ion in Cr2O3. It is concluded that the oxidation of CrN is controlled by the outward diffusion of Cr ions through the Cr2O3 layer formed on each CrN grain.

A comprehensive understanding of radiation effects in zircon, ZrSiO4, over a broad range of time scales (0.5 h to 570 million years) has been obtained by a study of natural zircon, Pu-doped zircon, and ion-beam irradiated zircon. Radiation damage in zircon results in the simultaneous accumulation of both point defects and amorphous regions. The amorphization process is consistent with models based on the multiple overlap of particle tracks, suggesting that amorphization occurs as a result of a critical defect concentration. The amorphization dose increases with temperature in two stages (below 300 K and above 473 K) and is nearly independent of the damage source (α-decay events or heavy-ion beams) at 300 K. Recrystallization of completely amorphous zircon occurs above 1300 K and is a two-step process that involves the initial formation of pseudo-cubic ZrO2.

The efficiency of far-IR germanium photoconductive detectors can be markedly improved by antireflective coatings. Recently, there has been an effort to develop several micrometer thick, low stress, amorphous carbon films for this purpose. To date, films of no more than 1 to 2 μm have been reported in the literature. In this paper we report the deposition of low stress carbon films which are over 5 μm thick and are effective antireflective coatings at wavelengths of up to Λ = 43 μm. Minimal stress, a requirement for good adhesion, was achieved with a chemical vapor deposition process (CVD) by controlling the hydrocarbon partial pressure (2.2 mTorr) and by doping the carbon film with nitrogen.

The defects and crystallinity of as-grown and annealed TiCx (grown by the high-pressure float-zone) were examined by TEM and double crystal x-ray rocking curves. Three types of subboundaries and planar defects within subgrains were observed in as-grown TiCx. Subboundaries are classified by structure as (i) wide-extended, fault-like defects (WEFLD's), (ii) edge dislocation arrays, and (iii) dislocation networks. Planar defects were observed at dislocation nodes of subboundaries and also within subgrains; this is the first reported observation of planar defects within TiCx subgrains. The misorientation and/or density of subgrains in TiCx was reduced significantly by annealing at 2300 °C in contact with graphite.

Microstructural characterization of silicon wafers subjected to controlled low-load scratching with a sharp indenter reveals that considerable plastic deformation occurs prior to the onset of fracture. In particular, a completely ductile response to scratching is observed at or below a Vickers load of 1 g, corresponding to penetration depths of 200 nm or less. This anomalous plasticity arises primarily as a result of a pressure-induced semiconductor-to-metal phase transition (Mott transition). Various levels of subsurface dislocation activity and cracking also contribute to the deformation. The relationships among the phase transformation, dislocation activity, and the onset of fracture are discussed. These findings can be applied to other areas of contact damage demonstrating anomalous plasticity, such as hardness testing and ductile-regime turning.

Pulsed-laser light was used to generate internal flaws in fused quartz. The size of the flaw produced was proportional to the amount of laser pulse energy above a threshold value of 2.5 mJ. Specimens of different flaw sizes were tested at room temperature under four-point bending. The bending strength decreased as the flaw size increased, and a Griffith relationship was established between the lateral flaw size and the critical stress at the flaw tip. Characteristic demarcation lines were observed on the fracture surfaces of specimens with a flaw size greater than 0.25 mm. It is suggested that the formation of the demarcation line is caused by a discontinuous change of stress intensity in the dynamic process of the crack propagation.

The role of aluminum as dopant in gas phase synthesis of titania powders was experimentally investigated in an aerosol flow reactor between 1300 and 1700 K. Titania was produced by vapor phase oxidation of titanium tetrachloride in the presence of dopant aluminum trichloride vapor. The presence of aluminum altered the particle morphology from polyhedral to irregular crystals. Energy dispersive analysis and transmission electron microscopy indicated that the powders were mixtures of crystalline titania and amorphous alumina. Analysis by XPS indicated significant enrichment of aluminum on the particle surface. Some aluminum titanate (up to 17% by volume) was formed at 1700 K when a high concentration of AlCl3 was used (AlCl3/TiCl4 ≥ 0.07). Measurements of lattice parameters by x-ray diffraction indicated that aluminum formed a solid solution in titania. While titania synthesized in the absence of aluminum was about 90% anatase, the introduction of aluminum resulted in pure rutile at AlCl3/TiCl4 = 0.07. The effects of aluminum on titania phase composition and morphology are explained by the creation of oxygen vacancies in the titania crystallites and by the enhancement of the sintring rate of titania grains.

The HNaMP2O7 (where M = Co and Ni) new Na+ superionic pyrophosphates were obtained by the hydrothermal method at lower PT conditions (T = 250 °C, P = 100 atm). The solubility, complexation with reference to the solvent-solute interaction, and the growth process have been studied in detail. A new investigation on the crystal structure of these compounds showed that the title compounds do not contain Zr as reported previously. The crystal morphology and properties have also been studied.

It was shown previously1 that cristobalite precipitates out of a mixture of borosilicate glass (BSG) and high silica glass (HSG) when sintered at temperatures ranging from 800 to 1200 °C. In this paper, both direct and indirect evidences are presented to conclude that the formation of cristobalite originates in HSG. It is proposed that the cristobalite is formed as a result of dissolution of HSG in BSG and precipitation at heterogeneously nucleated sites. The process of dissolution and precipitation continues until the whole HSG particle is consumed.

Low energy bombardment of CHn+ at 100-800 eV has been used to prepare TiC film at room temperature by dual ion beam sputtering. The ion bombardment energies and densities obviously affect the metallographic morphology, the crystalline orientation, and constituent ratio of TiC films. TiC films formed under 200-600 eV CHn+ bombarding with 120-190 μA/cm2 possess much finer and compact microstructure in the compressive stress state. Its hardness is in the range of 2650-2880 kgf/mm2. The tribological tests indicate that TiC films synthesized on AISI 52100 steel by DIBS with low energy bombardment exhibit low friction coefficient and good wear resistance.

Thin films in the Pb-La-Ti-O (PLT) system were prepared under two different oxygen partial pressure (Po2) conditions by multi-ion-beam reactive sputtering (MIBERS). The oxidation of the depositing species was determined from the deposition rate dependence on Po2 and the Po2 dependence of the positive secondary ion emission from the sputtering targets. Films deposited at high Po2 (Po2 greater than the critical partial pressure for oxidation of the Pb target surface) were fully oxidized, and they formed the pyrochlore phase during annealing. The low Po2 conditions (Po2 less than or equal to the critical partial pressure for oxidation of the Pb target surface) caused sputtering of incompletely oxidized Pb species, and the resulting oxygen deficient films produced phase-pure perovskite. The formation of the pyrochlore phase at high Po2 and the perovskite phase at low Po2 is independent of Pb content within the film; the phase formation is dependent on the oxidation state of the Pb, which is sensitive to both the Po2 and the sputtering rate of the Pb. A perovskite/pyrochlore phase formation model (PPFM) that incorporates annealing time, temperature, and heating rate, and thin film oxygen deficiency was developed to explain the formation of the perovskite and pyrochlore phase during postdeposition annealing of PLT thin films.

Lead- and titanium-based oxide thin films were prepared by the metal-organic chemical vapor deposition technique (MOCVD) and the relationship between the film structures and the processing parameters, such as the ratio of Pb/Ti precursors in the gas phase, substrate materials, substrate surface orientation, and growth temperature, was systematically studied. It was found that whether a single-phase stoichiometric PbTiO3 film could be obtained depended on both the Pb/Ti precursor ratio in the gas phase and the deposition temperature. Under appropriate conditions, stoichiometric PbTiO3, films could be obtained on all the substrates including silicon, MgO, α-Al2O3, SrTiO3, and LaAlO3. The PbTiO3 films grown on silicon substrates were always polycrystalline, whereas epitaxial PbTiO3 films were obtainable on all the other substrates. For epitaxial PbTiO3 films, the epitaxial relationship, crystallinity, and domain structures were found to be a function of both the substrate materials and surface orientation as well as the deposition temperature. X-ray rocking curves (ω scan) of the (100) and (001) planes of PbTiO3 epitaxial film and PbTiO3 single crystal revealed the inherent nature of the domain structures in PbTiO3.

Interfacial reactions of Ni/amorphous Si(a-Si) multilayers are studied by means of transmission electron microscopy (TEM) and cross-sectional transmission electron microscopy (XTEM). Transformation from a crystalline to an amorphous structure has been observed in as-deposited Ni/a-Si multilayers with small modulation periods. This phenomenon is suggested to be due to interdiffusion-induced solid state amorphization which is facilitated by the high density of interface in the shorter modulation period multilayers. A thermodynamic and kinetic explanation is given for this phenomenon.

Refined mode I and mode II stress intensity factors for short cracks perpendicular to a free surface driven by a Hertzian indenter have been calculated for the case where the sphere and substrate are made of the same material. Computer simulations of Hertzian indentation tests for a variety of random surface flaw distributions show that the ring crack is expected to form outside the contact radius in all cases and that for spheres of small radii, the fracture load is expected to be proportional to the sphere radius (Auerbach's law). Reconstruction of the surface flaw distribution using the “searched area” concept is described. A useful analytical approximation for the stress intensity factors is also presented.

Effects of the scale of precursor mixing on densification behaviors and phase-transformation kinetics of multicomponent aluminosilicate gels were examined using cordierite gels prepared by two different processing routes: a monophasic (single phase) gel having molecular homogeneity, and a triphasic gel in which constitutive precursor phases are uniformly mixed in a nanometer scale (∼50 nm). In the case of the monophasic cordierite gel, homogeneous molecular-scale mixing of precursors induces a direction formation of μ-cordierite without a preceding crystallization, and the densification stops at the onset of crystallization to μ-cordierite at 960 °C. On the other hand, the densification of triphasic cordierite gel was not affected by the crystallization of intermediate spinel phase at 700 °C. The triphasic gel continues to densify until amorphous silica matrix crystallizes to quartz at 1180 °C. The enhanced densification observed in the triphasic gel was attributed to the retarded crystallization of amorphous silica component caused by the increase in diffusion distances.

The perovskite phase in PZN-PMN-PT (PbZn1/3Nb2/3O3-PbMg1/3Nb2/3O3-PbTiO3) pseudoternary ceramics was stabilized by the addition of excess constituent divalent oxides (PbO, MgO, and ZnO). 5 mol% excess MgO or 7.5 mol% excess PbO was sufficient to eliminate the remnant cubic pyrochlore phase after sintering at 1100 °C for 1 h. The enhanced diffuse phase transition (DPT) and the decrease in the electrical resistivity were observed in the presence of excess ZnO or MgO. These were interpreted in terms of the additional formation of negatively charged, short-range ordered 1: 1 domains with a concomitant generation of charge carriers (holes). The behavior of excess MgO or ZnO at concentrations above 5 mol% was studied by examining complex impedance patterns.

Polycrystalline BaFe12O19 has been synthesized by pyrolysis of an aerosol produced by ultrahigh frequency spraying of a solution. Two precursor solutions have been used in order to study its influence on the formation temperature of the barium hexaferrite and on the microstructural and magnetic properties. The relationship between in situ temperature, pyrolysis precursor, and textural and magnetic properties of the products obtained is discussed.

Cu/Al2O3 bilayer samples were produced by vapor deposition and irradiated successively with 150 keV Ar ions up to a dose of 500 dpa. Ion beam mixing effects were studied by 2 Me V He+ Rutherford backscattering spectroscopy (RBS). Concentration depth profiles show the mixing of Cu, Al, and O atoms in the sample. Because of the low mixing efficiency found in this study, Al2O3-dispersion strengthened Cu alloys seem to be good candidates as structural materials in fusion reactors.

Barium titanate thin films were produced under the hydrothermal conditions, and their formation mechanism was investigated. The phase structure and surface morphology of the resultant films were directly dependent on the reaction conditions. The films that have a reaction time shorter than 8 h below the processing temperature of 150 °C in the 0.8 N Ba(OH)2 solution were composed of compounds with the component ratio m(Ba)/ m(Ti) < 1, and a flower-like surface morphology. With extended reaction time under the higher temperature, the films showed a multiphase structure and a mosaic or island-like surface morphology. In the case of 1.0 N, 1.5 N Ba(OH)2 solution, well-crystallized, monoperovskite BaTiO3 thin films having uniform, mirror-like, and visible-defectless surfaces were produced at a processing temperature of 180 °C after 24 h. The experimental results were explained by hypothesizing that the formation mechanism consists of a “dissolutions-crystallization process”.