The fracture behavior of high-purity alumina ceramics with grain sizes ranging from 2 to 13 μm is studied by means of the double torsion method. Crack-propagation tests conducted in air, water, and silicon oil, for crack velocities from 10−7 to 10−2 m/s, show that slow crack growth is due to stress corrosion by water molecules. An increase of the grain size leads to enhanced crack resistance, which is indicated by a shift of the V–KI (crack velocity versus applied stress intensity factor) plot toward high values of KI. Moreover, the slope of the curve is apparently higher for coarse grain alumina. However, if the R-curve effect is substracted from the experimental results, a unique V–KItip (crack velocity versus stress intensity factor at the crack tip) law is obtained for all alumina ceramics, independently of the grain size. This means that the crack-growth mechanism (stress corrosion by water molecules) is the same and that the apparent change of the V–KI law with grain size is a direct effect of crack bridging.

MnZn ferrites show extensive subcritical crack growth. In this process water plays an important role. The fracture surfaces of MnZn ferrites with three different stoichiometries were investigated with adsorption isotherm measurements, temperature-programmed desorption, diffusive reflection infrared Fourier transform spectroscopy (DRIFT), low-energy ion spectroscopy (LEIS), and x-ray photoelectron spectroscopy (XPS). The XPS results confirmed the presence of Mn, Zn, Fe, and O atoms in the surface region, but LEIS indicated that the outer layer of the fracture surfaces contained no Zn atoms. DRIFT confirmed that hydroxyl groups were present on the fracture surfaces. Experiments with H2S, for which the XPS is more sensitive, indicated that at low coverage pairs of S atoms bridge a pair of Fe atoms. With increasing coverage the S bridge shifts to one Fe atom while at the highest coverage each Fe atom is bonded to one S atom. In experiments with N2 the highest nitrogen absorption is found for the lowest oxygen concentration in the ferrite, which is probably related to the polarity of the surface. Both the adsorption and desorption tests indicated that N2 had a larger adsorption affinity to MnZn ferrite surfaces than H2O.

Mullite-based composites can be made by an in situ reaction process using silica-coated alumina (SCA) powder as a mullite precursor. In this paper we present the combined effects of zirconia and premullite seeds on the crystallization process and microstructure development. When zirconia is added without seeding, mullite formation proceeds through the formation of transient zircon. This phase provides a lower energy barrier for mullite nucleation and thus lowers the mullitization temperature. The presence of yttria as a stabilizer in zirconia reduces the activation energy for zircon formation and thus promotes the transient reaction. The addition of premullite seeds results in the nucleation of mullite from alumina and silica, and zircon does not form. At low seeding levels mullitization remains nucleation-controlled; however, once the seeding level exceeds 1–2%, this is no longer the case.

New low-dielectric-constant interlevel dielectrics are being investigated as alternatives to SiO2 for future integrated circuits. In general, these materials have very different mechanical properties from SiO2. In the standard model, electromigration-induced stress evolution caused by changes in the number of available lattice sites in interconnects is described by an effective elastic modulus, B. Finite element calculations were carried out to obtain B as a function of differences in the modulus, E, of interlevel dielectrics, for several stress-free homogeneous dilational strain configurations, for several line aspect ratios, and for different metallization schemes. In contradiction to earlier models, we found that for Cu-based metallization schemes with liners, a decrease in E by nearly two orders of magnitude has a relatively small effect on B, changing it by less than a factor of 2. However, B, and therefore the reliability of Cu interconnects, can be strongly dependent on the modulus and thickness of the liner material.

The effects of beryllium (Be) and solution temperature on the morphologies of iron intermetallics, silicon particles, and copper intermetallics, relative to the mechanical properties of 319.0 alloys, were investigated. The experimental results indicated that adding Be to the alloy can raise the Al–Al2Cu eutectic melting temperature, change some plateletlike shape (βndash;Al5FeSi) of iron intermetallics to comparatively harmless Chinese-script morphologies (α–Al8Fe2Si), and reduce the amount and average length of βndash;Al5FeSi platelets. During high-temperature solution treatment (>500 °C), the thinner and smaller the β–Al5FeSi platelets were, the faster they dissolved and fragmented. However, where the solution temperature exceeded the Al–Al2Cu eutectic melting point, the Al–Al2Cu eutectic melted and resulted in an ultrafine eutectic phase on quenching, which deteriorated mechanical properties. The fracture behavior of 319 alloy was affected by the morphologies of the iron intermetallics, silicon particles, and copper intermetallics. Fractographic analysis of tested compact tension specimens revealed that the fracture processes were mainly initiated by void nucleation at β–Al5FeSi platelets as a result of their cracking and decohesion from the matrix. Adding Be to the 319.0 alloy and optimizing the solution temperature could significantly decrease the number of fracture-initiation sites of β–Al5FeSi platelets and improve the tensile properties and fracture toughness.

Small-angle neutron scattering (SANS) and the method of contrast variation were used to measure porosity and crystallite surface area in the energetic system octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and to gauge the effects of mechanical deformation on the pore-size distribution and crystallite surface area. The crystallite surface area and the presence of voids (pores) in a high explosive system are known to affect its behavior and overall performance. Measures of these two quantities after an insult, resulting from various process and accident scenarios, can be used to predict the performance of an explosive system after process- and accident-related mechanical deformation. The contrast variation technique allows us to discriminate between internal pores and features that are on or contiguous with the crystallite surface. Measurements were conducted on loose powders of HMX (261 and 10 mm, volume averaged mean particle diameters) and pellets made by uniaxial consolidation to 7 and 10 vol% porosity, respectively. Analysis of the SANS data indicates significant alteration of the intragranular pore structure and systematic shifts in the surface area that are dependent upon mechanical deformation.

Pure, Nd doped, and Nd–Cr bidoped yttrium calcium oxyborate Yca4O(BO3)3 (YCOB), NdxY1−xCa4O(BO3)3 (NYCOB) with x = 0.86, and Cr:NdxY1−xCa4O(BO3)3 (Cr:NYCOB) with x = 0.45 and a small amount of Cr3+ ions crystallized with a fluorapatite-type structure in the monoclinic system. The unit cell constants were a = 0.8076(7), b = 1.6020(10), and c = 0.3527(2) nm with the angle β of 101.23° for the NYCOB and z = 2. The measured absorption spectra of NYCOB and Cr:NYCOB were compared to Judd–Ofelt (JO) theory. When applied, the JO theory of parity-forbidden electric-dipole transitions of rare earth ions on noncentrosymmetric sites demonstrates good agreement. The experiments showed that the Cr3+ ions were introduced into the crystalline lattice as a sensitizer to absorb the excitation energy and transfer it to the Nd3+ ions in the lattice structure.

Distribution characteristics of boundary phase in BaB2O4 added BaTiO3 ceramics were investigated with a focus on the curvature difference of solid–liquid interfaces at two-grain and triple junctions. High-resolution transmission electron microscopy revealed that the triple junction of solid grains showed the positive curvature of solid–liquid interface and consisted of the mixture of liquid phase and crystallized BaB2O4 phase. On the other hand, flat amorphous thin film of 2.5-nm thickness was observed at the two-grain junction. This kind of boundary phase distribution characteristic was explained by the solubility difference between two kinds of junctions of solid grains that had different curvature of solid–liquid interfaces.

When a eutectic melt is undercooled below its liquidus T1 by a critical amount, it undergoes metastable liquid-state spinodal decomposition. The resulting morphologies can be described as intermixing undercooled liquid networks of characteristic wavelength λ. At a temperature substantially below T1, λ can be <100 nm. When λ ≤ 100 nm, the undercooled liquid networks break up into nanometer-size droplets/strips driven apparently by surface tension. The morphologies of the tiny droplets/strips can be frozen by subsequent crystallization. The as-crystallized specimen is a nanostructured material. It is microvoid free and the size of the constituent grains is rather uniform. Two systems, Pd40.5Ni40.5P19 and Pd82Si18, were chosen to illustrate the synthesis process.

Thermal transport properties of multilayer thin films both normal and parallel to the layers were measured. Al/Ti multilayer films 3 μm thick, with individual layers systematically varied from 2.5 to 40 nm, were studied on Si substrates. Layers of Al and Ti were nominally equal in thickness, with actual composition determined for each specimen using energy dispersive spectroscopy. The thermal diffusivity both in the plane and normal to the plane of the films (thermal conductivity divided by specific heat per volume) was found to decrease significantly with decreasing bilayer thickness. Pure Ti and Al films as well as Cu films from 0.1 to 5 μm thick were also studied. In-plane electrical conductances of the Al/Ti multilayers were also measured.

New Ni-based bulk amorphous alloys in the alloy system Ni–Ti–Zr–(Si,Sn) were developed through systematic alloy design based upon the empirical rules for high glass forming alloys. Small additions of Si and/or Sn significantly improved the glass forming ability (GFA) of the alloys Ni57Ti23−xZr20 (Si,Sn)x leading to a Ni-based bulk amorphous alloy. The amorphous ribbons of the alloys Ni57Ti23−xZr20 (Si,Sn)x exhibited very high glass transition temperatures (Tg > 823 K), crystallization temperatures (Tx > 883 K), and large undercooled liquid regions (δTx > 50 K) implying the high GFA of the alloys. Fully amorphous rods with the diameter of up to 2 mm can be fabricated by a copper mold casting method. Development of the new Ni-based bulk amorphous alloys having high Tg,Tx, and δTx expands the practical applications of amorphous alloys as structural materials.

We investigated sol-gel-derived silica-based hard coatings on modified polyester substrates. The silica network was modified by incorporating an organic component and adding transition metal oxides. These modifications resulted in tailored thermal, optical, and mechanical properties of the coatings. Various low-temperature densification techniques were studied including sol-preparation procedure, enhanced solvent evaporation, ultraviolet irradiation, and low-temperature heating (below 150 °C). Oxygen plasma etching was applied to improve the adhesion of the sol-gel coatings on the plastic surface. Nanoindentation analysis revealed that the coatings have a surface hardness up to 2.5 ± 0.27 GPa and an elastic modulus up to 13.6 ± 0.4 GPa, approximately an order of magnitude higher than that of the plastic surface.

We performed ab initio Hartree–Fock molecular orbital calculations of solute elements in amorphous silicon nitride (Si–N) ceramics. To investigate effects of solute elements, X, such as boron, carbon, aluminum, silicon, and phosphorus, on stabilization of the Si–N network, we used model clusters representing local atomic structures in the Si–N network, and the solute elements were substituted for nitrogen. Bonding characteristics around the solute elements were analyzed, and bond energies of Si–X were also calculated using model clusters. It was found that, among these solute elements in amorphous Si–N, the Si–C bond is able to make the Si–N network more stable due to its high covalency.

The creep behavior of a cryomilled ultrafine-grained Al–Mg alloy was examined. The grain size ranged from 300 to 400 nm. The stress exponents ranged from 7.2 to 7.4. The apparent activation energy for creep, 83.7 kJ/mol at 27.5 MPa and 77 kJ/mol at 38 MPa, agreed well with the activation energy for grain boundary diffusion in aluminum. Transmission electron microscope analysis following creep at 300 °C to approximately 0.2% strain in 1411 h revealed the grain size was unchanged from its as-extruded size indicating significant thermal stability of this material at relatively high fractions of the melting temperature. The creep resistance of the Al–Mg alloy was rationalized in terms of an attractive interaction between grain boundary dislocations and incoherent particles within the boundary region, which suppressed grain boundary deformation. The grain boundary particles also led to high thermal stability by exerting a Zener pinning force on the grain boundaries, thus inhibiting grain growth at high temperatures.

Two kinds of obviously different-sized –Si3N4 whiskers were grown from silicon melt with different pretreatment vacuum conditions. Their growth interface structures were studied in a cross-section view from micro-areas to macro-areas by combination of micro-area state analysis with chemical shift mapping of Si Kβ bands using electron probe microanalysis. The one pretreated under the lower vacuum condition with a rotary pump was 10–20 μm in diameter and hundreds of micrometers in length, and another pretreated under the higher vacuum condition with a diffusion pump was 0.1–0.2 mm in diameter and 2–5 mm in length. The small Si3N4 whiskers were grown from the surface of the SiC particles within the Si melt. The large Si3N4 whiskers were grown from the surface of Si3N4 crucible. On the basis of these results, their growth mechanisms are discussed from the view of the nucleation sites, impurity source, and thermodynamic stability of the SiC particles. Compared with the Si3N4 grains, the SiC particles influenced the nucleation deeply and caused the process to grow small-sized crystals. Preventing the carbon impurities into the Si melt from forming the SiC particles in the pretreatment process was one effective way to grow the large-sized β–Si3N4 single crystals.

Structural studies of the strontium vanadate glasses of compositions xV2O5–(100 − x)SrO are reported. X-ray diffractograms, density, and oxygen molar volume, etc., of the glasses show that single-phase and homogeneous glasses were obtained in the composition domain x = 50 to 90 mol%. The network structure for the glass compositions with 90 and 80 mol% V2O5 is built up of the VO5 polyhedra, while the other glass compositions consist of the VO4 polyhedra. Density and glass transition temperature are observed to decrease with an increase in the V2O5 content. The magnetic susceptibility of the glasses shows an increase of concentration of the reduced V4+ ion with the increase of vanadium oxide content in the compositions. The well-resolved electron spin resonance structure observed for the glass composition with 50 mol% V2O5 gradually becomes poor and reduces to a single component line, which has been attributed to the increase of the hopping rate of charge carriers with the increase of the V2O5 content in the compositions.

An icosahedral (I) phase in coexistence with Al phase was found to precipitate in atomized Al93Fe3Cr2Ti2 and Al93Fe3Cr2V2 powders. The mixed structure was formed in the size fraction range up to 125 μm for the Al–Fe–Cr–V alloy, while the increase of the particle size to 125 μm for the Al–Fe–Cr–Ti powder led to the precipitation of Al23Ti9. The replacement of Cr by Mn for the Al93Fe3Cr2Ti2 powder caused a mixed structure of Al+I+Al23Ti9 +Al6Mn even for the ?26 mm powder. The formation tendency of the I-phase increased in the order of Al–Fe–Cr–V > Al–Fe–Cr–Ti > Al–Fe–Mn–Ti system. The decomposition temperature of the I-phase was about 790 K. The I particles were analyzed to have approximate compositions of Al84.2Fe7.0Cr6.3Ti2.5 and Al82.9Fe9.0Mn6.4Ti1.7, and the use of the analytical compositions enabled the formation of a mostly single I phase with an average grain size of 90 to 130 nm in the melt-spun state. Bulk I alloys in a cylindrical rod form were produced by extrusion of the atomized powders at 673 K and an extrusion ratio of 10. The extruded Al93Fe3Cr2Ti2 alloys exhibited good mechanical properties; i.e., σ 0.2 of 550 MPa, σ UTS of 660 MPa, and ε P of 4.5% at room temperature, and σ 0.2 of 330 MPa, σ UTS of 350 MPa, and ε P of 1.5% at 573 K. The high σ UTS exceeding 350 MPa at 573 K was superior to the final target of the United States Air Force and hence the I-based Al93Fe3Cr2Fe2 alloy is expected to be extended as a new type of high elevated temperature strength material.

The chemical interaction between a Si3N4 ceramic, with Al2O3 and MgO sintering additives, and DIN 100Cr6 steel was studied by means of static interaction couple experiments between 500 and 1200 °C. At 500 °C, the ceramic was chemically stable in contact with the steel. In the temperature range between 700 and 1100 °C, the silicon nitride dissociated in contact with the steel. The Si dissolved and diffused into the steel, whereas a nitrogen pressure built up in the micropores at the interface, limiting and inhibiting the reaction rate. The strength of the obtained interfacial bond was too low to withstand the residual stresses formed during cooling, and therefore, the interaction couples fell apart during cooling. Above 1100 °C, the nitrogen also dissolved and diffused into the steel, enhancing the overall rate of interaction. A strong interface was formed, resulting in a well-defined interaction layer on the ceramic side of the interaction couple. The mechanical pressures on the interaction couples were adjusted to study the influence of plastic deformation of the steel on the chemical interaction. Higher contact pressures resulted in more homogeneous and uniform interaction layers. The reactivity of plastically and elastically deforming steel, however, was found to be the same.

In this paper we derive an analytical expression for the indentation load–depth relation during loading in an indentation experiment, namely . The advantage over previously used expressions is that no additional empirical constants are necessary. A comparison between the new expression and results from finite element calculations shows excellent agreement.

We investigated several specimens of ASTM A710 steel containing copper-rich precipitates with variations in the final aging treatment. X-ray diffraction line-broadening and small-angle neutron-scattering experiments revealed the existence of the precipitates and associated coherency strain. We determined the nonlinear ultrasonic parameter β for each specimen by harmonic-generation experiments and measured the ultrasonic longitudinal velocity vL and attenuation αL. Although vL and aL showed no consistent trends, β increased with increasing strain. This correlation is compared to a microstructural model for harmonic generation that includes a contribution from precipitate-inned dislocations.