Elastic-viscoelastic correspondence, utilizing Boltzmann integral operators, was used to generate displacement–time solutions for spherical indentation testing of viscoelastic materials. Solutions were found for creep following loading at a constant loading rate and compared with step-loading solutions. Experimental creep tests were performed with different loading rate–peak load level combinations on glassy and rubbery polymeric materials. The experimental data were fit to the spherical indentation ramp–creep solutions to obtain values of shear modulus and time-constants; good agreement was found between the experimental results and known modulus values. A multiple ramp-and-hold protocol was examined for the measurement of creep responses at several loads (and depths) within the same test. Emphasis is given to the use of multiple experiments (or multiple levels within a single experiment) to test a priori assumptions made in the correspondence solutions regarding linear viscoelastic material behavior and the creep function.

Inversion boundaries (IBs) of a head-to-head or (0001)|(0001) (C+|C+) configuration bisect virtually every grain in typical commercial ZnO varistor ceramics. They are most often considered electrically inactive, and the effect on the grain growth behavior has been recently addressed. In this work, various configurations of ZnO bicrystals were prepared using different source crystals and strong barrier effects were observed in some (0001)|(0001) (C−|C−) bicrystals using crystals with higher impurity contents. The crystallographic polarity and impurity effects were systematically examined by doping C+|C+ and C−|C− bicrystals with single and double additives of Mn, Co, Ni, and Bi. Varying degrees of barrier effects including varistor-like behaviors were observed in C−|C− bicrystals depending on dopants, while C+|C+ bicrystals consistently exhibited negligible effects. Because the IBs in ZnO varistor ceramics preferentially expose C− surfaces in the grain boundaries, the superior property of commercial ZnO varistor ceramics is suggested to be assisted by the presence of IBs.

Pressureless sintered B4C relative densities as high as 96.7% were obtained by optimizing the soak temperature, and holding at that temperature for the minimum time required to reach terminal density. Although the relative densities of pressureless sintered specimens were lower than that of commercially produced hot-pressed B4C, their (Vickers) hardness values were comparable. For 4.45-cm-diameter, 1.35-cm-high disk-shaped specimens, pressureless sintered to at least 93.0% relative density, post-hot isostatic pressing resulted in vast increases in relative densities (e.g., 100.0%) and hardness values significantly greater than that of commercially produced hot-pressed B4C.

The microstructural changes in cryomilled and consolidated Al 5083 following compression testing at several temperatures are described. Prior to testing, the material had an average grain size of approximately 138 nm and exhibited a duplex microstructure, containing coarse grains between 500 and 2000 nm. After uniaxial compressive deformation at temperatures between 423 and 573 K (0.49–0.66 Tm), the average grain size increased to between 200 and 300 nm, consistent with the average grain size of extrusions formed from the same material at similar temperatures. The similarity in grain size distribution following uniaxial compression or extrusion despite differences in total strain and stress state imposed by each indicates that much of the deformation in the extrusion process occurs in coarse-grained regions.

Textured, thin films of BiFeO3 (∼120 nm thickness) were synthesized by chemical solution deposition from a mixture of iron- and bismuth- 2-methoxyethoxides on Si(100)/SiO2/TiO2/Pt substrates. The use of alkoxides ensured good homogeneity and a low degree of organics that further facilitated low crystallization temperatures. Crystalline films were according to x-ray diffraction already obtained at 480 °C. Precursor characteristics were investigated using thermogravimetry and differential scanning calorimetry, whereas phase purity, microstructure and film topography were examined by x-ray diffraction, transmission electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. A small (10%) Bi excess was found necessary to obtain dense, pore-free films. Such additions also prevented decomposition of BiFeO3 at high temperatures. The observed (012) texture is believed to originate from the growth mechanism as no relation to the substrate is found. This is also confirmed by observing (012) texture for films on glass substrates.

A novel, low-temperature synthesis method for producing BaxSr(1−x)TiO3 (BST) thin films patterned in the form of nanotubes (“honeycomb”) on Ti substrates is reported. In this two-step method, the Ti substrate is first anodized to produce a surface layer (∼300 nm thickness) of amorphous titanium oxide nanotube (∼100 nm diameter) arrays. In the second step, the anodized substrate is subjected to hydrothermal treatment in aqueous Ba(OH)2 + Sr(OH)2 at 200 °C, where the nanotube arrays serve as templates for their topotactic (shape-preserving) hydrothermal conversion to polycrystalline BST nanotubes. A simple geometrical model is proposed to elucidate the mechanism of the hydrothermal growth of BST nanotubes. This opens the possibility of tailoring the titanium oxide nanotube arrays and of using various precursor solutions and their combinations in the hydrothermal bath to produce ordered, patterned thin-film structures of various Ti-containing ceramics. These could find use not only in a variety of electronic, optoelectronic, and sensor device applications but also in biomedical and catalysis applications, where patterned thin films are desirable.

Various shapes and sizes of colloidal Co nanoparticles were fabricated by the polyol process using Co(acac)3, 1,2-hexadecanediol, oleylamine, and oleic acid within octylether. The rice-shaped Co nanoparticles with size of 30 nm and aspect ratio of 1.8 can be fabricated into a self-assembled form without assistance of surfactants. The addition of oleylamine as surfactant decreased the particle size and aspect ratio, and the addition of oleic acid made the surface of particle faceted without decreasing particle size from that of rice shape. The mixture of oleylamine and oleic acid produce differently shaped Co nanoparticles, including nanoprism, nanowire, and nanoflower according to the ratio of components, total amount of surfactant mixture, and reaction time. The fabricated nanoparticles showed ferromagnetic properties. These results showed that the various size and shape of metallic nanoparticles can be fabricated by the polyol process into controlled forms.

Nanoscaled Cr2O3 powder with an average particle size of 20–40 nm, coated on alumina particles, has been produced by means of chemical vapor deposition (CVD) in a fluidized chamber, using the pyrolysis of Cr(CO)6 precursor. Amorphous and crystalline Cr2O3 particles were obtained when the temperatures of the pyrolysis were 300 and 400 °C, respectively. To prepare nanoscaled Cr3C2 powder from the nanometer-sized Cr2O3, carbonizing behavior of the Cr2O3 particles was investigated. It was found that, when amorphous Cr2O3 powders were carbonized in graphite furnace at 1150 °C for 2 h in vacuum (10−3 Torr), the powder was transformed into Cr3C2, while the crystalline Cr2O3 was transformed into a mixture of Cr7C3 and Cr3C2. The examinations by x-ray diffraction, transmission electron microscopy, and energy dispersive spectroscopy confirmed the transformation of the nano-sized Cr3C2 powders. The results of thermogravimetry and differential thermal analysis indicated that the transformation temperature was ∼1089 °C for amorphous Cr2O3 and ∼1128 °C for crystalline Cr2O3.

The mechanical properties of intermetallic compounds in the Au–Sn system were investigated by nanoindentation. Measurements of hardness and elastic modulus were obtained for all of the confirmed room-temperature intermetallics in this system as well as the β phase (8 at.% Sn) and AuSn4. Overall, it was found that the Au–Sn compounds have lower hardness and stiffness than common Cu–Sn compounds found in solder joints. This finding is in contrast to common knowledge of “Au embrittlement” due to the formation of either AuSn4 or (Au,Ni)Sn4 intermetallic compounds. This difference in understanding of mechanical properties of these phases and the resulting joint strength is discussed in terms of reliability and possible failure mechanisms related to interface strength or microstructural effects. Indentation creep measurements performed on Au5Sn, Au–Sn eutectic (29 at.% Sn) and AuSn indicate that these alloys are significantly more creep resistant than common soft solders, in keeping with typical observations of actual joint performance.

Elastic deformation of coating/substrate composites was examined for axisymmetric indentations with three different geometries of flat-ended cylinder, sphere, and cone. Intensive theoretical considerations were made for the Boussinesq problems not only in its Fredholm integral equation of the second kind, but also in its Green function using the principle of superposition for the approximated contact stress distribution. The agreement and the disagreement between these two different numerical/analytical assessments for elastic surface deformations are discussed. Along with these theoretical considerations, experimental scrutiny was conducted for the theoretical predictions for spherical indentation by the use of a sol-gel-derived MeSiO3/2 film coated on a soda-lime glass plate. A novel technique is also proposed for estimating in a simultaneous manner the elastic moduli of both the coating film and of the substrate or the elastic modulus of the film and its thickness in spherical indentation tests.

The electromigration behavior of the high-lead and eutectic SnPb composite solder bumps was investigated at 150 °C with 5 × 103 A/cm2 current stressing for up to 1711 h. The diameter of the bumps was about 125 μm. The underbump metallization (UBM) on the chip side was sputtered Al/Ni(V)/Cu thin films, and the Cu pad on the board side was plated with electroless Ni/Au. It was observed that damages occurred in the joints in a downward electron flow (from chip side to the substrate side), while those joints having the opposite current polarity showed only minor changes. In the case of downward electron flow, electromigration damages were observed in the UBM and solder bumps. The vanadium in Ni(V) layer was broken under current stressing of 1711 h while it was still intact after current stressing of 1000 h. The electron probe microanalyzer (EPMA) elemental mapping clearly shows that the Al atoms in the trace migrated through the UBM into the solder bump during current stressing. Voids were found in the solder bump near the UBM/solder interface. The Sn-rich phases of the solder bumps showed gradual streaking and reorientation upon current stressing. This resulted in the formation of uniaxial Sn-rich phases in the middle of the solder bump, while the columnar and fibrous Sn-rich phases were formed in the surrounding regions. The formation mechanism of electromigration-induced damage to the UBM structure and solder bump were discussed.

In this paper, we derive corrected analytical expressions for calculating the hardness and modulus by the two-slope method. This method relies on the determination of the slopes of the loading and unloading curves rather than the indenter displacement as an input. These expressions take into account the correction factor α in the fundamental relations among contact stiffness, elastic modulus, and contact area, which is frequently forgotten or misused in the literature. It is shown that these corrected expressions allow measurements of the hardness and modulus in very good agreement with the commonly used technique based on the determination of the contact area. Additionally, the correction factor α can be easily determined if Young's modulus of the material is known.

A series of water-soluble silicon oxide materials was synthesized by the sol-gel reaction of tetramethoxysilane (TMOS)/3-aminopropyltrimethoxysilane (APTMOS) mixtures catalyzed by hydrochloric acid with varying TMOS/APTMOS ratios. Increase in TMOS composition made the products less water-soluble, and the richest TMOS composition for the water-soluble silicon oxide materials was found to be TMOS/APTMOS = 7/3 (mol/mol). Ultraviolet-visible spectroscopy of a 10 wt% aqueous solution of the product with TMOS/APTMOS = 7/3 showed a high transmittance in the visible region. Its infrared spectrum showed an absorptionband attributable to the Si–O bond, and the 29Si dipole decoupled/magic angle spinning–nuclear magnetic resonance spectrum exhibited signals in the regions of T3, Q3, and Q4, indicating a dense siloxane network structure. A peak due to an ordered structure with a 1.76 nm periodicity was observed in the x-ray diffraction profile, and a stripe pattern was observed in the transmission electron microscopy image. These results indicate that the rodlike silicon oxide macromolecules with a 1–2-nm diameter stack parallel. Thus a silicon oxide material with nano-ordered structure was successfully formed and such a structure produced the water solubility.

The reaction between Sn–xCu (x = 0.1, 0.3, 0.7, 0.9, and 1.5 wt%) solder alloys and Ni at 260, 280, and 290 °C for 60 s was studied to reveal the effect of Cu content on the composition and morphology of intermetallic compounds (IMCs) formed at the interface between solder and substrate. The results indicated that Cu concentration greatly affects both the composition and morphology of the IMC between the solder and Ni substrate. In particular, when the Cu concentration was less than or equal to0.3 wt%, (CuxNi1−x)3Sn4 IMCs were formed at the interface. When the Cu concentration was 0.7 wt%, large facets type of (CuxNi1−x)6Sn5 were mixed with (CuxNi1−x)3Sn4 in the IMC layer. At Cu concentrations higher than the eutectic one, e.g., 0.9 and 1.5 wt%, stick-shaped (CuxNi1−x)6Sn5 compounds were detected, but the (CuxNi1−x)3Sn4 IMCs disappeared. The formation and growth mechanism of the (CuxNi1−x)6Sn5 compound were analyzed. The evolution tendency of the composition and morphology of the IMCs at the three testing temperatures was found to be the same.

We studied tensile creep behavior in two silicon nitride ceramics, i.e., 4.8 mol% Lu2O3 (SN48) and 1.2 mol% Lu2O3 (SN12), at 1400–1500 °C under applied stress of 137–300 MPa. Time to failure of SN48 increased with decreasing applied stress and minimum strain rate. The stress–rupture parameter was 10.7 at 1400 °C and 11.4 at 1500 °C. Pore formation was confirmed in a creep-tested specimen of SN48 by transmission electron microscopy. These results suggest that SN48 was fractured by creep rupture. The minimum strain rate of SN12 was almost below the measurement system limitation at temperatures below 1500 °C. Time to failure tended to increase with decreasing applied stress. The stress–rupture parameter was 41 at 1400 °C and 73 at 1500 °C. These results suggest that SN12 was fractured by subcritical crack growth.

The interfacial adhesion energy was studied using the four-point bend method for boron carbo-nitride (BCxNy) deposited on dielectric and copper films. Twenty-five nanometer BCxNy films were deposited by chemical vapor deposition at 360 °C and 1 Torr using dimethylamine borane with no coreactant, NH3, or C2H4, producing different composition films, BC0.37N0.15, BC0.11N0.49, BC0.92N0.07, with dielectric constants of 4.1, 4.2, and 3.8, respectively. BCxNy films were deposited on dense and porous dielectrics, and copper. BCxNy films adhered strongly to the dielectric films and the composite beams snapped before debonding, revealing that the critical debond energy Gc exceeded 10 J/m2. The adhesion of BCxNy to oxidized copper increased with carbon content in the film, with the BC0.92N0.07 film beams snapping, and is possibly related to covalent bonding between surface oxygen and carbon in the film.

Indentation analysis based on the concept of representative strain offers an effective way of obtaining mechanical properties, especially work-hardening behavior of metals, from reverse analysis of indentation load–displacement data, and does not require measuring of the projected contact area. The definition of representative strain adopted in previous studies [e.g., Dao et al., Acta Mater.49, 3899 (2001)] has a weak physical basis, and it works only for a limited range in some sense of engineering materials. A new indentation stress-state based formulation of representation is proposed in this study, which is defined as the plastic strain during equi-biaxial loading. Extensive numerical analysis based on the finite element method has shown that with the new formulation of representative strain and representative stress, the critical normalized relationship between load and material parameters is essentially independent of the work-hardening exponent for all engineering materials, and the results also hold for three distinct indenter angles. The new technique is used for four materials with mechanical properties outside the applicable regime of previous studies, and the reverse analysis has validated the present analysis. The new formulation based on indentation stress-state based definition of representative strain has the potential to quickly and effectively measure the mechanical properties of essentially all engineering materials as long as their constitutive behavior can be approximated into a power-law form.

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