Microstructural evolution and interfacial reaction in the eutectic SnBi solder joint on the Ni/Au metallization with and without the current stressing of 6.5 × 103 A/cm2 at 70 °C for 5 to 15 days were investigated. Electromigration is found to have significant effects not only on the phase formation at the joint interface but also on the phase coarsening and mass accumulation of Bi in the solder. In the solder joint without the current stressing, only a thin Ni3Sn4 phase was formed at the joint interface. For the solder joint with the current stressing, in addition to the Ni3Sn4 phase, a thick Au–Ni–Bi–Sn phase was formed at the joint interface after 10 days. However, the Au–Ni–Bi–Sn phase was not observed at the anode-side joint interface after 15 days of current stressing. Coarsening of the Bi-rich grain in the solder joint with the current stressing was much faster than that without the current stressing. Mass accumulation of Bi was observed at the anode side of the solder joint with the current stressing and the thickness of the Bi-rich accumulation layer increased with current stressing time. Based on the accumulation rate of the Bi-rich layer and the growth rate of the Bi-rich grain, the product of diffusivity and effective charge number of Bi in the eutectic SnBi solder is calculated to be 4.72 × 10−10 cm2/s.

The paper presents the results of combined experimental, analytical, and computational studies of contact-induced deformation and cracking in dental multilayers. These include studies of individual layers and composite structures that consist of tri-layers of glass bonded to ceramic-filled polymer foundation with an acrylate-based join material. Loading-rate-dependent Young's moduli of the join and foundation materials were obtained from monotonic compression tests. Critical loads were also determined for the tri-layers from Hertzian contact tests at different loading rates. The fracture onset (sub-surface radial cracking) was detected using an in situ telescope. The measured rate-dependent Young's moduli were then incorporated into a finite element model that was used to predict the rate-dependent critical loads in the tri-layer system. Finally, the paper shows that the observed loading rate-dependence of the critical load (for radial cracking) is due to the combined effects of slow crack growth in glass and rate-dependent Young's moduli in the join and foundation layers.

Low-energy ball milling technique was successfully used to synthesis new glassy Zr52Al6Ni8Cu14W20 multicomponent alloy powders using mechanical alloying method. During the intermediate stage of milling the atoms of Zr, Al, Ni, and Cu migrated and diffused into the W lattice to form a body-centered cubic solid solution phase. As the milling time increases, the obtained metastable powders are subsequently subjected to continuous defects and lattice imperfections that lead to a gradual change in the free energy so that solid solution phase transformed to another metastable phase (glassy). The glassy powders that were obtained after 720 ks milling are fully amorphous and have spherical-like morphology with an average particle size of 0.60 μm in diameter. The synthetic glassy Zr52Al6Ni8Cu14W20 alloy powder, which exhibits a glass transition temperature of 811 K, crystallizes at a high temperature (884 K) through a single sharp exothermic peak with an enthalpy change of crystallization of −5.48 kJ/mol. Whereas the supercooled liquid region before crystallization of the obtained glassy powders is 73 K, the reduced glass transition temperature (ratio between Tg and liquidus temperatures) was found to be 0.46. The fabricated glassy powders were consequently hot-pressed into bulk samples in an argon gas atmosphere at several temperatures with a pressure of 936 MPa. The samples that were consolidated within the temperature of the supercooled liquid region are fully dense, with relative density above ∼99.82%, and maintain their original homogeneous glassy structure. They have high Vickers microhardness values in the range between 8.46 and 8.62 GPa. They also show very high fracture strength (2.13 GPa) with an extraordinary high Young's modulus of 138 GPa. Neither yielding stress, nor plastic strain could be detected for this glassy alloy, the elastic strain of which is 1.47%.

Cerium-doped Bi3.25La0.75Ti3O12 (BLT) thin films were fabricated by depositing sol-gel solutions on Pt/Ti/SiO2/Si 〈100〉 substrates. The Ce-doping in BLT up to 6.7% of Ti atoms did not affect the single-phase bismuth-layered structure but small modification was observed in structural orientation, which influenced the microstructure and ferroelectric properties of BLT films. As we did not observe any structural distortion in x-ray diffraction data, it was suggested that doped Ce4+ was converted to Ce3+ during the annealing at 750 °C, and cerium ions might be substituted at Bi-site in BLT films. The small amount of Ce doping (1% of Ti atoms) enhanced the remanent polarization and reduced the coercive field by about 17% in BLT films, and these films showed fatigue-free response up to 1010 switching cycles at 300 kV/cm applied fields. Moderately Ce-doped films (1.7% of Ti atoms) also showed fatigue-free response up to 1010 switching cycles in 200 kV/cm applied field, but the polarization was found to increase with switching cycles when applied field was higher than 200 kV/cm. After Ce doping, the oxygen vacancy concentration may decrease in BLT films, and consequently, one can expect less domain pinning and higher fatigue resistance. Under the high cycling field, the high probability of field-assisted unpinning may be the main cause for the increased polarization.

This paper quantitatively describes the loading-unloading response in nanoindentation with sharp indenters using scaling analyses and finite element simulations. Explicit forward and inverse scaling functions for an indentation unloading have been obtained and related to those functions for the loading response [L. Wang et al., J. Material Res.20(4), 987–1001 (2005)]. The scaling functions have been obtained by fitting the large deformation finite element simulations and are valid from the elastic to the full plastic indentation regimes. Using the explicit forward functions for loading and unloading, full indentation responses for a wide range of materials can be obtained without use of finite element calculations. The corresponding inverse scaling functions allow one to obtain material properties from the indentation measurements. The relation between the work of indentation and the ratio between hardness and modulus has also been studied. Using these scaling functions, the issue of nonuniqueness of the determination of material modulus, yield stress, and strain-hardening exponent from nanoindentation measurements with a single sharp indenter has been further investigated. It is shown that a limited material parameter range in the elastoplastic regime can be defined where the material modulus, yield stress, and strain-hardening exponent may be determined from only one full indentation response. The error of such property determination from scattering in experimental measurements is determined.

We have used transmission electron microscopy to observe the structural changes that have occurred in multi-walled carbon nanotubes (MWCNTs) because of acid treatment. After a thiolation reaction of the acid-treated MWCNTs using P4S10 in refluxing toluene, we have also used electron energy loss spectroscopy to characterize the changes on the nanotubes from sidewall functionalization. We have determined that the sulfur content bonded to the nanotubes is 0.6% in terms of the atomic content of the samples. Raman spectroscopy was used to examine the vibrational changes that occurred to the nanotubes as well as identifying new vibrational modes around 500 cm−1 characteristic of carbon-sulfur bonds.

Fe element was partially substituted by Zr and Co in an attempt to enhance the glass-forming ability, and mechanical and soft magnetic properties of Fe74-xNb6B17Y3(Zr, Co)x (x = 3, 5, 8) amorphous alloys. Both partial replacements resulted in the enhancement of the glass-forming ability, and 3-mm diameter rods with a fully amorphous structure were prepared by a copper mold casting method. Zr and Co containing Fe-based bulk amorphous alloys exhibited high compressive fracture strength of about 4 and 3.5 GPa, respectively. However, Zr and Co induced different effects on the magnetic properties. Whereas the partial replacement of Fe by Zr was found to decrease dramatically the saturation magnetization, the partial replacement of Fe by Co provided an increase of about 25% of the saturation magnetization.

Four CdTe ingots with gradually increased concentration of the Sn impurity have been grown by the vertical gradient freeze method and were characterized with glow discharge mass spectroscopy, photoinduced current transient spectroscopy, resistivity, photoconductivity, and photoluminescence techniques. It was shown that the Sn impurity strongly influences resistivity and photoconductivity of the material. Concentration of Sn must be higher than the total concentration of residual acceptors to reach strong compensation. The middle-gap donor level pins the Fermi-level. Photoconductive high resistivity material can be prepared with Sn concentrations in the melt in the range 1018–1019 cm−3. In total, 6 electron traps and 3 hole traps were identified in the band gap by several complementary techniques.

The structures of inorganic fullerene-like (IF) MoS2 nanoparticles produced by arc discharge in water are reported in this paper. To adjust the chemistry and structure of IF nanoparticles, 2H–MoS2, graphite and composite 2H–MoS2/graphite rods were used as electrodes in the arc synthesis. In comparison to using MoS2 as both anode and cathode, mixed electrodes (graphite and MoS2) significantly increased the discharge current. Various IF-MoS2 nanoparticles were successfully produced by the water-based arc method, and their microstructures were studied using a transmission electron microscope equipped with an x-ray energy dispersive spectrometer. The IF–MoS2 nanoparticles commonly had a solid core wrapped with a few MoS2 layers and exhibit some differences in size and geometry. The IF-MoS2 nanoparticles were typically 5–30 nm in diameter as observed by transmission electron microscopy. Tiny IF-MoS2 nanoparticles (<10 nm) along with fragments of lamellar MoS2 were produced from arc discharge in water using both graphite and MoS2 electrodes. Carbon nano-onions and hybrid nanoparticles consisting of carbon and MoS2 were synthesized by using mixed electrodes of graphite and 2H–MoS2. The hybrid nanoparticles were MoS2 cores covered by a graphite shell. Our results show that the water-based arc method provides a simple tool for producing a variety of nanoparticles including some familiar and some new hybrid structures.

Porous Pd42.5Cu30Ni7.5P20 bulk glassy alloy rods with porosities up to 71% were successfully prepared by water quenching in a 15 MPa hydrogen atmosphere, followed by heat treatment in a supercooled liquid state. Pores with sizes up to 80 μm were homogeneously distributed over the whole cross-sectional area. Under compressive deformation, the porous alloys with porosities exceeding 41% did not show macroscopic fracture in a wide compressive strain range up to 0.6. Mechanical tests with porous alloy rods whose pores are anisotropically oriented indicate that the plasticity of the porous alloy is strongly affected by stress concentration factor.

The mechanisms of nanoindentation on single-walled carbon nanotubes (SWCNTs) have been studied by using molecular dynamics simulation and continuum analysis during which a flat layer of diamond atoms is pressed down incrementally on a vertically aligned SWCNT. SWCNTs are divided into three distinct categories based on their aspect ratios, such that the nanotube behavior transits from a shell (short tube) to a beam (long tube). Molecular dynamics simulations are used to explore the diverse indentation characteristics in each domain, where the relationships between the strain energy and indentation depth during loading, unloading, and reloading are continuously recorded. The nanoindentation mechanisms are characterized by the critical indentation depth, maximum strain energy and force associated with buckling, as well as with the evolution of carbon bond length and morphology of the SWCNTs. Bifurcation behaviors are explored by investigating the loading-unloading-reloading behaviors of the nanotubes. Parallel finite element simulations are also used to study the pre- and post-buckling behaviors of SWCNT by incorporating the van der Waals interaction into the continuum code. It is found that, for the most part, continuum analysis can effectively capture the overall indentation characteristics, yet some details related to the atomic characteristics of nanoindentation may only be revealed by molecular dynamics simulation. Finally, an indentation mechanism map is derived by comparing behaviors of SWCNTs with different aspect and section ratios. Focusing on the effects of nanotube length, this paper is the first of a series of numerical studies on the indentation mechanisms of carbon nanotubes, which may be used to determine the intrinsic mechanical properties of SWCNTs by means of nanoindentation.

Composite formation between carbon nanotubes and polymers can dramatically enhance the electrical and thermal properties of the combined materials. We have prepared a composite from polystyrene and multi-walled carbon nanotubes (MWCNT) and, unlike traditional techniques of composite formation, we chose to polymerize styrene from the surface of dithiocarboxylic ester-functionalized MWCNTs to fabricate a unique composite material, a new technique dubbed “gRAFT” polymerization. The thermal stability of the polymer matrix in the covalently linked MWCNT-polystyrene composite is significantly enhanced, as demonstrated by a 15 °C increase of the decomposition temperature than that of the noncovalently linked MWCNT-polystyrene blend. Thin films made from the composite with low MWCNT loadings (<0.9 wt%) are optically transparent, and we see no evidence of aggregation of nanotubes in the thin film or solution. The result from the conductivity measurement as a function of MWCNT loadings suggests two charge transport mechanisms: charge hopping in low MWCNT loadings (0.02–0.6 wt%) and ballistic quantum conduction in high loadings (0.6–0.9 wt%). The composite exhibits dramatically enhanced conductivity up to 33 S m−1 at a low MWCNT loading (0.9 wt%).