Five Ni–Zr–B ternary eutectic alloys were synthesized by means of melt spinning and were found “amorphous” by standard surface x-ray diffraction. The thermal stability was determined by differential scanning calorimetry. Glass-formation ability (GFA) was characterized by reduced glass transition temperature among the five “amorphous” alloys. The existence of intermetallic compounds which are structurally complex and have bigger lattice parameters is proved to enhance the higher GFA. The effective suppression of nucleation and growth of intermetallic compounds plays a very important role for the glass formation.

We investigated superfast densification of nanocrystalline MgO powders by spark plasma sintering (SPS) between 700 °C and 825 °C under applied pressures of 100and 150 MPa. Fully-dense transparent nanocrystalline MgO with a 52-nm average grain size was fabricated at 800 °C and 150 MPa for 5 min. In-line transmissionsof 40% and 60% were measured compared to MgO single crystal, for the yellowand red wavelengths, respectively. Densification occurs by particles sliding over each other; the nanometric grain size and pores lead to the optical transparency. The light brownish color of the nanocrystalline MgO is due to the oxygen vacancy color centers, originating from the reducing atmosphere of the SPS process.

The internal friction of a silicon nitride with a sintering aid of yttrium oxide was measured from room temperature to 1400 °C. A mechanical loss peak was typically observed at 1000 °C on heating the as-sintered specimen; however, it disappeared on cooling. Also, the peak was not observed upon heating a specimen that had been heated above 1400 °C. When we carried out thermal cycling, raising terminal temperatures from 1050 to 1400 °C, the integrated intensity of the peak gradually decreased due to the progressive crystallization of a grain-boundary amorphous phase.

By studying reactions between Au foils and Sn(Cu) alloys, we found that the Au consumption rate depended on the Cu-content of the Sn(Cu) solders. The higher Cu-content alloys had faster Au consumption rates. When the Au foil was pre-coated with a Ni layer and then reacted with Sn(Cu) alloys having a Cu-content of morethen 1.5 wt%, a stable ternary (Cu,Ni)6Sn5 compound layer was observed on theAu foil. This ternary compound layer then served as a barrier layer that effectively prevented the Au foil from reacting with the molten solder. This result enabled the implementation of a flip-chip assembly process for the fabrication of optoelectronic devices.

Microscale polymeric structures with intricate three-dimensional (3D) shapes and nanoscale features were synthesized by using silica-based microshells of diatoms (unicellular algae) as transient scaffolds. Diatom microshells were immersed in dilute solutions of polymer precursors in volatile solvents. After extraction and solvent evaporation, the resulting thin films on the microshells were cross-linked to form rigid polymer coatings. Selective silica dissolution then yielded freestanding polymeric structures that retained the microshell shapes and fine features. By utilizing bioscaffolds capable of genetically precise and massively parallel replication, enormous numbers of polymeric micro/nanostructures with identical 3D shapes may be generated for various applications.

In this paper we present a new method of the rapid construction of magnetic phase diagrams in a temperature-composition space, using magneto-optic imaging with an indicator film technique (MOIF). The method is applied for mapping the diagram for the La1–xCaxMnO3 colossal magneto-resistive oxide, using the spread films deposited on a SrTiO3 substrate. The constructed magnetic diagram is in a good agreement with data on uniform films and bulk crystals of this system. The MOIF study of transitions under cooling and heating has revealed the formation of a non-magnetic phase in the area of temperatures from 5 K to 57 K and compositions from x = 0 to x = 0.5.

Bulk nanocrystalline body-centered cubic- (bcc) (Fe,Co) alloy with high saturated magnetization and good soft magnetic properties was synthesized by the simple process of casting and annealing for the glass-type Fe62.8Co10B13.5Si10Nb3Cu0.7 alloy. It crystallizes through two exothermic reactions. The cylindrical glassy rod with the diameter of 1.5 mm was produced by copper mold casting. The subsequent annealing at the temperature higher than that of the first exothermic peak causes the formation of bcc-(Fe,Co) nanocrystalline with particle sizes between 10 and 15 nm. The bcc-(Fe,Co) alloy rods exhibit good soft magnetic properties of 1.35 T for saturation magnetization and 5 A/m for coercive force.

We investigated the effect of lead zinc niobate (PZN) on the sintering behavior and piezoelectric properties of lead zirconate titanate (PZT) ceramics. The addition of PZN improved the sinterability of PZT ceramic so remarkably, that at additions of more than 10%, the specimens were fully dense at a temperature as low as 900 °C. The phase of the PZT-PZN ceramics was affected by PZN content and the Zr/Ti ratio in the PZT. With increasing PZN content, a lower Zr/Ti ratio was required for the morphotropic phase boundary (MPB). Specimens with the MPB composition showed the highest piezoelectric properties; d33 = 500 pC/N, kp = 0.68, and S33 = 0.38% at 2 kV/mm.

Using a Ti–Cu–Ni–Sn–Ta alloy as an example, we demonstrate a strategy for the in situ formation of nanocomposite microstructures that can lead to simultaneous high strength and ductility. Our approach employs copper mold casting for the production of bulk alloys from the melt, and the solidification microstructure is designed to be composed of micrometer-sized ductile dendrites uniformly distributed inside a matrix of nanoscale eutectic reaction products. The nanostructured matrix is achieved at a relatively deep eutectic, which facilitates the formation of an ultrafine eutectic microstructure over a range of cooling rates. The multi-component recipe stabilizes a ductile solid solution as the toughening phase and helps to reduce the eutectic spacing down to nanoscale. The multi-phase microstructure (including phase distributions, morphologies, and interfaces) has been examined in detail using transmission electron microscopy (TEM) and high-resolution TEM. The metastable eutectic reaction and the nanoscale spacing achieved are explained using thermodynamic and solidification modeling. The benefits expected from the microstructure design are illustrated using the high strength and large plasticity observed in mechanical property tests. Our nanocomposite design strategy is expected to be applicable to many alloy systems and constitutes another example of tailoring the microstructure on nanoscale for extraordinary properties.

By variation of reaction temperature and time during the hydrothermal synthesis process, TiO2 nanoparticles in anatase, rutile, and mixture of rutile-anatase phases are formed without adding any mineralizer. Differential thermal analysis studies indicate the rutile phase crystallization at a comparatively lower temperature and a low weight loss. The material synthesized by hydrothermal reaction required no post-calcination for the crystallization. Transmission electron microscopy, selected-area diffraction, Brunauer–Emmett–Teller, and x-ray diffreaction studies confirmed the compositions to be anatase and rutile with the particle size ranging from 5 to 25 nm with surface area as high as 260 m2/g for the anatase and 65 m2/g for rutile. The prepared nanoparticles exhibited a blue shift of the absorption edge in the ultraviolet-visible spectrum greater than 10 nm. The particles with average size around 5 nm showed two band edges in the absorption spectra attributed to two different particle sizes. Simple photocatalytic reactions were tried to demonstrate the photochemical activity of the synthesized material. The synthesized nanoparticles exhibited an ultraviolet radiation simultaneous photoreduction of Cr(VI) to Cr(III) and oxidation of formic acid into carbon dioxide and water.

Nanocrystalline tungsten oxide (WO3) films were electrodeposited potentiostatically at room temperature on transparent conducting substrates from an ethanolic solution of acetylated peroxotungstic acid prepared from a wet chemistry process. The changes that occur in the microstructure and the grain size of the as-deposited WO3 films as a function of annealing temperature are simultaneously accompanied by a continually varying electrochromic performance. X-ray diffraction studies revealed the transformation of a nanocrystalline as-deposited WO3 film into a highly crystalline triclinic WO3 as the annealing temperature was raised from room temperature to 500 °C. The microstructural evolution with the increasing annealing temperature of the as-deposited film was further exemplified by transmission electron microscopy (TEM) studies. While the as-deposited film was composed of uniformly distributed ultra fine nanograins, the most noticeable feature seen in these films annealed at 250 °C was the presence of open channels which are believed to promote lithium ion motion. Films annealed at 400 °C exhibited coarse grains with prominent grain boundaries that hinder lithium ion movement, which in turn reduces the film’s ion insertion capacity. In concordance with the TEM results, the 250 °C film had the highest ion storage capacity as it exhibited a charge density of 67.4 mC cm−2 μm−1. The effect of microstructure was also reflected in the high transmission modulation (64%) and coloration efficiency (118 cm2 C−1) of the 250 °C film at 632.8 nm. Contrary to the superior electrochromic performance of the 250 °C film, the optical switching speeds between the colored and bleached states of the as-deposited WO3 film declined considerably as a function of annealing temperature. Also, the diffusion coefficient for lithium ions was greater by at least an order of magnitude for the as-deposited film as compared to the 250 and 500 °C films. In this report, the influence of microstructural changes that are brought about by the annealing of the as-deposited WO3 films on their coloration-bleaching dynamics is evaluated in terms of their structural, electrochromic, and electrochemical properties.

This study used an analytical model for phase-transformation kinetics. We used different combinations of various nucleation mechanisms [mixed nucleation (site saturation plus continuous nucleation), Avrami nucleation, and site saturation plus Avrami nucleation] and growth mechanisms (volume diffusion-controlled growth and interface-controlled growth) for a single transformation. Our work incorporated the effect of impingement of the growing particles. These factors have been applied to the same experimental results to find out the prevailing mechanisms. We made a detailed analysis for the determination of the parameters of the analytical phase-transformation model, in order to determine the most reasonable nucleation and growth modes, and the values for the activation energies of nucleation and growth. We used the model to study the crystallization kinetics of Mg82Ni18 and Mg88.7Ni11.3, as measured by means of both isothermal and isochronal differential scanning calorimetry.

In view of obtaining a Si:H network at the onset of microcrystallinity at a high deposition rate, we have adopted an intelligent approach to find out a tricky plasma condition in radio frequency (rf) plasma-enhanced chemical vapordeposition that provides a better control on growth introducing retarded microcrystallization. The deposition parameter includes a combination of high electrical power applied to the (SiH4+H2)-plasma and high gas pressure in thereaction chamber. High rf power increases the number density of film-forming precursors as well as atomic H density in the plasma, which helps to increase thefilm deposition rate and to promote microcrystallinity, respectively. In addition,high pressure helps not only to increase the film-growth rate by producing a dense plasma but also retards the microcrystallization process by increasing significantlythe gas phase collision frequency and consequently reducing the effective reactivityof atomic H on the surface of a fast-growing Si:H network. A combination of high-power and high-pressure plasma conditions provides a reasonably wide rangeof H2 dilution to work with and better control in producing a Si:H network at theonset of microcrystallinity, while increasing the film-growth rate.

Micromachined fuel cells are among a class of microscale devices being explored for portable power generation. In this paper, we report processing and geometric design criteria for the fabrication of free-standing electrolyte membranes for microscale solid-oxide fuel cells. Submicron, dense, nanocrystalline yttria-stabilized zirconia (YSZ) and gadolinium-doped ceria (GDC) films were deposited onto silicon nitride membranes using electron-beam evaporation and sputter deposition. Selective silicon nitride removal leads to free-standing, square, electrolyte membranes with side dimensions as large as 1025 μm for YSZ and 525 μm for GDC, with high processing yields for YSZ. Residual stresses are tensile (+85 to +235 MPa) and compressive (–865 to -155 MPa) in as-deposited evaporated and sputtered films, respectively. Tensile evaporated films fail via brittle fracture during annealing at temperatures below 773 K; thermal limitations are dependent on the film thickness to membrane size aspect ratio. Sputtered films with compressive residual stresses show superior mechanical and thermal stability than evaporated films. Sputtered 1025-μm membranes survive annealing at 773 K, which leads to the generation of tensile stresses and brittle fracture at elevated temperatures (923 K).

Nanoindentation experiments were carried out on a columnar ∼1.5-μm-thick TiN film on steel using a conical indenter with a 5-μm tip radius. Microstructural examination of the contact zone indicates that after initial elastic deformation, the deformation mechanism of the TiN is dominated by shear fracture at inter-columnar grain boundaries of the TiN film. A simple model is proposed whereby the applied load is partitioned between a deforming TiN annulus and a central expanding cavity in the steel substrate. It is possible to obtain a good fit to the experimental load–displacement curves with only one adjustable parameter, namely the inter-columnar shear fracture stress of the TiN film. The implication of results in the context of the performance of TiN films in service is also discussed.

Short carbon fiber (SCF) filled high-density polyethylene conductive composites were studied in terms of time-dependent piezoresistive behaviors. The time-dependent change of resistance under constant stress or strain was found to be the succession of the previous pressure-dependent piezoresistance. Depending on the filler volume fraction and the level of the constant stress or strain, resistance creep and resistance relaxation with different directions were observed. An empirical expression similar to the Burgers equation could be applied to fit the data for both the resistance creep and the resistance relaxation. The fitted relaxation time as a function of pressure showed that there exist two competing processes controlling the piezoresistive behavior and its time dependence. Mechanical creep and stress relaxation of the composites were also studied, and a comparison with the time-dependent resistance implied that there is a conducting percolation network attributed to the physical contacts between SCF and a mechanical network formed by the molecular entanglement or physical crosslinking of the polymer matrix and the interaction between the filler and the matrix. It is believed that the two networks dominate the electrical and the mechanical behaviors, respectively.

Although crystalline silicon is not generally considered susceptible to fatigue crack growth, recent studies suggest that there may be fatigue processes in silicon micro-machined structures. In the present study, a micro-machined fracture specimen geometry was used to examine stable crack growth under fatigue loading. Crack length and loads were carefully monitored throughout the test to distinguish between environmentally assisted crack growth (stress corrosion) and mechanically induced fatigue-crack growth. Results revealed similar steplike crack extension versus time for the cyclic and monotonic tests. The fatigue crack-growth curve extracted from the crack extension data exhibited a nearly vertical slope with no evidence of accelerated crack-growth rates. Fracture surfaces for the monotonic and cyclic tests were similar, further suggesting that a true mechanical fatigue crack-growth mechanism did not occur. Explanations for the observed lack of fatigue crack growth are presented and discussed with respect to reported stress-life behavior.

A procedure for extracting simple constitutive parameters from microindentationtests is described. The analysis used to interpret the indentation tests is based onthe analysis of the spherical indentation test developed by Hill et al. for power law materials. Indentation tests are supplemented by scanning interference microscopyof the residual indented surface profiles and a method is suggested for using the residual surface profiles to estimate the actual contact surface. This, in turn, allowsfor the construction of the entire stress versus strain curve.

This paper describes the nanoindentation technique for measuring sputter-deposited Au and Cu thin films’ mechanical properties at elevated temperatures up to 130 °C. A thin, 5-nm Pt layer was deposited onto the Cu film to prevent its oxidation during testing. Nanoindentation was then used to measure elastic modulus and hardness as a function of temperature. These tests showed that elastic modulus and hardness decreased as the test temperature increased from 20 to 130 °C. Cu films exhibited higher hardness values compared to Au, a finding that is explained by the nanocrystalline structure of the film. Hardness was converted to the yield stress using both the Tabor relationship and the inverse method (based on the Johnson cavity model). The thermal component of the yield-stress dependence followed a second-order polynomial in the temperature range tested for Au and Pt/Cu films. The decrease in yield stress at elevated temperatures accounts for the increased interfacial toughness of Cu thin films.

The relative effects of Pb and Re doping on microstructure, irreversibility field, and electronic anisotropy of HgBa2Ca2Cu3O8+δ (Hg-1223) thick films grown on Ag substrates prepared by dip-coating were studied. Both Pb- and Re-doped films exhibit the dominant phase of Hg-1223, characterized by a superconducting transition temperature (Tc) of 133 K. Both dopants distribute homogeneously in the Hg-1223 grains and promote grain growth. Pb-doped films have larger colony size compared to the Re-doped. The irreversibility fields (Hirr) of (Hg,Re)-1223 are significantly higher than those of (Hg,Pb)-1223 at temperatures below 100 K. The logarithmic plots of Hirr versus (1 – T/Tc) show both Pb- and Re-doped have a crossover temperature reflecting a transition from two- to three-dimensional behavior with increasing temperature. Re doping significantly decreases the electronic anisotropy γ, which would enhance flux pinning and consequently improve the critical current density. The differences between Pb and Re dopants in affecting γ are explained in terms of crystal structure.