The thermal expansion coefficients of DyScO3 and GdScO3 were determined from298 to 1273 K using x-ray diffraction. The average thermal expansion coefficients of DyScO3 and GdScO3 were 8.4 and 10.9 ppm/K, respectively. No phase transitions were detected over this range, though the orthorhombicity decreased with increasing temperature. These thermal expansion coefficients are similar to other oxide perovskites (e.g., BaTiO3 or SrTiO3), making these rare-earth scandates promising substrates for the growth of epitaxial thin films of many oxide perovskites that have similar lattice spacing and thermal expansion coefficients.

Nickel has been widely used as an under-bump metallization (UBM) material in the microelectronics industry. The solid-state reaction between the eutectic SnAg solder bumps and three thicknesses of Ni/Cu UBM was investigated, with 5 μm-Cu/3 μm-Ni, 3 μm-Cu/2 μm-Ni, and 0 μm-Cu/1 μm-Ni. It was found that the shear strength of the solder bumps decreased after the solid-state aging at 150 °C for 200 h, and it did not change much after it was prolonged for 500 and 1000 h. Aging of the Ag3Sn intermetallic compound (IMC) and grain growth of the solder are responsible for the decrease in the shear strength. Furthermore, the shear test results indicated that the fracture mode switched from ductile to brittle for the solder bumps with 1 μm Ni after aging longer than 200 h, causing the strength of the solder to decrease abruptly. This is attributed to the consumption of the peripheral Ni layer after the solid-state aging for 1000 h. The Ni consumption rate was measured to be 0.02 μm/h1/2 at 150 °C.

Highly pure Co nanocrystalline powders were prepared by high-energy ball milling under the condition that all operations on the powders were performed in the glovebox filled with highly purified argon gas. A series of annealing experiments at different temperatures were carried out to investigate grain growth in the milled powders. The as-milled and annealed microstructures were observed and analyzed with transmission electron microscopy (TEM), high-resolution TEM, high-resolution scanning electron microscopy, and x-ray diffraction methods. Characteristics of the incontinuous grain growth in the milled nanocrystalline powders were found. It is considered by the authors that the sharp increase in nanograin size in certain intermediate-temperature region is a result of accelerated grain growth promoted by the stored energy as a supplied driving force, and through a particular dominant mechanism of nanograin rotations in contrast to grain boundary migration in polycrystalline materials.

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.

The influences of parameters on the low-temperature combustion synthesis of alumina particles from reactant mixture of aluminum nitrate and combustion fuel were studied using the particle size of as-synthesized alumina particles as a performance index. First, when urea was used as combustion fuel, it produced a higher combustion temperature and a larger particle size than the case when carbohydrazide was the fuel. Next, the combustion in air yielded a flame propagating through the reactant mixture, in contrast to a flame simultaneously ruptured from the entire reactant when the combustion was conducted in nitrogen. The particle size of the product obtained in nitrogen was 40% smaller than that obtained in air. Increasing the heating temperature could increase the alumina particle size due to the sintering effect, while combustion failed if the heating temperature was too small. The addition of diluent, excess fuel, and gas-releasing agents reduced the particle size. The increase of stirring speed also reduced the particle size. Next, if the reactant density (the amount of reactant mixture in the reacting container) was below a certain threshold value, the combustion failed to ignite. Increasing the reactant density was found to reduce the particle size due to the simultaneous reduction of combustion time and temperature. Finally, a liquid–gas reaction model was proposed and solved to study the threshold of combustion parameters.

Based on the general theoretical model proposed in Part I of this work [J. Mater. Res. 20, 1257 (2005)], a series of numerical simulations related to the self-propagating high-temperature synthesis in the Ti–C system is presented. A detailed and quantitative description of the various physical and chemical processes that take place during combustion synthesis processes is provided in Part II of this work. In particular, the proposed mathematical description of the system has been discussed by highlighting the relation between system macroscopic behavior obtained experimentally with the modeled phenomena taking place at the microscopic scale. Model reliability is tested by comparison with suitable experimental data being nucleation parameters adopted for the fitting procedure. The complex picture emerging as a result of the model sophistication indicates that the rate of conversion is essentially determined by the rate of nucleation and growth. In addition, comparison between model results and experimental data seems to confirm the occurrence of heterogeneous nucleation in product crystallization.

Ferroelectric nanolithography is a new approach to processing nanostructures, which can position multiple components made of various materials into predefined configurations. Local polarization in ferroelectric compounds is manipulated to control the surface electronic structure and direct attachment of molecules and particles. Here, the presence of optically excited electron-hole pairs on ferroelectric domains is confirmed, and reaction paths for photo reduction of several reactive metal particles are determined. Subsequent and simultaneous deposition of multiple metals is demonstrated, and the magnetic properties of Co based particles are confirmed.

The inner nacreous layer of gastropod mollusc Trochus niloticus is composed of ∼95 wt% planar arrays of polygonal aragonite-based tablets (∼8 μm wide, ∼0.9 μm thick, stacked ∼40 nm apart) and ∼5 wt% biomacromolecules. High-resolution tapping mode atomic force microscope images enabled nanoscale resolution of fractured tablet cross-sections, the organic component, and deformation of individual nanoasperities on top of tablet surfaces. Nanoindentation was performed on individual nacre tablets and the elastic modulus E and yield stress σy were reduced from elastic-plastic finite element simulations yielding E = 92 GPa, σy = 11 GPa (freshly cleaved samples) and E = 79 GPa, σy = 9 GPa (artificial seawater soaked samples). Images of the indents revealed extensive plastic deformation with a clear residual indent and surrounding pileup.

Human bone is a three-dimensional composite structure consisting of inorganic apatite crystals and organic collagen fibers. An attractive strategy for fabricating mimics of these types of composite biomaterials is to selectively grow apatite on polymers with control of structure, mechanical properties, and function. In the present study, silk/apatite composites were prepared by growing apatite on functionalized nanodiameter silk fibroin fibers prepared by electrospinning. The functionalized fibers were spun from an aqueous solution of silk/polyethylene oxide (PEO) (78/22 wt/wt) containing poly(L-aspartate) (poly-Asp), which was introduced as an analogue of noncollageous proteins normally found in bone. Silk fibroin associated with the acidic poly-Asp and acted as template for mineralization. Apatite mineral growth occurred preferentially along the longitudinal direction of the fibers, a feature that was not present in the absence of the combination of components at appropriate concentrations. Energy dispersive spectroscopy and x-ray diffraction confirmed that the mineral deposits were apatite. The results suggest that this approach can be used to form structures with potential utility for bone-related biomaterials based on the ability to control the interface wherein nucleation and crystal growth occur on the silk fibroin. With this level of inorganic–organic control, coupled with the unique mechanical properties, slow rates of biodegradation, and polymorphic features of this type of proteins, new opportunities emerge for utility of biomaterials.

A driver film method, in which a highly stressed overlayer is deposited to de-adhere a target film from a substrate, was developed to study the subcritical debonding behavior of Cu films from glass substrates. The driving force for debonding along Cu/glass interfaces was varied by depositing Cr overlayers to a range of thicknesses. One-dimensional crack growth was achieved by using C release layers and cutting strips from blanket films. Crack velocities, v, were measured and a wide strip solution was developed to obtain strain energy release rates, G. The Cu/Cr strips delaminated in a highly reproducible way, generating v–G plots similar to those seen in stress-corrosion cracking of bulk glass. Small variations in the amount of oxygen incorporated into the films during deposition strongly affected delamination rates. A reaction rate model for subcritical cracking by hydroxylation of the surfaces suggests that changes in oxygen content change the density of strong Cu–O–Si bonds across the interface.

In this work, the effect of a sol-gel ZrO2–3 mol% Y2O3 thin film on the fracture properties of a variety of brittle substrates was investigated. The results suggest that the film does not have any appreciable influence on the fracture behavior of crystalline substrates but dramatically affects the fracture properties of amorphous layers. In particular, a significant reduction of average fracture strength and a major increase of the Weibull modulus were observed on coated glassy slides. The origin of such variations is attributed to the generation of a homogeneous flaw population in the vitreous substrates, and the possible mechanisms for the production of flaws are analyzed. Implications of these results for the practical use of coated glassy layers are discussed.

Eu3+-doped zirconia nanopowders were prepared by the sol-gel technique using two different methods, based on the hydrolysis of zirconium n-propoxide, producing tetragonal and monoclinic zirconia under different preparation conditions. A detailed microstructure characterization was performed through wide angle x-ray scattering, small angle x-ray scattering, trasmission electron microscopy, and nitrogen physisorption measurements. The possible influence of the zirconia crystalline phases and particle sizes on the luminescence properties of the lanthanide ion was investigated. A detailed analysis of the emission spectra of the samples suggested that the dopant Eu3+ ions replace the Zr4+ ions in the zirconia crystal lattice. Moreover, samples prepared by the two different methods were characterized by different decay times of the Eu3+ ion luminescence.

Dense MgO ceramics with nanometer to submicrometer grain size were fabricated by high-temperature hot-isostatic pressing, low-temperature hot-pressing, and spark plasma sintering. The elastic properties were determined by sound wave velocity measurements. Young's and shear moduli of nanocrystalline MgO were lower by 13% than those with submicrometer grain size. Softening of the elastic properties was analyzed and related to the lower density and lower elastic moduli of the grain boundaries compared to the crystal interior. Young's and shear moduli of the grain boundaries were evaluated as 90 and 34 GPa, respectively. This leads to a more than 3-fold decrease in the effective elastic moduli with the decrease of grain size into the nanometer range.

ZnO nanorods with diameter of 30–200 nm were synthesized by a metalorganic chemical vapor deposition process in a hot-wall type chamber at elevated temperatures above 700 °C. At temperatures between 400 and 500 °C, ZnO thin films and wrinkles were synthesized. Above 500 °C, vertically aligned ZnO nanorods were grown on a Si and sapphire substrate without any catalysts. The range of diameter was 30–200 nm. When Au catalysts were deposited on the substrate prior to the deposition, nanocombs and nanosheets as well as nanorods were synthesized. In particylar, ZnO could be grown selectively along the pattern of the Au catalyst with the aid of a Au–Zn alloy.

In situ local measurement of sub-threshold strains generated during the electromigration of a 0.3-μm-wide Al interconnect was performed for the first time using convergent-beam electron diffraction (CBED) in a transmission electron microscope (TEM). Thermal strains were also analyzed and provided verification for the electromigration analysis. Spatially averaged strains resulting from thermal cycling and electromigration quantitatively agree with models and data from previous studies. However, the local strains exhibited variations as large as 2 × 10−3. After eliminating other possible mechanisms, the strain inhomogeneity is attributed to local plasticity through source-limited dislocation activity.

Al2O3/BN nanocomposites were fabricated through a novel chemical route involving hot-pressing of α–Al2O3 powders covered partly with turbostratic BN (t-BN). The nano-sized hexagonal BN (h-BN) particles were found to be homogeneously dispersed within the Al2O3 grains as well as at grain boundaries, which is indicative of nanocomposite structures. Thus, the present nanocomposites exhibited the unique properties of high strength and low Young’s modulus associated with nanocomposites. This paper discusses in detail the synthesis process and microstructural features of these materials.

The connection between parameters that can be measured by means of instrumented indentation with the real mechanical properties has been a matter of discussion for several years. In fact, even hardness is not a readily measurable magnitude since the real contact area depends on both the elastic and plastic properties of the sample. Recently, Dao et al. [ Acta Mater49, 3899 (2001)] proposed a method based on numerical fittings to calculate by a forward-reverse algorithm the elastoplastic properties of a sample from the load-penetration curve obtained with a sharp indenter. This work will show, in contrast, that it is not possible to measure uniquely these mechanical properties of a sample in that way.

A new type of Mg–Zn–Cu–Gd-based alloy strengthened by quasicrystal and Laves phase was developed. This alloy exhibits much better creep properties compared to AE42(Mg–4 wt% Al–2 wt% rare-earth) alloy, which is the benchmark creep-resistant magnesium die-casting alloy under the compressive creep condition of 180 °C and80 MPa. The new alloy also exhibits high room-temperature mechanical properties close to that of AZ91 alloy. The good mechanical properties are attributed to the special microstructure; the thermally stable icosahedral quasicrystals phase (i-phase) and Laves phase distributed along the grain boundary as a hard skeleton, and some fine β′1 precipitates distributed homogenously on the matrix. The dislocation morphology after the creep test was studied, and the strengthening mechanism was proposed.

Instrumented indentation is often used in the study of small-scale mechanical behavior of “soft” matters that exhibit viscoelastic behavior. A number of techniques have recently been proposed to obtain the viscoelastic properties from indentation load–displacement curves. In this study, we examine the relationships between initial unloading slope, contact depth, and the instantaneous elastic modulus for instrumented indentation in linear viscoelastic solids using either conical or spherical indenters. In particular, we study the effects of “hold-at-the-peak-load” and “hold-at-the-maximum-displacement” on initial unloading slopes and contact depths. We then discuss the applicability of the Oliver–Pharr method (Refs. 29, 30) for determining contact depth that was originally proposed for indentation in elastic and elastic-plastic solids and recently modified by Ngan et al. (Refs. 20–23) for viscoelastic solids. The results of this study should help facilitate the analysis of instrumented indentation measurements in linear viscoelastic solids.

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.