In the Ni–Mo system, two possible nonequilibrium states located near Ni3Mo were predicted through calculation of the total energies of eight possible structures of the A3B type as a function of their lattice constant(s) by applying the Vienna ab initio simulation package. Comparatively, Gibbs free energy diagrams were constructed from Miedema's model and, in general, the calculated results were in accordance with the prediction from ab initio calculation. Besides, the prediction of one of the nonequilibrium states was in agreement with the fact that a metastable hexagonal-close-packed Ni3Mo phase was indeed observed in Ni75Mo25 multilayer films upon thermal annealing, and calculated lattice constants matched well with those determined by diffraction analysis in experiments as well.

Combustion synthesis/micropyretic synthesis is a technique in which material synthesis is accomplished by the propagation of a combustion front across the sample. In some cases, the combustion front may propagate in an unstable mode where the propagation velocity and combustion temperature of the combustion front are altered periodically. In this study, the processing conditions leading to unstable combustion reaction were first studied theoretically. The boundary temperatures separating stable and unstable reactions were then determined. The numerical analysis showed that the combustion temperature and the propagation velocity changed periodically during unstable combustion. As the combustion reaction became unstable, the average propagation velocity and the oscillatory frequency of front propagation decreased. The products of unstable combustion synthesis possessed the banded structures, implying the occurrence of the unstable oscillatory propagation, as demonstrated experimentally. In this study, high activation energy combustion (Ti + 2B reaction) and low activation energy combustion (Ni + Al reaction) were both chosen to illustrate the effect of unstable combustion. It is the first time the experimental and numerical results were combined to investigate the temperature and propagation velocity variations during unstable combustion.

Electromigration-induced hillock growth in polycrystalline Al segments was extensively investigated. Hillocks composed of columnar grains grew near the anode by epitaxial Al addition at the interface between the Al and underlying TiN layer, which pushed up the original Al film. The hillocks rotated away from their initial (111) out-of-plane orientation in a manner consistent with the physical rotation of the hillock surface. Wedgelike and rounded hillocks were observed, and their formation is explained by the interaction between grain extrusion and grain growth. Trends elucidated by review of both thermal- and electromigration-induced hillock studies can be explained by the mechanisms identified in this work.

Optimum conditions for the synthesis of nonagglomerated BaTiO3 particles by salt-assisted spray pyrolysis (SASP) were investigated. The effect of particle residence time in the reactor and salt concentration on the crystallinity and surface morphology of BaTiO3 was examined by x-ray diffraction and scanning electron microscopy. Mixtures of a metal chloride or nitrate salt, dissolved in aqueous precursor solutions, were sprayed by an ultrasonic atomizer into a five-zone hot-wall reactor. By increasing the salt concentration or the particle residence time in the hot zone, the primary particle size was increased, and its surface texture was improved compared to BaTiO3 particles prepared by conventional spray pyrolysis. The SASP-prepared BaTiO3 crystal was transformed from cubic to tetragonal by simply increasing the salt concentration at constant temperature and residence time. Further thermal treatments such as calcination or annealing are not necessary to obtain nonagglomerated tetragonal BaTiO3 (200–500 nm) particles with a narrow size distribution. Increasing the carrier gas flow rate and decreasing the residence time in the hot zone resulted in cubic BaTiO3 particles about 20 nm in diameter.

In situ reinforced microstructures with well-dispersed elongated grains, up to 10 μm in length, embedded in matrices consisting of submicron equiaxed grains, were developed by hot pressing Y-, Yb-, and (Y + Yb)-doped a-sialon ceramics containing approximately 3 vol% extra liquid phase at a comparatively low sintering temperature, 1800 °C. The liquid phase, thermodynamically compatible with a-sialon, was introduced by raising the oxygen content of an already oxygen-rich α-sialon composition, e.g., by increasing the O/N ratio in RExSi12-(3x+n) Al3x+nOnN16−n. Two different α–Si3N4 precursor powders, one fine-grained and one coarse, and one coarse β–Si3N4 powder were used, and the influence of particle size and crystalline modification of the precursor Si3N4 powder on the formation of elongated a-sialon grains was investigated. The formation of elongated α-sialon grains was promoted by introducing an extra liquid phase and by using a fine-grained α–Si3N4 powder, whereas the coarse β–Si3N4 powder did not yield any elongated grains at all. The obtained in situ reinforced α-sialon ceramics were both hard and tough, with a Vickers hardness and a fracture toughness of 21 GPa and approximately 5 MPa m1/2, respectively.

The isothermal oxidation behavior of Ti2AlC at intermediate temperatures of 500, 600, 700, 800, and 900 °C in flowing air was investigated by means of thermogravimetric analysis, x-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM)/energy dispersive spectroscopy. An anomalous oxidation with higher kinetics at lower temperatures of 500 and 600 °C was observed although Ti2AlC exhibited good oxidation resistance at higher temperatures. As revealed by SEM scale morphology observation, oxidation-induced cracks present at temperatures of 500 and 600 °C resulted in poor protectivity of scales and accounted for the anomalous oxidation. The weight gain data for the remaining temperatures were analyzed with an instantaneous parabolic rate constant method by assuming a parabolic rate law. The variations of instantaneous parabolic rate constant with time reflected the complexity of the oxidation behavior of Ti2AlC at intermediate temperatures. These variations were discussed from the viewpoint of phase transformation of oxidation products on the basis of XRD, Raman spectroscopy, and SEM scale morphology observation. As indicated by XRD and Raman spectra, the scale formed on Ti2AlC at higher temperature was stable α–Al2O3 and rutile TiO2, while transition aluminas of γ–Al2O3, δ–Al2O3, θ–Al2O3, and TiO2 (anatase) were detected at lower temperatures. The whisker morphology of θ–Al2O3 at 800 °C and ridged morphology of α–Al2O3 at 800 and 900 °C were confirmed by SEM.

The sliding friction and wear performance of Al–Ni–Co–Si quasicrystalline coatings deposited by the high-velocity oxy-fuel technique were investigated under dry sliding conditions. This study indicated that changes in the imposed sliding test conditions modified the friction and wear behavior of quasicrystalline coatings. Qualitative analysis of the contact interface and wear debris were performed with the aim of understanding the role of the third body on the friction and wear processes. The dependence of the coefficient of friction on the sliding velocity and counterpart material was explained by the stick-slip behavior. It was also shown that test conditions favorable for the formation of thick intermediate layers and the densification of the coating subsurface led to low wear rates. Large cylindrical particles, formed by agglomeration of small wear debris, were suggested as a beneficial factor for the reduction of the coefficient of friction.

From synchrotron x-ray scattering measurements, it was found that epitaxially grown SnO2 film on sapphire has a variant structure with threefold symmetry with respect to the substrate and that the ultrathin interfacial layer is formed due to the lattice mismatch between SnO2 and Al2O3. The physical properties of the top surface, such as surface morphology, height profile, and roughness, were determined by atomic force microscopy. The height profiles of the film grown at 600 °C and room temperature revealed the asymmetrical and the ordinary symmetric Gaussian distributions, respectively. The difference originates from the dominant diffusion process at high substrate temperature.

The oxidation behavior of sputtered TiAlN thin-film barrier layers was studied by cross-section transmission electron microscopy. Bare 100-nm-thick TiAlN films on SiO2/Si began to oxidize from the surface after annealing in air for 10 min from about 550 °C. Annealing at 700 °C oxidized half of the layer thickness. A 100-nm-thick Pt overlayer on the barrier layer retarded macroscopic oxidation at 650 °C. However, a 10-nm-thick Pt overlayer accelerated oxidation as a result of the catalytic dissociation of O2 molecules to form O atoms, which oxidized the barrier layer at 550 °C to the same extent as without the thin Pt overlayer at 650 °C. The effects of other thin metal overlayers, such as Ru and Ir, were also investigated. Ru and Ir did not accelerate TiAlN oxidation due to the absence of catalytic activity.

Pulsed laser ablation deposition was used to fabricate Ni films. The structure of the as-deposited films is hexagonal (a = 0.267 nm and c = 0.435 nm), and its resistivity is nearly one order of magnitude larger than the resistivity of bulk Ni. No spontaneous magnetization was observed in the as-deposited samples. Annealing above 200 °C induced an irreversible structural transformation from the metastable hexagonal phase to the stable face-centered-cubic (fcc) one. Parallel to this transformation, the magnetic moment of the annealed Ni samples increased, and their resistivity decreased. On annealing at 440 °C, the structural transformation from the hexagonal-close-packed to the fcc phase was completed, and the magnetic moment, Curie temperature, and electrical resistivity of the fcc Ni films were found similar to the ones observed in bulk Ni. A direct correlation between the volume fraction of the fcc Ni phase in our films and their magnetic moment was established.

Textured as well as epitaxial thin AlN films are of great interest for a wide range of electro-acoustic and optoelectronic applications. Reduction of the deposition temperature is of vital importance in a number of applications due to thermal budget limitations. In this work we systematically studied the influence of the process parameters on the film properties and identified the factors leading to improved film quality as well as reduced deposition temperature with pulsed direct current sputtering in an Ar/N2 atmosphere. We demonstrated that fully textured (0002) films can be grown under a wide range of conditions. At the same time the full width at half-maximum (FWHM) of the rocking curve of the (0002) XRD peak was found to vary systematically with process conditions—depostion rate, process pressure, gas composition, and substrate temperature. The best films showed a FWHM of 1.2°. We found that by far the most important factor is the arrival energy of the sputtered Al atoms, which is primarily controlled by the process pressure. We report for the first time that fully textured AlN films with a FWHM of under 2° can be grown at room temperature. Other important factors are the ion and electron bombardment of the films and substrate temperature as well as gas composition, although their influence is not as dramatic. Generally, the film quality increases with temperature. Bias and electron bombardment within a certain range also lead to better films.

The dissolution behavior and kinetics of spinel lithium manganate LiMn2O4 with different particle sizes have been investigated in this study. The dissolution of manganese cations from LiMn2O4 is confirmed to occur when LiMn2O4 particles are immersed in the electrolytes. The amount of dissolved manganese ions markedly increases with a rise in temperature and a decrease in particle size, which implies that the capacity fading of LiMn2O4 at elevated temperatures is associated with manganese dissolution. On the basis of the isothermal analysis of reaction kinetics, the rate of manganese dissolution from LiMn2O4 is dominated by the rate of dissolution reaction. Smaller particles exhibit a larger reaction rate constant and higher activation energy of the dissolution process than the larger ones. Therefore, an increase in temperature has a more pronounced effect on the dissolution reaction of small particles than on that of large particles.

Various methods to access indentation data are considered on the basis of the load P–displacement h curve, its derivative, or its integral. This paper discusses and extends the various analytical models to estimate the indentation P–h curve, the slope, and the dissipated energy to aid the development of a concise methodology to analyze indentation data. Special consideration is given to the effect of pile-up and sink-in. Relationships for sharp and spherical indenters are presented and in addition for sharp indenters with a rounded tip. An overview over analytic expressions for the P–h curve is given and compared to finite element simulations and experimental data. An expression derived for the representative strain at the onset of yield under sharp and spherical indenters compares well with literature results. The effect of a rounded tip on the yielding under a sharp indenter is discussed. The ratio of loading to unloading slope and the ratio of the plastically dissipated energy to the total energy is related to hardness and elastic modulus. In combination these ratios can be used to determine the strain-hardening coefficient.

Silver nanoparticles were incorporated in a dispersion of micron-sized silver spheres for testing as a low-temperature reactive component to form conductive particle networks. The development of conductivity depended on the arrangement of the micron-sized particle network, the amount of material reacted to form necks at the points of contact of micron-sized particles, and sintering of the particle network. Nanoparticles reacted to bond the micron-sized particles, but the stress issues involved in nanoparticle sintering can cause macroscopic cracking. Critical processing variables include the state of particle dispersion, the heating rate, and the fraction of nano-sized material.

We present a facile method to measure Fickian diffusion coefficients of paramagnetic species in materials, using electron spin resonance (ESR) spectroscopy. The method requires no postannealing sample preparation, is adaptable to in situ measurement, and requires only that the spectrum of the paramagnetic species change monotonically with its local concentration. We illustrated this method with poly(ethylene-co-methacrylic acid) ionomers, using laminates prepared from the same copolymer neutralized with either paramagnetic Mn2+ or diamagnetic Zn2+. For Mn2+, the exchange interaction between neighboring Mn2+ caused the six-line hyperfine pattern to transform to a single broad signal, providing the measurement of local concentration. Diffusion coefficients of Mn2+ in this ionomer pair measured by ESR were compared with those for Zn2+ measured by conventional electron probe microanalysis and found to be in satisfactory agreement.

Thermal decomposition of supersaturated single-phase body-centered cubic (bcc) Fe100−xZnx (5≤ x ≤65 at.%) solid solutions, processed via mechanical alloying of high-purity metal powders, was investigated using x-ray diffraction and differential scanning calorimetry (DSC). At elevated temperatures the metastable solid solution decomposed into a stable equilibrium aggregate consisting of the pure bcc Fe phase and an intermetallic compound Fe4Zn9. The decomposition temperature decreased with increasing Zn concentration. The enthalpy of decomposition for various Fe–Zn solid solutions measured by the DSC was in the range of 1.2–3.5 kJ/mol. The enthalpy of mixing of the as-milled solid solutions from elemental Fe and Zn powders was estimated to be 0.5–1.7 kJ/mol. In addition, the activation energies of decomposition for these solid solutions were determined on the basis of the Kissinger analysis, and their values appeared to be independent of the Zn concentration in the alloy, with an average of 147 ± 17 kJ/mol.

Stress relaxation of a patterned thin film on diaphragms of different material and thickness was investigated through experimental study and numerical simulation. The diaphragm deflections, caused by relaxation of the residual stress in a patterned thin film residing on top, were measured using a Twyman–Green laser interferometer. The first diaphragm used was a Si3N4(top)/SiO2/Si composite diaphragm and the second a 0.5-μm-thick Si3N4 membrane. Custom-written simulation software, which uses a novel numerical algorithm named Nonlinear Sequential Analysis (N-LISA), was utilized to calculate the stress distribution in the patterned thin film and the diaphragm substrate. Agreement between the model and the experimental results was satisfactory. Simulation of the system balance between a tensile-stressed circular Ti film and a stress-free Si substrate of different thickness clearly shows a transition in the substrate behavior from a pure plate to a pure membrane. Interestingly, the deflection of the Si substrate caused by the residual stress in the Ti film reaches its maximum at a certain substrate thickness where plate and membrane characteristics coexist. This study addresses some basic mechanics issues involved in modern devices dealing with thin diaphragms.

High current electropulsing was applied to a low-carbon steel in the solid state. The relationship between grain size and experimental conditions was revealed. It was found that the ultrafine-grained (UFG) microstructure could be formed when electric current density, heating rate, and cooling rate all were high. The UFG samples prepared by applying electropulsing were free of porosity and contamination, and had no large microstrain. Also, their tensile strength was dramatically enhanced over that of their coarse-grained counterparts, without a decrease in ductility. The mechanism for grain refinement and formation of the UFG microstructure was discussed. It is proposed that the effect of a decrease in thermodynamic barrier and enhancement of nucleation rate in a current-carrying system cannot be neglected.

A two-parameter “area function” characterizing the depth-dependent projected area of an indenter was introduced and applied to a Berkovich tip. The two parameters have physical meaning, corresponding to the effective tip radius and effective cone angle. The indenter tip was calibrated on a commercial load-controlled Nano Indentert® XP (MTS Systems Corp., Eden Prairie, MN). All calibrations were carried out using the procedure of Oliver and Pharr [J. Mater. Res. 7, 1564 (1992)] using several homogeneous materials. Plane-strain modulus and hardness values deconvoluted from indentation load–displacement traces using the calibrated two-parameter area function compared well with the values determined using the empirical eight-parameter area function of Oliver and Pharr.

Crystallization of the Cu60Zr30Ti10 and Cu60Hf25Ti15 metallic glasses was studied by x-ray diffractometry, transmission electron microscopy, differential scanning and isothermal calorimetries. Metastable Cu–Zr–Ti and Cu–Hf–Ti cubic phases primarily precipitated in the Cu60Zr30Ti10 and Cu60Hf25Ti15 metallic glasses. The Cu60Zr30Ti10metallic glass crystallizes with low energy barrier for nucleation while crystallization of the Cu60Hf25Ti15 metallic glass takes place by nucleation and diffusion-controlled growth of cubic Cu–Hf–Ti phase particles with constant nucleation rate. The Cu60Hf25Ti15 metallic glass is characterized by a low activation energy for nucleation.