Al/Mg2Si composites were in situ fabricated by the usual die-casting technique, and effects of the Si contents in the composites on microstructures and tensile strengths were investigated. Experimental results show that extra Si contents in Al/Mg2Si composites induce a ductile matrix and a uniform distribution of in situ particles. The refined microstructures lead to an obvious increase in both strength and ductility of the metal matrix composites (MMCs). The effects of extra Si on both the solidification process and fracture characteristics of the Al/Mg2Si composites were analyzed.

High-temperature forging experiments have been carried out by axial compression testing on a Fe–41Al–2Cr alloy in order to determine the deformation systems operating under such high-speed, high-temperature conditions, and to examine the textures produced by such deformation and during subsequent annealing to recrystallize. Deformation is deduced to take place by the operation of 〈111〉 {110} and 〈111〉{112} slip systems at low temperatures and by 〈100〉{001} and 〈100〉{011} slip systems at high temperatures, with the formation of the expected strong 〈111〉 textures. The examination of the weak 〈100〉 texture component is critical to distinguishing the operating slip system. Both texture and dislocation analyses are consistent with the operation of these deformation systems. Recrystallization takes place extremely quickly at high temperatures (above 800 °C), that is within seconds after deformation and also dynamically during deformation itself. Recrystallization changes the texture such that 〈100〉 textures superimpose on the deformation texture. The flow stress peak observed during forging is found at a very high temperature. Possible origins of the peak are examined in terms of the operating slip systems.

Microstructure and phase transformation of a furnace-cooled eutectoid Zn–Al-based alloy were studied after laser beam bombardment using low-angle x-ray diffraction (XRD) and backscattered scanning electron microscopy (BSEM). It was found that the microstructure of the laser-beam-treated specimen consisted mainly of the supersaturated Zn-rich β′s phase particulates of about 1−2 μm in diameter. Three structure morphologies were observed. Microcracking occurred in the laserbeam-affected zone during laser processing. Two laser-processing-induced phase transformations, i.e., decomposition of the η′FC phase and a four-phase transformation, were detected using XRD and BSEM techniques, similar to phase transformations that occurred in the same eutectoid Zn–Al-based alloy after various thermal and thermomechanical processing procedures.

Nanoparticles of ZnS capped with tri-n-octylphosphineoxide (TOPO) and close to monodispersed have been prepared by a single-source route using ethyl(di-ethyldithiocarbamato)zinc(II) as a precursor. The nanoparticles obtained showed quantum size effects in their optical spectra, and the photoluminescence spectrum showed a broad emission that could be attributed to the surface traps. A blue shift of 0.31 eV in relation to the bulk material was observed. The selected area electron diffraction, x-ray diffraction pattern and transmission electron microscopy showed the material to be of the zinc blend structure. The crystallinity of the material was also evident from high-resolution transmission electron microscopy, which gave well-defined images of nano-sized particles with clear lattice fringes and a spacing of approximately 3 Å, corresponding to the (111) planes of the cubic crystalline ZnS phase and in the size range of 3.9–4.9 nm. The presence of strong phosphorus peak in the energy dispersion analytical x-ray pattern, together with a shift in infrared band for P = O of TOPO showed that the particles were TOPO capped.

The microwave dielectric properties of Ca[(Li1/3Nb2/3)1−xMx]O3−δ (M = Sn, Ti, 0 ≤ x ≤ 0.5) ceramics were investigated. In general, the ceramics prepared were multiphase materials. However, single-phase specimens having orthorhombic perovskite structure similar to CaTiO3 could be obtained in the vicinity of Sn = 0.2 to 0.3, and Ti = 0.2. As Sn concentration increased, the dielectric constant (εr) decreased and the quality factor (Q) significantly increased within the limited Sn concentration. As Ti concentration increased, the dielectric constant (εr) increased, the quality factor (Q) decreased, and the temperature coefficient of resonant frequency (τf) changed from a negative to positive value. The temperature coefficient of resonant frequency of 0 ppm/°C was realized at Ti = 0.2. The Q · fo value and εr for this composition were found to be 26100 GHz and 38.6, respectively.

MgxZn1-xSi: Ho3+, MgxZn1-xSe: Er3+, and MgxZn1-xSe: Tm3+ single crystals were grown by the closed-tube sublimation method. The single crystals crystallized into a zincblende structure at the composition x = 0.11 and a wurtzite structure at the composition x = 0.25, 0.32, and 0.41. The trivalent ions (Ho3+, Er3+, and Tm3+) of the rare-earth elements Ho, Er, and Tm site in Td and C3v symmetries in the single crystals with zincblende and wurtzite structures, respectively. Sharp emission peaks appeared in the photoluminescence spectra of the single crystals. These emission peaks are identified to originate from the radiation recombination between the energy levels of the trivalent ions sited in Td and C3v symmetries.

The objective of this work was to investigate the fundamental factors that govern the formation and magnitude of residual stresses in A2 tool steel fabricated using spray-forming techniques. To that effect, a finite-element method (FEM) was performed by using a commercial code, ABAQUS, to solve for the temperature and displacement fields. Moreover, the residual stresses in the spray-formed materials were measured using x-ray diffraction to compare the FEM results with experimentation. Two types of substrate material, copper and Rescor™ 780 cer-cast ceramic, were used to investigate the influence of heat conduction on residual stress in the preforms. Relatively good agreement was found between experimentation and theory. The results show that the residual stress varies greatly with the position in deposited preform and that heat-transfer coefficient at the interface of spray-formed material/substrate affects the distribution and magnitude of the residual stresses significantly.

The precipitation behavior of various phases during the aging process of an Ag–Li°Cu–Mg–Zr–Ag (Weldalite 049) alloy was investigated by high-resolution electron microscopy and in situ hot-stage microscopy. Two kinds of domains with L12-type ordered structures, which are considered to be δ′ and β′ phases, are observed with different domain sizes in the alloy quenched from 530 °C. In the early stage of aging at 190 °C, the δ′ phase is precipitated as surrounding the β' phase, and the δ′ domains appear with in-phase and antiphase relationships to the β′ lattices. In situ observations at 190 °C clearly show that the T1 phase precipitates predominantly on dislocations at subgrain boundaries and then is homogeneously formed in the matrix with increasing aging time. The nucleation of the S′ phase is associated with clustering of Cu and Mg in the matrix, and the S0 domains are grown with {210} habit planes.

We have studied the thermoelectric properties of a SiC-based thermoelectric semiconductor with Ag and polysilastylene (PSS) as a dopant and as a sintering additive, respectively. Ag is an effective dopant to decrease the electrical resistivity of the SiC-based p-type thermoelectric semiconductor. It introduces carrier (hole) concentration 103−104 times larger than the case of Al-doped SiC with the typical doping concentration. PSS can control the sample density, which is one of the important factors in decreasing the electrical resistivity and thermal conductivity of the sintered samples. The figure of merit of the sample with Ag 2.0 wt% and PSS 0.1 wt% was estimated to reach 4 × 10−4 K−1 at 700 °C. This value implies that the SiC/Ag system is one of the promising thermoelectric materials for a high-temperature region.

We report the soldering behaviors of high-temperature (300 °C) lead-free SnSb alloys on Cu foils and phased-in Cu–Cr thin films. By increasing the Sb content from 5 to 15 wt%, the solder surface became rougher and the wetting angle decreased from 50° to 20° on the Cu foils. Interfacial compounds were found to be Cu6Sn5 and Cu3Sn. The Cu6Sn5 showed a scallop-type morphology, whereas the Cu3Sn had a layer-type morphology. The growth of the latter was found to be diffusion limited. On phased-in Cu–Cr thin films, the solders showed much lower wetting angles than on the Cu foils, but the dewetting phenomenon was observed after 1 min of reflow time in the 85Sn15Sb alloy. In comparison, we found no dewetting of the high-temperature 95Pb5Sn solder.

Recent deformation experiments on semiconductors have shown the occurrence of a break in the variation of the critical resolved shear stress of the crystal as a function of temperature. These and many other examples in the literature evidence a critical temperature at which a transition occurs in the deformation mechanism of the crystal. In this paper, the occurrence of a similar transition in two polytypes of SiC is reported and correlated to the microstructure of the deformed crystals investigated by transmission electron microscopy, which shows evidence for partial dislocations carrying the deformation at high stresses and low temperatures. Based on these results and data in the literature, the explanation is generalized to other semiconductors and a possible relationship to their brittle–ductile transition is proposed.

To improve mechanical properties of NiAl, a method for making NiAl matrix composites containing oxide ceramics is introduced. The method involves oxidation of NiAl powder in air to form a thin and uniform oxide scale, mainly Al2O3, on the NiAl particles. The Al2O3 contents increase with increasing oxidation temperature. The NiAl/Al2O3 composites are then formed by hot-pressing the oxidized NiAl powder under vacuum atmosphere. Al2O3 inhibits the grain growth of NiAl during the hot-pressing. The residual stress and the Ni-rich NiAl composition exist in the hot-pressed NiAl/Al2O3 composites. Strength and toughness data on NiAl/Al2O3 composites indicate that the use of oxidation of NiAl powder is a viable technique for improving these properties over that of monolithic NiAl.

Pulsed laser deposition (PLD) of Ir thin films has been achieved by ablating an iridium target with a KrF excimer laser. The iridium deposition rate was investigated, over the (0.4–2) × 109 W/cm2 laser intensity range, and found to reach its maximum at (1.6 ± 0.1) × 109 W/cm2. At this laser intensity, the PLD Ir films were deposited at substrate deposition temperatures ranging from 20 to 600 °C. The PLD Ir films exhibited a (111) preferentially oriented polycrystalline structure with their average grain size increasing from about 10 to 30 nm as the deposition temperature was raised from 20 to 600 °C. Their mean surface microroughness (Ra) was found to change from an average value of about 1 nm in the 20–400 °C temperature range to a value of about 4.5 nm at 600 °C. As the deposition temperature is varied from 20 to 600 °C, not only does the stress of PLD Ir films change drastically from highly compressive (−2.5 GPa) to tensile (+0.8 GPa), but their room-temperature resistivity also gradually decreases in the 20–400 °C range and stabilizes for higher temperatures. In the 400–600 °C range, the resistivity of PLD Ir films was as low as 6.0 ± 0.2 μΩ cm, which is very close to the iridium bulk value of 5.1 μΩ cm. Thus, PLD Ir films exhibiting not only the lowest resistivity but also a nearly zero stress level can be grown at a deposition temperature of about 400 °C. The resistivity of the PLD Ir films can be described by a grain boundary scattering model.

In this study we combined nanoscratch testing with a multilayer sapphire and aluminum nitride single-substrate system to determine the effects of interface composition and structure on susceptibility to fracture of hard, thin tantalum nitride films. Nanoindentation tests showed that the elastic moduli of the tantalum nitride and aluminum nitride films, as well as the sapphire substrate, were essentially equal at 400 GPa. On both portions of the substrate, these tests also showed that near surface hardness was near 35 GPa. Nanoscratch tests triggered long blisters and circular spalls on both the sapphire and aluminum nitride portions of the substrate. The blisters showed that the tantalum nitride film was subjected to a compressive residual stress of −6.7 GPa. The spalls showed that failure occurred along the tantalum nitride film-substrate interface regardless of substrate composition. Most importantly, the blisters and spalls showed that the mode I componentof the fracture energies was essentially equal on both substrate materials at a value near 3.1 J/m2. These energies are on the order of the energies for metallic bonding.

The effect of solidification history on the resultant microstructure in atomized Al–2.56 wt% Fe and Al–6.0 wt% Fe powders was studied, with particular emphasis on droplet size, undercooling, and phase stability. The atomized Al–Fe powders exhibited four microstructural features, i.e., Al3Fe phase (now known as Al13Fe4), Al + Al6Fe, α–Al dendrite, and a predendritic microstructure. The presence of these phases was noted to depend on alloy composition and a kinetic phase competitive growth mechanism due to the initial undercooling experienced by the powders. The occurrence of structures of the predendritic, cellular, and/or dendritic type was properly predicted by the theory of dendrite growth into undercooled alloy melts for the case of large undercoolings.

A novel Tb3(Fe,Cr)29 single crystal, which has a monoclinic Nd3(Fe,Ti)29-type structure, is obtained using the Czochralski method by performing a proper heat treatment on the Tb2Fe16.46Cr1.23 crystal with a Th2Ni17-type structure. Thermomagnetic curves along the easy axis and magnetization curves along the easy and hard axes are presented for both crystals. The lattice parameters are a = 1.058 nm, b = 0.848 nm, c = 0.968 nm, α = γ = 90°, and β = 96.93° for the Tb3(Fe,Cr)29 single crystal. The Curie temperatures, saturation magnetizations, and magnetocrystalline anisotropy constants are compared between the Tb-2:17 and Tb-3:29 crystals. The magnetization behavior along the hard axis is quite different as a first-order magnetization process (FOMP) of type I for the Tb-2:17, but a FOMP of type II for the Tb-3:29 crystal is observed below room temperature. At low temperatures, magnetohistory effects are detected for both crystals.

The isothermal and cyclic oxidation behavior of PtAl and PtAl + Zr was studied followed by postoxidation microstructural and microchemical analyses. Their isothermal oxidation performance at 1200 °C was similar to that of NiAl and NiAl + Zr. In short (1-h) cycles, the cyclic oxidation resistance of undoped PtAl was found to be substantially better than NiAl. However, with longer (100-h) cycles, little improvement in the metal consumption rate was observed relative to NiAl. The addition of Zr to PtAl significantly improved cyclic oxidation performance in both short- and long-cycle tests. Spatially resolved energy dispersive spectroscopy indicated Zr segregation to both the metal–oxide interface and Al2O3 grain boundaries.

The precipitates in nitrogen-added type 316L stainless steels (SS) were investigated by transmission electron microscopy (TEM) after thermal aging. Besides carbides (M23C6 and M6C) and intermetallic phases, an unknown phase of an Fe–Mo–Cr(–Si) system n a filmlike morphology precipitated at grain boundaries. In spite of the similarity in ts chemical composition to that of the Laves phase, the phase of the Fe–Mo–Cr(–Si) system exhibited five-, three-, and twofold symmetries, which are generally observed in quasicrystals having icosahedral symmetry. This phase was formed from the intergrowth of small crystalline clusters of the Laves phase. Decreasing the nitrogen content to that of commercial type 316L grade suppressed the formation of the filmlike fivefold phase. This was attributed to the dissipation of small Laves clusters by M23C6 carbides, which increased as a result of the decreased nitrogen content.

Effective values of the thermal diffusivity, specific heat, and thermal conductivity of a porous 380-aluminum alloy prepared by melting in a gas-fired furnace, were determined as a function of the volume fraction of porosity. For that, photoacoustic, differential calorimetric, density, and image analyzer measurements were done. Thermal conductivity and specific heat capacity decrease with the increase of porosity, whereas the thermal diffusivity shows less dependence. Among the effective models for analysis of the thermal conductivity of a two-phase system, the Maxwell model best fits the experimental data, implying a homogenous distribution of the pores in the aluminum-alloy matrix.

Silicon L2,3 x-ray emission spectra (XES) of siloxene powder samples prepared according to Wöohler and Kautsky (Wöhler and Kautsky siloxene) are presented. The results are compared with the Si L2,3 spectra of the reference compounds a-Si, c-Si, SiO2, and SiOx. A close similarity of the electronic structure of Wöhler siloxene to that of a-SiO0.43: H and of Kautsky siloxene to that of a-SiO0.87: H is found. We determine the number of oxygen atoms per Si atom at ~0.5 in Wöhler siloxene and ~0.8 in Kautsky siloxene. The relative concentrations are in good agreement with the results of infrared absorption measurements on the same samples.