The creep behavior of Mg–14Li particulate composites containing 0,10,20, and 30 vol. % boron particles was evaluated from 230 to 280°C. The results reveal that the creep strength of the particulate composite is increased by a factor of eight over the Mg–14Li matrix with the addition of 30 vol. % boron. The body-centered cubic (bcc) Mg–14Li alloy is shown, however, to be much weaker than hexagonal close-packed (hep) pure magnesium. This difference is attributed to the high rate of atom mobility in the open structure of the Mg–14Li bcc alloy. It is predicted that a Mg–6Li–30B particulate composite, containing an hep matrix structure, will have a higher specific strength at 250°C than the new experimental aluminum base–high iron alloys prepared by rapid solidification processing.

The stability of YBa2Cu3O7−x superconductors toward reactions with CO2 in CO2/O2 gas mixtures has been studied during annealing at temperatures ranging from 600°C to 950°C. The results show that there are three different types of the reactions. The reaction products of these reactions all include BaCO3 and CuO, while the third product is dependent on the annealing temperature. At 600°C, YBa-carbonates were formed while Y2Cu2O5 and Y2BaCuO5 were formed at 815°C and 950°C, respectively. Transmission Electron Microscopy images show that the reactions started at grain boundaries with the formation of island-type precipitates.

Magnetically aligned YBa2Cu3O7-δ ceramics show resistivities approaching that of single crystals and improved transport critical currents in a magnetic field. Reduced microcracking and increased transport along the ab-plane are believed responsible for the improved performance over nonaligned ceramics. Aligned and nonaligned samples were prepared in parallel using a range of sintering and annealing temperatures. A rapid rise in density for samples sintered above 900°C in oxygen is accompanied by rapid grain growth, improved alignment, a drop in the room temperature resistivity, and an increase in the critical current. The presence of low melting point (i.e., Ba–Cu–O-rich) phases at grain boundaries is believed responsible for the rapid densification. However, the presence of this phase does not appear to be the most important factor limiting Jc. A high temperature oxygen anneal at 900°C improved performance as compared to anneals at 500°C, possibly due to the removal of carbon. For aligned samples sintered at 980°C, critical currents are over 200 A/cm2 at 77 K, ¼ tesla, and room temperature resistivities are below 350 μΩ-cm.

High resolution electron microscopy of the twin boundary layers in YBa2(Cu1−xMx)3O7+δ for x = 0 and 0.02 and M = Zn and Al showed that the boundary widths are ∼1 nm for the pure and the Zn substituted YBa2Cu3O7 and ∼3 nm for the Al substituted oxide. From two beam contract studies and the high resolution images, it was concluded that the respective lattice plane across the boundary is shifted by (⅓–½)·2d(110) along the boundary. The broadening of the layer by the Al substitution is also thought to be a cause for the reduction of the twin boundary energy, leading to an increased twin density.

Synthesis of YBa2Cu3O6+x from formic acid solutions of stoichiometric amounts of the initial materials has been investigated in the temperature range 750–950°C. The reaction is strongly influenced by the concentration of formic acid. Dilute solutions favor synthesis of purer samples under moderate conditions of temperature and sintering time. At lower temperature the same effect can be achieved if sintering time is longer, while at higher temperature, multiple grinding and heating at very short intervals are necessary to avoid formation of Y2BaCuO5. The observed effect of HCOOH concentration is explained by the different mechanisms involved in the decomposition of the formates obtained.

The surface morphology and near-surface chemical composition of high temperature superconducting Y–Ba–Cu–O thin films have been studied by Scanning Electron Microscopy (SEM) and Auger Electron Spectroscopy (AES) depth profiling. These films were fabricated on SrTiO3 substrates by RF diode sputter deposition and subsequent furnace annealing in oxygen. The chemical composition at and near the surface of thin films was found to differ from the bulk composition. At about 500 Å below the surface the Y, Ba, and Cu stoichiometry, as determined by AES, gradually approach that of the film interior. These results suggest that, for furnace annealed films, there may exist a minimum deposited Y–Ba–Cu–O film thickness in which superconductivity is possible. It was also found that the calculated copper concentration determined by AES during depth profiling is significantly lower than its actual value.

In order to obtain essential information on the formation process of the high-Tc phase in the Bi, Pb–Sr–Ca–Cu–O system, subsolidus phase equilibrium in the systems PbO(PbO2)–SrO–CuO and PbO(PbO2)–CaO–SrO has been studied, mainly by XRD analysis. A pseudoternary Pb–Sr–Cu–O solid solution was newly found. This solid solution has a wide solubility range including its typical composition Pb2.03Sr3Cu0.73O7.70. It has a hexagonal structure with lattice parameters a = 10.11 and c = 7.11 in AU. Composition dependences of the lattice parameters and the decomposition (incongruent melting) temperature of (Ca1−xSrx)2PbO4 solid solution are also reported.

The phase relations of equilibrium compounds in the pseudoternary system Bi2O3–(Ca,Sr)O–CuO at 850 and 900°C were studied. The ratio of Ca : Sr was fixed at 1:2. Starting materials of Bi2O3, CaCO3, SrCO3, and CuO with various ratios were mixed, pressed into pellets, and heated at or above and then brought back to 850 or 900°C for different durations to ensure that equilibrium had been reached. The products were cooled in air or quenched in liquid nitrogen and then identified by x-ray powder diffraction. At 850°C, only the superconducting phase, Bi2CaSr2Cu2Ox (2122), was observed inside the triangle. The other stable phases were all positioned on the boundary lines, and included CuO·⅗MO, CuO·MO, CuO·2MO, 1.½Bi2O3·0.9MO, Bi2O3·4MO, Bi2O3·9MO, and a solid solution, Bi2O3·xMO, where 0.16  x  0.82 and MO represents ⅓(CaO·2SrO). At 900°C, the above boundary line phases remained stable but the 2122 phase was not observed. The tie lines among the stable phases in the two isotherms were established.

Threshold displacement energies for atomic displacements along 〈110〉, 〈100〉, and 〈111〉 directions, and formation enthalpies of several symmetric interstitial atom configurations were calculated for Ni3Al by computer simulation using “embedded atom method” potentials. The Ni–Ni (100) dumbbell in the plane containing only Ni atoms has the lowest interstitial-atom enthalpy although the enthalpies of other configurations are similar. Interstitial configurations involving Al atoms all have much higher enthalpies. The anisotropy of the threshold energies in Ni3Al is similar to pure metals and no significant difference in threshold energy was observed for 〈110〉 replacement chains in rows containing all Ni atoms or alternating Ni–Al atoms. Various metastable interstitial atom configurations were observed, including crowd-ions. In addition, the spontaneous recombination volume for some configurations can be much smaller than in pure metals. The consequences of these results for radiation induced segregation and amorphization are discussed.

A NiTi intermetallic compound was cold rolled at room temperature by 30% and 60% thickness reductions, and microstructures were studied by means of transmission electron microscopy (TEM). In the cold-rolled samples we observed both a phase of nanometer-sized crystals and an amorphous phase. A substantially high dislocation density, 1013 to 1014/cm2, was evident in the transition region between crystalline and amorphous phases. A simple estimate of the elastic energy arising from this dislocation density is of the same order as the crystallization energy, suggesting that dislocation accumulation is a major driving force for amorphization in cold-rolled NiTi.

The kinetic master equation is developed in the pair approximation to study disorder ⇉ B2 order transformations in bee binary alloys. Coupled sets of rate equations for the pair variables are obtained for atom movements by either the direct interchange mechanism or the vacancy mechanism. Numerical integrations provide the nonequilibrium relaxations of short- and long-range order (SRO and LRO) and the vacancy balances between the two sublattices. For binary alloys, disorder ⇉ order transformations were studied for all combinations of interatomic interaction strengths, activation barrier heights, and alloy stoichiometry variations. After a transient vacancy relaxation, all cases began with a quick relaxation of SRO, followed later and independently by the growth of LRO and additional SRO. There were some variations in kinetic path through SRO and LRO, moderate variations in overall kinetics, and large variations in vacancy balance. Some nonphysical aspects of kinetics in the pair approximation are discussed.

The ternary alloy Mg2Ni0.75Pd0.25 was made by the Replacement-Diffusion Method (RDM). Using x-ray analysis, scanning electron microscopy, AES analysis, and the BET method, the authors were able to characterize the structure of the alloy and study its surface properties. It has been found that the alloy thus obtained has excellent surface properties compared to that prepared metallurgically.

The changes in the chemistry and morphology within the interphase region of an SCS6/Ti–6A1–4V metal matrix composite upon exposing the samples to varying heat treatments have been studied using Auger electron spectroscopy, TEM and convergent beam diffraction techniques. These changes, such as the formation of small TiC particles at one interface and the narrowing of a protective pyrocarbon layer at another, induce fracture to occur at different places within the interphase upon heating. The reasons for this are explained. Evidence for a change in phase of a TixSiy(C) layer to the more thermodynamically stable Ti5Si3 is also given.

The decomposition of the intermetallic compound PdSi by adding a small amount of Ag has been investigated by thermal analysis, metallographic measurement, and x-ray photoemission spectroscopy (XPS). Within the range of Ag concentration from 0 to 6 at.%, PdSi is decomposed in linear proportion to the concentration of Ag into Si and the ternary compound Pd2Si(Ag), which has the ratio of 16 PdSi molecules per single Ag atom. The PdSi is fully decomposed at Ag 10 at.%. In the ternary alloy included in the Pd–Si–Ag alloy involving Ag below 12 at. %, the atomic ratio of Si to metal atoms, which are Pd plus Ag, is nearly the same as the ratio in Pd-rich Pd2Si. Metallographic and XPS measurements indicate that the Ag atom included in the PdSi behaves as an electron donor with a large radius of the wave function; the Ag electron transfers to the anti-bonding state of PdSi and acts to decompose the compound. The Ag atoms seem to occupy the sites of Pd atoms in Pd2Si(Ag) which has been decomposed from PdSi.

Titanium reacts with pure Ge in two different ways: At low temperatures one observes the formation of Ti6Ge5 with some characteristics typical of diffusion-controlled reaction. Upon completion of this first stage Ti6Ge5 reacts with remaining Ge to form TiGe2, isomorphous with C54 TiSi2, in a process which is clearly controlled by nucleation. The same observations apply to reactions with a Ge alloy containing 25 at.% Si. With an alloy containing 50 at.% Si the two stages become merged, so that while remaining identifiable, they are much less distinct than with the previous conditions. The reaction behavior observed with a Ge alloy containing 80 at.% Si resembles that generally obtained with pure Si: there are no easily identifiable steps between the initial Si–Ti sample and the final one, Si–TiSi2. With both the 50-50 and 80-20 Si–Ge alloys the formation of the C54 structure is preceded by that of the C49 structure (ZrSi2 type), as with pure Si. The gradual merging of the diffusion-controlled reaction and that controlled by nucleation as the concentration of Si in the substrate increases implies that nucleation plays a significant role in the formation of TiSi2, even if that role cannot be easily isolated. Effects due to gas impurities on the path of the metal-substrate reaction have been analyzed. The resistivities of several pure and alloyed phases have been measured. Alloy scattering in the system TiSi2–TiGe2 is briefly discussed.

Time-dependent measurements of the melt and solidification behavior of amorphous Si, formed by ion implantation of In, have been obtained following irradiation with ∼3 ns ruby laser pulses. The recently observed buried In sheets formed under such conditions are shown to result from internal nucleation of melt, contrary to previous interpretations. Under no conditions was surface nucleation of either amorphous or crystalline Si observed from a surface melt. These results resolve previous inconsistencies in the understanding of phase formation during rapid melting and solidification of Si.

We have developed a new growth process for GaAs that combines advantages found in several methods currently in commercial use, while at the same time minimizing many of the problems inherent in these presently used processes. The new technique, a form of vertical Bridgman (VB) growth, is capable of producing either doped (semiconducting) or undoped semi-insulating GaAs with very low dislocation density.

Improved structural quality Hg1−xCdxTe epitaxial films have been grown by metal organic chemical vapor deposition (MOCVD) using the interdiffused multilayer process (IMP) on lattice-matched CdZnTe substrates at temperatures above 400°C with diethyltelluride. Double-crystal rocking curve data with values as low as 25 arcsec correlated with cross-sectional transmission electron micrographs. The process of growing alternate layers of HgTe/CdTe for improved compositional uniformity, and the inherent mismatch, was not detrimental to the structural quality, which was limited by that of the substrate.

The microstructures of five different diamond films formed by plasma-assisted chemical vapor deposition have been studied by transmission electron microscopy. The films were selected for study based on differences in their surface morphologies. The preferred orientations inferred from the symmetries of the crystals observed on the surfaces of these films were consistent with those measured by x-ray diffraction. A general characteristic of all of the diamond film microstructures was stacking faults and microtwins on {111} planes, but the densities and the distributions of the defects varied widely among the films. The observations of microstructure indicate that when a crystal grows so that {100} facets are formed, stacking faults and microtwins are confined to regions near its boundaries, and when a crystal grows so that {111} facets are formed, stacking faults and microtwins are distributed throughout its volume. Under some deposition conditions the defects are confined to bands in the crystal, and coincidence of these defect bands with small steps on the crystal facets suggests that the steps may be caused by the intersection of the bands with the surface.

An indentation-bend failure-stress method was used for measurement of R-curves in a series of PSZ ceramics with varying peak toughness. Dilatational transformation-stress constraints are included in the residual-stress driving force contribution to the applied stress intensity factor. A power-law fit to the form of the R-curve simplifies the analysis. While the resulting curves show the expected form, measured toughness values are high relative to the expected peak toughness. Limitations and the range of applicability of the indentation-bend technique are discussed.