The embedded atom method [M. S. Daw and M. I. Baskes, Phys. Rev. B 29, 6443 (1984) used to calculate phase stability, lattice vibrational frequencies, point defect properties, antiphase boundary energies, and surface energies and relaxations for Ni3Al. The empirical embedding functions and core-core repulsions used by this method are obtained. The equilibrium phases for the Ni-rich half of the composition range of Ni–Al are determined for 1000 K and compared with experiment. The elastic constants and vibrational modes of Ni3Al are calculated and the elastic constants are compared with experiment. The formation energy, formation volume, and migration energies of vacancies are computed, and it is found that the formation energy of vacancies on the Ni sublattice is less than that on the Al sublattice. The (100) antiphase boundary is shown to be significantly lower in energy than the (111) antiphase boundary. The surface energies and atomic relaxations of the low index faces are computed, and it is shown that for the (100) and (110) faces that the preferred surface geometry corresponds to the bulk lattice with the mixed composition plane exposed.

The successful synthesis of high-Tc YBa2Cu3O7 films by means of electron-beam codeposition are reported. Several important growth parameters have been surveyed in a preliminary way. The substrates investigated include Al2O3, ZrO2, MgO, and SrTiO3, The films were characterized by resistivity measurements, x-ray diffraction, microprobe, and Rutherford backscattering analysis. Some TEM and critical current density studies were also carried out. The best results to date have been obtained on SrTiO3 substrates with which polycrystalline epitaxial growth has been achieved. Resistive superconducting transitions with zero resistance at 89.5 K and a 2 K width have been observed in these films.

Hydrostatic pressure measurements of the superconducting transition temperature were made as a function of x in La2−xSrx CuO4. A sharp change in the behavior occurs between x = 0.2 and 0.25 in that the pressure derivative goes from positive to essentially zero. This result is discussed in the context of band structure models.

Microscopy and x-ray emission analysis have been performed on Y–Ba–Cu–O superconductors as a function of temperature using a scanning electron microscope equipped with a low-temperature stage. The samples exhibit a superconducting phase transition above liquid nitrogen temperature as determined by resistivity measurements and a demonstrated Meissner effect. Strong contrast changes in the micrographs due to the superconducting phase transition are found, which have been used to identify normal and superconducting regions of the sample. These samples are found to consist of particles with superconducting shells surrounding a nonsuperconducting core.

A study of the phases obtained in an aluminum manganese (Al86Mn14) alloy prepared under relatively slow solidification rates is presented. The identification of the phases presented in the alloy has been carried put using different techniques. Two of the phases were found to be crystalline in nature (Al, Al6Mn), two were amorphous (Al2O3, AlMn–O), and one of them was quasicrystalline (T phase). In the case of the quasicrystalline T phase an investigation on its structural characteristics was carried out, and a possible model for its structure is suggested, based on high-resolution images under fivefold diffraction conditions.

Thermal aging and irradiation experiments were carried out in Fe–Ni–Cr base alloys containing Ti or Nb as well as low levels of oxygen, nitrogen, and carbon. After aging, fine dispersions of TiC and NbC were formed. However, after irradiation the Ti-containing alloy precipitated Ti(N,O) rather than TiC, while the Nb-containing alloy precipitated NbC. Analysis of the energetics of these reactions reveals that the Ti(N,O) phase is thermodynamically more stable than the TiC phase, while the NbC phase is more stable than the NbO phase. These results are therefore consistent with observed behavior. While it is well known that irradiation can drive a system away from equilibrium, the present results show that irradiation also can catalyze the formation of a more stable phase at the expense of a persistent metastable phase.

An Al-5 wt. % Co alloy has been rapidly solidified from the liquid state, resulting in the formation of a slightly supersaturated aluminum solid solution and the monoclinic Al9Co2 phase. High-resolution electron microscopy and electron diffraction have been extensively employed to characterize the as-solidified as well as the annealed foils. The high-resolution micrographs of the as-solidified solid solution showed the presence of clustering and D 1a - type ordering on an extremely small microscopic scale. Annealing at temperatures above 623 K resulted in the precipitation of Al9Co2 in the form of platelets arranged in a Widmanstätten pattern. Orientation relationships between the Al9Co2 platelets and the matrix have been established. Guinier-Preston zonelike platelets on close-packed {111} planes, however, have also been observed upon electron irradiation in the annealed alloys, presumably due to the enhanced diffusivity of cobalt atoms.

Black crystals, displaying a micaccous habit, result from heating the 90 K superconducting phase YBa2Cu3O7−x above 1050°C. The crystals are tetragonal, P4/mmm, a = 3.863 (2) Å, c = 11.830 (4) Å, Z = 1, ρcal = 6.115 g/cm3. The 184 independent single-crystal reflections were used to refine the structure by least squares to R = 0.0374, wR = 0.0347. The structure contains Cu+ in twofold coordination and corrugated layers of Cu2+–O. The Ba2+ is in eightfold coordination between the Cu+ and Cu2+ layers and Y is in eightfold coordination between the Cu2+ layers.

Thin-film GdBa2Cu3Ox superconductors with an onset Tc > 90 K have been produced. The films were fabricated by thermal reaction in an oxidizing atmosphere of electron-beam deposited Ba/Gd/Cu multilayers. Attempts to produce the superconducting phase YBa2Cu3Ox by multilayer reaction were unsuccessful due to a positive heat of mixing between Y and Ba. The appearance of a wide superconducting transition in GdBa2Cu3Ox films may be the result of tunneling through a nonsuperconducting second phase.

The crystallography of the phases obtained by heat treating a Ni-34.7 at. % Al alloy with 0.9 at. % Hf and 0.04 at. % B was studied in detail using x-ray diffraction techniques. Particular emphasis was placed on characterizing the Ni5Al3 phase, which is obtained by quenching the B2 NiAl phase and aging the resultant martensite. The structure of the Ni5Al3 phase is confirmed to be orthorhombic with space group D192h (Cmmm) and lattice parameters of a0 = 0.7475 nm, b0 = 0.6727 nm, and c0 = 0.3732 nm. The transformation from B2 NiAl to L10 martensite is shown to involve a Bain distortion of the c/a ratio from 0.707 to 0.853, and the further ordering transformation to Ni5Al3 involves a further increase of this c/a ratio to 0.900.

The crystal structure and chemical composition of the intermetallic phase in a Fe-20%Cr-4%Al-0.5%Y (wt. %) alloy were investigated by electron microscopy. Convergent beam diffraction studies revealed that the intermetallic phase forms in three different crystal structures that could coexist in a single grain of the phase. The dominant crystal structure was shown to be hexagonal (a = 0.85, c = 0.84 nm) with a space group most likely to be P63/mmc. Within the hexagonal phase, regions of a rhombohedral crystal structure (a = 0.85, c = 1.26 nm) were observed that had grown in without an apparent phase boundary separating the two crystal structures. The third crystal structure was determined to be monoclinic (a = 0.97, b = 0.85, c = 1.07 nm, and beta = 97.3°) and formed by twinning on the {10$\overline 1$1} planes of the hexagonal phase. The chemical compositions of regions with different crystal structures were comparable and the stoichiometry of the intermetallic phase corresponds to (Fe,Cr)17 (Al,Y)2. The relationship of the observed crystal structures to those previously reported is discussed.

Single-crystal x-ray diffraction measurements made on a millimeter-size single icosahedral quasicrystal of an Al–Li–Cu alloy are reported. The point symmetries observed directly by real-time transmission Laue x-ray diffraction and the measured angles between the major symmetry axis are consistent with an icosahedral quasicrystal, and the peaks observed in the single-crystal diffraction scans are found to be indexable with six indices that belong to a primitive icosahedral Bravais quasilattice.

The thin-film interactions of Au with Ti, Zr, V, and Nb have been investigated between 350C and 700°C with Rutherford backscattering spectroscopy (RBS) and x-ray diffraction (XRD). Initially the most Au-rich phase is formed, except. with V, and it is followed sequentially by the more metal-rich ones in an increasingly layer-by-layer fashion. For Au reactions on Ti and Nb, all the intermetallic phases on the phase diagrams were observed. In the formation of Au4Ti, Au is the dominant moving species.

The Ni–Zr system is examined as a representative system for the formation of an amorphous phase by diffusion and for the crystallization of an amorphous phase by diffusion. High-resolution electron microscopy (HREM) is used to show that the amorphous phase grows by bulk diffusion through the amorphous material rather than by short-circuit diffusion. Also, the HREM shows that the amorphous phase formed by diffusion appears to be the same as the vapor-deposited amorphous phase. A correlation between crystallization temperatures (Tx) and the enthalpy of large-atom hole formation is given. This correlation predicts values of Tx that are lower than those predicted from the small-atom hole-formation model. The difference in hole-formation enthalpies for the large and small atoms is given as a criterion for amorphous-phase formation via diffusion.

Vacuum-annealed samples of single-phase orthorhombic YBa2Cu3O6.9 have been reoxygenated. The vacuum-annealed material is tetragonal, semiconducting at room temperature, and shows no superconductivity. Upon annealing these samples in 640 Torr O2 at 200°C, a partial return of 90 K superconductivity is observed; complete restoration is achieved following 300°C anneals. Oxygen uptake in vacuum-annealed pellets follows an Arrhenius relation with an activation energy of −27 kcal/mol. Deoxygenation and reoxygenation does not seem to affect the structure of the grain interconnects in the material. The maximum oxygen uptake for vacuum-annealed material occurs at 450°C, while the maximum magnetic Meissner effect is observed following oxygen annealing at 350°C.

The alloy Al70Si17Fe13 was subjected to a range of rapid solidification conditions and the resulting microstructures were evaluated. It was found that when solidification was sufficiently rapid to bypass the formation of primary intermetallic phases, the alloy consisted of spherical regions of amorphous (or microquasicrystalline) material surrounded by a crystalline phase(s). This microstructure is interpreted as the result of solidification of the amorphous phase from the melt by a first-order transformation. The structure of the amorphous phase is different from that of a liquid (or usual metallic glass).

Aluminum films 1–6 kÅ thick deposited on Pt or Pd layers developed voids after annealing between 200 and 275°C. Void formation was also observed when the Pt layer was deposited above the Al film. The amount of Al surrounding the voids increased as the voids grew. The rate of void growth decreased as the thickness of the initial Al film increased. The driving force appears to be surface tension. The controlling mechanism is diffusion along the Al/Pt or Al/Pd interface made possible by compound formation there.

It is shown that both icosahedral Al–Mn–Si and Mg–Al–Zn alloys give rise to the same variety of electron diffraction patterns as documented for icosahedral Al–Mn alloys. Subtle variations in intensity are ascribed to a different decorational motif in terms of the Mackay icosahedron and the Pauling triacontahedron. Icosahedral Al–Mn–Si alloys do not appear to be ordered on a superlattice basis.

Amorphous Zr–Rh and Zr–Pd hydrides are prepared both by hydriding metallic glasses and by hydriding metastable, polycrystalline fcc alloys. The thermal stabilities of the amorphous hydrides produced by these two distinct methods are examined by means of differential scanning calorimetry and are found to be similar. The enthalpy difference between the fcc phase and the amorphous phase of Zr81Rh19 is determined to be 0.6 kcal/mol. The thermal stability of Zr–Rh hydrides as a function of hydrogen concentration is investigated.

A scoping irradiation test was carried out to help define the performance of copper-base materials in potential fusion applications. Twenty-five different copper materials including oxide dispersion-stabilized and precipitation-hardened powder metallurgy alloys, as well as pure copper and solid solution-strengthened ingot alloys, were neutron irradiated to 13.5 dpa at 400°C in the Experimental Breeder Reactor II (EBR-II) fast reactor. Volumetric swelling and electrical conductivity data were measured for all irradiated materials, and four selected materials were characterized for mechanical property changes using a miniaturized disk bend test. A number of these copper alloys, especially those prepared by powder metallurgy techniques, showed low swelling (less than 0.3%), small changes in conductivity (less than ± 5%), and relatively small changes in yield strength with good post-irradiation ductility. Preliminary electron microscopy results show microstructural changes that are consistent with the results of the macroscopic studies. The pure copper materials showed significant changes in conductivity and high levels of swelling as a result of the neutron exposure. It is apparent that a variety of copper alloys can survive fast neutron exposures to at least 13.5 dpa at 400°C without unacceptable changes in density, conductivity, or yield strength. Further irradiation testing to much higher doses and experimental investigation of the effect of transmutation product gases are needed to fully define the response of available copper alloys to fusion reactor environments.