The superconducting phase Ba2YCu4O8 has been synthesized (as a bulk powder) in flowing oxygen. This was achieved by using the anionic oxidation/reduction method (or the SCD method), in which an aqueous solution containing oxidizing (NO−3 salts) and reducing components (e.g., acetate salts) is spray dried into an intimate mixture. At 300 °C, an internal exothermic oxidation/reduction reaction completely converts the spray-dried powder into the corresponding mixed oxides in one reaction step. Because the resultant mixed oxide powder is homogeneous on a fine scale, the final oxide phase can subsequently be produced at lower temperatures and shorter reaction times. Using this method, ∼93–94% phase pure Ba2YCu4O8 (as determined by x-ray diffraction) has been synthesized in flowing oxygen. Pellets of Ba2YCu4O4 fabricated from the mixed oxides were prepared and partially sintered by firing at 800 °C in flowing oxygen for 50 h. Resistivity and magnetic (AC) susceptibility measurements show onset Tc's of 82–84 and 72–73 K, respectively.

We investigated the stability of the CsCl-type compounds AlRu, SiRu, NiTi, and CuEr under heavy deformation by high-energy ball milling. As a result, nanocrystalline intermetallic compounds have been synthesized with a microstructure showing a mixture of highly strained crystallites (5–12 nm) with random orientation. Thermal analysis of the samples indicates stored deformation energies of 5–10 kJ/mole stored by incorporation of lattice defects, chemical disorder and grain boundaries, and an increase of the heat capacity of up to 13%. Chemical disordering of the crystal is monitored by means of the long-range order parameter. The observed decrease in chemical order can be explained by the high grain boundary density of nanocrystalline metals.

Percolation networks were observed in an immiscible Ag–Co alloy system after the Ag30Co70 alloy films were irradiated to a dose of 1 × 1016 Xe+/cm2 with 200 Kev Xe+ at room temperature. Fractal dimension D as well as percolation threshold Pc were calculated and exhibited good agreement with the results of the percolation theory. The mechanism of the formation of the ion-induced percolation structures is also discussed.

A layer of amorphous Mo–Al alloy is formed by ion-assisted solid-state interdiffusion reaction of a Mo/Al bilayer. Xe ion irradiation at 200 °C enhances the long-range diffusion of the dominant moving species while the formation of equilibrium compounds remains inhibited. The idea of using the temperature-dependent ion mixing at intermediate temperatures to promote a solid-state amorphization reaction opens the possibility of growing an amorphous phase in a system where both compound formation and interdiffusion are difficult

An amorphous Ni–B alloy was formed at the interfaces between layers of polycrystalline nickel and amorphous boron during electron-beam deposition of Ni/B/Ni trilayer structures. Formation of the amorphous alloy appears to be thermally-assisted and, in addition, the amorphous alloy regions can be extended by post-deposition ion-beam mixing. The existence of an upper limit to the thickness of the amorphous Ni–B alloy layer which forms (40 nm) indicates that the amorphous layer serves as a reaction or diffusion barrier. It has been shown for the first time that an amorphous metal-boron alloy is produced by thermal solid state amorphization reaction (SSAR).

A method for preparing YBa2Cu3O7−x from the simultaneous thermal decomposition of the nitrates of yttrium, barium, and copper in an anhydrous fused eutectic of sodium and potassium hydroxide is described. This method eliminates the need for any mechanical grinding or the introduction of carbon containing anions. Products formed are fine powders (∼1 μm) having mole ratios 1.00Y:2.00Ba:3.06Cu.X-ray diffraction analyses reveal that the initial products are Y(OH)3, BaO2, and CuO, which when air calcinated/oxygen annealed at 900–950 °C form the superconducting YBa2Cu3O7−x A mechanism is postulated for product formation as a function of reaction conditions.

Raman spectroscopy was employed to study Y–Ba–Cu–O films prepared by multilayer, reactive sputtering from separate Y, Cu, and Ba0.5Cu0.5 targets. A set of films having the composition YxBa2CuyOz with 0.7 < x < 1.8 and 2.8 < y < 3.5 and critical temperature with zero resistance, Tc(R = 0), ranging from 25 to 90 K was studied with the Raman technique. The correlation between Raman data and critical temperature, Tc, was investigated. This technique provides important information concerning the film crystallinity, homogencity, and impurity content (including other phases) which is useful in judging the quality of high Tc superconducting films. We also found that the rapid thermal annealing process is a very efficient way to reduce chemical reactions between the film and the substrate.

Effects of hydrofluoric acid (HF) treatment on the properties of Y–Ba–Cu–O oxides were investigated. No obvious etching of bulk Y–Ba–Cu–O and no degradation of zero resistance temperature were observed even though the oxides were placed into 49% HF solution for up to 20 h. Surface passivation of Y–Ba–Cu–O due to HF immersion was verified by subsequent immersion of Y–Ba–Cu–O in water. A thin layer of amorphous fluoride formed on the surface of the Y–Ba–Cu–O during HF treatment, which limited further reaction between Y–Ba–Cu–O and HF, and later reaction with water. Thin film Y–Ba–Cu–O was passivated by HF vapors and showed no degradation in Tc-zero after 30 min immersion in water. The properties of the surface layer of Y–Ba–Cu–O oxide after HF treatment are reported from Auger electron spectroscopy, x-ray diffraction, and scanning electron microscopy studies.

The pulsed laser deposition technique was used to deposit stoichiometric thin films from multi-component targets. By changing the target during deposition, multilayer thin film structures were fabricated. We have prepared multilayer structures consisting of alternating superconducting layers with different compositions and elements separated by thin insulating layers. The sharpness of the interfaces was studied by Auger spectroscopy depth profiling. Comparison of films deposited at room temperature and at 680 °C showed that a 10 nm yttrium stabilized zirconium oxide film can completely prevent gross interdiffusion between Y–Ba–Cu–O films and between Y–Ba–Cu–O and Si.

Twin roller quenching from the melt at cooling rates of ∼107 K s−1 was used on several Bi-containing high Tc compositions. Pure glass was obtained in most compositions and the route of crystallization was studied by differential thermal and thermogravimetric analysis, x-ray diffraction, and magnetic measurements. Heating of the glasses produced poorly crystallized short-range-order-only as determined by x-ray diffraction, despite passing through several exotherms, some of which were very strong. This anomalous behavior deserves further investigation. On heating to higher temperatures the expected double-copper-oxide-layer high Tc phase formed sluggishly via intermediate CuBi2O4 and/or single-copper-oxide-layer Bi2(Sr, Cu)2CuO4 phases. Considerable oxygen absorption of about 0.5 O per Cu occurs during these steps, peaking at about 680 °C; some of this oxygen is lost again by the time the high Tc phase forms just below the melting point.

Unidirectional and continuous carbon fiber tin-matrix composites were used for the packaging of the high-temperature superconductor YBa2Cu3O7–δ by diffusion bonding at 170 °C and 500 psi. Tin served as the adhesive and to increase the ductility, the normal-state electrical conductivity, and the thermal conductivity. Carbon fibers served to increase the strength and the modulus, both in tension along the fiber direction and in compression perpendicular to the fiber layers, though they decreased the strength in compression along the fiber direction. Carbon fibers also served to increase the thermal conductivity and the thermal fatigue resistance. At 24 vol. % fibers, the tensile strength was approximately equal to the compressive strength perpendicular to the fiber layers. With further increase of the fiber content, the tensile strength exceeded the compressive strength perpendicular to the fiber layers, reaching 134 MPa at 31 vol. % fibers. For fiber contents less than 30 vol. %, the compressive ductility perpendicular to the fiber layers exceeded that of the plain superconductor. At 30 vol. % fibers, the tensile modulus reached 15 GPa at room temperature and 27 GPa at 77 K. The tensile load was essentially sustained by the carbon fibers and the superconducting behavior was maintained after tension almost to the point of tensile fracture. Neither Tc nor Jc was affected by the composite processing.

The elastic properties of nickel beryllide have been evaluated from room temperature to 1000 °C. The room temperature modulus is measured to be 186 GPa, which is relatively low by comparison with other B2 aluminides such as NiAl and CoAl. Hardness measurements were carried out on specimens that had compositions over the range from 49 to 54 at. % Be, using both a Vickers microhardness tester and a nanoindentor. It was found that the hardness of NiBe exhibits a minimum at the equiatomic composition. This behavior is similar to that of aluminides of the same crystal structure, e.g., NiAl and CoAl. The effect of interstitial oxygen on the hardness of NiBe has also been studied and the results show that the presence of oxygen in NiBe can cause a significant increase in hardness. It is demonstrated that the hardness increase for the off-stoichiometric compositions is primarily caused by interstitial oxygen and can only be attributed partially to anti-site defects generated in off-stoichiometric compositions. Nickel beryllides appear to have some intrinsic room temperature ductility, as evidenced by the absence of cracking near hardness indentations.

Specimens of pure Fe and of Fe-0.8 mass % C, Fe-0.5 mass % Cr, Fe-4.0 mass % Cr, Fe-4.0 mass% Ni, and Fe-10.0 mass% Ni alloys were borided in boriding powder. A boron-compound layer developed consisting of a surface-adjacent “FeB” sublayer on top of an “Fe2B” sublayer. Layer-growth kinetics were analyzed by measuring the extent of penetration of the “FeB” and “Fe2B” sublayers as a function of boriding time and temperature in the range 1025–1275 K. Layer growth is dominated by B diffusion through “FeB/Fe2B”. This diffusion process is of strongly anisotropic nature. Consequently, ragged interfaces occur between the substrate and the boride layers. The depths of the tips of the most deeply penetrated “FeB” and “Fe2B” needles have been taken as measures for diffusion in the easy [001] diffusion directions. Assuming unidirectional B diffusion and parabolic growth, a simple model of layer growth has been given. It accounts for the specific volume difference between “FeB” and “Fe2B”. In contrast with earlier work, the model provides values for the kinetic parameters for growth of each of the phases in the boron-compound layer.

Microhardness and cantilever beam fatigue measurements were conducted on Fe–13Cr–15Ni base austenitic alloys that were implanted with boron and nitrogen ions either singly or simultaneously. The microstructure of the modified surface layer and dislocation slip modes after fatigue tests were investigated by optical and transmission electron microscopy. Both hardness and fatigue life were improved by ion implantation, but the greatest improvement was achieved when boron and nitrogen were implanted simultaneously. The degree of fatigue life improvement also varied with minor changes in the base alloying compositions: nitrogen was detrimental or ineffective in the presence of titanium, and boron was much more effective in the presence of molybdenum. Comparison of slip band morphology between the compression and tension cycles indicated that implantation improved the reversibility of surface slip and delayed crack initiation.

A nickel aluminide of composition Ni–23.5Al–0.5Hf–0.2B (at. %) is found to develop intergranular cavities with a quasi-equilibrium shape when it is creep deformed at high temperatures and low stresses. When the temperature is lowered and the stress significantly increased (by a factor of 10), crack-like noses form at the tips of the original quasi-equilibrium cavities. Although this observation is in general agreement with previously published computer simulations, certain complications are found as well. The experimental and theoretical relationships between growth rates and sizes of the crack-like noses are inconsistent, and growth rates vary from nose to nose. Possible reasons for these effects are discussed.

The structure of Nb–Al thin films after ion mixing was studied for compositions from 20 to 85 at. % Al as a function of temperature in the range between 40 and 620 K. The phase formation was determined by transmission electron microscopy. At lower temperatures, only supersaturated bcc-solid solution, NbAl, and amorphous phase were found throughout the studied composition range. Besides these phases irradiation at temperatures above 470 K causes the formation of a metastable crystalline compound at an overall composition close to Nb25Al75, and for T = 623 K the equilibrium compound NbAl3 is formed. The other intermetallic phases Nb2Al and Nb3Al have not been observed at any irradiation temperature. Calculations of the Gibbs free energies of the various phases are presented, and the reliability of extrapolations to regions of metastability with respect to temperature and composition is commented on. The phase formation during heavy-ion irradiation is discussed in the context of the calculated free energies and kinetic constraints. For temperatures above 300 K, the attainment of a metastable phase equilibrium between the bcc solid solution and the amorphous phase is proposed due to the influence of radiation enhanced diffusion.

We have used rapid e-beam heating and quenching to study metastable transitions between allotropic phases in Mn and to determine relative rates of transformation between the allotropes. The equilibrium α ⇉ β transition at 720 °C is bypassed and the metastable α ⇉ γ transition is observed to occur at a temperature (880 ± 30 °C) near that predicted thermodynamically (864 °C).

The microstructure of icosahedral Al(Mn) in melt-quenched surface alloys has been characterized with TEM. Single-phase alloys with 20 at. % Mn show angular misorientations (up to ∼7°) across internal boundaries radiating from the nucleation centers of grains. Lowering the Mn content results in fcc Al at grain boundaries and between branches of the icosahedral grains; the presence of Al-rich liquid around growing grains apparently eliminates the misorientations seen with 20 at. % Mn. The grains have a dense distribution of dislocation-like defects, but have sufficient orientational order to exhibit well-defined diffraction contours. Weak reflections in diffraction patterns from small areas (0.7 μm) of grains exhibit deviations from exact icosahedral symmetry positions which were analyzed to evaluate a phason strain tensor and characterize misordering defects in the quasicrystalline structure. A negative matrix element (m ≍–0.05) for a tensor axis along a twofold icosahedral axis accounts for most of the distortions in these patterns and those from other melt-quenched icosahedral Al(Mn) and Al(Mn, Si) alloys; this dominant element lowers the symmetry to D2. This axis is nearly perpendicular to the growth direction, which suggests that the misordering is due to rapid growth during the quench; however, the D2 distortion may also result from an elastic instability predicted for icosahedral phases. Distortions in Al(Cr, Ru) can be fit with a similar tensor but with m>0. Thus the phason character identified here may apply to other aluminum-transition metal icosahedral phases as well.

Ni3Ge-containing nickel-germanium alloys with 12.10 to 16.8 at. % Ge were investigated. Nickel-saturated Ni3Ge had a lattice parameter of 3.57015 × 10−10 m and contained 22.5 at. % Ge over the temperature range 650 to 1100 °C. However, the precipitates in the initial stages contained 24.44 at. % Ge and were almost cubic in shape. The strengthening effects of Ni3Ge were appreciable. In alloys containing higher percentages of germanium, precipitates were observed in as-quenched specimens. The hardness after quenching was high and did not change appreciably with time. Hardness was reduced in the presence of aluminum.

The solid state oxidation kinetics of Pb–Sn single-phase (2.5 at. % Sn) and eutectic alloys were studied with Auger Electron Spectroscopy combined with sputter depth profiling. The single-phase samples were oxidized in air in the temperature range 22 °C to 250 °C, while the eutectic samples were oxidized from 22 °C to 175 °C. Both alloys oxidize logarithmically between 22 °C and 90 °C and parabolically at temperatures greater than 120 °C. The activation energies for the parabolic oxidation of the single-phase and eutectic alloys are 69.5 and 67.1 ± 8 kJ/mole, respectively.