Selected area electron channeling patterns were used to identify the cleavage planes in a polycrystalline Al–23Ti–6Fe–5V alloy, which is an Al3Ti-based alloy having the Ll2 structure. Alloys like this one are of scientific and technological interest because they fracture by brittle transgranular cleavage, despite the availability of more than five independent slip systems in the Ll2 structure and their relatively low hardness when compared to ductile Ll2 alloys like Ni3Al. Homogenized bars of the levitation zone melted and directionally solidified alloy were fractured at room temperature in three point bending. The fracture surfaces, which consisted almost entirely of brittle transgranular cleavage facets, were examined in a scanning electron microscope (SEM) equipped to take channeling patterns. An optical microscope with a short depth of focus was inserted in the SEM column just below the objective lens, and by focusing it on several points on the cleavage facets, it was possible to orient the facets normal to the optic axis of the SEM prior to taking the channeling patterns. Of the eight cleavage facets examined in this study, six were of the {110} type and two were of the {111} type. Although it cannot be said that these are the only two cleavage planes in this alloy, the availability of more than one plane with low cleavage strength contributes to the brittleness of this alloy. These results are examined in the light of theoretical treatments of cleavage fracture, and comparisons are made with earlier studies on other Ll2 materials.

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.

A lattice statics Green's function method is described for calculating the atomistic structure of a solid near a grain boundary interface. First, a reference state is defined which is ‘near’ the equilibrium state. The Green's function for the reference state is obtained in terms of the perfect lattice Green's function by mapping the lattice sites of the reference state to the perfect lattice sites and solving the Dyson's equation within a supercell. This Green's function gives the response of the reference state which determines the atomic relaxations under the net forces which would be present in the reference state. The specific case of a ∑5 tilt boundary in a fec lattice has been considered, assuming the validity of the harmonic approximation.

The Embedded Atom Model (EAM) was utilized to analyze the energy and strain surrounding Au and Pt atoms substituted into a Ni crystal. Au substituted into Ni has a large positive size difference and a positive heat of mixing; Pt substituted into Ni has a large positive size difference and a negative heat of mixing. The EAM predicted highly anisotropic strain fields around the substitutional atom with large positive strains in the [110] direction and small or negative strains in the [100] and [111] directions. This is in contrast to the normal assumption that the strain around a substitution atom is spherically symmetric. The cohesive energy of the atoms around the substitutional atom was found to depend upon the crystallographic direction relative to the substitutional atom in addition to the radial distance from the substitutional atom. The EAM predicted an energy increase for Au substituted into Ni and an energy decrease for Pt substituted into Ni. The EAM results were compared with an elastic analysis.

We have fabricated superconducting composites composed of Y1Ba2Cu3O7–δ, copper oxide, and metallic silver. Sharp superconducting transitions were observed well above the liquid nitrogen temperature. The normal state resistivity of these composites was much lower than that of the pure ceramic Y1Ba2Cu3O7–δ. The critical current density was measured and it was comparable to that of ceramic superconductors. A substantial improvement of the mechanical properties has been achieved over those of the ceramic Y1Ba2Cu3O7–δ material.

The 2223, 1223, 1324, and 1122 phases in the Tl–Ca–Ba–Cu system were prepared from sample mixtures having the same stoichiometry as the final phase. Powder x-ray diffraction analysis was used to follow the formation of these phases at 867 °C for up to 2 h. The formation of the 2223 phase is shown to occur via the sequential transformations 2021 → 2122 → 2223. For the 1–2–2–3 and 1–3–2–4 samples, the sequential transformations 1021 → 2021 → 2122 → 2223 occur before the final 1223 and 1324 phases are obtained. For the 1122 phase the formation is preceded by the 1021 → 2021 → 2122 transformations. Using scanning electron microscopy, a phase with a glassy appearance was detected in many of the reacted samples. This “glassy” phase appears to be a precursor in the formation of the Tl–Ca–Ba–Cu phases.

Uniform spherical colloidal particles of mixed internal composition were obtained by aging at 90 °C solutions containing Cu(NO3)2 + Y(NO3)3 and Cu(NO3)2 + La(NO3)3, respectively, in the presence of urea. The molar ratio of metal ions in the solids precipitated from a given solution varied with the reaction time. After sufficiently long aging, this ratio corresponded closely to that in solutions in which the particles were generated. The original precipitates consisted of basic carbonates, which on calcination converted to mixed oxides of defined composition.

The influence of surface segregation on wetting of Pd2As and Pd50B25As25 to refractory metals has been studied by sessile drop and surface analytical techniques. The results indicate that the wetting behavior of Pd2As to W is strongly influenced by surface segregation of low-level bulk impurities in the alloy. At melting, the segregating impurities form an inert shell about the liquid alloy which inhibits reaction between alloy and substrate. A poorly-wetted droplet with a large contact angle results. Wetting is elicited by fracture of the high-surface tension shell during heat treatment. The efflux of pure alloy material from the interior of the droplet wets refractory metals with a contact angle of near-zero. The shell remnant floats atop the wetted alloy. Addition of B to the alloy to form Pd50B25As25 results in rapid attack of a Re support. Preliminary studies of the vapor pressure above the alloy and mass analysis of field evaporated ions show that Pd2As may be used as a liquid metal ion source of As. This is possible by means of successful reduction in As vapor pressure by over 10 orders of magnitude.

The microstructure and the coercivity of sintered Nd20Fe(73.5-x)B6.5Alx (x = 0, 2.5) permanent magnets are influenced by the Al concentration. In Al-containing magnets we found a homogeneous distribution of Al in the hard magnetic phase and the occurrence of an intergranular Nd(Fe, Al)2, phase between the hard magnetic grains. Our analytical TEM study revealed that in “Al2O3-doped” magnets the crystal structure of the Nd-rich intergranular phase partly changes from fcc (a = 0.52 nm) to hep (a = 0.39 nm, c = 0.61 nm), whereas the content of iron simultaneously decreases from 5–10 at.% to 1.5–4 at.%. A platelet-shaped phase, embedded in the Nd-rich intergranular phase, was determined as a Nd5Fe2 (B, O)x, phase. The influence of the microstructure on the coercivity in Al-doped magnets is discussed.

A melting point depression, δTM, has been observed for Sn in Ge/Sn (50 at.% Sn) dispersions which were prepared by mechanical milling of Ge and Sn powders. Sn and Ge are immiscible and form a fine dispersion of the pure components when milled in a high energy ball mill. The magnitude of δTM, as measured by DSC, increases with milling time, i.e., with refinement of the dispersion. Melting is observed to begin as low as 36 °C below the equilibrium bulk melting temperature. The magnitude of δTM is reduced by about 25% after melting the Sn. Subsequent remelts do not change δTM further. Impurities cannot account for δTM. While stored energy of cold work may contribute to 25% of δTM before Sn is melted, it is concluded that the major contribution to δTM comes from the nucleation of disorder/melting at the Ge/Sn interfaces.

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.

The lattice statics Green's function method for calculation of the atomistic structure of grain boundary interfaces in solids as described in Part I is extended to include anharmonic effects. It is shown that the ‘anharmonic’ response of a solid to ‘anharmonic’ forces can be represented in terms of the ‘harmonic’ response of the solid to an effective anharmonic force. The Green's function method then requires solving a finite order nonlinear matrix equation, which is done by using standard numerical methods. For the purpose of illustration, the method is applied to calculate the atomistic structure of a ∑5 tilt boundary in fec copper.

It is shown that a binary alloy with an AB3 stoichiometry on a bcc lattice may develop various combinations of B2 and DO3 order along its kinetic path toward equilibrium. The temporal evolution of these two order parameters is analyzed with an activated-state rate theory. Individual vacancy jumps are treated in a master equation formalism that involves first-nearest-neighbor (1nn) and second-nearest-neighbor (2nn) interactions. In our formulation, a set of coupled differential equations is obtained describing the time-dependence of six order parameters. These equations were integrated numerically for a variety of interatomic interactions and initial conditions. It was found that the relative rates of B2 and DO3 ordering, and hence the path of the alloy through the space spanned by the B2 and DO3 order parameters, depend on the relative strengths of the interatomic interaction potentials and on the temperature. For very strong 2nn interactions, a transient B32 structure was observed to develop at early times, although this phase disappeared as equilibrium was approached.

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.

The intermetallic compounds NiTi, NiTi2, CuZr, CuTi2, and Zr3Al were irradiated by 2 McV protons at various temperatures between –175 °C and –44 °C to a fluence of 1.9 × 1022 H+/m2. Transmission electron microscopy, electron diffraction, and x-ray diffraction were used to evaluate the extents of disordering and amorphization induced by irradiation in the samples. Both phenomena progressed to varying extents in the five compounds, depending on the irradiation temperature and dose. It was observed that the C-A transition began before the degree of long-range order was reduced significantly, and that the amorphous phase nucleated homogeneously throughout the crystalline matrix. A major finding of the current investigation is that the technique of scanning electron fractography provides a useful correlation between the features of the fractured surfaces and the microstructural alterations induced by the proton irradiations. When amorphization is complete the fracture surfaces are either featureless (e.g., NiTi2) or contain branching features resembling river patterns. In some cases (especially in CuZr) these are similar to the markings seen on the surfaces of fractured amorphous ribbons produced by melt-spinning. In general, however, there is not a particularly good correlation between the features on the fracture surfaces of the irradiated and melt-spun ribbons. When the microstructure consists of amorphous regions embedded in a partially disordered crystalline matrix, there is considerable evidence for irradiation-induced ductility. In such cases, exemplified by the results on NiTi and Zr3Al, the fracture surfaces contain dimples, characteristic of ductile fracture, suggesting that disordering promotes ductility.

Using TEM, Auger spectroscopy, EDX, and convergent beam electron diffraction, a thorough characterization of the interphase region between SCS6 fibers and Ti–6Al–4V matrix in a metal matrix composite has been performed. The interphase region is shown to be very complex, consisting of numerous layers of varying compositions and thicknesses. The chemical interaction of the fiber and matrix results in a 0.5–1.5 μm thick TiC layer. Evidence for the existence of a Tix Siy (C) layer is also presented. The SCS6 overlayer on the fibers has inhibited any chemical interaction between the matrix and the SiC filament itself, 60% of the interphase region originating from the SCS6 protective coating. In situ fracture experiments (in an Auger spectrometer) reveal that fracture takes place between the TiC and an amorphous carbon layer.

The thin-film interactions of Al with refractory metals (Co, Cr, Mo, Ta, Ti, and W) have been investigated. The composition and thickness of the reacted aluminide layers were determined by Rutherford backscattering and phase identification was made by x-ray diffraction. Scanning electron microscopy was used to examine the lateral uniformity. The initial aluminide phases to grow are the Al-rich phases: Co2Al9, Cr2Al13, MoAl12, TaAl3, TiAl3, and WAI12. These are the most Al-rich phases on the phase diagrams. The reaction temperatures varied between 350 and 525 °C.

The depth dependence of hardness in a well-annealed single crystal of silver has been characterized in nanoindentation experiments. The work is based on similar experiments performed by Chen and Hendrickson, but extends their results to indent depths on the nanometer scale. The hardness is generally found to increase with decreasing depth, with a rather sharp increase observed at depths of less than 50 nm. Using etch pitting to reveal the surface dislocation structure after indentation, the sharp rise in hardness is found to be associated with the disappearance of dislocation rosette patterns and any signs of near-surface dislocation activity, thereby suggesting that very small scale indentation plasticity may take place by nondislocation mechanisms. However, order of magnitude calculations show that possible alternatives, specifically, diffusional mechanisms, are too slow to make significant contributions. It is suggested that for very small indents, either the surface dislocation debris is quickly annealed out before it can be observed or indentation plasticity is accommodated entirely by subsurface dislocation activity.

The activation energies for self-diffusion of transition metals (Au, Ag, Cu, Ni, Pd, Pt) have been calculated with the Embedded Atom Method (EAM); the results agree well with available experimental data for both mono-vacancy and di-vacancy mechanisms. The EAM was also used to calculate activation energies for vacancy migration near dilute impurities. These energies determine the atomic jump frequencies of the classic “five-frequency formula,” which yields the diffusion rates of impurities by a mono-vacancy mechanism. These calculations were found to agree fairly well with experiment and with Neumann and Hirschwald's “Tm” model.

Rapidly quenched powders of Fe3Al were subjected to thermal annealings at temperatures well below the critical temperatures for B2 and DO3 ordering. X-ray diffractometry was used to measure the subsequent evolution of B2 and DO3 long-range order. It was found that the relative rates of change of B2 and DO3 order parameters were temperature dependent; hence at different temperatures the alloy passed through different states of order en route to thermal equilibrium. These temperature dependences of “kinetic paths” can be understood in terms of a theory of kinetic paths based on the kinetic master equation. The theory indicates that the temperature dependence of the observed kinetic paths originates from having first-nearest-neighbor interactions that are stronger than second-nearest-neighbor interactions. This seems consistent with previous thermodynamic analyses of critical temperatures of Fe3Al.