Two Ni-modified Al3Ti alloys (Al65Ni10Ti25 and Al62Ni8Ti30) were rapidly solidified by melt spinning. The resulting microstructure was studied using light microscopy and analytical electron microscopy. Significant variations in the microstructure and phases were observed between the two ribbons and through the thickness of each ribbon.A single-phase γ-TiAl structure was seen near the wheel side of the Al62Ni8Ti30 ribbon, having microcrystalline grains ∼ 100 nm in diameter. Second-phase particles of Λ-AlNiTi were found in the remaining regions of that ribbon as the structure became columnar due to reduced rates of cooling. The Al65Ni10Ti25 alloy exhibited a primary phase of π-Al6.5 NiTi2.5. A second phase of μ-Al2NiTi formed with morphology and distribution varying through thickness. Microchemistry measurements on the phases indicated substantial deviations (up to 14 at. %) from the stoichiometric compositions. Further, the π, γ, and μ are low-temperature phases that do not form by solidification under equilibrium conditions. The observation of these phases thus suggests significant undercoolings achieved during the melt-spinning processing of the present alloys. Both ribbons are brittle as spun.

A new hexagonal crystal structure modification of the rhombohedral Mu phase with A7B6 stoichiometry was observed in a cast alloy C-276. The hexagonal structure was determined to share the same lattice parameter along the a axis, while the dimension along the c axis was such that chex = 2/3crhomb. The space group of the hexagonal phase is suggested to be P 63/mmc and forms by a four-layer ABAB repeat, where A and B represent Zr4Al3 and MgCu2 structures, respectively. Details of the diffraction analysis are presented in this article.

A new type of brittle fracture was discovered in a Cu–Bi alloy bicrystal with a random misorientation interface. Macroscopically, fracture occurred along the interface with a low-energy release rate of order 50 Jm−2. Microscopically, the crack apparently propagated in a zigzag manner such that a cleavagelike fracture was produced, which consists of two sets of smooth {110} facets and one set of {100} facets with serrations corresponding to their intersections with {111} slip planes. Facet sizes are typically of order 1 by 5 μm or smaller. The very smooth facets and low-energy absorption suggest that a decohesion separation process has occurred along {110} planes, and the serrations suggest that substantial dislocation slip accompanied fracture of the {100} facets. The fracture surface morphology may be explained as the result of a similar morphology of Bi-induced microscopic faceting of the bicrystal interface or, instead, may result from fracture propagating in the vicinity of, but not quite along, the interface. Evidence is presented that favors the latter so that this is a rapid, cleavagelike, semiintergranular fracture that has not been observed in fee metals or alloys when an environment effect is not involved. Its faceted features resemble those of transgranular stress corrosion cracks in certain fee metals.

An investigation of the quasicrystalline phases obtained in alloys of Al86Mn14 under slow solidification rates is carried out. A quasicrystalline phase similar to the so-called T phase [L. Bendersky, R. J. Schaefer, F. S. Biancaniello, M. J. Boettinger, M. J. Kaufman, and D. Schechtman, Scr. Metall. 19, 909 (1985)] is found. However, this phase also shows a pseudofivefold axis and a threefold diffraction pattern similar to the same orientation in the reported phase of Al4Mn. The analysis of pseudofivefold diffraction patterns from different quasicrystalline grains shows elliptical arrangements of spots with different eccentricities. The presence of planar faults indicates the existence of slip pseudoplanes and slip directions in the quasicrystal. Different eccentricities might suggest that some of the reported quasicrystalline phases (T, T′, T″, …, etc.) are structural states obtained from the icosahedral quasicrystalline phase when particular stress environments are acting.

Results of in situ hot-stage electron microscopic investigations on the transformation behavior of icosahedral Mg32 (Al,Zn)49 and decagonal Al–Co quasicrystalline phases are presented. It is shown that in both the cases the transformation begins with the formation of fine holes. This has been interpreted on the basis of the lower density of the quasicrystalline phase. Differences in the transformation behavior between the icosahedral and decagonal phases are highlighted.

This study involved the ultrasonic measurement of the polycrystalline elastic constants of six face-centered-cubic Fe–Cr–Ni alloys, nominally Fe–19Cr–12Ni (at. %). In these alloys, Mo content ranged up to 2.4 at. %. Molybdenum lowers the Young and shear moduli, and it raises the Poisson ratio. Against expectation (because it increases volume), Mo raises the bulk modulus. Qualitatively, the results show that Ni raises the bulk modulus and Poisson ratio; but Ni lowers the Young and shear moduli. (Nickel decreases the alloy's atomic volume.) The discussion includes existing models based on 3d-electron theory.

After a short review on temperature dependence of the intrinsic coercivity in sintered Nd–Fe–B-type magnets is given, recent experimental results concerning the coercivity-anisotropy (HC–HA) correlation in B-rich Pr–Fe–B and Nd–Fe–B sintered magnets and the influence of the surface conditions of the sintered Nd–Fe–B magnets on the coercivity are reported. The results are interpreted in terms of the μoHc vs cμoHA – NIs plot, where Is is the spontaneous magnetization of R2Fe14B (R = Pr or Nd) and N is the effective demagnetization field coefficient.

Tracer diffusion of 60Co and 63Ni in the amorphous alloy NiZr near the equiatomic composition has been measured in the temperature range between 486 and 641 K using the ion-beam sputter-sectioning technique for serial sectioning. The temperature dependence for the diffusivities of Co and Ni in a-NiZr exhibit Arrhenius behavior; these can be expressed as follows: D∗co = 3.6 × 10−7 exp [− (135 ± 14) kJ mol−1 /RT] m2/s and D∗Ni = 1.7 × 10−7 exp [− (140 ± 9) kJ mol−1 /RT] m2/s. The values of D∗Ni are in good agreement with those measured by the Rutherford backscattering technique. The measured diffusivities were independent of time, indicating that no relaxation took place during diffusion.

Isothermal devitrification of Pd85Si15 amorphous alloys has been analyzed using differential scanning calorimetry (DSC) and x-ray diffractometry. Both as-quenched and aged amorphous ribbons were investigated. Crystallization of aged samples starts from the surface and proceeds several micrometers into the bulk. The product of this process is a layer of strongly textured palladium (111) followed by a mixture of Pd2Si, Masumoto MSI phase, and untextured palladium. Next, the crystallization occurs via a different (bulk) mechanism, resulting in a mixture of Masumoto MSII phase and untextured palladium. The bulk mechanism is the only one observed in as-quenched samples. The surface and bulk crystallization mechanisms are spatially decoupled and, therefore, the corresponding DSC data can be analyzed separately. This has been done according to the Kolmogorov–Johnson–Mehl–Avrami model and also using the recently developed concept of local value of Avrami exponent n. For both the surface and bulk crystallization the phase transition process cannot be characterized by a single value of n. Observed variation of n with the crystallized fraction x is explained by a considerable variation of the nucleation rate that takes place during devitrification.

Field emitter array (FEA) devices were constructed using thin-film fabrication techniques based on in situ eutectic composites containing either TaC or NbC fibers in a NiCr alloy matrix. The emission characteristics of the TaC devices were measured and compared to those of W–ZrO2 FEA's. Both devices produced the linear Fowler-Nordheim plots common to all field emission devices; however, the array current density of the TaC FEA's was more than two orders of magnitude lower than that of the W–ZrO2 FEA's. This was primarily due to the lower fiber density and lower field enhancement of the carbide fiber devices. If it were possible to produce cathode geometries comparable to those of the W–ZrO2 FEA's, a theoretical analysis indicates that emission performance of the TaC devices would be superior because of the lower work function of TaC. However, post-emission observations indicated that the carbide fiber emitters failed more readily than the tungsten emitters under comparable operating conditions.

The stage (s) and temperature (4.2≤T≤295 K) dependence of the c-axis resistivity ρc and the conductivity anisotropy (ρc/ρa), taking into account all available literature data as well as those from the laboratory, are examined. For all intercalants, the ρc (s, T) variations are highly similar. The temperature coefficient of resistivity is generally positive over the entire T range for the richest compounds; it slowly decreases in magnitude and changes sign as s increases. The sign change occurs for a compound between the second and fifth stage depending on the intercalant. At 4.2 Kρc is T independent. Except for a few stage 1 compounds, the anisotropy always rises upon decreasing T. An analysis of the existing c-axis conductivity models is given: these invoke phonon- and impurity-assisted hopping mechanisms, interlayer conducting paths, and stacking faults. Some unanswered questions are raised that may indicate directions of future research.

A study of the (00l), (hk0), and (hkl) reflections of stage 1 AsF5 intercalated graphite between 4.2 and 295 K has been done using synchrotron radiation for single-crystal samples and a linear detector setup for those based on highly oriented pyrographite (HOPG). The nature and temperature dependence of the structural ordering allow the materials to be classified into (at least) two types related to the degree to which the AsF5 has been converted into AsF−6 and AsF3. At 295 K a small amount of in-plane order is detected within the essentially two-dimensional (2-D) liquid intercalate attributed to small quantities of AsF5 and AsF−6 − AsF5-ordered phases. Lowering the temperature leads to increased phase separation through crystallization and to changes in the in-plane unit cells associated with each. The most marked structural change is an incommensurate-to-commensurate (I⇉C) transformation within the AsF5 phase, which starts at 215 ± 5 K. No new structural order is detected below 180 K. The (00l) studies give clear confirmation of the existence of separate phases with different values of interplanar distance. A smaller number of stage 2 compounds were examined. The most clearly different feature is that the I⇉C transformation is downshifted by ∼ 70 K. At room temperature, the stacking sequences are A/A/A … for stage 1 and A/AB/BC/CA … for stage 2.

Part I of this study has shown that first stage AsF5 intercalated graphite samples can be classified into two types of compounds, depending upon the nature of the structural modifications they undergo upon lowering the temperature from 295 to 4.2 K. These structural changes are related to demixing of the species contained within the intercalate resulting in the formation of phases rich in AsF5, AsF−6 − AsF5, or AsF3 depending on the degree to which the AsF5 has been converted into AsF−6 and AsF3. Resistivity studies have been carried out in the basal plane [ρa (T)] and along the c axis [ρc (T)]. The type 1 compounds, in which the AsF5 has undergone little conversion, manifest a ρa (T) transition related to the incommensurate-to-commensurate (I⇉C) transformation of the AsF5 in-plane unit cell and a rapid, structureless 300 to 200 K decrease in ρc (T). The type 2 compounds involving a greater degree of conversion of AsF5 into AsF3 and AsF6 yield more complex ρc (T) behavior from 300 to 200 K attributed to the more involved ordering phenomena; no anomalies are seen in ρa (T). In the case of the stage 2 compounds, changes in ρc (T) are seen down to lower temperatures in accord with structural data indicating a downshift of the I⇉C transformation by ∼ 70 K. The transport results are discussed in the light of the crystallographic data and the low-temperature results are analyzed within the framework of proposed conductivity models.

Thin films were sputter deposited from a Fresnoite (Ba2Si2TiO8) ceramic target at substrate temperatures lower than 175°C. The as-deposited thin films were near amorphous with a void network morphology. In spite of the fact that the film compositions were shifted from stoichiometry, x-ray diffraction studies showed that the films crystallized to form randomly oriented Fresnoite grains. The crystallization kinetics were quite sluggish and the resultant activation energy for the crystallization process was 370 ± 30 kJ/mol. Even after annealing for 10 h at 750°C an appreciable amount of amorphous material remained in the thin films. The short-range order in this amorphous material was changed from that of the as-deposited thin films. The overall devitrification kinetics of amorphous Fresnoite thin films at a fixed temperature were represented theoretically by an equation of Tool's type.

High-densified LiTaO3-type ceramics have been obtained by sintering at 900°C after the addition of small amounts of a LiF + MgF2 mixture. Partial hydrolysis of MgF2 and volatilization of either LiF, LiOH, or Li2O due to hydrolysis and partial substitution of F-ions by (OH−) occur during heat treatment. The ferroelectric Curie temperature Tc increases with the amount of additive. The ceramics have been polarized by heating to Tc and cooling down under a dc field. The piezoelectric and pyroelectric coefficients of such ceramics are approximately 30% and 20% of the corresponding values for a LiTaO3 single crystal.

Diffusion of 18O in the superconductor La2−x Srx CuO4−y has been measured as a function of x (0 to 0.20) between 300 and 500°C at an oxygen partial pressure of ≍ 1 atm. Concentration profiles were obtained using a secondary ion mass spectrometer. The diffusion coefficient decreases with increasing Sr additions from 0.1 to 0.2, primarily because of an increase in activation energy. This result, which is contradictory to the expectation that the diffusion coefficient should increase with increasing vacancy concentration caused by the added Sr, can be explained if oxygen vacancies are bound to Sr clusters. Measurements on samples with x = 0 or 0.05 were unsuccessful, probably because of porosity.

The pronounced anisotropy of shrinkage in the axial and the radial direction, observed in earlier studies on the sintering behavior of cordierite-type glass powder, is investigated in detail. It is shown that a planar orientation of the pore/solid interface exists that gives rise to an oriented shrinkage in the radial direction. The results show that the axial-to-diametral shrinkage ratio increases from a value of 0.3 to approximately 0.7 with increasing density, and that particle size and particle shape of the glass powders have little influence on shrinkage anisotropy.

Laser-beam-controlled heating appears to be an excellent technique for driving isothermal transformations in a thin solid film on a thick substrate. The transformation is detected by the change in optical properties of the film as it evolves from the initial to the final state. Results are presented for the amorphous-to-crystalline transition in 100 nm thick films of InSb and of some Te alloys on thick glass substrates. Discrimination between interface growth and homogeneous crystallization can be made from the data. The crystallization of InSb films can be desribed by an Avrami equation with a single activation energy of 154 ± 6 kJ/mol over the full range of measured crystallization times between 100μs and 1000s. For low temperatures the results are consistent with differential scanning calorimetry (DSC) measurements. For Te-alloy films, the large temperature interval covered by the experimental method enables clear observation of the curvature of the temperature-time-transmission (T–t–t) plot.

An elementary-reaction mechanism of diamond growth by a vapor deposition process is proposed. The central postulate is that the main monomer growth species is acetylene. The mechanism basically consists of two alternating steps: surface activation by H abstraction of a hydrogen atom from a surface carbon and the addition of one or two acetylene molecules. During the addition reaction cycle a number of solid C–C bonds is formed and hydrogen atoms migrate from a lower to an upper surface layer. The mechanism is in general agreement with the macroscopic views of the Russian researchers and is consistent with the numerous experimental observations reported in the literature.

The hardness of aluminum films on silicon are measured as functions of depth of the indenter. The films have thicknesses of 0.25,0.5, and 1.0μm. The adhesion between one film and the substrate has been reduced through the prior deposition of a 10 nm layer of carbon. In each case the hardness is found to increase as the indenter approaches the film-substrate interface, but the rate of increase is greater for a film with good adhesion than for one with poor adhesion. It is suggested that this increase results from the constraint on deformation of the film by the substrate. A physical model is proposed whereby the yield stress of the film, σo, and an average effective shear strength τ of the indenter-film and film-substrate interfaces, may be determined from the data.