Hot hardness has been measured in seven isostructural Be12X compounds: Be12Cr, Be12Mn, Be12V, Be12Mo, Be12Ti, Be12Ta, and Be12Nb. All vacuum-hot-pressed (VHP) materials exhibited similar hardness levels (800 to 1000 kg/mm2) at low temperatures (<600 °C), but sharply diverged at higher temperatures. Most compounds showed a sharp decrease in hardness above about one-half their melting temperatures except for Be12Nb and Be12Ti which maintained strength until higher temperatures. Ductile-brittle transition temperatures (DBTT's) of 600, 625, 690, 700, 700, and 850 °C were determined for Be12Cr, Be12Mn, Be12V, Be12Mo, Be12Ti, and Be12Nb, respectively. Hot-isostatically-pressed (HIP) and VHP Be12Nb heats both showed comparable behavior, indicating that the temperature required for macroscopic plasticity is not dependent on processing conditions. Differences in slip characteristics were observed between beryllides with similar melting temperatures, but differing DBTT's. Dislocations were activated on multiple slip systems in Bei2V during compressive deformation at 800 °C. Similar behavior was not observed in Be12Nb until test temperatures above 1000 °C. It is proposed that dislocation mobility may be related to the stability between Be12X and Be17X2 phases. Larger refractory metal atoms such as Nb may form faulted layers related to Be17X2 structures and thereby impede deformation at intermediate temperatures. Smaller atoms such as Cr, Mn, V, and Mo do not form a stable Be17X2 phase and thereby allow enhanced dislocation mobility at these temperatures.

Titanium hydrides having two different crystal structures were observed in α–Ti thin films grown epitaxially on sapphire substrates by e-beam physical vapor deposition. One of the hydrides (γ-hydride) had a face-centered tetragonal structure (c/a > 1) with an ordered arrangement of hydrogen atoms. The second hydride formed was the fcc δ-hydride. The γ-hydride grew as platelets in the α–Ti lattice with {10$\overline 1$0}Ti habit planes, whereas the γ-hydrides formed directly on the sapphire substrate parallel to the (0001)Ti. These hydrides are one of the principal causes of film decohesion.

In this paper, the possibilities of preparing TiC-reinforced Ni3Al-matrix composites by SM (self-propagating high temperature synthesis and melting process) were examined. Two kinds of composites, namely, commercial TiC-reinforcement and synthesized TiC-reinforcement Ni3Al-matrix composites, were fabricated. The effects of particle size of the commercial TiC on the mechanical properties of the Ni3Al-matrix composites were studied. The results show that the mechanical properties of the composites decrease with increasing particle size of the commercial TiC. The microstructures of 35 wt. % TiC + 65 wt. % Ni3Al composites produced by SM technology from the four elements Ti, C, Ni, and Al were examined. The results show that in these composites, the particle size of TiC synthesized in situ is fine and that the materials have considerable high-temperature bending strength and fracture toughness.

The reliability of integrated-circuit wiring depends strongly on the development and relaxation of stresses that promote void and hillock formation. In this paper an analysis based on existing models of creep is presented that predicts the stresses developed in thin blanket films of copper on Si wafers subjected to thermal cycling. The results are portrayed on deformation-mechanism maps that identify the dominant mechanisms expected to operate during thermal cycling. These predictions are compared with temperature-ramped and isothermal stress measurements for a 1 μm-thick sputtered Cu film in the temperature range 25–450 °C. The models successfully predict both the rate of stress relaxation when the film is held at a constant temperature and the stress-temperature hysteresis generated during thermal cycling. For 1 μm-thick Cu films cycled in the temperature range 25–450 °C, the deformation maps indicate that grain-boundary diffusion controls the stress relief at higher temperatures (>300 °C) when only a low stress can be sustained in the films, power-law creep is important at intermediate temperatures and determines the maximum compressive stress, and that if yield by dislocation glide (low-temperature plasticity) occurs, it will do so only at the lowest temperatures (<100 °C). This last mechanism did not appear to be operating in the film studied for this project.

The longitudinal ultrasonic velocities of four commercial aluminum alloys and Al(1.8 wt.% Si) were measured between room temperature and the solidus temperatures. In all of the samples, the velocity deviated significantly from a linear temperature dependence at the highest temperatures. In commercially pure (1100) aluminum, this effect is found to be consistent with reported low-frequency damping and elastic modulus changes that are associated with dislocations or grain boundaries. In the four heat-treatable alloys studied, an additional contribution to the nonlinear temperature dependence arises from the dissolution of precipitates at elevated temperatures. Irreversible velocity changes occur during the first heating, as a result of the recovery from work-hardening and heat treatments which were performed during the production of the material. Small hysteretic changes above ∼ 250 °C are correlated with the precipitation and dissolution of alloying elements. The activation energy for the hysteretic changes in Al(1.8% Si) is found to be 0.82 eV, which is consistent with precipitation limited by silicon diffusion along grain boundaries.

The formation of hillocks has been studied as a function of process parameter in patterned and unpatterned Al98.5wt. %Si1.0wt. %Cu0.5wt. % films deposited on chemical-vapor-deposited W-coated substrates. The effects of linewidth, substrate temperature during film deposition, and sintering time and temperature on hillock size were investigated. Three types of hillocks are found: the “surface hillocks”, the “side hillock”, and the “line hillock”. These are further classified by their shapes. The surface hillock and side hillock, which have been seen previously, form on patterned metal lines having linewidths greater than the larger Al alloy grain sizes (~3 μm). None is seen on linewidths between 0.9 and 2 μm where long-range grain boundary diffusion cannot occur. A new type of hillock, the line hillock, is seen to occur on metal structures having linewidths of 0.6 μm. The line hillock is inconsistent with the current understanding of hillock formation and may present severe restrictions on the downsizing of ultra-large-scale integrated devices.

A resonant frequency mechanical vibration method was used to nondestructively detect fatigue crack initiation in notched 304 stainless steel samples prepared by powder metallurgy. This method allowed the determination of an effective elastic modulus and the direct measurement of internal friction. Changes in the modulus and internal friction were found to correlate well with the presence of 50 μm long fatigue cracks. The length of the through cracks initiated at the notch was measured using surface replicas, which were examined in a scanning electron microscope. Small crack growth rate data were also obtained and plotted versus the stress intensity factor. The crack growth rates were compared with long crack data performed on compact tension samples of this material. The short cracks grew at intensity factors below the long crack threshold stress intensity factor.

A comparison of several solution syntheses with a solid-state route to the lead-containing high Tc phase of the Bi–Sr–Ca–Cu–O system has been performed using DSC, TGA, x-ray diffraction, electron microscopy, magnetic ac susceptibility, and critical-current measurements. A novel polymer solution synthesis route is shown to yield an increased percentage of the 2223 high Tc phase when sintering is performed at the low temperature end of this phase's stability range. Under the best preparative conditions given in the literature, however, the properties of samples obtained with the different synthetic methods described in the present study are shown to be similar. Samples derived from solution syntheses have been found to contain higher amounts of carbon precipitates, while samples derived from conventional solid-state synthesis contain CuO precipitates, according to energy dispersive spectroscopy analyses.

The utilization of tensile strength of carbon fibers in unidirectional carbon/carbon (C/C) composites was studied for a series of four mesophase-pitch-based carbon fibers in a carbon matrix derived from a polyarylacetylene (PAA) resin. The fibers had moduli of 35, 75, 105, and 130 Mpsi. Composite processing conditions ranged from the cured-resin state to various heat-treatment temperatures (HTT's) from 1100 to 2750 °C for the C/C's. Room-temperature tensile strength and modulus were measured for the various processing conditions, and were correlated with SEM observations of fracture surfaces, fiber and matrix microstructures, and fiber/matrix interphase structures. Fiber tensile strength utilization (FSU) is defined as the ratio of apparent fiber strength in the C/C to the fiber strength in an epoxy-resin-matrix composite. Carbonization heat treatment to 1100 °C results in a brittle carbon matrix that bonds strongly with the three lower modulus fibers, resulting in matrix-dominated failure at FSU values of 24 to 35%. However, the composite with the 130-Mpsi-modulus filament had an FSU of 79%. It is attributed to a combination of tough fracture within the filament itself and a weaker fiber/matrix interface. Both factors lead to crack deflection and blunting rather than to crack propagation. The presence of a weakened interface is inferred from observations of fiber pullout. Much of the FSU of the three lower modulus fibers is recovered by HTT to 2100 or 2400 °C, principally as a result of interface weakening, which works to prevent matrix-dominated fracture. With HTT to 2750 °C, there is a drop in FSU for all the composites; it is apparently the result of a combination of fiber degradation and reduced matrix stress-transfer capability.

Based on the results of Shiue and Lee [J. Appl. Phys. 70, 2947 (1991)], the effect of plastic zone and grain boundary on the dislocation emission criterion was investigated. The emission criterion is based on the concept of spontaneous emission. The critical stress intensity factor for dislocation emission increases with the increasing size of dislocation-free zone and the number of piled-up dislocations in the plastic zone, but decreases with increasing grain size. The ductile versus brittle behavior of material was determined by the competition of critical stress intensity factors for dislocation emission and crack propagation. A material with larger grain size is easier to emit dislocation and allows more dislocations to be piled up, so that it behaves more ductile.

During combustion/micropyretic synthesis, conditions that give rise to rapid solidification and rapidly solidified microstructures may be encountered. In this article, many such conditions are identified for the first time in a Ni–Al system. In addition, the banded structures and aligned dendrites that are encountered in this system are also examined. The various techniques of rapid solidification that may be initiated with combustion synthesis are examined and discussed.

Space groups and atomic coordinates for the 4H, 6H, 8H, 10H, 15R, and 21R polytypes of diamond are presented. The systematic method used to determine the highest symmetry space group for diamond polytypes is described.

A niobium beryllide, Nb2Be17, has been prepared by powder-metallurgy techniques and the mechanical properties characterized both at room and elevated temperatures. Microhardness and fracture toughness were measured at room temperature. Hardness and hot-hardness test results indicated that, although the material was brittle at low temperatures, it became plastic at elevated temperatures (>1000 °C). Creep properties of Nb2Be17 were studied at temperatures from 1250 to 1350 °C and applied stresses from 10 to 90 MPa. The stress exponent, determined from stress-change tests, was about 3, and the activation energy, determined from temperature-change tests, was about 575 kJ/mol. The creep of Nb2Be17 at high temperature is apparently controlled by dislocation glide; this proposal was supported by transient creep experiments. Comparisons have been made between the creep properties of Nb2Be17 and other intermetallics.

A simple model is described with which the entire force versus penetration behavior of indentation with a sphere, during loading and unloading, may be simulated from knowledge of the four test material parameters, Young's modulus, Poisson's ratio, flow stress at the onset of full plastic flow and strain hardening index, and the elastic properties of the indenter. The underlying mechanisms are discussed and the predictions of the model are compared with data produced by an ultra low load, penetration measuring instrument.

Optically generated thermal waves have been used to measure the thermal diffusivity of a unidirectional carbon fiber reinforced composite plate (CFRC) both parallel and perpendicular to the fiber direction. The optically generated thermal waves have been used in combination with a noncontact optical detection technique. The diffusivity perpendicular to the fiber direction can also be determined by attaching a pyroelectric detector to the back of the sample. The value obtained this way agrees well with the results from the optical detection technique. An anisotropy factor of about 18 has been measured for a unidirectional CFRC, which agrees well with literature values obtained with completely different techniques.

A Ni-Cr based hardfacing alloy has been plasma sprayed in ambient and low pressure atmospheres onto mild steel substrates. These coatings exhibit excellent wear and corrosion resistance; however, the significance of microstructure on properties has not been reported. This study relates the structure of the sprayed coatings to the processing conditions. X-ray diffraction results indicate phase separation in air plasma sprayed deposits, while low pressure plasma sprayed deposits exhibit a single supersaturated solid solution. Annealing of the air plasma sprayed coating shows dissolution of the bcc chromium phase, confirming its metastable nature. These results were confirmed using Extended X-ray Absorption Fine Structure (EXAFS) analysis, which further suggests a highly disordered structure, with partial oxidation of selected alloying elements, such as chromium. Transmission electron microscopy indicates a wide variety of microstructures in the air plasma sprayed deposit. In the case of low pressure sprayed deposit, the microstructures are homogeneous and uniform.

Precipitation of rhenium in β–NiAl was studied by analytical and high resolution electron microscopy. Extended solid solutions were created by solidification processing, and the precipitation and hardening behavior were studied. Evidence suggests that rhenium is initially precipitated as disks parallel to {100} of β-NiAl. Subsequent growth produces either a rod morphology or a pair of twin-related rods that form the shape of a butterfly. The twin plane of the butterfly is {1011} and this plane is nearly parallel to {110} of β–NiAl. A twinning transformation given by K1 = {1011}, K2 = {1013}, η1 = 〈1012 〉, and η2 = 〈3032〉 was determined for the butterfly-shaped particles. All of the precipitates exhibited an orientation relationship consisting of parallel close-packed planes and directions, i.e., (101//(0001) and [111]//[1210]. Performing the twinning transformation on a rhenium precipitate produces a variant rather than a new orientation relationship. After elevated temperature aging, a rod morphology was observed with the rod axes aligned parallel with either 〈121〉 or 〈131〉 of the β–NiAl matrix. A total of 24 different variants are possible based upon the observed orientation relationship and the two observed growth directions.

The dynamic behavior of a model for the passivation of a metal surface in contact with an aqueous solution is investigated. The model, which is characterized by a three-dimensional state space and five-dimensional parameter space, is obtained by combining elements from passivation models developed by Talbot and Oriani and by Sato. A three-dimensional subspace of parameter space has been studied; the remaining two dimensions are not thought to provide any additional interesting dynamics. The model exhibits remarkably rich dynamics, including the period-doubling, intermittency, and crisis routes to chaos, folds and bubbles in periodic portions of the attractor, and multiple attractors with complex, intertwined basins of attraction.

A digitization of the TEM pictures of fluorine-intercalated graphite fibers has been used to carry out quantitative measurements of the defect structure of this material. Emphasis is given to both the computer analysis technique and to the characterization of the defects. The amount of intercalation-induced disorder increases with increasing fluorine concentration. The fast Fourier transform of the digitized TEM image exhibits two diffuse spots, corresponding to the c-axis repeat distance of the intercalation compound. The length and width of the spots are a measure of the out-of-plane and in-plane disorder present in the fibers. From the fast Fourier transform, the distribution of interlayer repeat distances and the fraction of unintercalated graphite regions throughout the material is obtained. By selecting a small range of repeat distances and carrying out an inverse fast Fourier transform, the spatial distribution of material with a given repeat distance is determined. Regions with the same repeat distance are found to form islands. This particular feature of fluorine graphite intercalation compounds, as well as the nature of the microscopic defects and the staging behavior of fluorine-intercalated graphite fibers, are discussed in connection with the dual covalent and ionic nature of the carbon-fluorine bond in fluorine-intercalated graphite.

Earlier it was shown that some liquid metals may facilitate the cutting of hard materials, being strongly surface-active media with respect to these solids (decreasing their surface energy), e.g., Zn for steels, Cd for titanium alloys, etc. Recently, a similar physico-chemical principle has been proposed and realized in the course of active metals (Zn, Cd) depositing on the surface of a treated sample (ground tempered steel, 50 HRC) by means of reduction of their cations on a sample used as a cathode in a corresponding electrochemical cell, at room temperature, with a very small amount of active substance, and at very low current densities (∼50 mA/cm2); under such conditions, grinding is 1.5–2 times more effective than in the same aqueous solutions without current.