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Atomic-layer 2D crystals have unique properties that can be significantly modified through interaction with an underlying support. For epitaxial graphene on SiC(0001), the interface strongly influences the electronic properties of the overlaying graphene. We demonstrate a novel combination of x-ray scattering and spectroscopy for studying the complexities of such a buried interface structure. This approach employs x-ray standing wave-excited photoelectron spectroscopy in conjunction with x-ray reflectivity to produce a highly resolved chemically sensitive atomic profile for the terminal substrate bilayers, interface, and graphene layers along the SiC[0001] direction., Published in Physical Review Letters, v111 p215501-1/215501-5, 2013.

The functionality of NiO interfacial layers in enhancing bulk heterojunction (BHJ) organic photovoltaic (OPV) cell performance is investigated by integrated characterization of the electrical properties, microstructure, electronic structure, and optical properties of thin NiO films grown on glass/ITO electrodes. These NiO layers are found to be advantageous in BHJ OPV applications due to favorable energy band levels, interface passivation, p-type character, crystallinity smooth surfaces, and optical transparency. The NiO overlayers are fabricated via pulsed-laser deposition and found to have a work function of 5.3 eV. They are investigated by both topographic and conductive atomic force microscopy and shown to passivate interfacial charge traps. The films also have an average optical transparency of 80% in the visible range, crucial for efficient OPV function, and have a near-stoichiometric Ni:O surface composition. By grazing-incidence X-ray diffraction, the NiO thin films are shown to grow preferentially in the (111) direction and to have the fcc NaCl crystal structure. Diodes of p-n structure and first-principles electronic structure calculations indicate that the NiO interlayer is preferentially conductive to holes, with a lower hole charge carrier effective mass versus that of electrons. Finally, the implications of these attributes in advancing efficiencies for state-of-the-art OPV systems--in particular, improving the open circuit voltage (VOC)--are discussed., Published in Chemistry Materials v23, p2218 2226, 2011. Supported in part by NSF-ECS-0609064, DE-SC0001059.

Metal oxide semiconductor field-effect transistors, formed using silicon dioxide and silicon, have undergone four decades of staggering technological advancement. With fundamental limits to this technology close at hand, alternatives to silicon dioxide are being pursued to enable new functionality and device architectures. We achieved ferroelectric functionality in intimate contact with silicon by growing coherently strained strontium titanate (SrTiO3) films via oxide molecular beam epitaxy in direct contact with silicon, with no interfacial silicon dioxide. We observed ferroelectricity in these ultrathin SrTiO3 layers by means of piezoresponse force microscopy. Stable ferroelectric nanodomains created in SrTiO3 were observed at temperatures as high as 400 kelvin., Published in the Journal of Science, v324 p367-370, 17 April 2009.

Our Materials Engineering for Affordable New Systems (MEANS) program was centered on developing an integrated computational framework for predicting the conditions under which turbine blades can be produced that are free of deleterious solidification defects. We studied the solidification process over length scales from subnanometer to millimeter and produced a theory for defect formation. Close interaction with industry was necessary to ensure the resulting computational model will be in a form that is usable in their efforts to design new alloys and processing routes. Given the broad research focus of the project the MEANS team was composed of engineers and scientists from government laboratories, industry, and universities and is diverse in its research expertise. Our accomplishments include: Accurate prediction of liquid metal densities using ab initio molecular dynamics, development of a criterion for the stability of flows in mushy zones with heat loss, measurement of permeability of mushes using three-dimensional reconstructions, and measurement of the composition of the liquid and solid phases in mushy zones., The original document contains color images. All DTIC reproductions will be in black and white.

An analytical model for dry friction using a combination of dislocation drag and solid-solid interface theory was developed. This model, with no adjustable parameters, gives semi-quantitatively correct numbers for experimental friction coefficients in ultra-high vacuum, and is also consistent with a number of other experimental finding ranging from the formation of contact layers to temperature dependence. Experiments on macroscopic single crystals to explore the angular dependence of solid-solid friction were performed, and found to be consistent with theoretical predictions albeit complicated by noise in the measurements.

The equilibrium core structure of an isolated a/2<110?111! screw dislocations is calculated using a first-principles pseudopotential-planewave method within the Local Density Approximation of Density Functional Theory. In this work the local dislocation strain field is self-consistently coupled to the long-range elastic field using a flexible boundary condition method. This ab-inition adaptation of the Greens Function Boundary Condition method makes it possible to stimulate the dislocation in a very small periodic cell without compromising the fidelity of the final core configuration. Supercells of 210, 288, and 420 atoms are used to evaluate the local screw and edge displacement of a straight a/2<110?111! screw dislocations in y-TiAl. The predicted dislocation core is non-planar with significant portions of the dislocation core spread on conjugate ?111! glide planes. By applying a pure (111) shear stress the lattice friction stress is estimated to be approximately 0.006 micro in reasonable agreement with experimental observations. The non-planar character of the dislocation core suggests that the dislocation is sessile, and would readily glide on either of two ?111! slip planes. The dislocation core also produces small but significant edge components that are expected to interact strongly with non-glide (e.g., Escaig) stresses producing significant non-Schmid behavior., The original document contains color images. Performed in cooperation with UES Inc., Dayton, OH.

The temperature evolution of the magnetization depth profile in Gd layers of a strongly coupled fGds50 d/Fes15 dg15 multilayer is studied using x-ray resonant magnetic scattering (XRMS) and x-ray magnetic circular dichroism (XMCD) techniques. XRMS yields a spatially resolved, element-specific, magnetization depth profile, while XMCD spatially averages over this profile. The combined data inequivocally show the presence of an inhomogeneous magnetic profile within the Gd layers at all measured temperatures between 20 and 300 K. These inhomogeneous profiles, which feature enhanced magnetic ordering near the Gd/Fe interface, were refined using both a kinematic Born approximation and a recently developed distorted-wave Born approximation, both of which include the contribution of structural and magnetic interfacial roughness. Calculations of the static magnetic configuration within a mean-field approach that neglects interfacial roughness are in agreement with the measured inhomogeneous profile and its temperature evolution. The results suggest that the enhanced Gd magnetization near the interface arises from its proximity to magnetically ordered Fe., Pub. in Physical Review B., v70, p134420-1/134420-10, 2004.

The combination of bottom-up and top-down processes to organize nanophases in hybrid materials is a key strategy to create functional materials. We found that oxide and sulphide nanocrystals become spontaneously dispersed in organic media during the self-assembly of nanoribbon supramolecular polymers. These nanoribbon polymers form by self-assembly of dendron rodcoil molecules, which contain three molecular blocks with dendritic, rod-like, and coil-like architectures. In an electric field these supramolecular assemblies carrying bound nanocrystals migrate to the positive electrode in an etched channel and align in the field. In the system containing ZnO nanocrystals as the inorganic component, both phases are oriented in the hybrid material forming an ultraviolet lasing medium with a lower threshold relative to pure ZnO nanocrystals.

The dielectric properties of high k dielectric thick films prepared by thermal spray were investigated. BaTiO3 and Ba(0.68)Sr(0.32)TiO3 thick films were deposited using plasma spray on Ag-Pd screen-printed alumina substrates. The sprayed films were predominantly polycrystalline but contained an amorphous second phase. The dielectric constants of the films decreased with decreasing film thickness in 10 approx. 60 micrometer range. This was attributed to the presence of an interfacial layer between the film and the substrate as determined by capacitance measurements. The capacitance density of the interfacial layer was determined to be approx. 2.7 nF/sq cm. The capacitance density of the interfacial layer increased to 12 nF/sq cm after post heat treatment at 500 deg. C for 20 hours., This article is from the Mat. Res. Soc. Symp. Proc. Vol. 758 p85-60, 2003. Prepared in cooperation with Dept. of Materials Science and Engineering, SUNY-Stony Brook, NY. This article is from ADA417756 Materials Research Society Symposium Proceedings, Volume 758 Held in Boston, Massachusetts on December 3-5, 2002. Rapid Prototyping Technologies

Processing of bulk metallic glass (BMG) foams, using melt infiltration techniques, is reported for the first time. Foaming methods based on infiltration of two types of pattern materials are described: investment of a continuous refractory yielding very low relative density structures (5% dense relative to the BMG), and investment of a discontinuous refractory pellet bed yielding higher relative density (50-60% dense relative to the BMG). Both methods are capable of producing foam structures; however high surface area and diminished thermal conductivity, especially in lower density structures, make vitrification of the alloy difficult.

This project focuses on optimizing/understanding the growth and properties of YBCO, TBCCO, and lattice-matched dielectric films as well as YBCO superlattices by MOCVD and POMBE. Emphasis is on bulk film properties as well as film growth, interface evolution, and in situ studies of film growth processes. The objective of this program is to create via novel means and to understand the properties of interfacial growth regions between films of high-temperature superconducting (HTS) materials and insulating metal oxides. Improving the nature of such interfaces is a crucial barrier which must be surmounted before HTS materials can be successfully incorporated on a large scale into a myriad of advanced active and passive electronic device technologies. In addition, low melting-point advanced precursors are to be designed and synthesized for large scale HTS production. Studies of vapor transport properties and stabilities are carried out to assure that these precursors are of HTS manufacturing quality.

This supplemental grant was used to purchase a badly needed workstation for modeling of quantitative electron diffraction patterns from surfaces. The equipment purchased was an Hewlett-Packard 715/75 workstation. For reasons which are not completely clear, this computer ended up costing $58.78 less than the quote from Hewlett-Packard upon which the proposed budget was based. In addition to providing additional computing power for calculating diffraction patterns from surfaces, it also opened up completely new areas. Perhaps the most exciting of these is compute intensive image filtering based around Wiener filters 4-5 which have allowed us to directly resolve atomic surface structures at a resolution of better than 0.25 nm 1,3,6. We have also used these new filter methods of image restorations in a very large number of cases for work both directly supported by AFOSR and by other agencies. It is realistic to state that with these filters we have almost completely abandoned dark-room chemical printing for digital processing images, at a substantial long-term reduction in costs. jg p.3

The development of techniques for real-time in-situ imaging of surfaces and for spatially resolved spectroscopic imaging of surfaces is reviewed. The capabilities of Field-Ion Microscopy, In-Situ Transmission Electron Microscopy, Low-Energy Electron Microscopy, Point Projection Microscopy, In-Situ Scanning Electron Microscopy, NearField Scanning Optical Microscopy, Photo-emission Electron Microscopy, Plane-View Transmission Electron Microscopy, Reflection Electron Microscopy, Scanning Electron Microscopy with Polarization Analysis, Scanning Micro-cathodoluminescence, and Scanning Tunneling Microscopy are summarized. Surface structure, Imaging, TEM, STM, LEEm, PEEm, SEM, STEM, Prepared in cooperation with University of Maryland, College Park.

Thin solid films of C(60) and C(70) have been used as nucleation layers for the growth of diamond thin films on a variety of substrate surfaces, including metal, insulator and semiconductors. Compared to other forms of carbon, such as graphite, amorphous carbon, soot, etc. it is found that the nucleation density on C(70) is equivalent to that of diamond seeds themselves. On the other hand diamond nucleation of C(60) is less favorable. We argue from our experiments that the reason for C(70) to have such favorable nucleating properties is its chemical stability and geometry. A working model is proposed to explain the nucleation of diamond on solid C(70) films. Application of this work extending to the growth of diamond on a wide range of substrates is also discussed. Diamond nucleation, Carbon clusters.

Amorphous diamond films have been synthesized by pulsed excimer (ArF) laser ablation of graphite at room temperature. Detailed studies of the energy- dependent complex dielectric function in the energy range up to 40 eV have been carried out by Kramers-Kronig dispersion analysis of transmission electron energy loss spectroscopy and spectroscopic ellipsometry. Distinct from those of graphitic amorphous carbon and diamond-like carbon, the optical constants of amorphous diamond films are closely related to that of crystalline diamond, but with a smooth band structure, a decrease in the magnitude strength, and band shift towards lower energies. The variation of dielectric function from crystalline diamond to amorphous diamond is analogue to those of crystalline and amorphous semiconductors such as Si and Ge. The extracted optical energy band gap reaches 2.6 eV, the highest value among the reported results of amorphous carbon films. The implication of dielectric function to the bond structure analysis of a-D films has also confirmed its diamond character. All of these provide further evidence of the existence of amorphous diamond....Dielectric function, Amorphous diamond, Laser ablation.

Microwave plasma-enhanced chemical vapor deposition of diamond films on silicon carbide and tungsten carbide (with 6% cobalt) surfaces using fluorocarbon gases has been demonstrated. No diamond powder pre-treatment is necessary to grow these films with a (100) texture. The diamond films are characterized by scanning electron microscopy and Raman spectroscopy. The proposed nucleation and growth mechanism involves concurrent etching of the non- carbon component by atomic fluorine and deposition of diamond. Hydrogen is necessary in the growth process to limit the rapid etching of the substrate by fluorine atoms.

The objective of this research was to investigate the interface properties nee or successful metal matrix composites. Thermodynamic stability of the interface and the phases in the composite, nature of the bonding across the interface, and the energy and structure of the interface were studied. With TiC dispersed in Al prepared by the XD process, atomic resolution electron microscopy showed a sharp interface with large areas of partial coherence. The Al-TiC composite is remarkably ductile even at 15 vol.% TiC loading. This attributed to the ability of the Al to recrystallize at the interface forming semicoherent boundaries and to a high level of metallic binding between Al and Ti in TiC. On holding at 640 C the kinetics of the reaction, 13Al + 3TiC - A14C3 + 3Al3Ti, is rapid enough to be observed. This reaction leads to a substantial increase in strength and modulus but a reduction in ductility. Like steel, parts could be formed in the ductile state and then heat treated to increase hardness and modulus. At still higher temperatures, Al and TiC are the thermodynamically stable phases so no reaction occurs. Four Mg alloy matrix composites were received from Dow Chemical Corp.: Mg-6% Zn with SiC, Mg-3% Ce-l% Mn with SiC, Mg-9% Al-l% Zn with SiC, and Mg-9% Al-l% Zn with A12O3. All particle matrix interfaces appeared to be incoherent.

Second harmonic generation measurements were performed using 1.064 micro pulses provided by a ND:YAG laser. A bulk second-order susceptibility esu was observed at room temperature, which is about 1.5 times the X2 value of quartz. X2 values in a poling field were studied as a function of temperature; the largest value occurred at a nominal temperature of 140 degC where X2 is ten times larger than the room temperature value.

The nucleation and growth of diamond crystals on single crystal copper surfaces has been studied. Microwave plasma enhanced chemical vapor deposition (MPECVD) was used for diamond nucleation and growth. Prior to diamond nucleation, the single crystal copper surface is modified by carbon ion implantation at an elevated temperature (-820 C). This procedure leads to the formation of a graphite film on the copper surface, resulting in the great enhancement of diamond crystallite nucleation. A simple lattice model has been constructed to describe the mechanism of diamond nucleation on graphite as <111> parallel to <0001> and <110> parallel to <1120>. This leads to a good understanding of diamond growth on carbon-implanted copper surfaces., Prepared for publication in Journal of Materials Research

The nucleation and growth of diamond crystals on single crystal copper surfaces implanted with carbon ions has been studied. Microwave plasma enhanced chemical vapor deposition was used for diamond growth. The single crystal copper substrates were implanted either at room temperature or at elevated temperature (-820 degC) with carbon ions prior to diamond nucleation. This procedure leads to the formation of a graphite film on the copper surface which greatly enhances diamond crystallite nucleation. From our study we construct a simple lattice model for diamond growth on graphite as <111> parallel to <0001> and <110> parallel to <1120>. Nucleation, Diamond growth mechanism, Carbon-implanted, Copper crystals.

We have deposited hydrogen-free diamond-like amorphous carbon (amorphous diamond) films by ArF (193 nm) pulsed laser ablation of graphite. The deposition process is performed with the laser power density of only 5x10(8) W/cm2 at room temperature without any auxiliary energy source incorporation. The resulting films possess remarkable physical, optical and mechanical properties which are close to those of diamond and distinct from the graphite target used. The films have a mechanical hardness up to 38 GPa, an optical energy band gap of 2.6 eV and excellent thermal stability. Analysis of electron energy loss spectroscopy reveals the domination of diamond-type tetrahedral bonding structure in the films with the Sp3 bond fraction over 95%. Compared to other reported results of pulsed laser deposited diamond-like carbon films, our experimental results confirm that the laser wavelength or photon energy plays a crucial role in controlling the properties of the pulsed laser deposited diamond-like carbon films., Submitted for publication in the Journal of Materials Research.

The results of a comparison study of continuous diamond coatings deposited on tungsten carbide-6% cobalt tool inserts using CF4, and CH4, gas sources are presented. The CH4, grown diamond film utilizes a thin (1200 A) amorphous silicon interlayer for adhesion while the CF4, diamond film is deposited directly onto the tool insert. Diamond films produced with CF4, gas have much higher growth rates and better adhesion than diamond films grown with CH4, gas. The films are characterized by scanning and transmission electron microscopy, and Raman spectroscopy to determine film crystallinity and quality. Macroscopic indentation tests have been conducted to determine the adhesion of the films to the substrate, and an aluminum-17 % Si alloy is machined with the diamond-coated tool inserts to determine their performance in a machining environment. A mechanism for the growth of diamond on tungsten carbide-cobalt using CF4, gas is postulated., Submitted for publication in Surface and Coatings Technology.

Diffraction remains the premier tool for sampling the residual stresses in materials non destructively, the only one capable of determining the entire stress tensor, and with few assumptions. The technique has kept pace with the needs of researchers in the area of multiphase materials; now, the stresses can be separated into macro and micro components. The deviatoric macro and micro stress components and hydrostatic macrostress can be measured without knowledge of the unstressed lattice parameter. Bond strength of film and fiber and the yield stress can be examined by cooling samples, and there are new developments that enable gradients to be determined.

Ceramic rods have been sintered in cold wall single mode microwave cavities under a variety of conditions, including microwave heating and plasma heating. High sintering rates, high density and fine grain sizes were achieved for Beta-alumina and A12O3-TiC composites under favorable conditions. Thermal run-away often was observed in alumina during microwave heating if the heating rate was more than a few degrees per second. On the other hand, microwave plasma sintering of alumina was accomplished at very high heating rates (100 K/s)., This article is from 'Ceramic Transactions. Volume 21. Proceedings of the Symposium on Microwave Theory and Application in Materials Processing Annual Meeting of the American Ceramic Society (23rd) Held in Cincinnati, Ohio on April 29 - May 3, 1991,' AD-A253 631, p17-28.

We report for the first time that diamond composite films consisting of diamond particles, hydrogenated amorphous carbon, and/or fluorocarbon films can be successfully deposited on carbon steel and 304 stainless-steel substrates by plasma-assisted chemical vapor deposition. The use of thin silicon buffer layer proves to be effective in inhibiting surface catalytic effect of iron and also prevents carbon species from diffusing into the bulk. The composite films adhere well to the substrates even upon imposing a scratch load of 68 neutrons. They can also be bent up to 10 and still remain chemically inert and impermeable to salt solution. One of the potential applications of these films is for protective coating on sheet metal surfaces.

The thermogravimetric method is used to study the oxidation properties of plasma grown diamond films both with and without fluorine. The oxidation experiments are carried out over a temperature range of 600 C - 800 C and in pure oxygen at one atmospheric pressure. Our experiments show diamond films with fluorine are more resistant (by as much as a factor of 4 at 700 C) to oxidation. The activation energy for oxidation, on the other hand, is at least a factor of 2.3 lower for diamond films with fluorine. These results lead us to postulate that oxidation mechanisms for diamond films are quite different depending on whether there is fluorine or not. For diamond films without fluorine the oxidation seems to proceed as a rate limited reaction, while for films with fluorine the oxidation seems to be a diffusion limited reaction. There is also a weak dependence of oxidation rates on film density, crystal texture, and the phase composition of the diamond film.

Infrared and high resolution Raman spectroscopic probes of thin films of C60 and C70 are presented and discussed in terms of previous measurements, semi-empirical calculations and plausible molecular geometries.

Phase diagrams of the microphase morphologies for triblock copolymer melts are calculated for the weak segregation limit. The diagrams are found to be highly asymmetric with block copolymer composition., This article is from 'Multifunctional Materials Held in Boston, Massachusetts on November 29-December 1 1989. Materials Research Society Symposium Proceedings. Volume 175,' AD-A253 089, p345-350.

The objective of this research is to determine the interface properties needed for successful metal matrix composites and to learn how to achieve these properties. A number of factors have been selected for the study. These are thermodynamic stability of the interface, nature of the bonding across the interface, energy and structure of the interface, and role of adsorption at the interface. A number of systems have been chosen to probe these factors; namely, Al/TiC, Al/alpha-Al2O3, A1/MgAl2O4(spinel), Al/Al3(Tix, Zr1-x), Mg/SiC, Mg/MgO, and Mg/Al2O3. Techniques for preparing all of these composites have been worked out, including mechanical alloying followed by extrusion, arc melting, and liquid metal infiltration. MMCs also were obtained from Martin Marietta and Dow. Microstructures of the resulting MMCs are presented and discussed along with preliminary studies of some of the interfaces using transmission electron microscopy. In comparison to Al/SiC, Al/TiC and Mg/SiC show no evidence of chemical reaction at the interface during processing. Al/MgAl2O4(spinel) has superior mechanical properties to Al/alpha-AlO3, both prepared identically. (Author) (tr)

The stress tensors were measured with x-ray diffraction in both the ferrite and cementite phases of a 1080 steel specimen deformed in uniaxial tension. The macro- and micro-stresses were separated for all the components of the stress tensors. All the components except the hydrostatic components of the micro-stresses could be determined without an accurate value of the unstressed lattice parameter. Tensile stresses were found in the cementite and compressive stresses in the ferrite along the deformation direction. The tensile stresses in the cementite were quite large.

The objective of this research was to investigate two promising systems as the basis for high temperature aluminum alloys useful to 425 C (800 F). The first is a metal matrix composite consisting of an aluminum-magnesium alloy matrix reinforced by spinel (magnesium aluminate) particulate. The second system is Al3(ZrX), where X is vanadium or titanium dispersed in aluminum matrix. Here the lattice parameter of the Al3(ZrX) intermetallic particles nearly matches that of the matrix. Research on dilute alloys has shown a low coarsening rate for these intermetallics at 425 C. A study of aluminum alloys with a higher concentration of zirconium and vanadium was completed. The creep resistance at 410 C of the spinel composite was much better than that of the alumina composite. Extrusions containing 5 vol.% A13(V.75Zr.25) were prepared. The measured creep rate at 425 C is much lower than that of the current aluminum-iron-cerium alloys. An aluminum-vanadium intermetallic compound, however, forms at grain boundaries leading to a precipitate free zone which grows slowly at 425 C. Dilute alloys containing 1 vol.% A13(ZrTi) were then prepared and these show more promise than the aluminum-zirconium-vanadium alloys.

A low temperature (approx. 400 oC) plasma enhanced chemical vapor deposition process has been developed to grow diamond films for optical coatings application. Films with fine grains (< or = 3000 A) have been obtained by controlling diamond nucleation. The surface roughness of the films is on the order of 50-200. The optical transparency of the films is over 60% in the range of 0.6 micrometer wavelength, which is comparable to that of typed lla natural diamond. Using a block-on ring tribotester, it is found that the diamond films adhere well to quartz substrates.

Identifying the surface damage process, we studied two systems in some depth, TiO2 and NiO. In TiO2 there is a phase transition to TiO which spreads from the surface and is driven by oxygen desorption. This work provided the first indications that diffusion was the rate limiting step. In NiO there is no DIET, but knockon damage at higher voltages and two electron beam stimulated reaction one of which abstracts nickel and another reduction by carbon contaminants. (eg)

Experimental determination of the elastic constants is of fundamental importance in residual stress analysis with x-rays. Such constants are usually termed x-ray elastic constants. In certain materials changes have been observed in these elastic constants as a result of plastic deformation. However, since for some of such cases the d vs. sin psi plots used in the analysis were not linear, as predicted by theory, but oscillatory, the meaning of these variations was not fully understood. In this paper the meaning of x-ray elastic constants obtained from materials with oscillatory d vs. sin psi plots is examined. It is shown that x-ray diffraction analysis is a powerful tool that can be used to determine the effective elastic constants of the material under investigation, even when the material is inhomogeneous.

The microstructure of the aluminum base-iron-cerium and iron-molybdenum-vanadium alloys, which were developed for use up to 316 degrees centigrade, is not stable at 425 degrees centigrade (three-quarters of the absolute melting temperature of aluminum). Metastable dispersed phases are replaced by stable phases and particles of these coarsen rather rapidly with time. Creep loading accelerates these processes. Trialuminum-zirconium was predicted to be a preferable dispersed phase for strengthening aluminum for the 425 C temperature range because of good lattice matching with the aluminum matrix giving a low interfacial energy. This is true for the thermodynamically stable tetragonal phase but especially true for the metastable cubic phase. Dilute alloys were prepared by arc melting and these were aged to form precipitate dispersed phase. Substitution of vanadium for zirconium improved the lattice parameter matching for both cubic and tetragonal trialuminum-zirconium as well as increasing the stability of the cubic form. The coarsening rates of the particles at 425 C were 100 to 1000 times slower than for the aluminum-iron-cerium or molybdenum alloys, the aluminum-zirconium-vanadium alloy being better than the binary aluminum-zirconium alloy in this respect. These alloys are very promising as the basis for better high temperature aluminum alloys. (Author)

This report summarizes research on the determination of: (a) the dislocation densities of both edge and screw components using two positron annihilation techniques; and (b) the density of hydrogen traps by analysis of electrolytic permeation measurements. Dislocation densities of single crystal iron specimens deformed in three different manners were in good agreement with disclocation densities obtained by ETCH-PIT and TEM methods on the same specimens as well as being bracketed by three earlier TEM investigations. The positron lifetimes were 114 psec. in the trap-free bulk, 165 in an edge and 142 in a screw dislocation. The first two of these values are in good agreement with values obtained several previous authors using poorly characterized specimens. It had been assumed that positron trapping in a screw dislocation was very unlikely - so the value for the latter tyep of dislocation is an important result. The binding energies of a hydrogen atom to an edge was deduced to be 37.4 and to a screw is 25.6 KJ/mole. The density of hydrogen at different strains was in good agreement with the number of dislocation traps. The occupancy sites along the dislocation was approximately 20 percent.

The dispersed phases in the Al-8Fe, Al-10Fe-1.5Mo-1V, Al-8.8Fe-3.7Ce and Al-8.9Fe-6.9Ce RSP P/M alloys have been examined for composition and coarsening rate. Additionally, effects of prior heat treatment and deformation on particle coarsening have been studied. Energy dispersive spectroscopy on extracted particles from the Al-8Fe and Al-10Fe-1.5Mo-1V alloys in the as-received condition as well as after aging at 316 C indicated that the particles have compositions close to Al6Fe. In these two alloys, aging 240 hours at 425 C gives particles close to Al13Fe4 in composition. In A1-Fe-Ce alloys aged at 425 C, two kinds of particles are present with composition close to Al13Fe4 and Al10Fe2Ce. Some Al6Fe is seen in these alloys in the as-received condition and also after aging at 316 C. Overall coarsening rates of the dispersed phases indicate that at 375 and 425 C the Al-Fe-Mo-V alloy coarsens more slowly than the other three alloys. Creep deformation of the Al-8.8Fe-3.7Ce alloy enhances particle coarsening rates while no such effect is noted after fatigue deformation. A high temperature age preceding a low temperature age gives a stable microstructure at the lower temperature. The improved lattice matching previously observed in the equilibrium, tetragonal Al3(V0.875Zr0.125) over the unalloyed Al3Zr phase was also found in the respective metastable cubic phases. Originator-supplied keywords include: Ostwald ripening (coarsening); aluminum-iron cerium alloy; aluminum-zirconium-vanadium alloy; iron-molybdenum-vanadium alloy, and aluminum-molybdenum-vanadium alloy.

This project was an interdisciplinary effort attempting to quantify the relationships between the electrical and magnetic properties of transition metal oxides and their local defect arrangements. Highly specialized x-ray techniques were applied to establish defect structures in materials where electrical properties or magnetic properties were also studied. Quantum theoretical modelling of defect structures was also initiated.

In dispersion strengthened high temperature alloys the particle radius is theoretically predicted to be proportional to (Sigma DC sub 0 1/3 where sigma is the interfacial energy, D, the diffusivity, C sub 0 the solubility limit and t is time. Thus, information about sigma, D, and C sub 0 are needed to design and evaluate high temperature alloys. The A1-8Fe-3Ce alloy developed by Alcoa Research center is being studied on this basis. Assuming diffusion of iron is rate controlling, values of sigma are calculated indicating an incoherent interface; however, the coarsening is more complex than predicted by the simple theory. Low values of sigma are expected when there is good lattice matching across the interface. A13(Ti,Zr,Hf) is being studied seeking good lattice matching. A13,(Ti,Zr), A13(Ti,Hf), A13(Zr,Hf) have been studied to date and the best matching is obtained with A13(Ti0.75 Zr0.25) where the lattice mismatch between the compound and aluminum is 3-4%. (Author)

This objective of this research is to investigate two promising systems as th basis for high temperature aluminum alloys useful to 425 C (800 F). The first is metal matrix composite consisting of an aluminum magnesium alloy matrix reinforced by spinel (magnesium aluminate) particulate. The second system is tri aluminum (zirconium, vanadium) dispersed in aluminum matrix. Here the lattice parameter matches that of the matrix. Research on dilute alloys has shown a low coarsening rate for this intermetallic at 425 C. Study of more concentrated alloys is underway. A mechanical alloying liquid metal infiltration procedure for preparing specimens of the aluminum alloy matrix spinel composite has been worked out and specimens with 4 vol% spinel have been prepared. Also, 4 vol.% alumina composite samples were prepared for comparison. Spinel particles were within the aluminum alloys grains in contrast to the alumina which was at grain boundaries. The spinel composite had much better creep resistance at 410 C. Extrusions containing 5 vol.% tri-aluminum (0.75 vanadium, 0.25 zirconium) were prepared for this research by Lockheed-Palo Alto from rapidly solidified foil. The measured creep rate at 425 C is much lower than in the current aluminum-iron-cerium alloy. An aluminum vanadium intermetallic compounds, however, forms at grain boundaries leading to a precipitate free zone which grows slowly at 425 C. Keywords: Aluminum, High temperature alloys, Aluminum-zirconium-vanadium, Aluminum spinel.

The determination of residual stresses via x-ray diffraction is briefly reviewed, with particular emphasis on the triaxial stress state. A new method is proposed for determining the general stress tensor, which considerably reduces the variances of the stresses due to counting statistics and gradients. The procedure involves a generalized least square solution of strains measured at vario us tilts of the x ray beam to the sampled and a set of tilts not heretofore used is recommended to minimize these errors.

Research was conducted on Epoxy resins, the low temperature relaxation spectra of six epoxy resins was determined via thermally stimulated depolarization measurements. The effect of cross-linking and aging upon physical properties and fracture phenomena has been ascertained for the epoxy resin systems diglycidyl ether of butanediol, DGEB and 4-4' diaminodiphenyl sulfone, DDS. (Author)

High temperature alloys in order to maintain thier strength during long time exposure at high temperatures must have stable microstructures. The dispersed phase coarsening rates in the A1-7.5Fe-3.5Ce and A1-10Fe-1.5Mo-1V alloys, developed for high temperature applications, were compared at 475 and 575 C. To the extent that the average intercept length cubed, L3, is a linear function of time during isothermal aging, after an initial transient, the particle coarsening obeys the Lifshitz-Slyozov-Wagner theory. The interfacial energies estimated from the coarsening rates using the theory of particle coarsening show that the interfaces between the particles and matrix are high energy incoherent interfaces. The dispersed particles in the A1-10Fe-1.5Mo-1V alloy coarsen faster at both temperatures than the particles in the A1-7.5Fe-3.5Ce showing that the latter alloy is more stable at these temperatures. Since the diffusion in diffusion controlled coarsening usually occurs by a vacancy mechanism, plastic deformation should increase the rate of particle coarsening since plastic deformation increases the vacancy concentration. This has been confirmed in combined creep and coarsening studies with the A1-7.5Fe-3.5Ce alloy.