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Development and Evaluation of High-Temperature Tungsten Alloys : Summary Report

Description: Abstract: "Tungsten-rich alloys, developed for use at temperatures up to 2000F, exhibit ductility, fabricability and joinability not found in commercially-available materials. An envelope type of microstructure was produced in compositions containing at least 90 wt% tungsten by liquid-phase sintering of cold-pressed powders in hydrogen. At room temperature the alloys could be rolled extensively, and tensile elongations up to 25% were noted. Strength properties of a W-Ni-Fe base were improved by small quaternary additions. The ultimate tensile strength of a 90W-4.8Ni-3.2Fe-2Ru alloy was 46,700 psi at 2000F, compared to 30,000 - 35,000 psi for unalloyed tungsten or W-Ni-Fe; the 100-hour stress-rupture strength at 1600F was 15,000 psi. Excellent joints were produced by spot welding and localized induction heating. The oxidation resistance of unprotected 90 wt% tungsten compositions was not significantly affected by alloying."
Date: November 12, 1959
Creator: Holtz, F. C. & Van Thyne, R. J.
Partner: UNT Libraries Government Documents Department

Development and Evaluation of High-Temperature Tungsten Alloys : Final Report, October 1, 1960 - September 30, 1960

Description: This report summarizes investigations taken between October 1, 1959, to September 30, 1960 with the objectives of developing high-tungsten alloys which are readily fabricable into massive and complex shapes and which possess adequate strength for operation at temperatures up to 2000 F. Within this report, studies are divided into two main categories: alloy development and material fabrication techniques
Date: December 14, 1960
Creator: Holtz, F. C. & Van Thyne, R. J.
Partner: UNT Libraries Government Documents Department

Development and Evaluation of High-Temperature Tungsten Alloys : Quarterly Report No. 2, January 1, 1960 - March 31, 1960

Description: Abstract: "Room-temperature properties were determined for W-Ni-Fe-Ru base alloys containing Cr, Mo, Pd, and Ta; highest strength levels were found in W-Ni-Fe-Ru-Mo compositions. Annealing for 250 hours at 1600 F produced a precipitate in the matrix phase and increased hardness in some of the tungsten-base alloys under study. Oxidation tests at temperatures up to 2000 F showed that additions of Al, Cr, Mo, Pd, and Ti improved the oxidation resistance of the W-Ni-Fe base. A fused coating of AMS 4775 protected a 90W-6Ni-4Fe alloy for 72 hours in air at 2100 F."
Date: June 24, 1960
Creator: Holtz, F. C. & Van Thyne, R. J.
Partner: UNT Libraries Government Documents Department

Development and Evaluation of High-Temperature Tungsten Alloys : Quarterly Report No. 3, April 1, 1960 - June 30, 1960

Description: Abstract: "High-tungsten alloys were prepared by powder metallurgy techniques. Excellent strength and ductility at room temperature were found in the W-Ni-Mo-Ry system and in W-Ni-Fe alloys containing platinum and/or ruthenium. The effects of prolonged annealing at 1600 F on room-temperature properties were studied; W-Ni-Fe-Pt-Ru alloys were least affected by this treatment. Oxidation rates for most alloys at 2000 F were 2 to 4 times that of unalloyed tungsten; an exception was a W-Ni-Mo-Ru alloy which oxidized at 1/5 the rate of tungsten. Slip casting techniques and induction-sintering of loosely compacted powders were used to produce compacts of W-Ni-Fe materials having section thicknesses of 1 to 2 inches."
Date: August 10, 1960
Creator: Holtz, F. C. & Van Thyne, R. J.
Partner: UNT Libraries Government Documents Department

Development and Evaluation of High-Temperature Tungsten Alloys Quarterly Report: October-December 1959

Description: Abstract: "High-tungsten alloys were prepared by powder metallurgy techniques. Room-temperature strength properties were determined for W-Ni-Fe compositions with quaternary additions of Cr, Pd, and Ru; tungsten levels ranged from 80 to 94 wt%. Small (1-3 wt%) ruthenium additions were the most effective in improving strength. The oxidation resistance of a number of tungsten-base alloys was measured at 2000F. Quaternary W-Ni-Fe base alloys containing Al, Ru, Ti, and Zr were the most oxidation resistant, having values similar to unalloyed tungsten. Oxidation protection of a 90W-6Ni-4Fe material was accomplished by a fused coating of AMS 4775; the composite was tested for 482 hours in air at 2000F without damage to the base alloy."
Date: January 20, 1960
Creator: Holtz, F. C. & Van Thyne, R. J.
Partner: UNT Libraries Government Documents Department

Process Evaluation and Characterization of Tungsten Nitride as a Diffusion Barrier for Copper Interconnect Technology

Description: The integration of copper (Cu) and dielectric materials has been outlined in the International Technology Roadmap for Semiconductors (ITRS) as a critical goal for future microelectronic devices. A necessity toward achieving this goal is the development of diffusion barriers that resolve the Cu and dielectric incompatibility. The focus of this research examines the potential use of tungsten nitride as a diffusion barrier by characterizing the interfacial properties with Cu and evaluating its process capability for industrial use. Tungsten nitride (β-W2N) development has been carried out using a plasma enhanced chemical vapor deposition (PECVD) technique that utilizes tungsten hexafluoride (WF6), nitrogen (N2), hydrogen (H2), and argon (Ar). Two design of experiments (DOE) were performed to optimize the process with respect to film stoichiometry, resistivity and uniformity across a 200 mm diameter Si wafer. Auger depth profiling showed a 2:1 W:N ratio. X-ray diffraction (XRD) showed a broad peak centered on the β-W2N phase. Film resistivity was 270 mohm-cm and film uniformity < 3 %. The step coverage (film thickness variance) across a structured etched dielectric (SiO2, 0.35 mm, 3:1 aspect ratio) was > 44 %. Secondary ion mass spectroscopy (SIMS) measurements showed good barrier performance for W2N between Cu and SiO2 with no intermixing of the Cu and silicon when annealed to 390o C for 3 hours. Cu nucleation behavior and thermal stability on clean and nitrided tungsten foil (WxN = δ-WN and β-W2N phases) have been characterized by Auger electron spectroscopy (AES) and thermal desorption spectroscopy (TDS) under controlled ultra high vacuum (UHV) conditions. At room temperature, the Auger intensity ratio vs. time plots demonstrates layer by layer Cu growth for the clean tungsten (W) surface and three-dimensional nucleation for the nitride overlayer. Auger intensity ratio vs. temperature measurements for the Cu/W system indicates a stable interface up to 1000 ...
Date: August 2005
Creator: Ekstrom, Bradley Mitsuharu
Partner: UNT Libraries

Mechanical behavior of tantalum and tantalum-tungsten alloys: texture gradients and macro/micro-response

Description: We have examined the mechanical response of unalloyed Ta and Ta-W alloy annealed plates over a wide range of loadings. It was observed in general that Ta exhibits nonuniform mechanical behavior, for example, hourglassing of compression samples and multiple instabilities during tensile deformation. In contrast, the Ta-W alloys do not exhibit any unusual nonuniform behavior. This work presents data revealing the spatial distribution of texture in Ta and Ta-W alloys. Significant variations in texture both through the thickness and from one area of the plate to another were found to be characteristic of Ta. The dominant feature of the texture variations was found to be enhanced <111> crystal direction fractions at the center of the plate, with a decreasing fraction near the surface. We find that the variation in texture in the Ta-W alloys is substantially less than that seen in Ta with primarily a <100> cube texture throughout. This study suggest that the texture gradients are responsible for the nonuniform mechanical response of Ta and that the uniform behavior of the Ta-W alloys is a consequence of the absence of texture gradients.
Date: November 30, 1996
Creator: Lassila, D.H.; Schwartz, A.J.; LeBlanc, M.M. & Wright, S.I.
Partner: UNT Libraries Government Documents Department

Thermomechanical processing of tungsten-copper composites

Description: A tungsten-40 wt% Cu composite was consolidated by liquid-phase sintering and further processed to full density by a number of deformation methods. Fully dense materials were obtained by hot extrusion or cold rolling of the W-Cu composite. Subsequent processing by cold rolling, cold swaging, or hot swaging did not produce large changes in the aspect ratio of the W particles. The materials develop high hardness with small grain sizes of 5 {mu}m or less. The work-hardening, recrystallization, and grain growth of the material are characterized, and the hardness and tensile properties are related to processing parameters. Wire with tensile strengths up to 1120 MPa were produced. Further improvements in properties are anticipated with optimized processing parameters.
Date: May 1, 1996
Creator: Ohriner, E.K. & Bryskin, B.
Partner: UNT Libraries Government Documents Department

Directed Light Fabrication of Refractory Metals and Alloys

Description: This report covers work performed under Order No. FA0000020 AN Contract DE-AC12-76SN00052 for deposition of refractory pure metals and alloys using the Directed Light Fabrication (DLF) process and represents the progress in depositing these materials through September 1998. In extending the DLF process technology to refractory metals for producing fully dense, structurally sound deposits, several problems have become evident. 1. Control of porosity in DLF-deposited refractory metal is difficult because of gases, apparently present in commercially purchased refractory metal powder starting materials. 2. The radiant heat from the molten pool during deposition melts the DLF powder feed nozzle. 3. The high reflectivity of molten refractory metals, at the Nd-YAG laser wavelength (1.06{micro}m), produces damaging back reflections to the optical train and fiber optic delivery system that can terminate DLF processing. 4. The current limits on the maximum available laser power to prevent back reflection damage limit the parameter range available for densification of refractory metals. The work to date concentrated on niobium, W-25Re, and spherodized tungsten. Niobium samples, made from hydride-dehydride powder, had minimal gas porosity and the deposition parameters were optimized; however, test plates were not made at this time. W-25Re samples, containing sodium and potassium from a precipitation process, were made and porosity was a problem for all samples although minimized with some process parameters. Deposits made from potassium reduced tungsten that was plasma spherodized were made with minimized porosity. Results of this work indicate that further gas analysis of starting powders and de-gassing of starting powders and/or gas removal during deposition of refractory metals is required.
Date: May 14, 1999
Creator: Fonseca, J.C.; Lewis, G.K.; Dickerson, P.G. & Nemec, R.B.
Partner: UNT Libraries Government Documents Department

Electronic effects at interfaces in Cu-Cr, Mo, W, Ta, Re multilayers

Description: Interfacial electronic effects between Cu and the transition metals Cr, Mo, W, Ta, Re, are investigated by determining the strength of the white line absorption resonances on the L,,, edges of Cu in Cu{sub 5}/TM{sub 5} multilayers. X-ray absorption (XAS) was performed to study the white lines, which are directly related to the unoccupied states of Cu in the multilayers. The metallic multilayers are 2 mn in period and 200 mn in total thickness. Each period contains 5 monolayers of Cu and 5 monolayers of the transition metal: 40% of the atoms are at interfaces. These material pairs form ideal structures for the investigation of interfacial electronic effects as they form no compounds and exhibit terminal solid solubility. Only weak white lines are observed on the L3,2 edges of Cu since all the d-orbitals are filled. In the Cu/TM multilayers, however, we observed enhancement of the Cu white lines. We attribute this to the charge transfer from the `interfacial Cu atoms` d-orbital to the transition metal layers. Analysis of the white line enhancement enables calculation of the charge transfer from the Cu to the transition metal. Cu shows a charge transfer of about 0.03 electrons/interfacial Cu atom in Cu/Cr, 0.064 in Cu/Mo, 2048 0.35 in Cu/Ta, 0.17 in Cu/W , and 0.23 in Cu/Re. This charge transfer is consistent with the enhanced absorption energy of Cu on these materials as observed in thermal desorption experiments.
Date: April 1, 1998
Creator: Bello, A.F.; Van Buuren, T.; Kepesis, J.E. & Barbee, T.W., Jr.
Partner: UNT Libraries Government Documents Department

Topical Report Tantalum – 2.5% Tungsten Machinability Testing

Description: Protection Association (NFPA). NFPA 484, Standard for Combustible Metals, Chapter 9 Tantalum and Annex E, supplemental Information on Tantalum require cutting oil be used when machining tantalum because it burns at such a high temperature that it breaks down the water in a water-based metalworking fluid (MWF). The NFPA guide devotes approximately 20 pages to this material. The Kansas City Plant (KCP) uses Fuchs Lubricants Ecocut Base 44 LVC as a MWF. This is a highly chlorinated oil with a high flash point (above 200° F). The chlorine is very helpful in preventing BUE (Built Up Edge) that occurs frequently with this very gummy material. The Ecocut is really a MWF additive that Fuchs uses to add chlorinated fats to other non-chlorinated MWF.
Date: September 2, 2009
Creator: Lazarus, L. J.
Partner: UNT Libraries Government Documents Department

Deformation texture development in a model composite system

Description: Model composites fabricated with a polycrystalline copper matrix and continuous tungsten fibres were deformed in plane strain compression with the fibres perpendicular to the loading axis and parallel to the direction of zero strain. The development of texture in the matrix due to deformation was measured using x-ray diffraction. It was observed that the macroscopic texture development in the composite was weaker than for unreinforced copper. The pattern of deformation in the matrix was quantified using experimental measurements and finite element method calculations. By carefully sectioning the composite after deformation, texture measurements were conducted for regions which exhibited characteristic types of deformation. These measurements showed that there is a variety of local textures (some weaker, some stronger than the texture in the unreinforced matrix) which when summed give the result of a weak global texture. This result is in agreement with the predictions from the computer simulations of Bolmaro et al.
Date: May 1, 1995
Creator: Poole, W.J.; MacEwen, S.; Kocks, U.F. & Embury, J.D.
Partner: UNT Libraries Government Documents Department

Dynamic material properties of refractory materials: Tantalum and tantalum/tungsten alloys

Description: We have made a careful set of impact wave-profile measurements (16 profiles) on tantalum and tantalum-tungsten alloys at relatively low stresses (to 15 GPa). Alloys used were Ta{sub 97.5}W{sub 2.5} and Ta{sub 90}W{sub 10} (wt. %) with oxygen contents of 30--70 ppM. Information available from these experiments includes Hugoniot, elastic limits, loading fates, spall strength, unloading paths, reshock structure and specimen thickness effects. Hugoniot and spall properties are illustrated, and are consistent with expectations from earlier work. Modeling the tests with the Steinberg-Lund rate-dependent material model provides for an excellent match of the shape of the plastic wave, although the release wave is not well modeled. There is also a discrepancy between experiments and calculations regarding the relative timing of the elastic and plastic waves that may be due to texture effects.
Date: August 1, 1995
Creator: Furnish, M.D.; Chhabildas, L.C.; Lassila, D.H. & Steinberg, D.J.
Partner: UNT Libraries Government Documents Department

Fabrication and Testing of Full-Length Single-Cell Externally Fueled Converters for Thermionic Reactors

Description: Paper presented at the 29th IECEC in Monterey, CA in August 1994. The present paper describes the fabrication and testing of full-length prototypcial converters, both unfueled and fueled, and presents parametric results of electrically heated tests.
Date: August 1, 1995
Creator: Schock, Alfred
Partner: UNT Libraries Government Documents Department

The influence of tungsten alloying on the mechanical properties of tantalum

Description: In mechanical tests of tantalum-tungsten alloys with nominal tungsten contents between 0 and 10 wt % for strain rates between 0.000016 and 6800s{sup {minus}1} and temperatures between 77 and 400 K, the addition of tungsten noticeably reduces the strain-rate dependence of the flow stress of tantalum near yield. It also subtly alters the strain-rate behavior of the work hardening, making it more like that of copper, an fcc metal. These effects are reflected in the limiting strains for uniform plastic deformation calculated from our flow curves. For unalloyed tantalum, the instability strain appears to drop dramatically for strain rates in excess of approximately 0.005s{sup {minus}1}, whereas for tungsten bearing alloys, it remains unchanged or increases slightly. Tungsten alloys may therefore be preferable to unalloyed tantalum in applications that demand substantial ductility at high rates of strain. We briefly discuss possible mechanisms for plastic flow in tantalum and how they might be affected by tungsten additions to produce the effects we observe.
Date: February 3, 1994
Creator: Gourdin, W. H.; Lassila, D. H.; LeBlanc, M. M. & Shields, A. L.
Partner: UNT Libraries Government Documents Department

Tungsten-uranium penetrator target interaction

Description: Several studies performed in recent years have been directed at determining the penetration mechanism of long rod kinetic energy penetrators into Rolled Homogeneous Armor (RHA). Much of the work has centered on comparing U-0.75Ti and Tungsten Heavy Alloys (WHA), with the goal being to relate the superior ballistic performance of the uranium materials to a fundamental difference in penetration mechanisms. This has been found to be true, with the dominant mechanisms being adiabatic shear in U-0.75Ti and bulk deformation in WHA. Recent work has sought to achieve improvements in the ballistic performance of the tungsten materials via both mechanical property improvements and alloy modifications designed to bring about adiabatic shear. As an alternative, the authors propose the consideration of materials which utilize mechanisms other than bulk deformation and adiabatic shear to optimize ballistic performance. This paper will present the postmortem analysis of a uranium-20 vol% tungsten composite penetrator fired into RHA at 0{degrees} obliquity. The analysis shows that the penetration mechanism in this material is bulk heating and extensive co-melting of the target and penetrator at the penetration interface. The results of the analysis will then be compared to a similar analysis made of targets into which U-0.75Ti penetrators had been fired.
Date: October 1, 1994
Creator: Dunn, P. S. & Damkroger, B. K.
Partner: UNT Libraries Government Documents Department

Development of chromium-tungsten alloys

Description: Cr alloys containing 0-30 weight % W were investigated for their high temperature strength and oxidation resistance. These experimental alloys are intended for use in elevated temperature applications. Alloys were melted in a water-cooled, copper-hearth arc furnace. Microstructure of the alloys was studied using X-ray diffraction, scanning electron microscopy, and light microscopy. Meyer and Vickers hardness tests were utilized for measuring room temperature strength. A hot hardness tester with a spherical ruby indenter was used to study the strength of these materials between 800ºC and 1200ºC. A parabolic relationship was observed between load and indent size at all temperatures. On the other hand, decrease in hardness of the alloys with temperature was linear up to 1200ºC.
Date: March 1, 2004
Creator: Dogan, Omer N.; Alman, David E. & Hawk, Jeffrey A.
Partner: UNT Libraries Government Documents Department


Description: A Molybdenum--{sup 182}Tungsten (Mo-{sup 182}W) alloy was specified for an application that would ultimately result in the measurement of temperature and particle velocity during the steady state time following the shock loading of various materials. The {sup 182}W isotope provides a tag for the analysis of neutron resonance line shape from which the temperature may be calculated. The material was specified to have 1.8 atom percent W, with W-rich regions no larger than 1 {micro}m in size. Both the composition and W distribution were critical to the experiment. Another challenge to the processing was the very small quantity of {sup 182}W material available for the synthesis of the alloy. Therefore, limited fabrication routes were available for evaluation. Several synthesis and processing routes were explored to fabricate the required alloy components. First, precipitation of W onto Mo powder using ammonium metatungstate was investigated for powder synthesis followed by uniaxial hot pressing. Second, mechanical alloying (MA) followed by hot isostatic pressing (HIP) and warm forging was attempted. Finally, arc-melting techniques followed by either hot rolling or crushing the alloyed button into powder and consolidation were pursued. The results of the processing routes and characterization of the materials produced will be discussed.
Date: September 1, 1999
Partner: UNT Libraries Government Documents Department

Electrodeposited tungsten-nickel-boron: A replacement for hexavalent chromium

Description: Chromium, deposited from acidic solutions of its hexavalent ion, has been the rule for wear resistant, corrosion resistant coatings for many years. Although chromium coatings are durable, the plating process generates air emissions, effluent rinse waters, and process solutions that are toxic, suspected carcinogens, and a risk to human health and the environment. Tungsten-nickel-boron (W-Ni-B) alloy deposition is a potential substitute for hexavalent chrome. It has excellent wear, corrosion, and mechanical properties and also may be less of an environmental risk. This study examines the electroplating process and deposit properties of W-Ni-B and compares them with those of hexavalent chrome.
Date: April 1, 1995
Creator: Steffani, C. & Meltzer, M.
Partner: UNT Libraries Government Documents Department

Solid-state sintering of tungsten heavy alloys

Description: Solid-state sintering is a technologically important step in the fabrication of tungsten heavy alloys. This work addresses practical variables affecting the sinterability: powder particle size, powder mixing, and sintering temperature and time. Compositions containing 1 to 10 micrometer ({mu}M) tungsten (W) powders can be fully densified at temperatures near the matrix solidus. Blending with an intensifier bar provided good dispersion of elemental powders and good as-sintered mechanical properties under adequate sintering conditions. Additional ball milling increases powder bulk density which primarily benefits mold and die filling. Although fine, 1 {mu}m W powder blends have high sinterability, higher as-sintered ductilities are reached in shorter sintering times with coarser, 5 {mu}m W powder blends; 10{mu}m W powder blends promise the highest as-sintered ductilities due to their coarse microstructural W.
Date: October 1, 1994
Creator: Gurwell, W.E.
Partner: UNT Libraries Government Documents Department