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Interparticle movement and the mechanical behavior of extruded powder aluminum at elevated temperature

Description: This paper proposes a model and mechanism, based on relative motion of the extruded aluminum particles, to explain these effects. Quantitative stereology is used to support the concept. Stress-strain relations are derived for the uniaxial and biaxial behavior of powder aluminum and they are seen to fit the data from a number of uniaxial and tension-torsion test specimens. Implications of the model for forming of extruded powder metal products are discussed
Date: September 1, 1996
Creator: Peacock, H.B.
Partner: UNT Libraries Government Documents Department

CRADA final report for CRADA number C/Y-1203-0211, gelcasting of soft ferrite parts

Description: Soft ferrite parts utilized in areas such as high-energy physics have been successfully gelcast from powders supplied by the industrial partner. To achieve this, several modifications were necessary. First, the as-received ferrite powder was heated to 300, 500 or 800{degrees}C. X-ray analysis showed no changes in the crystal structure of the heat-treated powder even at 800{degrees}C, and particle size distribution and surface area analyses indicated that powders heat treated at 300 and 500{degrees} had mean size and surface area similar to those of the as-received powder. Second, to prevent the parts from shattering during the combined binder burn-off and sintering cycle, the solids loading of the gelcasting slurry was adjusted from 42 vol % to at least 50 vol % and the sintering schedule was modified slightly. These modifications resulted in the production of fired gelcast soft ferrite parts (50 mm {times} 13 mm pucks, {approximately} 125 mm OD {times} 100 mm ID {times} 25 mm rings) which sintered to {approximately}98% of the theoretical density. The partner was satisfied with the parts it received and has discussed pursuing follow-up activities in order to gelcast more complex shapes and large toroids.
Date: March 1, 1996
Creator: Omatete, O.O. & Van Dillen, G.L., Jr.
Partner: UNT Libraries Government Documents Department

Gelcasting of silicon preforms for the production of sintered reaction-bonded silicon nitride

Description: Gelcasting of silicon metal for the production of sintered reaction-bonded silicon nitride (SRBSN) was investigated in order to identify associated advantages over conventional forming techniques, i.e., die and isostatic pressing. Compacts were formed from identical powder mixtures by both gelcasting and pressing, and were nitrided and sintered to produce SRBSN ceramics using both conventional and microwave heating. Characterization of the samples included measurement of green density, green and nitrided pore structure, weight gain during nitridation, final density, microstructure, toughness, and flexural strength. It was found that a more uniform pore structure existed in the green gelcast samples. It is believed that this pore configuration aided in nitridation, and manifested itself in a more uniform final microstructure. In addition, improved mechanical properties were achieved in the gelcast samples. This improvement can be attributed to green microstructure homogeneity. An additional finding of this study was that microwave hearing combined with gelcast forming resulted in SRBSN materials with improved mechanical properties.
Date: December 1995
Creator: Kiggans, J. O., Jr.; Nunn, S. D.; Tiegs, T. N.; Davisson, C. C.; Coffey, D. W. & Maria, J.P.
Partner: UNT Libraries Government Documents Department

THE FABRICATION OF HOLLOW CYLINDRICAL FUEL ELEMENTS FROM URANIUM POWDER

Description: A description is given of the die designs, dry boxes, loading cans, vacuum pots, and other experimental equipment used for fabricating hollow fuel slugs from uranium metal powder. The details of equipment operation are also given, including the die lubrication, die loading, pressing, and inspection procedures. (auth)
Date: June 1, 1954
Creator: Fugardi, J.; King, R.E. & McCullough, H.M.
Partner: UNT Libraries Government Documents Department

Texture evolution in upset-forged P/M and wrought tantalum: Experimentation and modeling

Description: Preferred orientations in polycrystalline materials can significantly affect their physical and mechanical response through the retention of anisotropic properties inherent to the single crystal. In this study the texture evolution in upset-forged PIM and wrought tantalum was measured as a function of initial texture, compressive strain, and relative position in the pressing. A <001>/<111> duplex fiber texture parallel to the compression axis was generally observed, with varying degrees of a radial component evident in the wrought material. The development of deformation textures derives from restricted crystallographic slip conditions that generate lattice rotations, and these grain reorientations can be modeled as a function of the prescribed deformation gradient. Texture development was simulated for equivalent deformations using both a modified Taylor approach and a viscoplastic self-consistent (VPSC) model. A comparison between the predicted evolution and experimental results shows a good correlation with the texture components, but an overly sharp prediction at large strains from both the Taylor and VPSC models.
Date: November 1, 1997
Creator: Bingert, J.F.; Desch, P.B.; Bingert, S.R.; Maudlin, P.J. & Tome, C.N.
Partner: UNT Libraries Government Documents Department

An Evaluation of Power Law Breakdown in Metals, Alloys, Dispersion Hardened Materials and Compounds

Description: Creep at high stresses often produces strain rates that exceed those that would be predicted by a power law relationship. In this paper, we examine available high stress creep data for pure metals, solid solution alloys, dispersion strengthened powder metallurgy materials and compounds for power law breakdown (PLB). The results show that, if PLB is observed, then the onset of PLB is generally observed at about {epsilon}/D{sub eff} = 10{sup 13} m{sup -2}, where D{sub eff} is the effective diffusion coefficient incorporating lattice and dislocation pipe diffusion. The common origins of PLB for the various systems studied can be found in the production of excess vacancies by plastic deformation. Anomalous behavior in two pure metals (nickel and tungsten) and a solid solution alloy (Fe-25Cr and Fe-26Cr-1Mo) has been analyzed and provides insight into this excess vacancy mechanism. In metal systems, the onset of PLB is related to a change in the nature of the subgrain structure developed. In the PLB region, subgrains become imperfect containing dislocation tangles adjacent to the sub-boundary, and dislocation cells are evident. The dislocation tangles and cells are the source of excess vacancies and increase the creep rate above that predicted from power law creep. If subgrains do not form then PLB is not observed. In solid solution alloys, in which the dominant deformation resistance results from the interaction of solute atoms with moving dislocations, excess vacancies influence the diffusion of these solute atoms. PLB is not observed in many systems. This is attributed either to the presence of a high equilibrium vacancy concentration (because of a low activation energy for vacancy formation) or to the inability to form subgrains.
Date: October 20, 1999
Creator: Lesuer, D.R.; Syn, C.K. & Sherby, O.D.
Partner: UNT Libraries Government Documents Department

Effect of Extrusion Temperature on the Microstructural Development of Powder Metallurgy Ti-47A1-2Cr-1Nb-1Ta Alloy

Description: Effect of extrusion temperatures on the microstructural development of a powder metallurgy (PM) Ti-47Al-2Cr-1Nb-1Ta (at. %) alloy has been investigated. Microstructure of the PM alloy extruded at 1150 C consists of a fine-grained ({gamma} + {alpha}{sub 2}) two-phase structure in association with coarse grains of metastable B2 (ordered bcc) phase. In addition, fine {omega} (ordered hexagonal) particles are also found within some B2 grains. The PM alloy containing the metastable B2 grains displays a low-temperature superplastic behavior, in which a tensile elongation of 310% is obtained at 800 C under a strain rate of 2 x 10{sup -5} s{sup -1}. It is suggested that the decomposition of metastable B2 phase and microstructural evolution during the deformation play a crucial role in the low-temperature superplasticity of the PM TiAl alloy. A refined fully-lamellar (FL) microstructure with alternating {gamma} and {alpha}{sub 2} lamellae is developed within the PM alloy extruded at 1400 C. The creep resistance of the refined FL-TiAl alloy is found to be superior to those of the TiAl alloys fabricated by conventional processing techniques. Creep mechanisms for the PM alloy with a refined FL microstructure are critically discussed according to TEM examination of deformation substructure.
Date: June 29, 2000
Creator: Hsiung, L. & Nieh, T.G.
Partner: UNT Libraries Government Documents Department

Simulation of coarsening during laser engineered Net-Shaping

Description: Laser Engineered Net-Shaping, otherwise known as LENS{trademark}, is an advanced manufacturing technique used to fabricate complex near net shaped components directly from engineered solid models without the use of dies or machining. The ultimate objective of this project is to develop predictive simulation capability which will allow the LENS{trademark} processors to determine fabrication conditions given the material, shape, and application of the final part. In this paper, the authors will present an incremental achievement to meeting the ultimate goal, a model capable of simulating the coarsening of microstructural features under the unique thermal history to which a LENS{trademark} part is subjected during processing. The simulation results show how grains of very different shapes and sizes form within the same deposition line. They also show that relatively minor changes in the dynamic temperature profile results in microstructures with vastly different characteristics. The implications of this work for LENS{trademark} fabrication is that controlling the temperature profile is essential to tailoring the microstructure of a component to its application.
Date: September 1, 1997
Creator: Tikare, V.; Griffith, M.; Schlienger, E. & Smugeresky, J.
Partner: UNT Libraries Government Documents Department

Applied mechanics modeling of granulated ceramic powder compaction

Description: In ceramic manufacturing processes such as dry-pressing, correlations between applied compacting pressure and resultant powder compact density are essential for defining reliable process conditions for ceramic components. Pressure-density diagrams have been developed as a tool for both process control and for understanding the compaction behavior of different powders. These types of diagrams, however, pertain only to the averag@ properties of a powder compact and do not address a significant issue in powder compaction processes: the formation of density gradients within the compact. Continuum-based mechanics models of varying complexity have addressed the influence of frictional forces acting at the powder-die wall interface which dissipate the applied pressure throughout the compact. Resulting pressure distribution models are then typically coupled with empirical functions relating pressure and density to obtain a green density distribution in the compact. All of these models predict similar trends; however, none predict the distribution with sufficient accuracy to be considered as a design tool for industrial applications.
Date: August 1, 1995
Creator: Mahoney, F.M. & Readey, M.J.
Partner: UNT Libraries Government Documents Department

Chem-Prep PZT 95/5 for Neutron Generator Applications: Powder Fractionation Study of Production-Scale Powders

Description: The Materials Chemistry Department 1846 has developed a lab-scale chem-prep process for the synthesis of PNZT 95/5, referred to as the ''SP'' process (Sandia Process). This process (TSP) has been successfully transferred to and scaled-up by Department 14192 (Ceramics and Glass Department), producing the larger quantities of PZT powder required to meet the future supply needs of Sandia for neutron generator production. The particle size distributions of TSP powders routinely have been found to contain a large particle size fraction that was absent in development (SP) powders. This SAND report documents experimental studies focused on characterizing these particles and assessing their potential impact on material performance. To characterize these larger particles, fractionation of several TSP powders was performed. The ''large particle size fractions'' obtained were characterized by particle size analysis, SEM, and ICP analysis and incorporated into compacts and sintered. Large particles were found to be very similar in structure and composition as the bulk of the powder. Studies showed that the large-size fractions of the powders behave similarly to the non-fractionated powder with respect to the types of microstructural features once sintered. Powders were also compared that were prepared using different post-synthesis processing (i.e. differences in precipitate drying). Results showed that these powders contained different amounts and sizes of porous inclusions when sintered. How this affects the functional performance of the PZT 95/5 material is the subject of future investigations.
Date: June 1, 2003
Creator: MOORE, DIANA L.; VOIGT, JAMES A.; WATSON, CHAD S.; MCKENZIE, BONNIE B.; MOORE, ROGER H.; HUTCHINSON, MICHAEL A. et al.
Partner: UNT Libraries Government Documents Department

Automated thermal treatment of metals with a mechanically fluidized vacuum machine. Final report

Description: The ERIP project {open_quotes}Automated Thermal Treatment of Metals with a Mechanically Fluidized Vacuum Machine{close_quotes} produced more benefits in unintended areas than in the original intent of the program. The first project was directed to heat treating of solid parts using a retort half filled with fine powder. The treatment of metal powders was not originally envisioned at the time of proposal preparation. This second application, where the powder itself is being treated, has turned out to be multi-billion dollar market in which the Mechanical Fluidized Vacuum machine can create revolutionary changes. Consequently most efforts in recent years have been dedicated to further growth of the powder markets. These efforts procured a second ERIP grant titled {open_quotes}Thermal Heat and Diffusion Treatment of Bulk Powders.{close_quotes}
Date: September 5, 1997
Creator: Kemp, W.E.
Partner: UNT Libraries Government Documents Department

Low temperature fabrication from nano-size ceramic powders

Description: The objective of the compaction process is to produce a dense green-state compact from a nanosize powder that subsequently can be sintered at high temperatures to form a dense ceramic piece. High density in the green-state after pressing is of primary importance for achieving high densities after sintering. Investigation of the compaction behavior of ceramic powders, therefore, is an important part of characterization of raw ceramic powders and evaluation of their compaction behavior, analysis of interaction between particles, and the study of microstructure of green body (unsintered) during pressure-forming processes. The compaction of nanosize ceramic particles into high density green bodies is very difficult. For the nanosize materials used in this study (amorphous Si{sub 3}N{sub 4} and {gamma} Al{sub 2}O{sub 3}), there is no evidence by TEM of partial sintering after synthesis. Nevertheless, strong aggregation forces, such as the van der Waals surface forces of attraction, exist and result in moderate precursor particle agglomeration. More importantly, these attractive surface forces, which increase in magnitude with decreasing particle size, inhibit interparticle sliding necessary for particle rearrangement to denser bodies during subsequent compaction. Attempts to produce high density green body compacts of nanosize particles, therefore, generally have been focused on overcoming these surface forces of attraction by using either dispersive fluids or high pressures with or without lubricating liquids. In the present work, the use of high pressure has been employed as a means of compacting nanosize powders to relatively high green densities.
Date: June 1, 1995
Creator: Gonzalez, E.J.; Piermarini, G.J. & Hockey, B.
Partner: UNT Libraries Government Documents Department

Dynamic compaction of tungsten carbide powder.

Description: The shock compaction behavior of a tungsten carbide powder was investigated using a new experimental design for gas-gun experiments. This design allows the Hugoniot properties to be measured with reasonably good accuracy despite the inherent difficulties involved with distended powders. The experiments also provide the first reshock state for the compacted powder. Experiments were conducted at impact velocities of 245, 500, and 711 m/s. A steady shock wave was observed for some of the sample thicknesses, but the remainder were attenuated due to release from the back of the impactor or the edge of the sample. The shock velocity for the powder was found to be quite low, and the propagating shock waves were seen to be very dispersive. The Hugoniot density for the 711 m/s experiment was close to ambient crystal density for tungsten carbide, indicating nearly complete compaction. When compared with quasi-static compaction results for the same material, the dynamic compaction data is seen to be significantly stiffer for the regime over which they overlap. Based on these initial results, recommendations are made for improving the experimental technique and for future work to improve our understanding of powder compaction.
Date: April 1, 2005
Creator: Gluth, Jeffrey Weston; Hall, Clint Allen; Vogler, Tracy John & Grady, Dennis Edward
Partner: UNT Libraries Government Documents Department

Oxide strengthened molybdenum-rhenium alloy

Description: Provided is a method of making an ODS molybdenum-rhenium alloy which includes the steps of: (1) forming a slurry containing molybdenum oxide and a metal salt dispersed in an aqueous medium, the metal salt being selected from nitrates or acetates of lanthanum, cerium or thorium; (2) heating the slurry in the presence of hydrogen to form a molybdenum powder comprising molybdenum and an oxide of the metal salt; (3) mixing rhenium powder with the molybdenum powder to form a molybdenum-rhenium powder; (4) pressing the molybdenum-rhenium powder to form a molybdenum-rhenium compact; (5) sintering the molybdenum-rhenium compact in hydrogen or under a vacuum to form a molybdenum-rhenium ingot; and (6) compacting the molybdenum-rhenium ingot to reduce the cross-sectional area of the molybdenum-rhenium ingot and form a molybdenum-rhenium alloy containing said metal oxide. The present invention also provides an ODS molybdenum-rhenium alloy made by the method.
Date: December 1, 1998
Creator: Bianco, Robert & Buckman, William R. Jr.
Partner: UNT Libraries Government Documents Department

In-Reactor Monitoring of Zircaloy-2 Plutonium Recycle Test Reactor Pressure Tubes: Part 2, May and June, 1962

Description: Report containing the results of a two year program wherein the 85 zircaloy-2 pressure tubes in Hanford Laboratories' Plutonium Recycle Test Reactor (PRTR) were monitored. Experimental procedures and results are described.
Date: August 1962
Creator: Doman, D. R. & Pankaskie, P. J.
Partner: UNT Libraries Government Documents Department

Chem-Prep PZT 95/5 for neutron generator applications : development of laboratory-scale powder processing operations.

Description: Chemical synthesis methods are being developed as a future source of PZT 95/5 powder for neutron generator voltage bar applications. Laboratory-scale powder processes were established to produce PZT billets from these powders. The interactions between calcining temperature, sintering temperature, and pore former content were studied to identify the conditions necessary to produce PZT billets of the desired density and grain size. Several binder systems and pressing aids were evaluated for producing uniform sintered billets with low open porosity. The development of these processes supported the powder synthesis efforts and enabled comparisons between different chem-prep routes.
Date: December 1, 2003
Creator: Montoya, Ted V.; Moore, Roger Howard & Spindle, Thomas Lewis Jr.
Partner: UNT Libraries Government Documents Department

Exo-Melt{trademark} process for intermetallic powders

Description: The methods of powder production for intermetallics are reviewed. An innovative method known as Exo-Melt{trademark} is described for producing molten aluminides for gas- and water-atomization processes that require a molten metal stream. The Exo-Melt{trademark} process is based on the effective utilization of the heats of formation of aluminides from their constituent elements. The Exo-Melt{trademark} process principles are discussed along with a description of a furnace-loading sequence that uses the principles for practical applications. The benefits of the Exo-Melt{trademark} process are compared with the problems associated with the conventional melting process.
Date: June 1, 1996
Creator: Sikka, V.K. & Deevi, S.C.
Partner: UNT Libraries Government Documents Department

Microstructure Development During Sintering of TiC-Ni3A1 Cermets

Description: TiC-Ni{sub 3}Al cermets are under development for application in diesel engines because of desirable physical properties and wear resistance. Powder compacts with binder contents from 30-50 vol. % were fabricated by pressureless sintering under vacuum followed by low gas pressure isostatic pressing. Increasing the Ni{sub 3}Al content improved densification when using prealloyed powders as expected. However, when the Ni{sub 3}Al was formed by in-situ reaction synthesis of Ni and NiAl, densification decreased with higher binder contents. The final microstructure consisted of a ''core-rim'' structure with TiC cores surrounded by (Ti,W)C rims. In some cases, Ni and Al were also observed in the peripheral region of the rim structure. Grain sizes of the TiC increased with binder content and temperature. Preferred orientation of the Ni{sub 3}Al binder phase was observed due to very large grain sizes on the order of millimeters.
Date: October 22, 2001
Creator: Tiegs, T.N.
Partner: UNT Libraries Government Documents Department

Storage of hydrogen in powders with nanosized crystalline domains

Description: The term nanostructured materials is being used in the literature to denote different materials prepared by different techniques: (a) by the gas condensation of vapors in a partial vacuum and (b) by mechanical alloying, a high energy ball milling technique. The authors discuss the origin of this confusion and propose a differentiating nomenclature. They then discuss the use of particles with nanosized structures for the storage of hydrogen.
Date: September 1997
Creator: Schwarz, R. B.
Partner: UNT Libraries Government Documents Department

Directed light fabrication of refractory metals

Description: Directed Light Fabrication (DLF) is a metal, rapid fabrication process that fuses metal powders to full density into a solid replica of a computer modeled component. It has been shown feasible for forming nearly any metal and also intermetallics to near net shape with a single process. DLF of refractory pure metals is feasible, bypassing the extensive series of conventional processing steps used for processing these high melting point materials. Tungsten, tantalum, and rhenium were processed and show a continuous resolidified microstructure. Porosity was a problem for the tantalum and rhenium powders produced by chemical reduction processes but not for the tungsten powder spherodized in a plasma arc. Chemical analysis of powder compared to the DLF deposit showed reductions in carbon, oxygen and hydrogen, indicating that process parameters may also be optimized for evolution of residual gases in the deposits.
Date: November 1, 1997
Creator: Lewis, G.K.; Thoma, D.J.; Nemec, R.B. & Milewski, J.O.
Partner: UNT Libraries Government Documents Department