Sponsored by: SMD Refractory Metals and Materials Committee and Jt. MDMD/EPD Synthesis, Control and Analysis in Materials Processing
Program Organizers: Andrew Crowson, U.S. Army Research Office, Research Triangle Park, NC; Edward S. Chen, U.S. Army Research Office, Research Triangle Park, NC; Prabhat Kumar, Cabot Corp, Boyertown, PA; Willam Ebihara, Picatinny Arsenal, Picatinny, NJ; Enrique J. Lavernia, UC Irvine, Irvine, CA
Monday, PM Room: A4-5
February 5, 1996 Location: Anaheim Convention Center
Session Chairpersons: Andrew Crowson, U.S. Army Research Office, Research Triangle Park, NC; Enrique Lavernia, University of California at Irvine, Irvine, CA
1:30 pm Invited
SPRAY ATOMIZATION AND DEPOSITION OF TANTALUM ALLOYS: Weidong Cai, Huimin Liu, Enrique J. Lavernia, Department of Chemical Engineering and Materials Science, University of California, Irvine, CA 92717. Roger H. Rangel. Department of Mechanical & Aerospace Engineering, University of California, Irvine, CA 92717
In previous numerical analysis, the droplet-gas interactions that are present during spray atomization and deposition of a Ta-2.5W alloy using N2 gas were investigated. The numerical results demonstrate that at any axial distance, the droplet velocity, temperature, cooling rate and solidification rate all exhibit a maximum at the spray axis, and decrease to a minimum at the periphery of the spray cone, except for the locations where solidification occurs. The droplets in the periphery region solidify within a shorter flight distance relative to those at the spray axis due to longer night time in the periphery. Hence, the microstructure of spray deposited materials is predicted to be fine in the edges of the deposits as a result of high cooling rates associated with small droplets. Accordingly, in the present paper, a comparison with the experimental results is performed. To accomplish this, the spray atomization and deposition of tantalum alloys is conduced on a specially designed elevated temperature spray atomization and deposition facility. The alloys are melted in an induction skull melting crucible and then poured into a tundish in which the melt is delivered through a nozzle to an atomizer where the melt is atomized. Following the atomization, the droplets impinge onto a water-cooled substrate and eventually form a deposit. The microstructure of as-sprayed deposits is then analyzed by using optical and electron scanning microscopy.
2:00 pm
TANTALUM PRODUCTION BY VACUUM MELTING PROCESSES: Trung Q. Luong, H.C. Starck, 45 Industrial Place, Newton, MA 02161-1951
Tantalum and tantalum alloy wrought products are extensively used in the chemical process industry and in high temperature vacuum furnaces. Tantalum parts typically possess high ductility, excellent corrosion resistance, and very high melting temperatures. These properties can be enhanced or reduced by varying the amount of contained interstitial and other alloying elements. Careful control of operating parameters is critical in optimizing or negating the effects of these elements. This paper will discuss the consolidation of recycled tantalum by electron beam melting. It will also discuss the vacuum arc remelting of tantalum to refine grain size and to make alloy additions. The effects of material preparation, melting parameters, and alloy additions on finished products will be described.
2:20 pm
THERMOMECHANICAL PROCESSING OF Ta-l0W: R.W. Buckman Jr, Refractory Metals Technology, Pittsburgh, PA 15236; C. Bagnal1, Concurrent Technologies Corporation, Johnstown, PA 15904
The effect of the amount of prior cold work on properties of the solid solution strengthened alloy Ta-l0W has been investigated. Recrystallized Ta-l0W was reduced by both compressive and tensile operations at room temperature to four different levels of cold work ranging from 20% to 90% reduction in area. Tensile an compressive properties were measured and the recovery and recrystallization behavior was monitored. From the data obtained, a thermomechanical processing schedule is identified for producing Ta-l0W tubing with optimum high temperature properties in the recrystallized condition. This work was conducted by the National Center for Excellence in Metalworking Technology, operated by Concurrent Technologies Corporation on under contract to the U.S. Navy as part of the U.S. Navy Manufacturing Science and Technology Program.
2:40 pm
POWDERED TANTALUM METAL EXPLOSIVELY FORMED PROJECTILE LINERS: Ernest C. Faccini, Textron Defense Systems (TDS), 201 Lowell Street, Wilimington, MA 01887
TDS has successfully demonstrated aerostable EFPs produced from powdered Ta. A discussion of the result which TDS has obtained using a powdered metallurgy technique for the formation of EFP liner starting stock is presented. The data discussed shall include: grain size of the material, texture, pseudo-static engineering properties, dynamic stress-strain curves, flash x-rays of the EFPs produced from the starting stock, photographs of the recovered EFPs, cost ramifications of the process, comparison to wrought material which has been orbitally forged and comparison to wrought material which has been formed into plate. A brief discussion of the future of the process is also presented.
3:00 pm BREAK
3:15 pm Invited
P/M PROCESSING, CHARACTERIZATION, AND APPLICATION OF Ta-l0W: H. Clemens, R. Grill, P. Rodhammer, A. Voiticek, Plansee AG, A- 6600 Reutte/Austria
The tantalum alloy Ta-l0W (comp. in wt.%) was investigated with regard to its suitability as substrate material for coated fasteners to be used in the 'hot' structure of reusable space vehicles. The paper describes the P/M processing route of Ta-l0W rods which are the base for fastener production. Static recrystallization behavior as well as the grain growth dependence at elevated temperatures were investigated. The mechanical characterization was conducted for different material conditions, e.g., as-worked, recrystallized, and recrystallized + aged. The brittle-to-ductile transition temperature was determined by Charpy impact testing. Tensile tests and double-shear tests were performed at room temperature and elevated temperatures up to 1000deg.C and 1300deg.C, respectively. The crack propagation behavior was measured at room temperature. The obtained mechanical properties will be compared with those published for melt-metallurgically manufactured Ta-l0W. In addition, the feasibility of modified silicide coatings for oxidation protection of Ta-10W has been investigated. The results of oxidation tests and the consequence of local defects will be outlined.
3:45 pm Invited
TANTALUM POWDER CONSOLIDATION, MODELING AND PROPERTIES: Sherri R. Bingert, Victor D. Vargas, Haskell Sheinberg, Materials Science and Technology; Metallurgy, P.O. Box 1663, MS G770, Los Alamos National Laboratory, Los Alamos, NM 87545
A systematic approach has been taken to investigate the consolidation of tantalum powders. The effects of hot isostatic pressing (HIP) temperature and time; sinter temperature, time and ramp rate; oxygen content; and alloying an consolidation kinetics, microstructure, crystallographic texture, and mechanical properties have been evaluated. A micromechanics model, the Ashby HIP model has been employed to predict the mechanisms active during the consolidation (HIP and sinter) processes. This model also predicts the density of the end product and whether grain growth should expected under the applied processing conditions. It, however does not predict the overall shrinkage and part shape during consolidation. A finite element model, such as MARC, is an appropriate solution to these predictions, and is being applied (in concert with Ashby Model) to tantalum powder processing in order to optimize near-net shape consolidation conditions. Experimental and modeling results to date will be presented.
4:05 pm
MECHANICAL ALLOYING IN THE IMMISCIBLE Cu-Ta SYSTEM: Toshihara Fukunaga, Department of Crystalline Materials Science, School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-01, Japan
The mechanical alloying process has been studied on the Cu-Ta system which is characterized by a positive heat of mixing. The neutron diffraction and EXAFS measurements have been employed as a main tool to analyze the structural changes taking place during milling and DSC, XPS and the low temperature specific heat measurements as supplementary tools. The formation of an amorphous phase was confirmed not only from the structural studies but also from a change in the thermodynamical and electronic properties. The local atomic structure in the amorphous Cu-Ta is compared with that in the amorphous Ni-Ta with a large negative heat of mixing. The amorphization process can be understood as the preferential penetration of smaller atoms Cu into the bcc Ta crystallites. Studies of the ambient temperature effect in the Cu-Ta system thermodynarnically suggest that an increase in the interfacial energy is large enough to allow the formation of an amorphous phase.
4:25 pm
SHOCK COMPRESSION SYNTHESIS OF B1-TYPE TANTALUM NITRIDE: K.S. Vandersall, N.N. Thadhani, MSE, Georgia Institute of Technology, Atlanta, GA 30332-0245
Shock compression was used to synthesize tantalum nitride with the B1-type
(cubic) crystal structure which has been theoretically predicted to have high
hardness and high super-conducting critical temperature. Other processing
methods generally yield a non-stoichiometric low recovery product that must be
further processed before use in the bulk polycrystalline state. In the present
work, hexagonal phase (Co-Sn Structure) tantalum nitride powder was packed with
densities of ~35% and ~60% T.M.D into steel capsules, and shock loaded at 1.0
km/s impact velocity, corresponding to a 40-60 GPa calculated peak pressure.
X-ray diffraction and optical and scanning electron microscopy were used to
characterize the recovered compacts and starting powder. The conversion of the
hexagonal to the B1 phase was observed to depend on the initial porosity and
shock condition (pressure and temperature) within the sample. The highest yield
was obtained from the capsule with the lower packing density in the regions
toward the non-impact face which correspond to the highest pressure and
temperature. The lattice parameter of the shock synthesized B1 phase was
calculated to be 0.433 nm which coincides with a stoichiometry of approximately
TaN0.96.
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