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
Wednesday, PM Room: A4-5
February 7, 1996 Location: Anaheim Convention Center
Session Chairpersons: Jerry Wittenauer, Lockheed Missiles & Space Co., Palo Alto, CA; Edward S. Chen, U.S. Army Research Office, Researc Triangle Park, NC
1:30 pm Invited
THE VAPOR DEPOSITION OF Ta AND Ta COMPOUNDS: Erik Randich, Lawrence Livermore National Laboratory, Livermore, CA 94550
Ta and many of its compounds can be deposited as coatings by techniques ranging from pure thermal Chemical Vapor Deposition (CVD) to pure Physical Vapor Deposition (PVD). There are many vapor deposition techniques which are hybrids of the two methods. A review of the various deposition techniques which are more closely related to CVD than PVD will be presented. The advantages and limitations of the techniques will be compared. The need for new lower temperature processes and hence new precursor chemicals will be examined and explained. Areas for new research and development of these processes and materials will be explored.
2:00 pm
TANTALUM USAGE IN NICKEL-BASED SUPERALLOYS: Gary L. Erickson, Cannon-Muskegon Corporation, 2875 Lincoln Street, Muskegon, MI 49441
Tantalum has been an important superalloy constituent for nearly fifty years. Similar to W and Re, it is a refractory element partly characterized by it's relatively large atomic radius and contribution to superalloy strength through coherency strain. Unlike W and Re which primarily partition to the gamma solid solution, tantalum contributes to both the gamma and gamma prime superalloy constituents. Additionally, tantalum is beneficial to superalloy directionally solidified component castability and promotes good environmental properties resistance. Superalloy tantalum usage has continually increased since the commercialization of the directional solidification casting process for gas turbine engine blade and vane manufacture, partly because it helps prevent freckle defect formation in single crystal cast components. Furthermore, its usage has increased due to the ability to increase superalloy strengthener content in directionally solidified articles as opposed to equiaxe alloys. The narrative reviews the usage of tantalum in superalloys with a primary emphasis being placed upon directionally solidified compositions. It presents the rationale behind superalloy tantalum usage and the likely trend for its continued application in emerging materials for gas turbine engine hardware.
2:30 pm
APPLICATION OF PM TANTALUM FOR EFP LINER: T.K. Chatterjee, J Cross, U.S. Army Research Development & Engineering Center, Picatinny Arsenal, NJ 07806- 5000, C. Michaluk, Cabot Corporation, Boyertown, PA 19512
High Oxygen (250-450 ppm) content in P/M forged materials are characterized as having a higher flow stress and greater work hardening is greater at a low strain rate then at a higher rate. This behavior may be due to the intergranular tantalum oxide particles. In spite of the higher oxygen content, P/M forged tantalumexhibits favorable ductility. TEM study was performed on extruded and forged PM tantalum annealed at different temperatures. A comparison was made between these microstructures and in other microstructres previously revealed in tantalum that has been processed differently.
2:50 pm
NEW BARRIER LAYER OF TaSiN FOR Al INTERCONNECTION LAYER AND Ta2O5 CAPACITOR: Tohru Hara, Department of Electrical Engineering, College of Engineering, Hosei University, 3-7-2 Kajinocho, Loganei City, Tokyo 184
Barrier effect of TaSiN layer has been studied. This barrier layer with different compositions of Ta, Si and N is deposited, where precise composition is determined by Rutherford Backscattering spectroscopy measurement. This layer shows much better thermal stability when compared with other barrier layers. Fundamental properties of this layer and barrier effect of this layer for Al interconnection layer and for Ta2O5 dielectric layer is described. Other Ta layers, for instance, CVD Ta2O5 layer form memory capacitor and TaSi2 for sallicide gate in MOS LSIs are also described.
3:10 pm BREAK
3:20 pm Invited
CHEMISTRY MODIFICATIONS OF TANTALUM AND TANTALUM-TITANIUM-SCANDIUM ALLOYS BY PLASMA ARC MELTING: Paul S. Dunn, Deniece Korzekwa, Fermin Garcia, Materials Science and Technology: Metallurgy, P.O. Box 1663, MS G770, Los Alamos National Laboratory, Los Alamos, NM 87545
State-of-the-art melting of tantalum and titanium alloys have relied on electron beam (EB) or vacuum arc remelting (VAR) for ingot fabrication. The limited melting techniques for these materials are the result of high melting temperatures and reactivity with mold/crucible materials. In addition, the vacuum levels typically used in EB and VAR processing limit the alloy addition candidates to those elements with low vapor pressures. Plasma arc melting (PAM) provides an alternative for melting tantalum materials with the advantage of processing under ambient pressures. The current work examines processing parameters for melting two classes of materials; 1) high oxygen sintered tantalum powder and 2) a tantalum-titanium-scandium alloy. High oxygen tantalum powder: Attempts to EB melt the high oxygen tantalum resulted in continuous extinguishment of the electron guns due to the large amount of outgassing as the material melted. Plasma arc melting was used to consolidate the material and correlate oxygen levels with standard argon helium and argon/helium/hydrogen cover gases. Tantalum-titanium-scandium: The melting of the Ta-Ti-Sc alloy posed a major technical problem because of the boiling point of scandium, 2836deg.C, and the melting point of the alloy, 2650deg.C. Data and processing parameters will be presented that show scandium was maintained in the melt and ingot segregation is minimal.
3:50 pm
SINTERING OF HIGH SURFACE AREA TANTALUM POWDER: Sophie G. Dubois, Randall M. German, P/M Lab, The Pennsylvania State University, 118 Research Building West, University Park, PA 16802-6809
To achieve the high surface area required for the fabrication of high performance electronic capacitors, tantalum powders are usually plate-like or agglomerated. Understanding the sintering behavior of these powders is essential to improve the manufacturing process; however, solid-state sintering models and simulations have only been developed for spheres. Using the concept that the driving force for neck growth is provided by the curvature gradient, three different particle geometries were simulated: spherical, plate-like, and agglomerated. Computer simulations and experimental sintering results of plate-like and agglomerated powders were combined to identify the critical sintering parameters for high surface area tantalum powders. Sintering maps for tantalum powders were created to predict surface area reduction and shrinkage during sintering.
4:10 pm
PROCESSING TECHNIQUES FOR TANTALUM-CARBON COMPOSITES: Keith Axler, Patrick Rodriauez, Ramiro Pereyra, Gerald DePoorter, Los Alamos National Laboratory, Los Alamos, NM; Charles West, Patrick Doherty, BIRL Industrial Laboratory, Northwestern University, Evanston, IL.
A tantalum-based alloy with Ta2C inclusions has been developed and demonstrated as a construction material for use in severely corrosive metallurgical processing environments. Alloy development involved multi-step thermal processing to invoke specific microstructural features. Grain boundary precipitation of carbide from supersaturated conditions provides corrosion resistant attributes. The kinetics of carbide formation from supersaturated solid solutions of carbon in tantalum were established. Due to its exceptional corrosion resistance, this engineered material is well-suited for containment of molten metals and salts.
4:30 pm
HIGH TEMPERATURE DEFORMATION IN Ta-2.5 wt.% W ALLOY: Yong Li, Weidong Cai, Enrique J. Lavernia, Farghalli A. Mohamed, Department of Chemical Engineering and Materials Science, University of California, Irvine, CA 927l7
The effect of stress on the high temperature deformation behavior of Ta-2.5
wt. % alloy has been studied by conducting a series of compressive creep tests
at l350deg.C. The creep tests were performed using a specially designed
materials testing system in Argon atmosphere to prevent the oxidation of test
specimens at elevated temperatures. The stress dependence of the steady-state
creep rate in the alloy is discussed in reference to the creep behavior of
metals and alloys.
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