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Session Chairpersons: Jan-C. Carlén, Rhenium Alloys, Inc., P.O. Box 245, Elyria, OH 44036; Dr. R.H. Tuffias, Ultramet, 12173 Montague St., Pacoima, CA 91331
JOINING AND FABRICATING RHENIUM USING EXPLOSIVE METAL WORKING TECHNIQUES: Donald J. Butler, Sr. Project Engineer, Northwest Technical Industries, Inc., 2249 Diamond Point Road, Sequim, WA 98382
Rhenium has many unique and interesting properties, but some of those same properties make Rhenium difficult to fabricate and weld. Explosive metal working also has some interesting capabilities. Northwest Technical Industries, under contract from the NASA Lewis Research Center, has been successful using the explosive welding technique to join Rhenium to metals such as Tantalum, Molybdenum, TZM Molybdenum, Vanadium and C 103 Niobium. This paper will describe the explosive welding process and present the results of the work that has been completed with Rhenium. Also, this paper will describe how explosives can be used to form metal parts and explore the potential of using explosive metal forming techniques with Rhenium.
STATE OF THE ART FABRICATION PROCESSES FOR IRIDIUM/RHENIUM THRUST CHAMBERS: R. Tuffias, Ultramet, 12173 Montague St., Pacoima, CA 91331
Chemical vapor deposition (CVD) has been used to fabricate rhenium liquid rocket combustion chambers since 1977. CVD iridium was first applied to rhenium chambers for high temperature oxidation protection in 1984. Since that time, CVD iridium/rhenium (Ir/Re) chambers have been successfully hot-fire tested at various facilities in both nitrogen tetroxide/monomethyl hydrazine (NTO/MMH) and oxygen/hydrogen (O2/H2) bipropellants, at mixture ratios ranging from 4 to 17, for a total of nearly 200 hours. An alternate processing method is to form the rhenium by powder metallurgy and apply the iridium by electroplating. Hot-fire testing of this processing method to date includes 43 seconds in NTO/MMH and approximately 11 hours in O2/H2 at a mixture ratio of about 3, an oxidizing potential that may actually be benign to unprotected rhenium. This paper will discuss alternate processing methods and their relationship to fabricating Ir/Re combustion chambers, as well as test methods for evaluating their efficacy.
DEVELOPMENT OF BONDED RHENIUM/Nb-1%Zr TUBING FOR THE SP-100 SPACE NUCLEAR REACTOR: Michael Kangilaski, Advanced Methods and Materials, 1798 Technology Drive, #251, San Jose, CA 95110; E.D. Sayre (retired); D.C. Wadekamper, T.J. Ruffo, General Electric Company, San Jose, CA
The SP-100 Space Nuclear Reactor design required a rhenium barrier between the uranium nitride nuclear fuel and the niobium alloy cladding. For higher strength and thermal performance it was deemed desirable to metallurgically bond the rhenium tube to the Nb-1%Zr tube. The bonding was achieved by brazing both ends of the rhenium and Nb-1%Zr tubes with a special braze adapter and then hot isostatically pressing (HIP) the brazed assembly. A considerable amount of effort went into developing a two stage HIP cycle for the bonding. A relatively low pressure was chosen in the first stage to assure that the weaker Nb-1%Zr tube collapsed uniformly onto the rhenium tube without any deformation occurring in the stronger rhenium tube. Avoidance of deformation in the rhenium was necessary because rhenium has low ductility at the HIP'ing temperature of 1350°C. In the second stage the temperature and pressure were increased to assure metallurgical bonding of the rhenium and Nb-1%Zr tube.
A HISTORY OF RHENIUM IN HIGH-PERFORMANCE BIPROPELLANT ROCKET ENGINES: R.H. Tuffias, R.B. Kaplan, Ultramet, 12173 Montague St., Pacoima, CA 91331; M.A. Appel, Jet Propulsion Laboratory (retired), California Institute of Technology, Pasadena, CA
In the late 1 970s, the Jet Propulsion Laboratory (JPL) contracted Ultramet to provide oxidation protection for a carbon composite rocket engine thrust chamber using the liquid bipropellant fluorine/hydrazine, an application for which rhenium was selected. In the late 1990s, the first rhenium thrust chamber will fly in space. This paper will discuss the period between these two milestones and those that made it possible.
3:20 pm BREAK
DIRECTED LIGHT FABRICATION OF RHENIUM COMPONENTS: John O. Milewski, Dan J. Thoma, Gary K. Lewis, Materials Science and Technology Division, Los Alamos National Laboratory, P.O. Box 1663, MS G770, Los Alamos, NM 87545
Directed Light Fabrication (DLF) is a direct metal deposition process that fuses powder, delivered by gas into the focal zone of a high powered laser beam to form fully dense nearnet shaped components. This is accomplished in one step without the use of molds, dies, forming, pressing, sintering or forging equipment. DLF is performed in a high purity inert environment free from the contaminants associated with conventional processing such as oxide and carbon pickup, lubricants, binding agents, cooling or cleaning agents. Applications using rhenium have historically been limited in part by its workability and cost. This study demonstrates the ability to fuse rhenium metal powder, using a DLF machine, into free standing rods and describes the associated parameter study. Microstructural comparisons between DLF deposited rhenium and commercial rhenium sheet product is performed. This research combined with existing DLF technology demonstrates the feasibility of forming complex rhenium metal shapes directly from powder.
THE IMPACT OF THE MECHANICAL PROPERTIES OF RHENIUM ON STRUCTURAL DESIGN: A.J. Sherman, A.J. Fortini, B.E. Williams, R. Tuffias, Ultramet, 12173 Montague St., Pacoima, CA 91331
Pushed by extreme aerospace requirements, exotic materials with unusual properties are being pressed into service. One such material is rhenium. With a density of 21 g/cm3, it is an unlikely material for structural applications, but with an ultimate strength of 20,000 psi at 2000°C, it is the strongest metal at this temperature and comparable in strength to carbon composites up to 2500°C. In order to design structural parts, it is necessary to be able to model their load/ deflection relationship. Such analysis typically assumes that the material is elastic and conforms to Hooke's Law (stress being linearly proportional to strain). When the material becomes inelastic or plastic, failure is assumed to occur, since a permanent deformation takes place This limit is referred to as the yield strength. Typical yield strengths for engineering materials such as steel are roughly 60-80% of the material's ultimate strength. For these materials, then, a linear analysis permits a design range up to 60-80% of the ultimate capability of the material. As long as the material is operated in this range, the relationship between stress and strain remains constant. Rhenium, on the other hand exhibits a "classical yield strength" that can be as low as 10% of its ultimate strength, and its stress-strain relationship varies based on its previous stress history. If a structural design is based on this classical yield strength, 90% of the capability of the material is effectively discarded. Room temperature yield strength data for CVD (chemically vapor deposited) rhenium have included values as high as 45,000 psi and as low as 8,000 psi. Rocket engine designers are currently in a quandary as to the meaning of this data and how to use it to design components. This paper will discuss some of the strength data and present alternatives.
MATERIALS PROPERTY TEST RESULTS OF RHENIUM: Melvin L. Chazen, TRW Space & Technology Division, One Space Park, Bldg. 01-1050, Redondo Beach, CA 90278
The use of rhenium as a material of construction for high performance liquid apogee/ perigee or delta-V engine applications is very beneficial as the engine performance is less limited by operating wall temperatures due to the performance. Rhenium has a very high melting point (>5700F) but does require protection from oxidation from the products of combustion. Iridium has been demonstrated as a successful high temperature protective coating (melting point >4400P). There are two methods of producing rhenium thrust chambers for high performance engines which have been successfully demonstrated which are chemical vapor deposition of iridium lined rhenium and powder metallurgy rhenium coated with iridium. An investigation was conducted to determine the material properties of both CVD and PM rhenium which was sponsored by NASA-LeRC on the SSRT program. Material property tests consisted of tensile, ultimate, modulus and low cycle fatigue at room temperature, 1500F and 25OOF with a minimum number of tensile tests at 2700-3500F and high temperature creep at 3000F This paper presents these results which indicate that both CVD and FM rhenium are usable for flight engines. In addition a summary of the results of engine tests with experimental PM rhenium will be presented.
JOINING OF RHENIUM AND ITS ALLOYS: Sunder S. Rajan, Hughes Aircraft Company, Electron Dynamics Division, 3100 West Lomita Blvd., Torrance, CA 90509-2999
The processing parameters used to join rhenium and selected alloys containing rhenium are described. Resistance and laser welding as well as brazing processes as applied to these materials are reviewed. The metallurgical factors governing the choice of the process parameters and their influence on structural integrity are illustrated. The influence of alloy selection, use of proper filler materials and the factors governing their selection are reviewed. Experience has shown that pure rhenium, MolyRhenium and Tungsten/Rhenium alloys can be successfully joined by either welding or brazing processes.
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