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Session Chairpersons: Prof. Gerhard E. Welsch, Materials Science and Engineering, Case Western Reserve University, 514 White Bldg., Cleveland, OH 44106-7204; Michael Kangilaski, Advanced Methods and Materials, 1798 Technology Drive, #251, San Jose, CA 95110
STRESS/RUPTURE STRENGTH OF RHENIUM AT EXTREMELY HIGH TEMPERATURES: B. Fischer, D. Freud, Jena Polytechnic, Tatzendpromenade 1 b, D-07745 Jena, Germany; D. Lupton, W.C. Heraeus, GmbH, Heraeusstrasse 12-14, D-63450 Hanau, Germany
For the safe high-temperature use of rhenium we have the task of measuring the stress/rupture strength at extremely high temperatures. For stress/rupture tests on high melting metals we designed and built a test system that allows measurements to be made at temperatures up to 3,000°C under an inert atmosphere. Using this test unit we determined stress/rupture diagrams of rhenium in several material conditions in the range of 2,100°C to 3,000°C. The discussion of the measured values is based on me/allographic test results, scanning electron microscopy (SEM) images of rhenium samples after the stress/rupture tests, the determination of trace impurities using secondary ion mass spectrometry (SIMS) and the results of the residual gas analysis of rhenium.
INFLUENCE OF COLD ROLLING ON PLASTIC RESPONSE OF PM AND CVD RHENIUM: G. Subhash, B.J. Koeppel, Mechanical Engineering-Engineering Mechanics Department, Michigan Technological University, Houghton, MI 49931
Plastic response of rhenium (Re) produced by powder metallurgy (PM) and chemical vapor deposition (CVD) was investigated under uniaxial compression. The PM Re was also cold rolled by 50% and 80% reduction (denoted as PM50 and PM80, respectively) in thickness. Both cold rolled and CVD Re have been found to have a strong basal texture. Cylindrical specimens from the above four types of Re (i.e., PM, PM50, PM80 and CVD) were subjected to uniaxial compressive loads in the range of strain rates from 1x10-3 s-1 to 9.5 x 103 s-l. Low strain rate experiments were performed in an Instron machine and high strain rate experiments were performed in a split Hopkinson pressure bar. The deformed specimens were metallographically prepared and etched to study microstructural changes and identify the micromechanisms of deformation. Rhenium exhibited a two stage hardening in its plastic response. It revealed a high strain hardening rate and a strong strain rate sensitivity of flow stress. Increased cold work in the PM Re resulted in an increase in the initial yield stress with a concurrent reduction in the hardening rate and failure strain. CVD Re exhibited a distinctly higher hardening rate and ultimate flow stress than the above cold rolled PM Re. After accumulating a certain amount of plastic strain, the deformation in the specimens localized leading to formation of shear bands at an angle to the loading axis. Fracture immediately followed the shear bands. Twinning was found to be a dominant deformation mode in both PM and CVD Re. Extensive twinning was observed in larger grains of CVD Re. Twins in fine "rained PM specimens were less common and occurred primarily in the regions close to the shearband. Based on the experimental results and microscopic investigations, the micromechanisms of deformation responsible for the observed behavior of Re will be discussed.
STEADY STATE CREEP RATES OF W-4Re-0.32HfC: John J. Park, MS E506, Los Alamos Laboratory, Los Alamos, NM 87545; Dean L. Jacobson, Dept. of Chem, Bio. and Materials Engineering, Arizona State University, Tempe, AZ 85287-6006
Second phase particle-strengthened tungsten alloy, tungsten-4w/o rhenium-0.32w/o hafnium carbide (W-4Re-0.32HfC), was creep-tested at temperature ranges of 2200 to 2400K and stress ranges of 40 to 70 Mpa in a vacuum of better than 1.3 x 10-6 Pa (1 x 10-8 torr). The resulting steady state creep rates were applied to three particle-strengthened creep models and compared. The three creep models were Ansell-Weertman, Lagneborg, and Roesler-Arzt. None of the three models precisely predicted the steady state creep rates of W-4Re-0.32HfC. However, the recovery creep model of Lagneborg qualitatively fit the creep rates.
TEMPERATURE AND LOAD DEPENDENCE ON THE HARDNESS OF ROLLED RHENIUM SHEETS BEFORE AND AFTER ANNEALING: K. Peter, D. Lagerlöf, Seog-Young Yoon, Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106; Boris D. Bryskin, Jan-C. Carlén, Rhenium Alloys, Inc., Elyria, P.O. Box 245, OH 44036
The microhardness of rolled rhenium sheets was determined as a function of indentation load and temperature. Sheets of rhenium were produced from rhenium metal powder by pressing, presintering and sintering, followed by cold rolling. After a production anneal to define the structure of the starting material, sheet samples were deformed using cold rolling to about 30% strain in 5% deformation increments without intermediate annealings. One of the deformed samples was annealed at 1600°C for 20 minutes. The temperature dependence of the microhardness between room temperatures and 900°C (using 50° increments) was studied using a Nikon Model QM hot hardness tester equipped with a Vickers indentor. The load dependence of the microhardness was investigated using both a Vickers anda Knopp indentor, and the indentation size effect (ISE) was best explained using the normalized Meyer's law. The hardness of the annealed rhenium sheet approached that of the as-rolled sheets at large indentation loads because of workhardening under the indentor during indentation. The hardness at "zero load" (obtained from extrapolation of the load dependence of the hardness) suggests that the hardness is controlled by two different mechanism having different thermal activation. The activation energy of the mechanism controlling the hardness at low temperatures is approximately 0.02 eV whereas that at high temperatures is approximately 0.5 eV. The transition temperature between the two controlling mechanisms occurs at about 250C.
9:50 am BREAK
A REVIEW OF THE INTERACTION OF COLD WORK AND ANNEALING IN THE PROCESSING OF RHENIUM: O.S. Es-Said, Mechanical Engineering Department, Loyola Marymount University, Los Angeles,CA 90045; R.H. Titran, NASA Lewis Research Center, 21000 Brookpark Road, Mail Stop 49-1, Cleveland, OH 44135
Twinning is a dominant deformation mode in both PM and CVD rhenium. Although severe work hardening occurs during cold rolling, extensive twinning enables rhenium to retain moderate ductility. It is believed that as the deformation process progresses, twinning becomes the predominate mode contributing to the plastic deformation of rhenium. At all deformations, the hardness and strength of rhenium decreases at annealing temperatures corresponding to the temperature of the onset of recrystallization. It is known that the recrystallization temperature of rhenium decreases with increasing amounts of cold work, from 1750°C for 5% deformation to 1200°C for 40-60% deformation. This strong dependence exist because the nucleation of recrystallization occurs at the intersection of twin crystals and growth proceeds on the bases of the twins. When a polycrystalline material is deformed, the individual grains tend to orient themselves so that the active slip systems become more favorably oriented with respect to the direction of the principal strain. This leads to crystallographic anisotropy or preferred orientation. In a recent study, the effect of rolling mode on PM rhenium was evaluated. Samples rolled at a 45° direction showed a higher work hardening rate than samples rolled along the width and length of rolled sintered bars. This paper will review the interactions of cold work and annealing on the work hardening, recrystallization, and texture of rhenium.
SOLID SOLUTION MOLYBDENUM-RHENIUM ALLOYS: Lynn B. Lundberg, Materials Consultant, 2832 W. 33rd N., Idaho Falls, ID 83402; Boris D. Bryskin, Rhenium Alloys, Inc., P.O. Box 245, Elyria, OH 44036
It has been known for many years that the brittleness commonly seen in commercial-pure molybdenum around room temperature can be greatly reduced or eliminated by alloying with rhenium within the solubility range fro rhenium in molybdenum. Molybdenum-based solid solution alloys with rhenium represent a technically important class of refractory metal alloys whose behavior is reviewed in this paper. Mechanical and physical properties are reviewed as well as the fabrication characteristics of the alloys. Data from the vast amount of research performed on molybdenum-rhenium alloys in the former Soviet Union and more recently in Russia are referenced, summarized and reviewed. For the area of advanced materials' applications such analysis is appropriate to make intelligent decisions on how to proceed.
AN OVERVIEW OF W-Re ALLOYS FOR TEMPERATURE MEASUREMENT APPLICATIONS: D.A Toenshoff, R.D. Lanam, Engelhard-CLAL, 700 Blair Road, Carteret, NJ 07008
Two Tungsten-Rhenium alloy pairs are the predominant combinations used in the measurement of temperatures up to 2400°C and higher under protective inert or vacuum conditions. These alloy pairs are W-3Re vs. W-25Re and W-SRe vs. W-26Re. Other combinations are used in regional areas or for special applications. These include W vs. W-25Re and W-5Re vs. W-20Re. A historical review of the materials and the evolution of their use will be given. A discussion of alternate materials e.g. Ir vs. Ir-40Rh to measure high temperatures will be included. The effect of composition and environment on the EMF characteristics will be summarized. The future use of W-Re alloys for temperature measurement applications will be projected.
THE MECHANICAL PROPERTIES OF W-Re MADE BY PM METHOD: N. Danilenko, V. Panichkina, Yu. Podrezov, O. Radchenko, Frantsevich Institute for Problems of Materials Science, 3 Krjijanovskogo Str. 252680 Kiev, Ukraine
The tungsten sheets made by using the powder metallurgy method displayed low plasticity and were apt to delamination in the rolling plane. In order to improve plasticity of the sheets and suppress delamination the additions of the W-Re and HfO powders were employed. On the basis of such compositions the tungsten sheets were obtained which were plastically deformed at 223K. That sheets manifested the fracture toughness in the rolling plane by factor of five higher as compared with the initial sheets.
TECHNETIUM, A MANMADE SISTER ELEMENT AND BACKUP ALLOYING AGENT FOR RHENIUM: Edwin D. Sayre, 218 Brooke Acres Drive, Los Gatos, CA 95032
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