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Session Chairpersons: Dr. Evan K. Ohriner, Metals and Ceramics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6083; Forrest Hall, Hoskins,10776 Hall Road, P.O. Box 218, Hamburg, MI 48139-0218
METALLOGRAPHIC TECHNIQUE FOR INCREASED GRAIN BOUNDARY DELINEATION OF RHENIUM ALLOYS: Mitchell A. Jacobs, Jozef Fedko, Metallurgical Services Inc., Maywood, IL 60153
Current metallographic preparation techniques for rhenium alloys have been based on the etch and back polish technique due to the soft nature of the rhenium alloys. To date the etch and back polish technique has adequately removed the flowed rhenium material to reveal the microstructure. Recent technology has allowed new polishing media to provide better removal of the flowed material. The resulting microstructure exhibits two dimensional relief in a slightly overetched condition. The significantly increased grain boundary delineation permits better review of the grain size.
ION-IMPLANTATION DOPED RHENIUM AND REFRACTORY METALS: G. Welsch, P.T. Szozdowski, R.M. Collins, Materials Science and Engineering, Case Western Reserve University, 514 White Bldg., Cleveland, OH 44106-7204; K.T. Kim, Research Institute of Industrial Science and Technology, P.O. Box 135, Pohang, 790-600, Korea
Rhenium and other refractory metals in various product forms can be doped with potassium to stabilize an overlapping recrystallized grain structure for high temperature creep strength. Doping has been performed by ion-implantation into the surface layers of flat sheets. During fabrication of pressure-bonded or roll-bonded multi-layer composites the dopant was incorporated along strategically located internal planes. The dopant is arranged in planar arrays of fine bubbles which play the role of fenceposts as they anchor grain boundaries during recrystallization and grain growth. Doped layer composites can be heated to over 2000°C and maintain an overlapping "brick layer" grain structure whereas undoped layer composites develop grains and grain boundaries that transverse the entire width of the composite. Acknowledgment: The research was funded by The National Science Foundation.
THE INFLUENCE OF ROLLING DIRECTION AND ANNEALING ON THE TEXTURE OF RHENIUM SHEETS: Boris D. Bryskin , Jan-C. Carlén, Rhenium Alloys, Inc., P.O. Box 245, Elyria, OH 44036; K. Peter D. Lagerlöf, Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106; Neil Goldfine, JENTEK Sensors, Inc., Boston, MA 02135
SYNTHESIS AND APPLICATION OF ARTIFICIAL GRAIN STRUCTURES IN POTASSIUM-IMPLANTED RHENIUM: R.M. Collins, G. Welsch, Materials Science and Engineering , Case Western Reserve University, 514 White Bldg., Cleveland, OH 44106-7204
Layer composites of rhenium (re) were made by the chemical vapor deposition (CVD) process. The Re layers range from 0.05 to 0.10 mm in thickness. Between Re layer depositions, potassium atoms were injected into the metal matrix by ion implantation to a depth of 600 angstroms and a peak concentration of 1 at%. At high temperatures, the implanted atoms cluster and form bubbles that remain stable and act as barriers that pin grain boundaries thus producing a means for creating artificial grain architectures. The grain structure of the implanted CVD layer composites is compared to that of the un-implanted CVD composite. Room temperature tensile tests show that the artificial grain architecture increases the overall tensile strength of the CVD rhenium composite.
3:00 pm BREAK
TENSILE AND CREEP PROPERTIES OF RHENIUM AND RHENIUM ALLOYS: Michael Kangilaski, Advanced Methods and Materials, 1798 Technology Drive, #251, San Jose, CA 95110; M.M. Paxton, Westinghouse Hanford Company, Richland, WA
Tensile properties of rhenium sheet, produced by powder technology techniques, were established from room temperature to 2000°C. The strength of rhenium decreased gradually with increasing temperature while the elongation decreased drastically (from 20% to 5%) as the temperature increased from 1100 to 1200°C. The elongation remained below 5% at temperatures up to 2000°C. Tensile tests were also performed on rhenium -1% tungsten and rhenium-2% iridium. Both alloys were stronger than pure rhenium with the rhenium-1% tungsten alloy being the strongest. Limited creep and creep rupture tests were performed in the 1025 to 1225°C range. The creep tests, with relatively low stresses, indicated a very low stress exponent of 1.3.
MICROSTRUCTURE CHARACTERISTICS OF Mo-Re ALLOYS SINTERED AT MEDIUM TEMPERATURES: Rodolfo L. Mannheim, Jorge L. Garin, Department of Metallurgical Engineering, Universidad de Santiago de Chile, Casilla 10233, Santiago, Chile
Mixtures of molybdenum and rhenium powders with particle size distribution bearing 2µm average, were prepared in a planetary mill to yield the Mo-25%Re and Mo50%Re compositions. Tablets were then obtained by compaction at various pressures in the range of 300 to 800 MPa. The pieces were subject to sintering at temperatures of 1400 to 1700°C, under protecting atmosphere of Ar-10%H2 to avoid oxidation of the component metals. The solution of rhenium in the molybdenum matrix was followed by means of X-ray diffraction: it was found that at all sintering temperatures rhenium was totally dissolved in the Mo-25%Re, while small amounts of an intermediate phase were detected in the case of the Mo-50%Re alloy, in good agreement with the phase diagram. The densification of the sintered parts increased with temperature and compaction pressure up to values around 90%. The microstructure of the specimens was observed by means of scanning electron microscopy, while the homogeneity of the sintered alloys was corroborated by EDX line-scan analysis. The microstructure showed well defined equi-axed grains with some microporosity distributed across the surface. A few initial tests on cold rolling of the resulting specimens were conducted with very promising results; in fact, owing to the fine particle size of the powders, the sintering temperature can be lower than those normally utilized in the refractory metals industry.
EFFECT OF IRRADIATION ON THE TENSILE PROPERTIES OF RHENIUM: James A. Horak, Lockheed Martin Energy Systems, Inc., K-25 Technical Support Organization, P.O. Box 2003, MS7353, Oak Ridge, TN 37831; Michael Kangilaski, Advanced Methods and Materials, 1798 Technology Drive, #251, San Jose, CA 95110
Because of their capability for producing high power densities without interruption for long time periods (years) small, fast neutron energy spectrum nuclear reactors are candidates for applications such as orbiting satellites, lunar and Mars terrestrial power stations and manned trips to Mars. To provide high efficiency in the conversion of thermal energy to electrical energy, these reactors must operate at high temperatures (e.g. >1000°C) and they are cooled with liquid metals such as lithium. Because of its high temperature strength and excellent chemical compatibility with lithium, rhenium (Re) has been considered for use in nuclear reactors for space power. In a space reactor the Re would be subjected to fast neutron irradiation to fluences of more than 1x1022n/cm2 (Ea > 0.1MeV) during several years of operation. The current work was performed to provide information on the tensile properties of Re as a function of test temperature and the effects of neutron irradiation at high temperatures on these properties. Ductility of Re is high (~40%) at low temperatures but decreased abruptly to less than 5% at temperatures about ~900°C. The work hardening coefficient is very high at room temperature and decreases slowly with increased test temperature. Fast neutron iradiation at approximately 1000, 1100, and 1300°C to fluences of 8x1021 and 4x1022n/cm2 resulted in increases in strength and decreases in ductility for tests at room temperature, at the irradiation temperature, and at fifty degrees above the irradiation temperature. These effects decreased with increased irradiation temperature and increased with increased fluence. Also, irradiation lowered by more than 200°C the temperature of the abrupt increase in ductility.
MECHANICAL PROPERTIES OF Cr-Re ALLOYS AT HIGH TEMPERATURES: N. Brodnikovsky, V. Pisarenko, A. Rakitsky, A. Sameljuk, Frantsevich Institute for Problems of Materials Science, 3 Krjijanovskogo Str. 252680 Kiev, Ukraine
The microstructure and mechanical characteristics of cast alloys Cr-35 Re and Cr-18 Re have been investigated within the wide temperature interval (20-1300°C). It was found that under uniaxial tension within 20-600°C the plasticity of the alloys run into 10-20, whereas it decreased when the temperature rose above 700°C. The appearance of the plastic intercrystalline fracture at the temperatures above 900°C resulted in the sharp decrease of strength and plasticity of the alloys. It was established that small quantities of impurities (CN, C, O) contained in source materials effected the fracture mechanisms substantially. The additives of Fe to the alloys under investigation did not altered plastic characteristics at high test temperatures. The other perfomed research permitted to consider that the Cr-Re alloys can be obtained with high mechanical properties and within the temperature interval 700-1300°C.
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