Creep Deformation of Dispersion-Strengthened Copper
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I.
INTRODUCTION
THE development of future space and energy technologies, such as aerospace propulsion systems and fusion power plants, will require continuing improvements in the performance of materials that can resist high temperatures. One approach to meet this need is to develop the structural capabilities of high melting point materials such as ceramics, refractory metals, and intermetallic compounds that resist high operating temperatures in a static fashion. As an alternative, a variety of current and proposed engineering applications are based on the concept of active cooling in order to extend the operating temperatures of structural materials. 11~1In this approach, heat is extracted from a source, through the component, and dissipated through a cooling medium on the opposite side. The heat flux through these components is usually quite high and may fluctuate during a service cycle, thereby causing failure by thermal-mechanical fatigue. Thus, active cooling requires a structural material that has a high thermal conductivity as well as adequate creep and fatigue resistance at elevated temperatures. Because of its excellent thermal properties, copper has been proposed as a material for actively cooled components. For elevated temperature strength, dispersion strengthened (DS) copper alloys are particularly attractive due to their excellent combination of thermal and electrical conductivities, strength retention, and microstructural stability.t5.6] The superior elevated temperature strength of various DS alloys has motivated a great deal of study of their S.E. BROYLES, formerly Graduate Research Assistant, Division of Materials Science and Engineering, Department of Chemical Engineering and Materials Science, is Product Development Engineer, W.L. Gore and Associates, Inc., Flagstaff, AZ 86002. K.R. ANDERSON, Graduate Research Assistant, J.R. GROZA, Associate Professor, and J.C. GIBEL1NG, Professor, are with the Division of Materials Science and Engineering, Department of Chemical Engineering and Materials Science, University of Califomia, Davis, CA 95616-5294. Manuscript submitted November 15, 1994. METALLURGICALAND MATERIALSTRANSACTIONS A
creep behavior. These materials are characterized by high apparent stress exponents and high apparent activation energies for creep. The mechanisms responsible for the improvement of creep resistance are now reasonably well understood, as discussed by Arzt in a recent review.t7] However, relatively little of this previous work has involved studies of DS copper alloys. Recently, Arzt and co-workers have proposed a model for the creep of dispersion-strengthened alloys based on an attractive particle/dislocation interaction.17,s,91In the RrslerArzt model, the rate-controlling step in the creep process is the thermally activated detachment of a dislocation from the departure side of a particle. The time for glide between particles is assumed to be insignificant. In addition, climb over particles is assumed to occur easily and is not the ratecontrolling factor. The attraction
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