Creep behavior of copper-chromium in-situ composite
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1/8/04
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Creep Behavior of Copper-Chromium In-Situ Composite K.L. LEE, A.F. WHITEHOUSE, S.I. HONG, and A.M. RUSSELL Creep deformation and fracture behaviors were investigated on a deformation-processed Cu-Cr in-situ composite over a temperature range of 200 °C to 650 °C. It was found that the creep resistance increases significantly with the introduction of Cr fibers into Cu. The stress exponent and the activation energy for creep of the composite at high temperatures (400 °C) were observed to be 5.5 and 180 to 216 kJ/mol, respectively. The observation that the stress exponent and the activation energy for creep of the composite at high temperatures (400 °C) are close to those of pure Cu suggests that the creep deformation of the composite is dominated by the deformation of the Cu matrix. The high stress exponent at low temperatures (200 °C and 300 °C) is thought be associated with the as-swaged microstructure, which contains elongated dislocation cells and subgrains that are stable and act as strong athermal obstacles at low temperatures. The mechanism of damage was found to be similar for all the creep tests performed, but the distribution and extent of damage were found to be very sensitive to the test temperature.
I. INTRODUCTION
IN-SITU metal-metal composites are attractive materials for high-strength and high-conductivity applications. These composites, comprised of Cu containing a second-phase element X (where X is a bcc metal immiscible in Cu, such as Nb, Cr, Fe, Mo, or V) can be formed by mechanical working (swaging, extrusion, rolling, or drawing) of ductile two-phase mixtures prepared by using liquid-phase sintering, casting, or powder metallurgy techniques. The fibrous X metal can bear the higher fraction of load, while the surrounding Cu matrix gives good conductivity and ductility. Among the several Cu-X composites, Cu-Cr composites have been studied by several research groups and were found to possess a desirable combination of attributes.[1–13] Compared to other Cu-X composites, Cu-Cr composites offer lower cost (the cost of Cr is roughly one-tenth that of Nb), lower solubility of the X element in the Cu matrix, and a higher elastic modulus; these attributes make Cu-Cr composites a promising material for many potential applications, particularly at elevated temperatures such as aerospace propulsion systems and fusion power plants. The use of discontinuously reinforced Cu-Cr composites for high-temperature applications requires a comprehensive understanding of the mechanisms affecting their creep behavior. It is important to obtain detailed information on this composite’s creep behavior and creep fracture. Some reports have been published on the creep behavior of Cu containing less than 1 wt pct Cr in solid solution;[14,15] however, a literature search found no reports on the creep response of two-phase Cu-Cr composites. Hong et al.[16,17] examined the microstructural stability of Cu-based composites after highK.L. LEE, formerly Ph.D. Student, Department of Engineering, Universi
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