High-strength high-conductivity Cu-Nb microcomposite sheet fabricated via multiple roll bonding
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INTRODUCTION
REFRACTORY elements, such as W, Ta, Mo, Nb, and Cr, have limited solid solubility in copper. Therefore, creating a fine dispersion of refractory element particles within a copper matrix is an effective method of strengthening the copper. Due to the limited solid solubility of refractory elements, alloying copper with such elements does not adversely affect the electrical and thermal conductivity of copper. Therefore, Cu alloyed with refractory elements will possess high strength and high conductivity. Since refractory metals typically have high strength at elevated temperatures, Cu alloys dispersion strengthened with refractory particles may possess improved strength at elevated temperature and become good candidates for elevated-temperature applications. Special methods have been devised to melt and cast Cu-Nb microcomposites, m Dispersion of coarse Nb particles within a Cu matrix, as found in the cast Cu-Nb microcomposite, does not lead to effective strengthening. However, extensive deformation, as in a wire drawing operation, gives rise to ultrahigh-strength Cu-Nb wires. Extrusion and wire drawing operations of Cu-Nb alloys cause elongation of niobium dendrites into ribbons or filaments which are oriented along the axial direction. Thus, extensive mechanical deformation of the Cu-Nb gives rise to a microcomposite microstructure containing Nb ribbons, with 10-nm or finer thickness, uniformly S.C. JHA, Member of Technical Staff, J.A. FORSTER, Manager, Metallurgical Branch, and R.G. DELAGI, TI Fellow, are with Texas Instruments' Materials and Control Group, Attleboro, MA 02703. P.D. KROTZ, Metallurgical Engineer, is with Rockwell International Corporation, Rocketdyne Division, Huntsville, AL 35805. This article is based on a presentation made in the symposium "High Performance Copper-Base Materials" as part of the 1991 TMS Annual Meeting, February 17-21, 1991, New Orleans, LA, under the auspices of the TMS Structural Materials Committee. METALLURGICAL TRANSACTIONS A
distributed within the copper matrix. [2] The tensile strength of such cold-worked microcomposites is often greater than that predicted by the rule-of-mixture calculations, and a fundamental understanding of such phenomenon has been the subject of previous research.ta] The heavy deformation during wire drawing gives rise to high strength in heavily drawn Cu-Nb wires. This article describes the application of roll bonding technology for the production of high-strength Cu-Nb microcomposite sheet. In normal roiling operations, rolling reductions beyond 90 pct are impractical. Therefore, the true processing strain (~/=- In (Ao/AI), where A0 and AI are initial and final cross-sectional areas) during simple rolling operation, is limited to the order of 2 to 3, whereas the true processing strain during the wire drawing operations may exceed 12. In the work reported here, multiple roll bonding has been utilized to accumulate high processing strain in Cu-Nb sheets. This has led to the development of Cu-Nb sheet showing high strength and high c
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