High-strength high-conductivity Cu-Nb microcomposite sheet fabricatedvia multiple roll bonding

Abstract

Copper-niobium microcomposites are a new class of high-strength high-conductivity materials that have attractive properties for room- and elevated-temperature applications. Since Nb has little solid solubility in Cu, addition of Nb to Cu does not affect its conductivity. Copper-niobium microcomposites are melted and cast so that the microstructure of cast Cu-Nb ingots consists of 1-to 10μm Nb dendrites uniformly distributed within the copper matrix. Extensive wire drawing with a true processing strain (η > 12) of Cu-Nb alloy leads to refinement and elongation of Nb dendrites into 1-to 10 nm-thick filaments. The presence of such fine Nb filaments causes a significant increase in the strength of Cu-Nb wires. The tensile strength of heavily drawn Cu-Nb wires was determined to be significantly higher than the values predicted by the rule of mixtures. This article reports the fabrication of high-strength Cu-Nb micro-composite sheet by multiple roll bonding. It is difficult and impractical to attain high processing strains (η > 3) by simple cold rolling. In most practical cold-rolling operation, the thickness reduction does not exceed 90 pct (η ≅ 2). Therefore, innovative processing is required to generate high strength in Cu-Nb microcomposite sheet. Multiple roll bonding of Cu-Nb has been utilized to store high processing strain (η > 10) in the material and refine the Nb particle size within the copper matrix. This article describes the microstructure, mechanical properties, and thermal stability of roll-bonded Cu-Nb microcomposite sheet.