Anomalous increase in strength of i n s i t u formed Cu-Nb multifilamentary composites

Abstract

Cu-Nb wire composites with 0.105, 0.148, and 0.182 volume fraction of Nb filaments were produced in situ and their mechanical properties measured as a function of filament size and interfilament spacing. The yield stress and the ultimate tensile strength increased with both niobium volume fraction and overall composite reduction. At room temperature, the ultimate tensile strength of the Cu–18.2 vol% Nb composite reduced by 99.999% in cross-sectional area (100–200 Å filament thickness) reached the value of 2230 MN/m2 (323 ksi) and further increased to 2850 MN/m2 (413 ksi) when measured at 77 °K. These values are higher by a factor of 4 than the values predicted by the rule of mixtures based on the highest reported strength of both niobium and copper. The composite strength is as high as that of the best copper whiskers and is shown to closely approach the theoretical strength of the material. The anomalous increase in strength despite the low volume fraction of reinforcing filaments suggests that the filaments act primarily as barriers to the motion of matrix dislocations and that the strength of the filamentary material is only of secondary importance. This hypothesis is supported by microstructural obsevations (transmission and scanning electron microscopy) which reveal the deformation modes during composite fabrication and mechanical testing. The excellent transport properties (in both the normal and superconducting state) make these composites attractive as conductors for high-stress applications.

Microstructures and Mechanical Properties of Highly Electrically Conductive Cu–0.5, Cu–1 and Cu–2 at%Zr Alloy Wires

“…68) In particular, the wire drawn from Cu5 at%Zr with a drawing ratio (©) of 8.6 exhibited a remarkably high ultimate tensile strength, of 2.2 GPa. 8) Several studies describing the production and the characteristics of cold-worked materials such as CuAg, 916) CuCr 1720) and CuNb alloys, 21,22) in which lamellar structures of the second phase developed, have been reported. However, unlike CuZr alloys, 8) these materials did not exhibit strengths greater than 2 GPa at lean compositions.…”

Microstructure and properties of cold drawing Cu-2.5% Fe-0.2% Cr and Cu-6% Fe alloys

“…The composites were reported to be highly textured: Nb had a <110> orientation whereas Cu had <111> and <100> textures (Raabe et al, 1992;1995a). The reason was fully explained that the BCC phase was forced to curl and fold due to the constraint of the surrounding FCC matrix, which is able to accommodate axially symmetric flow (Bevk et al, 1978). The microstructure of the Cu-2.5% Fe-0.2% Cr alloy on the longitudinal section is similar to that of the Cu-6% Fe alloy, while there are only Cu filaments in the Cu-2.5% Fe-0.2% Cr alloy (Fig.…”

Effect of Alternating Magnetic Field on the Microstructure and Solute Distribution of Cu&ndash;14Fe Composites

“…Since deformation-processed Cu-Nb in situ composites were first discovered by Bevk in 1978, 1) Cu-X in situ composites have been the subjects of considerable studies, where X are body centered cubic (b.c.c) transition metals such as Cr, Zr, V, Fe or face-centered cubic (f.c.c) metals Nb and Ag.…”