Internal stresses in cold-deformed Cu-Ag and Cu-Nb wires

• Published in: Philosophical magazine (Abingdon, England) England), 2004-08, Vol.84 (24), p.2579-2593
• Main Authors: Han ¶, K., Lawson, A. C., Wood, J. T., Embury, J. D., Von Dreele, R. B., Richardson, J. W.
• Format: Article
• Language: English
• Subjects: Anelasticity, internal friction, stress relaxation, and mechanical resonances; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Mechanical and acoustical properties of condensed matter; Physics
• ISSN: 1478-6435; 1478-6443
• DOI: 10.1080/14786430410001689981

The co-deformation of Cu-Ag or Cu-Nb composite wires used for high-field magnets has a number of important microstructural consequences, including the production of very-fine-scale structures, the development of very high internal surface-area-to-volume ratios during the drawing, and the storage of defects at interphase interfaces. In addition, the fabrication and co-deformation of the Cu and Ag or Nb, which differ in crystal structure, thermal expansion, elastic modulus and lattice parameter, lead to the development of short-wavelength internal stresses in both composites. In this paper, these internal stresses are characterized by neutron diffraction and transmission electron microscopy as a function of the imposed drawing strain. The internal stresses lead to important changes in the elastic-plastic response, which is related to both magnet design and service life. The second derivative ∂ 2 σ/∂ 2 ε of the stresses with respect to strain is used to describe the low-strain anelasticity of the composites. The internal stresses in Cu-Nb are higher than in Cu-Ag and, consequently, the absolute values of (∂ 2 σ/∂ 2 ε) Cu-Nb are higher than those of (∂ 2 σ/∂ 2 ε) Cu-Ag at low strains.