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

• Published in: Philosophical magazine (Abingdon, England) Vol. 84; no. 24; pp. 2579 - 2593
• Main Authors: Han ¶, K., Lawson, A. C., Wood, J. T., Embury, J. D., Von Dreele, R. B., Richardson, J. W.
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis Group 21.08.2004; Taylor and Francis
• 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; Scanning electron microscopy; Inorganic compounds; Neutron diffraction; Niobium alloys; Experimental study; Stress-strain relations; Defects; Interfaces; Binary alloys; Composite materials; Transmission electron microscopy; Internal stresses; Anisotropy; Wires; Copper alloys; Anelasticity; Stress effects; Thermal annealing; Silver alloys; Transition element alloys; Distribution functions
• 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.