Deformation behavior of Nb3Sn type superconductors

Commercially available Nb3Sn type superconductors have at least four components with different shear modulus mu. All the components are polycrystalline and therefore the yield stress in shear is of order mu/500. The materials are subject to both thermal and mechanical stresses when in service. The stress levels can be well beyond the yield stress of the materials and therefore plastic flow occurs in selected components, such as Cu stabilizer and Cu-Sn matrix. Because deformation occurs at cryogenic temperatures and limited dynamic recover occurs, a high density of dislocations are accumulated. If the plastic deformation is large, deformation may be accommodated by twinning. The change of the deformation mechanisms will alter the strain-hardening rate and has an impact on the material properties. On the other hand, change of the microstructure can influence the plastic deformation behavior so that materials can be strengthened. This paper will first address the strain-hardening behavior of various components separately and then Nb3Sn superconductor composites. A semi-empirical model is introduced to address the possible practical strengthening approaches for Nb3Sn types superconductors.