Mechanical and Superconducting Properties of Multifilamentary Nb₃Sn Composites

Abstract

The interrelation of mechanical and superconducting properties with the microstructure of multifilamentary composites has been investigated. The fracture behaviour changed depending on the growth of the compound layer. When the layer is thin, multiple fracture is observed and the composite can be plastically deformed with a large elongation. On the other hand, when the heat tratment progresses and the layer thickness becomes thicker, the whole composite fractures at once after a small elastic elongation. There exists a critical thickness dividing these two modes, which has been determined theoretically as well as experimentally. The maximum global pinning force can be well described as a function of the inverse grain size of the compound. The strength of the compound is also made clear so as to be expressed as a function of the inverse grain size. Finally, we propose the structure of composites and the conditions of heat treatment to optimize both properties mentioned above.