On the micromechanics of multifilamentary superconducting composites

The mechanical properties of multifilamentary Nb3Sn composites depend on several interrelated effects. The elastic modulus is influenced by crystallographic texturing as well as internal stresses. The textures as they develop in the as-drawn composite are typical of FCC and BCC metals, as is the oblate filament shape of the Nb filaments, which can be understood in terms of the orientation restriction of slip systems in such materials. Jc versus strain measurements on a 12.25% Nb composite with 1.2 micron diameter filaments show that zero strain Jc's are obtainable well beyond 1.0% strain on the first cycle. However, the internal residual stresses are relieved by applied strains well below 1% and subsequent Jc vs. strain performance is markedly impaired. The possible advantages of ultrafine filament composites are discussed.