Properties of microfilamentary superconducting composites produced by a modified external diffusion method

Nb3Sn-based bronze matrix superconducting composites have been produced with micron-sized and submicronsized superconducting fibres by the external diffusion process, with precautions taken as recently recommended to suppress Kirkendall porosity. Such composites were found to carry overall critical current densities at 4.2 ° K in excess of 2 × 10⁴a/cm²at 15.4 T and over 10⁵a/cm²at 12 T; strains ca. 2% and stresses in the 500-1000 MPa range were sustained without degradation. It is seen that the finer fibres sustain higher intrinsic strains before degradation of Jc; and a method is demonstrated for the control of internal residual stresses by thermomechanical processing. The latter permits appropriate trade offs of fatigue life and zero-strain Jc.