Structure observed by neutron diffraction, mechanical behavior and critical current of multifilamentary Nb-Ti/Cu superconducting composite wire

Neutron diffraction measurements were carried out on multifilamentary Nb-Ti/Cu superconducting composite wire in order to clarify the structural anisotropy and the residual stresses arising from the fabrication process. Highly oriented structure was observed both for copper and Nb-Ti components. The residual stress of copper in the composite wire was estimated to be 40 MPa by means of PSD method, which was close to the yield stress of matrix, 30 MPa. The reason why the measured elastic modulus is lower than the predicted one based on the simple rule of mixtures was accounted for from the viewpoint of the formation of the texture. While the failure strain of filaments tested separately was nearly 2%, that of the composite with the copper ratio 7.83 was about 20%. The high failure strain of the composite was achieved through the formation of multiple necking of the embedded filaments. The average strength of the extracted filaments was 1240 MPa, which was about 10 times higher than that of the oxides and comparable to that of A15 compounds. The scatter of strength was much smaller than that of the oxides and A15 compounds. The critical current decreased with increasing applied strain, but nearly 80% of the critical current for unloaded samples was retained even after deformation up to 20% strain due to the enhanced failure strain of the filaments through the multiple necking.