Abstract
The microstructure of multifilamentary Nb—46·5 wt% Ti composites has been investigated by means of small-angle neutron scattering measurements. The scattering intensity was analysed by assuming that the shape of α-precipitates is a flat ellipse. The volume fraction Vf of α precipitates increased from 1·3 to 13·4% as a function of the degree of thermomechanical treatment and the average thickness of precipitates changed from 1·5 to 4 nm. The superconducting critical current density for the wires examined here exceeded 3000 A mm−2 at 5 T. The global pinning force density Fp, could be expressed as a function of the volume fraction of precipitates as Fp = Fp(0) + kVf 2/3, where k is a constant. The factor Fp(0) indicates the contribution from the substructure formed by heavy plastic deformation. The magnitude of Fp at high magnetic fields was found to be decreased remarkably by the final heat treatment. We attribute this effect to the recovery of the substructure.