We present results of microstructural examinations of grain size distribution, grain geometry, compositional gradients and local texture performed on Nb3Sn wires of various manufacturing techniques. Measurements were conducted using high-resolution TEM (transmission electron microscopy), EDX (energy-dispersive X-ray spectroscopy) and TKD (transmission Kikuchi diffraction). Findings include residuals of heat treatments and Sn gradients across subelements as well as single grains which are needed to correlate with magnetic measurements.
Feasibility of increasing the high field critical currents to the FCC target was previously demonstrated by means of fast neutron irradiation which produces defects in the crystal structure that serve as additional pinning centers. In the present study, the underlying mechanisms are investigated through microstructural TEM analysis in order to establish a link between defect density and critical current. Examinations of the defect structure were performed on Nb3Sn wires using weak-beam dark-field microscopy before and after irradiation in a nuclear research reactor.
This understanding of the correlation between microstructure and macroscopic performance will be required for manufacturing such high-performance superconductors in an industrial process.