Filament breakage in Bronze process Nb3Sn superconductors

Wire breakage during fabrication of bronze process Nb3Sn conductors has been linked to individual broken filaments within the wire. The wire breaks produce a cup and cone fracture with the tip of the cone centered on an enlarged filament rather than on the center of the wire. Samples of two different types of wire were sectioned longitudinally or cross-sectionally and examined for occurrence of irregular filaments. Enlarged and broken filaments were found and their occurrence analyzed. The enlarged heads of broken filaments are significantly harder than the matrix or the surrounding, undisturbed filaments. Broken filaments were found most frequently among filaments at the edges of filament groups near the center of the wire. Data on enlarged filament size distribution, hardness, and distribution within the wire are presented in the paper.