Abstract
In order to produce high current density NbTi multifilamentary superconductors a complex thermo-mechanical processing route is followed. The composites are initially cold drawn to strains of 5-7 and heat treated to produce α-Ti precipitates at grain-boundary triple points. Subsequent drawing and heat treatment cycles (typically 3-6) increase the volume of precipitate and refine the homogeneity and scale of the microstructure. A final strain of 3-4 distorts the α-Ti precipitates (initially equiaxed in cross-section) into ribbons less than 4nm in thickness. The thickness and distribution of these “normal” α-Ti ribbons in the superconducting β-NbTi matrix is thought to play an important part in the flux pinning properties of the microstructure. The thickness and distribution of the ribbons are related to the diameter and distribution of the α-Ti precipitates after the final heat treatment. Measurement of these parameters is clearly useful and has been successfully,
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