ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
A most important step in the critical current density (Jc) optimization of Nb-Ti is the large final drawing strain, in which α-Ti precipitates, initially approximately equiaxed and 100–200 nm in diameter, are drawn into ribbons, whose thickness (1–2 nm) is less than the superconducting coherence length [ξ (4.2 K)∼5 nm]. Using transmission electron microscopy, the precipitate thickness, spacing, cross-sectional area, and circumference were measured over the whole final drawing strain range. Each of these parameters was found to have a simple power dependence on the wire diameter. Tc, Hc2, and the resistivity (ρn) were also change considerably during the refinement of the precipitates. Directly after precipitation, Tc increased, and (dHc2/dT)Tc and ρn were reduced from the single-phase values. Drawing the wire returned these parameters to their single-phase values, as the precipitate thickness was reduced to less than ξ. This observation explains a long-standing peculiarity in this system, namely that the optimum Hc2 of high Jc conductors occurs for a composition close to Nb 46 wt.% Ti, even when the precipitation of 18 vol % of α-Ti shifts the matrix composition to a Nb-rich composition of theoretically lower Hc2.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.343624
