The Effect of Aluminum Additions on Nb3Sn Produced in the Solid State

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Abstract
Aluminum has been added to the niobium core, and in various quantities to the copper-tin bronze, of composite wires that have been reacted to form Nb3Sn. Small amounts of aluminum in the bronze enhance the growth rate of Nb3Sn layers; aluminum in the core, and greater amounts in the bronze displacing some of the tin, cause a reduction in growth rate. Layer thickness is a function of (reaction time)0.67. Microprobe analysis revealed the presence of aluminum in the reacted layers only for specimens with aluminum additions to the core and in substantial quantities to the matrix. Critical current densities are primarily a function of reacted layer thickness; composition and temperature of reaction play a secondary role. Specimens in which some aluminum was successfully incorporated in thin (1- to 1.5-µm) layers of Nb3Sn showed maximum current densities, close to 109 A/m2 in transverse fields of 16 T, and 7 to 8 × 109 A/m2 at 10 T. In fields up to 8T these materials are superior to the best reported V3 Ga.