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Ahsfmet--In framc of Se.C.R.E.T.S. international task Nb3Sn strands with 50 nnd 60 % of Cu fraction have been produced and romprrativc research of their performance (Q, I,, Jt, RRR, etc.) have bccn carricd out. Strand design and processing wcre identical. However, thc dccrcasc of Cu fraction vrluc has influenced on RRR value as well us Cr-phted and barc strands. By method of subsequent approximntion the estimntion of diffusion coefficients of Cr into Cu by R275IR20 values of both strands have been carricd out. These calculations have shown that Nb,Sn strand after renction at the standard regime (575'C 150 11 f 65OoC 200 h at lo-' Torr) characterized the value of diffusion cocfficicnt -lo-" cm%, that has led to Cr penetration into oxygen free Cu in not more than 40 pm of depth. Thc cnlcuhtions of RHR intcgral vsliic vcrsus reaction timc and Cu thickness have also been done. The relation of diffusion coefficient and microstracture of Cu-stabilization has been discussed.

Multifilamentary bronze-processed Nb3Sn-based composites have been studied by the methods of TEM and SEM. Ti as a doping element required for an enhancement of superconducting characteristics, especially in high magnetic fields, was inserted either in a bronze matrix, or in Nb filaments of a composite. It has been found that Ti diffuses into the growing Nb3Sn layer in both cases, and affects positively its structure and superconducting characteristics of a composite as a whole, especially in case of the doped matrix. When Ti is added to Nb filaments, it forms fine particles of intermetallic compounds with Sn in the nanocrystalline diffusion layer. When these particles are formed, grain boundaries of the diffusion Nb3Sn layer purify from segregations, and grains in the vicinity of these particles coarsen, which negatively affects the current-carrying capacity of a composite. That’s why an optimal amount of Ti in Nb should be chosen, when Ti mainly dissolves in the Nb3Sn phase increasing its superconducting properties and not deteriorating its grain structure.

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