Chromium diffusion into plated Nb/sub 3/Sn strands deduced from electrical resistivity measurement

During the reaction heat treatment of Cr-plated Nb/sub 3/Sn multiflamentary strands the purity, and hence resistance ratio, of the Cu stabilizer becomes measurably degraded. The present study exploits the power of resistance-ratio (RR) measurement in exploring the role that Cr plays in this degradation. It is deduced that during the reaction heat treatment (RHT) of unplated strands oxygen diffusion (from the surrounding atmosphere) and subsequent internal oxidation can result in exceptionally high values of RR. Chromium on the other hand has two deleterious influences: (i) it retards the ingress of oxygen thus inhibiting the tendency towards high RR development; (ii) it diffuses in, and itself degrades RR. It is also pointed out that some of the lost RR can be recovered by subjecting the strand to prolonged moderate temperature post-RHT step-cooling from 600/spl deg/C.<>