Enhancement of the irreversible axial-strain limit of Y-Ba-Cu-O-coated conductors with the addition of a Cu layer

A Cu protection layer added to yttrium-barium-copper-oxide-(YBCO-) coated conductors substantially enhances the irreversible strain limit ϵ irr for the onset of permanent electrical damage of the composite. This enhancement is of significance since it enables these conductors to meet the most severe strain requirements for applications such as electric generators. The conductors studied had either a Hastalloy-C substrate with an ion-beam-assisted deposition template or a rolling-assisted biaxially textured Ni-W substrate. The irreversible strain limit, obtained from critical-current measurements as a function of axial tensile strain at 76 K and self-field, increased from about 0.4% to more than 0.5% for both types of coated conductors with an added Cu layer, either by electroplating or lamination. This improvement is due only partially to the differential thermal contraction between Cu and the other conductor components. We believe that the Cu layer also enhances the fracture toughness of YBCO, thus acting as crack inhibiter/arrester.