The deformation behavior of the surrounded Cu stabilized YBCO coated conductor based
on the Hastelloy substrate and its influence on the critical current were precisely
investigated. The mechanical properties were assessed at room temperature and 77 K. The
greatest contribution was brought by two metallic components of the Hastelloy substrate
and Cu stabilized layers. The internal strain exerted on the superconducting
YBCO layer was determined directly by using synchrotron radiation facilities. The
thermally induced residual strain with compressive component decreased during
the tensile loading and changed to a tensile component at the force free strain
(Aff), at which the internal stress becomes zero in the YBCO layer. Beyond
Aff, the increasing rate of internal strain slowed down, suggesting brittle behavior, that is, the
formation of micro-cracks. The applied strain dependence of the critical current
could be divided into two regions. In the reversible region, the strain dependence
obeyed the intrinsic strain effect and was well expressed by the Ekin formula.
Beyond the reversible limit, the critical current decreased rapidly with strain. The
degradation is suggested to be attributed to the formation of cracks in the YBCO layer.
The force free strain evaluated from the mechanical properties was 0.26%. On
the other hand, the strain at the critical current maximum was observed to be
0.035–0.012%. These facts suggest re-examining the hypothesis supposing that the critical
current maximum appears at the force free strain in YBCO coated conductors.
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