We present a new experimental technique to measure the delamination strength under transverse tensile stress of YBa2Cu3O7-δ coated conductors for electric power applications. The delamination strength, defined as the tensile stress at which the ceramic layers delaminate from one another, is measured at 76 K for different sample configurations. The delamination strength is reduced by as much as 40% when the conductor is slit to smaller width, a standard fabrication process, and this reduction is due to damage to the ceramic layers near the edges of the conductor. We found that the delamination strength of slit coated conductors can be raised significantly by reinforcing the conductor by laminating it with copper strips and adding solder fillets at the edges. In relatively strong conductors, where the delamination strength is as high as 15 MPa, the critical current does not degrade before actual delamination. This fact greatly simplifies sample characterization of practical high-strength conductors, since only mechanical measurements need to be made. The critical current does, however, degrade significantly as a function of transverse stress before delamination in weak conductors that have relatively low delamination strength below 15 MPa. We discuss how a soft metallic layer in YBCO coated conductors may limit the transverse stress that the superconducting layer experiences in applications.
Citation: Superconductor Science and Technology
Pub Type: Journals
delamination strength, elctro-mechanical porperties, high-temperature superconductors, YBCO