Study of Delamination in REBCO Coated Conductor by Transmission Electron Microscopy

REBCO coated conductor has very promising applications as the conductor for high field magnets for particle accelerators and nuclear fusion reactors. One of its main failure modes is the delamination of its multilayer structure. Despite the decade-long efforts by the superconducting magnet community, the microscopic understanding of the delamination and the methods of mitigation are still lacking. This work presents the transmission electron microscopy (TEM) investigation of the microstructures of the Superpower Inc. REBCO coated conductor to correlate with its delamination strength. We looked into the microscopic cause of the buffer layer delamination of low delamination strength tape. We found that the low delamination strength tape primarily delaminated at MgO/Y₂O₃ interface, and it was due to nano-voids formed at the Y₂O₃ top surface adjacent to the IBAD MgO layer. Higher density nano-voids would reduce the MgO and Y₂O₃ contact area resulting in a weaker bonded interface. The dislocations with extra planes inserted at the REBCO/LaMnO₃ interface also resulted in a weaker REBCO/ LaMnO₃ interface.