Applied current induced degradation of delamination strength of coated conductors and microscopic mechanism revelation

Abstract

Abstract Coated conductors in superconducting coils experience transverse stresses caused by thermal stress and large electromechanical forces during operation, which risk the coated conductors’ delamination due to their multilayer structure. However, the mechanical–electrical coupling between the transverse stresses and applied currents involved during delamination remains insufficiently clarified. Focusing on this issue, here we conducted an experimental investigation on the delamination behavior of coated conductors when carrying superconducting currents. Through the simultaneous measurements of voltage and force signals during the delamination, we found with the increased applied current the correlation coefficient between the two increment variables elevated, however, statistical delamination strength from Weibull distribution showed a significant decreased behavior. Magneto-optical imaging on the delaminated surface of the sample indicated a mixing fracture model of superconducting layers. Further microscopy results demonstrated BaCeO 3 as dendritic structure generated at the delamination sites of samples with low delamination strength. It was thought the thermal stress caused by local quenching and the lattice mismatch between the BaCeO 3 and YBa 2 Cu 3 O 7-δ are the two fundamental reasons for the degraded statistical delamination strength. These findings indicate that the effect of applied current should be considered when establishing stress management criteria for REBCO coated conductors in superconducting magnets.