Interfacial bonding enhancement of reel-to-reel selective electrodeposition of copper stabilizer on a multifilamentary second-generation high-temperature superconductor tape

A reel-to-reel copper selective electrodeposition process over a multifilamentary second-generation high-temperature superconductor (2G-HTS) has been demonstrated in our previous work. If the interfacial bonding between the deposited copper layer and the underlying silver overlayer is weak, it might lead to delamination in applications including magnets, motors and generators. In this study, two approaches have been used to improve the copper–silver bonding without the degradation of superconductor performance. The first approach is acidifying the electrolyte by adding sulfuric acid, by which the kinetics of copper electrodeposition is enhanced, resulting in finer microstructure at the copper–silver interface and thus, improved interfacial bonding strength. The second approach consists of blocking the electrolyte outflow at the entrance of the reel-to-reel electroplating cell, by which the occurrence of large copper seeds on the tape caused by the heavy turbulence flow is effectively prevented. With these two improvements together deployed in the process, the peeling strength between the copper and silver layers of the 2G-HTS tape has been improved from <0.3 N to >2 N in 90° peeling and from <0.5 N to >3.0 N in 180° peeling, without any degradation on the superconducting performance.