Enhancement of electro-mechanical behaviors in RE–Ba–Cu–O composite superconducting tapes with laser slit edges

Abstract

The slit technique is an essential process for narrowing the second-generation high-temperature superconducting (2G-HTS) tapes. It is still very challenging to eliminate edge defects introduced during slitting. In this work, we developed a set of reel-to-reel laser slit (LS) equipment for narrowing 2G-HTS tapes using a femtosecond infrared laser. In comparison with the commonly used mechanical slit (MS) technique, the LS technique produced no cracks at the tape edges. Electro-mechanical behaviors of 2G-HTS tapes with MS and LS edges were compared in liquid nitrogen conditions. The results of the uniaxial tensile tests showed only a minor difference in irreversible tensile stress/strain of the two kinds of tapes. However, uniaxial tensile fatigue tests showed that the critical current (I c) retention of the LS tapes was about 14% higher than that of the MS tapes after 104 cycles (@ 77 K, σ max = 0.8σ y, and a stress ratio of 0.1). Moreover, U-Spring compressive tests revealed that no irreversible I c degradation occurred on the LS tapes under compressive strain up to −0.8%, with high reproducibility. On the contrary, the irreversible compressive strains of the MS tapes were rather scattered, ranging from −0.75% to −0.2%. Enhancement of electro-mechanical behaviors is strongly linked to fewer edge defects in the LS tapes. This research demonstrates significant advantages of the LS technique over the conventional MS technique, showing its promising prospects for demanding applications.