IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 20, NO. 3, JUNE 2010 1549 Electrical and Mechanical Characterization of Coated Conductors Lap Joints G. Celentano, A. Augieri, A. Mauretti, A. Vannozzi, A. AngrisaniArmenio, V. Galluzzi, S. Gaudio, A. Mancini, A. Rufoloni, I. Davoli, C. Del Gaudio, and F. Nanni Abstract—Electrical and mechanical characterizations of YBCO coated conductors diffusion joints obtained in a 2 mm wide, Cu stabilizer free commercial tape provided by SuperPower Inc. were reported. Two conductor pieces were overlapped for a length of 20 mm and kept in contact under a pressure as high as 80 MPa. A face-to-face approach was used, with or without an additional Ag tape insert. The joint was realized by Ag diffusion at a tem- perature of 200 and 400 C in N and O atmosphere, respectively. The resistivity of the joint was measured at 77 K in N bath. The mechanical properties of the joint were characterized by means of single-lap tensile test operated at room temperature at a rate of 0.5 mm/min. The best results were obtained by high temperature joining in O atmosphere. The resistivity of the joints was as low as m . This value is almost halved if an Ag insert is used. The mechanical properties of the joints are strongly de- pendent on the use of an Ag insert, since maximum load as high as 60 N can be applied if no additional insert is used. This value enhances to about 100 N when an Ag insert is employed. How- ever, the joint obtained at low temperature in N atmosphere is also interesting since the joint resistivity was slightly increased to m and a maximum load as high as 50 N was ob- tained indicating that diffusion joints can be safely handled. These results are promising in perspective of oxygen free diffusion joints in Cu stabilized coated conductors. Index Terms—Ag, coated conductors, diffusion joints, single-lap test, YBCO. I. INTRODUCTION T HE development of joining technology of HTS Re-123 based coated conductors is a key issue towards their prac- tical application. In spite of the remarkable progress registered during the last decade in the field of HTS coated conductors, only few studies on joint processing were reported to date [1]–[4]. Mainly, three types of joining techniques were taken into consideration: superconducting joint, non-superconducting joint using a low melting temperature soldering material and diffusion joint. Anyway, the reliability of a joint technique is strictly dependent on the application. For large scale power Manuscript received October 19, 2009. First published April 05, 2010; current version published May 28, 2010. G. Celentano, A. Augieri, A. Mauretti, A. Vannozzi, A. Angrisani Armenio, V. Galluzzi, S. Gaudio, A. Mancini, and A. Rufoloni are with ENEA-EU- RATOM, I-00044 Frascati, Italy (e-mail: celentano@frascati.enea.it). I. Davoli is with University Tor Vergata, 00133 Rome, Italy. F. Nanni and C. Del Gaudio are with INSTM-Research Unit of Department of Science and Chemical Technologies-University Tor Vergata, 00133 Rome, Italy. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TASC.2010.2043833 applications, the last two techniques are considered the most appropriate. On the other hand, diffusion joint, which does not use soldering material, but just involves interdiffusion of Ag stabilizing layers, is expected to reduce the resistance across the joint because there is no additional resistance of a soldering material and contact resistance. Thus, for the joining of the superconducting tapes it is generally believed that the diffusion joint technique is most applicable. Previous studies have shown that with diffusion technique joints obtained in overlapped single tapes retained high critical current and exhibited very low contact resistivity [1], [5], [6]. The coated conductor tape consists of a multi-layered struc- ture composed mainly by a flexible metallic substrate (Stain- less Steel, Hastelloy or nickel based alloys) coated by YBCO films, the protective Ag layer, and an optional Cu stabilizer [7]. The diffusion joint technique was used only in case of Cu stabi- lizer free and/or Cu stabilizer removed samples because of the highly oxidizing conditions used in these studies [1], [5], [6]. By controlling the main parameters governing the diffusion process such as temperature, time duration and surface condition con- tact resistivity as low as m can be reached when joints are heated up to 500 C, demonstrating that joint resistance is ultimately governed by the YBCO/Ag interface properties [1]. Considering that, similar joint resistivity can be achieved even for lower joint processing temperatures provided that diffusion between Ag layers is sufficiently promoted. For temperature in the range of 200–300 C, the joint processing can be performed in nitrogen atmosphere without, in principle, significant YBCO oxygen losses and thus performance degradation [8], [9]. In this paper joint between the Ag sides of two coated con- ductors using Ag diffusion technique are prepared and electri- cally and mechanically characterized. For this purpose commer- cial YBCO stabilizer free coated conductors, named SF2050, manufactured by SuperPower Inc., have been employed. Joints are obtained at both 200 and 400 C in nitrogen and oxygen at- mosphere, respectively. The insertion in the joint area of an ad- ditional thin Ag tape reduces the contact resistance. Low con- tact resistivity, m has been achieved without any degradation of the flowing across the joint. Mechanical test showed high resistance to tensile load which is greatly improved with additional Ag tape. II. EXPERIMENTAL This work has been carried out with stabilizer free com- mercial YBCO coated conductors (type SF2050 manufactured by SuperPower Inc.). The 2 mm wide tape is a IBAD-coated conductor fabricated on 50 m thick Hastelloy C276 substrate. Considering the sequence of the buffer layer architecture, 1051-8223/$26.00 © 2010 IEEE