DOI: 10.1002/adem.201300415 The Project SupraMetall: Towards Commercial Fabrication of High-Temperature Superconducting Tapes** By Marco Witte,* G€ unter Gottstein, Nicole de Boer, Stefan Gilges, Jutta Kl € ower, Michael B € acker, Oliver Brunkahl, Brygida Wojtyniak, Werner Mader, Matthias Svete, Sven-Martin H € uhne, Sabine Lepper, Regina B € ohm and Manuela Schebera The aim of the joint industrial and academic project “SupraMetall” is to enable the large scale production of superconducting tapes. This is a report of the recent achievements in the production of cube textured metal substrates and the coating techniques of the buffer and superconductive layers. The final coated conductor tapes of 2 m length reached critical current densities of 120 A/cm-width. 1. Introduction Hundred years after the discovery of superconductivity by Kammerlingh–Onnes, the phenomenon is close to achieving introduction to a wide area of technological applications, especially after the discovery of high temperature supercon- ductivity by Bednorz and M€ uller [1] where cheap liquid nitrogen may be used as a cooling agent. Applications are possible in many different fields as, e.g., power lines, use in motors or generators, magnets or fault current limiters. The outstanding features of high temperature supercon- ductors (HTSC) are the lack of ohmic resistance and the possibility to achieve extremely high energy densities, both leading to a strong increase of energy efficiency. A drawback of HTSC is that their grain boundaries act as obstacles for the current flow if their misorientation is larger than 4°. [2] Thus, high energy densities can only be reached with single crystals or polycrystals with a very pronounced orientation alignment, i.e. a very sharp crystallographic texture. First developments focused on the production of powder-in- tube tapes consisting of silver filaments filled with super- conducting Ba 2 Sr 2 Ca n1 Cu n O 2nþ4þx (BSCCO)-powder, forming its texture during a variety of rolling steps. [3] Because of the high raw material costs for the powder in tube technique and the low critical density in magnetic fields, very soon the development of 2nd generation HTSC tapes, consisting of thin HTSC-layers on a metal substrate, was initiated. [4] The thin HTSC layer is formed by rare earth-barium cuprates (REBCO), e.g., YBa 2 Cu 3 O 7–x (YBCO). In order to achieve high current densities near single crystal growth of YBCO is required which is accomplishable by the use of strongly textured metal substrates, which serve as a template for the alignment. Here, Ni–5 at%W is the material of choice, as it forms a very sharp cube texture after rolling to over 90% reduction and subsequent annealing. [5–8] By alloying with W, the mechanical properties are enhanced, which is especially important for the high temperatures coating processes. Also, the addition of W reduces the ferromagnetism of Ni, which is beneficial for AC applications. Nevertheless, the presence of Ni requires a dense buffer layer to prevent the diffusion of Ni ions into the YBCO layer, which would lead to a degradation of its superconducting properties. Those buffer layers also need a variety of attributes, as they must inhibit the diffusion of Ni into the superconductor as well as the oxidation of the metal substrate, which would interfere with the oriented growth of the superconducting layer. Furthermore, the buffer layers have to transfer the texture of the metal substrate to the HTSC layer, as any texture loss decreases the superconducting current density. There are several materials that comply with one or two of the required characteristics, but only a few meet all needs, making them an adequate buffer for YBCO superconductors. [9] Such buffer materials are, e.g., MgO, Y 2 O 3 , yttria-stabilized [*] M. Witte, Prof. G. Gottstein Institut f€ ur Metallkunde und Metallpyhsik RWTH Aachen, Kopernikusstr. 14, 52056 Aachen, Germany E-mail: marco.witte@o2online.de Dr. N. de Boer, S. Gilges, Dr. J. Kl€ower Outokumpu VDM GmbH Kleffstr. 23 58762 Altena, Germany Dr. M. B€acker, Dr. O. Brunkahl, B. Wojtyniak Deutsche Nanoschicht GmbH, Heisenbergstr. 16, 53359 Rheinbach, Germany Prof. W. Mader, M. Svete, S.-M. H€ uhne Institut f€ ur Anorganische Chemie, Universit€at Bonn, R€omerstr. 164, 53117 Bonn, Germany Prof. S. Lepper, R. B€ohm, M. Schebera Hochschule Bonn-Rhein-Sieg, Fachbereich Elektrotechnik, Maschinenbau und Technikjournalismus, Grantham-Allee 20, 53757 Sankt Augustin, Germany [**] The authors gratefully acknowledge the financial support of the Fond for Regional Development of the European Union and co- financing by the German state of North Rhine-Westphalia within its program “Regionale Wettbewerbsf€ahigkeit und Besch€aftigung” ADVANCED ENGINEERING MATERIALS 2014, 15, No. 9999 © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 1 FULL PAPER