ASPECTS OF FORMING METAL-CLAD MELT-PROCESSED Y-BA-CU-O TAPES

Melt-processing of Y-Ba-Cu-O superconductor in a usable form for magnet winding requires the development of a cladding with demanding properties. Numerous recent efforts in cold forming Bi-based superconductor tapes have been successful because a silver tube can be used to constrain the ceramic material, which is sintered at much lower temperature than the Y-Ba-Cu-O. Typical high temperature metals which can be used to encase Y-Ba-Cu-O during sintering do not permit ready diffusion of oxygen as silver does. Recently, the full or partial recovery of superconductivity has been achieved in transition-metal-doped Y-Ba-Cu-O due to the partial-melt processing. Our effort concentrates on making a tape of Y-Ba-Cu-O up to 25 cm long in nickel cladding by using the partial-melt processing. Magnetic and transport current measurements of the tapes are performed and discussed. Transport critical currents at 4.2 K of greater than 600 amperes have routinely been carried by these tapes. Magnetization measurements indicate these high currents can be maintained up to 40 K. Aspects of selecting a criterion for establishing the transport critical current are discussed as they relate to applications.