Cube-textured substrates for YBCO-coated conductors: microstructure evolution and stability

Abstract

The realization of YBCO-based coated conductors with high critical current density involves the deposition of highly biaxially textured YBCO films. The use of epitaxial growth shifts this requirement to the template used for YBCO deposition. In the rolling-assisted biaxially textured substrate (RABiTS) approach, an appropriately oriented template is provided by a cube-textured substrate. The development of a cube texture is the result of recrystallization occurring in a heavily deformed tape, which is activated by high-temperature annealing. In the case of Ni-based alloys, thermal treatment at temperatures ranging from 900 to 1150??C for at least 30?min is commonly used. The determination of the minimum conditions for thermal treatments in terms of temperature?time involved in the recrystallization process is therefore of practical interest. In this work, Ni?5 at.% W alloy has been studied as a substrate for YBCO-coated conductors. 100??m thick tapes have been obtained through heavy cold rolling, followed by annealing in high vacuum. Different thermal treatments with rates of 20??C?min?1 have been performed in order to study the formation and the evolution of the cube texture. Moreover, the annealing time has been varied in order to inspect the thermal stability of the substrate microstructure at the relatively high deposition temperature of YBCO films. It is found that the substrate begins recrystallizing at 700??C and that the cube texture is fully developed at temperatures higher than 800??C, while annealing at 900??C for 1?h produces a stable microstructure at the typical YBCO deposition conditions.