Abstract : This study concerns the development of biaxial textured substrates for the second generation of high temperatures superconductor known as “coated conductor”. The substrate was obtained with a rolling annealed process. The materials used are industrial alloys Cu55Ni44Mn (Constantan) and Cu70Ni30. Compared to NiW alloys, generally used, these copper-nickel alloys are nonmagnetic at 77 K and thus allow AC applications; moreover they are cheaper.
Tests on different rolling mills, with or without lubrication and by modifying the rate of work hardening made it possible to highlight skin effects and to optimize deformation processes.
The annealing temperatures were selected following characterizations of texture before and after annealing as well as in-situ measurements by hard X-ray diffraction during the rise in temperature.
Rollings higher than 98% and annealings between 900°C and 950°C in protective atmosphere made it possible to obtain ribbons having a strong cubic texture with an out of plan misorientation of 5° and an in plan misorientation of 8°. Part of the surface is however twinned (between 8% and 10%) which causes locally high disorientation.
The surface roughness was controlled and improved by the use of mirror polished rollers, the optimization of the annealing conditions (atmosphere and length of the dwell) as well as the addition of an electropolishing stage.
Mechanical and magnetic tests, as well as an oxidation study, were performed to check the behavior of the ribbon under the conditions of use and under the conditions met by the tape during the all process.
A LZO protective layer was successfully coated on the substrate. The conditions of a pretreatment under sulphurized atmosphere, necessary to a good epitaxy of the layer were given.
Finally, tests have been made to develop Cu-Ni-Y alloys which should allow to grow in-situ protective layer.