Characterization Of Microstructure And Properties Of Cu-Ni Alloy Substrates For Coated Conductors

Recently, the second generation high temperature superconductors(HTS) have received a host of interest in electrical and magnetic applications, among which YBa2Cu3O7-?(YBCO) coated conductor attracted the most attention for its high intrinsic irreversible field and high critical current density under high magnetic field. The rolling assisted biaxially textured substrates(RABiTS) technique is considered as the most cost-effective approach to obtain long lengths of textured-metal substrate for YBCO coated conductor.Binary Cu-Ni alloys have been considered as possible candidate substrate material to alternate the Ni-W system. In the present work, we have systematically investigated the deformation and recrystallization textures of several Cu-Ni alloys using x-ray diffraction(XRD) and electron backscatter diffraction(EBSD) technique. The micro-hardness was also evaluated as a function of annealing temperature. In addition, magnetic property of Cu-Ni alloys was explored and the Curie temperature was calculated by using the linear extrapolation for the purpose of optimizing the chemical component in metal substrate.Comparative characterization of Cu-Ni substrates for coated conductors showed that a similar rolling texture was observed in the cold rolled condition for the three alloys. For each material, annealing at higher temperature results in a much stronger cube texture but the fraction of annealing twin boundary was quiet low. When annealing at low temperature, it was presumed that the increase of Cu element increased grain boundary mobility, which then lead to the enhancement of twin boundary and reduced the fraction of cube texture. However, this effect was weakened at higher temperature and the fraction of cube texture in the three Cu-Ni alloys became similar. In addition, magnetization measurements indicate that the increase of Ni content can effectively increase the saturation magnetization in Cu-Ni alloys. The comparatively low ferromagnetism for both Cu-53 at.% Ni and Cu-49 at.% Ni alloys suggests that substrates produced using these materials will benefit from reducing hysteresis losses for AC applications.The microstructure and crystallographic texture have been investigated in a non-ferromagnetic Cu-44 at.% Ni substrates after heavy cold rolling and subsequent annealing at different temperatures. Annealing at higher temperature will result in a pronounced cube texture accompanied by twinning. When annealing at 1100?, a much sharper cube texture was developed, where the fraction of cube texture is almost 100% and the fraction of annealing twin boundary was quiet low. Low-temperature isothermal annealing was chosen for Cu-44 at.% Ni substrates in order to separate the effects of recrystallization and grain growth. In the process of recrystallization, the grain sizes for recrystallized grains of cube and non-cube orientations were estimated from the EBSD data. Cube-oriented grains have a size advantage compared to grains of other orientations, thus creating a strong cube texture in the fully recrystallized sample. Meanwhile, a large number of annealing twin boundary was formed. During grain growth, as the annealing temperature is quiet low, the majority of grains of non-cube orientations are consumed by cube-oriented grains, which further increases the area fraction of the cube texture and decreases the fraction of annealing twin boundary slightly.