Preparation And Research Of Y₂o₃/ag Composite Tapes For Ybacuo Coatings

Ag is a substrate material which is commonly used in the field of superconducting. Ag substrates have no chemical diffusion with Y123 at deposition temperature, which makes it possible to deposit superconducting films directly on them. Using Ag substrates can not only simplify complicated techniques and cut costs of preparing YBaCuO tapes, but also make it easy to realize large-scale production. However, the tensile strength of Ag becomes very low after a long time of heattreatment. In this paper, high melting point oxide Y2O3 was doped into Ag, in order to improve the mechanical properties of Ag composites which were used as substrates of YBaCuO tapes, and YBaCuO coating was prepared by MOD method on one of the Y2O3/Ag substrates.In this paper, Y2O3/Ag composites with different Y2O3 contents were prepared by powder metallurgy method. Hardness, tensile strength and elongation percentage of Y2O3/Ag composites were tested. The results indicated that these properties tended to increase then decrease with the increase of Y2O3 content. When 1wt% Y2O3 was doped, tensile strength and elongation percentage reached the maximum. They were both higher than that of pure Ag by 24%. Hardness reached the maximum when 2wt% Y2O3 was doped, and it was higher than that of pure Ag by 36%. The optimum content of Y2O3 was 1.2wt%. The density of Y2O3/Ag composites decreased with the increase of Y2O3 content under the same sintering condition, and there was no linear relationship between porosity and Y2O3 content. The density increased with the extension of sintering time on condition that the Y2O3 content was fixed, and the porosity showed the opposite trend.Methods of cold rolling and annealing at high temperature were adopted to prepare Y2O3/Ag composite substrates. The impacts of rolling pass, annealing temperature and reduction on the orientation of Y2O3/Ag substrates were discussed. The results indicated that (220) preferred orientation which was relatively stronger was obtained in the condition of 12 rolling pass on the premise of 82% reduction, but rolling pass didn't affect (220) preferred orientation badly. The (220) preferred orientation couldn't be improved remarkably by raising rolling reduction when the reduction had been up to a certain extent. It was formed during the process of cold rolling. During the following process, some grains departed from (220) orientation and turned to other low-energy orientations. So (220) orientation degraded obviously after annealing. After second rolling, other orientations in low-energy sites absorbed stacking fault energy and turned to (220) orientation, which was stronger after annealing at 700℃than other annealing temperatures. The (220) orientation of substrates almost consisted of {110}<111> texture after second rolling and annealing. This texture was weak and its content was 2.71%. There was also a little {110}<100> texture and its content was even less.A primary experiment was carried out to prepare YBaCuO coating on one of the Y2O3/Ag substrates by MOD method. The results indicated that the component of the coating was Y123, but the intensity of each YBaCuO peak was weaker than that of the Y2O3/Ag substrate. The (00l) orientation of the YBaCuO film was not very strong.