The Top-seeded Melt Infiltration Process Of Ybco High Temperature Superconducting Bulk

YBCO HTS bulk materials, because of high critical temperature and excellent electromagnetic properties, are widely used in the field of superconducting magnets, energy storage flywheel, HTS maglev and other aspects. In order to further improve the critical current density, effective flux pinning center has to be introduced into the YBCO bulk superconductors, to improve the critical current density. Many experimental results have proved that second phase inclusions can act as strong flux pinning centers.The precursor powders for fabrication of YBCO bulk, such as YBa2Cu3O7-δ(Y123), Y2BaCuO5(Y211),BaCuO2(011), Ba3CuO5(035) and Y2Ba4CuWOx(YW2411) were prepared by soild state reaction method.YBCO bulks with different YW2411 additions have been fabricated by top seeded and infiltration growth process(TSIG).The surface morphology, microstructure and levitation force of the samples have been observed and measured. The growth process of single domain has been monitored and recorded by an insitu high temperature video camera.In the preparation of YW2411 doped YBCO bulk superconguctors,XRD pure YW2411 powders were prepared by solid state sintering at temperature of 1030℃for three times with an internal milling process. The microstructures of the YBCO bulk were observed by SEM. The result indicates that the size of YW2411 particles is about 150nm, which is much smaller than that of the Y211 particles. The YW2411 particles are of spherical or elliptical shape, when the YW2411 dopant is less than 5wt%; The YW2411 particles are tending to become needle shape when the dopant is greater than 5wt%.The leviation force of the YBCO bulks is much different with different additions of YW2411 particles, it is increasing to a peak vaule and decreasing later with the increasing of YW2411 additions, the largest levitation force is about 33.6N obtained in the sample with 5wt% YW2411 additions.The growth process of TSIG YBCO bulks has been monitored and recorded based on an in situ high temperature video camera. It is found that the starting epitaxial growth temperature of YBCO crystal from the seed is about 1010℃;the growth rate of YBCO crystal at different temperatures, different times and different positions have been calculated,the growth rate is increasing with the increasing supercooling of temperature, when△T<15℃,and decreasing with the increasing of△T,when△T>15℃.This result is helpful for us to improve the working efficiency during the fabrication process of high quality of YBCO bulk superconductors.