Joining of multi-seeded YBCO melt-textured samples using YBCO/Ag composites as welding material

Welding of multi-seeded melt-textured YBCO is investigated and compared with the re-joining of two halfs cut from a single domain. The key procedure consists in controlling the growth direction and using as welding material, a thin layer cut from a YBCO/Ag melt-textured single domain. Microstructure analysis and superconducting characterization reveals that high quality joints were obtained. The spacer layer is composed of one single 123 grain which has the same orientation as the two adjacent domains and is nearly free from voids and agglomeration of secondary phases. A good connectivity between the sample and the welding part is obtained as well as a fine distribution of 211 particles. Whereas a number of serious macroscopic faults prevents high superconducting currents across the grain boundary of the as grown multi-seeded material, the applied “repairing” results in a high quality of the joint which allows an “effective” current density of nearly 10 kA/cm 2 at 77 K. In this case, the current density is limited rather by the residual misorientation (overall or local) between the adjacent regions of the separately grown single grains than by the quality of the welding zone. Contrary, the superconducting properties of a reference sample which was re-built by welding the two halfs cut from one melt-textured YBCO single domain sample are comparable to those of the original samples. This welding technique was applied for the first time to join two independent YBCO single domains grown from two separated seeds in a multi-seeded sample.