Influence of crystal plane on the welding quality of YBCO bulk superconductor

The microstructure of welds parallel to the {1 0 0} and the {1 1 0} crystal planes of the single-grain YBa2Cu3O7/Y2BaCuO5 (Y123/Y211) bulk superconductors welded by Ag foil has been studied. It is shown that a zone free of small Y211 particles is formed along the both sides of the welds. Formation of this zone is explained by higher Y content in the melt produced during heating and leaking out of the weld. The different morphology of the rest solidified liquid in the welds, which has a tendency to form films in the {1 0 0} welds and granules in the {1 1 0} welds, is associated with different surface energies of welded surfaces. Cracking suppression of the {1 1 0} welds was observed and is ascribed to higher fracture toughness for this plane. The quality of the weld is confirmed by the trapped field measurements.