Tensile strength and fracture surface topography of Sm-Ba-Cu-O bulk superconductors

Scanning electron microscopy observations have been made on fracture surfaces induced by tensile tests of Ag-added SmBa2Cu3Oy/Sm2BaCuO5 composite bulk superconductors melt-grown in O-2 and 1%O-2/Ar atmospheres. It was deduced that the inferior tensile strength in the bulk grown in 1%O-2/Ar, as compared with that of the bulk -town in O-2 was caused by the larger size and volume fraction of the included voids. The tensile strength of a specimen with a fracture surface consisting of multiple facets was lower than that with a single facet for the bulks grown in both conditions. It was found that a rectangular facet on the fracture surface is a possible origin for the fatal crack and that the secondary phase particles oil that area act as anchoring points for initial crack propagation.