Fracture behaviour and its relation to critical current of silver-sheathed Ba₂YCu₃O_7-x superconducting composite wires and tapes

Abstract

Silver-sheathed Ba₂YCu₃O_7-x superconducting composite wires and tapes were prepared by rolling, drawing, swaging and pressing methods. The fracture behaviour and its influence on critical current at O T at 77 K of the Ba₂YCu₃O_7-x were investigated. The oxide was found to show multiple fracture under applied tensile stress, and the critical current density and tensile strength of the oxide in the rolled, swaged and pressed samples were higher than those in the drawn samples. When the working amount was high, the current density and the strength of the oxide were found to become high. Within the present conditions, there was a correlation between critical current density and cracking stress: the higher the cracking stress, the higher the critical current density became. The cracking stress of the present oxide was determined to be 50MPa at most, being far lower than that of the Nb₃Sn compound (800 to 2000 MPa). The critical current density of the rolled, swaged and pressed samples was reduced rapidly when exerted stress on the oxide exceeded the cracking stress, while the reduction in the drawn samples occurred gradually. A strong dependence of the critical current, as a function of applied stress and cracking stress of the oxide, on the measured portion due to scatter in the size of defects contained in the oxide, was found.