Filament densification process is one of the key factors that determine the critical current capacity of Bi-2212 round wires. Multi-filament wires with well-densified filaments and better Ag-superconductor interface are expected to have less pores and better grain connectivity during the partial melting heat treatment. However, in traditional powder-in-tube (PIT) deformation process, there are some existing problems of synergistic deformation due to the difference in mechanical performance between powder and metal sheath. We report a novel and feasible approach for the fabrication process Bi-2212 Round Wires by applying ultrasonic vibration during deformation process. Bi-2212 round wire short samples were fabricated by introducing ultrasonic-vibration drawing process during both the single-filament and multi-filament stages of cold drawing processes with the ultrasonic vibration of 20 kHz and varied amplitudes. The influence of ultrasonic-vibration drawing process on Ag metal sheath, filament density, Ag/superconductor ratio, wire dimension, drawing force, and the superconducting properties of final wires have been systematically studied. Soften effect of ultrasonic vibration on the Ag metal can be deduced with the decreasing drawing flow stress and drawing force under certain amplitude. It was found that powder densification could be promoted and higher filament volume fraction as well as high wire diameter uniformity had been reached with the introduction of ultrasonic drawing process, leading to the enhancement of J_c and J_E after proper heat treatment.

Keywords: Bi-2212, Synergistic Deformation, Ultrasonic Vibration, Cold Working