Microstructure, texture and critical current of Ag-sheathed 2223 multifilament tapes

Abstract

An Ag-sheathed 2223 multifilament tape was produced by the powder-in-tube method. The various parts of the tape were heat treated at different temperatures under reduced oxygen partial pressure. The microstructure and the texture were characterized by synchrotron x-ray diffraction and SEM and correlated with Jc. In the low temperature range (<826 °C), the 2223 fraction and the c-axis alignment of 2223 grains increased with increasing temperature. A significant increase of Jc (from 1 to 41 kA cm-2) was observed in this range, indicating that the phase purity and the texture were the major controlling factors. In the medium temperature range (826-830 °C), the 2223 fraction and the grain alignment tend to saturate, and Jc remains nearly constant at a level of 40 kA cm-2. In the high temperature range (830-836 °C), the 2223 fraction and the grain alignment remained unchanged but Jc decreased with increasing temperature. The drop in Jc was related to the presence of an amorphous phase and a small amount of 2201 phase, indicating that the grain connectivity has become the major current-limiting factor. The variations in the filament shape, density and alignment within the multifilament tape were characterized. The influence of the inhomogeneous structure on Jc is discussed.