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

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 J(c).

In the low temperature range (<826 degrees C), the 2223 fraction and the c-axis alignment of 2223 grains increased with increasing temperature. A significant increase of J(c) (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 degrees C), the 2223 fraction and the grain alignment tend to saturate, and J(c) remains nearly constant at a level of 40 kA cm(-2).

In the high temperature range (830-836 degrees C), the 2223 fraction and the grain alignment remained unchanged but J(c) decreased with increasing temperature. The drop in J(c) 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 J(c) is discussed.