Microstructural studies of Ag and Ag alloy sheathed Tl-1223 tapes

The influence of processing conditions on the grain size, alignment and connectivity, porosity, secondary phase content and presence of extended defects in PIT Tl-1223 tapes has been studied for samples prepared by both sintering and in situ reaction mechanisms. Tape thickness reduction by cold rolling resulted in grain refinement due to precursor or 1223 particle crushing, and some grain alignment especially in tapes prepared by in situ reaction. By contrast, an increase in grain connectivity was observed in rolled tapes prepared by sintering. The abnormal grain growth of 1223 crushed grains was observed in the case of tapes prepared by sintering. An increase in secondary phase content observed during extended annealing is related to thallium loss. Shear defects were formed at higher rolling deformations, and suggested to be particularly detrimental for transport currents.