Studies on Superplastically Deformed 123/Ag Composites

Composites containing 25 vol% Ag were compressed at room temperature to over 110% at 850°C in air. Measurement of the strain rate sensitivity yielded a value of 0.5, characteristic of superplastic deformation. As deformed materials had sub-micron grain size and significant c-axis texture parallel to the pressing direction. TEM examination showed that the grains were highly defected and that the grain boundaries were clean. The Tc was however low with an onset of 50K and a width of ~10K. Annealing studies were carried out with an aim to “fully oxygenate" the material and anneal out a minimal number of defects to obtain higher transition temperatures, at the same time retaining a significant defect density for enhanced flux-pinning. Magnetization measurements were performed after most anneals in order to evaluate intragranular and intergranular properties. Results indicate the presence of unusually high Jc's at low temperatures after the final anneal (Tc onset ~90°K). The observations may be explained by highly superior intragranular properties coupled with increased local current loop size.