Studies on superplastically deformed 123/Ag composites

Composites containing 25 vol% Ag were compressed at room temperature to over 110% at 850/spl deg/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 T/sub c/ was however low with an onset of 50 K and a width of /spl sim/10 K. 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 J/sub c/'s at low temperatures after the final anneal (T/sub c/ onset /spl sim/90/spl deg/K). The observations may be explained by highly superior intragranular properties coupled with increased local current loop size.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>