Title :
Studies on superplastically deformed 123/Ag composites
Author :
Goyal, A. ; Wang, Z.L. ; Sun, Y.R. ; Kroeger, D.M. ; Thompson, J.R. ; Chou, Y.T. ; Yun, J. ; Harmer, M.P.
Author_Institution :
Div. of Metals & Ceramics, Oak Ridge Nat. Lab., TN, USA
fDate :
6/1/1995 12:00:00 AM
Abstract :
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.<>
Keywords :
annealing; barium compounds; composite superconductors; compressibility; critical current density (superconductivity); electron microscopy; flux pinning; grain boundaries; grain size; high-temperature superconductors; magnetisation; plastic deformation; silver; superconducting transition temperature; superplasticity; transmission electron microscopy; yttrium compounds; 300 K; 50 K; 850 C; 90 K; TEM; YBa/sub 2/Cu/sub 3/O/sub 7/-Ag; YBa/sub 2/Cu/sub 3/O/sub x//Ag composites; annealing; clean grain boundaries; compression; critical current density; critical temperature; defect density; flux-pinning; intergranular properties; intragranular properties; local current loop size; magnetization; strain rate sensitivity; sub-micron grain size; superplastic deformation; Annealing; Grain boundaries; Grain size; Magnetic materials; Magnetic properties; Magnetization; Performance evaluation; Pressing; Strain measurement; Temperature sensors;
Journal_Title :
Applied Superconductivity, IEEE Transactions on