High Density Bulk Shape Rapid Consolidation of the Yba 2 Cu 3 0 7-X Superconductor
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HIGH DENSITY BULK SHAPE RAPID CONSOLIDATION OF THE YBa 2 Cu307_, SUPERCONDUCTOR* S. V. RELE**, R. V. RAMAN**, H. S. MEEKS**, and R. L. ANDERSON**, ** Ceracon Inc, 3463 Ramona Ave., Ste. # 18 Sacramento CA 95826 R. N. SHELTON*** and M. D. LAN*** ***Department of Physics, University of California, Davis CA 95616 *Sponsored by: Defense Advanced Research Projects Agency under contract #MDA-972-B8-C-0051. Abstract A novel rapid densification technique for fabrication of bulk shape YBa 2Cu307_xSuperconductor is presented. The Ceracon process is a one-step, quasi-isostatic consolidation route utilizing conventional P/M equipment and set-up. The Ceracon technology has enabled successful fabrication of bulk shapes such as discs, cylinders, hollow cylinders and spheres along with significant increases in the density up to 95-98% of the theorertical. The superconducting volume fraction is preserved due to short hold times at the operating temperatures and avoidance of high processing temperatures. Results based on densities, microstructure, susceptibility measurements, X-ray diffraction patterns and TGA measurements are discussed. Bulk high temperature superconductors have been limited in their applications by non-optimal values of mechanical and superconducting properties. The poor properties exhibited by the ceramic superconductors can be attributed to unfavorably modified properties of the bulk material resulting from processing conditions used in conventional consolidation techniques. A novel processing route, namely the Ceracon Process, for the fabrication of high density bulk YBCO superconductor is discussed. The Ceracon process (shown in Fig.l) is a unique, one-step, quasi-isostatic, hot consolidation technique [1] akin to Hot Isostatic Pressing (HIPing) but utilizes a ceramic particulate material as a pressure transmitting medium (PTM), instead of the gas used in HIPing. Cold iso-pressed green preforms are preheated and subsequently immersed in hot ceramic PTM. Pressures up to 900 MPa are applied to the PTM for hold times up to 200 seconds. The uniaxial pressure applied to the grain bed is transmitted to the superconductor as quasi-isostatic pressure and consolidation of the part occurs in a time span of minutes. The Ceracon processed samples are maintained at 930*C for 24 h in flowing oxygen and slowly cooled to room temperature to allow for full recovery of oxygen content, critical to the formation of the superconducting phase. The control parameters for this process include the part temperature, the PTM temperature, the pressure, part preheat time and hold time at the high temperature and pressure. The Ceracon-consolidated and annealed YBCO specimens were characterized for physical density, microstructure (optical and SEM), magnetization measurements, thermogravimetric analysis and X-ray diffraction. Magnetic measurements were performed in a Quantum Design magnetometer with an applied field of 20 G. Fig. 2 (a) and (b) show a polarized light optical micrograph and a scanning electron micrograph in the secondary imag
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