The high-temperature superconducting phase YBa2Cu3O7−δ has been found to be unstable with respect to and decompose into other metal oxides (Y2BaCuO5, CuO, Cu2O, BaCuO2, and others) at stresses greater than 100 MPa at temperatures from 700 to 950 °C. Hot isostatic pressing and hot uniaxial pressing were used to apply pressure to and to densify porous YBa2Cu3O7−δ. X-ray diffraction and scanning electron microscopy/x-ray spectroscopy were used to determine phase purity before and after pressing. The instability of the superconducting phase should be considered during the development of hot mechanical densification and shape-forming processes, since a limit exists for the time at temperature and pressure that the YBa2Cu3O7−δ phase can withstand before decomposing.

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The response of ceramic superconductors and ceramic composites to compressive stresses at high temperatures has been examined. Monolithic YBa,Cu,O,-, and composite YBa,Cu,O,-,/Ag were tested at constant true strain rates from to lo-, s-' at temperatures from 800" to 950°C.Fine-grained monolithic YBa,Cu,O,-, appears to have a regime of superplastic deformation between temperatures of 850" and 950°C at strain rates from to s-I. The addition of 20 vol% Ag to a coarser-grained material enhances the ductility of the ceramic and lowers the flow stress by a factor of 3 to 10. However, there is no evidence of superplasticity in the composite material in the range of temperature and strain rate where it was tested.