SUPERPLASTIC BEHAVIOR OF YBA2CU3O7-X/AG SUPERCONDUCTORS

High-temperature deformation characteristics of YBa2Cu3O7-x oxide (YBCO) and YBa2Cu3O7-x/Ag composite (YBCO/Ag) in uniaxial compression have been investigated. A compression test was carried out at temperatures from 780-930 degrees C at initial strain rates between 10(-6) and 10(-4) s(-1). YBCO/Ag composites with fine, dense and equiaxed grains were compressed over 120% with no indication of failure at higher temperatures, and the strain-rate sensitivity exponent, m, was found to be about 0.42-0.46 between 890 and 930 degrees C. They are considered to be one indication of superplasticity. The activation energy for deformation was 500-580 KJ mol(-1). The specimens suffered grain growth slightly during the deformation at 930 degrees C and the majority of growth might be a function of exposure time, temperature and silver content, but each grain maintained the equiaxed shape after extensive superplastic deformation. This is consistent with a grain-boundary sliding mechanism. The silver at grain boundaries acts to decrease the activation energy for deformation and promote the grain-boundary sliding.