Abstract
In order to investigate the high temperature deformation characteristics in YBaiCu307-, oxide superconductor, the compression test was performed at temperatures from $890^{\circ}C$ to $930^{\circ}C$ at initial strain rate between $1.0 x 10^{-5}s^{-1}\; and \; 1.0^{-4}s^{-1}$. As the temperature increased and the initial strain rate decreased, the flow stress decreased. The strain rate sensitivity exponent measured as 0.41-0.46, supporting occurence of a superplastic deformation. The activation energy for superplastic deformation was calculated as 500-580KJ/mol, which decreased with increasing Ag content. Microstructure of the superplastically-deformed specimens showed that a grain growth occurred during deformation, and it appeared to be considerable when Ag content increased, but most grains still remained equiaxed after deformation. In this study, the deformation mechanism of YBCO superconductor was the grain boundary sliding with the diffusional accommodation and the contribution of the gram boundary sliding to the total strain was estimated to be 65%.
YBCO산화물초전도체의 고온변형 특성을 조사하기 위하여 $890^{\circ}C$ ~ $930^{\circ}C$의 온도범위에서 $1.0 x 10^{-5}s^{-1}\sim 1.0^{-4}s^{-1}$의초기변형속도로 압축시험을 수행하였다. 변형온도가 증가함에 따라 또한 초기변형속도가 감소함에 따라 flow stress는 감소하였다. 변형률속도 민감지수는 0.41-0.46이었다. 이는 초소성 변형이 일어났음을 보여준다. 초소성변형에 대한 활성화 에너지는 약 500 ~ 580KJ/mol이었으며 Ag첨가량이 증가할수록 활성화에너지는 감소하였다. 초소성변형된 시편들의 미세조직 관찰결과 변형중에 결정립 성장이 일어났으며 Ag양이 증가함에 따라 이러한 현상을 뚜렷하였다. 변형후 결정립 형태는 등축상을 유지하였다. 이러한 결과로 볼때, YBCO 초전도체의고온변형기구는 확산을 동반한 결정립계 미끄러짐으로써 그 비율은 전 변형량중 약 65%정도였다.
