DEVELOPMENT OF IN-SITU FABRICATION PROCESS OF COLUMNAR YBCO/Ag COMPOSITES

Superconducting and mechanical properties of unidirectionally solidified YBCO are improved by Ag addition.However，many gas holes formed in YBCO/Ag composites melted/solidified in the atmosphere。In YBCO/Ag composites melted in a vacuum to reduce the gas holes and solidified in the atmosphere，Ag particle-rich zone formed near the central region of the sample.These Ag particles and gas holes changed thermal conductivity of composite and the effective temperature gradient in the sample。The distributions of Ag particles and gas holes were measured and the changes in thermal conductivity and the effective temperature gradient were estimated by applying the rule of mixtures.123columnar crystals in YBCO/Ag composites developed under the critical solidification condition of G&gt；A·R，where A=6*10^5，G was temperature gradient(K/cm)，and R was solidification rate(mu m/s)。The above critical condition is a little harder than that(A=4*10^5)for YBCO without Ag，because of the diffusion barr…More ier effect of Ag particles at the 123 interface.Ag particles became larger at the 123 interface by the monotectic reaction and were trapped within123phase when they exceeded a critical size..At the central region of the cell，Ag-free zones formed by pushing Ag particles from the interface。The crystallographic orientations of123cellular facet interfaces were measured，and the normal growth rate(Ri)of each interface was estimated from the trace of the cell tip，which was detected by the above Ag-free zones：Ri(001)=0.47R-0.61R，and Ri(100)=Ri(010)=0.62R-0.70R.From the measured critical radius(Ro)of Ag particles trapped in the 123phase，the relationship beten ro and growth of the wereFurther，the interface resistivities(Rho C)of YBCO/Ag joints fabricated by solid state processing and liquid state processing were measured，and the minimum rho c as low as about10^&lt；-12&gt；OMEGA·m^2was obtained in both cases，which satisfied the stability criteria for composite conductors.Less：Less

Superconducting and mechanical properties of unidirectionally solidified YBCO are improved by Ag addition. However, many gas holes formed in YBCO/Ag composites melted/solidified in the atmosphere. In YBCO/Ag composites melted in a vacuum to reduce the gas holes and solidified in the atmosphere, Ag particle-rich zone formed near the central region of the sample. These Ag particles and gas holes changed thermal conductivity of composite and the effective temperature gradient in the sample. The distributions of Ag particles and gas holes were measured and the changes in thermal conductivity and the effective temperature gradient were estimated by applying the rule of mixtures. 123 columnar crystals in YBCO/Ag composites developed under the critical solidification condition of G>A・R,where A=6*10^5, G was temperature gradient (K/cm), and R was solidification rate (mu m/s). The above critical condition is a little harder than that (A=4*10^5) for YBCO without Ag, because of the diffusion barr … More ier effect of Ag particles at the 123 interface. Ag particles became larger at the 123 interface by the monotectic reaction and were trapped within 123 phase when they exceeded a critical size.. At the central region of the cell, Ag-free zones formed by pushing Ag particles from the interface. The crystallographic orientations of 123 cellular facet interfaces were measured, and the normal growth rate (Ri) of each interface was estimated from the trace of the cell tip, which was detected by the above Ag-free zones : Ri (001) =0.47R-0.61R,and Ri (100) =Ri (010) =0.62R-0.70R.From the measured critical radius (ro) of Ag particles trapped in the 123 phase, the relationship between ro and the growth rate (Ri) of faceted planes was given by the equation : Ri=b/ro, where b=1.05. Further, the interface resistivities (rho c) of YBCO/Ag joints fabricated by solid state processing and liquid state processing were measured, and the minimum rho c as low as about 10^<-12> OMEGA・m^2 was obtained in both cases, which satisfied the stability criteria for composite conductors. Less