NbTi/Nb/Cu超電導多層板におけるα-Ti析出に及ぼす時効熱処理時間の影響

抄録

The influence of aging time on the size and quantity of Ti precipitates in the NbTi layers of NbTi/Nb/Cu superconducting multilayer sheets and on the critical current density (J_c) was studied. Ti precipitates with a length of about 250 nm and a thickness of about 100 nm had been already precipitated at the grain boundaries after the aging at 623 K for 8 h. The orientation relationships between these large precipitates and the NbTi matrix were (0001)_α\varparallel(1\bar10)_β and [11\bar20]_α\varparallel[111]_β . When aging time exceeded 336 h, an other fine precipitate with a length of about 50 nm and a thickness of about 3 nm appeared in the matrix. The volume fraction and sizes of the large precipitates increased with increasing aging time, but they did not serve effectively as the pinning points of fluxons. The practically useful J_c could not be obtained until the fine precipitates began to precipitate after aging longer than 336 h.