Influence of heat treatment strain parameters on the structure and J/sub c/ of Nb-48.5 wt.% Ti superconductor
A multistage heat treatment has been used to form a homogeneous heterophase structure in the Nb-48.5wt.% Ti alloy. The fixed parameters of this treatment were the following: the number of annealings was 4, the temperature and total duration were 390/spl deg/C and /spl sim/400 hours respectively. The degree of plastic strain between consecutive annealings changed across a wide range (/spl epsiv//sub int/= 0.1-1.22). The wire drawing schedule was chosen with both equal and unequal values of /spl epsiv//sub int/. The values for the final strain, /spl epsiv//sub fin/, ranged from 2.3 to 5.6. When equal values of /spl epsiv//sub int/ were used, the level of J/sub c/ obtained in the superconductor was 3640 A/mm/sup 2/ (at 5 T, 4.2 K). When unequal values of /spl epsiv//sub int/ where used in the deformation schedule the J/sub c/ achieved 3840 A/mm/sup 2/. TEM was used to quantitatively evaluate the degree of diffusional decomposition in a supersaturated solid solution at different stages of alloy treatment.