Influence of heat treatment strain parameters on the structure and Jc 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°C and ∼400 hours respectively. The degree of plastic strain between consecutive annealings changed across a wide range (ε_int= 0.1-1.22). The wire drawing schedule was chosen with both equal and unequal values of ε_int. The values for the final strain, ε_fin, ranged from 2.3 to 5.6. When equal values of ε_int were used, the level of J_c obtained in the superconductor was 3640 A/mm² (at 5 T, 4.2 K). When unequal values of ε_int where used in the deformation schedule the J_c achieved 3840 A/mm². TEM was used to quantitatively evaluate the degree of diffusional decomposition in a supersaturated solid solution at different stages of alloy treatment.