Influence of Thermomechanical Working Schedules on Critical Current Density and Structure of Superconductor Nb-Ti Base Alloys

Abstract

Results are presented of staged determination of critical current density and structure of superconductor HT-50 and HT-55 wires unannealed and subjected to four intermediate anneals at 400°C. The wires produced without intermediate anneals have a single phase structure. with an increase of deformation jc grows monotonously, the size of β-matrix subgrains is reduced. The maximum jc equal to 0.48×l05 A/cm2 in the field of 5T is reached in the HT-55 alloy. In specimens subjected to intermediate anneals the first anneal leads to a more than order of magnitude increase of jc which is related to the α-phase precipition along the boundaries in the HT-50 alloy and also within the subgrains in the HT-55 alloy. The subsequent deformation cycles effect an increase of jc, a decrease of the sizes of the α -phase and the β-matrix subgrains while intermediate anneals have an opposite effect. A non-uniform precipitation of the α-phase is noted across the filaments. At the final stages of deformation a drastic increase of jc to 3.2×l05 A/cm2 and to 3.9×l05 A/cm2 in the field of 5T is observed in HT-50 and HT-55 alloys, respectively. There is a common dependence of jc on the β-matrix subgrain size for HT-50 and HT-55 alloys.