Influence of Thermomechanical Working Schedules on Structure and Properties of HT-50 and HT-55 Superconductor Alloys

The results of the staged critical current and structure determination are given for HT-50 and HT-55 superconductor wire specimens subjected to four intermediate anneals at 400°C. After the first anneal, Jc of both the alloys grows by more than an order of magnitude which is related to an intergranular and, in the case of HT-55 alloy, also an intragranular α-phase precipitation. Subsequent deformation cycles of thermomechanical working (TMW) effect an increaseof Jc, a decrease of α-phase and β-matrix subgrain sizes, while intermediate anneals have an opposite effect. An increase of Jc is observed at the final stage of drawing. The specimens of HT-50 and HT-55 alloys have, respectively, Jc = 3.2×105 A/cm2 and 3.9×10 A/cm5 A/cm2 in a field of 5T. The value is shown to depend on the size of β-matrix subgrains, the boundaries of which are decorated with α-particles.