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Monocore powder-in-tube MgB2 strands were cold-drawn and heat-treated at 600Cand 700C for times of up to 71 hours and structure-property relationshipsexamined. Drawing-induced elongation of the Mg particles led, after HT, to atextured macrostructure consisting of elongated polycrystalline MgB2 fibersseparated by elongated pores. The superconducting Tc, Jc and Fp were correlatedwith the macrostructure and grain size. Grain size increased with HT time atboth 600C and 700C. Jc and hence Fp decreased monotonically but not linearlywith grain size. Overall, it was observed that at 700C, the MgB2 reaction wasmore or less complete after as little as 30 min; at 600C, full reactioncompletion did not occur until 71 h. into the HT. Transport, Jct(B) wasmeasured in a perpendicular applied field, and the magnetic critical currentdensities, Jcm\bot(B) and Jcm{\phi}(B), were measured in perpendicular andparallel (axial) applied fields, respectively. Particularly noticeable was thepremature dropoff of Jcm\bot(B) at fields well below the irreversibility fieldof Jct(B). This effect is attributed to the fibrous macrostructure and itsaccompanying anisotropic connectivity. Magnetic measurements with the fielddirected along the strand axis yielded a critical density, Jcm\bot(B), forcurrent flowing transversely to the strand axis that was less than and droppedoff more rapidly than Jct(B). In the conventional magnetic measurement, theloop currents that support the magnetization are restricted by the lower ofJct(B) and Jcm{\phi} (B). In the present case the latter, leading to thepremature dropoff of the measured Jcm(B) compared to Jct(B) with increasingfield. This result is supported by Kramer plots of the Jcm{\phi} (B) and Jct(B)data which lead to an irreversibility field for transverse current that is verymuch less than the usual transport-measured longitudinal one, Birr,t.

Drawing induced texture and the evolution of superconductive properties with heat treatment time in powder-in-tube in-situ processed MgB2 strands