Microstructure and Superconducting Properties of Rapid Heating, Quenching, and Transformation (RHQT) Powderin-Tube Nb_3Al Wires Doped with Sn Element

摘要

Properties of rapid heating, quenching, and transformation (RHQT)-treated powder-in-tube (PIT) Nb_3Al_(1-x)Sn_x wires are studied herein. After the RHQ process, the body-centered cubic (bcc) phase is formed in the Sn-doped Nb_3Al wires. The transformed superconducting A15 phase shows a uniform microstructure and homogenous component distribution feature. With the increase of the Sn doping level, the critical transition temperature (T_c), critical current density (J_c), and irreversibility field (B_(irr)) of the superconducting wires increase first and then reduce, achieving the highest Tc value of 17.6 K and the smallest ΔT_c of 0.6 K in the 4% Sn doped Nb_3Al wire. The 4% Sn addition helps to improve the layer J_c of the sample to 2.1 × 10~5 A cm~(-2) at 8 K and 5 T, which is about 2.5 times that of the pure Nb_3Al sample. Furthermore, the Nb_3Al_(1-x)Sn_x (x = 0.04) wire gives the highest Birr value of 17.22, 13.23, and 9.11 T at 8, 10, and 12 K, respectively. The addition of Sn helps to achieve stoichiometric Nb_3Al A15 phase and formation of precipitations with the size of 10 nm, which might act as the flux-pinning center.