Microstructure and Composition Comparison of Ti‐ and Ta‐Doped Nb3Al Superconducting Wires Fabricated by RHQT Process

Herein, the microstructure and composition of the Ti‐ and Ta‐doped Nb3Al superconductor fabricated by rapid heating, quenching, and transformation (RHQT) process are compared. After rapid heating and quenching (RHQ) process, body‐centered cubic (bcc) phase is formed in all the wires, showing dark stripe and bright contrast morphology in the backscattered electron (BSE) images. After transformation heat‐treatment, all wires consist of A15 phase and show the same morphology as that of the quenched samples. Near‐stoichiometric composition is shown in 3 at% Ti‐ and Ta‐doped Nb3Al samples, but when doping amount is 10 at%, Ti‐doped sample has constant Nb content of 67 at% and Ta‐doped sample has Al + Ta content of 25 at%. Superconducting properties of both 3 at% Ti‐ and Ta‐doped Nb3Al samples are comparable and much superior than that of 10 at% doped samples, including critical temperature (Tc), critical current density (Jc), and irreversible field (Birr). Though 10 at% Ta‐doped Nb3Al has higher Tc than 10 at% Ti‐doped sample, it presents wider ΔTc value and lower Jc performance. When increasing the measurement temperature from 8 to 10 K, the decay ratio of Birr value for Ti‐doped Nb3Al superconductor follows the scaling law; however, the Ta‐doped samples are not the case. A15 phase powder‐in‐tube (PIT) transformed and body‐centered cubic (bcc) phase as‐quenched (Nb1−xTix)3Al and (Nb1−xTax)3Al (x = 0.03, 0.1) wires are prepared by rapid heating, quenching, and transformation (RHQT) method. The effects of Ti and Ta additions on the crystal structure, microstructure, and superconducting properties of Nb3Al superconductors are compared and analyzed by X‐ray diffractometer (XRD), micro‐XRD, scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDS), and magnetic properties tests.