Microstructure and Superconducting Properties of Rapid Heating, Quenching, and Transformation (RHQT) Powder‐in‐Tube Nb₃Al Wires Doped with Sn Element

Abstract

Properties of rapid heating, quenching, and transformation (RHQT)‐treated powder‐in‐tube (PIT) Nb3Al1−xSnx wires are studied herein. After the RHQ process, the body‐centered cubic (bcc) phase is formed in the Sn‐doped Nb3Al 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 (Tc), critical current density (Jc), and irreversibility field (Birr) of the superconducting wires increase first and then reduce, achieving the highest Tc value of 17.6 K and the smallest ΔTc of 0.6 K in the 4% Sn doped Nb3Al wire. The 4% Sn addition helps to improve the layer Jc of the sample to 2.1 × 105 A cm−2 at 8 K and 5 T, which is about 2.5 times that of the pure Nb3Al sample. Furthermore, the Nb3Al1−xSnx (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 Nb3Al A15 phase and formation of precipitations with the size of 10 nm, which might act as the flux‐pinning center.

Improvement of critical current density J c in powder-in-tube rapid heating, quenching and transformation Nb3Al wires by doping with nano-SnO2

“…All the initial billets were swaged to the final precursor wires with diameter of 1.6 mm. The precursor wires were cut into short wires of length 14 cm to carry out the rapid heating and quencing (RHQ) treatment [35]. The wires were rapidly heated to over 1900 • C and quenched to a liquid Ga bath to generate the bcc structure Nb(Al) ss , followed by annealing at 800 • C and 10 h. The heating temperature during the RHQ process was measured by an infrared twocolor thermometer (CTratio 1MH1, Optris) that was calibrated using the melting point of pure Fe and Ni wires.…”

“…The Al concentrations of all the samples are near stoichiometric (24 ± 1 at.%) (their measurement locations are marked by the arrows in the figure). Formation of small Kirkendall voids with a size of a few hundred nanometers is attributed to the faster diffusion of Al atoms than of Nb atoms during the rapid heating process [35], which leaves vacancies at the Al sites that aggregate to form large voids. Figure 3 shows the mapping area and the elemental distribution of the 1 wt% n-SnO 2 doped Nb 3 Al wires.…”

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

“…The precursor wire was cut into pieces of 14 cm length and then was mounted on a self‐made static rapid heating and quenching (RHQ) equipment. [ 25 ] In the RHQ process, the short precursor wire was rapidly Ohmic heated to ≈2000 °C within 2 s with heating energy density of 10–14 J mm −3 and then immediately catapulted into the liquid Ga bath to realize quickly quench. The quenched samples were annealed in a vacuum tube furnace at 800 °C for 10 h that was known as transformation process to obtain A15 superconducting phase.…”