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

Abstract

Higher electromagnetic forces can be applied on Nb 3 Al superconductor, which shows much better strain tolerance than that of Nb 3 Sn, [1] making it suitable for application in fields of nuclear fusion devices, particle accelerators, and nuclear magnetic resonance. [2,3] However, the bronze or inner-tin route used for practical Nb 3 Sn superconductor fabrication is not feasible for Nb 3 Al, because of formation of non-superconducting Nb-Al-Cu phase during heat-treatment, thus Nb 3 Al can only be obtained through binary reaction between Nb and Al. [4] The equilibrium content of Al in Nb 3 Al ranges from 17 to 21.5 at%, [5] which shows poor superconducting properties. [6] After decades of development, rapid heating, quenching, and transformation (RHQT) process was used to fabricate high critical current density ( J c ) Nb 3 Al superconductors with near-stoichiometric composition and high-density defects presented. [7] Nb-Al precursor wire was first rapidly heated to about 2000 °C within 2 s and then quickly quenched in liquid Ga both to obtain ductile Nb-Al supersaturated solid solution (short as Nb(Al) ss ) wire with bcc structure; then the Nb(Al) ss wire was annealed at 800 °C for 10 h to transform to A15 phase). During the bcc ! A15 phase transformation process, atom diffusion distance was several lattice cells, which hinder the long-range composition distribution and form high-density stacking fault (SF) in the newly formed A15 phase to accumulate the crystalline lattice disarrangement. [3]