Title :
Applicability of Reel-to-Reel RHQ Treatments to
Precursors With a Ta/Cu/Ta Three-Layer Filament-Barrier Structure
Author :
Takeuchi, T. ; Nakagawa, Koichi ; Tsuchiya, K. ; Banno, N. ; Matsumoto, Akiyoshi ; Iijima, Y. ; Kikuchi, A. ; Nakamoto, Takamichi
Author_Institution :
Nat. Inst. for Mater. Sci. (NIMS), Tsukuba, Japan
Abstract :
A tension-free rapid heating and quenching (RHQ) simulator was previously employed to demonstrate that a ductile and normal-conducting Cu layer can suppress a magnetic field instability and improve bending strain tolerance. However, a molten Cu barrier caused the filament to be shifted from the original location, and excess heating caused the Cu to locally corrode a Ta layer, through which it diffused into the filament, thereby embrittling the resulting wire. In some cases, the swelling molten-Cu tore the Ta skin. Fabrication of a long piece of Ta/Cu/Ta barrier Nb3Al wire is attempted using reel-to-reel RHQ treatment of a modified precursor with a thicker Ta skin that would tolerate both tension forces in a section of the wire between electrodes and pressure from the swelling of molten-Cu. In the optimum RHQ condition (VRHQ: 9.5 V), a 50-m piece of Ta/Cu/Ta barrier precursor was successfully reel-to-reel RHQ treated to form a bcc supersaturated-solid solution (Nb(Al)ss) without bursting of the Ta skin. Microstructural analysis revealed that the molten Cu, into which Ta dissolved, diffused into the jelly-roll filament, mainly through a region of partially melted Al-rich Nb( Al)ss. The critical current density of the filament Jc (18 T, 4.2 K) was optimized by the deformation of Nb(Al)ss and compared favorably with the conventional precursor.
Keywords :
aluminium alloys; bending; copper; critical current density (superconductivity); crystal microstructure; electrodes; niobium alloys; quenching (thermal); solid solutions; swelling; tantalum; Nb deformation; Nb3Al; RHQ simulator; Ta layer; Ta skin; Ta-Cu-Ta; Ta-Cu-Ta barrier precursor; Ta-Cu-Ta barrier wire; Ta-Cu-Ta three-layer filament-barrier structure; bcc supersaturated-solid solution; bending strain tolerance; ductile Cu layer; electrodes; excess heating; filament critical current density; jelly-roll filament; magnetic field instability; microstructural analysis; modified precursor; molten Cu barrier; normal-conducting Cu layer; optimum RHQ condition; partially melted Al-rich Nb region; quenching; reel-to-reel RHQ treatments; size 50 m; swelling molten-Cu; tension forces; tension-free rapid heating; voltage 9.5 V; Electrodes; Heat treatment; Heating; Integrated circuits; Magnetic fields; Skin; Wires; Deformed-and-transformed; drawability; partial melting; reaction of Cu with Ta;
Journal_Title :
Applied Superconductivity, IEEE Transactions on
DOI :
10.1109/TASC.2012.2236876