Influence of Ti and Ta doping on the irreversible strain limit of ternary Nb₃Sn superconducting wires made by the restacked-rod process

Abstract

Nb 3 Sn superconducting wires made by the restacked-rod process (RRP ®) were found to have a dramatically improved resilience to axial tensile strain when alloyed with Ti as compared to Ta. Whereas Ta-alloyed Nb 3 Sn in RRP wires showed permanent damage to its current-carrying capacity (I c) when tensioned beyond an intrinsic strain as small as 0.04%, Ti-doped Nb 3 Sn in RRP strands exhibits a remarkable reversibility up to a tensile strain of about 0.25%, conceivably making Ti-doped RRP wires more suitable for the high field magnets used in particle accelerators and nuclear magnetic resonance applications where mechanical forces are intense. A strain cycling experiment at room temperature caused a significant drop of I c in Ta-alloyed wires, but induced an increase of I c in the case of Ti-doped strands. Whereas either Ti or Ta doping yield a similar enhancement of the upper critical field of Nb 3 Sn, the much improved mechanical behavior of Ti-alloyed wires possibly makes Ti a better choice over Ta, at least for the RRP wire processing technique. * Contribution of NIST, an agency of the US government, not subjected to copyright.

Elastic Anisotropy in Multifilament <inline-formula> <tex-math notation="TeX">$\hbox{Nb}_{3}\hbox{Sn}$</tex-math></inline-formula> Superconducting Wires

“…Since a similar Nb3Sn texture is observed in Ti and Ta-doped RRP wires [9], texturing cannot explain why the irreversible strain limit in Ti doped RRP wires is higher than in Ta-doped RRP wires [19]. In conjunction with the mechanical properties of Nb3Sn, those of the Nb diffusion barrier may also influence the irreversible strain limit of the composite wire [20,21].…”

Strain and Magnetization Properties of High Subelement Count Tube-Type ${\rm Nb}_{3}{\rm Sn}$ Strands

“…3. This strand has an intrinsic irreversible strain limit 1051-8223/$26.00 © 2011 IEEE of about 0.23% on average, which is comparable to the PIT conductors [11] and regular Internal-Tin conductors [12].…”

Nonuniform Distribution of Elements in RRP® Nb3Sn Wires Doped Using Nb–Ti Rods

“…This is a recent change to move away from the use of Nb 3 Sn wires with Ta doping because of concerns with strain management and because Ti-doped wires appear to process better and give longer piece lengths. It has been established [4] that with the same HT, filament fracture occurs at a lower strain in Nb 3 Sn wires with Ta doping than with Ti doping, as detected by the irreversible axial strain limit of critical current (ε irr ). Accompanying ongoing work to investigate ε irr in Nb 3 Sn wires with different amounts of Ti doping, this paper reports the non-uniform phase distribution of four RRP ® Nb 3 Sn wires with a level of doping that is in the range of the accepted optimal doping amounts of Manuscript Ta and Ti that have conventionally been adopted from work by Suenaga [5].…”