Effects of Titanium Addition to the Niobium Core on the Composite-Processed Nb<SUB>3</SUB>Sn

Abstract

Effects of titanium addition to the niobium core on the composite-processed Nb3Sn superconductor have been investigated. Composites consisting of a Nb-0.0.5,1,2,3,4 at%Ti alloy core and a Cu-7 at% Sn alloy matrix were fabricated into single-core and 16-core multifilamentary wires, and then heattreated to form Nb3Sn layers. An enhanced formation rate of Nb3Sn layer with increasing titanium content has been observed, while the Nb3Sn grain size slightly increases with the titanium addition. The titanium addition of 1-2 at% to the niobium core produces a small increase in Tc, and further titanium addition decreases it. The addition of titanium to the core increases Hc2 by 4T in accordance with the increase in the normal state resistivity. Hc2 of about 25T has been obtained at 4.2K by the titanium addition. Jc's of Nb3Sn at high fields (H>13T) are remarkably increased by the titanium addition, which is been obtained at 4.2K and 16T for a single core wire and a 160-core multifilamentary wire, respectively. The Nb-Ti/Cu-Sn composite wire seems to be quite promising for applications in high magnetic fields ranging from 12 to 16 T.

Effect of Zn addition and Ti doping position on the diffusion reaction of internal tin Nb3Sn conductors

“…The reason for the smaller grain size in 14Zn-MT0.2 is considered to be the smaller amount of Ti addition. As previously reported, the grain size tends to decrease at decreasing Ti addition in the Nb 3 Sn layer [41,47].…”

“…Ti doping is known to improve the upper critical field and high-field J c performance [40][41][42][43][44][45][46]. For Ti doping, two paths are possible in the bronze process, namely doping to the Nb cores and the bronze matrix.…”

Optimization of Nb3Sn and MgB2wires

“…Thus, 3 times more Ta atoms are needed for obtaining the same increase of ρ o as for Ti, Ga or Ni additives. As already mentioned, the maximum value of B c2 is obtained for ∼1.5 at.% Ti [10][11][12], while the maximum for Ta additives is observed at ∼4 at.% Ta [9][10][11][12], i.e. a factor 3 higher.…”

“…The pseudobinary phase fields of the A15 phase in the systems Nb-Sn-Ta and Nb-Sn-Ti were determined, using quantitative data reported on alloyed filamentary Nb 3 Sn wires. These measurements were performed on bronze route wires reacted at temperatures between 725 and 800 • C above 24 h [9][10][11][12], where the filaments are fully reacted and consist of equiaxed grains only, showing a quite homogeneous Sn distribution. Since longer annealing times only lead to larger grains, but do not cause observable changes in the atomic compositions, the A15 phase limits in the filaments are thought to be quite close to thermal equilibrium, thus allowing the representation of the phase fields shown in figures 1 and 2.…”

“…From the pseudobinary phase diagrams represented in figures 1 and 2, it follows that there are characteristic Figure 2. Pseudobinary A15 phase field of the system Nb-Sn-Ti, as derived from the data of Tachikawa et al [11], Suenaga et al [10], Tafto et al [7] and Asano et al [12], in the temperature range between 700 and 750 • C. differences between Ta and Ti additives. It should be noted that the binary A15 type compound Ta 3 Sn exists and is superconducting at T c = 6.4 K, while the binary compound Ti 3 Sn crystallizes in the DO 19 phase.…”