Superconducting Properties of Titanium Alloys (Ti-64 and Ti-6242) for Critical Current Barrels

We have measured the superconducting properties of the titanium alloy Ti-6Al-4V (Ti-64) as supplied and following two of the heat treatment schedules used for the Nb3Sn strands in the ITER tokamak. The Ti-64 alloy is the standard choice in the superconducting community for the barrels used to make critical current (I
_C
) measurements in high magnetic fields at cryogenic temperatures. Ti-64, which has a two-phase alpha + beta microstructure and contains vanadium (n.b. T
_C
(V) ~ 5.4 K), is superconducting at 4.2 K in fields up to 3 T. We have also measured Ti-6Al-2Sn-4Zr-2Mo-0.2Si (Ti-6242), which is in the near alpha phase and contains tin (n.b. T
_C
(Sn) ~ 3.7 K). The critical temperature of Ti-6242 is 2.38 K, which is lower than the 5.12 K of Ti-64. Hence Ti-6242 is a better choice of barrel material for I
_C
measurements required at 4.2 K in low fields up to 3 T, because it remains in the normal state.