Effect of ECAP on Change in Microstructure and Critical Current Density of Low Temperature Super-Conducting Monowire

Investigation of the Correlation between Initial Microstructure and Critical Current Density of Nb-46.5 wt%Ti Superconducting Material

“…The Nb tube served as a diffusion barrier which prevented the formation of intermetallic compound between Cu and NbTi. The Cu tubes acted as paths for a current flow in the case of a rapid change from a super-conducting state to a non-superconducting state, as well as thermal and electrical stabilization layers [16].…”

“…Figure 1 shows the overall process concept for making the superconducting NbTi monowire from the initial NbTi billet. For ease of comparison, the ECAP process used in our previous study is shown together [16]. In ECAP, if the specimen is pressed after being inserted into the top inlet of the ECAP mold, it undergoes a high level of shear deformation by passing through a channel with a 90 • bending angle [18][19][20][21][22][23][24][25].…”

“…All images are taken from an axial direction. BSE images of ECAPed specimen with strain 2.0, and hot rolled specimen with strain 0.7, are reused from references [16,17], respectively.…”

“…In this study, NbTi billet was deformed until the accumulated strain reached 2.0 by applying repeated hot rolling at a process temperature of 600 • C to compare results to our previous studies [16,17]. Thereafter, groove rolling, drawing and intermediate heat treatments were applied to make the final NbTi monowire.…”

“…Recently, our research group reported on a paper that analyzed the effect of initial strain level of NbTi billet on superconducting properties using equal channel angular pressing (ECAP) [16]. It was revealed that superconducting properties can be improved by applying severe plastic deformation in the NbTi billet.…”