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

Abstract

We have investigated the effect of initial microstructures on the change in critical current density (Jc) of Nb-46.5 wt%Ti (NbTi) superconducting material. It is well known that α-Ti phases distributed in NbTi material act as a flux pinning center, resulting in an improvement in critical current density. Therefore, it is crucial to obtain the grain-refined microstructure, which is strongly related with precipitation of uniformly distributed fine α-Ti phases and higher volume faction of α-Ti phases, as α-Ti phases are precipitated at the grain boundaries and triple points during heat treatments. Therefore, in order to characterize the effect of initial microstructure of NbTi on critical current density, different initial microstructures were obtained by applying equal channel angular pressing (ECAP) and hot rolling with different strains. It was revealed experimentally that hot rolling with a higher strain is efficient for obtaining the initial microstructure, which has equiaxed fine grains of β-NbTi with the aid of dynamic recrystallization, and which is helpful for precipitating fine α-Ti phases during intermediate heat treatment. Furthermore, it was confirmed that critical current density can be enhanced by obtaining a smaller α-Ti phase, a higher aspect ratio of α-Ti phase, a higher volume fraction of α-Ti phase and a ribbon-like folded α-Ti phase.

In-situ investigation of the decomposition process in cold-rolled Nb53Ti47 alloy

“…Boenisch et al [ 29 ] investigated the thermal stability of NbTi alloys in a wide concentration range. Moon et al [ 30 ] and Kim et al [ 31 ] showed the relationship between the initial structure and the critical current density, while other authors observed changes in the microstructure due to various external influences [ 2 , 6 , [32] , [33] , [34] ]. Storozhilov et al [ 35 ] investigated the effect of severe plastic deformation on the decomposition of supersaturated solid solution in Nb–48.5 wt % Ti.…”

Effect of Low Annealing Temperature on the Critical-Current Density of 2% C-Doped MgB2 Wires Used in Superconducting Coils with the Wind-and-React (W&R) Method—High-Field and High-Temperature Pinning Centers

“…Currently, they are many different superconducting materials, e.g., high-temperature superconductors [ 1 ], including iron-based superconductors [ 2 ], NbTi [ 3 ], and Nb 3 Sn [ 4 ]. However, now, it seems that the MgB 2 material is the most promising one for the production of coils because it consists of cheap components (low price of wires) and is characterized by high critical temperature (39 K liquid hydrogen, cryocooler), low anisotropy (wires made using the powder-in-a-tube method), and high upper critical field [ 5 , 6 ].…”