The point pinning centers and critical current density in NbTi wires

Abstract

The results of this work show that annealing under 0.4 GPa isostatic pressure does not influence the critical temperature (Tc) of the NbTi wire, which is about 9 K. Moreover, our studies indicate that annealing under pressure of 0.4 GPa reduces the irreversible magnetic field (Birr), and that annealing under any degree of pressure does not lead to Cu diffusion into the NbTi core. Scanning electron microscope images show that the NbTi core in the superconducting wire has NbTi fibers with a diameter of about 200 nm. Our studies show that isostatic pressure heat treatment significantly accelerated the formation of Ti precipitates on the NbTi grain boundaries. Furthermore, the studies indicate that the higher strain density obtained during cold treatment formed a larger number of α-Ti precipitates.