New nanoscale artificial pinning centres for NbTi superconductors

Abstract

The efficiency of new artificial pinning centres have been investigated in NbTi using the oxide dispersion strengthening (ODS) concept more typically applied to steels and Ni-superalloys. NbTi alloys containing a dispersion of nanoscale Y2Ti2O7 particles have been successfully manufactured through a powder metallurgy route by mechanical alloying Nb, Ti and Y2O3 nanopowders using high energy ball milling and subsequent consolidation and annealing. The microstructure and superconducting properties of the NbTi-Y2O3 have been characterised after each processing step. After 40 h of ball milling, the Y2O3 particles are dissolved into the nanostructured NbTi matrix formed by mechanical alloying of Nb and Ti. On annealing at temperatures above 800 °C the dissolved Y and O react with Ti from the matrix, and fine Y2Ti2O7 particles (<5 nm) are precipitated. These NbTi-Y2Ti2O7 composites showed excellent superconducting performance, with JC of 5.2 kAmm−2 at 4.2 K, 5 T, considerably higher than Y2O3-free bulks manufactured using the same process and NbTi wires manufactured using the conventional thermomechanical process. The results suggest that ODS powder processing is a promising new route to manufacture NbTi alloys containing artificial pinning centres that give superior superconducting properties.