Kinetic neutron diffraction study of Nb₃Sn phase formation in superconducting wires

Abstract

The kinetics of Nb3Sn phase formation in commercial multifilamentary wires have been studied as a function of time and temperature using time-resolved, in situ neutron diffraction. This work shows that at higher temperatures the Nb3Sn phase forms in a fraction of the recommended annealing time. A temperature-independent Avrami exponent of n = 0.51 ± 0.01 was observed, indicating a diffusion-controlled growth mechanism, and a large apparent activation energy of Ea = 10 ± 1 eV is reported where the energies of nucleation and growth both contribute.

Phase transformations during the reaction heat treatment of powder-in-tube Nb3Sn superconductors

“…Powder diffraction is an alternative method frequently used for phase analysis, and the Nb 3 Sn formation kinetics in strands of the IT design has been successfully studied by in situ neutron diffraction [7]. However, the signal-to-noise ratio obtained by neutron diffraction experiments has not been sufficient to monitor the diffraction peaks of weekly diffracting phases, such as for instance the orthorhombic NbSn 2 and Nb 6 Sn 5 .…”