Stress distribution and lattice distortions in Nb₃Sn multifilament wires under uniaxial tensile loading at 4.2 K

Abstract

The lattice parameter changes in three types of Nb$_{3}$Sn superconducting wires during uniaxial stress-strain measurements at 4.2 K have been measured by high-energy synchrotron x-ray diffraction. The nearly-stress-free Nb$_{3}$Sn lattice parameter has been determined using extracted filaments, and the elastic strain in the axial and transverse wire directions in the different wire phases has been calculated. The mechanical properties of the PIT and RRP wire are mainly determined by the properties of Nb$_{3}$Sn and unreacted Nb. This is in contrast to the bronze route wire, where the matrix can carry substantial loads. In straight wires the axial Nb$_{3}$Sn pre-strain is strongest in the bronze route wire, its value being smaller in the PIT and RRP wires. A strong reduction of the non-Cu elastic modulus of about 30\\% is observed during cool-down from ambient temperature to 4.2 K. The Nb$_{3}$Sn Poisson ratio at 4.2 K measured in the untwisted bronze route wire is 0.35. The present study also shows that the process route has a strong influence on the Nb$_{3}$Sn texture.