Enhancement of Critical Current Densities by the Prebending Strain at Room Temperature for Nb₃Sn Wires

Abstract

The influence of a repeated bending strain at room temperature on the critical current densitiy of bronze route Nb3Sn wires was investigated. We found that the critical current Ic is significantly increased by applying a repeated bending load (pre-bending treatment) at room temperature. The maximum enhancement of Ic was approximately twice at 16 T for CuNb-reinforced Nb3Sn wires by a 0.5% prebending strain and the critical current density Jc became about 528 A/mm2 at 4.2 K and 16 T. A comparison of the stress dependent Ic values obtained before and after applying prebending treatments for CuNb/Nb3Sn wires indicates that not only the stress dependence of Ic but also the maximum Ic at the axial strain-free state are improved. The improvement of the stress dependent Ic is in agreement with the prediction made based on the calculation using the uniaxial stress/strain distribution model. Moreover, the increase in the maximum Ic may be related to the release of stress/strain states along the radial direction through prebending treatments.