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

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 I_c is significantly increased by applying a repeated bending load (pre-bending treatment) at room temperature. The maximum enhancement of I_c was approximately twice at 16 T for CuNb-reinforced Nb₃Sn wires by a 0.5% prebending strain and the critical current density J_c became about 528 A/mm ² at 4.2 K and 16 T. A comparison of the stress dependent I _c values obtained before and after applying prebending treatments for CuNb/Nb₃Sn wires indicates that not only the stress dependence of I_c but also the maximum I_c at the axial strain-free state are improved. The improvement of the stress dependent I_c is in agreement with the prediction made based on the calculation using the uniaxial stress/strain distribution-model. Moreover, the increase in the maximum I _c may be related to the release of stress/strain states along the radial direction through prebending treatments.