Neutron Diffraction Study on Prebending Effects for Bronze Route<tex>$rm Nb_3rm Sn$</tex>Wires Without Reinforcement

Abstract

The critical current, upper critical field and critical temperature of bronze route Nb 3 Sn commercial wires are enhanced by applying a repeated bending strain at room temperature, i.e., "prebending strain". In order to investigate the prebending effects from a viewpoint of a residual strain, axial and lateral residual strains were evaluated directly by neutron diffraction at room temperature. We found that the axial residual strain changes from 0.10% to 0.02 % but the lateral one is unchanged by applying a prebending strain of 0.5% for an ordinary bronze route (Nb Ti) 3 Sn wires without reinforcement. Hence, in the case of the ordinary Nb 3 Sn wires without reinforcement, the prebending treatment modifies only the axial residual strain states independently to the lateral one, although it may depend on the wire structure. The critical current properties under the axial tensile strain suggest that the axial residual strain is reduced by about 0.11% but the radial residual strain unchanged by the prebending treatment of 0.5%. This is consistent with the results of the neutron diffraction.

Residual strain dependence on the matrix structure in RHQ-Nb3Al wires by neutron diffraction measurement

“…It indicates that thermal stress shows a significant effect in the axial direction. Similar behavior can be seen in strain distribution of the Nb3Sn [10]. In the given direction, the samples A and B showed almost the same residual strain in the Nb 3 Al filament.…”

“…Residual strain of Nb 3 Sn in bronze processed Nb 3 Sn wire has been estimated to be about -0.2 --0.1% at the room temperature by a single-peak analysis in the axial direction [9,10]. The residual strain of Nb 3 Sn was shown to have a significant effect by Cu.…”

Residual Strain in a ${\rm Nb}_{3}{\rm Sn}$ Strand Mounted on a Barrel for Critical Current Measurements

“…Changes of the axial pre-strain have been reported to occur also under cyclic tensile loading [9] and bending [10] of bronze route strands at RT. A reduction of the axial pre-strain in the A15 phase should cause a measurable increase of after the 2nd cool down, with respect to measured after the 1st cool down.…”

Internal Strain Measurement for a <inline-formula> <tex-math notation="TeX">$\hbox{Nb}_{3}\hbox{Sn}$</tex-math></inline-formula> Rutherford Cable Using Neutron Diffraction

“…In the meantime, it has become known that the superconducting properties of Nb 3 Sn strands can be improved by a mechanical treatment at room temperature [2]- [4]. We found that what is called the prebending treatment reduces the residual strain [5], [6].…”