Critical current of a rapid-quenched Nb₃Al conductor under transverse compressive and axial tensile stress

Abstract

The electromechanical behavior of a Nb 3 Al wire manufactured according to the RHQT process (rapid-heating, quenching and transformation) has been investigated at magnetic fields between 15 and 19 T at 4.2 K. Of particular interest was the critical current, I c , as a function of transverse pressure up to 300 MPa and as a function of axial tensile stress. The studied wires are pieces of a 870 m long copper stabilized Nb 3 Al wire with a rectangular cross section of 1.81 mm × 0.80 mm. It was observed that the critical current at 300 MPa transverse pressure, applied to the narrow side, is reduced to 93%, 90% and 88% of its stress free value at 15 T, 17 T and 19 T, respectively. After unloading from 300 MPa I c recovers to 94% and 97% at 19 T and 15 T, respectively. A field dependence of the effect is visible above 200 MPa. For completeness, the critical current was also measured under axial tensile strain. The maximum of I c is at 0.15% applied strain and irreversibility has been observed above 0.26%. Finally a stress versus strain measurement at 4.2 K has been carried out allowing the conversion from axial strain to stress.

Improvement of electromechanical properties of an ITER internal tin Nb3Sn wire

“…Further, again for the jacketed wire, strain sensitivity at tensile strains Ͼ0.8% and 19 T is reduced ͑change in the slope͒, which has also been observed in bronze route Nb 3 Sn wires with an extended irreversibility strain limit. 34 Due to the fact that I c in this strain range is reversible, excludes any artifact of the measurement ͑e.g., slipping of SS͒. At this moment it can only be speculated that these observations are related to a multidimensional strain effect.…”

Observation of A15 phase transformation in RHQ-Nb3Al wire by neutron diffraction at high-temperature

“…Strain in a superconducting wire is known to influence superconducting characteristics such as its critical current [14][15][16]. For Nb 3 Al filaments subjected to a heat treatment to induce the A15 phase transition, thermal stress occurs during the cooling stage due to the different coefficients of thermal expansion (CTE) between the materials in the composite wire.…”

Low Critical Current Sensitivity of RHQT ${\rm Nb}_{3}{\rm Al}$ Wires Under Transverse Compressive Stress Up to 300 MPa

“…Under axial tensile testing at 4.2 K, behaves elastically up to about 270 MPa [18], whereas is plastically deformed at relatively low stress [17]. The difference of vs. transverse stress of and may be explained, at least partially, by the mechanically strong Nb matrix in the case of and the weak bronze matrix in the case of .…”