Cryogenic Tension Response of Monel Sheath MgB2 Superconducting Wires

We report the effects of cryogenic temperature on tensile responses for the heat-treated Monel sheath MgB₂ superconducting wires. A variable temperature cryostat system was used to provide a cooling environment from room temperature (RT) to the liquid nitrogen temperature (LNT), and a small cryogenic-type extensometer was used to measure strains of the MgB₂ wires under tension loading. Under a range of cryogenic temperatures, we recorded the corresponding stress-strain relations during the wire stretching and obtained the tensile and yield strengths, Young's modulus and toughness energy of the Monel sheath MgB₂ wires. It was shown that their ultimate tensile strengths always increased linearly with decreasing temperature, but an obvious nonlinear feature on the yield strength and toughness energy appeared, whereas the Young's modulus was almost independent on the cryogenic temperature in our tested range. In addition, for the purpose of comparison and practical application, the properties at 4.2 K were extrapolated for the Monel sheath MgB₂ composite wires based on measured data of tensile behaviors from RT to LNT, which were compared with the experimental data in the other literature.