Mechanical Properties and Strain-Induced Filament Degradation of Ex Situ and In Situ $MgB_{2}Wires$

We have compared the mechanical properties and the degradation of the critical current after uniaxial tensile loading at room temperature (RT) and at 77 K of ex situ and in situ $MgB_2$ wires. The strain that the wires can withstand without degradation is at 77 K substantially higher than at RT. In order to explain the mechanical behavior of the wires, the lattice distortions of the different wire constituents and their texture have been measured simultaneously with the composite wire stress and strain in a high-energy synchrotron beamline. The different $MgB_2$ microstructure in both wire types is revealed in filament cross sections prepared by the focused-ion-beam technique and in fracture surfaces.