Mechanical properties and densification mechanism of powder-in-tube Ba_xK_1-xFe₂As₂ superconductors

Abstract BaxK1-xFe2As2 (BaK-122) iron-based superconductors (IBSs) have been considered to be promising for high-field applications. The transport J c performance of BaK-122 wires and tapes is continuously enhanced by introducing advanced fabricating methods. The mass density of BaK-122 superconducting core in wires and tapes is important to the transport J c performance and related to the mechanical behavior during preparation. In this work, the mechanical property parameters including Poisson's ratio-density, yield strength-density, and elastic modulus-density of BaK-122 IBS powder were examined via uniaxial compression experiments. The density-dependent mechanical constitutive of BaK-122 was obtained for the first time. The relationship function between density and Vickers hardness of BaK-122 was established as HV0.05=0.0249ρ5.332 based on the numerical simulation of hardness testing, and a method for characterizing the BaK-122 core density was developed. It had been found the sheath materials and preparation method have great influences on the stress state of the BaK-122 core, and then affect the density. The densification mechanism and corresponding improvement method were revealed to provide guidance for preparing high-density BaK-122 wires and tapes. Finally, the generalized relationship between density and the superconducting transport J c was established according to lots of experimental data from multiple BaK-122 samples, which has confirmed the positive correlation of ρcore and J c. We comparatively discussed the various cold-work and heat-treatment processes used in our team for preparing the BaK-122 wires and tapes, and the critical factors affecting the transport performance were summarized.