Microhardness as a tool for the filament density and metal sheath analysis in MgB₂/Fe/(Cu) wires

Abstract

Vickers microhardness measurements have been carried out on MgB2 composite wires deformed in iron sheaths. Because the local hardness of these composite materials can be simply measured, we can use these values as an indication of the density of the ceramic core. An array of microhardness measurements have been done for single- and multi-core MgB2 wires subjected to variable deformation and heat treatment processes. The results show how the fabrication process can affect the core density, and so the critical current density, as well as the properties of the metal sheath before and after sintering heat treatments.

Properties of stabilized MgB2composite wire with Ti barrier

“…Really surprising is that the maximal hardness at ϕ = 5.9 correlates with minimal J c and vice versa the maximal J c is measured for the lowest filament density (HV0.05 = 175). Cyclic behaviour of filament density with the area reduction was already presented and explained for powdered filaments [15,16]. The J c maxima at the local density minima are not yet understood.…”

Large transport Jc in Cu-sheathed Sr0.6K0.4Fe2As2 superconducting tape conductors

“…The diffusion of Cu and the composition deviation of superconducting phase easily induce severe porosity at the interface, and apparently break the electrical contact between Cu sheath and Sr-122 core 35,36 . This disadvantageous phenomenon can be avoided by the simple HP method, because it can greatly reduce the pores and cracks by combining the deformation and heat treatment in a single step 17 .…”

MgB2cable made from two-axially rolled wires

“…Microhardness data are frequently used for filament density evolution in composites made by the PIT technique (e.g. Bi-2223 or MgB 2 [13,14]). The wires and cables described above consist of 15% MgB 2 , 35% Ti and 50% Cu.…”