Properties of near- and sub-micrometre Al matrix composites strengthened with nano-scale in-situ Al 2 O 3 aimed for low temperature applications

MgB2 cables made of thin wires manufactured by IMD process

“…Present Rc-B cable with Ti barrier has lower losses than Rc-B-Ta, which can be ascribed by lower barrier's resistivity, see figure 14. While a similar ρ ∼ 2 × 10 -8 Ωm was measured for Ta and Al-B sheath [26] used for bough cables, by one order of magnitude higher resistivity of Ti barriers (>2 × 10 -7 Ωm) plays also a role of resistive barrier reducing the coupling currents inside the cable.…”

Ultra-lightweight superconducting wire based on Mg, B, Ti and Al

“…Similar correlation (sheath softening) is observed by the micro-hardness (HV 0.005 ) data, which decreased from HV 0.005  = 68 to 43 as the peak temperature increased from 640 to 646.5 °C, respectively (see Table 1). Nevertheless, the achieved HV 0.005  = 43 for the Al-Al 2 O 3 sheath of the wA wire remains still much higher than that of pure Al (HV 0.005  = 27) 21 due to a dense net of low angle grain boundaries effectively stabilized by Al 2 O 3 dispersoids. The observed differences are attributed only to structural changes in the Al + Al 2 O 3 material (and formation of thicker Al 3 Ti layer) subjected to different heat treatment.…”

“…The nano-dispersoids stemmed from native amorphous (am)-Al 2 O 3 layers on as-atomised Al powders 20 . The induced shear deformation broke up the Al 2 O 3 layers into am-Al 2 O 3 platelets during the cold working steps 21 , and some remnants of the fractured am-Al 2 O 3 platelets remained at high angle grain boundaries, see the white arrow in Fig. 5(a).…”

“…The free volume between the Ti tube and Mg rod was filled by a B99.8% powder (<1 µm size) in a glove-box under pure Argon atmosphere. The Mg/B/Ti composite was rotary swaged down to 6.2 mm diameter, cleaned, and inserted into a HITEMAL tube with 6.3 mm inner diameter and 9.1 mm outer diameter, that was machined from an as-extruded Al + 1.37 vol.% Al 2 O 3 rod 21 . The Mg/B/Ti/Al + Al 2 O 3 composite rod was rotary swaged down to 7.5 mm and then groove rolled to a rectangular wire with a cross-section of 1.02 × 1.02 mm 2 .…”

“…Thermally stable ultrafine-grained Al stabilized by a small content of nano-scale Al 2 O 3 formed in situ in Al matrix, named HITEMAL (high temperature aluminum), was produced by a powder metallurgy approach 19,20 . HITEMAL shows attractive mechanical and recently also electrical properties at low temperatures 21 . The first attempt to make an Al-stabilized MgB 2 wire was made using Ta diffusion barrier and HITEMAL outer sheath 22 , which demonstrated the possible production of Al-sheathed MgB 2 wires.…”