Composition changes in thin-filament MgB2/Ti/GlidCop® wires heat treated at variable periods

•0.2 × 0.2 mm wires were made from 30 filaments of SiC-doped MgB2 in Ti barrier.•The Cu–Ti diffusion processes pose limitations to heat treatment period.•Si accumulated in an inner layer of Ti barrier protects filaments from Cu diffusion.•Si changes mechanism of MgB2 filament contamination during annealing.•Al2O3 in GlidCop Al-60® sheath does not cause additional diffusion into filaments.

30-Filament SiC-doped MgB2 wires with outer dimensions of 0.2 × 0.2 mm were heat treated (HT) at 800 °C and variable HT period. Diffusion between Ti barrier and GlidCop Al-60® sheath and gradual deterioration of individual filaments was observed by energy dispersive spectroscopy (EDS) on polished and ion beam treated wire cross-sections. Combination of Ti barrier with SiC-doping is shown as very advantageous because Si accumulated in an inner layer of Ti barrier after SiC decomposition protects MgB2 filaments from Cu diffusion better than pure Ti barrier. Al2O3 in used GlidCop Al-60® does not cause additional diffusion into filaments. Observed changes in wire microstructure explain the affected superconducting properties in dependence on the HT period.

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