The investigation of the effect of niobium artificial doping with titanium on Nb3Sn superconductors properties

The effect on titanium doping of Nb filaments, and thus on the properties of bronze processed multifilamentary Nb3Sn wires and wires with internal tin sources with copper volume fraction up to 65 % has been analysed. Either titanium rods or rods of the Nb-50Ti alloy, inserted in the axial area of each filament, were used as a source of titanium. The influence of doping on the quantity, composition, structure and superconducting properties of intermetallic compound Nb3Sn after heat treatments at 570–750°C with duration up to 350 h was investigated by means of electrical measurements, optical metallography and methods of microanalysis and X-ray analysis. It was shown that the non-copper critical current density of the doped wires attained 600 and 270 A/mm2 in 12.5 and 16 T respectively for bronze processed wires and 800 and 300 A/mm2 for wires with internal tin source. Upper critical field calculated in accordance with Kramer’s extrapolation was equal to 29–32 T.