The 210-filamentary superconductor based on Nb37Ti-22Ta ,wt.% alloy was obtained by using the electric arc melting and deformation processing. During alloy drawing we used four isochronal intermediate heat treatments at the temperature 425OC. The total heat treatment duration was varied from 50 to 1000 hours. The true plastic strain value between heat treatments was 0.4 and after the final treatment was 3-5. The kinetics of phase transformation in the ternary alloy was investigated by the method of transmission electron microscopy. The J, value increases with an increasing quantity of the precipitated alpha-phase in medium magnetic fields. The J, (5 T, 4.2 K) value reaches 3000 A/mm2 or more. In high fields, J,(10.4 T, 2.05 K) for the given superconductor was equal to 1600 A/mm2. The parameters responsible for the shape of pinning force curve are determined for different treatment conditions.
A theory of magnetic pinning due to randomly distributed pinning centres in the form of
parallel ribbons is developed. The interaction between a vortex and pinning centres is
studied with an account of the magnetic field gradient near the ribbon surface. The
critical current density and the average bulk pinning force are determined as a
function of the magnetic field and normal phase content. A comparison with
experimental data confirms the qualitative reliability of the theoretical results.
A high-resolution atomic probe is used to analyze the chemical composition of an optimally thermo-mechanically worked niobium-titanium nanostructured superconducting alloy. Variations of the elemental composition in the matrix are found at the mesoscale level, and it is shown that they are much larger than technological nonuniformities of the chemical composition of the alloy. Nanoscale nonuniformities are found in the structure of the β phase. It is established that the order parameter of the titanium atoms is 1 and there is no clustering of the atoms and no short-range chemical order.
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