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The effect of multiple prolonged heat treatment on the structure and critical current density in Nb50 wt% Ti composites was studied in the case of monofilamentary superconductors. The treatment temperature range, in which high ic vaiues can be obiained, is aeierminea. i i n e iniiuence o i intermeaiaie ireaimenis on the increase in the quantity of precipitated a-phase is studied. The exponent specifying the kinetics of particle growth from the supersaturated solid solution is estimated. The interrelation between the critical current density and the quantity of precipitated phase is established. The maximum critical current density is 4 x IO5 A cm-' (E = 5 T).

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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.

The mechanical properties under uniaxial compression of cylindrical samples of ultrafine-grain (UFG) zirconium (grain size ∼0.4μm) obtained by intense plastic strain (IPS)—a combination of extrusion, annealing, and drawing—have been studied in the temperature range 4.2–300K. The mechanical characteristics of UFG zirconium have been studied in two structural states and the results are compared with each other as well as with the characteristics of coarse-grain polycrystals of this material (state 1—samples after IPS, state 2—samples after IPS and annealing). It has been established that grain-size reduction under IPS substantially increases the yield stress of polycrystals (by a factor of 6 at 300K and by a factor of 4 at 77K) while maintaining a large reserve of plasticity up to 15%. Two stages of strain hardening and a decrease of the plastic-flow activation volume with increasing strain has been recorded in the strain diagrams of UFG zirconium. It is concluded that the main mechanisms determining the yield stress and strain hardening are the same for ultrafine- and coarse-grain zirconium: intragrain dislocation slip and twinning occur in parallel and interact with one another.