Mechanical properties of superconducting Nb--Ti composites

Pseudoelastic behavior and serrated stress--strain curves were found in both superconducting composites and Nb--Ti alloys at 4.2 K. The exact mechanisms of these effects are not clear at this time, although it seems possible that a reversible stress-induced martensitic transformation in the Nb--Ti could be occurring. Both of these effects could result in rather large temperature increases and could have adverse effects on the superconducting behavior of the conductor. The degree of the effects, which originate in the Nb--Ti, depends critically on the composite geometry. Differences in tensile behavior were found in composites with straight filaments compared to those with twisted filaments. A possible explanation is that the twisted filaments have a spring action and do not act upon the matrix in the same manner as straight filaments. As a first approximation, the rule of mixtures seems to be useful in predicting the tensile properties