Stress/strain characteristics of PIT MgB₂ tapes with Ni sheath

The stress/strain dependence of critical current and the mechanical properties of nickel sheathed PIT MgB₂ mono-core tapes with various kinds of metal powders addition to the core were evaluated at 4.2 K in the magnetic field of 2 T. No marked change in the stress-strain curve was found by the powder addition. The critical current was markedly enhanced by In and Sn powder addition. The critical current was almost constant irrespective of strain up to the irreversible strain where a steep degradation of critical current begins. The irreversible strain for the tape increased from 0.25 to 0.50% by the addition of In and Sn powder. The In addition also suppressed a slight increase in the critical current with strain. The effects of Ag and Cu addition are less as compared with those of the low melting point metal powder such as In and Sn. SEM observations on the longitudinal section of In added tape after the tensile test clarified that the cracks were few and rather large as compared with those in the tapes with no addition or high melting point metal powder addition. The strain characteristics were compared with those of MgB₂ with other sheath materials and those of a conventional Nb₃Sn wire.