CORRELATION OF SUPERCONDUCTING AND METALLURGICAL PROPERTIES OF A TI-20 AT .PERCENT NB ALLOY

Abstract The effects of heat treatment and cold work on the superconducting properties of Ti-20 at. % Nb have been studied by measurement of magnetization, M(H), critical current density, Jc(H) and transition temperature, Tc. The metallurgy has been determined by electron and optical microscopy and x-ray diffraction. Quenching the recrystallized alloy from the single phase β region above 500°C produces a martensitic α″ phase characterized by Hc2 = 50 koe, Tc = 6·5°K and a high Jc arising from pinning of flux lines by the α″ structure. After very short ageing times at 330°C the α″ reverts to the β phase and Hc2 and Tc fall to 15 koe and 4·5 °K respectively and Jc drops by several orders of magnitude. On further ageing ω-Ti precipitates and Hc2 and Tc increase because of Nb enrichment of the matrix. Pinning by the ω precipitate causes Jc to increase. A pronounced peak effect in the Jc(H) and M(H) curves has been studied in detail. There is strong evidence for a barrier to flux line entry into the pinning centres below the peak field. This barrier may be due to a Nb-rich shell surrounding the ω precipitate. If the quenched alloy is worked, the α″ phase is retained and Tc and Hc2 are unaltered. On ageing, the α″ reverts to strained β but Tc, Hc2 and Jc do not drop as in the recrystallized alloy. Prolonged ageing produces a significant growth of α-Ti precipitate and Tc, Hc2 and Jc all increase as in the recrystallized alloy. © 1969 Taylor & Francis Group, LLC.