Superconductivity in amorphous+crystalline Ti-(Nb or V)-Si-B ductile alloys obtained by rapid quenching from the melt

Ductile superconductors with a duplex structure consisting of amorphous and bcc phases have been found in rapidly quenched alloys of the Ti70−xNb30(Si-B)x and Ti60-xV40(Si-B)x quaternary systems. Continuous ribbons of these alloys were produced in the form of about 1-mm width and 0.02-mm thickness using a modified single roller quenching apparatus. The silicon content in these duplex alloys was limited to the range between about 7 and 19 at. % and the boron content was in the range of about 0 to 9 at. %. The superconducting transition temperature Tc increased with decreasing metalloid content and/or with replacement of silicon by boron. The highest values obtained were 7.3 K for Ti57Nb30Si10B3 and 4.7 K for Ti45V40Si8B7, which are much higher than those of Ti-Nb and Ti-V base amorphous superconductors. The upper critical magnetic field Hc2 and the critical current density Jc for the Ti55Nb30Si7B8 alloy were about 5.1×106 A/m at 4.2 K and of the order 3.5×104 A/cm2 at zero applied field and 4.2 K. Although the superconducting properties of the duplex alloys are still insufficient for practical use, the information that the duplex structure produces a remarkable improvement in the superconducting properties without a detectable change or loss of ductility seems to be very important from the technological point of view.