Superconducting Properties and Crystalline Structure of High-Performance Nb3Al Wires Fabricated by RHQ and Mechanical Alloying Methods

In this paper, we compare the superconducting properties of Nb3Al wires prepared by two different techniques. The first is the in situ powder-in-tube method: first, the powder of the Nb-Al saturated solid solution, Nb(Al)ss, prepared by mechanical alloying is filled into a metal niobium tube, and then subjected to cold working such as swaging and drawing to form a wire. Heat treatment at 800-1000 °C converts the Nb(Al)ss phase to the Nb3Al phase. Another method is to use the jelly-roll technology to make the Nb-Al precursor wire, then use the rapid heating and quenching (RHQ) process to form the Nb(Al)ss phase, and finally, to transform the Nb(Al)ss phase into Nb3Al by heat-treatment at 800-900 °C. We found that although both the mechanical alloying method and the RHQ technique can make the Nb(Al)ss phase, the properties of the finally obtained Nb3Al wire have a big gap: the Nb3Al wire prepared by the RHQ process has much higher Tc and Jc. Phase structure analyses show that the RHQ energy density in the RHQ method plays a similar role as the milling time does in the mechanical alloying method, both of these parameters play important roles in controlling the crystal structure and microstructure of the Nb3 Al wires.