The Reaction Process of NbAl Interface in Rod-in-Tube Strands

We investigated the reaction process of NbAl in samples prepared by the rod-in-tube method. Precursor strands were isothermally heat-treated at a very wide temperature range from 800 to 1,400 °C for 48 h. As a result, we obtained NbAl3 and NbAl diffusion layers below 1,000 °C; NbAl3 and Nb2Al at 1,000 to 1,200 °C; and NbAl3, Nb2Al, and a small amount of nonstoichiometric Nb3Al at 1,400 °C. Diffusion or reaction layers were observed clearly by scanning electron microscope for all of the samples mentioned above. Furthermore, nonstoichiometric Nb3Al phase can be found only at 1,400 °C through a higher resolution. Additionally, magnetic measurement results also show that the superconducting transition temperature is about 14.8 K only for the sample obtained at 1,400 °C for 48 h.