The influence of phase formation routes on the microstructure and critical current density of Nb3Al superconductor prepared by mechanical alloying and subsequent sintering

The phase formation mechanism, microstructure and superconducting properties of Nb3Al prepared by mechanical alloying and subsequent sintering were systematically investigated in this work. It was found that when the milling time is less than 16h, the Nb3Al is formed via the reaction between the Nb2Al that crystallizes from Nb-Al amorphous phase and residual Nb during subsequent sintering process. Whereas the milling time exceeds 16h, the Nb3Al transforms directly from Nb-Al supersaturated solid solution (Nb(Al)(ss)) during subsequent sintering process. Due to this difference in phase formation route, the grain size of M16h sintered sample is larger than that of M12h and M20h sintered samples. Besides, the intergranular connectivity of M16h sintered sample is the poorest among them. These factors make the critical current density (J(c)) of M16h sample abnormally lower than that of both M12h and M20h samples. According to these results, the highest J(c) (about 1 x 10(4) A cm(-2) at 4.2K, 6T) is obtained for the sample prepared by 20h ball milling and subsequent sintering at 850 degrees Cfor 5h.