Preparation of Nb3Al superconductor by powder metallurgy and effect of mechanical alloying on the phase formation

Adoption of powder-in-tube method to fabricatesuperconducting wire can realize a large application ofNb3Al prepared by powder metallurgy. Powder metallurgywas used to synthesize Nb3Al under various heat-treatmentconditions, annealing temperature was varied from 700 to1,000 C and heating time was varied from 10 to 50 h.X-ray diffraction patterns reveal that a reaction between Nband Al took place and formed NbAl3 phase. Under currentheat-treatment conditions （annealing temperature wasvaried from 700 to 1,000 C and heating time was variedfrom 10 to 50 h）, NbAl3 was so stable that it did not furtherreact with the unreacted Nb and was not sensitive to theheat-treatment condition. By mechanical alloying, adoptionof high-energy ball milling significantly decreases particlesize and enhances surface free energy, which promotes theformation of Nb3Al phase. X-ray diffraction patternsindicate that relatively pure Nb3Al phase was obtainedunder the same heat-treatment condition. Energy-dispersiveX-ray analysis measurement demonstrates that theobtained samples were close to the right stoichiometry ofA15 structure Nb3Al.