Thermodynamic analysis of nanocrystalline and amorphous phase formation in Nb-Al system during mechanical alloying

Mixtures of pure elemental Al and Nb powders of Nb-75 at-% Al and Nb-25 at-% Al composition were mechanically alloyed. Phase transformation of the powder mixtures was investigated by X-ray diffraction technique. It was found that mechanical alloying of the Nb-75 at-% Al powder mixture led to the formation of Nb( Al) solid solution and subsequent formation of DO22-NbAl3 intermetallic compound, and no amorphous phase was formed after longer milling times. The results showed that mechanical alloying of Nb-25 at-% Al for 8 h led to the formation of amorphous phase, and Nb3Al intermetallic was not formed during milling. A thermodynamic analysis was carried out based on the semiempirical theory of Miedema. This analysis showed that there is a driving force for the Nb-Al binary to form a solid solution for all compositions while the amorphous phase is stable in the range of 0.1 <= x(Al)<= 0.95.