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

Abstract

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.