Comparative Thermodynamic Analysis of Nanocrystalline and Amorphous Phase Formation in Nb/Al and Nb/Sn Systems During Mechanical Alloying

Elemental powders of niobium-tin and niobium-aluminum were mechanically alloyed by Spex ball mill, respectively, in order to fabricate disordered nanocrystalline Nb3Sn and Nb3Al. The solid solution phase transitions of MA powders before and after heat treatment were characterized using X-ray diffraction (XRD) analysis. The microstructural analysis was performed using scanning electron microscopy (SEM). Results showed that mechanical alloying (MA) of Nb75Sn25 for 28 h led to the formation of the Nb3Sn intermetallic phase, while mechanical alloying of Nb75Al25 until 41 h did not show formation of the intermetallic phase. A thermodynamic analysis was performed based on the semiempirical theory of Miedema. The theory's results showed that the intermetallic phase has a minimum Gibbs free energy compared to solid solution and amorphous states in both systems. Therefore, the most stable phase is intermetallic compound. But in case of the Nb/Al, the Nb3Al intermetallic compound was not formed during milling and needs heat treatment.