Synthesis and formation mechanism of nanostructured NbAl3 intermetallic during mechanical alloying and a kinetic study on its formation

The feasibility of nanocrystalline NbAl3 intermetallic synthesis by mechanical alloying, and its formation kinetics were investigated. The structural changes of powder particles during milling were studied by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques and the reaction mechanism and activation energy (Eα) for the formation of NbAl3 compound were determined under nonisothermal conditions using differential thermal analysis (DTA). DTA results of the specimens mechanically treated for 3 h showed a temperature decrease from 933 °C to 454 °C for the formation of NbAl3 and suitable thermal stability of nanostructured NbAl3. Two isoconversional methods, of Starink and Friedman (FR) were used to determine the activation energy, Eα, for NbAl3 formation reaction and its variation with conversion degree (α). The results showed that Starink method lead to values of Eα which are comparable to the results obtained by FR method.

► NbAl3 is formed after 6 h of milling and no other intermediate phase is formed. ► The activation energy for formation of NbAl3 intermetallic varies slightly with α. ► Activation energy at α = 0.5 for formation of NbAl3 is 356 kJ mol−1. ► KAS, Tang, FWO and Starink methods are in good agreement.