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 (E-alpha) 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 degrees C to 454 degrees 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. E. for NbAl3 formation reaction and its variation with conversion degree (a). The results showed that Starink method lead to values of E-alpha, which are comparable to the results obtained by FR method. (C) 2011 Elsevier B.V. All rights reserved.