Amorphization and nanocrystalline Nb3Al intermetallic formation during mechanical alloying and subsequent annealing

In this paper the formation as well as the stability of Nb₃Al intermetallic compounds from pure Nb and Al metallic powders through mechanical alloying (MA) and subsequent annealing were studied. According to this method, the mixture of powders with the proportion of Nb-25 at% Al were milled under an argon gas atmosphere in a high-energy planetary ball mill, at 7, 14, 27 and 41 h, to fabricate disordered nanocrystalline Nb₃Al. The solid solution phase transitions of MA powders before and after annealing were characterized using X-ray diffractometry (XRD). The microstructural analysis was performed using scanning electron microscopy (SEM) as well as transmission electron microscopy (TEM). The results show that in the early stages of milling, Nb(Al) solid solution was formed with a nanocrystalline structure that is transformed into the amorphous structure by further milling times. Amorphization would appear if the milling time was as long as 27 h. Partially ordered Nb₃Al intermetallic could be synthesized by annealing treatment at 850 °C for 7 h at lower milling times. The size of the crystallites after subsequent annealing was kept around 45 nm.