Investigations of the formation mechanism of nanostructured NbAl3 via MASHS reaction

The nanostructured NbAl3 intermetallic compound was synthesized using the mechanically-activated self-propagating high-temperature synthesis (MASHS) technique. This process results from the combination of two steps: a short duration ball-milling of a pure elemental Nb+3Al powder mixture followed by a self-propagating high-temperature synthesis (SHS) reaction induced by the Nb+3Al reaction exothermicity. Synchrotron time-resolved XRD coupled with a 2D infrared camera were used to investigate the structural and thermal evolutions during the SHS reaction, and to study in situ the mechanism of NbAl3 formation. The influence of the incoming heat flux and the mechanical activation effect on the phase transformation kinetics induced by the SHS process were studied. Owing to the temporal resolution of 100 and 200 ms between two consecutive diffraction patterns and IR images, respectively, it was shown that solid niobium reacts with liquid aluminium via a heterogeneous nucleation reaction, to form the NbAl3 compound by successive combustion fronts.