In-situ time resolved X-ray diffraction study of the formation of the nanocrystalline NbAl3 phase by mechanically activated self-propagating high-temperature synthesis reaction

The mechanically activated self-propagating high-temperature synthesis (MAS HS) technique was used to produce a NbAl3 intermetallic compound. This proc ess results from the combination of two steps: a mechanical activation of t he Nb + 3Al powder mixture which is followed by a self-propagating high-tem perature synthesis (SHS) reaction, induced by the exothermal character of t he reaction Nb + 3Al. An original experiment was designed to study in-situ the formation of the NbAl3 phase in the combustion front: time-resolved X-r ay diffraction coupled with an infrared imaging technique and a thermocoupl e measurement were performed to monitor the structural and thermal evolutio n during the SHS reaction. Owing to the temporal resolution of 100 ms betwe en two consecutive diffraction patterns, it was possible to observe several steps before obtaining the niobium aluminide compound. Indeed, the phase t ransformations corresponding to the aluminum melting plateau, the subsequen t temperature increase to the ignition temperature, and the fast reaction b etween niobium and molten aluminum at such a temperature were well-identifi ed. The NbAl3 intermetallic compound resulting from the MASHS process is na nostructured. (C) 1999 Elsevier Science S.A. All rights reserved.