Solid state reactions induced by mechanical alloying in metal-silicon (metal = Mo, Nb) systems

Stoichiometric Mo₃₃Si₆₆ and Nb₃₃Si₆₆ have been alloyed by mechanical alloying (MA) from the elemental powders and the process has been monitored by X-ray diffraction (XRD) technique. Nanocrystalline intermetallic compounds were obtained for either compositions: the NbSi system gave the expected NbSi₂ compound, while in the MoSi system both αMoSi₂ (low temperature phase) and βMoSi₂ (high temperature phase) with the latter being the dominant phase, were promoted by the milling action. The metastable equilibrium αMoSi₂↔βMoSi₂, as well as the tendency to reaction of prealloyed MoSi samples, have been examined by means of differential thermal analysis (DTA), followed by X-ray identification of the formed phases. Finally, the oxygen influence on phase transformation induced by both milling action and thermal treatment has been examined. It has been found that oxygen pick-up not only strongly inhibited the solid state reactions in the process of mechanical alloying but also caused the destabilization of the already formed intermetallic compounds.