Abstract:Mechanical alloying of Mo-Si (Mo₃₃Si₆₇) and V-Si (V₇₅Si₂₅) powder mixtures was activated by high energy ball milling at ambient temperature.The metastable phase transitions in both systems during milling were investigated by X-ray diffraction, scanning and transmission electron microscopy.It is found that the alloying processes are closely related to the milling conditions.As far as the Mo-Si system is concerned,ball milling leads to the formation of both α-MoSi₂ (room temperature phase) and β-MoSi₂ (high temperature phase),but lower energy milling favors the formation of β phase,while higher energy milling promotes the formation of α phase.In addition,if the milling energy is high enough,the Mo/Si reaction is governed by ase lf-propagating high temperature process.On the other hand, two different pathways of phase transition in the V-Si system were also identified depending on the milling intensity,i.e.weak milling leads to amorphous transition, whereas intensive milling causes the formation of V₃Si and V₅Si₃ intermetallic compounds.Finally,the thermodynamics and kinetics related to the different phase transitions in the two systems were discussed.

Key words: mechanical alloying;phase transitions;energy transfer;Mo-Si;V-Si