SEQUENCE OF PHASE-FORMATION DURING MECHANICAL ALLOYING IN THE MO-SI SYSTEM

In this work, the sequence of phase formation during mechanical alloying (MA) in the Mo-66.6 at.% Si, Mo-37.5 at.%Si, Mo-25at.%Si systems and the phase transition in MoSi2 upon mechanical activation have been studied using electron microscopy, X-ray diffraction and differential thermal analysis. It has been found that, in all the systems under study, molybdenum disilicide is the first phase to form during MA. In this case, during MA in the Mo-37.5 at.%Si and Mo-25at.%Si systems, molybdenum disilicide forms in the amorphous state. The phases Mo5Si3 and Mo3Si form by the interaction of amorphous molybdenum disilicide with molybdenum under MA, which leads initially to the formation of amorphous molybdenum silicides the compositions of which are close to that of the crystalline phases Mo5Si3 and Mo3Si, and then to the precipitation of crystalline phases. It has been shown that MA in the Mo-66.6 at.%Si system and the mechanical activation of molybdenum disilicide are accompanied by the phase transition form alpha-MoSi2 to beta-MoSi2.