Synthesis and formation mechanisms of molybdenum silicides by mechanical alloying

Abstract

The synthesis and formation of MoSi 2, Mo 5Si 3, and Mo 3Si compounds by the mechanical alloying of Mo Si powder mixtures has been investigated. Ball-milling experiments were conducted for the composition range of 10–80 at.% Si. The formation of molybdenum silicides, especially MoSi 2, during mechanical alloying and the relevant reaction rates markedly depended on the powder composition. The spontaneous formation of αMoSi 2 during mechanical alloying at 67 at.% Si (MoSi 2 stoichiometry) proceeded by a mechanically-induced self-propagating reaction (MSR), the mechanism of which is analogous to that of the self-propagating high-temperature synthesis (SHS). At the compositions of 54 and 80 at.% Si, however, the formation of MoSi 2 proceeded by the gradual formation of both the α and /gb phases instead of the MSR mode. The formation of Mo 5Si 3 during mechanical alloying was characterized by a slow reaction rate as the reactants and product coexisted over a long period. The milling of Mo-rich powder mixtures up to 150 h did not lead to the direct formation of Mo 3Si. The Mo 3Si phase appeared only after brief annealing at temperatures of 800°C and above.