Nanostructure and phases formation under mechanical alloying of binary powder mixtures of Fe and sp-elements (M); M=C, B, Mg, Al, Si, Ge, Sn

Full text: Common and distinctive features of mechanical alloying (MA) of Fe with sp-element have been established using a complex of experimental methods including Moessbauer spectroscopy. The common regularities are the following: the formation of a nano-structural state in α-Fe particles, sp-atoms penetration along the α-Fe grain boundaries, their segregation and the first Fe-M phase formation in the interfaces (boundary and close-to-boundary distorted zones) at the initial stage of MA. In MA α-Fe with Al (Si, Ge, Sn) having approximately equal (Al, Si, Ge) or substantially larger (Sn) atomic size intermetallic compounds are formed in interfaces at the first stage. At the final stage supersaturated solid solutions (SSS) are formed in the grain bulk if sp-element concentration in the initial mixture xM≤32 at.% Si (Ge, Sn) and ≤50 at.% Al. In the Fe-Al (Si, Ge) systems the sp-element concentration in SSS becomes maximum simultaneously with the SSS formation, while in the Fe-Sn the SSS is saturated with Sn gradually. In MA α-Fe with C and B having a small radius an amorphous like phase (Am(Fe-M)) is formed in interfaces at the initial stage. The Am(Fe-B) formation is characterized by a substantially slower kinetics in comparison with that of the Am(Fe-C) one. If xM>15 at.% C(B) the second stage - the carbide and boride formation - takes place after amorphization. In the case of immiscible in equilibrium elements (Fe and Mg) mechanical alloying is a one-stage process of the SSS formation with the Mg concentration of not higher than 7 at.%