Kinetic process of mechanical alloying in ${\mathrm{Fe}}_{50}{\mathrm{Cu}}_{50}$

It is shown that mechanical alloying in the immiscible Fe-Cu system is governed by the atomic shear event and shear-induced diffusion process. We found that an α-to-γ phase transformation, as evidenced by the Nishiyama-Wasserman orientation relationship, occurs by simultaneous shearing process when the grain size reduces to about 20 nm and Cu content reaches 20 at. % in ${\mathrm{b}\mathrm{c}\mathrm{c}-\mathrm{F}\mathrm{e}}_{\mathrm{rich}}\mathrm{Cu}$ grains in the intermediate stage of milling of ${\mathrm{Fe}}_{50}{\mathrm{Cu}}_{50}.$ Further milling promotes the interdiffusion between ${\mathrm{f}\mathrm{c}\mathrm{c}-\mathrm{F}\mathrm{e}}_{\mathrm{rich}}\mathrm{Cu}$ and ${\mathrm{f}\mathrm{c}\mathrm{c}-\mathrm{F}\mathrm{e}\mathrm{C}\mathrm{u}}_{\mathrm{rich}},$ which is favored because of the similarity of the lattice structures, until a complete fcc Fe-Cu solid solution is formed. The results provide significant insight into the understanding of recent experiments showing that chemical mixing of immiscible elements can be induced by mechanical alloying.