Thermodynamic and kinetic justification for amorphization by mechanical alloying ofA-Bmetal couples with zero heat of mixing ΔHmix

While amorphization by solid-state reaction is limited to multilayers of A-B metal couples with large negative heat of mixing Δ${\mathit{H}}_{\mathrm{mix}}$≪0, mechanical alloying allows amorphization of mixtures of some pure metals with Δ${\mathit{H}}_{\mathrm{mix}}$≊0. We have recently shown that for an amorphous phase in a sharp concentration gradient there is critical thickness ${\mathit{x}}_{\mathit{c}}$ below which crystallization is thermodynamically disallowed. We show here that ${\mathit{x}}_{\mathit{c}}$ is very small when Δ${\mathit{H}}_{\mathrm{mix}}$≊0 but that in mechanical alloying the simultaneous growth and deformation of the amorphous interlayers allows them to grow substantially in volume while remaining under the critical thickness ${\mathit{x}}_{\mathit{c}}$.