Gibbs-Thomson effect in nanocrystalline Fe-Ge

We studied the phase transformation behavior of chemically disordered bcc ({α}) phase Fe_1-xGeₓ alloys near the Fe₃Ge stoichiometry synthesized in the nanocrystalline state by mechanical alloying of the elemental constituents. The evolution of the equilibrium L1₂ ordered (ε^') phase was seen to occur via a metastable DO₃-ordered (α₁) phase, but a significant α₁→ε^' phase transformation took place only after the growth of the grains. This behavior is understood with the help of a capillary effect or the Gibbs-Thomson effect wherein the grain boundary energy of the nanosize grains raises the Gibbs free energy of the ε^' phase relative to the α₁ phase for small sizes and the ε^' phase grows only after a certain grain size is reached.