Gibbs-Thomson effect in nanocrystalline Fe-Ge

Abstract

We studied the phase transformation behavior of chemically disordered bcc (α) phase (Formula presented) alloys near the (Formula presented) stoichiometry synthesized in the nanocrystalline state by mechanical alloying of the elemental constituents. The evolution of the equilibrium (Formula presented) ordered (Formula presented) phase was seen to occur via a metastable (Formula presented)-ordered (Formula presented) phase, but a significant (Formula presented) 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 (Formula presented) phase relative to the (Formula presented) phase for small sizes and the (Formula presented) phase grows only after a certain grain size is reached. © 2000 The American Physical Society.