The Growth Kinetics and Interfacial Energy of Coherent γ-Fe Particles in Cu-Fe Alloys

Abstract

The growth of coherent γ-iron precipitates in Cu-0.4%Fe and Cu-1.2%Fe alloys aged at 873 and 973 K was examined by transmission electron microscopy to evaluate the interface energy between copper and coherent γ-iron.
The growth kinetics of γ-Fe particles could be described by the law of the Lifshitz-Wagner theory, \barR∝t^1⁄3 (\barR: mean particle radius, t: ageing time), and the distribution of particle size was also in agreement with that expected from the above theory.
The interface energy of coherent γ-iron in copper, which was evaluated from the growth rates of γ-iron particles based on the theory, increased with increasing volume fraction of particles. Furthermore, it was largely affected by a slight difference in the values of solubilities (equilibrium molar concentration of solute) as reported by some workers; it varied from about 0.25 to 0.35 J/m² depending of the values of solubilities used. It was concluded by examing the methods used for determining the solubilities of iron in copper that the fomer value, 0.25±0.05 J/m², was more reasonable for the interface energy of coherent γ-iron. The value was about one-half of the interface energy between copper and incoherent γ- or α-iron (about 0.52 J/m²), which was estimated from the dihedral angle of these incoherent particles existing in the grain boundaries of the matrix.