CLUSTERING OF CARBON ATOMS IN alpha-IRON*

Abstract

Binding and migration energies and atomic configurations have been calculated for small carbon clusters in {alpha}-iron. A mathematical model was used which consisted of a spherical crystallite containing about 530 atoms which were treated as individual particles, surrounded by an elastic continuum with atoms imbedded in it. A two-body central force was used to simulate the interaction between nearest and next nearest. neighboring iron atoms in the crystallite and another was used for the iron-carbon interaction. The dicarbon, tricarbon, and tetracarbon binding energies were 0.14, 0.36, and 0.66 eV respectively, and the binding energy continued increasing for larger clusters by approximately 0.31 eV per additional carbon atom. The most stable configurations for clusters were very thin platelets on {001} planes in which the individual carbon atoms occupied octahedral sites. The axes of the carbon atoms were parallel to each other and perpendicular to the platelet~ lbe migration energy of the platelets was higher than the single carbon migration energy, and the migration mechanism consisted of peripheral atoms moving around the e.dges of the platelet.