On Clustering in Real Cottrell Nanosegregations in Metallic Materials

By analyzing some known data of 3D atomic force microscopy for metallic materials and a number of other theoretical and experimental results, including data on the "dislocation" dissolution of cementite in pearlitic and martensitic steels, clustering in real Cottrell "atmospheres" (nanosegregations) is considered and their characteristics (including the number of impurity atoms per dislocation of atomic length) are determined, which differ significantly from the classical theoretical models. In particular, Cottrell boron nanosegregations on edge dislocations in an ordered intermetallic compound FeAl containing 40 at. % Al and 0.04 at. % B, as well as Cottrell carbon nanosegregations on screw dislocations in martensitic steel are considered. The presence of Fe₃B and Fe₃C type clustering in such nanosegregations, which is not taken into account in the framework of the classical models of Cottrell's "atmospheres" ("clouds"), is shown. It is shown that in metallic materials (FeAl–B, Fe–C, Al–Fe, Pd–H) in real "atmospheres" (nanosegregations) on dislocations a certain clustering takes place (including the formation of bordde-like, carbide-like, intermetallic-like and hydride-like structures), which differs from the classical theoretical models of Cottrell's "atmospheres". In particular, the methodology for determining the impurity diffusion coefficient in the areas of nanosegregations on dislocations in metallic materials is considered (using the Pd–H, Al–Fe, Fe–C systems as an example).