TEM study of NbC heterogeneous precipitation in ferrite

Abstract

The heterogeneous precipitation of NbC in ferrite has been quantitatively characterized by transmission electron microscopy in a Fe–C–Nb model alloy for different isothermal heat treatments. The elongation and size distribution of precipitates were derived using dark field imaging. For each precipitation state, the precipitation of NbC occurs on dislocations due to the as-quenched state. This precipitation mechanism leads to characteristic arrays of precipitates in which precipitates grow in a self-similar manner. A detailed study of these arrays has shown that most dislocations decorated by these arrays are edge dislocations with ⟨112⟩ type line vectors. There is only one variant on a given dislocation. This selection can be interpreted by the interaction between dislocation and precipitate strain fields.