Kinetics of heterogeneous grain boundary precipitation of NbC in α-iron: A Monte Carlo study

We propose Monte Carlo simulations of the NbC grain boundary (GB) precipitation kinetics in α-iron, based on an atomic description of the main mechanisms that control the kinetic pathway. The simulation involves realistic diffusion mechanisms, with a rapid diffusion of C atoms by interstitial jumps and a slower diffusion of Fe and Nb atoms by vacancy jumps; a simple model of the GB which reproduces the equilibrium segregation properties of Nb and C; and a point defect source which drives the vacancy concentration towards its equilibrium value. Depending on the precipitation conditions, Monte Carlo simulations predict different kinetic behaviours, including early segregation of C atoms at the grain boundaries, transient precipitation of metastable carbides, and homogeneous and heterogeneous NbC precipitation.