Monte Carlo Simulation of NbC Precipitation Kinetics in α-Fe

摘要

Using a vacancy diffusion mechanism for substitutional elements and an interstitial mechanism for carbon atoms, we propose a Monte Carlo method for simulating the coherent precipitation of niobium carbide in α-iron. Iron, niobium, and carbon atoms are distributed on a rigid, simple cubic lattice which describes both the bcc ferrite structure and the fcc NaCl-type structure of NbC. The Monte-Carlo parameters have been fitted with good accuracy to the experimental diffusion and equilibrium data. A residence time algorithm has been adapted in order to handle both the fast interstitial C diffusion and the slow substitutional Nb and Fe diffusion. Depending on the concentration and temperature, the simulations exhibit two kinds of kinetic paths: formation of transient iron carbides at high supersaturation, and nucleation of NbC precipitates at low supersaturation. Not only can the resulting kinetics of nucleation be compared with the classical theory but the simulations also provide information on cluster size, shape and density on the atomic scale which can then be directly compared with tomographic atom probe (TAP) results.