Authors: Rodolfo A. Pérez, Patrick Gas, Philippe Maugis
Abstract: Experiments of niobium diffusion at infinite dilution and Nb reaction-diffusion in pure
iron and in ferrites with different amounts of carbon were performed, for comparison, in order to
understand the influence of carbon on the diffusion process in the Nb-Fe system. A proportional
decrease of the diffusion coefficient with the increasing amount of carbon was found. This effect
seems to be stronger than in the self-diffusion analyzing the literature; moreover SIMS
measurements in niobium- implanted samples show a redistribution of carbon during the first steps
of the diffusion process. For those reasons, a stronger effect of carbon-niobium interaction over the
carbon-vacancy interaction seems to be responsible for the decrease in the diffusion coefficient.
163
Authors: Michel Perez, Eglantine Courtois, Daniel Acevedo Reyes, Thierry Epicier, Philippe Maugis
Abstract: High Resolution Transmission Electron Microscope and Electron Energy Loss
Spectroscopy and have been used to characterize the structure and chemical composition of
niobium carbonitrides in the ferrite of a Fe-Nb-C-N model alloy at different precipitation stages.
Experiments seem to indicate the coexistence of two types of precipitates: pure niobium nitrides
and mixed sub-stoichiometric niobium carbonitrides. In order to predict the chemical composition
of these precipitates, a thermodynamical formalism has been developed to evaluate (i) the
nucleation and growth rates (classical nucleation theory) and (ii) the chemical composition of nuclei
and existing precipitates. A model based on the numerical resolution of former equations, is used to
compute precipitates size distribution evolution at a given temperature. The predicted compositions
are in very good agreement with experimental results.
4196
Authors: Alexis Deschamps, Fabien Perrard, Françoise Bley, Patricia Donnadieu, Philippe Maugis
Abstract: This paper presents a physically based precipitation model which aims at describing
precipitation kinetics when it occurs exclusively on dislocations. We present specific nucleation,
growth and coarsening equations, which are integrated in a set of differential equations. This model
is successfully applied to the case of precipitation of NbC in a ferritic steel, whose kinetics has been
determined by small-angle neutron scattering.
4161
Authors: Céline Hin, Frederic Soisson, Philippe Maugis
Abstract: The precipitation of niobium carbides in industrial steels is commonly used to control
the recrystallization process or the amount of interstitial atoms in solid solution. It is then important to understand the precipitation kinetics and especially the competition between homogeneous and heterogeneous precipitation, since both of them have been observed experimentally, depending on the alloy composition, microstructure and thermal treatments. We propose Monte Carlo simulations of NbC precipitation in α-iron, based on a simple atomic description of the main parameters which control the kinetic pathway : - realistic diffusion properties, 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 grain boundaries which reproduces the equilibrium segregation
properties of Nb and C - a point defect source which drives the vacancy concentration towards its equilibrium value. Depending on the precipitation conditions, MC simulations predict different kinetic behaviours, including homogeneous and heterogeneous NbC precipitation, early segregation of C atoms and its importance as a first stage for NbC precipitation, wetting phenomena on grain boundaries and transient precipitation of metastable carbides.
721
Authors: Philippe Maugis, Frederic Soisson, Ludovic Lae
Abstract: We test the main approximations of the classical laws for nucleation, growth and
coarsening by comparison with atomistic simulations of the kinetics of precipitation. We investigate the kinetics of phase separation in dilute A-B solid solutions by precipitation of B atoms in the Arich matrix. Classically, the kinetics is represented by the time evolution of the total number of particles and their mean radius. In this work, the kinetics is predicted by three types of models: (a) an Atomic-scale Kinetic Monte Carlo (AKMC) model based on a vacancy diffusion mechanism, (b) a Cluster Dynamics model, and (c) the MultiPreci model, based on the coupling of the classical laws of nucleation, growth and coarsening. Cluster Dynamics and the Multipreci model have been parameterized such that the thermodynamic and kinetic parameters (solubility, diffusion coefficient, interface energy) be identical to that of the AKMC. Under these conditions we find that the classical laws are in good agreement with the atomistic simulations as long as the thermodynamics of the solid solution remains strictly regular. As expected, Cluster Dynamics compares better with the atomistic simulations, especially if a precise description of the energetics of the smallest clusters is applied.
671
Authors: Philippe Maugis, M. Gouné, P. Barges, D. Dougnac, D. Ravaine, M. Lamberigts, Tadeusz Siwecki, Y. Bi
1313
Authors: Dominique Gendt, Philippe Maugis, G. Martin, Maylise Nastar, Frederic Soisson
1779
Authors: Philippe Maugis, Dominique Gendt, S. Lanteri, P. Barges
1767
Authors: Philippe Maugis, G. Martin
389