Precipitation of niobium carbonitrides in ferrite: chemical composition measurements and thermodynamic modelling

• Published in: Philosophical magazine letters 2007-09, Vol.87 (9), p.645-656
• Main Authors: Perez, M., Courtois, E., Acevedo, D., Epicier, T., Maugis, P.
• Format: Article
• Language: English
• Subjects: Cross-disciplinary physics: materials science; rheology; Engineering Sciences; Exact sciences and technology; Materials; Materials science; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Precipitation
• ISSN: 0950-0839; 1362-3036
• DOI: 10.1080/09500830701427003

High-resolution transmission electron microscopy and electron-energy loss spectroscopy 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 understand the chemical composition of these precipitates, a thermodynamic formalism has been developed to evaluate the nucleation and growth rates (classical nucleation theory) and the chemical composition of nuclei and existing precipitates. A model based on the numerical solution of thermodynamic and kinetic equations is used to compute the evolution of the precipitate size distribution at a given temperature. The predicted compositions are in very good agreement with experimental results.