Diffusion properties of Fe-C systems studied by using kinetic activation-relaxation technique

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• 作者：Oscar A. Restrepo^a ; ^d ; ^{oa.restrepo.gutierrez@umontreal.ca" class="auth_mail" title="E-mail the corresponding author} ; Normand Mousseau^a ; ^{normand.mousseau@umontreal.ca" class="auth_mail" title="E-mail the corresponding author} ; Fedwa El-Mellouhi^c ; Othmane Bouhali^d ; Mickaë ; l Trochet^a ; Charlotte S. Becquart^b
• 关键词：Defects ; Diffusion ; Activated dynamics ; Kinetic Monte Carlo ; Fe&ndash ; C ; Corrosion ; Steel
• 刊名：Computational Materials Science
• 出版年：2016
• 出版时间：1 February 2016
• 年：2016
• 卷：112
• 期：part_PA
• 页码：96-106
• 全文大小：3576 K

文摘

Diffusion of carbon in iron is associated with processes such as carburization and the production of steels. In this work, the kinetic activation–relaxation technique (k-ART) – an off-lattice self-learning kinetic Monte Carlo (KMC) algorithm – is used to study this phenomenon over long time scales. Coupling the open-ended ART nouveau technique to generate on-the-fly activated events and NAUTY, a topological classification for cataloging, k-ART reaches timescales that range from microseconds to seconds while fully taking into account long-range elastic effects and complex events, characterizing in details the energy landscape in a way that cannot be done with standard molecular dynamics (MD) or KMC. The diffusion mechanisms and pathways for one to four carbon interstitials, and a single vacancy coupled with one to several carbons are studied. In bulk Fe, k-ART predicts correctly the 0.815 eV barrier for a single C-interstitial as well as the stressed induced energy-barrier distribution around this value for 2 and 4 C interstitials. For vacancy–carbon complex, simulations recover the DFT-predicted ground state. K-ART also identifies a trapping mechanism for the vacancy through the formation of a dynamical complex, involving C and neighboring Fe atoms, characterized by hops over barriers ranging from ∼0.41 to ∼0.72 eV that correspond, at room temperature, to trapping time of hours. At high temperatures, this complex can be broken by crossing a 1.5 eV barrier, leading to a state ∼0.8 eV higher than the ground state, allowing diffusion of the vacancy. A less stable complex is formed when a second C is added, characterized by a large number of bound excited states that occupy two cells. It can be broken into a V–C complex and a single free C through a 1.11 eV barrier.