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A first-principles reassessment of the Fe-N phase diagram in the low-nitrogen limit

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Abstract
Nitriding of steels has been widely used for almost a century. However, insight in two important precipitating phases for low concentration through-thickness nitriding is still lacking, hindering further development of the process. Due to their metastable nature, manufacturing large homogeneous samples of Fe4N and Fe16N2 is very challenging. Consequently, measuring thermodynamic properties, such as heat capacity and free energy, has proven difficult at best. In this work, we have calculated those thermodynamic properties using density-functional theory (DFT) for Fe4N, Fe16N2 and ferrite with nitrogen in solid solution. This information is a prerequisite to improve the accuracy of larger-scale modeling approaches of iron nitrides. We used the free energies to construct the temperature/concentration phase diagram for low nitrogen concentrations from to . Both the range of metastability for Fe16N2 and the nitrogen solvus confirm the experimental data. On the other hand, it was concluded that the experimental Curie temperature for Fe16N2 is severely underestimated because of the thermodynamic instability above 400 K.
Keywords
Materials Chemistry, Metals and Alloys, Mechanical Engineering, Mechanics of Materials, Nitride materials, Thermodynamic properties, Precipitation, Magnetization, Density-functional theory, GENERALIZED-GRADIENT-APPROXIMATION, TOTAL-ENERGY CALCULATIONS, CLUSTER VARIATION METHOD, EXCHANGE INTERACTIONS, MAGNETIC-PROPERTIES, ELASTIC-CONSTANTS, GROUND-STATE, IRON NITRIDE, TEMPERATURE, DIFFRACTION

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MLA
De Waele, Sam, et al. “A First-Principles Reassessment of the Fe-N Phase Diagram in the Low-Nitrogen Limit.” JOURNAL OF ALLOYS AND COMPOUNDS, vol. 775, 2018, pp. 758–68, doi:10.1016/j.jallcom.2018.09.356.
APA
De Waele, S., Lejaeghere, K., Leunis, E., Duprez, L., & Cottenier, S. (2018). A first-principles reassessment of the Fe-N phase diagram in the low-nitrogen limit. JOURNAL OF ALLOYS AND COMPOUNDS, 775, 758–768. https://doi.org/10.1016/j.jallcom.2018.09.356
Chicago author-date
De Waele, Sam, Kurt Lejaeghere, Elke Leunis, Lode Duprez, and Stefaan Cottenier. 2018. “A First-Principles Reassessment of the Fe-N Phase Diagram in the Low-Nitrogen Limit.” JOURNAL OF ALLOYS AND COMPOUNDS 775: 758–68. https://doi.org/10.1016/j.jallcom.2018.09.356.
Chicago author-date (all authors)
De Waele, Sam, Kurt Lejaeghere, Elke Leunis, Lode Duprez, and Stefaan Cottenier. 2018. “A First-Principles Reassessment of the Fe-N Phase Diagram in the Low-Nitrogen Limit.” JOURNAL OF ALLOYS AND COMPOUNDS 775: 758–768. doi:10.1016/j.jallcom.2018.09.356.
Vancouver
1.
De Waele S, Lejaeghere K, Leunis E, Duprez L, Cottenier S. A first-principles reassessment of the Fe-N phase diagram in the low-nitrogen limit. JOURNAL OF ALLOYS AND COMPOUNDS. 2018;775:758–68.
IEEE
[1]
S. De Waele, K. Lejaeghere, E. Leunis, L. Duprez, and S. Cottenier, “A first-principles reassessment of the Fe-N phase diagram in the low-nitrogen limit,” JOURNAL OF ALLOYS AND COMPOUNDS, vol. 775, pp. 758–768, 2018.
@article{8730983,
  abstract     = {{Nitriding of steels has been widely used for almost a century. However, insight in two important precipitating phases for low concentration through-thickness nitriding is still lacking, hindering further development of the process. Due to their metastable nature, manufacturing large homogeneous samples of Fe4N and Fe16N2 is very challenging. Consequently, measuring thermodynamic properties, such as heat capacity and free energy, has proven difficult at best. In this work, we have calculated those thermodynamic properties using density-functional theory (DFT) for Fe4N, Fe16N2 and ferrite with nitrogen in solid solution. This information is a prerequisite to improve the accuracy of larger-scale modeling approaches of iron nitrides. We used the free energies to construct the temperature/concentration phase diagram for low nitrogen concentrations from  to . Both the range of metastability for Fe16N2 and the nitrogen solvus confirm the experimental data. On the other hand, it was concluded that the experimental Curie temperature for Fe16N2 is severely underestimated because of the thermodynamic instability above 400 K.}},
  author       = {{De Waele, Sam and Lejaeghere, Kurt and Leunis, Elke and Duprez, Lode and Cottenier, Stefaan}},
  issn         = {{0925-8388}},
  journal      = {{JOURNAL OF ALLOYS AND COMPOUNDS}},
  keywords     = {{Materials Chemistry,Metals and Alloys,Mechanical Engineering,Mechanics of Materials,Nitride materials,Thermodynamic properties,Precipitation,Magnetization,Density-functional theory,GENERALIZED-GRADIENT-APPROXIMATION,TOTAL-ENERGY CALCULATIONS,CLUSTER VARIATION METHOD,EXCHANGE INTERACTIONS,MAGNETIC-PROPERTIES,ELASTIC-CONSTANTS,GROUND-STATE,IRON NITRIDE,TEMPERATURE,DIFFRACTION}},
  language     = {{eng}},
  pages        = {{758--768}},
  title        = {{A first-principles reassessment of the Fe-N phase diagram in the low-nitrogen limit}},
  url          = {{http://dx.doi.org/10.1016/j.jallcom.2018.09.356}},
  volume       = {{775}},
  year         = {{2018}},
}

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