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Thermodynamics of the iron-nitrogen system with vacancies. From first principles to applications
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Karimi, Aurash and Auinger, Michael (2020) Thermodynamics of the iron-nitrogen system with vacancies. From first principles to applications. Journal of Alloys and Compounds, 821 . 153343. doi:10.1016/j.jallcom.2019.153343 ISSN 0925-8388.
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Official URL: https://doi.org/10.1016/j.jallcom.2019.153343
Abstract
Density Functional Theory (DFT) and Atomistic Kinetic Monte Carlo is employed in this work to assess the thermodynamic behaviour of the α (BCC) and γ (FCC) allotropes in the iron-nitrogen system. The calculated nitrogen solubility at unit nitrogen activity from (250 < T < 1538°C) is found to be significantly underestimated, beyond the uncertainty range of the calculation, in both phases. The boundary of the α-γ phase change as featured in Lehrer diagrams is calculated within the nitriding potential (0.001 < r_N < 10) and temperature (300 < T < 900°C) ranges. The boundary shows good agreement with experimental data, but the calculated α region is consistently smaller than the data suggests. Motivated by the existence of grain boundaries and other common defects which cause far more unoccupied volume within iron than is expected in idealised lattice structures, the effect of excess vacancy concentrations in varying ranges between 10^{−12} < c_v < 10 at.% on nitrogen solubility and the α-γ phase change is quantified. It is shown how discrepancies between the theoretical ideal crystal and experimental data can be "corrected" by excess vacancies to model the non-ideality of iron lattices in reality, and evidence is given for the validity of this correction.
Results are presented in an applied context, allowing opportunities for experimental verification.
| Item Type: | Journal Article | ||||||||
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| Subjects: | Q Science > QC Physics Q Science > QD Chemistry T Technology > TA Engineering (General). Civil engineering (General) T Technology > TN Mining engineering. Metallurgy T Technology > TS Manufactures |
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| Divisions: | Faculty of Science, Engineering and Medicine > Engineering > WMG (Formerly the Warwick Manufacturing Group) | ||||||||
| Library of Congress Subject Headings (LCSH): | Metals -- Mechanical properties, Alloys -- Mechanical properties, Solid state chemistry, Phase transformations (Statistical physics) , Point defects, Thermodynamics | ||||||||
| Journal or Publication Title: | Journal of Alloys and Compounds | ||||||||
| Publisher: | Elsevier BV | ||||||||
| ISSN: | 0925-8388 | ||||||||
| Official Date: | 25 April 2020 | ||||||||
| Dates: |
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| Volume: | 821 | ||||||||
| Article Number: | 153343 | ||||||||
| DOI: | 10.1016/j.jallcom.2019.153343 | ||||||||
| Status: | Peer Reviewed | ||||||||
| Publication Status: | Published | ||||||||
| Access rights to Published version: | Restricted or Subscription Access | ||||||||
| Date of first compliant deposit: | 12 December 2019 | ||||||||
| Date of first compliant Open Access: | 12 December 2020 | ||||||||
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