The diffusion of nitrogen in alpha iron

Thomas, W.R.; Leak, G. M.

doi:10.1080/14786440608520473

Cited by 19 publications

(4 citation statements)

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“…These calculations show excellent agreement with experimentally verifiable parameters, such as the migration energy barrier for C diffusion, where ab initio values of 0.86 eV 33,36 , 0.87 eV 37 and 0.90 eV 34 are in good agreement with the experimental value of 0.87 eV 2,38 . For N, an equally good agreement is seen for the migration barrier, where a value of 0.76 eV was found by ab initio calculations 34 and a value of 0.78 eV was found experimentally 39 . Calculations in austenite are, however, limited primarily to solute dissolution, diffusion and their influence on the electronic structure and local geometry 33,[40][41][42] although calculations of vacancy-C binding have been performed 43 .…”

Section: Introductionsupporting

confidence: 57%

“…For N, an equally good agreement is seen for the migration barrier, where a value of 0.76 eV was found by ab initio calculations 35 and a value of 0.78 eV was found experimentally. 40 Calculations in austenite are, however, limited primarily to solute dissolution, diffusion, and their influence on the electronic structure, local environment, and stacking fault energies, 34,[41][42][43][44][45][46] although calculations of vacancy-C binding have been performed. 47 In this work we present a detailed study of the energetics, kinetics, and interactions of He, C, and N solutes in model austenite and austenitic systems using DFT.…”

Section: Introductionmentioning

confidence: 99%

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First-principles study of helium, carbon, and nitrogen in austenite, dilute austenitic iron alloys, and nickel

et al. 2013

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An extensive set of first-principles density functional theory calculations have been performed to study the behavior of He, C, and N solutes in austenite, dilute Fe-Cr-Ni austenitic alloys, and Ni in order to investigate their influence on the microstructural evolution of austenitic steel alloys under irradiation. The results show that austenite behaves much like other face-centered cubic metals and like Ni in particular. Strong similarities were also observed between austenite and ferrite. We find that interstitial He is most stable in the tetrahedral site and migrates with a low barrier energy of between 0.1 and 0.2 eV. It binds strongly into clusters as well as overcoordinated lattice defects and forms highly stable He-vacancy (V m He n ) clusters. Interstitial He clusters of sufficient size were shown to be unstable to self-interstitial emission and VHe n cluster formation. The binding of additional He and V to existing V m He n clusters increases with cluster size, leading to unbounded growth and He bubble formation. Clusters with n/m around 1.3 were found to be most stable with a dissociation energy of 2.8 eV for He and V release. Substitutional He migrates via the dissociative mechanism in a thermal vacancy population but can migrate via the vacancy mechanism in irradiated environments as a stable V 2 He complex. Both C and N are most stable octahedrally and exhibit migration energies in the range from 1.3 to 1.6 eV. Interactions between pairs of these solutes are either repulsive or negligible. A vacancy can stably bind up to two C or N atoms with binding energies per solute atom up to 0.4 eV for C and up to 0.6 eV for N. Calculations in Ni, however, show that this may not result in vacancy trapping as VC and VN complexes can migrate cooperatively with barrier energies comparable to the isolated vacancy. This should also lead to enhanced C and N mobility in irradiated materials and may result in solute segregation to defect sinks. Binding to larger vacancy clusters is most stable near their surface and increases with cluster size. A binding energy of 0.1 eV was observed for both C and N to a [001] self-interstitial dumbbell and is likely to increase with cluster size. On this basis, we would expect that, once mobile, Cottrell atmospheres of C and N will develop around dislocations and grain boundaries in austenitic steel alloys.

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Section: Introductionsupporting

confidence: 57%

Section: Introductionmentioning

confidence: 99%

First-principles study of helium, carbon, and nitrogen in austenite, dilute austenitic iron alloys, and nickel

et al. 2013

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“…5 (c) shows the precipitates of γ′-Fe 4 N obtained from a 220 spot of γ′ iron nitride (shown as a white circle in the SADP). According to the Fe-N diagram, the ε-Fe 2-3 N formed in nitriding would decompose during furnace cooling to the γ′-Fe 4 N precipitates with lamellar structure presenting an (0001) ε //(111) γ′ , [1][2][3][4][5][6][7][8][9][10] γ′ // [11][12][13][14][15][16][17][18][19][20] ε orientation relationship of ε-Fe 2-3 N with γ′-Fe 4 N [35,36].…”

Section: Resultsmentioning

confidence: 99%

“…The nitriding treatment is based upon nitrogen diffusion in the ferrite matrix [9][10][11][12][13][14]. For the optimization of the nitriding, one should know the behavior of alloying elements in relation to the precipitation phenomenon and the effects on hardness and residual stresses.…”

Section: Introductionmentioning

confidence: 99%