Thermodynamics and long-range order of interstitials in an h.c.p. lattice: Nitrogen in ε-Fe2N1 − z

Abstract

Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Download date: 11-05-2018Pergamon Actu mawr. Vol. 45. No. 5, pp. 2013-2025, 1997 f: 1997 Acta Metallurgica Inc. PII: S1359-6454(96)00307-2

Thermodynamics of the Fe-N and Fe-N-C Systems: The Fe-N and Fe-N-C Phase Diagrams Revisited

“…It is, however, noted that octahedral sites adjacent in the c direction cannot be occupied simultaneously. [14,30] G u Fe:N , and G u Fe:Va of the hypothetical non-magnetic compounds Fe a C c , Fe a N c , and Fe a Va c , the so-called end-members, with Fe:C, Fe:N, and Fe:Va denoting that the second sublattice is fully occupied by C, N, and Va, respectively, the excess Gibbs energy G u;ex and the magnetic contribution G u;mag .…”

“…As an additional information, the activity curves for c 0 from References 25 and 82 and for e in References 17 and 89 were used. However, these so-called absorption isotherms obtained from gaseous nitriding of Fe specimens are affected by the establishment of steady states instead of true metastable equilibrium at the surface of the specimen at higher temperatures and N contents, [1,13,14] making it impossible to use all data above 823 K (550°C). Already at lower temperatures, but high N contents (>30 at.…”

“…pct N) already at 723 K (450°C). [14] Until today, the experimental data set for the Fe-N system as compiled in Reference 12 is the most complete experimental description of the system and largely provides the basis for the optimisation of thermodynamic parameters in the present work. Recently, some additional data on the constitution of the system have been published [13,15] that are also considered in the present work.…”

“…In general, for the intermediate phases c 0 and e, these descriptions only consider random mixing of nitrogen on an interstitial sublattice, and thus excess Gibbs energy parameters have to be introduced to describe the deviation of the real system from such ideal behavior. Theoretical approaches to describe the thermodynamics of nitrogen ordering and disordering have been presented for c 0 [25][26][27][28][29] and e. [14,27,[30][31][32][33] Upon nitrocarburizing of Fe, a simultaneous uptake of N and C into the substrate occurs. [1] Upon only nitriding of technical steel, interactions of N and C have to be considered as well, due to (initial) C present in the substrate.…”

Generalization of first-principles thermodynamic model: Application to hexagonal close-packed ε-Fe3N

“…One phase of major importance is the iron-based nitride ε-Fe 2 N 1 − z developing on steel surfaces during nitriding. ε-Fe 2 N 1 − z can be conceived as a hexagonal close-packed sublattice of iron atoms, where the nitrogen atoms reside in an ordered way on a sublattice formed by the octahedral interstices [1].…”