An evaluation of the Fe-N phase diagram considering long-range order of N atoms in {gamma}{prime}-Fe{sub 4}N{sub 1{minus}x} and {var_epsilon}-Fe{sub 2}N{sub 1{minus}z}

Journal Article · Mon Apr 01 04:00:00 EST 1996 · Metallurgical Transactions, A

OSTI ID:250733

Kooi, B J; Somers, M A.J.; Mittemeijer, E J ^[1]

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1. Delft Univ. of Technology (Netherlands). Lab. of Materials Science

The chemical potential of nitrogen was described as a function of nitrogen content for the Fe-N phases {alpha}-Fe[N], {gamma}{prime}-Fe{sub 4}N{sub 1{minus}x}, and {var_epsilon}-Fe{sub 2}N{sub 1{minus}z}. For {alpha}-Fe[N], an ideal, random distribution of the nitrogen atoms over the octahedral interstices of the bcc iron lattice was assumed; for {gamma}{prime}-Fe{sub 4}N{sub 1{minus}x} and {var_epsilon}-Fe{sub 2}N{sub z}, the occurrence of a long-range ordered distribution of the nitrogen atoms over the octahedral interstices of the close packed iron sublattices (fcc and hcp, respectively) was taken into account. The theoretical expressions were fitted to nitrogen-absorption isotherm data for the three Fe-N phases. The {alpha}/{alpha} + {gamma}{prime}, {alpha} + {gamma}{prime}/{gamma}{prime}, {gamma}{prime}/{gamma}{prime} + {var_epsilon}, and {gamma}{prime} + {var_epsilon}/{var_epsilon} phase boundaries in the Fe-N phase diagram were calculated from combining the quantitative descriptions for the absorption isotherms with the known composition of NH{sub 3}/H{sub 2} gas mixtures in equilibrium with coexisting {alpha} and {gamma}{prime} phases and in equilibrium with coexisting {gamma}{prime} and {var_epsilon} phases. Comparison of the present phase boundaries with experimental data and previously calculated phase boundaries showed a major improvement as compared to the previously calculated Fe-N phase diagrams, where long-range order for the nitrogen atoms in the {gamma}{prime} and {var_epsilon} phases was not accounted for.

• OSTI ID: 250733
• Journal Information: Metallurgical Transactions, A, Journal Name: Metallurgical Transactions, A Journal Issue: 4 Vol. 27; ISSN 0360-2133; ISSN MTTABN
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ABSORPTION
AMMONIA
BCC LATTICES
CHEMICAL COMPOSITION
CRYSTAL LATTICES
EQUILIBRIUM
FCC LATTICES
HCP LATTICES
HYDROGEN
IRON NITRIDES
ISOTHERMS
NITROGEN
PHASE DIAGRAMS
SOLID SOLUTIONS
TEMPERATURE DEPENDENCE