Growth and microstructure of iron nitride layers and pore formation in ε-Fe3N
-
C. Middendorf
Abstract
Layers of ε-Fe3N and γ′-Fe4N on ferrite were produced by nitriding iron single crystals or rolled sheets of iron in flowing ammonia at 520 °C. The nitride layers were characterised using X-ray diffraction, light microscopy as well as scanning and transmission electron microscopy. The compound layer consists of ε-Fe3N at the surface and of γ′-Fe4N facing the ferrite. After 4 h of nitriding, pores develop in the near surface region of ε-Fe3N showing more or less open porosity. Growth of the entire compound layer as well as of the massive and the porous ε-Fe3N sublayer is diffusion-controlled and follows a parabolic growth rate. The γ′-Fe4N layer is formed as a transition phase within a narrow interval of nitrogen activity, and it shows little growth in thickness. The transformation of γ′-Fe4N to ε-Fe3N is topotactic, where the orientation of the closed-packed iron layers of the crystal structures is preserved. Determination of lattice plane spacings was possible by X-ray diffraction, and this was correlated to the nitrogen content of ε-Fe3N. While the porous layer exhibits an enhanced nitrogen content corresponding to the chemical composition Fe3N11, the massive e Fe3N layer corresponds to Fe3N1.0. The pore formation in ε-Fe3N11 is concluded to be the result of excess nitrogen atoms on non-structural sites, which have a high mobility. Therefore, recombination of excess nitrogen to molecular N2 at lattice defects is preferred in ε-Fe3N with high nitrogen content compared to stoichiometric ε-Fe3N1.0 with nitrogen on only structural sites.
Abstract
Ein Schichtsystem von Eisennitriden auf Ferrit wurde durch Nitrieren von Eiseneinkristallen und -blechen im Ammoniak-Strom bei 520 °C hergestellt und mittels Röntgenbeugung sowie lichtmikroskopisch und elektronenmikroskopisch charakterisiert. In der Verbindungsschicht, welche sich aus ε-Fe3N an der Oberfläche und γ′-Fe4N an den Ferrit grenzend zusammensetzt, entsteht nach ca. 4 h Nitrieren im oberflächennahen Bereich von ε-Fe3N ein Porensaum mit weitgehend offener Porosität. Das Wachstum der gesamten Verbindungsschicht sowie der dichten ε-Fe3N-Schicht und des Porensaums erfolgt diffusionskontrolliert nach einem parabolischen Zeitgesetz. Die γ′-Fe4N-Schicht entsteht als Übergangsphase in einem engen Intervall der Stickstoffaktivität und weist ein geringes Dickenwachstum auf. Die Umwandlung von γ′-Fe4N in ε-Fe3N erfolgt topo-taktisch unter Beibehaltung der Orientierung der dicht gepackten Eisenlagen beider Kristallstrukturen. Über die Bestimmung von Netzebenenabständen aus der Lage von Röntgenreflexen gelang der Nachweis eines erhöhten Stickstoffgehaltes im Porensaum von ε-Fe3N mit der Zusammensetzung Fe3N11 im Vergleich zur porenfreien ε-Fe3N-Schicht mit Fe3N1.0. Die Porenbildung in ε-Fe3N11 wird auf Überschuss-Stickstoffatome auf nicht-strukturellen Oktaederplätzen zurückgeführt, die eine erhöhte Beweglichkeit im Gitter besitzen und damit an Kristallfehlern mit höherer Wahrscheinlichkeit zu molekularem N2 rekom-binieren können, als dies in stöchiometrischem ε-Fe3N1.0 mit ausschließlich auf strukturellen Plätzen befindlichen Stickstoffatomen der Fall ist.
Funding statement: The authors would like to thank Dr. D. Brunner, Max-Planck-Institut für Metallforschung, Stuttgart, for supporting the iron single crystal. Financial support by the Deutsche Forschungsgemeinschaft and by the Fonds der Chemischen Industrie is gratefully acknowledged.
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© 2003 Carl Hanser Verlag, München
Articles in the same Issue
- Frontmatter
- Editorial
- Editorial
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- The role of oxidation-induced cavities on the failure of the thermally grown oxide on binary β-NiAl alloys
- Phase stability of Y + Gd co-doped zirconia
- Mechanisms governing the distortion of alumina-forming alloys upon cyclic oxidation
- High-temperature oxidation of FeCrAl alloys: the effect of Mg incorporation into the alumina scale
- Nonlinear dielectric properties at oxide grain boundaries
- TEM observations of singular grain boundaries and their roughening transition in TiO2-excess BaTiO3
- Processing of dense MgO substrates for high-temperature superconductors
- Microwave-induced crystallization of polysilazane-derived silicon carbonitride
- Schottky barrier formation in liquid-phase-sintered silicon carbide
- SrTiO3: a model electroceramic
- Optical properties and electronic structure of oxidized and reduced single-crystal strontium titanate
- Spreading of liquid Ag and Ag–Mo alloys on molybdenum substrates
- Nanoalloying in mixed AgmAun nanowires
- Never ending saga of a simple boundary
- Comparison of interfacial chemistry at Cu/α-alumina and Cu/γ-alumina interfaces
- Microstructure of Cu2O/Si interfaces, made by epitaxial electrodeposition
- Metal/oxide interfaces and their reaction with hydrogen
- Amorphous films at metal/ceramic interfaces
- Some thoughts on source monochromation and the implications for electron energy loss spectroscopy
- Determination of the contrast transfer function by analysing diffractograms of thin amorphous foils
- Progress in the preparation of cross-sectional TEM specimens by ion-beam thinning
- Quantification of interfacial segregation by analytical electron microscopy
- Quantification of elemental segregation to lath and grain boundaries in low-alloy steel by STEM X-ray mapping combined with the ζ-factor method
- Microstructure of Al/Ti metallization layers
- Connectivity of CSL grain boundaries and the role of deviations from exact coincidence
- Effect of laser shock processing on the microstructure and mechanical properties of pure Cu
- Growth and microstructure of iron nitride layers and pore formation in ε-Fe3N
- Phase diagram of the Al–Cu–Fe quasicrystal-forming alloy system
- Notifications/Mitteilungen
- Personal/Personelles
- Gesellschaftsnachricht
- International Conferences
Articles in the same Issue
- Frontmatter
- Editorial
- Editorial
- Articles/Aufsätze
- The role of oxidation-induced cavities on the failure of the thermally grown oxide on binary β-NiAl alloys
- Phase stability of Y + Gd co-doped zirconia
- Mechanisms governing the distortion of alumina-forming alloys upon cyclic oxidation
- High-temperature oxidation of FeCrAl alloys: the effect of Mg incorporation into the alumina scale
- Nonlinear dielectric properties at oxide grain boundaries
- TEM observations of singular grain boundaries and their roughening transition in TiO2-excess BaTiO3
- Processing of dense MgO substrates for high-temperature superconductors
- Microwave-induced crystallization of polysilazane-derived silicon carbonitride
- Schottky barrier formation in liquid-phase-sintered silicon carbide
- SrTiO3: a model electroceramic
- Optical properties and electronic structure of oxidized and reduced single-crystal strontium titanate
- Spreading of liquid Ag and Ag–Mo alloys on molybdenum substrates
- Nanoalloying in mixed AgmAun nanowires
- Never ending saga of a simple boundary
- Comparison of interfacial chemistry at Cu/α-alumina and Cu/γ-alumina interfaces
- Microstructure of Cu2O/Si interfaces, made by epitaxial electrodeposition
- Metal/oxide interfaces and their reaction with hydrogen
- Amorphous films at metal/ceramic interfaces
- Some thoughts on source monochromation and the implications for electron energy loss spectroscopy
- Determination of the contrast transfer function by analysing diffractograms of thin amorphous foils
- Progress in the preparation of cross-sectional TEM specimens by ion-beam thinning
- Quantification of interfacial segregation by analytical electron microscopy
- Quantification of elemental segregation to lath and grain boundaries in low-alloy steel by STEM X-ray mapping combined with the ζ-factor method
- Microstructure of Al/Ti metallization layers
- Connectivity of CSL grain boundaries and the role of deviations from exact coincidence
- Effect of laser shock processing on the microstructure and mechanical properties of pure Cu
- Growth and microstructure of iron nitride layers and pore formation in ε-Fe3N
- Phase diagram of the Al–Cu–Fe quasicrystal-forming alloy system
- Notifications/Mitteilungen
- Personal/Personelles
- Gesellschaftsnachricht
- International Conferences
