Continuous and discontinuous precipitation in Fe-1 at.%Cr-1 at.%Mo alloy upon nitriding; crystal structure and composition of ternary nitrides

Tobias Steiner*, Sai Ramudu Meka, Bastian Rheingans, Ewald Bischoff, Thomas Waldenmaier, Guma Yeli, Tomas L. Martin, Paul A J Bagot, Michael P. Moody, Eric J. Mittemeijer

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

7 Citations (Scopus)
380 Downloads (Pure)

Abstract

The internal nitriding response of a ternary Fe–1 at.%Cr–1 at.%Mo alloy, which serves as a model alloy for many CrMo-based steels, was investigated. The nitrides developing upon nitriding were characterised by X-ray diffraction, scanning electron microscopy, electron probe microanalysis, transmission electron microscopy and atom probe tomography. The developed nitrides were shown to be (metastable) ternary mixed nitrides, which exhibit complex morphological, compositional and structural transformations as a function of nitriding time. Analogous to nitrided binary Fe–Cr and Fe–Mo alloys, in ternary Fe–Cr–Mo alloys initially continuous precipitation of fine, coherent, cubic, NaCl-type nitride platelets, here with the composition (Cr½,Mo½)N¾, occurs, with the broad faces of the platelets parallel to the {1 0 0}α-Fe lattice planes. These nitrides undergo a discontinuous precipitation reaction upon prolonged nitriding leading to the development of lamellae of a novel, hexagonal CrMoN2 nitride along {1 1 0}α-Fe lattice planes, and of spherical cubic, NaCl-type (Cr,Mo)Nx nitride particles within the ferrite lamellae. The observed structural and compositional changes of the ternary nitrides have been attributed to the thermodynamic and kinetic constraints for the internal precipitation of (misfitting) nitrides in the ferrite matrix.

Original languageEnglish
Pages (from-to)1509-1537
Number of pages29
JournalPhilosophical Magazine
Volume96
Issue number15
Early online date27 Apr 2016
DOIs
Publication statusPublished - 23 May 2016

Keywords

  • Atom probe tomography (APT)
  • CrMoN
  • Fe–Cr–Mo
  • Microstructure characterisation
  • Nitriding

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