Gas nitriding behavior of refractory metals and implications for multi-principal element alloy design

Yu Hsuan Lin, Andre Bohn, Justin Y. Cheng, Anette von der Handt, Nathan A. Mara, David L. Poerschke

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Multi-principal element alloys (MPEAs) comprise a large, flexible compositional space that enables tuning of their chemistry, structure, and properties. To facilitate the development of nitriding-based surface-enhancement strategies that harness a broad compositional space, this study examined the gas nitriding behavior of Hf, Mo, Nb, Ta, Ti, and Zr as a function of time, temperature (750 and 1000 °C), and nitriding potential (i.e. ammonia-to-hydrogen ratio). These metals were selected because they have a strong driving force to form nitrides, and appear in many promising refractory MPEA compositions. The nitriding temperatures were selected based on the phase transformation temperature of Ti and Zr, and the nitriding potentials were chosen such that all elements are expected to form nitrides. Mass gain measurements indicate that all six elements follow parabolic kinetics. The microstructure observations and quantitative microchemical analysis show formation of dense and well-adhered compound layers for Mo, Nb, and Ta. Thick diffusion zones appear in Hf, Ta, Ti, and Zr, and diffusion coefficients were fit to the composition profiles. Partial delamination of the compound layer occurred for Ti and Zr. Peak hardness values above 30 GPa are obtained in the dense compound layers, and the solute hardening of the underlying alloy is correlated with the nitrogen content. The results provide insight into the dynamics of nitride compound formation relative to interstitial dissolution of nitrogen, and are discussed in the context of MPEA composition and processing design.

Original languageEnglish (US)
Article number169568
JournalJournal of Alloys and Compounds
StatePublished - Jun 25 2023

Bibliographical note

Funding Information:
This research was supported primarily by the Office of Naval Research ( ONR ) award N00014-20-1-2732 , monitored by Dr. David Shifler. J.Y. Cheng is supported in part by DOE NNSA under cooperative agreement number DE-NA0003960 . The shared equipment used in this work is supported by NSF MRI DMR-1229263 (Hitachi SU8230), NSF EAR-1625422 (EPMA). SEM-EBSD, TEM characterization, and hardness measurements were carried out in the Characterization Facility, University of Minnesota, a member of the Materials Research Facilities Network (, which is partially supported by the NSF through the MRSEC (Award Number DMR-2011401 ) and the NNCI (Award Number ECCS-2025124 ) programs. The authors are grateful to Dr. Nicholas Seaton for EBSD assistance.

Publisher Copyright:
© 2023 Elsevier B.V.


  • Diffusion
  • Gas-solid reactions
  • Mechanical properties
  • Nitride materials
  • Refractory metals

MRSEC Support

  • MRFN


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