Comparison of Nitriding Behavior of Mo-Ti Alloys in NH3 and N2 Gases

Masahiro Nagae, Akihiro Kunisada, Jun Takada, Yutaka Hiraoka, Yoshito Takemoto, Moritaka Hida, Hideyuki Kuwahara

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)


For dilute Mo-Ti alloys and pure Mo nitrided at 1100°C for 16h in NH3 and N2 gases, microstructural observations through optical and transmission electron microscopes, X-ray diffraction analysis and hardness measurements were carried out and the nitriding behavior in N2 and NH3 gases was compared. A surface layer of γ-Mo2N with Hv∼1700 was formed for the nitriding in NH3 gas of 1 atm. In contrast, the surface layer was absent for nitriding in N2 gas at pressures below 10 atm, whereas the β-Mo2N layer was formed at a pressure of 15 atm. In an internal nitriding layer formed beneath the surface layer of Mo-Ti alloys nitrided in NH3 gas, extremely small and plate-like particles of 2∼4nm in width and approximately 0.45nm in thickness were clearly found to precipitate on {100} planes of the matrix. Furthermore, a large coherent strain field was observed in the matrix around each Ti-nitride precipitate. Such a dispersion of the small precipitates resulted in remarkable hardening in the nitrided alloy. The hardness of the internal nitriding layer of the alloys nitrided in NH3 gas was much higher than that in N2 gas. The difference in hardness can be explained in terms of the differences not only in size of the Ti-nitride precipitates but also in their distribution density.

Original languageEnglish
Pages (from-to)189-194
Number of pages6
JournalFuntai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy
Issue number2
Publication statusPublished - Feb 1998


  • Dispersion-hardening
  • Internal nitriding layer
  • Mo-Ti alloy
  • N nitriding
  • NH nitriding
  • TEM observation

ASJC Scopus subject areas

  • Mechanical Engineering
  • Industrial and Manufacturing Engineering
  • Metals and Alloys
  • Materials Chemistry


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