Effect of excitation states of nitrogen on the surface nitridation of iron and steel in d.c. glow discharge plasma

Shigeo Sato, Hirokazu Hirai, Sawa Araki, Kazuaki Wagatsuma

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)

Abstract

The plasma nitriding phenomena that occur on the surfaces of iron and steel were investigated. In particular, the correlation between the kinds of nitrogen radicals and the surface nitriding reaction was investigated using a glow-discharge apparatus. To control the excitation of nitrogen radicals, noble gas mixtures were used for the plasma gas. The highly populated metastables of noble gases selectively produce excited nitrogen molecules (N2) or nitrogen molecule ions (N2+). The optical emission spectra suggested that the formation of N2-rich or N2 +-rich plasma was successfully controlled by introducing different kinds of noble gases. Auger electron spectroscopy and XPS were used to characterize the depth profile of the elements and chemical species on the nitrided surface. The nitride layer formed by a N2+-rich plasma had a much higher nitrogen concentration than that by a N 2-rich plasma, likely due to the larger chemical activity of the N2+ species as well as the N2+ sputtering bombardment to the cathode surface. The strong reactivity of the N2+ species was also confirmed from the chemical shift of N 1s spectra for iron nitrides. An iron nitride formed by the N2 +-rich plasma has higher stoichiometric quantity of nitrogen than that formed by the N2-rich plasma. Besides the effect of nitrogen radicals on surface nitridation, the contribution of the chromium in steel to the nitriding reaction was also examined. This chromium can promote a nitriding reaction at the surface, which results in an increase in the nitrogen concentration and the formation of nitride with high nitrogen coordination.

Original languageEnglish
Pages (from-to)964-970
Number of pages7
JournalSurface and Interface Analysis
Volume43
Issue number6
DOIs
Publication statusPublished - 2011 Jun

Keywords

  • AES
  • XPS
  • glow discharge optical emission spectroscopy
  • plasma nitriding

ASJC Scopus subject areas

  • Chemistry(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Materials Chemistry

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