Surface analysis of nitride layers formed on Fe‐based alloys through plasma nitride process

Abstract

Nitriding phenomena that occur on the surfaces of pure Fe and Fe-Cr alloy (16 wt% Cr) samples were investigated. An Ar + N 2 mixture-gas glow-discharge plasma was used so that surface nitriding could occur on a clean surface etched by Ar + ion sputtering. In addition, the metal substrates were kept at a low temperature to suppress the diffusion of nitrogen. These plasmanitriding conditions enabled us to characterize the surface reaction between nitrogen radicals and the metal substrates. The emission characteristics of the band heads of the nitrogen molecule ion (N 2 + ) and nitrogen molecule from the glow-discharge plasma suggest that the active nitrogen molecule is probably the major nitriding reactant. AES and angle-resolved XPS were used to characterize the thickness of the nitride layer and the concentration of elements and chemical species in the nitride layer. The thickness of the nitride layer did not depend on the metal substrate type. An oxide layer with a thickness of a few nanometers was formed on the top of the nitride layer during the nitriding process. The oxide layer consisted of several species of N x -Fe y -O, NO + , and NO 2 − . In the Fe-Cr alloy sample, these oxide species could be reduced because chromium is preferentially nitrided.

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

“…Figure 2 shows the dependence of the intensities of the Fe I line under the ArN 2 and NeN 2 plasmas on the applied d.c. voltage. Some of the results for an ArN 2 atmosphere were reported in our previous study 7. The intensity of the Fe I spectral line increased with an increase in the applied d.c. voltage for both mixture gas plasmas.…”

“…It should be noted that the nitrogen concentration of the nitrided surfaces of SUS430 increased slightly, compared to that of HPFe. According to our previous study, the chromium in SUS430 can preferentially form nitrides in a plasma nitriding process,7 which results in an increase in the nitrogen concentration of the nitrided surface of SUS430. The Fe 2p, Cr 2p and O 1s spectra for the nitrided SUS430 in the NeN 2 plasma are representatively shown in Fig.…”

“…The helium matrix gases were mixed with argon gas to compensate for the low capability of helium ion sputtering and to suppress the energy transfer from He m to N 2 +* to control the N 2 + /N 2 * population. It should be mentioned that the nitrogen in noble gas mixture plasmas has complex effects on the noble gas sputtering: the chemical reaction between nitrogen radicals and iron substrate,11 the resonant energy transfer from metastables of noble gases to nitrogen molecule 7, 10. These phenomena reduces sputtering yields by the noble gas ions during the nitriding process.…”

“…Therefore, we can expect that there is a close correlation between the characteristics of nitride layers and the excited nitrogen states in plasmas. In our previous study where a nitriding process was investigated using an ArN 2 mixture plasma, it was found that a high density for the N 2 * species can be produced in the plasma, and that the partial pressure of nitrogen gas has a significant effect on the population of nitrogen radicals and the resultant nitrided surface 7. Although it can be expected that sputtering implantation of N 2 + efficiently activates the surface nitriding reaction compared to chemical reactions with N 2 *, the correlation between these nitrogen radicals and the surface nitriding reaction has not been well characterized due to the difficulty of controlling the kind of nitrogen radicals.…”

Iron Nitride Nanoparticles for Enhanced Reductive Dechlorination of Trichloroethylene

“…The first two correspond to oxidized Fe x N and pristine Fe x N, respectively. 53,57,58 The other two spectral lines can be attributed to adsorbed ammonia and NO species. 30,31,53,57 Both species are likely to be present on the particle surface in small amounts given that ammonia was used as the nitrogen source in the nitriding process and the NO species are typically detected on the surface of nitrided metals.…”