Effects of hydrogen on iron nitriding in a pulsed plasma

Abstract

A low frequency DC pulsed plasma used for iron nitriding is studied by means of an electrostatic probe and optical emission spectroscopy. The evolution of the electron density leads to the determination of the electron-ion recombination coefficient. The variations of this coefficient and the measurement of some emission lines of neutral iron and of excited states of neutral and ionic molecular nitrogen as a function of the percentage of H2 give additional insights into the role of hydrogen during the nitriding process. Thus the presence of vibrational states of nitrogen-N2(C3 Pi u, B3 Pi g, A3 Sigma u+), N2+(B2 Sigma u+)-late in the afterglow confirms their importance in such plasma assisted surface treatments.

The influence of the respective durations of the discharge and the afterglow on the reactivity of a DC pulsed plasma used for iron nitriding

“…In our case, the mean electron energy, deduced from probe measurements, decays slowly from 0.4 to 0.3 eV except during the first 0.1 ms of the post-discharge (Hugon et al 1993) and α can be assumed constant. Taking α = 2 × 10 −7 cm 3 s −1 (Mehr and Biondi 1969), we thus get for n eo a value around 6×10 11 cm −3 for pressures of 3 and 4 Torr, which increases up to 1.3 × 10 12 cm −3 for a pressure of 1 Torr, in relative agreement with previous Langmuir probe measurements (Bougdira 1990, Henrion et al 1992. For times in the late afterglow (t ≥ 2 ms), the curves in figures 4 and 5 no longer match the linear variation.…”

“…The decay of the line intensity during the post-discharge is reported in figure 4. The quite linear variation of these curves (represented in log scales) (for time less than or equal to 1-2 ms is characteristic of populating the Fe(z 5 F) level by electron collisions during the afterglow (Bougdira 1990, Henrion et al 1992. Indeed, by assuming that the main loss process for electrons and ions during the afterglow is dissociative recombination, then the electron density decay may be written n e (t) = n eo /(1 + αn eo t) where t represents the time variable (t = 0 at the discharge cut-off), n eo stands for the electron density at t = 0 and α is the recombination coefficient.…”

Time-resolved diagnostics and kinetic modelling of the ignition transient of a H2 + 10% N2 square wave modulated hollow cathode discharge

“…With the aim of elucidating the detailed kinetics, pulsed discharges are considered helpful [4,18] since specific plasma processes occurring at different rates can be evinced by adjusting the duration of the pulses. Besides, N 2 -H 2 dc pulsed discharges could be advantageous in plasma nitriding for several technical reasons [13,19,20], which also stimulates their study.…”

Experimental study of the temporal evolution of N2(C3Πu) and N2(B3Πg) in a nitrogen pulsed discharge

“…There is great interest in such a process as plasma is a source of reactive species for the formation of nitride alloy and that the sample heating up to the temperature for nitride production is obtained by ion bombarding. During the process, arcs occur which damage the sample, but the use of pulsed discharges inhibits these arcs [3,4]. Moreover, the pulse mode being adjustable, the pulse repetition rate makes it possible to monitor the sample heating.…”