Systematic study on influence of the nitriding parameters on pure iron superficial layer properties

Abstract

Results obtained on pure iron samples submitted to a plasma nitriding process are presented. The main goal of this study was to understand how the treatment temperature, time nitriding, and DC or pulsed glow discharges affect the properties of the superficial layer. X-ray diffraction (glancing angle geometry), Mössbauer spectroscopy, electron probe microanalysis, and Vickers micro-hardness were used as analytical techniques. The results indicate that the compound layer presents a mixture of hexagonal ε-Fe x N (3.2⩾ x⩾2) and cubic (γ′-Fe 4N) phases, with fractions depending on the preparation conditions. Also, in the DC process the γ′-phase seems to be correlated with the hexagonal phase x=3.2, while in the AC process, it is correlated to the hexagonal phase x⩽3. Strikingly, this phase diminishes in both AC and DC processes, as the depth increases. We have also observed that, for the hexagonal phases in the DC process, and as the nitriding time increases, the x=3.2 phase fraction increases. Finally, we have observed that a pulsed process with a frequency f=4 kHz forms almost the same relative amounts of hexagonal and cubic phases produced in the DC process.