Plasma Species Analysis for Insitu Assessment of Surface Treatments

In order to gain the maximum potential from plasma technology in surface engineering, knowledge is required about the influence of particular plasma phase species on the treatment response. In this study, optical emission spectroscopy (OES) is used in situ, without disturbing the treatment environment, to monitor the active species observed in three different types of nitriding plasma: direct current (dc), active screen, and plasma immersion ion implantation (PI₃). The spectral information obtained is considered in conjunction with metallurgical characterisation of nitrided steel samples, using optical microscopy, glow discharge optical emission spectroscopy, X-ray diffraction, and microhardness testing. Active screen and dc nitriding have a similar nitriding effect in low alloy steel testpieces. OES evidence shows that both ions and neutrals are involved in the plasma reactions and a multistage theory is the model of best fit for nitrogen mass transfer in these dc powered plasma nitriding techniques. OES analysis can be used for in situ monitoring of treatment quality in PI₃ nitriding.