The influence of the ion current density on plasma nitriding process

In this paper, we report a comprehensive nitriding study carried out using low-alloy steel AISI 4140, combining nitrogen ion-beam (IB) implantation and pulsed plasma (PP) nitriding. Quantitative relationships among hardness, nitrogen bulk profile concentration, and current ion densities are reported. The hardness profile showed a linear relationship with the nitrogen concentration. The samples were characterized by photoemission electron spectroscopy (XPS), X-rays diffraction analysis (XRD), scanning electron microscopy (SEM) and in-depth nanohardness measurements. Samples treated by ion-beam-implantation showed the presence of a compound layer formed principally by ɛ-Fe3N and γ′-Fe4N. On the other hand, samples treated by pulsed plasma nitriding showed only the existence of γ′-Fe4N. In the later set of samples, was possible to prove that hardness is proportional to the ion current density.